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.
In order to explore the characteristics and influence factors of atmospheric boundary layer inversion in Yinchuan City and their relationship with winter PM2.5 pollution, based on the sounding and surface meteorological observation data at Yinchuan meteorological station and the air quality monitoring data in Yinchuan City from 2015 to 2020, the characteristics of atmospheric boundary layer inversion and surface meteorological elements are analyzed. And on this basis that the influence of inversion and surface meteorological elements on PM2.5 pollution weathers in winter is explored. The results are as follows: (1) The inversions in atmospheric boundary layer are more easily to occur in the early morning than in the evening in Yinchuan City, and most of the inversions are ground inversions, they are stronger and thinner than suspension inversions. The inversion frequency and thickness are the largest in winter and the smallest in summer, while the inversion intensity is the strongest in autumn and the weakest in summer. (2) In winter, the inversions are easily to occur on a sunny day with average surface wind speed from 1.0 to 1.5 m·s-1 and relative humidity from 30% to 60%. (3) Ground inversion is one of the main meteorological factors affecting PM2.5 pollution weathers in winter. When the inversion thickness exceeds 596 m and the intensity exceeds 1.4 ℃·(100 m)-1, PM2.5 pollution weathers are easily to occur, and the pollution is aggravated with the increase of inversion thickness and intensity. (4) Under PM2.5 pollution weathers in winter, the sky is mostly sunny in the early morning, the average surface wind speed is usually less than 1.3 m·s-1, the relative humidity is greater than 54%, and the pollution is aggravated with the increase of humidity. (5) The boundary layer height is significantly negatively correlated with PM2.5 mass concentration, and the lower boundary layer height is, the heavier PM2.5 pollution is.
In order to better exploit the detection advantages of wind profile radar in upper layer, the detection data of ST wind profile radar during 2014-2017 from Huainan Climate and Environment Observatory (HCEO), Institute of Atmospheric Physics, Chinese Academy of Sciences, were used to evaluate the detection performance of ST wind profile radar under different detection mode combinations, and the influence of meteorological environment on detection performance was explored. On this basis, the applicability of detection mode combinations was discriminated in practical operations. The results show that ST wind profile radar can achieve different detection purposes by combining high or low modes with switching altitude. However, there are differences in detection performance under different combinations of mode. On the one hand, the detection performance of radar gradually decreases before the mode conversion and rapidly increases after the mode conversion, while it gradually decreases with height under the high mode. On the other hand, the detection performance of radar doesn’t change significantly in process of the conversion, while it gradually decreases after the high mode to a certain height. In addition, the reducing degree of detection performance gradually increases as the transition altitude approach in autumn and winter. The precipitation reduces the detection performance in lower and middle layers of troposphere. So, we select suitable mode combination based on the detection performance of radar to atmospheric boundary layer, troposphere and stratosphere.
Based on the hail data from eleven ground meteorological observation stations in the eastern agricultural region of Qinghai Province from 1961 to 2020, the temporal and spatial distribution of hail days, hail diameter, duration and disaster risk characteristics were analyzed by using statistical methods. The main conclusions are as follows: (1) The hail days in the agricultural area of eastern Qinghai Province decreased with climate tendency rate of 11.6 d·(10 a)-1 in the past 60 years, which passed the significance test of α=0.05, and after 1995, the anomaly of the total number of hail days changed from the positive to the negative. Hualong was the area with the largest number of hail days, and the number of hail days in Jianzha was the least. (2) Hail occurred mainly from May to September each year with seasonal differences. The diurnal variation of hail was obvious, and the peak occurred at 16:00 BST in the afternoon. (3) The number of hail days was positively correlated with altitude of stations and the correlation coefficient between them was as high as 0.97.(4) In the past 60 years, the hail processes with hail diameter less than 6 mm and the duration less than 9 min accounted for 58.33% and 73.55% of the total number of hail processes, respectively. (5) Xunhua was a low-risk area for hail, Hualong, Huangzhong and Huangyuan were medium-risk areas for hail, and Ledu was a high-risk or extremely high-risk area for hail, which was basically consistent with historical hail disasters.
Based on the cloud characteristic parameters retrieved by FY-2G satellite and hourly precipitation from July to September 2018, April to September 2019, and April to July 2020 in the eastern region of Qinghai Province, the indications of cloud top height, cloud top temperature, cloud optical thickness and cloud particle effective radius to precipitation frequency and precipitation intensity were analyzed. The results are as follows: (1) The cloud optical thickness was the strongest indicator of precipitation frequency for single cloud characteristic parameter. The frequency of moderate rain and heavy rain showed an obvious increasing trend with the decrease of cloud top temperature, increase of cloud top height and cloud optical thickness, while the frequency of light rain showed a decreasing trend. (2) The double cloud characteristic parameters (cloud optical thickness and cloud top temperature) were better indicators for precipitation frequency than single cloud characteristic parameter, the precipitation frequency increased with increase of cloud optical thickness and decrease of cloud top temperature. When cloud optical thickness was between 21 and 30 and cloud top temperature was greater than 0 ℃, the frequency of light rain was largest. When cloud optical thickness was greater than 40 and cloud top temperature was between -45 and -31 ℃, the frequency of moderate rain was largest. When cloud optical thickness was greater than 40 and cloud top temperature was less than -45 ℃, the frequency of heavy rain was largest. (3) The triple cloud characteristic parameters (cloud top temperature, cloud optical thickness and cloud particle effective radius) were more indicative for precipitation frequency than single cloud characteristic parameter and less indicative than double cloud characteristic parameters.
Meteorological prediction is one of the most important and challenging task in the modern world．In general，climate is highly non －linear and complicated phenomena，which require advanced method and computer modeling for their accurate prediction． This paper provides a survey of available literature of some methodologies employed by different researchers for the weather forecast based on the methods of data mining at home and abroad． It briefly introduced the concepts and traits of some data mining methods in atmospheric science，separately discussed the basic principles of these data mining methods used in weather forecasting，including the advantages and disadvantages． Finally，the author points out some existing difficulties of data mining methods used in weather forecasting ，and puts forward key points of future research and current trends of the research．
Based on the conventional data of Micaps and Doppler radar data，the rain to heavy snowfall event occurred in Langfang from 31 October to 1 November 2009 has been analyzed．The results show that the major influencing system of this heavy snowfall was the 500 hPa trough，wind shear line at the level of 700 hPa and 850 hPa，the inverse trough at ground level．And this snowstorm weather was a typical backflow over north China process．Vapor transportation from Bohai was the important source of steam for this snowfall．The strong convergence at the lower level resulted in strong ascending motion．The rise of the height of warm advection and echo tops would be one of criterions for snow enhancement．According to the echo characteristics of Doppler radar in Beijing，after 1－2 hours of the height of the 0℃layer bright band decreases quickly，it could be concluded that rainfall weather would change into snowfall weather in Langfang of Hebei Province．
Abstract:Results from the data of meteorological disasters in 2008 in Langfang show that the torrential rain and flood disasters are the most damageable．From 1949 to 2007，the direct economic losses caused by the torrential rain and flood disasters are 198．673 billion， which are 82．2%of those caused by all the meteorological disasters．The sustainable development of national and local economic is significantly affected by the torrential rain and flood disasters．Based on the system theories and principles of natural disasters evaluation，8 indexes are calculated，including topographic index(H)，intensity(C)and frequency(R)index of the torrential rain and lood disasters，onomical disaster bearing capacity index(E)，economic loss index(E')，life vulnerability index(L)，life damage ndex(L')and disaster relief index(K)，respectively．Combined disaster index were obtained for each county after systematically assessed the regional differences in risks of the torrential rain and flood disasters in Langfang，and 4 grades(extremely high，high，medium and low)were used to divide the torrential rain and flood disasters．Studies on the division of the torrential rain and flood disasters an provide us scientific basis for the precaution of the torrential rain and flood disasters and reduction of their economic losses and taking effective measures to these disasters．
Abstract: The reflectance spectra were measured of some featured crops and typical vegetation with the ASD Handheld FieldSpec spectrometer FR2500 in Gansu province． By the computer programming technology，the spectra database of typical ground objects in northwest China was set up． This paper mainly introduces spectrum data collection，the establishment course of database system，application and problems of database．
Soil heat flux plays an important role in energy flux exchange between land and atmosphere, especially in arid and semi-arid region. Based on soil heat flux at Zhangye National Climate Observatory, the diurnal variation of soil heat flux and the relationship between that and radiation flux are analyzed under different weather conditions for clear, cloudy and rainy day.The results show that the soil accepted heat from the air on clear day, on the contrary, the output heat of soil exceeded the input on cloudy and rainy day. In addition, most values of soil heat flux are negative in autumn and winter season, and positive in spring and summer .
According to the date of thunderstorm-day from1968 to 2007 and lightning disaster statistics data from 1998 to 2007 in Langfang, combined with its economic status and population density, vulnerability analysis, evaluation and vulnerability division of lightning disaster aremade. Four indices are selected to evaluate the vulnerability of lightning disaster in Langfang, including annual mean thunderstorm days (M), lightning disaster frequency (R), economic vulnerabilitymodule(D), economic lossmodulu(D), vital vulnerabilitymodule(L) and life and injurymodulus (L’). Based on them, the vulnerability assessmentstructure of thunderstorm disasters in each counties ofLangfang are given. Then, the vulnerability assessment indices of thunderstorm disasters are classified as five gradeswith given values. The comprehensives vulnerability assessment indices of these nine counties are also graded as corresponding five degrees. Finally, vulnerability division of the lighting disaster is obtained based on the vulnerability degree values of the nine counties in Langfang. The result shows thatKaifaqu and Guangyang districtbelong to themaximal damageable area, Xianghe county, Bazhou city, Sanhe city, AncidisrictandGu’an county belong to the high damageable area.The restcounties belong to themedium dam- ageable area. Scientific basismightbe provided for the planning of regionalprevention and reduction of lightning disaster in Langfang.
Based on the summarization of the former similar researches about land surface dewfall, this article systematically discusses dewfall’s formation mechanism and analyzes the relation between dewfall and climatic aswell as environmental factors, such as temperature, humidity, windspeed, cloud, topography, and so on. The ecological and climatic effects and biochemics effects about land surface dewfall are discoursed also, and some p roblems in the p resent research on dewfall are pointed out finally.Key words: dewfall; formation mechanism; ecological and climatic effects
Based on themonthly p recip itation data during 1951 - 2000 from 19 meteorological stations in Guizhou p rovince, the regional characteristics of p recip itation anomalies in summer are studied by usingmethods of the fuzzy assembling analysis, emp irical orthogonal function ( EOF) analysis and wavelet analysis on normalized anomaly of 19 stations’monthly averaged rainfall. The results show that five obvious rainfall periods occurred in the recent 50 years, includingwet in the early 1950 s, dry from the middle of the 1950 s to the early 1960 s, wet from the middle of 1960 s to the end of 1960 s, dry in the 1970 s and 1980 s, wet after the 1990 s, at the same time , the total rainfall p resented increasing trend. The coincident variability occurred in summer rainfall of Guizhou, but some regional differ2 ence also existed. The variations of p recip itation anomalies in summer can be divided into five spatial patterns, namely dry (wet) in the whole p rovince, dry (wet) in the east and wet ( dry) in the west, dry (wet) in the south and wet ( dry) in the north, dry (wet ) in the middle and east part butwet ( dry) in the southwest, dry (wet) in the southwest and wet ( dry) in other areas. It p resented ob2 viousmultip le time scales of 10 - 12 years, 4 - 5 years and 2 - 3 years variations for different rainfall patterns.
The weather characteristics, circulation background and the formation mechanism of the abnormal lasting high temperatureand drought event occurred in Chongqing in summer of 2006 are analyzed by using reanalysis data of NCEP, OLR and SST data. Re2sults show that the abnormity ofWest Pacific Subtrop ical High resulted in this lasting high temperature and drought event, and this ab2normity ofWest Pacific Subtrop ical High was greatly affected by such factors as the abnormal position and strength of Southern AsiaHigh, changes of Polar vortex and subtrop ical jet stream, warmingWest PacificWarm Pool and so on.
Based on temperature and p recip itation data during 1961 - 2006 ofQaidamu Basin , the influence of climate change on desertification was analyzed using the method of cumulative departure. Results show that climate warming trend there is obvious, and desertification area is increasing, vegetation degradation and soil salinity are severe. The warming climate, frequently heavywind and ascending evaporation are major natural causes resulting in desertification of Qaidamu Basin.
At first，the meaning of the water transfer processes(wTP)over land Surface is set forth and its uniqueness in arid and semi—arid region is discussed in this paper．Later，the sensitivity ofthe ecology and soil characteristics in arid and semi—arid region to the WI’P is presented．The domestic and foreign research advances on WTP is summed also．Finally，the deficiency on the WTP study in arid and semi —arid region is analyzed and the way to research the珊there is suggested．
Based on precipitation data in 126 surface stations in Northwest China, using REOF and tial characteristics of summer preclpltahon mNnlthwest China were analyzed in the paper. Results Blur-clustering method, the spa-show that the northeastern side of Tibetan Plateau is the most tion is mostly a half of that nant. PTPClpltatlOn trend In sensitive region to summer precipitation in Northwest China, the rainy 凡e月凡On (July to August) precipita-m a peal pears Wlth less Taln are mOTe than Ta1nV VeaTS in the region, and dry and flood years al'e a.Itel'- .Tune is ascending changing in recent 40 years, changing slowly in July, and descending in August, fiom the liner trend, the summer precipitation is nnconspicnonsly. Moreover, temperature departure and precipitation departure percent present reverse phase, and temperature is rising in recent 40 years.
Analysis of the climatological features of Jiangnan rainy season precipitation anomalies shows that the month with the most frequent anomalies of precipitation in Jiangnan is J une and the region is located in the middle of Jiangnan. The SVD analysis points out that the related sea surface temperature anomaly (SSTA) distributes in the pattern as a“seesaw”. The key region is just located in the most evident correlation area. The key period of SSTA impact is from May to J uly in the previous year in which SSTA has the best negative correlation with April to May precipitation in Jiangnan. Under the influence of SSTA“seesaw”pattern the precipitation anomalies in the following April to J une in East China exhibit opposite phase on both sides of the Yangtze River , the most evident correlative region is Jiangnan and the middle of which is located in the most obvious area of SSTA impacts.
