The changes of low-level wind field play an important role in the formation of sudden precipitation, which can change the flow field structure in the lower atmosphere, thereby affect the stability and vertical movement of the lower atmosphere and promote the development of convective clouds. Based on wind profile radar data at Chang’an Station, observation data, the fifth generation atmospheric reanalysis data released by the European Center for Medium Range Weather Forecasting, and Doppler radar data, this study analyzed the evolution characteristics of the low-level wind field during three typical sudden precipitation events under the control of the subtropical high at the northern foothills of the Qinling Mountains in midsummer. These events occurred on August 6, 2023, from 11:00 to 12:00 (referred to as “Process I”), July 13, 2023, from 00:00 to 01:00 (referred to as “Process II”), and August 3, 2022, from 18:00 to 19:00 (referred to as “Process III”). The results show that all three events occurred under the circulation background of the subtropical high combined with the intrusion of cold air at low level, exhibiting strong suddenness. For Process I and Process II, the intrusion of cold air at low level was characterized by westerly winds, while for Process III, it was characterized by easterly winds. Before the precipitation, the atmosphere over the Chang’an region was in a significantly unstable state, with weak vertical wind shear in the middle troposphere, which was the main reason for the highly localized nature of these three precipitation events. In midsummer, the multi-year average low-level wind speed at Chang’an Station generally exhibited a single-peak pattern, the wind speed initially increased with height and then decreased. The average wind speed below an altitude of 1 000 meters did not exceed 3.14 m·s?1, and the hourly wind speed shows distinct diurnal variation characteristics. The low-level wind direction displayed a counterclockwise rotation with increasing height, shifting gradually from southwesterly to southeasterly winds.The 4-6 h before the occurrence of three sudden precipitation processes, there was a cold air intrusion process in the low-level over Chang’an, and the wind speed was significantly bigger than the multi-year average. With the continuous invasion of low-level cold air, the 2 m temperature decreased rapidly, the air pressure rose, convection was triggered, and heavy precipitation occurred. The continuous intrusion of low-level cold air could generate strong mesoscale frontogenesis in the lower atmosphere, providing energy and triggering conditions for sudden precipitation. On the other hand, due to the obstruction of the local terrain at the northern foot of the Qinling Mountains and the Guanzhong Basin, the low-level cold air was forced to rise, promoting an increase in precipitation.

Heavy rainfalls and floods, waterlogging triggered by rainstorms are one of the most serious natural disasters in Ningxia. This paper constructs an integrated rainstorm hazard risk warning model in Ningxia to effectively predict the risk of heavy rainfall and issue risk warnings in advance, by using the Analytic Hierarchy Process (AHP) and Delphi method, and considering four factors including hazard, exposure, vulnerability, and disaster mitigation capacity, the model incorporates 14 evaluation indicators such as population, economy, elevation, and vegetation etc. in Ningxia. Combined with GIS technology, a rainstorm event simulation was conducted. The results show that the model comprehensively and objectively reflected integrated risk distribution during rainstorms. The analysis of the rainstorm on July 10, 2022 indicated that the regions with the highest hazard were Jinfeng District and Xixia District of Yinchuan, Litong District of Wuzhong, Qingtongxia County, eastern Yanchi County, and Yuanzhou District of Guyuan; the highest exposure was in Yinchuan; the highest vulnerability was in western Qingtongxia, Tongxin County, Haiyuan County, Xiji County, and Pengyang County; the weakest disaster mitigation capacity was in Haiyuan County, and the highest integrated risk areas were Jinfeng District of Yinchuan, Litong District of Wuzhong, Haiyuan and Xiji County. Integrating the model with smart grid forecasting, the integrated rainstorm hazard risk can be calculated, which provides scientific basis for precise prevention in practical operations.

Examine the relationship between tropical Pacific sea surface temperature (SST) and precipitation in China has scientific significance for improving China's climate prediction level. Based on the long-term monthly rain gauge data of 160 stations in China and the monthly SST index from Climate Prediction Center (CPC), USA, this paper explores the response characteristics of precipitation in China to tropical Pacific SST changes through a new method of lag cumulative correlation. The results are as follows: (1) This method is able to reveal the cumulative effect of previous abnormal SST on the precipitation effectively, so as to provide a basis for selecting the optimal predictive factors. (2) Among Ni?o1+2, Ni?o3, Ni?o4, and Ni?o3.4 SST indices, previous Nino1+2 index has the most significant relationship with China’s precipitation. More precisely, the positive correlation between Ni?o1+2 timeseries and the 4-month lagged precipitation, and the negative link between 2-month cumulative Ni?o1+2 time series and the the 9-month lagged precipitation in China are most significant. (3) The Ni?o1+2 SST can distinctly influence the precipitation in China's monsoon regions, with the strongest positive feedback are as primarily locate in the eastern part of the Qinghai-Tibet Plateau and Yunnan Province. (4) The linear fitting between the Ni?o1+2 time series and the average precipitation of China with a lag of 4 months shows that the fluctuation trend of fitted precipitation is consistent with that of the rain gauge data, with relative small fitting errors in winter and spring and larger errors in summer and autumn.

The typical fog and haze episode in the Sichuan basin from December 16, 2014 to January 27, 2015 was selected according to the method of determination of fog and haze days at a single station and the regional fog and haze process. Based on air quality index (AQI), mass concentration of pollutant, meteorological element characteristics and atmospheric circulation, the characteristics and mechanism of the generation, evolution and transformation of this continuous fog and haze weather were studied. The results are as follows: (1) The fog and  haze process was characterized by strong intensity, long duration and wide range. (2) Both mass concentration of pollutant and AQI were highly consistent with the fog and haze weather process, and the main pollutant in this fog and haze process was PM2.5, followed by PM10. (3) It can be seen from the process of formation, evolution and transition of a longlasting severe fog and haze episode that there were stages of pollutant accumulation with different intensities, reaching the peak value and rapidly weakening. Therefore, the intensity of fog and haze weather process was closely related to weather situation and vertical structure of boundary layer. The average temperature was 1.24 ℃ higher than the normal years, the rainfall was 34.77% lower than the same period, relative humidity was 2.67% lower than the same period, sunshine hours was 10.33 hours more than the same period, and wind speed was close to or slight higher than that of the normal years. The stable atmospheric circulation feature provided favorable environmental field for fog and hazy weather and heavy air pollution. Strong temperature inversion layer, sinking motion in the boundary layer and convergence in weak wind fields on the ground prevented water and pollutants from diffusing to the upper air.

Based on the ozone mass concentration monitoring data near surface of Yinchuan and ground and upper meteorological observation data over Eurasian area from 2014 to 2016, the influence of meteorological conditions on ozone mass concentration was probed systematically from two aspects of meteorological factors and atmospheric circulation pattern. The results show that the ozone mass concentration near surface of Yinchuan was positively correlated with air temperature and negatively correlated with relative humidity, respectively. The vertical mixing played a dominant role when the wind speed was low, the ozone mass concentration was positively related with wind speed, while the horizontal diffusion played an important role when the wind speed was high, the ozone mass concentration was negatively related with wind speed. The southerly wind and wind direction towards Helan Mountain were conducive to the increase of ozone mass concentration. There were five circulation patterns on ozone polluting days in Yinchuan: trough and ridge pattern (44%), wide trough pattern (21%), subtropical high pattern (16%), northeast ridge pattern (8%) and others pattern (11%). The inversion layer near surface and sea-level low pressure system (or inverted trough) were important synoptic systems which caused ozone pollution in Yinchuan.

Based on the daily precipitation data of 269 meteorological observation stations in the south area of West China from 1971 to 2017 and the NCEP/NCAR reanalysis data, etc., the change of autumn rain intensity and the characteristics of corresponding atmospheric circulation anomalies in the south area of West China were analyzed, the key area of atmospheric cold source over the Tibetan Plateau affecting autumn rain was sought, and the influences of atmospheric cold source in the key area on autumn rain intensity in the south area of West China were diagnosed. The results show that the intensity of autumn rain in the south area of West China hadn’t a significant change trend as a whole, and its interannual change might be affected by the hysteresis of anomalous changes of atmospheric cold source over the Tibetan Plateau in previous winter (January). When the atmospheric cold source over the Tibetan Plateau was abnormally strong (weak) in previous winter, it could stimulate the cyclonic (anti-cyclonic) anomalous circulation from the South China Sea to the western Pacific and maintain until summer. The continuous westward (eastward) airflow on the south side of the cyclone (anti-cyclone) caused surface warm water over the western (central) Pacific to travel eastward (westward), which caused anomalous warm (cold) of sea temperature in the equatorial central Pacific, then stimulate a cyclonic (anti-cyclonic) circulation in the western Pacific region. The water vapor conditions were poor (good) in the south area of West China under the control of northerly (southerly) winds in the west side of the cyclone (anti-cyclone), the precipitation was less (more), and autumn rain was weak (strong).

Based on the ozone mass concentration data in Ningxia from 2015 to 2018, the variations of O3 mass concentration in five cities of Ningxia were analyzed and compared, and the influences of airflow on O3 mass concentration in five cities of Ningxia were discussed by using back trajectory cluster analysis method and the global data assimilation system. The results show that the 90% quantile of O3 mass concentration in Shizuishan was the highest (159 μg·m-3), followed by Yinchuan (154 μg·m-3), Zhongwei (149 μg·m-3), Wuzhong (137 μg·m-3), and Guyuan (132 μg·m-3) during 2015-2018. In the past four years, the O3 mass concentration in Shizuishan decreased slightly, while that in other four cities increased. The days on which  primary pollutants was O3 was 124 days in Shizuishan, 119 days in Zhongwei and 103 days in Yinchuan. The days on which primary pollutants was O3 and air quality was good and  light pollution increased in all 5 cities. Except for Guyuan, the frequency of O3 pullution processes with 6 d and 7 d  duration increased in other cities, especially in Yinchuan and Zhongwei. For Shizuishan, Yinchuan and Wuzhong, the middle-distance and short-distance northwest airflow accounted for the highest percentage of the total airflow trajectory, followed by the southeast airflow and the north airflow. For Zhongwei and Guyuan,the percentage of the southeast airflow  was the highest, followed by the short-distance northwest airflow, and then the middle-distance and long-distance northwest airflow. The northern airflow from central Mongolia, central and western Inner Mongolia, across the northern and central Ningxia was the most important transport path affecting the O3 mass concentration, while the southeastern airflow from south central Shaanxi, northeastern Gansu and middle east Ningxia was the most important transport path affecting the ozone mass concentration in Shizuishan, Yinchuan, Wuzhong and Zhongwei.

Based on the routine upper level and surface meteorological observation data, the temperature of black body(TBB) data from FY-2G satellite and ECWMF dataset with a spatial resolution of 0.125°×0.125°, a regional snowstorm occurring in Shaanxi Province on 3 January 2018 was analyzed. The results show that the regional snowstorm occurred under the background of 500 hPa deep trough caused by cut-off low, 700 hPa southwest jet and 850 hPa easterly air flow. The efficient water vapor from Bay of Bengal and East China Sea was transited by strong low level southwest jet and easterly air flow, respectively, which was one of the main causes of the snowstorm. The intrusion of cold flow in middle level was the main trigger mechanism. Strong upward motion caused by the upper level divergence and low level convergence and the development and maintenance of positive vorticity in middle and low level were the dynamic mechanism of the snowstorm. The meso-β scale convective cloud cluster with minimum TBB  of -50 ℃ developed in the process of eastward moving of convective cloud cluster with the length of 1100 km, the width of 40 km and TBB equal to or less than -40 ℃, which caused the short-time heavy snowfall with precipitation intensity more than or equal to 2 mm·h-1. As an elevated convection case, the updraft increased due to the slantwise convection triggered by conditional symmetric instability. The echo band was parallel to 0-6 km vertical wind shear, and the snow area was consistent with the moving direction of the flow.

Based on the data of wind profiler and radiosonde of Beijing observatory station from 2014 to 2018, and the surface data of MICAPS in the same period, the errors and correlations of horizontal wind between wind profiler data and sounding data were compared and analyzed under different precipitation conditions. It could provide reference for application of wind profiler data in precipitation forecast. The results are as follows: (1) In general, the U-component wind of wind profiler was smaller than sounding data at all levels. The error of the U-component wind between the wind profiler data and sounding data was small and the correlation was good under precipitation condition. The root mean square error (RMSE) and correlation coefficient of U-component on 850 hPa varied greatly under precipitation condition, which reflected that the cloud bottom had a certain influence on detection of U-component by wind profiler. The errors of U and V-component wind above 500 hPa were relatively large. (2) Compared with different precipitation conditions, the U-component wind of wind profiler was smaller than sounding data under rainfall and thunderstorm weather condition, and the average error was relatively small and correlation was better under rainfall condition. During shower (snow shower) processes, the error range on different heights were large. The absolute value of average error on 700 hPa was the biggest under thunderstorm condition, followed by 850 hPa. In other precipitation cases, the error of the upper layers was basically greater than that of the lower layers. The V-component wind of wind profiler was larger than sounding data under snowfall condition, and the RMSE below 700 hPa was smaller than that under rainfall, shower (snow shower) and thunderstorm condition, while the RMSE above 700 hPa was the opposite. The error on 700 hPa under thunderstorm condition was large and the correlation was poor. The variation range of the RMSE and correlation coefficient on each height level were small under rainfall condition.

Based on the daily maximum temperature from 98 weather stations of Shaanxi Province and monthly reanalysis data from NCEP/NCAR, sea surface temperature (SST) from NOAA, and circulation indexes from National Climate Center of China, the causes of extremely high temperature weather process in Shaanxi in July 2017 were analyzed, and the preceding signals were discussed. The results show that the extremely high temperature weather process lasted for nearly 20 days in July 2017 in Shaanxi, and its intensity was the second level since 1961. The process of high temperature event was divided into two stages. The high temperature at the first stage occurred in the north and central part of Shaanxi from 9 to 14 July 2017, while at the second stage it expanded southward to the south of Shaanxi from 19 to 27 July 2017, and the intensity reached the maximum. At the first stage of high temperature, the most areas of Shaanxi were in positive geopotential height anomaly field from Xinjiang to Hetao area. The anomalous strong sinking movement and northerly warm advection in low level caused the high temperature weather. At the second stage, the western Pacific subtropical high (WPSH) obviously moved to the north and the west, the upper-level jet stream and the South Asian high (SAH) travelled clearly eastward, which led to the enhancement of the anomalous sinking motion and moving southward, combined with the increase of warm advections intensity and range in low level, further made the high temperature to expand southward and its intensity reached the maximum. In addition, the study found that the anomaly of previous SST from May to June in the key area of tropical western Pacific (10°S-15°N, 160°E-140°W) was significantly positive correlated with high temperature in the south and central of Shaanxi in July, so it was a reliable preceding signal to forecast high temperature. When the previous SST from May to June was higher in the key area, SST connected with WPSH, SAH and zonal wind over East Asia via exciting wave train in teleconnection, which affected the temperature change in central and southern Shaanxi, it might be the main reason of extremely high temperature event in this area in July.

The surface temperature is much different at different positions of sand dune or even same position but at different time or different weather condition The temperature features are discussed based on observations at different position of  sand dune on clear or sand-dust day, bare land or different vegetation cover. The daily maximum surface temperature appears on the coping of the sand dune, the minimum temperature and the greatest diurnal temperature range appear on the windward slop.The coping and windward slop of sand dune have the greatest diurnal temperature range, but the leeward slop is contrary.The daily variation of surface temperature is larger on clear day than that under dust weather condition on the coping, windward slop, leeward slop and at the left wing. The time of the maximum and minimum temperature at 20 cm depth of the windward slop and the leeward slop is contrary to that of the surface temperature under clear or dust weather condition. From 0 to 20 cm depth of the windward and leeward slop, the diurnal temperature range is gradually decreasing, the time of the maximum and minimum temperature is different on clear day and dust weather, and the daytime temperature difference is large on clear day or dust weather condition.The surface temperature of vegetation cover and bare land have biggish variation. The daily variation is larger in sunniness cover than that of shade cover of vegetation.

Based on the conventional observation data, the ground - based 12 - channel radiometer and wind p rofile radar data from October 25 to 27 2007, the fogweather event occurred in Beijingwas analyzed. The results are as follows: (1) The fog event occurred under the large - scale weather background, and the upper, low and surface weather situation were helpful to the fog’s forming and lasting; (2) With the radiometer retrieved p roduction, the upper, low and surface humidity scheme and the fog lastingmechanism could be found very clearly; (3) The surface temperature, the inversion layer thickness and its biggest intensity variation under 2 000 meters were concerned nearly with the fog change and visibility. The fog beginningwas consistentwith the biggest range of the surface temperature dropp ing, and there was the temperature inversion especially grounding inversion during the fog period. The surface relative humidity was above 83% , and 90% for thick fog, 97% for strong fog. There wasn’t some liquid water in the beginning of the fog, but after one hour the liquid water appeared at the level of 100 meters, and itwas biggest at this level before the weather system coming;(4) The horizontalwind speed was smaller under the level of 600 or 700 meters, and near the level of 600 meters the wind shearwas
obvious during the fog period; (5) It kep t the feeble up and down airflow in the boundary layer during the fog period.

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weather has been gained with statistics. By using the forecasting products of Ningxia meso一、tale model MMS, a simulative analysis
has been done on it's related physical quantities, which has gained a valuable results.