Intensity Index Of The East Asian Trough Based On Amplitude And Its Relationship With Winter Climate In East Asia

The East Asian Trough is one of subsystems of the East Asian Winter Monsoon.As an important activity center in the middle troposphere of the East Asian Winter Monsoon,the intensity of the East Asian Trough has a significant impact on the weather and climate in East Asia.This paper had defined the Amplitude Intensity Index of East Asia Trough by using the 500 hPa geopotential height data from the NECP / NCAR monthly mean reanalysis dataset,and the long-term variation characteristics of the East Asian Trough has been analyzed.By comparing with other indexes of the East Asian Trough,the relationship and difference between the characteristics of the East Asian Trough have been discussed.The development and evolution of the East Asian trough during the period from October to April had been studied.The influence and possible mechanism of the East Asian trough on the winter climate of East Asia have been studied and discussed by using correlation analysis and synthetic analysis.The main conclusions are as follows:(1)The Amplitude Intensity Index of East Asia Trough can be used to characterize the strength of the East Asian Trough.When Amplitude Intensity Index of East Asia Trough is larger,the strength of the East Asia Trough is stronger.On the contrary,when Amplitude Intensity Index of East Asia Trough is smaller,the strength of the East Asia Trough is weaker.From 1948 to 2018,the intensity of the East Asian Trough showed a weak increase trend.(2)There was a good correlation between the different characteristic indexes of East Asian Trough,which meant that different East Asian Trough indexes both could describe the long-term variation characteristics of East Asian Trough and have similarities.But the differences between East Asian Trough indexes have indicated that the East Asian Trough has many characteristics.When the East Asian Trough changes,there was a good relationship between the changes of various characteristics.But the different characteristics of the East Asian Trough were not identical,which meant that they have relative independence.(3)From October,the 500 hPa geopotential height in the area of the East Asia Trough has been decreasing,and reached the minimum value in January.The intensity of the East Asia Trough and the characteristic index of the East Asia Trough have been increasing.From March,the 500 hPa geopotential height in the area of the East Asia Trough has been increasing,the intensity of the East Asia trough and the characteristic index of the East Asia trough have been decreasing until there was no obvious trough structure in East Asia.(4)There was a close relationship between the East Asian Trough and the surface temperature of East Asia in winter.When the Amplitude Intensity Index of the East Asian Trough was larger,the 500 hPa geopotential height field showed that the intensity of the East Asian Trough and the European Trough both became stronger.In the sea level pressure field,the Siberian High pressure enhanced.The anomalous anticyclone over the Siberian region caused a significant increase in westerly winds of area north of 60°N.The cold air eventually invaded the East Asian coast,resulting in a significant decrease in the surface temperature of the East Asian coast area in winter.When the Amplitude Intensity Index of East Asian Trough was smaller,the situation is reversed.(5)The East Asian Trough has influence on the winter precipitation in East Asia.When the Amplitude Intensity Index of the East Asian Trough is larger,the area north of 20°N is the water vapor divergence area,and it is under the control of the downdraft caused by the East Asian Trough,which is not conducive to precipitation in eastern China and the Korean Peninsula.However,in the area south of 20°N,strong north wind anomaly causes the cold air invade the tropical region,triggering a strong upward movement,which is beneficial to the precipitation in the low latitudes of East Asia such as the Philippines and Malaysia.