Feature Analysis About Intraseasonal Oscillation Of East Asian Summer Monsoon

In this study, the NCEP/NCAR reanalysis data of day-mean (includes wind, humidity, temperature) are used and the method of the summer monsoon index I_SMφ defined by LianYi etc is employed. According to the summer monsoon's character of oscillation along longitude direction established in our country and quantum jump to the north, we classified summer monsoon into three types: the west kind, the middle kind and the east kind. After choosing feature years for each type, dynamic diagnosis analysis and dynamic character contrast among each kind are done. They include 850hPa wind field, V850hPa two weeks in standard oscillation field.The main active path of summer monsoon was listed. The main characters of three path's activities were given. In the early days, there was one positive center at the position established. With the summer monsoon to the north, the positive center also had a position that moves to the north. In other words, there was cooperation of the south wind in the process of the summer monsoon movement to the north.The atmospheric 10-20 days period at 850hPa longitudinal wind spreads to the south and to the north, while the north is the main spread character. There's little change of the spread to the south in each longitude. And in the three types, the spread to the south also have no large difference. In other words, summer monsoon have no or little influence to the spread to the south of the atmospheric 10-20 days' oscillation at 850hPa longitudinal wind.There is an important relationship between the character of Atmospheric 10-20 days' oscillation to the north at 850hPa longitudinal wind and the type of the summer monsoon. To the west type, the spread to the north along 110°E or even westward is clearly stronger than the spread along other longitudes. To the middle type, the spread to the north along 110°E～115°E is the strongest. To the east type, the spread to the north along 115°E or even eastward is clearly stronger than the spread along other longitudes. That is to say that the strongest spread to the north and the summer monsoon's northward route are similar.Atmospheric oscillation of 10-20 days period at 850hPa longitudinal wind spreads latitudinal to the west and to the east, and the west is supposed to be the main spread character. The spread to the east is rather weaker, and has no rules. The spread to the west has definite rule, and it is rather strong at 20°N and the southern latitude. While at 25°N and even higher latitude the spread turns weaker. There is relationship between the position that the longitudinal wind spread to the west and the summer monsoon's type. To the west type, the western spread could reach 105°E and even on the west side. To the middle type, the western spread could reach on 110°E～115°E. However, to the east, the western spread could only reach 120°E. That is to say, the longitudinal position that the west spread reached and the longitudinal position that summer monsoon move to the north are nearly consistent.The oscillation of atmospheric 10-20 days at 500hPa vorticity longitudinal spreads to the south and to the north. And the spread to the north is the main spread character. And summer monsoon have no or little influence to the spread to the south for this spread. There is a direct relationship between the character of Atmospheric 10-20 days' oscillation to the north at 500hPa vorticity and the longitudinal position the summer monsoon at. To the west type, the spread to the north along 100°E and 105°E is stronger than the spread along other longitude position. To the middle type, the spread to the north is very evident along 110°E～115°E, while to the east type, the spread to the north along 120°E or even easter is clearly have the strongest spread intension. That is to say, the strongest spread to the north of the atmospheric 10-20 days oscillation at 500hPa vorticity and the summer monsoon's main northward route are accordant.Atmospheric 10-20 days' oscillation at 500hPa vorticity latitudinal spread exists both to the west and to the east, and the spread to the west is the main spread character. The spread to the east is rather weaker. Take 20°N as dividing line, there's nearly no spread to the east in south part of the line, while in the north part of the line, the spread become stronger. There's no obvious rule of the spread to the east, and summer monsoon have no obvious influence to the east spread. Spread to the west of the atmospheric 10-20 days' oscillation at 500hPa vorticity has definite rule, and the spread to the west is rather strong at 20°N and the southern latitude, while at 25°N and even higher latitude the spread turns weaker. There is consistent relationship between the position that the 500hPa vorticity's spread to the west and the summer monsoon's type. To the west type, the western spread could reach 110°E and even lower longitude. To the middle type, the western spread could reach the center of 110°E～115°E. To the east one, the western spread could reach mainly at 120°E, which means that the longitudinal position that the western spread reached and the main longitudinal position that summer monsoon movement to the north are nearly consistent.