The Relationship Between The Change Characteristics Of Atmospheric Angular Momentum And The Summer Subtropical Jet And Its Influence On The Climate Of East Asia

Atmospheric angular momentum is an important basic quantity of atmosphere,which is closely related to the atmospheric circulation and weather and climate.In order to study the relationship between the variation of atmospheric angular momentum and the subtropical jet streams and its influence on the East Asian climate,this paper first analyzes the characteristics of atmospheric angular momentum,and then uses the Singular Value Decomposition method(abbreviation for SVD)to study the relationship between the atmospheric angular momentum change and the subtropical jet.Finally,a regression analysis method is used to study the influence of the anomalous subtropical jet,caused by the anomaly of atmospheric angular momentum,on the East Asian Climate and its influence mechanisms.The main conclusions of this study are as follows:(1)The tropical easterlies are the source region of angular momentum,the strong transport center for angular momentum is mainly located in the middle and upper troposphere,and the easterlies,which show deviation to the north hemisphere in summer,transport most of the angular momentum to the south,weaken the center of the mid-latitude center in the northern hemisphere and make it move towards the north.In the tropics,the angular momentum changes from negative anomalies to positive anomalies around the 1970 s.The mid-latitude in the northern and southern hemisphere accounts for positive anomalies before the 1970 s,then change from positive anomalies to alternation between positive and negative in the 1970 s and 1990 s,and negative anomalies predominate after the 1990 s.The large-value centers for angular momentum and its transport in summer are mainly concentrated in the middle and high latitudes.The change ranges are between northern 60° and southern 60°.The angular momentum transport at the mid-high latitudes is featured as alternative transport to both the south and north.In addition,the Arabian Sea to the South China Sea have southwards strong transport area.The variation of the momentum transport in the middle and high latitudes has changed more dramatic than in the tropics.(2)When the phase of the first mode of SVD(abbreviation for SVD-1)is positive(negative)from 1951 to 2016,the angular momentum transport of the tropical easterly belt decreased(enhanced),the subtropical jet streams increased(weakened).When the phase of the second mode of SVD(abbreviation for SVD-2)is positive(negative)in 1951-2016,the subtropical jet center moves northward(southward)when the angular momentum transport of the mid-latitude increases northward(the tropical transport enhances southward).The impact of SVD-1 on temperature and precipitation in China is mainly the negative anomalies of the Yangtze and Huaihe River Basins' temperature,and the significant reduction of precipitation in the middle and lower reaches of the Yellow River.The impact of SVD-2 on the climate is mainly shown as the significant increase in temperature in the Yangtze and Huaihe River Basins,and the precipitation increases in the Yellow River Basin while decreases in the Yangtze-Huaihe River Basins.The relationship between SVD-1 and the temperature in South China,the southern part of Southwest China,and the precipitation in the middle and lower reaches of the Yellow River,the downstream of Yangtze River Basin,are significantly affected by the long-term trend,while the relationship between SVD-2 and climate is mainly affected by the interannual timescale.(3)There is an interdecadal variability coupling relationship between angular momentum changes and subtropical jet streams.Both have different characteristics in two periods,1951-1970 and 1971-2016.The angular momentum transport in SVD-1 is significant anomalies in East Asia,South China Sea and South Indian Ocean before the 1970 s,with the most extensive anomalies in the South Indian Ocean.However,after the 1970 s,the major anomalies are located in East Asia,South China Sea and mid-latitude South Pacific.Accordingly,the subtropical jet streams change from the variation of the intensity of the center before the 1970 s to the variation of the meridional movement.The relationship between SVD-1 and climate has obvious interdecadal variability.Temperature in the Yangtze and Huaihe River basins before the 1970 s change from negative anomalies to significant positive anomalies,while the positive anomalies in the northwest and northeast have not passed the significant test after the 1970 s.Precipitation in the Yangtze and Huaihe River basins before the 1970 s change from positive anomalies to significant negative anomalies,and the precipitation in the Yellow River Basin is significantly positive after the 1970 s.The precipitation field is characterized by the distribution of more in the south and less in the north,Since the 1970 s.(4)The anomalous area of angular momentum transport in SVD-2 has changed from northern China before the 1970 s to alternative distribution of positive and negative anomalies in the upper reaches of Eurasia.Accordingly,the subtropical jet streams center changes from variation of a meridional movement before the1970 s to variation in the intensity of the center west of 120°E.The relationship between SVD-2 and temperature changes from large-scale negative anomalies before the 1970 s to negative anomalies in the north and positive anomalies in the south of the Yangtze River Basins,and the distribution of the precipitation field changes from north negative anomalies and south positive anomalies before the 1970 s to north positive anomalies and south negative anomalies.