Studies On The Weather And Climate Characteristics Of Rainstorm And Its Formative Causes In Gansu Area

Gansu province is the sensitive area of climate change and ecological fragile area, there are many types of meteorological disasters。There are drought, strong wind, sandstonn,heavy rainfall, hail,frost and dry-hot wind and so on. Meteorological disasters accounted for88.5%of all natural disasters in Gansu province,18.5%higher than the national average condition. Therefore, improving the monitoring,warning and prediction ability of heavy rain and avoiding disadvantages, are the key to make disaster prevention and mitigation, to promote economic and social development, to ensure the safety of people’s lives and property, That is important and far-reaching significance.Firstly, using history datasets of80meteorological stations of gansu province from1980to2009, we summarized space-time distribution, the extreme value distribution of rainstorm, frequency distribution of precipitation weather in Gansu, and then summed up the heavy rain weather climate characteristics in gansu province. On this basis, we analyzed17regional heavy rain weather processes from2000to2010, and categoriesed the circumstances of these processes to three types:subtropical high northwest southwest airflow type, low east west high, low vortex type. And then selecting three types of heavyrain in recent years for analysis, we summarized the Gansu rainstorm evolution characteristics In the main circulation pattern of global warming, environment, Provide strong technical support for the storm weather.For the Northwest rainstorm occurs, Often accompanied by the westward shift of the typhoon northward, the easterly flow near north of the low pressure circulation (jet) of Typhoon directly to the Western Pacific moisture transport to the heavy rain area along the western edge of the Pacific subtropical ridge, increase the probability of occurrence of the Northwest regional heavyrain, also conducive rainstorm extremum appears.we choose four heavy rain weather processes, using backward trajectory analysis methods to analyze the relationship between the typhoon and heavy rain, the water vapor source of heavy rainfall in northwest under of China. The terrain has a very important impact of rainstorms, In this paper, we did the sensitivity test of Terrain uplift and reduce in view the weather process of southeastern Gansu Province from27to28Aug2006, In order to examine the bell terrain the rainstorm system power, thermal factors and the role of the heavy rain. According to the vortex self-organization dynamics ideas, Analyzed6rainstorm processes from2006a to2008a of Gansu Province. through a census of TBB development evolution in these rainstorms, To get the storm clouds of self-organizing criteria and indicators of Northwest region, To further enhance the understanding of the genetic mechanism rainstorm, good rainstorm warning and forecast favorable theoretical basis.Accoding above content analysis, the results show that:1) The rainstorm first appeared in lth Apr, and the latest day is18th Oct in Gansu. The max daily precipitation station is in Pingliang. The frequency of precipitation of Gansu Province is gradually increasing from west to east, the rainstorm mainly concentrated in Longnan, Tianshui, Pingliang, Qingyang, and the region where occured the maximum times of rainstorms still appear in the southeast of Longnan. The heavy rain occurred mainly from June to September, and June is the most(Accounting for82.6%of the number of rainstorm), August followed by. Nearly30a, torrential rain showed an increasing trend, especially the Hexi region rainstorm increased more obvious.2) The regional rainstorm circulation of Gansu contain3types:Southwest airflow type the northwest side of the subtropical high, Western low East high type, Vortex-type. Nearly10a, Southwest airflow type the northwest side of the subtropical high is the most common rainstorm weather situation in Gansu.3) By the analysis of moisture sources, it showed that:Typhoons of the South China Sea and the East China Sea typhoon type accounted for41%of all types of the Gansu regional rainstorm process.The presence of typhoons in the South China Sea, strengthening the northward transport of water vapor in the South China Sea, conducive to produce regional rainstorm.4) Resulting in Gansu heavy rain precipitation clouds generally range from2to4small clouds of about35x35km2merger, the merger process is generally combined two with two. The merge time of Range about110km×110km2clouds is generally3～4h, Range about200km×200km2clouds is generally9～10h, and the Range greater than220km x220km2clouds will not self-organizing.5) The TBB center value of the heavy rain clouds basically in about220K in Gansu, Weaker strength than the China’s South precipitation cloud, and the precipitation fluid moving faster. It is showed that:Vortex self-organization is also an important reason to cause formation of arid and semi-arid regions heavy rain and other weather disasters, which has a positive role in promoting good rainstorm warning and forecast further enhance the understanding of the mechanism of heavy rain causes.6) The bell terrain has a good relationship with rainfall intensity, but had no significant effect with the rainstorm range. By the test of elevation (or decreased) Bellmouth terrain, it is showed that:the Special terrain effect for rainfall was obviously before and in the precipitation occurred, but no longer significant after; The elevation terrain strengthen the power uplift of the terrain at the windward slope, increased the vertical speed and low-level convergence, strengthening storm intensity.