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Warm-sector heavy rainfall (WR), shear-line heavy rainfall (SR), and frontal heavy rainfall (FR) are three types of rainfall that frequently occur during the pre-summer rainy season in south China. In this research, we investigated the differences in microphysical characteristics of heavy rainfall events during the period of 10-15 May 2022 based on the combined observations from 11 S-band polarimetric radars in south China. The conclusions are as follows: (1) WR has the highest radar echo top height, the strongest radar echo at all altitudes, the highest lightning density, and the most active ice-phase process, which suggests that the convection is the most vigorous in the WR, moderate in the FR, and the weakest in the SR. (2) Three types of rainfall are all marine-type precipitation, the massweighted mean diameter (Dm, mm) and the intercept parameter (Nw, mm-1m-3) of the raindrops in the WR are the largest. (3) The WR possesses the highest proportion of graupel compared with the FR and SR, and stronger updrafts and more abundant water vapor supply may lead to larger raindrops during the melting and collision-coalescence processes. (4) Over all the heights, liquid and ice water content in the WR are higher than those in the SR and FR, the ratio of ice to liquid water content in the WR is as high as 27% when ZH exceeds 50 dBZ, definitely higher than that in the SR and FR, indicating that the active ice-phase process existing in the WR is conducive to the formation of heavy rainfall. [ABSTRACT FROM AUTHOR]

In this paper, the data of Automatic Weather Stations (AWSs), ERA5 reanalysis, sounding, wind profile radar, and dual-polarization radar are used to study an extreme rainfall event in the south China Coast on 11 to 12 May 2022 from the aspects of thermodynamics and microphysical characteristics under the influence of low-level jets (LLJs). Results show that: (1) The extreme rainfall event can be divided into two stages: the first stage (S1) from 0000 to 0600 LST on May 12 and the second stage (S2) from 0700 to 1700 LST on the same day. During S1, the rainfall is mainly caused by the upper-level shortwave trough and the boundary layer jet (BLJ), characterized by strong upward motion on the windward side of mountains. In S2, the combined influence of the BLJ and synoptic-system-related low-level jet (SLLJ) increases the vertical wind shear and vertical vorticity, strengthening the rainstorm. In combination with the effect of topography, a warm and humid southwest flow continuously transports water vapor to farther north, resulting in a significant increase in rainfall over the study area (on the terrain's windward slope). From S1 to S2, the altitude of a divergence center in the upper air decreases obviously. (2) The rainfalls in the two stages are both associated with the mesoscale convergence line (MCL) on the surface, and the wind field from the mesoscale outflow boundary (MOB) in S1 is in the same direction as the environmental winds. Due to a small area of convergence that is left behind the MOB, convection moves eastward quickly and causes a short duration of heavy rainfall. In S2, the convergence along the MOB is enhanced, which strengthens the rainfall and leads to strong outflows, further enhancing the surface convergence near the MOB and forming a positive feedback mechanism. It results in a slow motion of convection and a long duration of heavy rainfall. (3) In terms of microphysics, the center of a strong echo in S1 is higher than in S2. The warm-rain process of the oceanic type characterizes both stages, but the convective intensity in S2 is significantly stronger than that in S1, featuring bigger drop sizes and lower concentrations. It is mainly due to the strengthening of LLJs, which makes small cloud droplets lift to melting levels, enhancing the ice phase process (riming process), producing large amounts of graupel particles and enhancing the melting and collision processes as they fall, resulting in the increase of liquid water content (LWC) and the formation of large raindrops near the surface. [ABSTRACT FROM AUTHOR]

This study explores the potential for directly assimilating polarimetric radar data (including reflectivity Z and differential reflectivity ZDR) using an ensemble Kalman filter (EnKF) based on the Weather Research and Forecasting model to improve analysis and forecast of Tropical Storm Ewiniar (2018). Ewiniar weakened but brought about heavy rainfall over Guangdong, China after its final landfall. In the present study, two experiments are performed, one assimilating only Z and the other assimilating both Z and ZDR. Assimilation of ZDR together with Z effectively modifies hydrometeor fields, and improves the forecast of the intensity, shape and position of rainbands. Forecast of 24-hour extraordinary rainfall =250 mm is significantly improved. Improvement can also be seen in the wind fields because of cross-variable covariance. The current study shows the possibility of applying polarimetric radar data to improve forecasting of tropical cyclones, which deserves more research in the future. [ABSTRACT FROM AUTHOR]

The objective of this research was to acquire a raindrop size distribution (DSDs) retrieved from C-band polarimetric radar observations scheme for the first time in south China. An observation period of the precipitation process was selected, and the shape-slope (μ-Λ) relationship of this region was statistically analyzed using the raindrop sample observations from the two-dimensional video disdrometer (2DVD) at Xinfeng Station, Guangdong Province. Simulated data of the C-band polarimetric radar reflectivity ZHH and differential reflectivity ZDR were obtained through scattering simulation. The simulation data were combined with DSD fitting to determine the ZDR-Λ and log10(ZHH/N0)-Λ relationships. Using Xinfeng C-band polarimetric radar observations ZDR and ZHH, the raindrop Gamma size distribution parameters μ, Λ, and N0 were retrieved. A scheme for using C-band polarimetric radar to retrieve the DSDs was developed. This research revealed that during precipitation process, the DSDs obtained using the C-band polarimetric radar retrieval scheme are similar to the 2DVD observations, the precipitation characteristics of rainfall intensity (R), mass-weighted mean diameter (Dm) and intercept parameter (Nw) with time obtained by radar retrieval are basically consistent with the observational results of the 2DVD. This scheme establishes the relationship between the observations of the C-band polarimetric radar and the physical quantities of the numerical model. This method not only can test the prediction of the model data assimilation system on the convective scale and determine error sources, but also can improve the microphysical precipitation processes analysis and radar quantitative precipitation estimation. The present research will facilitate radar data assimilation in the future. [ABSTRACT FROM AUTHOR]

On May 20th 2007, a brief but severe downpour rainstorm occurred in the coastal areas of Maoming and Yangjiang with rainfall of 115 mm per hour. Data from NCEP/NCAR reanalysis with 1°x1° resolution, Doppler weather radar, conventional surface observations, high-altitude radiosonde and wind profiler radar were used to analyze characteristics and contributions of synoptic scale and mesoscale systems during this torrential rainstorm. The results showed that: (1) the storm was caused by a quasi-linear mesoscale convective system (MCS) and the slow-movement of this system was the primary trigger of the torrential downpour; (2) water vapor was abundant, nearly saturated and in steady state throughout the atmosphere before the storm; intrusion of the weak dry and cold air in the middle level and a striking "dry above and wet below " structure had increased the atmospheric instability; (3) low-level southwesterly airflow from a low pressure (trough) at the Beibu Gulf provided abundant water vapor at the onset of the rainstorm; a deep dry layer was formed by dry and cold air behind the high-level trough, which facilitated latent heat release; upper-level divergence and low-level convergence circulations also provided vertical uplift for warm and moist air at the lower level; (4) Topography only played a minor role as the MCS developed and strengthened over relatively flat coastal terrain. Low level density flow induced by convection triggered new convective cell generation at the leading edge of the convective system, thereby playing a key role in the change of temperature gradient at lower layers, and resulting in strengthening atmospheric instability. [ABSTRACT FROM AUTHOR]

Spatio-temporal distribution characteristics and variation trends of tropospheric NO2 in Pearl River Delta (PRD) urban group and its adjacent areas were analyze from 2005 to 2013 based on remote sensing data from ozone monitoring instrument (OMI) satellite, and further explored the impact of human activities on NO2. Compared with the ground observation data, the OMI NO2 remote sensing data displayed high reliability. Due to active industrial production, high car ownership, great energy and power consumption, the average tropospheric NO2 concentration (7.4×1015 molec/cm2) of PRD region is about 3 times of the adjacent areas. At the same time, the regional high pollution NO2 in PRD region as a whole, the urban group effect is remarkable. Sinusoidal model can well fit the periodic variation of the NO2 in PRD and adjacent areas. NO2 concentration was highest in winter while lowest in summer. The concentration of NO2 in PRD region is decreasing in recent 9 years, which has a significantly negative correlation with the second industry output and car ownership. This suggests that the nitrogen oxide emissions governance in PRD region had achieved initial results. The concentration of NO2 increased significantly in the eastern and northern Guangdong Province, there are good positive correlations with the second industrial outputs and car ownerships, it is thus clear that industrial emissions and automobile exhausts are important sources of NO2 in these regions. The concentration of NO2 in western Guangdong area is stable. [ABSTRACT FROM AUTHOR]

A squall line in front of the tropical cyclone Pabuk occurred in the west of the Pearl River Delta to Zhanjiang on August 8th, 2007 when the storm approached South China. The development, structure and environmental conditions for this squall line were investigated in this study, with particular attention paid to the possible connection of this squall line with Pabuk. The observational data employed in this study are from soundings, Doppler weather radars and wind profile radars. The following six major conclusions are drawn by our observational analyses. (1) This squall line developed gradually from individual convective cells, and land breeze may be responsible for the onset of the squall line. (2) The path and intensity of the squall line were modulated by the environmental conditions. The squall line propagated along the coastline, and it was stronger on the landing side of the coastline compared with the surrounding in-land regions and oceanic regions. (3) The typical characteristics of tropical squall lines were seen in this squall line, including the cold-pool intensity, vertical structure and the wake flow stratiform precipitation at its developing and mature phases. (4) The environmental conditions of this squall line resemble those of tropical squall lines in terms of deep moist air and low convection condensation level. They also resemble mid-latitude squall lines in terms of the convective instable energy and vertical wind shear in the lower troposphere. (5) Two roles were played by the strong wind around Pabuk. On the one hand, it made the atmosphere more unstable via suppressed shallow convection and increased solar radiation. On the other hand, it enhanced the land-sea thermal contrast and therefore strengthened the sea breeze and the resultant water vapor transport. The sinking temperature inversion prevented the occurrence of low-layer weak convection and accumulated convection instability energy for the development of the strong convection. [ABSTRACT FROM AUTHOR]

Particle number size distribution (PNSD) between 10 nm and 20 urn were measured in the Pearl River Delta(PRD) region in winter 2011. The average particle number concentration of the nucleation mode (10-20 nm), Aitken mode (20-100 nm), accumulation mode (100 nm-1 urn) and coarse mode (1-20 µm) particles were 1 552, 7 470, 4 012, and 19 cm-3, respectively. The volume concentration of accumulation mode particles with peak at 300 nm accounted for over 70% of the total volume concentration. Diurnal variations and dependencies on meteorological parameters of PNSD were investigated. The diurnal variation of nucleation mode particles was mainly influenced by new particle formation events, while the diurnal variation of Aitken mode particles correlated to the traffic emission and the growth process of nucleation mode particles. When the PRD region was controlled by a cold high pressure, conditions of low relative humidity, high wind speed and strong radiation are favorable for the occurrence of new particle formation (NPF) events. The frequency of occurrence of NPF events was 21.3% during the whole measurement period. Parameters describing NPF events, including growth rate (GR) and source rate of condensable vapor (Q), were slightly larger than those in previous literature. This suggests that intense photochemical and biological activities may be the source of condensable vapor for particle growth, even during winter in the PRD. [ABSTRACT FROM AUTHOR]

Objective: To observe the effects of electroacupuncture (EA) stimulation of different tissues (nerve stem, muscular layer) at "Huantiao" (GB 30) acupoint on expression of hosphorylated c-jun N-terminal kinase (p-JNK) and c-jun (p-c-jun) proteins in the lumbar spinal cord in rats with sciatic nerve injury, so as to explore its mechanism underlying improvement of peripheral neuropathic damage., Methods: Forty-eight SD rats were randomly divided into normal, model (the left sciatic nerve severed), GB 30 deep needling (the acupuncture needle tip was inserted to the sciatic nerve trunk to elicit an instantaneous jerk of the hind limb) and GB 30 shallow needling (the needle tip was inserted to the muscle layer to evoke a local muscular contraction) groups (n = 12 rats in each group). EA stimuli were delivered at 2 Hz/100 Hz, 1 mA, 20 min in duration per treatment for 10 consecutive days. Histopathological changes were observed by Hematoxylin-eosin (HE) staining and immunohistochemical assay was carried out to examine the pathological change of spinal segments (L4-L5) and the expression of p-JNK and p-c-jun proteins, respectively., Results: For rats with the sciatic nerve severed, the spinal neurons became swelling, degeneration or even apoptosis. Acupuncture intervention reduced the number of apoptosic neurons and improved the pathological change, which was relatively better in the.deep needling group than in the shallow needling group. Likewise, the elevated spinal p-JNK and p-c-jun expression levels of the model group were significantly reduced by EA intervention (deep needling vs shallow needling, P < 0.01., Conclusion: Acupuncture can improve the spinal pathological changes in rats with sciatic nerve injury, which is probably achieved by decreasing the p-JNK and p-c-jun expression and inhibiting the JNK signaling pathway, and thereby, reducing the apoptosis of the spinal neurons. Deep needling results in greater benefits than shallow needling.