Regional Heavy Rainfall Characteristics And Extended Period Forecast Model Of Autumn Rain In Western China

This article selects 373 stations in 6 provinces including Hunan,Chongqing,Sichuan,Guizhou,Shaanxi,Ningxia,and Gansu according to the "Regulations on the Monitoring of Autumn Rain in West China(Trial)" issued by the Forecast and Network Division of the China Meteorological Administration,and defines the autumn and rain seasons in West China.The rainy period,the start day of autumn rain in West China,the end day of autumn rain in West China,the special year of autumn rain in West China,the length of autumn rain in West China,the amount of autumn rain in West China and other indicators.Introduce the Huaxi autumn rain index,which determines the strength of the Huaxi autumn rain,analyze the case of the significant period of the Huaxi autumn rain in 1983 with the highest intensity of the Huaxi autumn rain,and filter the potential height field from the start to the end of the year of the Huaxi autumn rain.The daily wave packet diagram explores the cycle and path changes of low-frequency energy before and after the start of the rainy season.Finally,based on the low-frequency weather map method,the distribution characteristics of the low-frequency system in West China's autumn rain period are analyzed,and the forecast model and statistical model of the precipitation in West China's autumn rain are proposed.The main conclusions are as follows:(1)The autumn rainy season in western China starts at the end of August at the earliest and at the latest in mid-September.The difference between the regions is relatively small.The difference between the area that starts early and the area that starts late can be about 20 days,and the start date of the rainy season is slow The slow image develops in the late direction,and the end date of the rainy season is opposite to the start date,and it is developing in the early direction.(2)The regional difference in the duration of the rainy season in autumn in western China is relatively small,basically around 80 days,the longest time in Changning County,Sichuan Province is up to 84 days,and the shortest is the Luding Station in Sichuan Province,the rainy season is only 38 days.The average rainfall in the rainy season is about 208 mm.In 1981,the most precipitation,the precipitation in the rainy season reached 331.4mm,while the least precipitation in 2012 was only 78.6mm.At the same time,the factors that affect regional precipitation in western China are not only the amount of precipitation but also the number of days of precipitation,which is clearly reflected in the abnormal precipitation year.(3)The West China Autumn Rain Index,which affects the intensity of West China Autumn Rain,is introduced.As time goes by,the change of West China Autumn Rain Days is mainly in a relatively stable state,and the West China Autumn Rain comprehensive intensity index includes both West China Autumn Rain Precipitation and Precipitation Days.,Can well reflect the intensity of autumn rain in West China.The West China Autumn Rain Intensity Index is positively correlated with the West China Autumn Rain Precipitation Days and positively correlated with the West China Autumn Rain Precipitation.When the West China Autumn Rain Precipitation is abnormally strong(weak),the West China Autumn Rain Precipitation increases(decreases),and the West China Autumn Rain Precipitation Days means the rain period increases(shortens).(4)Select 1983 as the strongest year of the autumn rain intensity in West China.Starting from September 10,1983,there is an anticyclonic circulation on the eastern side of Lake Baikal,so that the cold air from Siberia can go south to the autumn rain area in West China,and the Qinghai-Tibet Plateau There is an anticyclonic circulation nearby,and the lower high layer forms a hot low pressure,which provides conditions for precipitation;on September 28,there is a strong cyclonic circulation on the west side of Lake Baikal,and the South China Sea region guides the warm and humid southeast airflow to the western China rain area;On October 10 th,there was a strong anticyclone circulation in the waters near the East China Sea,which caused a large range of high-latitude regions in China to be controlled by strong low-frequency anticyclones,thus making the autumn rain area in West China within a strong ridge area,with precipitation in It reached near the peak within this time period;on October 30,the warm and humid air north of the Bay of Bengal affected most areas of West China due to the northerly airflow,and the intensity of precipitation weakened.(5)According to the low-frequency characteristics of autumn rain in West China and the low-frequency characteristics of the atmosphere during this period,we established a low-frequency forecast model of autumn rain in West China,and we divided the key areas of low-frequency systems.The area between 10°?70°N and70°?145°E is divided into 8 key areas;when area ? has low frequency cyclone activity on the west side of Lake Baikal and low frequency anticyclone activity on the east side,it is conducive to cold in Siberia and high latitudes The air is transported to the south;when low-frequency cyclones appear in zone VI,it will be beneficial to the transportation of Mengwan water vapor to the autumn rain zone in West China;the Indian-Burmese trough appears in zone ? to strengthen the southwest air flow;if the west subtropical high in zones ? is strong,Transport water vapor from the Western Pacific Ocean to the West China autumn rain region;the occurrence of low-frequency cyclones in Region IV will increase the intensity of autumn rain in West China;if there is fluctuation in the plateau region of Region III and it moves eastward,it may affect precipitation(6)The prediction model is tested through the activity period of the low-frequency system in each key area,and the comprehensive forecast accuracy rate during the nine significant precipitation periods in the West China autumn rain period in the past decade is about 58%;the extension of the West China autumn rain precipitation is established The statistical model of the forecast is tested and verified.The success rate of the model return is about 46%,and the success rate of the model forecast is about 45%.