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In 1979, Herbert Riehl and Joanne Simpson (Malkus) analytically estimated that 1600–2400 undilute convective cores vertically transport energy to the tropopause at any given time within a region where upper-tropospheric energy is only exported from the tropics. The focus of this paper is to update this estimate using modern satellite observations, compare hot tower frequency and intensity characteristics to all deep convective cores that reach the upper troposphere, and document hot tower spatiotemporal variability in relation to precipitation and high cloud properties within the tropical trough zone (between 13 °S and 19 °N). Cloud vertical profiles from CloudSat and CALIPSO measurements supply convective core diameters and proxies for intensity and convective activity, and these proxies are augmented with brightness temperature data from geostationary satellite observations, precipitation information from IMERG, and cloud radiative properties from CERES. Less than 35% of all deep cores are classified as hot towers, and we estimate that 800–1700 hot towers occur at any given time over the course of a day, with the mean maximum core and hot tower frequency occurring at the time of year when peak convective intensity and precipitation occur. Convective objects that contain hot towers frequently contain multiple cores, and the largest systems with five or more distinct cores most frequently occur in regions where organized mesoscale convective systems and the highest climatological mean rain rates are known to occur. Analysis of co-located radar and infrared brightness temperatures reveals that passive observations alone are not sufficient to unambiguously distinguish hot towers using simple brightness temperature thresholds. [ABSTRACT FROM AUTHOR]

From 31 January to 5 February, 2024, Henan Province experienced a rare freezing rain and snow process characterized by a long duration,substantial cumulative precipitation,significant snow depth,low temperatures,and complex precipitation phases.Based on the national meteorological observation data,dual-polarization radar data,and hourly reanalysis data of ERA5,a diagnostic analysis of the event's extremity,phase evolution,and causes of the freezing rain and snow was conducted.The results are as follows.During the process,5 national meteorological stations reached or exceeded the maximum snow depth of the historical records in February.At many stations,the minimum temperature has reached or set a new historical record in early February.Precipitation was observed from at least 68.3% of national meteorological observation stations in a single day,with the longest continuous precipitation at a single station being nearly 29 hours.The stable maintenance of a large-scale circulation system was one of the main reasons for this process.The persistent intrusion of the strong cold air in the lower troposphere provided both dynamic uplift and sustained cooling conditions for the freezing rain and snow process.Exceptionally strong southerly airflow provided ample moisture and momentum,enhancing unstable stratification.For precipitation phase identification,relying solely on a single-layer temperature is insufficient.Instead,the entire atmospheric layer temperature should be considered to predict possible precipitation phases.When the entire atmospheric layer temperature is below 0℃,precipitation is pure snow.If there is a melting layer or the cloud consists of supercooled water droplets,mixed precipitation will occur.Dual-polarization radar's correlation coefficient and differential reflectivity products are useful for distinguishing between sleet and pure snow.A correlation coefficient close to 1 and differential reflectivity between-1 and 0 dB indicates pure snow,while a correlation coefficient less than 1 and differential reflectivity greater than 1 dB indicate sleet.

Canonical understanding based on general circulation models (GCMs) is that the atmospheric circulation response to midlatitude sea‐surface temperature (SST) anomalies is weak compared to the larger influence of tropical SST anomalies. However, the ∼100‐km horizontal resolution of modern GCMs is too coarse to resolve strong updrafts within weather fronts, which could provide a pathway for surface anomalies to be communicated aloft. Here, we investigate the large‐scale atmospheric circulation response to idealized Gulf Stream SST anomalies in Community Atmosphere Model (CAM6) simulations with 14‐km regional grid refinement over the North Atlantic, and compare it to the responses in simulations with 28‐km regional refinement and uniform 111‐km resolution. The highest resolution simulations show a large positive response of the wintertime North Atlantic Oscillation (NAO) to positive SST anomalies in the Gulf Stream, a 0.4‐standard‐deviation anomaly in the seasonal‐mean NAO for 2°C SST anomalies. The lower‐resolution simulations show a weaker response with a different spatial structure. The enhanced large‐scale circulation response results from an increase in resolved vertical motions with resolution and an associated increase in the influence of SST anomalies on transient‐eddy heat and momentum fluxes in the free troposphere. In response to positive SST anomalies, these processes lead to a stronger and less variable North Atlantic jet, as is characteristic of positive NAO anomalies. Our results suggest that the atmosphere responds differently to midlatitude SST anomalies in higher‐resolution models and that regional refinement in key regions offers a potential pathway to improve multi‐year regional climate predictions based on midlatitude SSTs. Plain Language Summary: Variations in the ocean surface temperature (SST) influence the atmospheric circulation and thus climate over land. Canonical understanding is that tropical SSTs are more important than SSTs in midlatitudes. However, this understanding is based on climate models that don't resolve processes at scales less than 100 km. Here, we show that by increasing the atmospheric model resolution to resolve features on smaller scales, such as weather fronts, we find a larger atmospheric circulation response to midlatitude SST anomalies in the North Atlantic. North Atlantic SST anomalies can be predicted multiple years in advance, and a larger atmospheric circulation response to these predictable SST anomalies therefore implies increased predictability of climate over the surrounding land regions. Key Points: There is a large circulation response to idealized Gulf Stream sea‐surface temperature (SST) anomalies in an atmospheric model with 14‐km regional grid refinementThis response is weaker or absent in simulations with 28‐km or coarser resolution, which do not fully resolve mesoscale frontal processesTransient‐eddy fluxes of heat and momentum are modified as fronts pass over warm SSTs, leading to a large‐scale circulation response [ABSTRACT FROM AUTHOR]

The frequency of heatwaves in the Arctic is on the rise under global warming. These occurrences not only profoundly impact the local ecological environment but also exert remote effects on East Asia and even the global climate. Yet, there exists a noticeable dearth of research focus on Arctic compound daytime-nighttime heatwaves, limiting our comprehension of Arctic climate dynamics. We investigated the occurrence and extinction mechanism for compound daytime-nighttime heatwaves in the Barents–Kara Sea (BKS) during the boreal autumn and explored their association with the sea ice variability. Our results show that a significant dipole pattern appears in the geopotential height two days before the occurrence of compound daytime-nighttime heatwaves in the BKS during autumn, characterized by a negative anomaly centered over Greenland and a positive anomaly centered over the BKS. A robust southerly anomaly in the middle of this dipole pattern facilitates the continuous inflow of warm, moist air from the Atlantic Ocean to the BKS. Both the strong intrusion of moisture and the transport of heat (positive temperature advection) driven by the large-scale atmospheric circulation increase downward latent heat flux, sensible heat flux and net longwave radiation. These factors collectively increase the near-surface temperature over the BKS, ultimately leading to the occurrence of compound daytime-nighttime heatwaves in this region of the Arctic. The extinction of compound daytime-nighttime heatwaves in the BKS is a result of the weakening of the transport of heat and intrusion of water vapor caused by changes in the large-scale circulation. The intrusion of water vapor and the transport of heat significantly reduce the sea ice concentration in most of the BKS. This reduction in sea ice persists for an additional day after the termination of compound daytime-nighttime heatwaves in the BKS. A process of positive atmospheric temperature feedback on a sub-monthly scale may potentially influence the maintenance of compound daytime-nighttime heatwaves in the BKS during the boreal autumn.

Diurnal temperature range (DTR), as a core indicator of the Earth system, exhibits obvious temporal and spatial variations, which is not entirely consistent over global. The historical simulation capabilities of 19 Coupled Model Intercomparison Project 6 (CMIP6) models for DTR were firstly evaluated against CRU_TS v4.04 data. Future changes under three shared socioeconomic pathways (SSP1-2.6, SSP2-4.5, SSP5-8.5) in DTR were projected using a multi-model ensemble mean (MME), and its interannual variations were seasonally explored through empirical orthogonal function (EOF) analysis. The results indicated that CMIP6 models could reflect the decreasing trend of DTR during 1901–2014, with the global spatial correlation coefficient between models and observation ranging from 0.4 to 0.7. MME outperformed individual models in both spatial and temporal variations, indicating higher accuracy and reliability. The future changes of DTR exhibited significantly decrease across the northern hemisphere and increase in the South America, and change magnitude enlarged with time extension and emission intensity, especially by more than 0.4 °C under SSP5-8.5. The decreasing trend of global DTR was kept in SSP2-4.5 and SSP5-8.5, while SSP1-2.6 changed increasing trend during 2015–2100. DTR showed seasonal variations and was mainly influenced by colder months. The dominant modes of interannual DTR and their relationship with the 500 hPa geopotential height, the 200 hPa U wind, and the outgoing longwave radiation showed higher features in tropical regions. The highly positive correlation between the first mode of DTR and the Niño3.4 index in December/January/February (DJF) is 0.67, indicating significant influence of the El Niño-Southern Oscillation on DTR. [ABSTRACT FROM AUTHOR]

Disentangling the response of tropical convective updrafts to enhanced aerosol concentrations has been challenging. Leading theories for explaining the influence of aerosol concentrations on tropical convection are based on the dynamical response of convection to changes in cloud microphysics, neglecting possible changes in the environment. In recent years, global convection‐permitting models (GCPM) have been developed to circumvent problems arising from imposing artificial scale separation on physical processes associated with deep convection. Here, we use a global model in the convective gray zone that partially simulates deep convection to investigate how enhanced concentrations of aerosols that act as cloud condensate nuclei (CCN) impact tropical convection features by modulating the convection‐circulation interaction. Results from a pair of idealized non‐rotating radiative‐convective equilibrium simulations show that the enhanced CCN concentration leads to weaker large‐scale circulation, the closeness of deep convective systems to the moist cluster edges, and more mid‐level cloud water at an equilibrium state in which convective self‐aggregation occurred. Correspondingly, the enhanced CCN concentration modulates how the physical processes that support or oppose convective aggregation maintain the aggregated state at equilibrium. Overall, the enhanced CCN concentration facilitates the development of deep convection in a drier environment but reduces mean precipitation. Our results emphasize the importance of allowing atmospheric phenomena to evolve continuously across spatial and temporal scales in simulations when investigating the response of tropical convection to changes in cloud microphysics. Plain Language Summary: How does air pollution affect thunderstorm intensity over the tropical ocean? Past studies have proposed different pieces of evidence but generally neglect the interplay between the development of thunderstorms and the long‐range movement of air that redistributes the Earth's thermal energy and moisture. Here, we address this question by investigating results from idealized numerical experiments in which a global domain is used to simultaneously simulate the response of individual thunderstorms and large‐scale air motion to pollution. We found that pollution makes the thunderstorms keep less moisture in their surroundings, limiting the intensity of thunderstorms and weakening the large‐scale air motion that supplies moisture to thunderstorms. Our results suggest that the interplay between the development of thunderstorms and the long‐range movement of air is crucial in determining the effects of pollution in the tropical atmosphere. Key Points: A global model with horizontal grid length in the convective gray zone is used to investigate aerosol indirect effectsPollution leads to weaker large‐scale circulation, the closeness of convection to the moist cluster edges, and more mid‐level cloud waterPollution facilitates deep convection development in a drier environment but reduces mean precipitation [ABSTRACT FROM AUTHOR]

Mesoscale convective systems (MCSs) are crucial in modifying the water cycle and frequently induce high‐impact weather events over eastern China. Radar and Climate Prediction Center (CPC)‐4 km satellite‐derived infrared cloud top temperature (Tb) data were used to thoroughly analyze the long‐term climatology of MCSs over eastern China, particularly in the Yangtze–Huaihe River Basin (YHR) in the warm season from 2013 to 2018. For the first time, we contrasted the effects of data set selection and threshold setting on research outcomes. The large‐scale environments of MCSs initiation were also investigated using the latest global reanalysis data ERA5. It is found that striction of thresholds, including duration, reflectivity/Tb, area, and linearity, would lead to a greater proportion of early‐morning MCSs. Satellite‐identified MCSs differed from radar‐derived ones, exhibiting afternoon diurnal peaks, faster movement speeds, longer travel distances, and expansive impact areas. The center of MCS and related precipitation shifted northward from Pre‐Meiyu to Post‐Meiyu seasons, contributing to up to 20% of total rainfall, with most MCSs moving along eastward trajectories. MCSs typically had the most substantial impact in the Meiyu season because of the most prolonged duration, largest convective core area, and strongest precipitation intensity. Warm‐season MCSs initiated ahead of midlevel troughs and were related to strong anomalous low‐level convergence and midlevel upward. The circulation anomalies were the strongest in the Pre‐Meiyu season among the three subseasons, with most moisture sourced from the southwest. Plain Language Summary: This work used radar and satellite data to analyze the climate characteristics of a kind of large thunderstorms known as mesoscale convective systems (MCSs) in the Yangtze–Huaihe River Basin (YHR) in eastern China. These systems cover large areas, lasting from a few hours to a few days. The analysis revealed that stricter tracking thresholds would lead to more early‐morning MCSs. Satellite‐identified MCSs differed from those identified by radar. They tended to have more thunderstorms in the afternoon, move faster, travel longer distances, and cover larger areas. MCSs also contributed to up to 20% of the total warm‐season rainfall in the YHR. MCSs typically had the most substantial impact in the rainy season of eastern China from mid‐June to mid‐July. Warm‐season MCSs initiated ahead of low‐pressure systems and were related to strong anomalous low‐level convergence and midlevel upward motion. During the time before the rainy season, the large‐scale forcing needed to be anomaly enough to trigger MCS formation. Most of the moisture that caused MCSs came from southwest direction instead of stemming locally during this period. Key Points: Six‐year climatology of warm‐season mesoscale convective systems (MCSs) in Yangtze–Huaihe River Basin is investigated using satellite, radar data, and ERA5Criteria setting for tracking MCSs noticeably influences the derived featuresMeiyu season MCSs featured longest duration, largest areas, and heaviest precipitation, while the background circulation anomalies are the weakest [ABSTRACT FROM AUTHOR]

The classification of torrential rain is crucial to the flood mitigation and water resources, but the relevant research in the Haihe River Basin (HRB) is lacking. In this study, 156 regional torrential rain events from 1972 to 2022 were classified into two types using cluster analysis: eastern type and southern type. The eastern type is the typical torrential rain in the HRB, accounting for 61.5% of the total days, whereas the southern type mainly occurs in the piedmont plain with larger intensity and scope, which would pose more severe hazards. Corresponding large‐scale circulation patterns of the two types reveal a clear relationship between the HRB torrential rain and ascending motion, associated with the anomalies of low‐level moisture convergence and upper‐level wind divergence. The anomalous upper‐level divergence is accompanied by the northward expansion of South Asian High and intensified westerly jets. In the eastern type, strong low‐pressure anomalies north of Lake Baikal at mid‐level produce anomalous northwesterlies. The cold air from mid–high latitudes encounters enhanced southwesterly moist air accompanied by the northward expansion of Western Pacific Subtropical High (WPSH), resulting in the low‐level moisture convergence. In the southern type, the low‐level anomalous convergence is caused by a relatively weak cyclonic anomaly and significantly strengthened southeasterly moisture from the Pacific. The enhancement of southwesterlies results from the cooperative effect of the remarkably northwesterly WPSH and low‐pressure anomalies in South China Sea. As a whole, the eastern type is the result of convergence of cold air and southwesterly moisture driven by a dipole pattern at mid–high latitudes, whereas the southern type is mainly attributed to the accumulation of abundant southeasterly water vapour. This classification can identify high‐risk areas for torrential rain in the HRB and contribute to the forecast skills of extreme precipitation. [ABSTRACT FROM AUTHOR]

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Understanding extreme precipitation events (EPEs) and their underlying dynamical processes and moisture transport patterns is essential to mitigate EPE-related risks. In this study, we investigate the dynamics of 75 EPEs (> 100 mm day-1) over the territory of Ukraine in the recent decades (1979-2019), of which the majority occurred in summer. The EPEs are identified based on precipitation observations from 215 meteorological stations and posts in Ukraine. The atmospheric variables for the case study analysis of selected EPEs and for climatological composites and trajectory calculations were taken from ERA5 reanalyses. Moisture sources contributing to the EPEs in Ukraine are identified with kinematic backward trajectories and the subsequent application of a moisture source identification scheme based on the humidity mass budget along these trajectories. The large-scale atmospheric circulation associated with EPEs was studied for a selection of representative EPEs in all seasons and with the aid of composites of all events per season. Results show that EPEs in summer occur all across Ukraine, but in other seasons EPE hotspots are mainly in the Carpathians and along the Black and Azov Seas. All EPEs were associated with a surface cyclone, and most with an upper-level trough, except for the winter events that occurred in situations with very strong westerly jets. Isentropic potential vorticity anomalies associated with EPEs in Ukraine show clear dipole structures in all seasons, however, interestingly with a different orientation of these anomaly dipoles between seasons. The analysis of moisture sources revealed a very strong case-to-case variability and often a combination of local and remote sources. Oceanic sources dominate in winter, but land evapotranspiration accounts for 60-80% of the moisture that rains out in EPEs in the other seasons. Taken together, these findings provide novel insight into large-scale characteristics of EPE in Ukraine, in a region with a unique geographical setting and with moisture sources as diverse as Newfoundland, the Azores, the Caspian Sea, and the Arctic ocean. [ABSTRACT FROM AUTHOR]

A severe flooding hit southern China along the Yangtze River in summer 2020. The floods were induced by extreme rains, and the associated dynamic and thermodynamic conditions are investigated using daily gridded rainfall data of China and NCEP-NCAR reanalysis. It is found that the June–July rainfall over the Yangtze River Basin (YRB) experienced pronounced subseasonal variation in 2020, dominated by a quasi-biweekly oscillation (QBWO) mode. The southwestward-moving anomalous QBWO circulation was essentially the fluctuation of cold air mass related to the tropospheric polar vortex or trough-ridge activities over the mid-high latitude Eurasian in boreal summer. The southwestward-transport of cold air mass from mid-high latitudes and the northeastward-transport of warm and moist air by the strong anomalous anticyclone over the western North Pacific provided important large-scale circulation support for the extreme rainfall in the YRB. The analysis of streamfunction of water vapor flux demonstrates that a large amount of water vapor eastward zonal transport from the Bay of Bengal and Indo-China and northward transport from the South China Sea provided the background moisture supply for the rainfall. The quasi-biweekly anomalies of potential and divergent component of vertically integrated water vapor flux played an important role in maintaining the subseasonal variability of rainfall in June–July of 2020. The diagnosis of moisture tendency budget shows that the enhanced moisture closely related to the quasi-biweekly fluctuated rainfall was primarily attributed to the moisture convergence. Further analysis of time-scale decomposition in the moisture convergence indicates that the convergence of background mean specific humidity by the QBWO flow and convergence of QBWO specific humidity by the mean flow played dominant roles in contributing to the positive moisture tendency. In combination with adiabatic ascent over the YRB induced by the warm temperature advection, the boundary layer moisture convergence strengthened the upward transport of water vapor to moisten the middle troposphere, favoring the persistence of rainfall during June–July. The vertical moisture transport associated with boundary layer convergence was of critical importance in causing low-level tropospheric moistening. By comparison, the horizontal moisture advection played a secondary important role in the quasi-biweekly oscillation of rainfall in June–July 2020. [ABSTRACT FROM AUTHOR]

Based on China's daily precipitation data of 2415 stations and ERA5 hourly reanalysis data from 1961 to 2019, the station-based and regional precipitation events over Northwest China (NWC) are identified and sorted into persistent precipitation (PP, duration & 2 days) events and non-persistent precipitation (NPP, duration = 1 day) events; and then changes in the persistence structure of the PP and NPP events over NWC and the long-term mean adjustment of the related large-scale circulation configuration are analyzed. The results show that PP and NPP both witness an increasing trend over most parts of NWC. In terms of the total precipitation at most stations and the regional mean, contributions from PP have been increasing, while those from NPP have been decreasing. This demonstrates that the wetting trend in NWC is mainly caused by the increase in PP. Through analyzing the large-scale circulation corresponding to regional PP events at several representative levels, we found that the westerly jet at 200 hPa, the ridge/trough systems at 500 hPa, and the Mongolian low at sea level are the key circulation systems responsible for regional PP events over NWC. As for long-term mean changes after and before 1990 (a shifting point recognized by previous studies), it is found that the extent of the South Asian high becomes larger and the westerly jet shifts northward by approximately 1.5 degrees in the upper troposphere. The ridge near the Ural Mountains and the ridge downstream of NWC strengthen by approximately 10–30 hPa at 500 hPa. Furthermore, the difference between the Mongolian low trough and its surrounding high pressure increases by approximately 2 hPa at the sea level. The combinations of circulation changes from upper to lower levels facilitate the strengthening of ascending motions. These adjustments in circulations create more favorable conditions for PP to occur over NWC in the last three decades. [ABSTRACT FROM AUTHOR]

The multi-year simulation of tropical cyclones (TCs) over the Western North Pacific (WNP) in the variable resolution (VR) CAM-MPAS model is studied. Experiments with the global quasi-uniform low resolution of 120 km (MPAS-UR) and the variable resolution mesh of 30–120 km refined over East Asia (MPAS-VR) are integrated from 1980 to 2005 following the Atmospheric Model Intercomparison Project protocol. By utilizing an objective detection method, TCs in ERA5 reanalysis and model simulations are tracked and compared against observations. MPAS-VR shows significant advantages over MPAS-UR as indicated by more realistic TC counts, intensities, lifetime distribution, and seasonal variation. The large-scale circulation and precipitation patterns associated with TCs are also improved in MPAS-VR relative to MPAS-UR. Based on the theory of Dynamic Genesis Potential Index, the multi-year TC records are further used to quantify the dependence of TC genesis on various dynamical environmental factors from the perspective of seasonal variation. We find that in ERA5, the relative contribution of the 500 hPa vertical pressure velocity term to TC genesis exceeds that of the 200–850 hPa vertical wind shear term, which is responsible for the August peak and strong seasonal variation of TC genesis. MPAS-UR fails to capture such relationship while MPAS-VR performs much better in this regard, suggesting that the higher skills in simulating the relative contributions from different dynamical environmental factors to the simulated seasonal cycle of TC genesis may explain the improvements from MPAS-UR to MPAS-VR. [ABSTRACT FROM AUTHOR]

Co-occurring extreme heat, drought, and moisture events are increasing under global warming and pose serious threats to ecosystem and food security. However, how to effectively link compound agrometeorological disasters (CADs) with climate change has not been well assessed. In this study, we focus on the comprehensive influence of large-scale climate factors on CADs rather than extreme meteorological elements. The results indicate that there are two main CADs of spring maize in Shenyang, Northeast China (NEC), including concurrent drought and cold damage (DC) and drought in multiple growth periods (MD). The related circulation anomalies at mid–high latitudes are identified as four patterns, namely, the Northeast Asia Low (NEAL) and Ural High (UH) patterns affecting DC, the Baikal High and Okhotsk Low (BHOL), and the Northeast Asia High (NEAH) patterns leading to MD. The vertical profile and water vapor transport anomalies further demonstrate the influence mechanism of large-scale circulation on compound heat–moisture stresses. This study highlights the role of atmospheric circulation, which can provide effective predictors for these synergistic agrometeorological disasters. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the influence of large-scale circulation on the flow field in a cabin mockup. The velocity was measured by ultrasonic anemometers (UA). Then, this study analyzed the turbulence kinetic energy spectra of the velocity fluctuation signal. The turbulence kinetic energy spectra of the measurement points reflect the flow characteristic of the large-scale circulation in the cabin mockup. The results contribute to the understanding of the role of the thermal plume on the large-scale circulation in the cabin. The large-scale circulations impact on air quality was also investigated, and the contaminant distribution was measured using tracer gas in the cabin. The two large-scale circulation interactions made the air flow mixing approximately uniform.

In the summer of 2012 and 2013, two northeastward-moving Tibetan Plateau vortices (referred to as TPV) moved out of the Tibetan Plateau (referred to as plateau), and then caused heavy rain in the northwest region. In 2013, The moving path of TPV was more eastward, and the heavy rain intensity was stronger, and the falling area was eastward and wider. Based on the ERA-Interim reanalysis data and the stational precipitation data, the large-scale circulation and the influence of TPVs on the heavy precipitation were compared and analyzed during the movement of the two TPVs. The wet potential vortex is used to diagnose the two rainstorms. The results show that the Hetao high pressure ridge at 500 hPa and the westerly jet at 200 hPa have a significant impact on the movement of TPVs. The configuration of divergence (convergence) in the upper (lower) layer of the lower vortex benefits to a stronger upward movement, which provides powerful dynamic conditions for the rainstorms. The convergence of the vortex in the lower level is conducive to the transport of water vapor to the rainstorm area. The diagnostic results of barotropic wet potential vortex (MPV1) indicate that the rainstorm area in 2013 has stronger unstable conditions; the diagnosis of baroclinic wet potential vortex (MPV2) indicates that warm and humid air from the western Pacific is transported to the center of rainstorm in 2013.

The ultraviolet‐imaging spectrograph that comprises Global‐scale Observations of the Limb and Disk (GOLD) mission in geostationary orbit at 47.5°W longitude has taken full disk images at high cadence throughout the deep solar minimum period of 2019–2020. Synoptic (i.e., concurrent and spatially unified and resolved) observations of thermospheric temperature and composition at ∼150 km altitude are made for the first time, allowing GOLD to disambiguate temporal and spatial variations. Here we analyze the daytime effective temperature and column integrated O and N2 density ratio (ΣO/N2) data simultaneously observed by GOLD over 120°W–20°E longitude and 60°S–60°N latitude from 13 October 2019 to 12 October 2020. Daily zonal mean values are calculated for each latitude and compared with NRLMSIS 2.0 and simulations from the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X). On average, the GOLD observations show higher temperatures than Mass Spectrometer Incoherent Scatter radar (MSIS) and WACCM‐X by ∼20–60 K (5%–10%) and 80–120 K (12%–18%), respectively. The ΣO/N2 ratios observed by GOLD are larger than the MSIS results by ∼0.4 (40%) but smaller than the WACCM‐X simulations by ∼0.3 (30%). The observed and modeled results are correlated at most latitudes (r = 0.4–0.8), and GOLD, MSIS, and WACCM‐X all display a similar seasonal variation and change with latitude. WACCM‐X simulates a larger annual variation in ΣO/N2, suggesting that the thermospheric circulation is overestimated and atmospheric waves and turbulence transport are not properly represented in the model. Plain Language Summary: The thermosphere (∼90–800 km altitude) is where energy inputs from the lower and middle atmosphere, solar ultraviolet and X‐ray variability, and solar wind energy inputs combine to produce the large but poorly understood variability of the upper atmosphere and ionosphere. The Global‐scale Observations of the Limb and Disk (GOLD) mission has flown an ultraviolet‐imaging spectrograph, which provides for the first time geostationary orbit images of daytime thermospheric temperature and composition ratio for major constituents O and N2 (ΣO/N2) near 150 km in the thermosphere. These observations are concurrent and spatially unified and resolved, allowing to distinguish between temporal and spatial variations. For this study, we validate the GOLD observations by comparing them with state‐of‐the art model results from NRLMSIS 2.0 and NCAR's Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X) throughout October 2019–October 2020 at extreme quiet solar activity conditions. We notice that the GOLD observations are overall correlated with the Mass Spectrometer Incoherent Scatter radar and WACCM‐X results and all reveal a similar seasonal variation pattern and dependence on latitude. This study suggests that the models can capture the observed large‐scale features in daytime temperature and composition in the thermosphere. Key Points: Thermospheric effective temperature and ΣO/N2 from Global‐scale Observations of the Limb and Disk (GOLD) are compared to model simulations in 2019–2020 at deep solar minimumTemperatures observed by GOLD are higher than both model results and the GOLD ΣO/N2 ratios are larger than Mass Spectrometer Incoherent Scatter radar but smaller than Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X)Seasonal trends are consistent between GOLD and models but WACCM‐X simulates a larger annual variation in ΣO/N2 in both hemispheres [ABSTRACT FROM AUTHOR]

Understanding the contributions of large-scale atmospheric circulation and local land surface processes to precipitation is essentially important for the climate prediction. This study adopts a dynamic adjustment (DA) approach based on constructed circulation analogs to quantitatively isolate the contribution of atmospheric circulation to summer land precipitation (Pr) over Asian mid-low latitudes during 1980–2019. The atmospheric circulation factor is represented by the 500 hPa geopotential height (Z500), and the residual component after DA is regarded as the contribution from land surface processes via evaporation mainly resulting from soil moisture (SM). The results indicate that the key SM-Pr feedback areas are mainly located in northeast China and the northern Indian Peninsula. The key influencing area of Z500 on the land Pr anomaly shows a "- + -" tripole pattern in the mid-latitude region. Atmospheric circulation determines the magnitude of summer land Pr, while the residual components reflect the land–atmosphere coupling effect and dominate Pr trend. This conclusion is helpful for better understanding the evolution mechanism of summer climate over Asia mid-low latitudes and may also have application value for climate prediction. [ABSTRACT FROM AUTHOR]

Most research of stratospheric aerosol injection (SAI) for solar radiation modification has focused on injection of SO _2 . However, the resulting sulfuric acid aerosols lead to considerable absorption of terrestrial infrared radiation, resulting in stratospheric warming and reduced cooling efficiency. Recent research suggests that solid particles, such as alumina, calcite or diamond, could minimize these side effects. Here we use, for the first time, the atmosphere–ocean–aerosol–chemistry–climate model SOCOLv4.0, incorporating a solid particle scheme, to assess the climatic impacts of SAI by these injection materials. For each substance, we model tropical SAI by means of constant yearly injection of solid particles, aimed to offset the warming induced by a high-GHG emission scenario over the 2020–2100 period by 1 K. We show that solid particles are more effective than sulfur at minimising stratospheric heating, and the resulting side-effects on the general atmospheric circulation, stratospheric moistening, and tropopause height change. As a result, solid particles also induce less residual warming over the arctic, resulting in greater reduction of GHG-induced polar amplification compared to sulfuric acid aerosols. Among the materials studied here, diamond is most efficient in reducing global warming per unit injection, while also minimizing side effects.

Smoke aerosols released through frequent springtime fire activity over the Indochina Peninsula (ICP) seriously affect regional air quality, climate, and human health. However, the mechanisms driving the interannual variability of these smoke aerosols are not well understood. By analyzing multi-source historical (1980–2020) smoke aerosols and meteorological reanalysis data, we explore the response of springtime smoke aerosol changes over the ICP to the interannual variability of the Indian Ocean (IO) sea-surface temperature (SST). Our findings show a positive correlation between the variability of springtime smoke aerosol loading and the preceding winter Southeast IO (SEIO) SST anomalies. Warmer SEIO SST tends to weaken the trans-equatorial flow (TEF) and the local Hadley circulation. This weakening of the TEF impedes cyclone development in the Bay of Bengal (BOB), thereby reducing southwest water vapor transport. Simultaneously, enhanced westerly winds over the northern BOB are blocked by the northwestern mountains of ICP. These winds converge and rise on the windward slopes, while descending on the leeward side with diminished humidity. Collectively, these dynamics lead to drier and hotter local meteorological conditions that favored fire-induced smoke aerosol emissions. Our findings highlight the role of the SEIO in regulating smoke aerosol variability and provide a scientific basis for developing strategies to manage smoke aerosol emissions over the ICP.

This study examines the linear orthogonal modes associated with monthly precipitation in the northeastern United States, from CESM1 LENS (35 ensemble members, 1979–2005) and two reanalysis datasets (ERA5, 1950–2018 and NOAA-CIRES-DOE 20CRv3, 1950–2015). Calendar months are aggregated together, and any linear trends in data are removed. Using region-averaged precipitation anomaly time series and monthly anomalies for several global 2D atmospheric fields, a linear orthogonal decomposition method is implemented to iteratively extract time series (based on field and geographic location) of absolute maximum correlation. Linear modes associated with this method are then projected onto the full set of 2D fields to provide physical insight into the mechanisms involved in generating precipitation. In this region, the first mode is associated with vapor transport from the Atlantic seaboard, the second mode is characterized by westward vapor transport associated with extratropical cyclones, and the third mode captures vapor transport from the Gulf of Mexico during the fall and winter. However, the third mode is less robust in the spring and summer. Results are generally consistent across the datasets, and applying multiple linear regression with the linear modes to predict the precipitation anomalies produces R-squared values of around 0.54–0.65 for CESM1 LENS, and around 0.58–0.88 for reanalysis, with the lowest values generally in the spring and late summer. The influence of low-frequency climate variability on the modes is considered for CESM1 LENS, and the modes in late winter can be predicted with some success via a combination of several, prominent large-scale teleconnection patterns. [ABSTRACT FROM AUTHOR]

This study investigates the roles of the boreal summer intraseasonal oscillation (BSISO) in the diurnal rainfall cycle over Hainan Island during the warm season (April-September) using 20-year satellite-based precipitation, ERA5 and the outgoing longwave radiation data with the phase composite analysis method. Results show that the spatial distributions of the hourly rainfall anomaly significantly change under the BSISO phases 1-8 while no clear variations are found on the daily and anomaly daily area-averaged rainfall over the island. During the BSISO phase 1, the rainfall anomaly distinctly increases in the morning over the southwest and late afternoon over the northeast of the island, while suppressed convection occurs in the early afternoon over the southwest area. Under this circumstance, strong low-level westerly winds bring abundant moisture into the island, which helps initiate the nocturnal-morning convection over the south coastal area, and drives the convergence region of sea breeze fronts to concentrate into the northwest. Opposite to Phase 1, an almost completely reversed diurnal cycle of rainfall anomaly is found in Phase 5, whereas a positive anomalous rainfall peak is observed in the early afternoon over the center while negative peaks are found in the morning and late afternoon over the southwest and northeast, owing to a strong low-level northeasterly anomaly flow, which causes relatively low moisture and enlarges a sea-breeze convergence area over the island. During Phase 8, strongest moisture is found over the island all through the day, which tends to produce highest rainfall in the afternoon with enhanced anomalous northerly. These results further indicate that multiscale interactions between the large-scale circulations and local land-sea breeze circulations play important roles in modulating diurnal precipitation cycles over the tropical island. [ABSTRACT FROM AUTHOR]

Convective momentum transport (CMT) is the process of vertical redistribution of horizontal momentum by small‐scale turbulent flows from moist convection. Traditional general circulation models (GCMs) and their multiscale modeling framework (MMF) versions poorly represent CMT due to insufficient information of subgrid‐scale flows at each GCM grid. Here the explicit scalar momentum transport (ESMT) scheme for representing CMT is implemented in the Energy Exascale Earth System Model‐Multiscale Modeling Framework (E3SM‐MMF) with embedded 2‐D cloud‐resolving models (CRMs), and verified against E3SM‐MMF simulations with 3‐D CRMs and observations. The results show that representing CMT by ESMT helps reduce climatological mean precipitation model bias over the western Pacific and the ITCZ regions, which is attributed to the weakened mean easterlies over the Pacific. Also, CMT from simulations with 2‐D and 3‐D CRMs impose a similar impact on Kelvin waves by reducing their variability and slowing down their phase speed, but opposite impacts on the Madden‐Julian Oscillation (MJO) variability. The ESMT scheme readily captures the climatological mean spatial patterns of the zonal and meridional components of CMT and their variability across multiple time scales, but shows some differences in estimating its magnitude. CMT mainly affects the MJO by decelerating its winds in the free troposphere, but accelerates its near‐surface winds. This study serves as a prototype for implementing CMT scheme in the MMF simulations, highlighting its crucial role in reducing model bias in mean state and spatiotemporal variability. Plain Language Summary: Small‐scale turbulent flows from moist convection typically lead to the vertical redistribution of large‐scale winds (referred to as convective momentum transport [CMT]). Due to the coarse grids that are too large to resolve small‐scale flows, traditional earth system models poorly represent the CMT, and thus rely on parameterizations that empirically describe the magnitude and vertical profiles of the CMT. In contrast, the default Energy Exascale Earth System Model‐Multiscale Modeling Framework (E3SM‐MMF) is an earth system model with a 2‐D (one horizontal dimension and one vertical dimension) cloud‐resolving model embedded within each coarse grid so as to better resolve small‐scale flows, although it still lacks the necessary information to fully calculate CMT due to the lack of the third dimension. Here we implemented the explicit scalar momentum transport (ESMT) scheme to represent CMT in the E3SM‐MMF associated with 2‐D small‐scale flows at each coarse grid. The results show that in general CMT helps reduce model biases in predicting time‐mean precipitation and winds as well as the spatiotemporal variability of tropical convection. The ESMT scheme reproduces the spatial patterns of CMT as simulated by the E3SM‐MMF model with 3‐D small‐scale flows. Lastly, we focused on the Madden‐Julian Oscillation, the dominant intraseasonal variability in the tropics, as an example to investigate the impact of CMT. Key Points: Convective momentum transport (CMT) affects large‐scale circulation and convective organization, and representing CMT reduces model biases in Energy Exascale Earth System Model‐Multiscale Modeling Framework simulationsExplicit scalar momentum transport scheme captures the spatial pattern of CMT comparable to 3‐D cloud‐resolving models that explicitly model CMTCMT damps the free tropospheric circulation associated with the Madden‐Julian oscillation, but accelerates its near‐surface winds [ABSTRACT FROM AUTHOR]

The large-scale circulation, dynamic, and thermodynamic factors related to the lack of genesis of tropical cyclones in the Northwestern Pacific and the South China Sea in July 2020 were preliminarily analyzed by using the NCEP reanalysis datasets and tropical cyclone data created by the Chinese Meteorological Administration. By analyzing the Dynamic Genesis Potential Index (DGPI), we found that the anomalies of large-scale circulation limited typhoon activities by affecting tropospheric vertical wind shear and vertical movement. The Mascarene High was significantly weaker than usual, resulting in a weaker Somali jet stream. The cross-equatorial air flow was not active, and the easterlies consistently prevailed over the east of the Philippines and the South China Sea, which was not conducive to the establishment of monsoon trough over this region, thus affecting the formation of tropical disturbance. The center of the polar vortex in the Northern Hemisphere was closer to the Western Hemisphere in July 2020, and thus the cold air activities in the Eastern Hemisphere were not significantly affected, and the Subtropical High was more westward. The South Asian High was stronger and more eastward than before, and the oceanic trough was cut off by the strong easterlies of the South Asian High, which enhanced the downdraft over this region, and eventually intensified the Subtropical High. The downdraft in the middle of the troposphere limited the formation and development of tropical cyclones. Furthermore, due to the anomalous circulation at mid- and high-levels, the vertical wind shear over the east of Luzon Islands and the South China Sea was 2~4 m/s higher than normal in July, and 4~8 m/s higher over parts of the South China Sea. At the same time, the relative humidity in the lower troposphere was relatively low, and the atmospheric stratification was stable. Both dynamic and thermal conditions were not conducive to the further development of tropical disturbances. [ABSTRACT FROM AUTHOR]

Severe wind events which occur in the metropolis of Beijing in China bring major catastrophes. Characteristics of severe winter and spring wind events over Beijing during the past 40 years have been analyzed. An artificial intelligence-based method is adopted to categorize the favorable large-scale circulation patterns and dominant weather systems. Four categories are concluded and compared to each other in terms of distributions of geopotential height at 500 hPa, temperature at 500 hPa, sea level pressure and their corresponding anomalies in 1979–2019. It is found that the first category (T1) which is dominated by strong cold trough at upper levels with strong cold-core high locating at surface is the most conducive circulation pattern, while the fourth category (T4) which is controlled by weak trough and strong ridge with strong low cyclone at surface is the least one. The second and third categories, represented by T2 and T3, are under the control of strong cold trough and warm ridge at upper levels with weak high at surface, and of weak trough and strong ridge with strong low cyclone at surface, respectively. Characteristics and differences under different backgrounds of global temperatures are analyzed by separating the past 40years into two distinct periods. The decreasing trends of intensities of the trough and ridge, the temperature at 500hPa, together with the surface systems, are found to be responsible for the decrease in severe wind events in T1, T2 and T3 in the last 20 years, while T4 is distinct to the other three categories with little change in its circulation pattern, and thus continues contributing to the severe wind events over Beijing. The results found in this study with the usage of an AI-based algorithm will benefit for the operational forecasting for extreme wind events over Beijing.

During the winter half-year (previous October–April), the mid-latitude westerlies flows around the Tibetan Plateau (TP) and generate a dynamic low-pressure trough on its south side and a high-pressure ridge on its north side. In this study, we define the vorticity perturbation as the difference between local vorticity and the meridionally-averaged vorticity. Then, the difference of averaged vorticity perturbation at 600 hPa in the two key areas where the trough and ridge are located is used to represent the intensity of the flows around the Tibetan Plateau (FAT). The evolution characteristics of FAT in the winter half-year, as well as in autumn, winter and spring, are analyzed. Moreover, under global warming, in winter the relationship of FAT to the precipitation and temperature in China are discussed. The results show that FAT steadily exists on both sides of TP during the winter half-year. With the north-south migration of the mid-latitude westerlies, the FAT gradually strengthens in autumn, with the strongest intensity and the widest range in winter, and begins to weaken in spring. The intensity of FAT (IFAT) has a decreasing trend and a quasi-4a period variation on the interannual scale in all the time, both of which are closely related to the mid-latitude westerlies upstream of TP. Represented by the winter when IFAT is strongest, the IFAT is significantly correlated to the change of precipitation and temperature in most parts of China under global warming, especially in the convergence area over central-eastern China. There is also a significant correlation between IFAT and the precipitation and temperature anomalies in Northwest China, TP, and Northeast China. This relationship between the FAT anomaly and the climate anomaly in China in winter can be well explained by analyzing the anomalies of large-scale circulation, outgoing longwave radiation and water vapor flux divergence. The FAT anomaly maybe one of the reasons for the climate extreme events in China in winter.

A realistic representation of the Southern Ocean (SO) in climate models is critical for reliable global climate projections. However, many models are still facing severe biases in this region. Using a fully coupled global climate model at non-eddying (1/2 ∘) and strongly eddying (1/10 ∘) grid resolution in the SO, we investigate the effect of a 0.5 °C, 1.0 °C and 1.6 °C warmer than observed SO on i) the spin-up behaviour of the high-resolution simulation, and ii) the representation of main dynamical features, i.e., the Antarctic circumpolar current (ACC), the subpolar gyres, the overturning circulation and the Agulhas regime in a quasi-equilibrium state. The adjustment of SO dynamics and hydrography critically depends on the initial state and grid resolution. When initialised with an observed ocean state, only the non-eddying configuration quickly builds up a strong warm bias in the SO. The high-resolution configuration initialised with the biased non-eddying model state results in immense spurious open ocean deep convection, as the biased ocean state is not stable at eddying resolution, and thus causes an undesirable imprint on global circulation. The SO heat content also affects the large-scale dynamics in both low- and high-resolution configurations. A warmer SO is associated with a stronger Agulhas current and a temperature-driven reduction of the meridional density gradient at 45 ∘ S to 65 ∘ S and thus a weaker ACC. The eddying simulations have stronger subpolar gyres under warmer conditions while the response in the non-eddying simulations is inconsistent. In general, SO dynamics are more realistically represented in a mesoscale-resolving model at the cost of requiring an own spin-up. • High-res. simulations of the Southern Ocean should be initialised from observations. • Initiating Southern Ocean nest from biased control run entails spurious hydrography. • Resolved vs. parameterised mesoscale dynamics lead to distinct mean circulation. • Ocean heat content major player setting meridional density gradient and circulation. • More realistic Southern Ocean in mesoscale-resolving model at cost of own spin-up. [ABSTRACT FROM AUTHOR]

The eastern part of Europe is very poorly represented in the Global Network for Isotopes in Precipitation (GNIP) database, mainly because the monitoring of the stable isotopes in precipitation started only recently compared with other regions. In this respect, the main objective of this article is to fill the gap in the GNIP database over the eastern part of Europe and show the temporal variability and potential drivers of an extended network of δ18O values in precipitation collected from 27 locations in Romania and the Republic of Moldova. We also present the first high-resolution map of the spatio-temporal distribution of δ18O values in precipitation in Romania and the Republic of Moldova, according to an observational dataset. According to our results, the stations from western and northern Romania tend to have LMWLS with higher values than those from southwestern Romania. The monthly variation of the δ18O and δ2H showed a clearly interannual variation, with distinct seasonal differences, following the seasonal temperatures. The analysis of the spatial distribution of stable isotopes in precipitation water was made on the basis of both observational data and modeled data. This allowed us to study the origin of the air moisture and the interaction with regional and local patterns and to analyze the link between the spatial δ18O variations and the large-scale circulation patterns on a seasonal scale. [ABSTRACT FROM AUTHOR]

Previous studies have suggested that interocean interactions can improve our understanding of climate's impacts on extreme weather events. The present study investigates how the interaction between the tropical eastern Pacific and Atlantic Oceans impacts extreme weather events over Tanzania. Results illustrate that the proposed Trans‐Atlantic‐Pacific Ocean Dipole index (TAPODI) is significantly correlated with the short rains over Tanzania. The wavelet coherence analysis showed that the variability of the short rains was influenced principally by the TAPODI on the interannual (1–5 years) scale. The association between TAPODI and short rains is in‐phase, with the phase of TAPODI lags that of the short rains by 90°. The positive phase of the TAPODI is associated with the advection of moist air from the Congo basin that favours ascent motion and leads to above‐normal rainfall over Tanzania. The negative phase of the TAPODI is related to sinking motions, accompanied by divergent winds at low level that block winds from the Congo basin and the western Indian Ocean, hence leads to below‐normal rainfall over Tanzania. Therefore, the study revealed the interactions between the tropical Pacific and Atlantic Ocean, which will improve the climate predictability and prediction of the short rains over Tanzania. [ABSTRACT FROM AUTHOR]

We investigate the large-scale circulation (LSC) in a turbulent Rayleigh-Bénard convection flow in a cubic closed convection cell by means of direct numerical simulations at a Rayleigh number Ra = 106. The numerical studies are conducted for single flow trajectories up to 105 convective free-fall times to obtain a sufficient sampling of the four discrete LSC states, which can be summarized to one macrostate, and the two crossover configurations which are taken by the flow in between for short periods. We find that large-scale dynamics depends strongly on the Prandtl number Pr of the fluid which has values of 0.1, 0.7, and 10. Alternatively, we run an ensemble of 3600 short-term direct numerical simulations to study the transition probabilities between the discrete LSC states. This second approach is also used to probe the Markov property of the dynamics. Our ensemble analysis gave strong indication of Markovianity of the transition process from one LSC state to another, even though the data are still accompanied by considerable noise. It is based on the eigenvalue spectrum of the transition probability matrix, further on the distribution of persistence times and the joint distribution of two successive microstate persistence times. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 1)'. [ABSTRACT FROM AUTHOR]

Rainfall amount in mid-summer (July and August) is much greater over eastern than western Sichuan, which are characterized by basin and plateau, respectively. It is shown that the interannual variations of extreme rainfall over these two regions are roughly independent, and they correspond to distinct anomalies of both large-scale circulation and sea surface temperature (SST). The enhanced extreme rainfall over western Sichuan is associated with a southward shift of the Asian westerly jet, while the enhanced extreme rainfall over eastern Sichuan is associated with an anticyclonic anomaly in the upper troposphere over China. At low levels, on the other hand, the enhanced extreme rainfall over western Sichuan is related to two components of wind anomalies, namely southwesterly over southwestern Sichuan and northeasterly over northeastern Sichuan, which favor more rainfall under the effects of the topography. Relatively speaking, the enhanced extreme rainfall over eastern Sichuan corresponds to the low-level southerly anomalies to the east of Sichuan, which curve into northeasterly anomalies over the basin when they encounter the mountains to the north of the basin. Therefore, it can be concluded that the topography in and around Sichuan plays a crucial role in inducing extreme rainfall both over western and eastern Sichuan. Finally, the enhanced extreme rainfall in western and eastern Sichuan is related to warmer SSTs in the Maritime Continent and cooler SSTs in the equatorial central Pacific, respectively. [ABSTRACT FROM AUTHOR]

Precipitation induced mudflows are a major and longstanding threat in Uzbekistan, impacting on many properties and livelihoods. In this paper, the role of large-scale atmospheric circulation in producing the conditions necessary to initiate mudflows in piedmont areas of Uzbekistan have been evaluated based on historical and scenario (Representative Concentration Pathways; RCP8.5) experiments along from 10 Coupled Model Intercomparison Project Phase 5 (CMIP5) models. Applying the well-established circulation weather type (CWT) technique, and CMIP5 models reveal that mudflow generating large-scale circulation flows will increase by up to 5% to the end of the century. Considering the historical simulations over 1979–2005 and following the projections of RCP8.5 emission scenario for the target period of 2071–2100, precipitation climatology has been evaluated using bias correction techniques. By this way, the synthetic rainfall series were linked to a central proxy – a mudflow generating weather types, such as cyclonic (C), westerly (W) and south-westerly (SW) in order to diagnose potential changes in mudflow occurrences given the changed CWT characteristics by running the statistical-empirical algorithm of antecedent daily rainfall model (ADRM) and statistical logistic regression (LRM). Results for the important weather types (C, W and SW) confirm that mudflow activity will increase in the selected region as precipitation values associated with the CWT C and W flows in CMIP5 projections are expected to increase in the warm season for the target period of 2071–2100.The research focuses on piedmont areas of Uzbekistan as it has remained poorly understood due to limited climate research, particularly, in mountain areas. This is important in the face of climate change, which is likely to increase pressure upon high mountain areas that may need to investigate more frequent mudflow occurrences.

This study classifies the summer extreme high temperatures (EHT) over South China into Day‐EHT, Night‐EHT and Mixed‐EHT (corresponding to EHT with extreme coverage only in daytime, only at night and both in daytime and at night) and compares their associated circulation patterns. All types of EHT are associated with the intensification and expansion of western Pacific subtropical high (WPSH). Concurrently, anomalous subsidence occurs over South China, which reduces the cloud cover and favours daytime warming. However, different types of EHT feature different circulation configurations. Day‐EHT are influenced by the northwestward‐extending WPSH and tropical cyclones, manifesting an abnormal anticyclonic‐cyclonic pair. Anomalous northeasterly winds dominate over South China, which cause lower humidity and faster heat dissipation and thus the EHT disappear at night. Night‐EHT are related to the westward‐extending WPSH and intensified East Asian westerly trough, presenting a subtropical anticyclonic anomaly and a mid‐latitude cyclonic anomaly. Anomalous southwesterly and northerly flows meet around South China, favouring more water vapour convergence in situ. The above‐normal humidity results in smaller amplitude of cloud cover reduction and weaker daytime warming compared to Day‐EHT, but favours heat maintenance and Night‐EHT. Moreover, the mid‐high‐latitude wave train preceding Day‐EHT (Night‐EHT) lies more northward (southward) with the upstream high‐pressure anomaly occurring around the Ural Mountains (Caspian Sea). Mixed‐EHT combine the anomalies for Day‐EHT and Night‐EHT and weak humidity anomaly occurs over South China, thus the daytime EHT could persist until night albeit cools down slightly. These distinguished features indicate that different types of EHT should be considered separately for better forecast and projection of EHT. [ABSTRACT FROM AUTHOR]

Extreme precipitation in the Northern French Alps are mainly associated with large‐scale circulations (LSCs) bringing moist air from the Atlantic Ocean and the Mediterranean Sea—two atmospheric influences that are very frequent in the climatology. In this work, we investigate what characterizes the Atlantic/Mediterranean circulations driving extreme precipitation in the Northern French Alps in comparison to 'random' Atlantic/Mediterranean circulations. We focus on extreme 3‐day precipitation over two medium size neighbouring catchments from 1950 to 2017. Atlantic and Mediterranean circulations are identified using an existing weather pattern classification established for Southern France. Every single LSC is characterized using three atmospheric descriptors based on analogy in geopotential shapes at 500 hPa over Western Europe that were introduced in previous works. They are (a) the celerity, characterizing the stationary nature of a geopotential shape, and (b) the singularity and relative singularity, characterizing the resemblance of a geopotential shape to its analogs, in other words the way this geopotential shape is closely reproduced in the climatology. We add to these analogy‐based descriptors a new (non‐analogy) descriptor accounting for the strength of the low and high‐pressure systems. We show that Atlantic/Mediterranean circulations driving extreme 3‐day precipitation in the Northern French Alps are the Atlantic/Mediterranean circulations featuring the strongest centres of action as well as the most stationary and the most reproducible geopotential shapes—characteristics that are rare for both atmospheric influences. In the Atlantic case, these characteristics appear to be even more pronounced and rare with regard to the whole climatology, pointing LSC as an important driver of extreme precipitation. In the Mediterranean case, these characteristics appear to be more random with regard to the whole climatology, pointing a more balanced contribution between specific LSC and humidity in driving extreme precipitation. [ABSTRACT FROM AUTHOR]

The large-scale circulation, Indian summer monsoon (ISM), has a strong influence on the Tibetan Plateau (TP) since its onset and intensity have profound impacts on regional precipitation, which then can supply water for glaciers, lakes, rivers and social demands. Weakening monsoon intensity and longer monsoon duration seem contradictory, as a weaker monsoon tends to produce less precipitation, while a longer duration increases the probability of precipitation. Past research has focused on how ISM’s intensity affects precipitation, with little consideration of the impacts of ISM duration. Here, we investigate the long-term (1979–2100) variability in the ISM’s duration and intensity. We find a prolonged ISM from 1979 to 2018, accompanied by monsoon weakening. Different combinations of duration and intensity have resulted in different spatial patterns of precipitation across the southeastern TP. Weakening and prolonged ISM is helpful to produce more precipitation around the southeastern TP, with intensity acting as a dominant control. Afterwards, an obvious impact can be found on potential water availability. Climate projections suggest that the ISM will weaken and lengthen until 2100, thereby increasing precipitation and potential water availability across the southeastern TP. This long-term trend should receive more attentions as increased regional extreme precipitation will increase the probability of flood risks until the end of this century.

This article analyzes recent trends in extreme precipitation in the Southwestern Alps and compares these trends to changes in the occurrence of the atmospheric influences generating extremes. We consider a high-resolution precipitation dataset of 1 × 1 km2for the period 1958–2017. A robust method of trend estimation in extreme precipitation is considered, based on nonstationary extreme value distribution and a homogeneous neighborhood approach. The results show contrasting trends in extreme precipitation depending on the season. In autumn, most of Southern France shows significant increasing trends, with increase in the 20-year return level between 1958 and 2017 as large as its average value over the period, while the Northern French Alps and the Swiss Valais show decreasing extremes. In winter, significant increasing extremes are found in the valleys and medium mountain areas surrounding the Northern French Alps, while the inner French Alps, the Swiss Valais and the Aosta Valley show significant decreasing trends. In the other seasons, the significant trends are mostly negative in the Mediterranean area. Comparing these trends to changes in the occurrence of the atmospheric influences generating extremes shows that part of the significant changes in extremes can be explained by changes in the dominant influences, in particular in the Mediterranean influenced region that shows the most organized trends. In particular, the strong positive trends in extreme precipitation in autumn in Southern France are concomitant with an increase in Mediterranean influence generating extremes.

The cultivation of edible fungal species represents a profitable agricultural sector and an interesting climatic‐impact oriented topic. This article focuses on Boletus edulis that develops in Pinus sylvestris forests in Soria (Castile and León in the Iberian Peninsula). This work aims at evaluating the extent to which the climate variability modulates the fungi production, both at local and regional/synoptic scales. With this purpose, the relationship between B. edulis production and various climatic variables such as precipitation, temperature, soil moisture and soil temperature has been explored based on observations during 1995–2014 over the study area as well as reanalysis data. The study evidences the relative importance of humidity in the B. edulis production both at the surface and the subsurface. In general, it can be said that wet conditions early in the production season together with cooler summers and mild autumns enhance the B. edulis growth. Evidences of the particular relevance of soil conditions at the beginning of the production season on the total annual production have been provided. In addition, the age of the trees that host the fungi species seems to play as well a pivotal role in the amounts of production obtained. Such a detailed analysis, including local relevant climatic information along with the investigation of the large‐scale features that impact the production of edible fungi species has not yet been developed over this region. [ABSTRACT FROM AUTHOR]

Extremely anomalous features of Meiyu in 2020 over the Yangtze-Huai River basin (YHRB) and associated causes in perspective of the large-scale circulation are investigated in this study, based on the Meiyu operational monitoring information and daily data of precipitation, global atmospheric reanalysis, and sea surface temperature (SST). The main results are as follows. (1) The 2020 YHRB Meiyu exhibits extremely anomalous characteristics, which are the most prominent since the 1980s. The 2020 Meiyu season features the fourth earliest onset, the third latest retreat, the longest duration, the maximum Meiyu rainfall, the strongest mean rainfall intensity, and the maximum number of stations/days with rainstorm. (2) The extremely long duration of the 2020 Meiyu season lies in the farily early onset and late retreat of Meiyu in this particular year. The early onset of Meiyu is due to the earlier-than-normal first northward shift and migration of the key influential systems including the northwestern Pacific subtropical high (NWPSH) and the South Asian high (SAH) along with the East Asian summer monsoon, induced by weak cold air activities from late May to early mid-June. However, the extremely late retreat of Meiyu is because of later-than-normal second northward shift of the associated large-scale circulation systems accompanied with strong cold air activities, and extremely weak and southward located ITCZ over Northwest Pacific in July. (3) The extremely more than normal Meiyu rainfall is represented by its long duration and strong rainfall intensity. The latter is likely attributed to extreme anomalies of water vapor convergence and vertical ascending motion over the YHRB, resulting from the compound effects of the westward extended and enlarged NWPSH, the eastward extended and expanded SAH, and the strong water vapor transport associated with the low-level southerly wind. The extremely warm SST in the tropical Indian Ocean seems to be the key factor to induce the above-mentioned anomalous large-scale circulations. The results from this study serve to improve understanding of formation mechanisms of the extreme Meiyu in China and may help forecasters to extract useful large-scale circulation features from numerical model products to improve medium-extended-range operational forecasts. [ABSTRACT FROM AUTHOR]

Abstract The representation of orographic drag remains a major source of uncertainty for numerical weather prediction (NWP) and climate models. Its accuracy depends on contributions from both the model grid‐scale orography and the subgrid‐scale orography (SSO). Different models use different source orography data sets and different methodologies to derive these orography fields. This study presents the first comparison of orography fields across several operational global NWP models. It also investigates the sensitivity of an orographic drag parameterization to the intermodel spread in SSO fields and the resulting implications for representing the Northern Hemisphere winter circulation in a NWP model. The intermodel spread in both the grid‐scale orography and the SSO fields is found to be considerable. This is due to differences in the underlying source data set employed and in the manner in which this data set is processed (in particular how it is smoothed and interpolated) to generate the model fields. The sensitivity of parameterized orographic drag to the intermodel variability in SSO fields is shown to be considerable and dominated by the influence of two SSO fields: the standard deviation and the mean gradient of the SSO. NWP model sensitivity experiments demonstrate that the intermodel spread in these fields is of first‐order importance to the intermodel spread in parameterized surface stress, and to current known systematic model biases. The revealed importance of the SSO fields supports careful reconsideration of how these fields are generated, guiding future development of orographic drag parameterizations and reevaluation of the resolved impacts of orography on the flow.

Energy field of spherical-cap bubble. [Display omitted] • Three multiphase phenomena analysed: added mass, drift, wake. • These micro-scale events produce large-scale transport and mixing. • The spherical-cap bubble was used as the object for demonstration. The goal was to present an approach where the micro-scale events related to single-particle motion directly translate onto higher levels and produce large-scale observable phenomena related to transport and mixing. Three multiphase hydrodynamic effects were considered, analysed and discussed: added mass, drift, wake. Although the results are of general validity, the spherical-cap shape (cap bubble) was used as the definite object for demonstration. It was shown how the unsteady inertial effect of added mass (coefficient C), irrelevant for mixing, is related to the steady kinematic concept of Darwin drift (coefficient D) that is directly associated with mixing. It was shown how the inviscid drift and the viscous wake operate and contribute to the resulting circulation and mixing. List of currently available formulas for C was completed, which are usable for estimation of D. [ABSTRACT FROM AUTHOR]

Focussing on the major cities of Brisbane, Sydney, and Melbourne in southeast Australia, this study seeks to determine the environmental factors that distinguish between heavy rainfall events (HREs) and extreme rainfall events (EREs). Using daily rain gauge observations, HREs and EREs are defined for each domain based, respectively, on the 95th and 99th percentiles of wet‐day rainfall for the period 1979–2018. K‐means clustering is applied to mean sea‐level pressure, data from ERA5 to obtain a set of representative large‐scale circulation patterns associated with these events. Composite synoptic maps, mean vertical profiles, and a series of column‐integrated diagnostics are then examined for each cluster and used to compare the environmental characteristics of HREs and EREs. For all three cities, HREs are associated with an upper‐level trough to the west, with large‐scale ascent, positive column water vapour (CWV) anomalies, and strong moisture transport over the analysis domain. For Brisbane and Sydney, the clusters are characterised by a coastal trough/low with moist onshore flow from the Tasman and Coral Seas. For Melbourne, circulation patterns are more distinct, with clusters characterised by a front, a cut‐off low, and an inland trough. Compared with HREs, EREs show a more amplified upper‐level trough, with stronger vertical motion and larger CWV anomalies over the analysis domain. In Brisbane and Sydney, EREs also feature stronger and deeper onshore flow, promoting enhanced moisture transport. A diagnostic termed upward vapour transport, which combines the key ingredients of high CWV and large‐scale ascent, is shown to discriminate well between HREs and EREs in all three domains. In contrast, surface temperature, which is frequently linked to rainfall extremes via Clausius–Clapeyron scaling, shows significant overlap between the different event categories, particularly for Brisbane and Sydney. [ABSTRACT FROM AUTHOR]

Spontaneous and stochastic reversal of large scale flow structure is an intriguing and crucial phenomenon in turbulent Rayleigh-Bénard type natural convection. This paper proposes a new control approach to eliminate the reversals through stabilising the corner flows using two small sidewall controllers. Based on a series of direct numerical simulations, it is shown that the control can successfully stop the growth of corner vortices and suppress the reversal of large-scale circulation, if the width of sidewall controllers installed within or near the top of corner vortices is large enough. When the controllers are located around the centre, they can easily break up the large-scale structures or even divide the single roll mode into a double-roll mode for very large widths. Moreover, the influence of sidewall controllers on the heat transport is studied. It is shown that the heat transport efficiency can be slightly enhanced or suppressed when the proper location and width are chosen. The present findings provide a new idea to control the large-scale flow structure and reversals in thermally driven convection through sidewall controlling. [ABSTRACT FROM AUTHOR]

Simulations of the spread of radioactive contamination (RC) with cesium-137 (137Cs) as a passive impurity were performed using the Institute of Numerical Mathematics Ocean Model (INMOM) to assess the radiation threat from the Komsomolets nuclear submarine (NS) on the northeastern slope of the Norwegian Sea at a depth of 1680 m caused by the possible leakage of radionuclides from the reactor compartment into the surrounding sea water. These simulations have shown that RC in the bottom layer generally spreads along the depth slope to the north and south of the source. Such a variability of the direction of RC transport is caused by the variability of the bottom current velocities, which is confirmed by the data of field measurements. As the distance from the source increases, the concentration of RC significantly decreases due to dilution in the surrounding waters. In the interior of the sea, the concentration is several orders of magnitude lower than in the source. The inflow of RC into surface waters due to turbulent mixing and convective motions of waters in the complex three-dimensional structure of circulation in the Norwegian Sea is simulated. It is shown that the excess of the surface concentration of RC over the bottom one observed in the measurements cannot be associated with emissions from the Komsomolets. The near-surface concentration of RC is most likely caused by the spread of RC from nuclear processing plants in northern Europe. In general, it has been shown that the currently possible RC from the Komsomolets does not exceed the background level of radioactive contamination of the waters of the Norwegian Sea. [ABSTRACT FROM AUTHOR]

Biogeochemical cycling in the Southern Ocean (SO) plays a key role in the global sea-air CO2balance and in the ocean anthropogenic carbon inventory (Ito et al., 2010; Khatiwala et al., 2009; Sarmiento et al., 2004). Some previous studies suggest a decreasing trend in the Southern Ocean carbon sink (Le Quéré et al., 2007; Lovenduski et al., 2007; Wetzel et al., 2005). We investigate the interannual and decadal variations in sea-air CO2flux and phytoplankton production in the SO with hindcast simulations by an ocean biogeochemical model. Decreasing trends in sinking POC and primary production are found from 1979 to 2003, concurrent with a decreasing trend in carbon uptake from the atmosphere. Simulations show substantial interannual and decadal variability in productivity. The sea-air CO2flux is significantly correlated with sinking POC, especially in high productivity regions of the Southern Ocean. Both mixed layer depths and iron concentrations are important to the long-term trends in production and phytoplankton community structure. Sea ice cover also plays an important role at high latitudes. Variability in dust deposition in recent decades has little influence on total SO productivity and carbon uptake, however, there are regional impacts near dust source regions. Accurately representing mixed layer depths and their impacts on phytoplankton light stress are critical for understanding how climate change impacts SO ecosystems and biogeochemistry.

The Songhua River Basin is one of the main grain-producing areas in China, and local climate change has had a direct impact on grain production during the past several decades. This study focused on changes in mean and extreme climate conditions in the Songhua River Basin during the period 1961–2014. We founded that the precipitation decreased slightly over most of the basin; however, an increasing occurrence of extreme events was detected in the northern and eastern parts of the basin, especially for the number of very wet days and, correspondingly, how much those days contributed to total precipitation. By contrast, the mean, maximum and minimum temperature values between 1961 and 2014 showed statistically significant positive trends in almost all regions of the basin. The rate of change was greater for minimum temperature than maximum temperature, which resulted in a significant increasing trend for the number of warm nights and an overall decreasing trend in the annual mean diurnal temperature range. Generally, the magnitudes of changes in temperature were more remarkable than the magnitudes of changes in precipitation over the Songhua River Basin. If we take both precipitation and temperature changes into account, the areas sensitive to climate change during the last five decades were in the southern and central parts of the Songhua River Basin.