The Community Land Model version 4.5(CLM4.5), driven by the atmospheric forcing dataset CRUNCEP, was used to simulate the spatial and temporal characteristics of soil moisture across the Tibetan Plateau from 1981 to 2016. Compared with station data and two reanalysis products (i.e., the ERA‐Interim and GLDAS‐CLM), it is found that CLM4.5 can well reproduce the spatial and temporal variations of soil moisture in the Tibetan Plateau. This study reveals the relationship between soil moisture on the Tibetan Plateau in May and summer precipitation in eastern China and the physical mechanism for the impact of soil moisture on summer precipitation. Singular value decomposition (SVD)analysis shows that the surface soil moisture in the south‐central Tibetan Plateau was positively related to the summer precipitation in South China and negatively related to that in the middle and lower reaches of the Yangtze River and Northeast China. The soil moisture in the western Tibetan Plateau was the opposite of that in the south‐central region. The wetter the surface soil moisture in the south‐central Tibetan Plateau in May was, the lower the surface temperature, sensible heat flux and net longwave radiation flux, and the higher the latent heat flux and net shortwave radiation flux and leading to weaker surface heating. In contrast, lower surface soil moisture in the western Tibetan Plateau led to stronger surface heating. This led to a weaker western Pacific subtropical high and a more northerly rain belt. The weather in South China was controlled by large cyclonic circulations forming convergences and updrafts that led to more rainfall in South China. The precipitation in the middle and lower reaches of the Yangtze River and Northeast China was less under the control of the anomalous anticyclone than that in South China, and vice versa.

At present, few studies have focused on the impact of circulation patterns on aerosol pollution in the Pearl River delta region (PRD) region based on the objective circulation classification method. Based on PM_2.5 observation data, meteorological observation data, Aerosol Robotic Network (AERONET) aerosol observation data and European Center for Medium-Range Weather Forecasting (ECMWF) ERA (European Reanalysis)-Interim data in the PRD during 2013 to 2017, the air pollution level, meteorological conditions, and aerosol optical and radiation characteristics in different circulation patterns are studied in this paper. Using ECMWF ERA-Interim sea level pressure, nine circulation patterns were determined based on the T-mode principal component analysis (PCA) combined with the k-means clustering method. There were significant differences in PM_2.5 values under different circulation patterns, indicating that the change of atmospheric circulation is an important factor driving the change of air quality. The prevailing wind in winter (northerly wind) facilitates the transport of pollutants from the north of the PRD and forms severe air pollution, while the prevailing wind in summer (southerly wind) brings clean air from the South China Sea; additionally, a high frequency of precipitation benefits the wet scavenging of pollutants, resulting in improved air quality in the PRD region. The impact of circulation patterns on the AOD (aerosol optical depth) is basically similar to that of the PM_2.5 concentration. The study also found that the annual average total radiation was negatively correlated with the annual average PM_2.5 concentration. In future, we plan to identify which methods and data are suitable for circulation classification in the PRD region.

NCEP–NCAR reanalysis data and a 47-yr daily precipitation dataset from a network of 42 rain gauges are used to analyze the atmospheric heat source (<Q₁>) anomaly over the Tibetan Plateau (TP) and its influence on the summer precipitation anomaly in the Sichuan–Chongqing region. Results show that the vertical advection of <Q₁> over the central TP is a major factor affecting summer precipitation in the Sichuan–Chongqing region. When the vertical advection of <Q₁> over the central TP is strengthened, the South Asian high shifts further than normal to the south and east, the western Pacific subtropical high shifts further than normal to the south and west, and the Indian low weakens. This benefits the transport of warm moist air from the low latitude oceans to the Sichuan–Chongqing region. Correspondingly, in the high latitudes, two ridges and one trough form, which lead to cool air moving southward. These two air masses converge over the Sichuan–Chongqing region, leading to significant precipitation. In contrast, when the vertical advection of <Q₁> over the central TP is weakened, the South Asian high moves to the north and west, the subtropical high moves eastward and northward, and the Indian low strengthens. This circulation pattern is unfavorable for warm air advection from the south to the Sichuan–Chongqing region, and the cool air further north cannot move southward because of the presence of two troughs and one ridge at high latitude. Thus, ascent over the Sichuan–Chongqing region is weakened, resulting in less precipitation.

Based on the in situ data of the soil moisture-observation networks established at Maqu, Naqu, Ali, and Shiquanhe (Sq) on the Tibetan Plateau (TP), and using five evaluation indices [Pearson correlation coefficient (R), root mean square error (RMSE), mean deviation (bias), standard deviation ratio (SDV), and unbiased RMSE (ubRMSE)], the applicability of soil moisture datasets [COMBINED, ACTIVE, PASSIVE, ERA5, ERA5-Land (LAND), ERA-Interim (INTERIM), CLSM, and NOAH] was comprehensively evaluated. The results showed that, at the observation-network scale, ACTIVE exhibited the best applicability in Maqu (R = 0.704, ubRMSE = 0.040 m3/m3), COMBINED performed best in Naqu (R = 0.803, bias = 0.016 m3/m3), LAND displayed the best consistency with observations in Ali (R = 0.734, bias = −0.035 m3/m3), and ERA5 not only showed the best performance in Sq (R = 0.793, bias = −0.037 m3/m3) but also exhibited good results in the other three observation networks (R > 0.6). In a smaller-scale evaluation in Maqu, ACTIVE performed best, followed by ERA5. The COMBINED and PASSIVE products had serious gaps in Ali and Sq, and had the worst applicability in the western TP. In conclusion, considering the correlation results and temporal and spatial continuities, ERA5 is the most suitable soil moisture dataset for the TP.

Based on runoff data collected at the Zhimenda station, reanalysis data from the National Centers of Environmental Prediction/National Centers of Atmospheric Research (NCEP/NCAR), and observation data from ground stations in China, this study analyzes the characteristics of changes in runoff in the source region of the Yangtze River (SRYR) during the flood season (from July to September), the relationship between runoff and antecedent rainfall, and the impact of the westerly jet (WJ) on rainfall in the coastal zone of the SRYR. The results show the following. The runoff in the SRYR displays a significant interannual and interdecadal variability. The runoff in the SRYR during the flood season is most closely related to 15-day (June 16 to September 15) antecedent rainfall in the coastal zone of the SRYR. In turn, the antecedent rainfall in the coastal zone of the SRYR is mainly affected by the intensity of the simultaneous WJ over a key region (55–85°E, 45–55°N). When the intensity of the WJ over the key region is greater (less) than normal_,the jet position moves northward (southward), and the easterly (westerly) wind anomalies over the region to the west of the SRYR become unfavorable (favorable) to the transport of water vapor from high-latitude regions to the SRYR. In addition, the southerly wind over the equatorial region cannot (can) easily advance northward, which is unfavorable (favorable) to the northward transport of water vapor from the low-latitude ocean. Hence, these conditions result in a decrease (increase) in the water vapor content in the SRYR. Furthermore, the convergence (divergence) anomalies in the upper level and the divergence (convergence) anomalies in the lower level result in the descending (ascending) motion over the SRYR. These factors decrease (increase) the rainfall, thereby decreasing (increasing) the runoff in the SRYR during the flood season.

In this study, National Centers for Environmental Prediction (NCEP) Final (FNL) operational global analysis data and meteorological observation data from 2013 to 2017 were used to evaluate the impact of seasonal changes and different circulation classifications on the dynamical downscaling simulation results of Weather Research and Forecasting (WRF) in the Pearl River Delta (PRD) region. The results show that the dynamical downscaling method can accurately simulate the time variation characteristics of the near-surface meteorological field and the hit rates of a 2-m temperature, 2-m relative humidity, 10-m wind speed, and 10-m wind direction are 92.66%, 93.98%, 26.78%, and 76.78%, respectively. The WRF model slightly underestimates the temperature and relative humidity, and overestimates the wind speed and precipitation. For precipitation, the WRF model can better simulate the variation characteristics of light rain and heavy rain, with the probability of detection are 0.59 and 0.69, respectively. For seasonal factors, the WRF model can conduct a perfect simulation in autumn and winter, followed by spring, while summer is vulnerable to extreme weather, so the result of the simulation is relatively poor. The circulation type is an important parameter of downscaling assessment. When the PRD is controlled by high pressure, the simulated results of WRF are good, and when the PRD is affected by low pressure or extreme weather, the simulation results are relatively poor.