Climatic Characteristics Of Autumn Rain In West China And Analysis Of Its Causes

This paper's circulation data is originate from the National Centers for Environmental Prediction / National Centers for Atmospheric Research reanalysis dataset,sea surface temperature(SST)data is originate from provided by NOAA dataset and the rainfall data at 373 national meteorological stations in 1976-2015 years required by “Business Regulations of Monitoring Autumn Rainfall in West China(Trial Implementation)”.Butterworth band-pass filter is used to extract interannual and interdecadal signals of autumn rainfall index in West China,each circulation,SST field and combine with EOF,the Morlet complex continuous wavelet,Mann-Kendall method,the optimal segmentation method and correlation to analyze climatic characteristics and causes of the autumn rainfall in West China.The result shows the annual precipitation in western China has unique characteristics of two peak.The north region is the same as the beginning of the south region of Autumn Rainfall in West China and the end of the north region is earlier than the south area,and the southern region shows the characteristics of long and strong rainy season.Whether in interannual or interdecadal scale,the autumn rainfall region in West China is mainly characterized by the whole area agreement pattern and the opposite pattern between north and south.The first modal time series' cycle is about 5 years,and the second mode time series' cycle is about 4 years on interannual scale and the first modal time series' cycle is about 16 years,and the second mode time series' cycle is about 9 years on Interdecadal scale on interdecadal scale.The time series' abrupt change years of the first mode of interannual scale are 1960,1985,2003,the second mode are 1952,1958,1995,2006.The time series' abrupt change years of the first mode of interdecadal scale are 1969,1987,1963,1995,2000,the second mode are 1964 and 1990.When the mutation point is tested,it is found that the optimal segmentation method is more advantageous than the other four methods.The circulation system that affects the interannual and interdecadal scale is not the same,but the first mode of each scale is significant,and the second mode is very weak.On the interannual scale,the key affecting system of the autumn rain are the low pressure of the lower South Asian high pressure,the southeast monsoon,the Balkhash Lake low pressure,the western Pacific subtropical high and the subtropical westerly jet,and on the interdecadal scale,the key affecting systems of the autumn rain are the cold pressure in East Asia,Aleutian low and the southwestern airflow of Bangladesh.The upper circulation system are low pressure of Central Asia,Northeast Asia and the Pacific area.The significant correlate area of the interdecadal changes of SST and the autumn rainfall in west China is much more than others,which are mainly related.The positive abnormal of SST of India Ocean,the east equatorial Pacific,the central Pacific,the negative abnormal of SST of sea area near the Bering Strait and the northern Antarctic sea in spring,summer,autumn and the negative abnormal of SST of the sea area of Southeast Asia can promote the consistent pattern in the whole region of the autumn rainfall in west China.In the next year of eastern El Nino,the spatial distribution of autumn precipitation in west China is more in the northwest and less in the southeast,the precipitation in the southwest and the northeast are equal,but there is not much precipitation in the whole region.In the next year of central El Nino,the spatial distribution of autumn precipitation in west China is more than in the northwest,in the southwest and in the southeast,and the precipitation in the northeast is higher than that in the southeast,and the whole area is stronger than the eastern type.In the next of the mixed type of El Nino,the spatial distribution of autumn precipitation in West China is more than in the southwest,northeast,northwest and Southeast,and the whole area is stronger than the eastern and central type.The selection of different climatic criteria has a great influence on the classification of El Nino events.In different types of El Nino year,the subtropical high is more eastward than the average climate,and its intensity is low,and the southeast monsoon is weaker than the average climate,but only the south-west Bengal air flow is stronger than the average of the climate standard period in the central type and the mixed type.