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The lightning clustering algorithm for spaceborne lightning observations clusters events into flash products and plays a crucial role in lightning-related research. This paper modified the lightning clustering algorithm based on the routine algorithm of Lightning Mapping Imager (LMI) and applied it to lightning events recorded by the LMI in 2019 to study the flash duration and flash area and specially to reveal the extreme lightning. To reveal the temporal and spatial features of lightning, the MCA (modified cluster algorithm) flash products defined flash duration and flash area. The results showed that continental regions have higher lightning frequencies but smaller events per flash, flash durations and flash areas than the ocean. The Tibetan Plateau has a low lightning frequency and smaller flash duration and area than eastern China. The flash count, events per flash, flash duration and flash area are higher during nighttime than during daytime. The relationship between flash duration and flash area showed distinct regional differences. In the MCA flash product, about 0.6% (0.1%) flashes have duration (area) that exceeds 1.0 s (5,000 km2). Finally, we analyzed two extreme lightning cases in eastern China, where the longest flash duration was 4.748 s and the largest flash area was 17,100 km2. This research contributes to advancing our understanding in the features of space-based lightning in the Eastern Hemisphere and applications to convection study. • Clustering algorithm was modified to study lightning with extreme duration and area. • Lightning duration and area both implied regional differences. • Quantitative relationship of duration and area was established in different regions. • The longest flash duration/largest flash area was 4.75 s/17100 km2 in eastern China. [ABSTRACT FROM AUTHOR]

In December 2023, a super warm spell occurred in the North China Plain, setting a new daily maximum temperature record for all Decembers since 1961. By using station observed temperatures in China and NCEP/NCAR reanalysis datasets, this paper examines the extremity of the event. The peak temperature anomaly during the event exceeded 13 °C for the entire region mean and exceeded 22 °C for a single station, both of which have never been observed before. Further analyses indicated that the super warm spell event was not limited in a local area, but rather had a significant large-scale background, characterized by a remarkable dipole temperature anomaly spatial pattern in the Eurasian continent. Composite analyses revealed that one of the dominant circulation factors was the Siberian high. Prior to the occurrence of the historic warm spell days, the Siberian high was generally weaker than normal by 2–3 standard deviations. During this super warm spell event, the Siberian high was the fifth weakest in the research period. The composite results indicate that the weaker Siberian high weakened the local meridional pressure gradient and blocked the cold air from high latitudes. In addition to the Siberian high, the sea level pressure anomaly pattern in Asia, both in the composite and in 2023, also shows a typical dipole structure. The dipole structure weakens the large-scale meridional pressure gradient and maintains the zonal circulation in the Eurasian continent. This may be related to the anomalous polar front jet. In December 2023, the polar front jet was the strongest during the research period. A stronger polar front jet typically weakens the winter monsoon by promoting zonal circulations, resulting in higher temperatures across most of Asia. Thus, it can be inferred that the super warm spell in early December 2023 in the North China Plain was the result of a combination of the polar front jet and the Siberian high. • A record-breaking warm spell in Dec 2023 occurred under a large-scale dipole of temperature anomalies in Eurasia continent. • The common and individual general circulation characteristics are compared and diagnosed. • The strongest polar front jet and the fifth weakest Siberian high in December jointly contributed to the event. [ABSTRACT FROM AUTHOR]

Global warming has caused severe regional water security risks, and from the theory of the hydrological cycle, the daily extreme temperature could also bring an impact on the streamflow volume, which could be even more important than the average temperature. Therefore, based on the level of the maximum or minimum temperature warming scenarios, a variety of meteorological datasets were selected to assess the asymmetric effect of increased daily extreme temperature on the streamflow from a multi-scale perspective by using the Variable Infiltration Capacity (VIC) model. Model simulations indicate that the streamflow experiences more significant changes in response to the maximum temperature than in response to the minimum temperature, and the relationships of streamflow with both the maximum and minimum temperatures show an upwards parabolic response function, but the response function varies with the type of warming. Additionally, the seasonal and monthly duration curves results show that the increases in both the maximum and minimum temperatures demonstrate a similar response that leads the proportion of the flood period streamflow to be increased (Tmin : 0.16–0.53%/°C; Tmax : 0.11–0.51%/°C). When the minimum temperature increases, the higher the original temperature in the region, the greater the proportion of the flood period streamflow increases. However, when the maximum temperature increases, the opposite effect occurs. • This paper included a numerical analysis of the sensitivity of streamflow to daily extreme temperature increases. • This paper discusses in detail the regional asymmetric effect of daily extreme temperature increase to streamflow. • A relatively complete picture of the hydrological processes caused by daily extreme temperature rise is presented. [ABSTRACT FROM AUTHOR]

Attenuation correction of measured reflectivity (Z H) and differential reflectivity (Z DR) is critical in short-wavelength radar applications, especially during extreme precipitation events such as heavy rain. This paper develops an improved self-consistent approach (improved ZPHI method) for attenuation correction in practical environment. In particular, a non-negative constraint is imposed on the specific attenuation, which is inferred from the monotonic increasing characteristic of differential propagation phase (Φ DP). The copolar correlation coefficient (ρ HV) is used to partition the Φ DP profiles into independent range segments, which are featured by different hydrometeor phases such as liquid rain or mixed-phase precipitation. Additional minimization constraint is imposed on the cost function of the difference between preprocessed Φ DP and reconstructed Φ DP to ensure its appropriate convergence. In addition, an exponential Z DR − Z H relation derived from local raindrop size distribution (DSD) data is applied in the procedure of Z DR correction. Polarimetric measurements from a C-band radar (CPOL) in Hangzhou of China during two extreme precipitation events are used to demonstrate the improved attenuation correction method. DSD observations from disdrometers and radar data from a nearby system operating at non-attenuated frequency (i.e., S-band) at Huangshan Mountain are used to evaluate the attenuation correction performance. This paper also studies the impact of attenuation correction on the radar-derived quantitative precipitation estimation (QPE) product, through cross-comparison with rain gauge observations. Results show that the polarimetric observations from CPOL radar are effectively enhanced and more consistent with collocated S-band measurements and the simulated radar moments based on DSD data. Hourly rainfall products derived from R (Z H) and R (Z H , Z DR) are significantly improved, which are comparable to R (K DP) after attenuation correction. • An improved attenuation correction method is proposed for C-band polarimetric radar applications. • The routinely operating C-band radar in Hangzhou, China is used to demonstrate the proposed attenuation correction scheme. • Cross-comparison with disdrometer data and collocated S-band observations shows great performance of this correction method. • The QPE products derived from R (Z H) and R (Z H , Z DR) are significantly improved after attenuation correction. [ABSTRACT FROM AUTHOR]

The Chinese meteorological satellites Fengyun (FY) have recently developed rapidly, resulting in a substantial wealth of precipitable water vapor (PWV) products. However, these latest operational PWV products still need to be systematically validated. In this paper, we focus on the PWV products derived from the FY-3D/Medium Resolution Spectral Imager II (MERSI-II), FY-2H/Visible and Infrared Spin Scan Radiometer (VISSR), and FY-4A/Advanced Geostationary Radiation Imager (AGRI), and test their performance by using the global navigation satellite system (GNSS) data. We find that FY-4A/AGRI performs best in various regions of China in 2021. Compared to GNSS-PWV, FY-4A/AGRI PWV has a correlation coefficient 0.95, a root mean square error (RMSE) of 4.67 mm, and a mean deviation (MB) of −0.73 mm, respectively. Significant discrepancies between FY-PWV and GNSS-PWV are observed in the Qinghai-Tibetan Plateau (MB: −4.86 mm for FY-2H/VISSR and − 5.12 mm for FY-4A/AGRI) and the Sichuan Basin (MB: 5.52 mm for FY-2H/VISSR, and 3.82 mm FY-4A/AGRI). All FY-PWVs exhibit season-dependent variations, and their discrepancies with GNSS-PWV during winter are smaller than in summer. Finally, we analyze the distribution and changes of water vapor in China from 2019 to 2022 using the preferred FY-4A/AGRI PWV. The results reveal a gradual decrease in the annual mean water vapor content, diminishing by approximately 0.33 mm during this period. Notably, this decrease occurs in southern China, and the water vapor content spikes in summer, culminating at 23.59 mm in 2022. Our findings strongly correlate with the precipitation changes documented in the China Climate Bulletin (2022). • This study is an application of 3S (remote sensing, GNSS, and GIS) technology in meteorology. • A harmonized standard method has been used for the evaluation of FY-PWVs. • FY-4A/AGRI PWV exhibits the best consistency with GNSS PWV in mainland China. • The distribution and changes of water vapor in China in recent years have been investigated. [ABSTRACT FROM AUTHOR]

Aerosol types have crucial and distinguished impacts on climate effects and cause the difference of air pollution. However, direct retrieval of aerosol type by satellite remote sensing is difficult, and the satellite products of aerosol type are seriously lacking. At present, the identification of aerosol type is mainly based on ground-based observation data, but the coverage area of ground-based stations is limited, and large-scale spatial continuous monitoring cannot be carried out. The existing aerosol type identification methods based on satellite data need to combine multiple satellites data (e.g. Moderate-resolution Imaging Spectroradiometer (MODIS), Ozone Monitoring Instrument (OMI), etc.) which leads to a low temporal resolution. The research about aerosol type identification only based on geostationary satellite data is lacking. Therefore, aerosol type identification based on the multi-parameter threshold method and the neural network method are proposed and compared in this paper. The neural network jointly using spectral and temporal information was trained and tested by the measurements from 26 sites of Aerosol Robotic Network (AERONET) and Sun-Sky Radiometer Observation Network (SONET). For the overall validation, the aerosol type identification based on the neural network is better than that based on the multi-parameter threshold method, and the accuracy reaches 71.44%. Atmospheric environment monitoring and quantitative remote sensing can be supported by this study. • Aerosol type, neural network, geostationary satellite [ABSTRACT FROM AUTHOR]

The distribution of ice particles strongly affects the microphysical processes in mixed-phase clouds, but the inhomogeneity of ice distribution is not well understood. In this paper, based on airborne in-situ measurements from three flights on May 31, 2021 in Hulun Buir, China, the inhomogeneity and clustering of ice distribution in a stratiform cloud is quantitatively analyzed using the pair correlation function (PCF). The results show that ice clusters on scales of a few kilometers dominate the inhomogeneity of the ice distribution. Due to the cumulative impact of ice clusters on different scales, the probability of finding relative high ice concentration within a lag of 80 m can be enhanced by 0.1 to 3.5 times. On average, the scale of ice cluster is ∼100 m for a sampling distance of 1 km, and increases to 3.2 km for a sampling distance of 20 km. It is also found that the ice growth is not fast enough to cluster the ice water content (IWC), and the inhomogeneity of IWC is strongly influenced by ice generation in addition to ice growth in the observed cloud. The results are helpful to better understand the distribution of ice in mixed-phase cloud, and provide potentially important information to improve the parameterizations of microphysics in models. • The inhomogeneity of ice distribution in mixed-phase stratiform cloud is quantitatively analyzed using airborne measurement. • Ice clusters on scales of a few kilometers dominate the inhomogeneity of the ice distribution. • Averagely, the ice cluster scale increases from 100 m to 3.2 km as the sampling distance increases from 1 km to 20 km. [ABSTRACT FROM AUTHOR]

When flying through clouds that co ntain supercooled liquid water, aircraft can accumulate ice at levels that can be dangerous to flight. Similarly, in the field of weather modification, the amount and distribution of a cloud's supercooled water content is an important indicator of artificial precipitation. The G-band water Vapor Radiometer (GVR) is a small instrument that can be mounted on aircraft. Its operating frequency is highly sensitive to low liquid water content, which is particularly suitable for detecting supercooled water in different parts of clouds during changes in flight position. In order to explore supercooled water, we installed such an instrument with four double-sideband receiver channels centered at 183.31 ± 1, ±3, ±7, and ±14GHz, under the right wing of a King Air B-10KL that we used to perform a series of outfield observations and artificial precipitation missions. In this paper, we discuss the feasibility of detecting supercooled liquid water in the clouds over North China with a GVR. A Back Propagation (BP) neural network algorithm that takes into account flight details including aircraft altitude, climate background and geographic location variations was developed to retrieve supercooled liquid water path (SLWP). A numerical simulation test using the radiosonde data as test samples showed that the retrieval results correlate highly with the radiosonde data calculation results, and that the algorithm was applicable for different seasons and different geographical locations. The algorithm was then applied to the aircraft outfield observations of supercooled liquid water and the results were compared with hotwire, another cloud liquid water observation instrument installed on the aircraft. Results here showed agreement in terms of trend. The observation of SLWPs over clouds thought to be of 0-value shows that the root mean square error of retrieval results is as low as 0.2 g m−2. This paper demonstrates that it is feasible to measure supercooled water over North China with GVR using the retrieval algorithm used here, which obtained good results and is able to compensate for the lack of reliable supercooled water detection instruments on the aircraft. • The feasibility of detecting supercooled liquid water in the clouds over North China with a GVR is discussed. • A Back Propagation(BP) neural network algorithm was developed to retrieve supercooled liquid water path(SLWP). • The numerical simulation test showed that the algorithm is applicable for different seasons and varied geographic locations. • The comparison of observations reveals that GVR is more reliable for the detection of supercooled water. [ABSTRACT FROM AUTHOR]

This paper examines the local and non-local climatic effects of wetter arid areas of Northwestern China (ANWC) in summer using a fully coupled climate model. In response to soil moisture increase, the local air temperature significantly decreases, and precipitation increases in summer. The wetter ANWC results in a warmer and rainless climate over the Central part of North China Plain (CNCP). While the influence of increasing soil moisture on the Tibetan Plateau (TP) precipitation is negligible due to the high altitude. A cooler climate over ANWC leads to an abnormal descending motion occurring. Meanwhile, an anomalous high pressure and an abnormal anticyclonic circulation occurs in 500 hPa over the west of ANWC. Correspondingly, a huge anomalous cyclone circulation occurs over the northeastern part of China and Mongolia, which can hinder the northward movement of the East Asian summer Monsoon (EASM) and reduce the water vapor transport into Central China Plain. As a result, the weakened EASM thus leads to rainless over CNCP. As soil moisture increases over ANWC is stronger, the magnitudes of the influence on the atmospheric field become larger. This study highlights the wetter ANWC effect on local climate and provides more information about the mechanism of wetter ANWC remote effect on non-local climate. • This paper examines the local and non-local climatic effects of wetter arid areas of Northwestern China (ANWC) in summer using a fully coupled climate model. • It finds that the wetter ANWC can result in a warmer and rainless climate over the Central part of North China Plain (CNCP) through a complex atmospheric circulation response. • A cooler climate leads to an abnormal descending motion occurring over ANWC. • A huge anomalous cyclone circulation over the northeastern part of China and Mongolia can block the East Asian summer Monsoon northward and decrease the water vapor transport into Central China Plain. • This study highlights the wetter ANWC effect on local climate and provides more information about the mechanism of wetter ANWC remote effect on non-local climate. [ABSTRACT FROM AUTHOR]

Knowledge of vertical distribution of air pollutants is important for understanding the mechanisms underlying haze pollution. In this paper, we characterize the vertical structure of air pollutants based on ground-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements in the wintertime in Hefei, East China. Both NO 2 and aerosol show exponentially decreasing profile with high concentrations concentrated close to the surface, suggesting the major emissions are at ground level. SO 2 profiles extend to slightly higher altitudes than NO 2 , which might be due to the SO 2 emissions from elevated point sources (e.g., power plants). Elevated HCHO was observed in the middle layer during noon time, probably indicating that the larger effect of the photochemical formation of atmospheric HCHO rather than direct HCHO emissions. Potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) models were used to evaluate the potential sources of Hefei's air pollution in the lower, middle and upper boundary layer. The results revealed that the major regional source of NO 2 and aerosol were located in the northern and eastern part of Anhui and the transport mainly occured in the lower layer. Transported SO 2 from the northwestern regions in the middle layer made great contribution to SO 2 in Hefei. HCHO was mostly produced locally while the transport of HCHO from potential source areas was negligible. To further explore the potential source contributions affecting haze pollution, PSCF and CWT analysis for heavy haze episodes suggested that the potential source areas for aerosol were almost located in the northern region, the northwestern region, and the YRD region. Our findings provide a more comprehensive understanding for regional transport through the study on potential sources at different altitudes, which are useful for designing collaborative air pollution control strategies on a regional scale. • Vertical distribution of air pollutants is investigated to identify potential sources at different altitudes during winter. • Both NO 2 and aerosol show exponentially decreasing profile with high concentrations concentrated close to the surface. • SO 2 and HCHO profile typically extended to higher altitudes than NO 2 and aerosol did during winter. • The main potential sources for aerosol were located in the northern region, the northwestern region, and the YRD region. • This study is useful for designing collaborative air pollution control strategies on a regional scale. [ABSTRACT FROM AUTHOR]

For regions where limited in-situ observations are available for use as a reference, such as in China, the understanding of how changes in the Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol retrieval algorithm impact the data quality is limited. In this paper, the MODIS-Aqua Aerosol Optical Thickness (AOT) Collection 5 (C5) and 6 (C6) Dark-Target (DT) products are evaluated by comparison with similar products from the China Aerosol Remote Sensing NETwork (CARSNET) and the Aerosol Robotic Network (AERONET) in China for the year 2008. The validation data are analyzed for key factors affecting the results of the MODIS-DT aerosol retrieval algorithm, including surface type, aerosol loading and aerosol absorption. The impacts of the change from the C5 to the C6 versions of the MODIS AOT retrieval algorithm are discussed in detail. The main findings are: (1) The agreement from retrieval aspects between both MODIS C5/C6 and CARSNET-AERONET for most AOT values over distinct regions indicates that the conclusions obtained from C5 hold for C6; (2) MODIS-DT has an extended coverage (more retrievals) with good quality due to the change of upstream data (calibration, cloud masking, etc); (3) About 64% of the MODISDT C6 AOT data over China fall within the (±0.15 AOT ± 0.05) error envelope; (4) positive AOT differences between C6 and C5 over relatively dark surfaces and negative differences over relatively bright surfaces due to the change of surface parameterization have been observed; (5) the AOT difference between MODIS and CARSNET-AERONET relating to AOT loading is not significant, especially for large AOT; (6) MODIS-DT performs well for absorbing aerosol over relatively bright surfaces. • MODIS/Aqua AOT C5/C6 DT products are evaluated to understand the effects of different parameters on algorithm performance. • Both MODIS C5 and C6 DT show good quality over China under different surface and atmospheric conditions. • MODIS C6 DT aerosol product has an extended coverage with good quality over China. [ABSTRACT FROM AUTHOR]

Sand / dust occurrences are one of major disasters in arid and semi-arid areas. Understanding its time evolution as well as the impact factors is crucial for policy makers to protect human from health and economic losses. In this paper, we investigate the features of spring sand/dust frequency during 1961–2016 based on 201 surface meteorological stations in northern China, which are divided into four regions as Xinjiang, Northwest China, North China, and Northeast China according to the spatial distribution of sand/dust frequency. Although the regional mean sand/dust frequency exhibits a general declining trend in the last 56 years, it shows fluctuations with the maximum occurrence in the 1970s and the minimum in the 2010s, and abrupt changes can be found in the late 1980s by the Lepage test. We choose 1961–1988 as the active sand/dust period and 1989–2016 as the inactive sand/dust period. Apparent differences are found between these two epochs in the large-scale atmospheric circulations. The geopotential height over Mongolia and Inner Mongolia of China at mid-and lower troposphere became much higher, and the Asian polar vortex weakened and shrank noticeably in the inactive sand/dust period. For 1961–1988, a meridional dipole pattern of significant correlation in heights at mid-and lower levels was dominant over the northeastern Eurasian continent, while for 1989–2016, sand/dust frequency seems to have much closer relationship with local circulation and a zonal dipole structure at lower troposphere dominated over China. The relationship between the 850 hPa vorticity over Mongolia and sand/dust frequency was strengthened after the late 1980s for the western areas, but that was weakened for the eastern areas of northern China. Besides, the intensity of Asian polar vortex at 500 hPa had higher correlation with sand/dust frequency during 1989–2016 particularly for Northwest China. All these findings are important to refine reliable models for short-term climate prediction of sand/dust occurrence in East Asia. • Spring dust frequency decreased generally during 1961–2016 over northern China. • Significant abrupt changes of dust frequency occurred in the late 1980s. • Atmospheric circulation and its relationship with dust frequency differed between 1961 and 1988 and 1989–2016. [ABSTRACT FROM AUTHOR]

In this paper, 34 western track typhoons making landfall over China during the period of 2006–2016 from Jun. to Oct. are taken as research objects. They are divided into strong and weak monsoon influenced categories according to the East Asian summer monsoon index. Using precipitation product that was derived from hourly precipitation observed at automatic weather stations (AWS) in China and retrievals from CMORPH [CPC (Climate Prediction Center) morphing technique] satellite data, Japanese 55-year Reanalysis products (JRA-55) and Blackbody brightness temperature (TBB) data from FengYun 2E (FY-2E) satellite, precipitation intensity and distribution characteristics of strong monsoon influenced typhoons. In addition, the weak monsoon influenced typhoons was compared through composite analysis. Furthermore, to explore the water vapor conditions, dynamic factors, thermal structure, development conditions of mesoscale convective systems, and long-term typhoon maintenance mechanisms of typhoons under both conditions. This research is attempted to obtain the regularity of influences exerted on typhoon precipitation intensity and distribution by summer monsoon, and the possible influencing mechanisms of summer monsoon on typhoon precipitation. Results show that the stronger (weaker) the monsoon flow is, the stronger (weaker) the precipitation intensity of post-landfall western typhoon. Monsoon provides a sufficient amount of water vapor through direct moisture channel. The stronger monsoon flow is, the more obvious the coupling of low-level convergence and upper-level divergence, and thus provides a stronger lifting for typhoon precipitation. A strong monsoon condition is more conducive to the genesis and development of mesoscale convection system. A strong monsoon condition is also favorable for the maintenance of post-landfall typhoon's warm core structure, thereby prolonging the precipitation through delaying the decay of typhoons. All these factors lead up to the influences on precipitation of typhoons by summer monsoon directly or indirectly. • Strong monsoon flow does lead to a significant increase and asymmetry in precipitation. • Stronger monsoon flow provides stronger lifting for typhoon precipitation through more obvious coupling of low-level convergence and upper-level divergence. • A strong monsoon condition is more conducive to the genesis and development of mesoscale convection system. • A strong monsoon condition can prolong the precipitation through delaying the decay of landfall typhoons by the maintenance of warm core structure. [ABSTRACT FROM AUTHOR]

Weather radar has demonstrated the ability to monitor wildfires and associated smoke plumes. However, the long-range, S-band operational radar network has severe limitations in providing high-resolution observations in the lower atmosphere due to the earth curvature. This paper presents an innovative technique of using shorter-range, low-power, fast scanning X-band radar for monitoring wildfires. Sample observations from wildfire events in southern China show that the polarimetric radar correlation coefficient of wildfire echoes varies from 0.55 to 0.75, with an average value of 0.61; the differential reflectivity varies from 2.28 to 5.08 dB with an average value of 3.99 dB; the differential propagation phase varies from 40.27° to 69.27°, with an average value of 56.66°; and all observables exhibit subtle changes at different scanning elevation angles. In addition, changes in echo intensity observed by higher elevation scans lag behind those observed by lower elevation scans, and the change of wildfire area lags behind the variation of echo intensity. Given the emerging interest in deploying such compact, cheaper X-band systems for urban hydrometeorological applications, it is expected that these radars, customized with flexible scan strategy, will provide new opportunities and advantages in wildfire detection and mitigation. • Weather radar has demonstrated the ability to monitor wildfires and associated smoke plumes • The operational long-range, S-band radar has severe limitations in providing high-resolution low-level measurements • The compact and low-power X-band dual-polarization radar is more efficient in monitoring wildfire and its evolution • The polarimetric observables, especially the correlation coefficient, can effectively identify the wildfire smoke plumes [ABSTRACT FROM AUTHOR]

Abstract Elucidating the vertical structures of clouds is key to reducing the uncertainty in cloud-induced climate forcing; however, we do not yet know explicitly about the cloud structures that form over Beijing, China, and how they vary. In this paper, we document vertically resolved cloud structures and their climatological variation based on three-year (1 January 2015 to 31 December 2017) ground-based Ka-band (35 GHz) millimeter-wave cloud radar (MMCR) measurements. Cloud top height (CTH) and radar reflectivity are higher in summer and autumn than in spring and winter. We verified the MMCR measurements of the CTH and cloud base height (CBH) independently based on observations from the Himawari-8 and CL51 ceilometer at the same station, respectively. The CTH decreased as the thickness of the cloud layer increased. This may have been due to the mechanism used to determine the CTH, which was based on data from the satellite infrared channel. There were two peaks in the CBH distribution, located at 0–1 km and 5–6 km, whereas the frequency of the CTH peaked at an altitude of 9–10 km, between 1200 and 1800 LST. Precipitating clouds tended to be located at lower altitudes and exhibited stronger radar reflectivities than non-precipitating clouds. The cloud frequency tended to peak in autumn and reached a minimum in winter. In terms of the seasonality of clouds at various levels, middle- and high-level clouds were dominant over Beijing, with high and low (precipitating) clouds concentrated between May and October. Mid-altitude clouds occurred more frequently in winter and spring. CTH peaked in summer due to the strong solar radiation received by the surface. In contrast, minimum CBH occurred in winter. The cloud heights were higher and radar reflectivities larger than reported in previous studies. These results are correlated with urban warming effects. Understanding the properties of clouds will not only be of benefit to researchers carrying out cloud forcing studies, but will also provide key validation data for climate model simulations. Graphical abstract Unlabelled Image Highlights • The cloud vertical structures in Beijing are elucidated using 3-year observations • Cloud structures from MMCR, Himawari-8 and ceilometer agree with each other very well • Cloud top heights are shown to decrease as the cloud layer thickness increases [ABSTRACT FROM AUTHOR]

Abstract The objective of this paper is to study the spatial and temporal variation characteristics of the UNESCO aridity index (AI) at annual and seasonal temporal scales in northwestern China during the 55-year study period (1961–2015). Based on climate data from 178 meteorological stations provided by the China Meteorological Data Service Center, AI trends were investigated by the Mann-Kendall test. The results showed that the annual and seasonal AIs displayed a mixed pattern of positive and negative trends for the period of 1961–2015 across the study area. In most regions, both annual and seasonal AIs exhibited slightly positive trends in northwestern China. Significant (P <.05) positive and negative annual trends were detected at 38 and 6 stations, respectively. The highest magnitude of the positive annual trend (0.0037 per year) appeared at Xining station, and the greatest decreasing annual trend (−0.0041 per year) appeared at Minxian station. In terms of seasonal AI, its trend magnitudes varied from −0.0058 to 0.0035 in spring, from −0.0062 to 0.0087 in summer, from −0.0105 to 0.0048 in autumn and from −0.0002 to 0.0443 in winter each year. Our study demonstrated that the AI spatial distribution may tend to be spatially homogeneous in the long term. Abrupt changes varied in different regions and seasons. Nevertheless, the positive trend shifts mostly began in the 1980s and became significant in the following decades. The correlation analysis indicated that the AI in winter and spring was probably mainly affected by the Indian Ocean Warm Pool Strength Index (IOWPSI), while the Multivariate ENSO Index (MEI), the Niño3.4 Sea Surface Temperature Anomaly Index (Niño3.4 SSTA) and the Southern Oscillation Index (SOI) were likely to be the conjoined influencing factors of the AI in summer and autumn. The spatiotemporal features of the long-term AI provided in this study may enhance our scientific understanding of the impacts of recent climate change on dryness/humidity changes in northwestern China; furthermore, this information might potentially be applied in other areas for comparison purposes. Highlights • Most of the significant trends were positive, whose shifts mostly began in the 1980s. • The arid areas were becoming more humid and vice versa. • The IOWPSI was the most dominant factor in winter and spring. [ABSTRACT FROM AUTHOR]

This paper investigates the annual and seasonal precipitation variability at 20 stations over upper Indus River basin (UIRB) by using an innovative trend analysis (ITA) method, Mann-Kendall (MK) and Sen's slope estimator tests. Moreover, the annual precipitation time series is investigated for five precipitation intensities i.e. light, low, moderate, high and heavy; and on a seasonal scale for extreme values i.e. light and heavy precipitation intensities. Annual precipitation showed an increasing trend at four stations in the northeast region and a decreasing trend at two stations in the southeast region of UIRB. On a seasonal scale, the results showed that Garidopatta, Peshawar, Astore and Gupis stations are more sensitive to seasonal precipitation variabilities. Changes in heavy precipitation (> 90th percentile) are found more severe in winter and summer seasons in the northern regions suggesting a probable flooding aggravation. However, a reduction in flooding event observed during the spring season in the southern regions of the UIRB indicating a shift in the precipitation regime from south to north. The results of light precipitation (< 10th percentile) intensity showed that winter and spring seasons are more vulnerable to the occurrence of prolonged drought events. Moreover, ITA method has the advantage of detecting the sub-trends in the precipitation series because of its ability to present the results in graphical format. The results of this study could help to understand seasonal and annual precipitation variability over UIRB and will have imperative insinuations for further studies. [ABSTRACT FROM AUTHOR]

Understanding future climate change is crucial for securing and managing water supplies necessary for agricultural activities in China, particularly in rainfed agriculture regions. This paper evaluates the projected climate change for nine major agricultural zones in China, using ensembles of regional climate models (RCMs) simulated under the Coordinated Regional Downscaling Experiment-East Asia second phase (CORDEX-EA-II) framework. The simulations were conducted for two climate scenarios (RCP2.6 and RCP8.5) at a 25 km grid spacing, with three RCMs (RegCM4, REMO, and WRF) driven by multiple CMIP5 global climate models (GCMs). The study compares the RCM simulations to the driving CMIP5 and the recent CMIP6 ensembles, focusing on surface temperature, precipitation, and surface relative humidity for the present day (1981–2010), mid-future (2036–2065), and far future (2070–2099) periods. The model evaluations indicate that the GCM and RCM simulations are consistent with observations, with RCMs showing better performance than the driving GCMs. The results show that both GCMs and RCMs project increased temperature and precipitation in most agricultural zones of China in the future, with the CMIP6 ensembles projecting the largest temperature increase and the CORDEX-EA-II ensemble showing the finest spatial details. Relative humidity is projected to decrease over major rice-producing areas of South China in the CORDEX-EA-II, CMIP5, and CMIP6 ensembles. This study provides valuable information to support climate change adaptation and mitigation efforts in China, particularly in the agricultural sectors. • CORDEX-EA-II simulations demonstrate better model performance over China. • Temperature and precipitation are projected to increase in the future. • Relative humidity is projected to decrease over South China. [ABSTRACT FROM AUTHOR]

Besides the traditional hybrid covariance data assimilation (referred to as “HCDA” in this paper) method, the hybrid gain data assimilation (referred to as “HGDA”) has been proposed recently to combine the ensemble Kalman filter and variational methods, showing potential advantages in global models. To evaluate the impact of HGDA on regional and meso-scale numerical weather prediction using WRF model over east China, both single observation tests and full cycling experiments for 3-weeks in July 2013 were conducted using the 3DVar, EnKF, HCDA and HGDA methods. The results of single observation tests showed that the analysis increments of HGDA retained more characteristics of the EnKF than HCDA because of utilizing the EnKF analysis ensemble mean in the re-center step. Both the hybrid data assimilation methods showed superiority over the pure EnKF and 3DVar in full cycling experiments. The average RMSE of HGDA was slightly smaller than the HCDA. It was also found that the HGDA method showed its advantage over HCDA at shorter leading time and yielded the highest precipitation score. For rainfall field, the HGDA had the best results in terms of intensity and coverage. Furthermore, the HGDA showed better results for supplying sufficient moisture conditions over rainfall area, such as precipitable water and water vapor flux. The uplift vertical velocity that contributed to the improvement of precipitation simulation was also strengthened. In general, both of the hybrid data assimilation methods showed better results than EnKF and 3DVar. Especially, the HGDA method showed advantage benefiting from the utilization of optimal EnKF analysis mean and 3DVar analysis which equals to the linearly combination of the gain matrix, considering the total error variance. [ABSTRACT FROM AUTHOR]

Quantitative precipitation estimation (QPE) is one of the important applications of weather radars. However, in complex terrain such as Tibetan Plateau, it is a challenging task to obtain an optimal Z – R relation due to the complex spatial and temporal variability in precipitation microphysics. This paper develops two radar QPE schemes respectively based on Reflectivity Threshold (RT) and Storm Cell Identification and Tracking (SCIT) algorithms using observations from 11 Doppler weather radars and 3264 rain gauges over the Eastern Tibetan Plateau (ETP). These two QPE methodologies are evaluated extensively using four precipitation events that are characterized by different meteorological features. Precipitation characteristics of independent storm cells associated with these four events, as well as the storm-scale differences, are investigated using short-term vertical profile of reflectivity (VPR) clusters. Evaluation results show that the SCIT-based rainfall approach performs better than the simple RT-based method for all precipitation events in terms of score comparison using validation gauge measurements as references. It is also found that the SCIT-based approach can effectively mitigate the local error of radar QPE and represent the precipitation spatiotemporal variability better than the RT-based scheme. [ABSTRACT FROM AUTHOR]

Regional precipitation patterns may change in a warmer climate, thereby increasing flood and drought risks. In this paper, annual, annual maximum, intense, heavy, moderate, light, and trace precipitation are employed as indicators to assess changes in precipitation patterns under two scenarios in which the global mean temperature increases by 1.5 °C and 2.0 °C relative to pre-industrial levels using the regional climate model COSMO-CLM (CCLM). The results show that annual precipitation in China will be approximately 2.5% higher under 1.5 °C warming relative to the present-day baseline (1980–2009), although it will decrease by approximately 4.0% under an additional 0.5 °C increase in global mean temperature. This trend is spatially consistent for regions with annual precipitation of 400–800 mm, which has experienced a drying trend during the past half century; thus, limiting global warming to 1.5 °C may mitigate these drying conditions. The annual maximum precipitation continues to increase from present day levels to the 2.0 °C warming scenario. Relative to the baseline period, the frequency of trace and light precipitation days exhibits a negative trend, while that of moderate, heavy, and intense precipitation days has a positive trend under the 1.5 °C warming scenario. For the 2.0 °C warming world, the frequency of days is projected to decrease for all precipitation categories, although the intensity of intense precipitation increases. Spatially, a decrease in the number of precipitation days is expected to continue in central and northern China, where a drying trend has persisted over the past half century. Southeastern China, which already suffers greatly from flooding, is expected to face more heavy and intense precipitation with an additional 0.5 °C increase in global mean temperature. Meanwhile, the intensity of intense precipitation is expected to increase in northern China, and the contribution of light and moderate precipitation to the annual precipitation is expected to decrease in southeastern China. Therefore, flood risk in northern China and drought risk in southern China should draw more attention for a global air temperature increase from 1.5 °C to 2.0 °C. [ABSTRACT FROM AUTHOR]

In recent years, climate extreme events have caused increasing direct economic and social losses in the arid region of northwestern China. Based on daily temperature and precipitation data from 1960 to 2010, this paper discussed the linear trend and abrupt changes of climate indices. The general evolution was obtained by the empirical orthogonal function (EOF), the Mann-Kendall test, and the distribution-free cumulative sum chart (CUSUM) test. The results are as follows: (1) climate showed a warming trend at annual and seasonal scale, with all temperature indices exhibiting statistically significant changes. The warm indices have increased, with 1.37%days/decade of warm days (TX90p), 0.17 °C/decade of warmest days (TXx) and 1.97 days/decade of warm spell duration indicator (WSDI), respectively. The cold indices have decreased, with − 1.89%days/decade, 0.65 °C/decade and − 0.66 days/decade for cold nights (TN10p), coldest nights (TNn) and cold spell duration indicator (CSDI), respectively. The precipitation indices have also increased significantly, coupled with the changes of magnitude (max 1-day precipitation amount (RX1day)), frequency (rain day (R0.1)), and duration (consecutive dry days (CDD)). (2) Abrupt changes of the annual regional precipitation indices and the minimum temperature indices were observed around 1986, and that of the maximum temperature indices were observed in 1996. (3) The EOF1 indicated the overall coherent distribution for the whole study area, and its principal component (PC1) was also observed, showing a significant linear trend with an abrupt change, which were in accordance with the regional observation results. EOF2 and EOF3 show contrasts between the southern and northern study areas, and between the eastern and western study areas, respectively, whereas no significant tendency was observed for their PCs. Hence, the climate indices have changed significantly, with linear trends and abrupt changes noted for all climate indices, which will have serious impacts on water resources and ecological environment in the arid region of China. [ABSTRACT FROM AUTHOR]

The regional and longer-duration dust weather in the Taklimakan Desert (TD) is mostly caused by the east-pathway dust events, which bring large amounts of dust aerosol to impact the local weather and air quality, but the dust-induced radiation feedback on meteorological processes and the dust cycle in TD is still unclear. Both dust absorption and scattering of shortwave (SW) and longwave (LW) radiation are important for dust radiation feedback (DRF), while most numerical simulations neglect the dust LW scattering effect. In this paper, we modify WRF-Chem v3.8.1 (Weather Research and Forecasting model coupled with chemistry) to include the full dust radiation effect in an only-dust simulation. Three east-pathway TD dust events were simulated by this modified WRF-Chem. For each dust event, four sensitive experiments were conducted: with SW + LW DRF, with only SW DRF, with only LW DRF, and without DRF. The modified WRF-Chem can reproduce the dust evolution and reasonably simulate the DRF. DRF enhances the mean 2-m air temperature (T2m) field by ∼1 °C in the TD and lowers the daily T2m range in the southern TD by 1.9–4.3 °C. The positive feedback of mean T2m owns mostly to two equally important contributors, i.e., the dust LW radiation impact and the synergistic impact between dust SW and LW radiation quantified by the factor separation technique. For these dust events, DRF enhances both dust loading (10–20%) and dust deposition in most TD areas, but with different impacts on the dust emission in the hinter (increasing) and the southern edge (decreasing) of the TD area. With a dynamic lift caused by mountain forcing and the DRF, the dust plume could be lifted higher in the southern TD. • Dust radiation effect of the east-pathway TD dust event is simulated by a modified WRF-Chem. • Dust radiation feedback enhances the mean T2m field by ∼1 °C. • Synergistic impact between dust SW and LW radiation contributes significantly to the mean T2m field. • Dust radiation feedback enhances TD dust loading by 10–20%. [ABSTRACT FROM AUTHOR]

The coastal area of Guangdong Province underwent an extreme rainstorm in Aug. 2018. In this paper, using the convection-permitting WRF simulation results, a comparative analysis was given to the cloud microphysical conversion processes simulated under four cloud microphysics schemes, i.e. WSM6, WDM6, WSM7 and WDM7, as well as the accompanying latent heat budget. The maintenance mechanism of the rainstorm is discussed. In all four schemes, water vapor condensing into cloud water and accretion of cloud water by rain water were the top two conversion processes. In WSM6/WDM6 scheme, the third largest conversion process was accretion of rain water by graupel; in WSM7/WDM7, however, the third largest was cloud water evaporating to water vapor. The most important source of rain water was accretion of cloud water by rain, but the differences in hydrometeors conversion between rain water and graupel, snow and hail were the leading cause of differences in simulated rainfall under different schemes. The top three releasing latent heat processes were water vapor condensing into cloud water, water vapor deposited to cloud ice, and snow sublimation. The top two absorbing latent heat processes were cloud water and rain water evaporating to water vapor. In WSM6/WDM6/WSM7 schemes, the third major process of absorption of latent heat was snow sublimating to water vapor, in WDM7, however, it was hail melting into rain water. Compared with ice-phase processes, liquid-phase processes provide more latent heat. Differences in the release and absorption of latent heat were found in the mid-high troposphere. Hydrometeors in the troposphere maintain efficient conversion and release large amounts of latent heat that formed positive feedback with convection, which was the critical reason for the development and maintenance of the extreme rainstorm. • The top two microphysical conversion and latent heat processes of four schemes were consistent. • Conversion between rain water and graupel, snow and hail led different rain intensity. • Liquid-phase processes provided more latent heat than ice-phase processes. • Differences in latent heat processes were mainly found in the mid-high troposphere. • Rapid conversion of particles and latent heat processes formed positive feedback with convection. [ABSTRACT FROM AUTHOR]

Understanding the uncertainty of satellite aerosol products for different surface types is very important for algorithm optimization and related applications. Ground-based aerosol observations provided by AERONET are most often used to validate satellite aerosol products. However, AERONET ground-based sites are unevenly distributed in China, mainly concentrated in urban areas, with few sites in other surface types, leading to limitations in evaluating the accuracy of products for different surface types. To address this issue, the National Civil Space Infrastructure Satellite Aerosol Product Validation Network (SIAVNET) is constructed to complement ground-based aerosol observations for multiple surface types in China and support the validation research of satellite aerosol products. The main purpose of this paper is to introduce SIAVNET and analyze the supplementary role it plays in the validation of satellite aerosol products for different surface types in China. Firstly, this study introduces the supplementation of SIAVNET to ground-based observations in different surface types. SIAVNET supplements 21 sites with multiple surface types, mainly supplementing vegetated areas, with 17 sites. In particular, SIAVNET places a site in bare land, which fills the gap of ground-based observation for bare land. Then, to further demonstrate the supplemental value of SIAVNET observation in the validation of satellite aerosol products, the accuracy of MODIS aerosol products with four different resolutions (i.e., 1 km, 3 km, 10 km, and 1°) for different surface types in China is evaluated using all ground-based observations. For bare land, the accuracy of different resolution products is obtained based on SIAVNET observations, with 50.91%–69.23% of the retrievals falling within the expected error, which fills the validation gap for bare land. For vegetated areas, compared to the AERONET-only based products evaluation, the use of SIAVNET significantly affects the validation results in grassland for the 3 km and 10 km products, with the proportion of retrievals falling within the expected error decreasing from 78.61%, 74.30% to 64.16% and 63.17%, failing to reach satisfactory levels (66%). For urban areas, supplemental SIAVNET observations have almost no effect on the validation results for the different aerosol products obtained based on AERONET. These results are expected to provide guidance for detailed satellite aerosol product validation over China using SIAVNET data. • SIAVNET complements the 21 sites with multiple surface types, especially filling the gap of observations in bare land. • By using the SIAVNET data, the accuracy of aerosol products over China is obtained. • The supplement of SAVNET-China data significantly influences the validation results of 3 km and 10 km products in grassland. [ABSTRACT FROM AUTHOR]

The statistical methods based on extreme value theory have been traditionally used in meteorology and hydrology for a long time. Due to climate change and variability, the hypothesis of stationarity in meteorological or hydrological time series was usually not satisfied. In this paper, a nonstationary extreme value analysis was conducted for annual maximum daily precipitation (AMP) at 631 meteorological stations over China for the period 1951–2013. Stationarity of all 631 AMP time series was firstly tested using KPSS test method, and only 48 AMP time series showed non-stationarity at 5% significance level. The trends of these 48 nonstationary AMP time series were further tested using M-K test method. There were 25 nonstationary AMP time series mainly distributed in southern and western China showing significant positive trend at 5% level. Another 5 nonstationary AMP time series with significant negative trends were near northern urban agglomeration, Sichuan Basin, and central China. For these nonstationary AMP time series with significant positive or negative trends, the location parameter in generalized extreme value (GEV) distribution was assumed to be time-varying, and the trends were successfully characterized by the nonstationary GEV models. For the remaining 18 nonstationary AMP time series mainly in the eastern portion of China, no significant trend was detected. The correlation analysis showed that only 5 nonstationary AMP time series were significantly correlated with one or two of the four climate indices EASMI, WPI, SOI, and PDO. Then, the location and scale parameters in the GEV distribution were modeled as functions of the significantly correlated climate indices. The modeling results in this study showed that the nonstationary GEV distributions performed better than their stationary equivalents. Finally, 20-year and 50-year return levels of precipitation extremes at all 631 stations were estimated using the best fitting distribution for the year 1961 and 2013, respectively. [ABSTRACT FROM AUTHOR]

Investigation of the number concentration of ice nucleating particles (INP) in the deposition nucleation mode during a dust event is reported. The results discussed in this paper are the first continuous INP measurements in Xinjiang, northwest of China, over a period with a strong dust event. The average INP concentration at − 20 °C and 22% of supersaturation with respect to ice during non-dust days is found around 11 particles per liter, but it reached several hundred per liter in a dust event. A close correlation is also found between the INP number concentration with the number concentration of aerosol particles larger than 0.5 μm in diameter measured during a dust event, which means that a higher concentration of larger particles induced higher INP number concentration. Parameterizations were developed based on measurements to represent the variations of INP concentration with temperature, supersaturation, and the number concentration of aerosol particles with size larger than 0.5 μm. It should be the first ever, as we have known so far, to measure ice nuclei and aerosol properties simultaneously in a desert area and to contrast INP concentrations in dust and dust-free days, and could advancing our understanding of the effects of dust particles on ice nucleation. [ABSTRACT FROM AUTHOR]

In this paper, the HYSPLIT model, driven with reanalysis meteorological data from 1978 to 2013, was used to understand the potential transport characteristics of dust and salt dust emanating from the playa of Ebinur Lake in arid northwest China. Daily air parcel trajectories were computed forward for 8 days from an origin centered over Ebinur Lake at 100 m above ground level. Air parcel trajectory density plots were mapped for seven levels: 0–100 m agl., 100–500 m agl., 500–1000 m agl., 1000–1500 m agl., 1500–2000 m agl., 2000–3000 m agl., and 3000–5000 m agl. These show that potential dust transport pathways have clear seasonal differentiation. The potential transport distance of dust and salt dust is greatest in spring and summer. In autumn and winter, the potential transport of the high-density air trajectory is below 1000 m traveling a shorter distance. Potential dust transport pathways showed notifying directivity in different seasons and heights. Southeast in spring and summer, and north to northeast in autumn and winter are the two main potential transport channels of dust and salt dust. Accordingly, dust and salt dust from the playa of Ebinur Lake may influence the atmospheric processes and biogeochemical cycles of a vast region. The main area of influence of dust and salt dust is close to the source area, and will significantly accelerate the melting of snow and ice in the Tianshan Mountains. This highlights the urgent need to combine remote sensing, isotope and other methods to further research the transport characteristics of dust and salt dust from the playa of the Ebinur Lake. [ABSTRACT FROM AUTHOR]

Based on monthly rainfall station data from the National Climate Prediction Center of China Meteorological Administration, reanalysis monthly data from NCEP/NCAR including the monthly mean and long-term mean values for geopotential height, winds of multi-levels, NOAA(National Oceanic and Atmospheric Administration) monthly Sea Surface Temperature (ERSSTV5), the causes of anomalous excessive precipitation in 2021/2022 winter over South China (SC) are investigated by Liang-Kleeman information flow, composite and wave flux methods. The results show that the winter precipitation over SC in 2021/2022 DJF is far more than normal, and the associated circulation patterns are obviously different from those induced by traditional La Niña, especially in the Atlantic and East Asia areas south to Lake Baikal. In 2021/2022 DJF, the Tibet Plateau (TP) exists anomalous cyclone with strong ascending motion, which directly affects the circulation patterns in Eastern China and thus the precipitation in SC. It is a significant causal relationship for the earlier season velocity potential at 850 hPa (related to the anomalous SST) over the tropical Atlantic to later DJF anomalous vertical motions over TP. Especially when the anomalies in tropical Atlantic leads one month before, the relationship is closest. The anomalies of the tropical Atlantic can stimulate the Rossby wave train which propagates downstream, corresponding to the abnormal cyclonic circulation over TP. In the early autumn to winter of 2021/2022, the 850 hPa potential velocity anomalies in the tropical Atlantic were significant with positive phase. The Rossby wave train excited by the potential velocity anomalies and then propagated along the great circle path and global jet stream (GJT) over South Asia (SA), formed an anomalous cyclonic with ascending motion over TP and lead more precipitation over SC in winter of 2021/2022. Winter rainfall, usually accompanying with lower temperature, will bring severely bad influence on traffic, power supply, communication, agriculture and people's lives. The results of this paper can provide a reference for further understanding the causes and mechanism of DJF rainfall over SC. • The winter precipitation over SC in 2021/2022 DJF is extremely more than normal, and the associated circulation patterns are obviously different from those induced by La Niña, especially in the Atlantic and East Asia areas south to Lake Baikal. • Strong ascending motion over TP(Tibet Plateau) affects the circulation patterns directly in eastern China and lead to the excessive precipitation in SC during 2021/2022 DJF. • The anomalies over the tropical Atlantic can stimulate the Rossby wave train and propagate downstream, and the Rossby wave trains allow energy to propagate to TP area with wave flux convergent, contributing certainly to the anomaly cyclone circulation there. [ABSTRACT FROM AUTHOR]

Abstract: Based on the various fog remote sensing information products abstracted from the polar orbit meteorological satellite data (NOAA and FY), this paper analyzes the characteristics of the frequency and distribution that dense fogs have taken place in the Beijing district from 2001 to 2005. Among those information products, the statistical graph of the foggy days in Beijing from 2001 to 2005 by means of satellite remote-sensing reflects the frequency that dense fog has occurred in the different regions in Beijing; and the statistical graph of the foggy days of each season by satellite remote-sensing shows the characteristics of the temporal and spatial change of the fog distribution in Beijing in different seasons; the fog degree index(like pixel-level spatial measurement) by satellite remote-sensing reflects the fog frequency difference on unit area in different counties of Beijing. Meanwhile, based on the satellite remote-sensing pictures, data on the main meteorological elements that contribute to the formation of fog, geographic information, and DEM data, this paper makes an analysis in 3 areas, the traits of the fog distribution in the different regions of Beijing in different seasons; meteorological causes for temporal and spatial changes of the main fog types (advection fog, radiation fog). This paper also gave a brief introduction of the general principles of meteorological satellite remote sensing fog, fog information extraction method, as well as the process of satellite orbit selecting according to the ground visibility, data processing and product generation. [Copyright &y& Elsevier]

A hybrid downscaling model for operational prediction of summer precipitation at 160 stations over China is proposed in this paper. The prediction model is conducted in February, and six predictors extending from the tropics to high latitudes with specific mechanisms are involved. Simultaneous sea level pressure over pan-East Asia and spring sea surface temperature (SST) over the tropical Atlantic Ocean are from the Climate Forecast System version 2 (CFSv2). The others are observational predictors including winter SST over the tropical Indian Ocean, sea ice concentration (SIC) over the Hudson Bay–Baffin Bay–Davis Strait in winter and the Barents–Kara Sea in autumn, and winter outgoing longwave radiation over the tropics. Different predictors impact the summer precipitation of different regions in China. Validations for schemes based on individual predictors (IP-schemes) and all predictors (HD-scheme) indicate that downscaling schemes outperform CFSv2 in predicting summer precipitation over China, especially the HD-scheme. The temporal and spatial anomaly correlation coefficient, root-mean-square errors, and ratio of the same sign (RSS) are estimated. For RSS (Anomalous RSS), the results are improved from 27.8% (23.8%) for CFSv2 to 77.8% (61.9%) for HD-scheme. Notably, the RSSs of IP-schemes based on SIC are equivalent to that of HD-scheme. This partly emphasizes the importance of preceding Arctic sea ice to summer rainfall in China. Moreover, two cases from hindcasts and two from the operational application are chosen for further validation of the prediction skill of HD-scheme. The case studies confirm that the hybrid downscaling model proposed in this paper not only outperforms CFSv2 but can also be applied well to real-time forecasting of summer precipitation over China. • One-season‑leading hybrid downscaling prediction model for summer rainfall in China. • Combination of the year-to-year increment method and spatially coupled downscaling approach. • Considering predictors with specific mechanisms from tropics to high latitudes. • Considering both simultaneous and preceding predictors • Well applied in real-time forecasting [ABSTRACT FROM AUTHOR]

Understanding the lightning climatological distribution is of great significance but remains challenging which is in part due to the lack of continuous and uniform lightning observations. In this paper, for the first time, an 11-year ground-based cloud-to-cloud lightning dataset of China National Lightning Detection Network from 2010 to 2020 is used to investigate the lightning climatology over China's land area in terms of spatial distribution, seasonal, monthly and diurnal variations. Lightning activity in China's land area generally decreases from south to north and from east to west. The mean cloud-to-ground lightning density of China's land area is 0.9 fl km−2 yr−1, with the average maximums (exceeding 10 fl km−2 yr−1) are found in the south and east coastal provinces, such as Guangdong, Hainan, Fujian and Zhejiang Province. The lightning activity in spring, summer and autumn seems consistent throughout the daytime cycle, with the lightning activity is rather weak in the morning and most active in the afternoon, while winter lightning appears to be more active in the nighttime and in the very early morning produced from nocturnal thunderstorms. The cloud-to-ground lightning activity in the tropical and subtropical areas within 15–25°N is mainly concentrated in the late spring and early summer, with two weak peaks in May and August, while lightning in mid latitudes within 25–55°N mainly occurs in the summer (June–July-August). The percentage of positive cloud-to-ground lightning flashes with peak current higher than 75 kA is more than 3 times than that of negative cloud-to-ground lightning flashes. Meanwhile, the mean peak current of cloud-to-ground lightning flashes shows an inverse diurnal pattern to the cloud-to-ground lightning activity. • Cloud-to-ground lightning climatology over Chinese continent is first investigated. • Lightning activity generally decreases from south to north and from east to west. • More lightning occurs in the summer in mid latitudes within 25–55°N. • Winter lightning is unique, usually produced from nocturnal thunderstorms. [ABSTRACT FROM AUTHOR]

Actual evapotranspiration (AE) is a key component of water cycle. The arid climate of northwest China makes water supply a major constraint on AE. Water source analysis is of great significance to study the causes of AE change. In this paper, we presented an assessment of AE trends in northwest China based on GLEAM (AE_GLEAM), an ensemble of six reanalyses (AE_reanalyses), and a complementary-relationship-based AE dataset (AE_CR). Both AE_GLEAM and AE_reanalyses increased significantly (p < 0.001) during 1981–2017. AE_CR also increased to a certain extent, but the rate was slower. In general, the increasing trends of AE were mainly found in mountainous areas, such as the Altai, Tianshan, Karakoram, Kunlun, Altun, and Qilian Mountains. For these regions, AE was even higher than precipitation in terms of both the climatological mean and the linear trends. It demonstrated that terrestrial water storage (S) could give supplementary supply for AE. Therefore, we extended the Budyko framework to evaluate the effect of S on AE. Taking the landscape parameter n = 1.8 as a reference, S contributed approximately 27% of total water availability for AE. Overall, S seemed to be a major contributor to the increasing AE in the Altai, Tianshan, Qilian, and Altun Mountains. Precipitation was the main source of evaporated water in the western Tianshan to Karakoram Mountains, where potential evapotranspiration also contributed to the increase in AE. In the case of different n values, the contribution from S had a deviation range of −16.9% to 8.5%. This model provides an opportunity to assess the response of AE to S in the absence of observational data. [Display omitted] • Actual evapotranspiration (AE) increased significantly in northwest China during 1981–2017. • The increasing trends in AE were mainly found in mountainous areas. • AE variability was controlled not only by water supply from precipitation but also by other water sources. • Terrestrial water storage (S) contributes approximately 27% of total water availability for AE. • S seems to be a major contributor to the increasing AE in the Altai, Tianshan, Qilian, and Altun Mountains. [ABSTRACT FROM AUTHOR]

This paper aims to test the ability of the WRF-Chem model to simulate sand storms in Northwest China and improve the simulation results by introducing remote sensing soil moisture data into WRF-Chem. We conducted sensitivity tests, including parameterization scheme tests and soil moisture tests using WRF-Chem. By comparing various combinations of parameterization schemes, which have considerable impacts on sand emissions, the most suitable parameterization scheme for WRF-Chem to simulate sand storms in Northwest China was selected for establishing models in future research. Based on the optimal combination of parameterization schemes, the sensitivity of sand emissions to soil moisture was tested, indicating that soil moisture has a substantial influence on sand emissions and revealing a nonlinear relationship between sand emissions and soil moisture. Although sand simulations are sensitive to soil moisture, the sand emission volume does not always increase with decreasing soil moisture content. Moreover, the soil moisture content simulated by WRF-Chem is quite different from that observed by satellites. Therefore, we selected ten sand storms that occurred in Northwest China in 2009–2018, including weak, moderate and strong sand storms, to explore the responses of sand storms of different intensities to soil moisture. Some experiments were conducted in two scenarios: scenario A was simulated only by WRF-Chem, and scenario B was designed by replacing the initial soil moisture field in WRF-Chem with soil moisture satellite data from AMSR2 and AMSR-E. Comparing the simulation results with in-situ ground-based and satellite-based measurements indicates that WRF-Chem can capture strong sand storms and some moderate sand storms, but the ability to simulate weak sand storms needs to be greatly improved. After introducing remote sensing soil moisture data into WRF-Chem, the simulation of sand emissions becomes more accurate, substantially improving the simulation results. Among the ten simulated sand storms, the AOD (aerosol optical depth) and PM10 simulation accuracies are improved for five and seven sand storms, respectively. After this improvement, the AOD correlation coefficient can reach 0.63, and the PM10 correlation coefficient can reach 0.60. • The paper screened out the best parameterization scheme of sand storm simulation that is suitable for northwestern China. • Improved the simulation results of the WRF-Chem model using soil moisture remote sensing data. • WRF-Chem can better capture strong and some moderate sand storms, but need to improve weak sand storm simulation ability. [ABSTRACT FROM AUTHOR]

This paper investigates the vertical structure and turbulence activities in fog events. Three fog cases that occurred in the winter of 2010 over Tianjin, China were selected, including two advection–radiation fog events and an advection fog event. Field observations collected at a 255-m tall meteorological tower in Tianjin were analyzed, including turbulence measurements using the eddy covariance systems installed at three levels, measurements of temperature, horizontal wind and humidity collected at 15 levels, surface radiation fluxes and horizontal visibility. The results suggest that the advection fog was more enduring and thicker than the advection–radiation fog. The fog events were characterized by low wind speed throughout the fog layer. A temperature inversion and low-level jet were observed above the advection–radiation fog layer. The surface net radiation reflected some differences among the fog events. The collapse of turbulence was a necessity for the formation fog, and moderate turbulence was favorable to the development and maintenance. The heat and water vapor fluxes in the advection–radiation fog were weaker than those in the advection fog, in which the stratification was slightly unstable. The relationships among the turbulent transport efficiencies of water vapor, temperature and momentum were examined. The results suggest the applicability of local similarity in the fog layer for the momentum transport efficiency. [ABSTRACT FROM AUTHOR]

Dust aerosols play an important role in climate change, however, the annual emissions simulated from dusty weather and dust devils are largely underestimated than observed, possibly due to the lack of gust on dust emission contribution under stationary weather conditions. This study estimates the gust emission by the use of 1-year measurements of 10-min wind speed from two field sites in Dunhuang (sandy desert) and Yumen (gravel desert) in northwestern China, and the concurrent estimations of dusty weather and dust devils are examined as well. The results show that: 1) about 25% of gust could contribute to dust emission throughout the year regardless in Dunhuang or Yumen. 2) Three dust processes have diverse occurrence times and intensities, i.e. gust could occur at any time with fiercer fluctuation in dust emission than dust devils and dusty weather which mainly occur between April and September and in spring, respectively. 3) During the non-dusty seasons, both dust devils and gust are prominent with gust overwhelmingly contributing the most, while during the dusty season when three mechanisms co-exists, dusty weather outperforms the others in Dunhuang, but takes a relatively even share of around 33% as the other two in Yumen. 4) On an annual scale, gust is the highest and second-highest contributor to the annual total dust emissions in Yumen and Dunhuang, respectively. This study not only highlights the nonnegligible contributor/mechanism of gust to dust emission, complementing the existing emission mechanisms to form a complete dust emission mechanism system, but also sheds light on a new perspective explaining the largely underestimated dust aerosols that are significant in the assessment of climate effects. • Significant diurnal, monthly and seasonal variability of gust emission. • Gust emission occurs randomly with the fiercest fluctuations. • Gust emission is overwhelmingly dominant during the non-dusty season. • 18.5– 50.4% of annual total dust emission is from gust in sandy deserts and Gobi. • Wind gust is an important and new dust emission mechanism. [ABSTRACT FROM AUTHOR]

The Directional Polarimetric Camera (DPC) is the first Chinese satellite-borne multi-angle polarimetric sensor onboard the GaoFen-5 (GF-5) satellite, which was launched on May 9th 2018. In this paper, we present the spatiotemporal variability of satellite-measured aerosol components (such as, black carbon, brown carbon, iron oxides contained in mineral dust etc.) over North China Plain (36–41°N, 113–123°E) for a heavily haze-polluted case, to demonstrate the first successful retrievals of aerosol component content and optical property directly from the DPC/GF-5 instrument measurements. We also reveal the relationship between absorbing/scattering component mass ratio and aerosol absorption based on the multi-angle polarimetric satellite measurements, which presents comparable agreement with previous laboratory studies and field studies for an indirect validation of aerosol component retrievals. In addition, the feasibility, stability and uncertainty of the aerosol optical property and component content retrievals from DPC multi-angle polarimetric observations were evaluated and assessed by sensitivity tests. The distributions of DPC/GF-5 aerosol optical depth (AOD) are in line with satellite-observed MODIS (Moderate-resolution Imaging Spectroradiometer) AOD and ground-based CARSNET (China Aerosol Remote Sensing Network) AOD products. Therefore, the multi-angle polarimetric satellite measurements show an encouraging potential for the comprehensive inversion of aerosol optical, microphysical and chemical properties. The results and further applications of this component algorithm in the future are helpful to reduce the uncertainty of climate change assessment by providing the measurements of aerosol component, in particular for black carbon, brown carbon, and iron oxides contained in dust, with large and extensive spatiotemporal scale. [Display omitted] • We propose a new aerosol retrieval application to multiangle polarimetric observation. • The first successful retrieval of aerosol component content from DPC is presented. • Satellite-measured BC, BrC and iron oxides are characterized in a haze-polluted case. • We reveal the link of satellite-measured absorbing/scattering component ratio to AAE. [ABSTRACT FROM AUTHOR]

Based on the principle of light propagation, it is necessary to obtain the ratio (R MN) of atmospheric aerosol mass concentration to the imaginary part of the atmospheric equivalent refractive index for measuring aerosol mass vertical flux. In this paper, the factors affecting the R MN values are analyzed by numerical calculation under an ideal state and by using observational data. Numerical calculations show that the R MN is mainly determined by the aerosol particle size distribution (PSD), hygroscopicity parameters and relative humidity. With the same relative humidity, the smaller the geometric mean diameter (Dg) is, the larger the R MN , and when the aerosol particle hygroscopicity parameter is greater than 0.14, the greater the relative humidity is, the smaller the R MN. Comprehensive experiments were conducted in urban Hefei, and the results of observations at Hefei confirm the numerical results. Data from ten cities across China also confirm the numerical results. The order of geometric mean diameter of aerosol particles at the ten sites can be determined by the order of R MN , and the order of hygroscopicity parameters at the ten sites can be determined by the order of the change rate of R MN with relative humidity. The geometric mean diameters of aerosol particles are different among the ten sites, while the hygroscopicity parameters are similar. • The ratio (R MN) of TSP mass concentration to the imaginary part of the atmospheric equivalent refractive index is defined • The R MN is mainly affected by aerosol particle size distribution, relative humidity and hygroscopicity parameter. • The order of geometric mean diameter of aerosol particles at the ten sites can be determined by the order of R MN. • The variation of R MN with relative humidity reflects hygroscopicity parameter (α) of the aerosol particles. [ABSTRACT FROM AUTHOR]

This paper explored the projected changes in precipitation, maximum temperature (T max), and minimum temperature (T min) over the Yangtze River Basin (YRB) based on 23 Global climate models (GCMs) from the Coupled Model Intercomparison Project phase 6 (CMIP6). The Empirical Quantile Mapping (EQM) approach was firstly applied to correct the biases in the GCMs. Next, the future changes were investigated by analyzing the multi-model ensemble (MME) of the bias-corrected dataset during 2025–2044 (near-term), 2045–2064 (mid-term), and 2081–2100 (long-term) periods, with reference to the baseline period 1995–2014, under three integrated scenarios (SSP1-2.6, SSP2-4.5, and SSP5-8.5) of the Shared Socioeconomic Pathways (SSPs) and the Representative Concentration Pathways (RCPs). Results show that: (1) the biases in CMIP6 GCMs can be effectively corrected by EQM, and the MME performs better than individual models for each climatic variable. (2) Precipitation over the YRB from 2025 to 2100 is projected to increase at the rate of 9.66 mm/decade, 13.45 mm/decade, and 21.01 mm/decade under SSP1‐2.6, SSP2‐4.5, and SSP5‐8.5, respectively. In the long-term, the annual precipitation is projected to increase by 10.41%, 10.66% and 15.80%, under SSP1‐2.6, SSP2‐4.5 and SSP5‐8.5, respectively. (3) T max (T min) over the YRB is projected to increase by 0.09 (0.07) °C/decade, 0.29 (0.27) °C/decade, and 0.66 (0.64) °C/decade under SSP1‐2.6, SSP2‐4.5, and SSP5‐8.5, respectively. In the long-term, T max (T min) averaged over the YRB is projected to increase by 1.75 (1.50) °C, 2.72 (2.54) °C and 5.04 (4.85) °C under SSP1‐2.6, SSP2‐4.5 and SSP5‐8.5, respectively. (4) Uncertainties in the projected precipitation and temperature over the YRB were reduced based on MME. But further researches, such as selecting the superior models with respect to the regional climate of the YRB from the CMIP6 and using the ensemble methods that assign weight based on the performance of each model, are still needed to provide more reliable climate projections. • Projected changes were explored by 23 CMIP6 GCMs under the three SSP-RCP scenarios. • Biases in the GCMs were corrected by Empirical Quantile Mapping (EQM) method. • Multi-model ensemble (MME) was used to reduce the uncertainties. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a multi-functional moving-cut high-dimensional model representation (MC-HDMR) approach is developed for simulation of multi-component input and output aerosols. This method leads to an aerosol prediction database system based on full thermodynamic models such as ISORROPIA. The developed prediction system can efficiently compute the prediction of aerosol thermodynamic equilibrium in high-dimensional domains with a large range of aerosol concentrations from 10-9 molm-3 to 10-5 molm-3 and for different types of aerosols including aerosols containing sea salt component. Numerical computations show the great computational efficiency of the method that its CPU-time cost is much less compared to ISORROPIA. Three types of aerosols of urban, non-urban continental and marine are considered and the multi-component outputs predicted by the approach are in great agreement with those by ISORROPIA and AIM2. Actual aerosol examples in European and Asian cities are simulated by the approach and ISORROPIA and AIM2. Numerical results match very well and show heavier traffic pollution at the areas of HU02, IT01 and NL09 among six European stations, more anthropogenic pollution in Shanghai than other three Asian cities, and Hong Kong''s aerosols affected by the marine environment. [Copyright &y& Elsevier]

Abstract: In this paper, the variability of daily temperature in the Yangtze River Delta (YRD) for the period 1958–2007 was investigated by selecting three typical temperature variables (daily minimum, mean and maximum temperatures) and the diurnal temperature range (DTR). Three variability patterns of daily mean temperature and two variability patterns of daily minimum and maximum temperatures were first classed, and then statistical properties of three temperature variables in 1958–1985 and 1986–2007 were analyzed. After that, temporal trends of three temperature variables and DTR were detected. Finally, the impacts of urbanization on the variability of daily temperature were investigated. Results indicate that: (1) daily mean temperature shows more complex variability than daily minimum and maximum temperatures; (2) in 1986–2007 three temperature variables have bigger mean values but smaller C v (coefficient of variance) values, and are more close to normal probability distribution; (3) three temperature variables show positive trends in 1986–2007, and the increase of daily mean temperature is more due to the increase of daily minimum temperature in the northern YRD but due to daily maximum temperature in the mid and southern YRD; (4) in the mid and southern YRD, daily maximum temperature has bigger increasing magnitude than daily minimum temperature in 1986–2007, causing positive trend of DTR; and (5) rapid urbanization causes normal distribution of three temperature variables, and notably increasing magnitude of daily temperature and DTR in 1986–2007 at the lower reaches of the Yangtze River and the Hangzhou Bay. [Copyright &y& Elsevier]

Abstract: To improve the air quality during the 2008 Beijing Olympic Games, the Beijing Municipal Government enforced a series of emission control measures. This provided a valuable case study to evaluate the effectiveness of these aggressive measures on mitigating air pollution and improving the atmospheric environment. In this paper, we report the first results of the chemical and Sr isotopic compositions of the rainwater in Beijing during the 2008 Olympic year. The ionic composition of samples show that Ca2+ and NH4 + were the dominant cations, accounting for about 76–97% of the total cations, and that SO4 2− and NO3 − were the major anions, accounting for 61–91% of the total anions measured. Using Na as the indicator of marine origin and Al as that of terrestrial inputs, the proportions of sea salt and terrestrial elements were estimated from elemental ratios. The calculated results indicate that the major chemical components were mainly of non-sea-salt origin. Good correlation between Ca2+ and Sr2+ (R 2 =0.85) in rainwater samples indicates the potential of Sr as a provenance tracer for Ca. Sr2+ concentrations in rainwater samples ranged from 0.01 to 2.87μmoll−1, with 87Sr/86Sr ratios from 0.7092 to 0.7109. All of the samples had a 87Sr/86Sr ratio higher than that of seawater. The 87Sr/86Sr isotopic and elemental ratio systems show that the data set of rainwater was mainly distributed between the seawater end-member (~0.70917) and the soil dust end-member (0.7111–0.7115), and the analysis indicate that the effect of anthropogenic inputs could decrease in 2008. Comparisons of the chemical composition of the rainwater in different periods show that all chemical components, except NH4 +, had the lowest concentration levels during the Olympic Game period. The VWM concentrations of major ions in the rainwater decreased significantly during the Olympic period by up to 29% for SO4 2−, 39% for NO3 −, 38% for Ca2+, 51% for Mg2+, 57% for K+, and 44% for Na+, compared with the pre-control period. The concentrations of almost all species decreased during the 2008 Olympics, most likely due to both strict emission controls and favorable meteorological conditions. [Copyright &y& Elsevier]

Abstract: Size distributions can provide important information about aerosol sources, formation, and growth mechanisms. However, compared to size distributions of inorganic aerosols, size distributions of carbonaceous aerosols have been much less studied and reported in the literature. In this paper, we systematically measured size distributions of elemental carbon (EC), organic carbon (OC), oxalate, polycyclic aromatic hydrocarbons (PAHs), as well as major inorganic ions in urban aerosols in Shenzhen, China. Totally 24 sets of samples were collected using a ten-stage micro orifice uniform deposit impactor (MOUDI) during October 2009 to February 2010. Three lognormal modes contained in the size distributions of species were resolved based on positive matrix factorization (PMF) analysis of the measured dataset, corresponding to the condensation (peak=0.34μm), droplet (peak=0.84μm), and coarse (peak=5.4μm) modes, respectively. The mean concentrations of EC in the condensation, droplet, and coarse modes were 2.20, 1.18, and 0.64μgm−3, respectively, and the modal characteristics of EC indicate that fresher local combustion emissions contributed mostly to aerosol EC in the urban atmosphere of Shenzhen. The mean concentrations of OC in the condensation, droplet, and coarse modes were 2.29, 3.34, and 3.51μgm−3, respectively, and the modal characteristics of OC indicate that its sources were more primary in the condensation mode while more secondary in the droplet mode. The modal characteristics of aerosol oxalate and PAHs suggest that they were predominantly from in-cloud secondary formation and local emissions, respectively. [Copyright &y& Elsevier]

Abstract: A seven-year analysis of clear-sky column-integrated aerosol optical properties and direct radiative forcing at Gosan in Korea is presented in this paper; the Gosan site is heavily impacted by aerosols emitted from the Asian continent. MODIS and AERONET Sun/sky radiometer measurements showed significant seasonal and geographical variability in aerosol optical depth (AOD), with high AODs over the east coastal industrialized regions of China in spring and summer. At the Gosan site, the monthly mean AOD at 675nm ranged between 0.12 and 0.36. High AODs were observed from April to June (>0.33), while low-to-moderate monthly mean AODs were apparent during the remaining months. The single scattering albedo (SSA) exhibited relatively low values from February to May (<0.93), indicating the presence of light-absorbing aerosols, whereas high values of SSA (>0.93) were observed during the remaining months. The annual average clear-sky direct forcing (forcing efficiency) at the surface was −27.55±9.21W m−2 (−91.85±11.12W m−2 τ −1) and at the top of the atmosphere (TOA) was −15.79±4.44W m−2 (−53.76±6.70W m−2 τ −1), thereby leading to an atmospheric absorption of 11.76±5.82W m−2. From March to June, the surface aerosol radiative forcing (forcing efficiency) ranged between −27.29 (–85.33) and −34.76W m−2 (−97.19W m−2 τ −1), whereas at TOA it ranged between −16.84 (−51.82) and −19.10W m−2 (−56.05W m−2 τ −1), and the atmospheric forcing ranged between 10.45 and 16.41W m−2. The atmospheric forcing (i.e., atmospheric absorption) caused an increase in atmospheric heating (about 1.5 to 3.0K day−1). The strongest radiative heating was observed from April to May (>2.5K day−1). [Copyright &y& Elsevier]

Abstract: The objective of this paper is to evaluate the reliability of urban heat island intensity (UHII) as an indicator of urban heating. The diurnal patterns of air and surface-temperature based UHII and variations in urban and rural area heating were analyzed and discussed. The detailed air-temperature based UHII patterns were determined in one urban and four suburban areas of Hong Kong. UHII was determined as spatially-averaged air-temperature difference between an urban/suburban area and its surrounding rural area. Additionally, reported air and surface-temperature based UHII patterns were integrated in the discussion to carry out a comprehensive analysis. The urban and rural area heating variations (i.e., the diurnal variations in net radiation, sensible heat flux, latent heat flux, and heat stored by an area) were examined in the light of UHII patterns to validate UHII as an indicator for urban heating. It is noted that the air-temperature based UHIIs were higher and positive in the night-time but lower and negative during the daytime. On the other hand, most of the surface-temperature based UHIIs, investigated through satellite data were positive during both the daytime and night-time. It is revealed that UHII can well reflect urban heating during night-time and early morning. However, the lower and negative UHII during solar peak time (daytime when solar radiation is the dominant source of heating) has seemingly not been representing urban heating. [Copyright &y& Elsevier]

Abstract: In this paper warm cloud microphysical parameters including cloud droplet number concentration (N c), liquid water content (q l ) and effective radius (r e) from 75 flights around the Beijing area during 2005 and 2006 are summarized. Average N c (cm−3) for Cu, Sc, Ac, As and Ns are 376±290, 257±226, 147±112, 60±35 and 60±84, respectively. Many records of high N c above 1000 cm−3 are observed. The large standard deviations indicate a large variation of N c and q l in this region. The maxima of q l reach 1.4 g m−3 in Cu and 1.0 g m−3 in Sc, respectively. Different parameterizations of effective radius are examined with the in-situ data in this area. There are different ways to obtain the prefactor representing the relationship between effective radius and mean volume radius. Significant systematic errors are found to be at the large sizes when the prefactor is expressed with relative dispersion under the Gamma Distribution. Fixed prefactor of 1, which was widely used, even produces much larger error. A prefactor of 1.22 is found to be better than the former two methods by fitting with the observed data. The effective radius is further parameterized as functions of mean volume radius, liquid water content and cloud droplet number concentration. We suggest that the effective radius can be parameterized as r e,p ≈1.20r v +0.22–1.28/r v 2, which is a practical and more accurate scheme without too much computation complexity. [Copyright &y& Elsevier]

Abstract: This paper retrieves the three dimensional (3D) wind fields and studies the evolution of the 3D wind fields and the formation mechanism of the sudden heavy rainfall on Meiyu front on 26th–27th June 2003 in Huaihe river basin in China, using the volume scan data of the dual-Doppler radar located in Hefei and Maanshan cities. Due to the effect of the low level trough, low level jet and the convergence line at the low and medium levels, it produced a heavy precipitation in Anhui province. It shows clearly that the primary feature of this event is local, sudden and short timed. It is a convective-stratiform mixed cloud precipitation based on the radar echo analyses. The meso-β-scale convective system (MβCS) and the meso-γ-scale system located on the MβCS played an important role on this heavy rainfall. The meso-β-scale convective cloud has high precipitation efficiency. The dual-Doppler retrieved wind reveals that the heavy rainfall was caused by the meso-β-scale convergence lines at the low and the medium levels. The convergence line triggered and maintained the heavy rainfall. There were strong convergence and vorticity at the low and medium levels of the MβCS. The convergence line spread from west to east and the position of the convergence line at the medium levels is westward of the ones at the low levels. When the convergence line at the low and medium levels began to weak, the precipitation began to weak too. The intensity of the precipitation weakened remarkably when the convergence line dissipated. The 3D kinematic conceptual structure model of this heavy rainfall case is also given. [Copyright &y& Elsevier]

Abstract: Shanghai is the largest industrial and commercial city in China, and its air quality has been deteriorating for several decades. However, there are scarce researches on the level and seasonal variation of fine particle (PM2.5) as well as the carbonaceous fractions when compared with other cities in China and around the world. In the present paper, abundance and seasonal characteristics of PM2.5, organic carbon (OC) and elemental carbon (EC) were studied at urban and suburban sites in Shanghai during four season-representative months in 2005–2006 year. PM2.5 samples were collected with high-vol samplers and analyzed for OC and EC using thermal-optical transmittance (TOT) protocol. Results showed that the annual average PM2.5 concentrations were 90.3–95.5 μg/m3 at both sites, while OC and EC were 14.7–17.4 μg/m3 and 2.8–3.0 μg/m3, respectively, with the OC/EC ratios of 5.0–5.6. The carbonaceous levels ranked by the order of Beijing > Guangzhou > Shanghai > Hong Kong. The carbonaceous aerosol accounted for ∼30% of the PM2.5 mass. On seasonal average, the highest OC and EC levels occurred during fall, and they were higher than the values in summer by a factor of 2. Strong correlations (r =0.79–0.93) between OC and EC were found in the four seasons. Average level of secondary organic carbon (SOC) was 5.7–7.2 μg/m3, accounting for ∼30% of the total OC. Strong seasonal variation was observed for SOC with the highest value during fall, which was about two times the annual average. [Copyright &y& Elsevier]

In midsummer (July-August) of 2017, the high temperature (HT) frequency in China breaks the record since 1951. For each HT threshold from 35 °C to 40 °C, the frequency is beyond the normal by 2.58–3.46 standard deviations. Specifically, the HT events in southern China make major contributions to the new record, and they demonstrate obvious temporal variations. The strongest episode in southern China appears in mid-to-late July and lasts for nearly 20 days. The westward extension and intensification of the western Pacific subtropical high (WPSH) is usually considered as the leading factor of the HT in southern China. However, the diagnostic analysis in this paper shows that the 2017 HT event does not correspond to the intensification of the whole WPSH but to its western part, and there is a cyclonic circulation anomaly over the western Pacific warm pool, which is closely related to the southward extension of the middle-latitude trough over the east side of Japan. This circulation pattern is favorable for the southward retreat of the WPSH northern boundary over the warm pool, which results in the shape change and even the split of the high. Then the west part of the high is incapable of withdrawing eastward, and it dominates over the southern China steadily, leading to the persistent HT events. This conclusion is further confirmed by the statistical analysis both of the multi-year circulations and the typical HT extreme case in 2013, which could provide reference for the sub-seasonal prediction of HT in southern China. • China suffered the record-breaking extreme high temperature event in July-August 2017 since 1951. • Middle-latitude trough over the East of Japan was first found in causing a constant westward WPSH. • The leading influence of the trough could be considered in the forecast of HT event in southern China. [ABSTRACT FROM AUTHOR]

Radar data assimilation (DA) can improve short-term precipitation forecasts. However, assimilating radar observations into a numerical prediction model may produce spurious precipitation and large errors in the position and magnitude of precipitation, and high-frequency cyclic assimilation may exacerbate this problem. In this paper, a severe convection case that occurred on 27 June 2018 over eastern China was used to investigate the impacts of the radar DA frequency and large-scale constraint on precipitation forecasts. The Weather Research and Forecasting (WRF) three-dimensional variational (3D-Var) DA system was used to assimilate radial velocity and reflectivity data. The sensitivity of the DA frequency using 15-min and 1-h assimilation intervals was examined first, revealing that the 15-min DA interval produced a greater overprediction bias of precipitation. A diagnosis of the analysis fields showed that higher-frequency DA cycling produced excessive wind speed and water vapor convergence at low levels and exaggerated upward movement. Then, the large-scale constraint was imposed on the regional model by the spectral nudging (SN) technique, which assimilated Global Forecast System (GFS) forecast field data during the forecast periods. The results demonstrated that the application of SN could significantly reduce the positional deviation of the precipitation forecast and the magnitude of overpredicted precipitation. SN could effectively adjust large-scale circulation fields, thereby improving the conditions of water vapor convergence. Moreover, SN also improved the forecasts of surface variables such as wind, temperature, and humidity. • The impacts of the radar data assimilation frequency and large-scale constraint on precipitation forecasts are investigated. • A higher frequency of radardata cyclic assimilation leads to a larger overprediction bias of precipitation. • Using the spectral nudging to assimilate GFS forecast data in the forecast periods can improve precipitation forecasting. [ABSTRACT FROM AUTHOR]