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.
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 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．
