The Characteristics And Mechanism Of Rossby-Wave Energy Vertical Propagation In South Asia High Region

Strong east wind prevails in the stratosphere in summer and Rossby wave energy is difficult to spread upward from the troposphere to the stratosphere.Conversely,west wind prevails in the stratosphere in winter and Rossby wave energy is easy to be propagated.Therefore,the propagation of Rossby wave energy into the stratosphere in winter is considered most in the previous studies.In fact,because of South Asia high pressure anticyclonic circulation over the summer plateau which means strong east wind is not alone,Rossby wave energy may also be propagated upward in the South Asia high pressure zone,thus affecting the temperature,wind field and atmospheric composition of the stratosphere.Therefore,using ERA-interim daily reanalysis data,the characteristics and mechanism of Rossby wave propagation energy crossing tropopause in South Asia high pressure zone in summer are studied.The results shows that Rossby wave energy can be propagated to the stratosphere from the window area in the northwest of South Asia high,and can reach the stratopause,but in other parts of the high pressure in South Asia,Rossby wave energy cannot be transmitted through the tropopause or cannot be propagated after being transmitted through the tropopause.The characteristics of the Rossby waves across tropopause propagation in South Asia high are affected by zonal wind and the allocation of the temperature-pressure field.The reason for the transmission of Rossby wave energy in the northwest region of South Asia high through the tropopause is the prevailing west wind and the westerly jet appears at a very low frequency.However,the northeast region of South Asia high also prevails west wind.The reason that Rossby wave energy cannot travel across the tropopause is that strong west wind occurs more frequently.The south region of South Asia high prevails east wind and the lower stratosphere of this area is stable,so the energy of Rossby wave is difficult to spread.The south region of South Asia high is located near the Iranian plateau sinking zone of the Tibetan plateau circulation in the troposphere,resulting in the stable layer here which prevents Rossby wave energy propagation.The southeast region of South Asia high is located in South China sea-western Pacific tropical convergence zone in the troposphere,resulting in the unstable layer here which means that the Rossby wave energy is propagated relatively weakly,and cannot continue to spread after reaching the tropopause.The different configuration of the tempreture pressure field in the vicinity of South Asia high has obvious influence on the formation of planetary wave propagation characteristics.Because of the eddy heat flux anomaly,the Rossby wave can propagate upward in the northwest region.As the phase of temperature field is close to the pressure field,Rossby wave cannot propagate upward in northeast region.The phase of temperature field is obviously ahead pressure field in southwest region,for what the Rossby wave in this region cannot progate upward.On the other hand,the opposite phase in southeast region provides condition for the propagation of Rossby wave in troposphere.The cyclonic structure of plateau summer monsoon has a good correlation with vertical transmission intensity of Rossby wave energy,South Asia high is associated with it by plateau summer monsoon.Compared to the west wind,the vertical wind shear has a greater correlation with vertical transmission intensity of Rossby wave energy,which means baroclinicity has a closer connection with vertical transmission of Rossby wave energy.The east-west movement of South Asia high shows good correlation with the movement of northeast center,plateau summer monsoon makes a second contribution to it.The phase relation between temperature field on different height and the center of South Asia high on 100hPa makes different influence to the vertical transmission of Rossby wave energy.The phase relation on 200hPa mainly affects the intensity and the phase relation on 350hPa mainly affects the longtitude position of downward propagation center.It's worth noting that,the three characteristic parameter of South Asia high show no correlation with both intensity and location of Rossby wave energy vertical transmission.