In order to improve the understanding of the characteristics of low-level wind shear in the arid regions of northwest China and to provide reliable meteorological service guarantee for the flight safety of civil aviation in this region, the low-level wind shear reports received at 17 airports in Xinjiang region located in the arid regions of northwest China were statistically analyzed by using airport speech aircraft report, airport routine observation live message, Vaisala meteorological automatic observation system data, aircraft airborne detection data, and European Centre for Medium-Range Weather Forecasts (ECMWF) fifth-generation atmospheric reanalysis data (ERA-5), and a typical low-level wind shear event at Kashgar Airport was analyzed. The results show that low-level wind shear occurs in all seasons in Xinjiang, with the highest frequency in summer. Low-level wind shear occurs frequently in the height range of 90-300 m, mainly in the period from noon to evening. Medium-intensity low-level wind shear occurs most frequently, and small aircraft are more likely to encounter low-level wind shear. When the low-level wind shear occurs, the airport is often under the influence of westerly airflow type, low vortex type and low trough type in the 500 hPa situation field, and is often accompanied by low-level jet, ground gale and convective cloud. The special terrain environment is also one of the reasons that affect the frequent occurrence of low-level wind shear in some airports in Xinjiang. After analyzing a typical low-level wind shear case at Kashgar Airport, it was found that under the background of low-trough weather situation, the aircraft encountered strong wind shear during approach and re-flight, including strong horizontal wind direction, wind speed shear and strong vertical wind shear. Under the influence of small and medium-sized systems, the aircraft is very likely to encounter downburst during the descent process, which leads to strong low-altitude wind shear.

The Jinsha River basin is an important ecological barrier and clean energy export area in China, while its downstream is a dry and hot valley section with frequent high temperature weathers. Conducting high temperature weather circulation characteristics and diagnostic analysis is of great significance for improving the prediction level of high temperature disaster weather and the efficiency of energy dispatch in this region. Based on the daily maximum temperature data from meteorological stations and the fifth generation atmospheric reanalysis dataset ERA5 (Reanalysis v5) from the European Center for Medium-Range Weather Forecasts (ECMWF) from 1981 to 2020, the atmospheric circulation of high temperature weather in the lower reaches of the Jinsha River were classified by using K-means cluster analysis method, and the dynamic and thermal factors of high temperature weather were diagnosed and the physical quantities thresholds that characterize the high temperature weather were established. The results show that the atmospheric circulation patterns of high temperature weather in research area could be divided into three types, including warm-ridge type, subtropical high-Tibetan high type and Tibetan high type. During the high temperature period, there is a strong downdraft with strength above 0.25 Pa·s^-1 in the middle and upper layers. The sky is clear and cloudless with strong radiation. The near ground is directly heated by thermal low pressure with strength lower than 800 hPa. According to the diagnosis, the high temperature in the lower reaches of the Jinsha River is mainly caused by non-adiabatic heating. The contribution of temperature advection to local temperature rise is negative and the contribution of vertical adiabatic is close to zero. However, the downdraft is favorable for the surface to receive more solar radiation, which increases the non-adiabatic heating of the surface, resulting in high temperature weather in the lower reaches of the Jinsha River.

With the continuous intensification of global warming and the frequent occurrence of regional drought events, many measures to cope with drought events have been taken in recent years. In order to analyze the effectiveness of relevant measures, the Panzhihua and Liangshan Prefecture (referred to as “Panxi Area”) in Sichuan Province is taken as an example to study the evolution characteristics of drought in the region in the past 20 years, so as to serve local production and development. The Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature (LST) data of MODIS were used to calculate the Temperature Vegetation Drought Index (TVDI) in Panxi Area from 2003 to 2022, and the changes of TVDI on different time scales and drought evolution characteristics over the past 20 years were analyzed. The results are as follows: (1) Droughts in the Panxi area mostly occurs from March to May in spring, and the TVDI value is the lowest around October each year, which is also the period less prone to drought. (2) The drought in Panxi Area was alleviated year by year, and the areas of drought-free and drought-severe areas monitored by TVDI had little change.The area of light drought has increased, with an average increase of 5.30% after 2013. On the other hand, the area of medium drought has decreased, with an average decrease of 5.67% after 2013. (3) The drought in Zhaojue, Butuo and Yuexi has eased obviously, while the drought in Muli, Miyi and Huili has an aggravation trend. (4) The regional drought is relatively stable in most areas, accounting for 82.59% of the total area, while the drought center changes little from south to north, but it has a trend of westward migration.

In order to make a further understand of the difference and representativeness between gridded merging real-time product and observed data, the paper evaluated and corrected the CLDAS 2 m temperature merging product based on the observational data of automatic stations in Lanzhou and Wuwei region. The results are as follows: (1) The hourly temperature and daily minimum temperature products are lower than observations, and these errors decrease with the altitude going up below 2 500 m. The mean error of the daily maximum temperature product is negative around the altitude of 1 500 m, and changes to positive values above 1 500 m, then the positive mean error increases with the increase of altitude. The errors of daily maximum and minimum temperature are larger than those of hourly temperature, but their mean errors are all within 2 ℃. (2) The near gridding validation further shows that the diurnal change of CLDAS hourly temperature is generally similar to observations in the daytime, while it is relatively 0.2 ℃ lower than observations at night. The daily average temperature of CLDAS merging product is generally lower about 1 ℃, and the negative deviation in Lanzhou urban area is relatively small. Spatial distribution of high temperature days above 30 ℃ of merging products is basically consistent with observations, but there are more actual high temperature days in Lanzhou urban area. (3) Both the linear regression and the decaying averaging method have a certain correction effect on CLDAS temperature merging products, and the latter has a better correction effect. The correction effect becomes better with the altitude increasing. To sum up, the CDLAS temperature merging products can better reflect the characteristics of actual temperature change in Lanzhou and Wuwei region, but its ability to reflect the daily maximum and minimum temperature is not as good as the hourly temperature, and the error is relatively large in complex terrain.

A torrential rain struck Qingyang on July 15, 2022, which is located in semi-arid region of eastern Northwest China, causing the daily rainfall and hourly rainfall at several stations to exceed the historical extreme values. The formation mechanism of the torrential rain in semi-arid region of Northwest China is analyzed based on multi-source observation data and ERA5 reanalysis data, so as to provide some useful reference for rainstorm forecast in arid and semi-arid areas. The results show that the torrential rain process occurred under the background of weak synoptic scale baroclinic forcing, weak unstable energy and deep wet layer in the complex terrain of the Loess Plateau, with characteristics of strong locality and long duration of heavy precipitation, which is a warm-sector torrential rain. The special circulation configuration of South Asian high, western Pacific subtropical high and pressure system at the lower level is conducive to the occurrence and development of mesoscale convective system. Convective initiation and development were triggered by surface wind convergence line and low-level southerly jet. Development and long-time maintenance of the low-level jet intensified surface convergence line continuously. The left side of low-level jet (rainstorm area) formed two stable secondary circulations with the right side of the exit and entrance of it, respectively, which is the key factor for the maintenance of the convective system. The release of condensation latent heat caused local frontogenesis and low-level positive vorticity development, which is another important factor for development and maintenance of convective systems, and it is also an important reason for maintenance of atmospheric instability. The mesoscale convective system exhibited deep, low center of mass and quasi-stationary characteristics under the combined effects of the above mentioned factors, the radar echoes were characterized by backward propagation and train effect.

In the flood season (from June to August) of 2020, Gansu Province experienced intensive precipitation with long duration and wide ranges. The performances of three global models (ECMWF, GRAPES_GFS and NCEP_GFS) and four regional models (GRAPES_3 km, GRAPES_LZ10 km, GRAPES_LZ3 km and regional model SMS-WARMS in East China) for 24-hour accumulated precipitation forecast were evaluated in this paper. The main results are as follows: (1) The ECMWF model surpassed the other two global models in forecast performance, while among regional models, the GRAPES_3 km and the SMS-WARMS were better, and the latter was more stable. (2) The regional models had lower accuracy of rain probability forecast and TS, ETS, POD than those of global models for light and moderate rain, but for rainstorms they outperformed global models; the POD and Bias of regional models for heavy rain and rainstorms were significantly higher than those of global models. (3) According to the differences of 500 hPa circulation pattern, the precipitation in Gansu could be divided into two types including subtropical high marginal type and low trough type. Four subtropical high marginal precipitation processes and three low trough precipitation processes in flood season of 2020 were tested and evaluated. For global models and regional models, they all had better capability in predicting precipitation with different magnitudes for the former type than the latter one. The ECMWF model and regional models were better than the NCEP_GFS model and the GRAPES_GFS model in predicting heavy rain and rainstorm. Among global models, the ECMWF model had the best forecast effect for the two precipitation types, and the East China regional model had the best forecast effect for the two precipitation types among regional models. (4) All the seven models had good forecasting capability for the spatial orientation of moderate and heavy rain for both rainfall types, while the forecast effect of rainfall location for subtropical high marginal type was better than that of low-trough type, but the predicted precipitation intensity was stronger than observations, especially for the center of precipitation.

Based on hourly precipitation data at 146 automatic weather stations of Lanzhou from 2012 to 2019, the refined characteristics of precipitation in Lanzhou were analyzed from different time scales. The results are as follows: (1) The average annual precipitation was less in the north and more in the south of Lanzhou, and that was more in the edge and less in the interior from 2012 to 2019. The inter-annual change of precipitation was obvious from 2012 to 2019, the precipitation in 2018 was abnormally more by 46%, while that in 2015 and 2017 was abnormally less, especially in 2015 it was less by 30%. (2) The precipitation mainly concentrated in July and August in Lanzhou, and it in the south was obviously more than that in the north due to the influence of atmospheric circulation situations, while the spatial difference of precipitation wasn’t obvious in other months. (3) The diurnal variation of rainfall was obvious in Lanzhou, the precipitation was less in morning and more at night, and the range of rainfall was larger at night and smaller in the daytime. The precipitation in urban areas was generally less than that in mountain areas under the influence of altitude, and it mostly concentrated from afternoon to evening due to heat island effect, the convective rainfall was more, while the diurnal distribution of rainfall was more uniform in mountain areas, the fluctuation was smaller as a whole. (4) Overall, the frequency of short-time heavy rainfall in Anning district of Lanzhou was the highest, but the short-time heavy rainfall at Liuhe station of Gaolan county and Xujiamo station of Yongdeng county was the most frequent, and that in Yongdeng county was a critical concern.

Based on the hourly precipitation data at 81 national meteorological observation stations of Gansu Province from 1981 to 2018 and NCEP reanalysis data, the climate and circulation characteristics of extreme rainstorms were emphatically analyzed in different falling areas of Gansu Province. The results are as follows: (1) The extreme rainstorm weathers occurred mainly in Longnan, Tianshui, Pingliang and Qingyang of eastern Gansu, and the heavy rainfall centers concentrated in Kangxian and Huixian of Longnan. The extreme rainstorms were classified into four types including eastern Gansu, southern Gansu, southeastern Gansu and dispersion patterns, according to the falling areas of rainstorms. (2) The extreme rainstorms were easily to occur in July and August in Gansu, especially in mid-August. The extreme rainstorms in southern Gansu were earlier than in eastern Gansu. The precipitation of extreme rainstorms at night was more than in the daytime as a whole, the night rain characteristic was remarkable in Gansu, especially in southern Gansu and southeastern Gansu. In additional, the convective characteristic was significant in Gansu. (3) There were 2.5, 5 and 10 years period of extreme rainstorms in Gansu during 1981-2018, and the 2.5-year periodic oscillation was obvious. (4) The extreme rainstorms in Gansu were correlated with the subtropical high, and the falling area of rainstorm was significantly related to the location of subtropical high. Moreover, the extreme rainstorms in eastern Gansu were also related to the easterly airflow at the bottom of northern high ridge, the extreme rainstorms with dispersion pattern were related to the tropical low pressure in South China Sea, while the extreme rainstorms in southern and southeastern Gansu depended on the intensity and location of short-wave trough in Tibet Plateau.

Based on conventional meteorological observation data, FY4A satellite data, vegetation cover data and reanalysis data, the formation mechanism, transmission characteristics and influencing factors of a largescale severe dust storm occurring from March 14 to 18, 2021 in northern China were analyzed. The results are as follows: (1) Drought, high  temperature, less rainfall and low vegetation coverage in the earlier period in most parts of northern China provided a good sand source condition for occurrence of the strong sand dust storm weather. (2) The dust weather was caused by the strong development of Mongolia cyclone and the combined action of cold high pressure behind it. (3) The dust weather process was divided into two stages. At the first stage it was caused by the strong winds passing behind the ground cold front, which mainly occurred in North China and Northeast China. At the second stage it was caused by the southward diffusion of highaltitude dust that did not dissipate at the early stage and the backflow of east wind, which mainly occurred in Northwestern China. (4) The analysis of physical quantities such as horizontal helicity, the mixing layer height and vertical velocity showed that the dust emission conditions were insufficient in most areas of China, so the sand dust weather was mainly affected by the upstream sand dust transportation. For the eastern region of China, the contribution of dust storm was mainly from the southern part of Mongolia. While in Northwest China it was mainly contributed by Mongolia and its own dust.

Based on the lightning monitoring data of 33 lightning location monitoring stations and real-time lightning disaster data of 48 counties in Qinghai Province from 2010 to 2019, the spatial distribution and risk zoning of lightning disasters in Qinghai Province were analyzed by using mathematical statistics and ArcGIS spatial analysis method. The results show that the regions with more lightning frequency and strong positive and negative lightning current intensity were mainly distributed in the central and eastern part of Qinghai Province, while the areas with high value of thunderstorm days were mainly distributed in the Qilian Mountain and the southern part of Qinghai Province. The lightning disaster risk presented obvious regional differentiation in Qinghai Province. The high-risk regions were mainly located in Kunlun Mountains, Qilian Mountains, Nyainqentanglha Mountains, Bayan Har Mountains and Anyemaqen Snowy Mountains, as well as part of the southern grazing area of Qinghai Province. The northwest of Qaidam Basin, the southeast pastoral area of Qinghai Province and some areas around Qinghai Lake were medium-risk areas. The risk level in most of the eastern agricultural area, part of Qaidam Basin, Wudaoliang and Tuotuo River area was relatively lower.

Based on the drought disaster data of the Heng-Shao drought corridor from 1961 to 2018, the meteorological drought composite index (MCI) was used to study the drought monitoring and evaluation methods of the Heng-Shao drought corridor. The results are as follows: (1) During the peak period of crop water demand (from June to October), the drought events with weighted mean of regional MCI (DI) less than or equal to -0.5 and the process duration greater than or equal to 16 days were included in the statistics, and the three elements such as the extreme intensity, cumulative intensity and duration of DI index were the best factors for annual regional drought assessment. Furthermore, based on the three elements of DI index, the annual assessment index of regional drought (MCI_e) calculated by using the TOPSIS method was the best. (2) Based on the MCI_e index, the combined grading method of average value and standard deviation was used to obtain the threshold of regional drought degree for normal, drought, severe drought, and extreme drought years. It was found that the MCI_e index had a strong ability to assess extreme drought years and normal years in the Heng-Shao district, and had good assessment ability for 2019 and 2020. Furthermore, the extreme disaster year in 2013 was simulated, it was found that the MCI_e index could better capture the change of drought in the Heng-Shao drought corridor. Therefore, the MCI_e index could support the rapid assessment and early warning of drought in the Heng-Shao drought corridor to some extent.

Abstract: Based on the ground meteorological observation data of Hohhot station from 1981 to 2018, air quality data from 2014 to 2018 and nighttime light data from 1992 to 2013, the atmospheric self-cleaning ability index (ASI) was calculated, and the variation characteristics of atmosphere self-cleaning ability in Hohhot city in the past 38 years and its influencing factors were discussed.The results show that ASI was negatively correlated with air quality index (AQI), and the relationship between them could be expressed by a power function. The smaller the ASI was, the greater the risk of air pollution would be. The annual average ASI in Hohhot  declined significantly, especially after the 21st century. Compared to precipitation, wind speed and mixed layer height were more important to ASI. The positive correlation between the cold air active days and ASI was significant. After the 21st century, the cold air activity was obviously weak, which had a certain influence on ASI. The nighttime light index and the nighttime light area had a significantly negative correlation with ventilation. To some extent, the urbanization process played a role in the decline of ASI, especially after the 21st century.

Based on  daily rainfall  from 34 national  meteorological observation stations in the Hetao area , Inner Mongolia during 1961-2018, extreme precipitation events and extreme precipitation processes were analyzed in the past 58 years. Atmospheric circulation features of typical extreme precipitation processes were aslo analyzed. The main results are as follows: (1) Average annual precipitation decreased from southeast to  northwest, and precipitation was rich from July to August. The precipitation decreased significantly in August and increased significantly in May, June and December. (2) The thresholds of extreme precipitation became lower from southeast to  northwest, the historical maximum extremum occurred in Wushenzhao  of Ordos,  the historical minimum extremum occurred in Hailisu of Bayannur. The frequency of extreme precipitation events was more than five times in most areas, the intensity became weaker from southeast to northwest. (3) The extreme precipitation events was most from July to August, and its intensity was strongest in August. The frequency of extreme precipitation events and the intensity increased significantly in September. (4) The annual average extreme precipitation process intensity decreased significantly, the process precipitation was concentrated in Tumote Zuo Banner, Ejin Horo Banner and the city of Huhhot. (5) The extreme precipitation processes were influenced by the southwest flow at the front of trough, and the plentiful vapor and exceptionally strong updraft flow could easily cause extreme precipitation events.

Based on the daily precipitation data of 15 meteorological stations in the Dadu River Basin during 1961-2016, the areal precipitation of the upper, middle and lower reaches of the Dadu River Basin was caculated by using arithmetic average method. And the spatial and temporal distribution characteristics of its areal precipitation were analyzed. In addition, the beginning and ending date of the rainy season in the Dadu River Basin were calculated in this article. The results are as follows: (1) The areal precipitation of the middle and upper reaches of the Dadu River Basin showed an upward trend, while that of the lower reaches showed a downward trend. The relative variability and range of annual precipitation in the lower reaches were the largest, followed by the middle and the upper reaches. The areal rainfall was maximum in the Dadu River Basin in summer, it was about 50%-60% of the annual precipitation. The monthly average areal rainfall in the Dadu River Basin was 100-200 mm from May to September, and 5-20 mm from November to the following February. The peak of areal rainfall in the Dadu River Basin from north to south was delayed about a month. (2) The beginning and ending period of the rainy season calculated by the conversion index of the rainy season was more stable than that calculated by the heavy rainfall. The lower reaches of the Dadu River Basin entered the rainy season at the earliest, followed by the middle and the upper reaches. The upper reaches of the Dadu River Basin ended the rainy season at the earliest, followed by the middle and the lower reaches. The duration of rainy season in the upper, middle and lower reaches were 172 days, 182 days and 195 days, respectively. (3) Under the condition of heavy precipitation occurring in the upper reaches of the Dadu River Basin, the probability of heavy precipitation occurring in the middle and lower reaches at the same time was very small. Nevertheless, the heavy precipitation often occurred in the middle reaches of the Dadu River Basin at the same time when heavy precipitation occurred in the lower reaches.

Theweather systems and a relatedmesoscal convective systems, causing severe heavy rain in the south-eastGansu Province during 27-28 Aug 2006, are successfully simulatedwithMM5 models. Trumpet-shaped topography prominently increased rainfall in Gangu county. The rise of the terrain enhanced the low level convergence and verticalmovementover thewindward side of the terrain.The dynamical enforced rise of the terrain emerged at the prophase and the time of the rainfal.l
．

The main functions of Surfer software，ActiveX automation technique and the interface of VB application and Surfer are introduced in this paper．It is also introduced how to combine the strong ability of development using VB software and the strong mapping in  Surfer based on the interface．and the key program to Ca／Ty out the interface technique and a case of application automatic mapping are presented．

The large range rare fog process which occurred in East China from November 30 to December 4 in 2004 was analyzed, including the circulation background, its adjustment and evolvement, the climatic background, the atmospheric stratification condition and the vapor condition near surface, etc. Results show that the warm advection at the low level, the stable atmospheric stratification and the abundant vapor condition resulted in this rare fog process, and fog dissipation needs the cold air invasion with the cold front.