Based on the rainfall station observations and the products of Multi-source Merged Precipitation Analysis System of China Meteorological Administration (CMPAS), eight kinds of satellite-based precipitation products (FY-4A, CMOPRH-RT, IMERG-Early, IMERG-Late, GSMaP-Now, GSMaP-Gauge, PERSIANN-Now, PERSIANN-CCS) are comprehensively evaluated during the recordbreaking extremely heavy precipitation process in East Gansu on July 15, 2022 by using quantitative analysis, classification and struc⁃ tural similarity methods. The results show that eight kinds of satellite-based precipitation products basically reflect the spatial distribu⁃ tion characteristics of precipitation with more in the central and eastern regions and less in the northwest. Except for the GSMaP-Now product, the other seven satellite-based precipitation products all underestimate the precipitation at the center of the rainstorm. The eight kinds of satellite-based precipitation products have a good ability to describe the peak value of heavy precipitation, and both peak stages of the heavy precipitation process are reflected, but all of them seriously underestimate the magnitude of heavy rainfall and above. For precipitation of different magnitudes, the GSMaP-Gauge is the best for estimating precipitation of magnitude below torrential rain, while the CMOPRH-RT is the best for heavy rain and above, and all products cannot correctly hit the precipitation of torrential heavy rainfall. In terms of the structural similarity index, the CMOPRH-RT product can best represent the structural distribution of the precipitation process from three aspects of total precipitation, precipitation magnitude, and precipitation morphological distribution. In summary, for this precipitation event, the CMOPRH-RT precipitation product had the best performance in all aspects.

The northwest region of China is located in the hinterland of Eurasia, in which the source of water vapor is scarce, and drought is its main climatic feature. In recent years, with the continuous increase of regional precipitation, the warming and wetting in Northwest China has attracted great attention from all walks of life. In order to scientifically respond to social concerns, the team used multi-source data to conduct in-depth research on the phenomenon of warming and wetting in Northwest China from multi-scale and multi-dimensional perspectives, and found that the trend of wetting in Northwest China had significant and nonlinear enhancement characteristics. It is recognized that the wetting in Northwest China is expanding eastward, and the land surface evapotranspiration there has a special negative feedback mechanism on climate warming. It is estimated that the warming and wetting trend will still maintain in Northwest China in this century, and the wetting trend is driven by multi-factor comprehensive driving mechanism. The multi-aspect impacts of the warming and wetting in Northwest China are evaluated, and the technical countermeasures to deal with the warming and wetting there are put forward, and the research results of “the enhancement and eastward expansion of climate warming and humidification, formation mechanism and important environmental impacts in Northwest China” are formed. The major consultation report based on the research results has played an important decision-making support for the national strategies such as the development of the western region in the new era and the ecological protection and high-quality development of the Yellow River Basin. The research results were selected as “China's Top Ten Scientific and Technological Progress in Ecological Environment” in 2022, and have also received extensive attention from the international academic communities.

Precipitation is closely related to the occurrence and development of clouds. The study for the characteristics of convective cloud is of great significance to the precipitation monitoring and prediction, as well as researches of precipitation mechanism. A torrential rain struck Qingyang on15 July 2022, which is located in semi-arid region of Northwest China, causing the daily rainfall and hourly rainfall at several stations to exceed the historical extreme values. Based on products of the advanced geostationary radiation imager (AGRI) from FY-4A and FY-4B geostationary satellite, fusion products of micro-wave humidity sounder (MWHS) and micro-wave temperature sounder (MWTS) from FY-3D polar orbit satellite, the cloudsytem evolution, macro and micro characteristics of cloud, and the atmospheric environmental conditions during this torrential rainstorm event were analyzed. The results are as follows: (1) The rainstorm cloud top types formed from supercooled water clouds, mixed clouds, opaque ice clouds and multi-layer clouds. The cloud top types of heavy precipitation are mainly opaque ice clouds, and the height of cloud top is more than 14 km. The rainstorm cloud system is deep and mainly composed of small ice particles, and accompanied by strong updraft. (2) In this rainstorm event, there exist a process of convective cloud formation, merging and strengthening, and the continuous influence of convective clouds leds to the occurrence of extremely heavy rain. Precipitation was closely related to the black body temperature (TBB) of cloud top and its variation. Low TBB corresponded to heavy precipitation, and the TBB drops rapidly before the heavy precipitation. (3) Before the occurrence of heavy precipitation, atmospheric stratification is shallow convective instability. The strong humidification in the middle and lower layers is the main reason for the development of convective instability. The difference of absolute humidity in the lower layers leads to the difference of instable conditions and precipitation intensity.

Based on the hourly precipitation data from 302 regional automatic weather stations in the Loess Plateau arid region of eastern Gansu from 2013 to 2020, digital elevation model data from shuttle radar topography mission and ERA5 reanalysis data of European Centre for Medium-Range Weather Forecasts, etc., the spatio-temporal distribution characteristics of short-term heavy rainfall are analyzed, and on this basis that the relationship between it and topography, geography factors is discussed. Then combined with an extremely short-term heavy rainfall event in 2021, the influence mechanism of terrain is summarized. The results are as follows: (1) The short-term heavy rainfall mainly occurs in summer in the Loess Plateau arid region of eastern Gansu, and in July the proportion of short-term heavy rainfall days （35.9%） is the most and the extremity is the strongest, while in August the proportion of short-term heavy rainfall times (46.9%) is the most and the rainfall intensity is the strongest. The rainfall intensity mainly ranges from 22.0 to 31.0 mm·h^-1, and it shows a multi-modal diurnal distribution with the most active, strongest and most extreme from 17:00 BST to next 00:00 BST, whose proportion of times is 56.8%. (2) The spatial distribution of the occurring times and hourly precipitation extremum of short-term heavy rainfall events is extremely uneven. The occurring times is less in the northwest and more in the southeast, it decreases sharply with the increase of rainfall intensity, and the short-term heavy rainfall occurs frequently in the area with valley bell-mouth topography, moreover, the palm landform is also the high incidence area of heavy precipitation above 30.0 mm·h^-1. The extremum is small in the middle and large in the northeast and southwest, the large value mostly distributes in eastern Qingcheng and western Heshui. (3) The influence of geographical and topographic factors on occurring times of short-term heavy rainfall is significant, and its contribution comes from geographical location, while their influence on precipitation extremum isn’t obvious. In general, the topographic forced uplift isn’t main influence mechanism on short-term heavy rainfall in the Loess Plateau arid region of eastern Gansu. (4) The mountain-valley wind circulation and surface mesoscale convergence line induced by it are important inducement for the formation of short-term heavy rainfall in valley bell-mouth topography area in the Loess Plateau arid region of eastern Gansu.

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.

An extremely heavy rainstorm occurred on 14-15 July 2022 in Longdong, Gansu Province, which is located in semi-arid region, the daily rainfall and hourly rainfall intensity at several stations broke the historical extreme values. Based on the minutely and hourly precipitation observation data from 20:00 BST 14 to 20:00 BST 15 July 2022, the daily and hourly precipitation data from 192 regional meteorological stations since the establishment of them in Qingyang of Gansu Province, and the CMPAS (CMA Multi-source Merged Precipitation Analysis System) 10-minute and hourly precipitation data, the precipitation characteristics and extremity of the torrential rain event are analyzed. The results show that the extremely torrential rain event is characterized by large cumulative precipitation, concentrated rainfall area of rainstorm and above, strong convective precipitation, stable and less movement of the rainfall centers, and long duration of short-term strong precipitation, among which the extremities of cumulative precipitation, hourly precipitation intensity and short-term heavy precipitation duration are obvious. The heavy rainstorm center, Zhaijiahe station, is located in the middle and north part of Qingcheng County, the maximum accumulated rainfall is 373.2 mm, which is the maximum since the station establishment, and is nearly twice of daily precipitation extreme values at all national stations in Gansu Province. The maximum hourly rainfall is 84.9 mm, ranking the third in historical records at all stations in Qingyang, and the longest duration of short-term strong rainfall is as long as 6 hours, which is the maximum in historical records at all stations in Qingyang since establishment of them. The evolution of minutely precipitation shows that the precipitation intensity in the heavy precipitation center has pulsating change, and the precipitation location has swing in the east, west, south and north, but the swing amplitude is small.

Extreme precipitation events in arid areas often lead to huge casualties and economic losses, the study on its evolution characteristics and formation mechanism can provide an important support for improving the accuracy of weather forecast. A rainstorm process occurred on 13 August 2022 in Jinta County of Gansu Province, which was located in arid region of Northwest China. Both daily precipitation and hourly precipitation broke through the historical extreme value at national meteorological station Hexi Corridor, and their extreme and local characteristics were significant. European Centre for Medium-Range Weather Forecasts (ECMWF) fifth-generation global atmospheric reanalysis (ERA5) and observation data were used in this paper to analyze the causes of the rainstorm. The results show that the rainstorm occurred in the north side of the stable South Asia high, and the dynamic forcing in the upper and middle level of troposphere was weak. The baroclinic system, the lower level shear line and surface cold front in front of the 500 hPa short-wave trough, was mainly located in the lower level. The continuous transport of low-level water vapor around the thermal over the Qinghai-Tibet Plateau provided the extreme water vapor condition and the moderate intensity stratification instability for the rainstorm area. In front of the formation of surface cold front, the regional difference of low-level water vapor transport in central and eastern parts of Jiuquan City formed an obvious wet frontal and dryline. The meso-γ-scale convective system which caused extreme short-term heavy precipitation was triggered by the dryline, and developed into deep moist convection leading to extreme heavy rain at the intersection point of the cold front and the dryline. The local characteristics were significant during the development of the dryline convective cells to deep moist convection.

Abstract: The two regional shorttime heavy precipitation processes occurred in southeastern Gansu on April 19-20, 2019 (hereinafter using abbreviation “4·19”) and on April 26-27, 2019 (hereinafter using abbreviation “4·26”). Based on the conventional meteorological observations and ERA5 reanalysis data, the dynamic characteristics of two processes were analyzed through the diagnosis of physical quantities including frontogenesis function, temperature advection and vertical wind shear. The results are as follows: (1) The two processes belonged to baroclinicfrontogenesis severe convection, in which cold advection existed in the upper air, cold and warm air converged in low level, and obvious cold fronts and cold shear lines existed on the ground. (2) Under the same significant baroclinic atmospheric conditions, the dynamic characteristics of the two processes were significantly different. “4·19” process presented the characteristics of frontal precipitation, in which the cold air was relatively deep, strong and cold advection in the middle and low layers drove the lowlevel frontogenesis, and convection occurred under the dynamic unstable conditions forced by uplift of the front. However, “4·26” process had obvious characteristics of convective precipitation, in which cold air was diffused in the lower and near ground layers, and convective activity occurred under the combined action of near ground layer frontogenesis and lowlevel jets, and it was dominated by thermal instability. (3) The frontogenesis functions on 700 hPa and 850 hPa could quantitatively describe the temporal and spatial distribution and evolution characteristics of affecting systems in the lowlevel and near ground layer. Since the near ground layer trigger system was difficult to define due to the influence of terrain, especially in “4·19” process the pathes of cold air in the lower layer and near ground layer were complicated, the frontogenesis function could be used as a physical quantity index for the near ground layer trigger system.

 Based on monthly precipitation data at 116 meteorological stations of Inner Mongolia, NCEP/NCAR reanalysis data, NOAA sea surface temperature (SST) and 130 climate monitoring indexes from National Climate Center of China, the drought-flood abrupt alternation index (DFAI) in summer was calculated in Inner Mongolia, and on this basis the climate regions were divided. The anomalous characteristics of atmospheric circulation and SST in drought-flood abrupt alternation years in each climate region of Inner Mongolia were analyzed. The relations between DFAI in summer in each climate region of Inner Mongolia and previous circulation and SST indexes were discussed, and the prediction models of DFAI in summer were established in each climate region of Inner Mongolia. The results are as follows: (1) The transition characteristics from drought to flood weakened from late spring and early summer to midsummer, while that from flood to drought strengthened in each climate region of Inner Mongolia in recent 39 years. (2) The location and intensity of east Asian trough and western Pacific Ocean subtropical high had significant difference in western Inner Mongolia in drought-flood alternation years, and the water vapour supply and vertical motion were significantly different. The cold vortex intensity in northeast China, water vapour and vertical motion were significantly different in northeastern Inner Mongolia in drought-flood alternation years. (3) The DFAI in summer in Inner Mongolia had significantly negative correlation with previous SST of Indian Ocean, tropical western Pacific Ocean warm pool, Kuroshio region and the northeast of northern Pacific Ocean. (4) The prediction models of DFAI in summer in Inner Mongolia based on previous atmospheric circulation and SST indexes had certain prediction ability, which could provide some reference for the prediction of drought-flood abrupt alternation in summer in Inner Mongolia.

Based on the daily minimum temperature observation data in southeast of Gansu Province during 1969-2018, the variation of extreme low temperature events was analyzed, then 74 circulation characteristic quantities from National Climate Center were used to research the circulation system affecting the extreme low temperature events. The results are as follows: (1) The frequency of annual extreme low temperature events in southeast of Gansu Province reduced obviously with a rate of 2.3 d·(10 a)-1 in the last 50 years, and the reduction was most significant in summer and slowest in winter. There was an abrupt change of extreme low temperature days in 1987, after the abrupt change, the frequency of extreme low temperature events was relatively lower. (2) Compared with the climatic mean, the intensity of extreme low temperature events tended to increase, before 1987, the low temperature intensity anomaly increased with a rate of 0.2 ℃·(10 a)-1, while after 1987, the extrem low temperature intensity anomaly increased with a rate of 1.2 ℃·(10 a)-1. (3) The intensity of extreme low temperature in spring, summer, autumn and winter mainly ranged from -5.0～5.0 ℃, 10.0～15.0 ℃, -5.0～10.0 ℃, -20.0～-10.0 ℃, and the occurrence frequencies were 61.9%, 90.1%, 73.4% and 73.1%, respectively. (4) There was a positive correlation between extreme low temperature events and Eurasian meridional circulation in southeast of Gansu Province. The extreme low temperature events was related with cold air, the area index of western Pacific subtropical high and the intensity of polar vorticity center in the northern hemisphere in winter, while it was related with subtropical high northern boundary of South China sea, subtropical high northern boundary of the western Pacific and polar vorticity intensity of the Pacific in spring. The composited analysis of geopotential height fields indicated that Mongolia was a cold high pressure center on ground, and polar vorticity center was located in the eastern hemisphere from 500 hPa to 100 hPa, the westerly belt prevailed meridional circulation, and east Asian large trough in the westerly belt was deep and westward, the region of southeast of Gansu was controlled by strong northwest airflow after the trough, which was favourable to forming extreme low temperature events.

Based on the daily precipitation data at 107 weather stations in Inner Mongolia and NCEP/NCAR reanalysis data, the causes of anomalous heavy rain in the middle and west of Inner Mongolia in summer of 2018 were analyzed. The results show that the precipitation in Inner Mongolia in summer of 2018 was significantly more than the normal, it mainly concentrated in July, and the precipitation was 50% to 4 times more than the normal in the midwest. The anomalous configuration of circulation at different levels of troposphere was the main cause of more precipitation in summer of 2018 in midwest Inner Mongolia. There was a trough near Baikal Lake on 500 hPa, the blocking high near Ural Mountain and Okhotsk Sea was active, and the meridional span over mid-high latitudes increased, which was beneficial to moving southward of cold air. The ridge line of the western Pacific subtropical high was anomalous northward due to the strong East Asian summer monsoon, the water vapor supply was sufficient. The unstable atmospheric stratification provided sufficient energy for precipitation. The westerly jet axis was to the north, and the midwest Inner Mongolia located in the south side of the jet axis, which caused enhancement of divergence at upper level. Combined with the convergence at middle and lower level of troposphere, they led to the development of upward movement from the lower to the upper of troposphere. The westerly jet was to the north and its disturbance was weaker along north-south direction, and the convective activity over tropical northwestern Pacific was strong, which was conducive to motivate EAP wave, and resulted in maintaining steadily of the anomalously northward subtropical high over the mid-latitude region.

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.

A torrential rain and hail stroke Shijiazhuang on July 26，2011． The strong and cold air flow on 500 hPa and above resulted in sharp shifts of synoptic situation at high altitude in twelve hours，with short wave trough moving southward rapidly，which caused the failure of radiosonde observation and numerical forecast． Based on other monitoring data，obvious characteristics of the dramatic changing weather were analyzed． Firstly，according to satellite images，the comma cloud above the Great Bend of the Huanghe River had long and stout tail，with a tendency of developing southward． The dark area at the rear part of clouds indicated the intrusion of dry cold air，which developed into convective clouds with warm and moist air at low altitude． The tail fracture suggested the acceleration of moving southward of cold air． Secondly，the Shijiazhuang single station element variation showed that the surface potential pseudo equivalent temperature was 8 ℃ higher than the normal value，which indicated abnormal instability energy． Strong convective weather with the largest precipitation was located in the intensive zone of pseudo equivalent potential temperature，which reached 90 ℃ at the energy center． The difference of pseudo equivalent potential temperature within 100 km was more than 25 ℃． Finally，the radar echoes arranged zonally from the southwest to the northeast with the strongest echo of 65 dBZ in the front． Gust front formed before the strongecho，its maximum positive and negative speed were both larger than 20 m/ s． The squall line moved from west to east and its path and intensity ditermined the path and intensity of precipitation and hail． The transformation of wind direction and formation of surface convergence line were 21 min and 30 min ahead of the precipitation，respectively．

This paper analyzed the continuous detecting data ofLanzhou CINRAD /CC Radar abouta hailprocess occurred in Dingxi on July 18, 2008, summarized themain characteristics of the radarproducts during this hailprocess such as reflectivity, radial velocity,RCS vertical section, vertical integrated liquid content and so on. Then it discussed the detection methods for monitoring hail by DopplerRadar, found out the typical echo characteristic of supercell storms such as hook echo, bounded weak echo region(BWER),echowal,l suspended echo, obvious influx nick, existingmesocyclone etc., and summed up some informationwhich are good fornowcasting ofhai,l such as severe change ofVIL, corresponding relationship ofET and hailprocess, obvious three-body scatter characteristic and so on, these information will be of great value for us to detect severeweather events by radar.

The ARPSmesoscale model is imp roved bymodifying cloud microphysical scheme. Three new p redictands and theirmicrophysical p rocesses, including the number concentration of rain (Nr) , snow (Ns) and hail (Nh) , are introduced into the model. One case of stratocumulus cloud in North China is simulated by the imp roved ARPS model. The characteristics of cloud development, p recip itation, cloud microphysical structure and cloud microphysical p rocess are investigated. The cse study suggests that the distribution of stratocumulus p recip itation is nonhomogeneouswith some p recip itation significance regions, and the cloud microphysical structure is nonhomogeneous in space. The vertical accumulating liquid water content in cumulus is higher than that in stratus; the ice phasep rocess leads this p recip itation, and the melting of graupel is the main source of rain.

New GenerationWeather Radar has become a chief means of monitoring the severe convective weather events occurred in Lanzhou and its surrounding areas. This paper analyzed data error sources in radar front - end and back - end p rocessing. Itwas found that clutter, radar antenna gain, monitoring distance and data interpolation, coordinate conversion, remote transmission to several ter2 minals are mainly error sources in radar front - end and back - end p rocessing, respectively.