Study On The Relationship Between The East Asia And South Asia Summer Monsoon And Its Influence

In this paper,first of all,we determine the two Asian tropical summer monsoon subsystems’ strength index(the South Asian summer monsoon and the East Asian tropical summer monsoon) by using the65years of multi-daily reanalysis data of wind filed, geopotential height filed,sea surface temperature filed which are provided by NCEP/NCAR,and the53years of nationwide daily precipitation data from753stations.Then,according to the two summer monsoons strength index,analysis the changes in the strength with the type of summer rainfall corresponding relationship.Secondly in order to further explore the relationship between the two tropical monsoon,we propose the two summer monsoons’boundary index,and analysis the boundary index;Last we make a simple discussion about the strength index and boundary index impact on the climate.and their possible mechanism. We can make following conclusions:(1) On850hPa layer,the degree of intensity of the monsoon trough can reflect changes in monsoon strength,by comparing vorticity and OLR,we found that vorticity can be used to character the monsoon trough on850hPa well.and use the vorticity to define the strength of the Asian Summer Monsoon.The Asian summer monsoon tropical can be divided into four types:all strong years,all weak years,dipole strong years,dipole weak years.We analysis the circulation type of the four types strength,and found that every type has its circulation type obviously different from other types of strength at high,medium,low level.Then classify the rainfall type and four types of strength,every type of strength has its own rainfall type,there are huge difference.(2)To further explore the relationship between the two monsoon,we define a boundary index according to vorticity.The theoretical basis for its definition is based on the wave theory of ’there must have a ridge between two troughs’,by calculating the minimum vorticity to characterize the two Asian tropical summer monsoon boundary,and analysis the decadal changes by the boundary index,and boundary on decadal changes can be divided inti three stages:eastern type(from1948to1960),central type(from1961to1992),western type(from1993to2012).And the mutation to the western type through the99%confidence test.Three types of boundary have their own circulation model:when the boundary is eastern type,the low-level southwesterly winds strengthen,the West Pacific subtropical high weakened and back East at middle-level.,the strength of the South Asian high weakened too at high-level.when the boundary is central type,the low-level southwesterly winds weakened a little.the West Pacific subtropical high is not significantly reduced at middle-level.and the strength of the South Asian high is basically no change at high level,when the boundary is western type,the low-level southwestern winds weaken abnormal obviously,the West Pacific subtropical high is significantly strengthened westward at middle-level.the strength of the South Asian high also will be strengthened at high level.(3)At last,according to the monsoon strength index and boundary index,we explore their influence on climate,and the following conclusions can be made:when the East Asian tropical summer monsoon is stronger,the summer rainfall is less in the Yangtze river region,whereas is opposite.The southern summer rainfall and boundary are mutation in the same year,their possible mechanism is that boundary mutation can influence the whole layer of water vapor flux divergence,and then influence southern summer rainfall to change.The ENSO and boundary type statistics found:strong La Nina years,there is a very large possible that the two tropical summer monsoon boundary is eastern.Boundary mutation can influence sea surface temperature by affecting shortwave radiation flux and latent heat flux.