Analysis Of Extreme Precipitation In Northwest China And The Application Of FY Satellite Data In Short-time Heavy Rainfall

Using daily precipitation observation data observed at 756 stations from 1979 to 2008 in China, NCEP\NCAR reanalysis data, circulation index, hourly precipitation observation data of regional stations in Gansu province, radiosonde and surface observation data, images and products of FY-2E satellite data, time/space distribution and evolution characteristics of extreme precipitation in northwest China were analyzed, the cause of the abnormal extreme precipitation events in each season was discussed, statistical analysis of some indicators from satellite product parameters in the process of short-time heavy rainfall in gansu province were made, and the applicability of these indicators in the forecast was verified. Main conclusions are as follows:The threshold of extreme precipitation in the northwest of China is much lower than that in southeast China, high value area is located in the southeast, low value area is in Junggar basin, Turpan basin and Qaidam basin. The extreme precipitation accounted from 22% to 44% of total rainfall.1 and 2 days duritive extreme precipitation frequency were much different in different region,1-day extreme precipitation duration is in the majority. Spatial variation trend of extreme precipitation had no consistency in the region.The days of summer extreme precipitation accounted for 67.5%, most occured in July. The days of autumn extreme precipitation were more than that in spring, winter is the least. The variation trend of 1-day extreme precipitation throughout the year was increased, extreme precipitation in autumn was increased most significantly, summer was not; 2 days extreme precipitation throughout the year showed a trend of slow increase, summer extreme precipitation increased more than spring, autumn decreased slowly.1-day extreme precipitation could mutate in all three seasons from 1979 to 2008, in different year 2 days extreme rainfall only mutated in autumn. There were multiple time scale variation of extreme precipitation in the northwest region, three of them were particularly significant within 2-year,3-yearand 5-year Quasi-periodic oscillation.The impact of El Nino and La Nina on the frequency of extreme precipitation events is asymmetrical. There was a better corresponding relationship between El Nino and less extreme precipitation.500 hPa geopotential height over northern Pacific Occean was on the high side in the years of less extreme rainfall while in the years of more extreme rainfall,500 hPa geopotential height over northern Atlantic Occean was on the high side.200 hPa zonal wind speed in the anomalistic year of spring extreme precipitation was much different from the conventional year, but it was not significant in summer and autumn. Warm and wet flows in low level from the southern region had direct impact on extreme rainfall in the northwest region. Extreme precipitation in spring had more response to the circulation changes in the same period than those in summer and autumn, SOI had the most obvious affect on extreme rainfall. Summer extreme precipitation had more response to the circulation changes in early winter.The synoptic characteristics of short-time heavy rainfall process of southwest type in southeastern Gansu are:the flow coming from southwest before the trough over Tibetan Plateau, the warm advection, the western extension of the western Pacific subtropical high, the south airflow and low vortex with shear line at 700 hPa. Lower level with high energy and humidity contributed to the strong development of convection system, the short-time heavy rainfall occured. Combined with simulated rainfall results of WRF and the change of TBB, this type of short-time heavy rainfall could be forcasted. The area of simulated precipitation above 50 mm and TBB decreased more than 20℃ within 2 hours can be made as the key area. There is high possibility of short-time heavy rainfall in the next 6 hours.