Evaluation For The Calculation Of The Vertical Velocity In The South Asia High Using Two Thermodynamic Methods

In this paper,two thermodynamic methods,thermodynamic equation and isentropic trajectory simulation,are presented to calculate the vertical velocity over the South Asian High?SAH?in June,July,August and September 2012 and 2016 which may avoid the deviations from the kinematics method using the mass continuity equation.In order to improve the accuracy,high-resolution heating rate datasets was introduced:sounding observation data of the Ali Sound Station at the center of the South Asian High,revised MLS V4.2 L2 and AIRS V6.0 L2 satellite data.The vertical velocity calculated by the thermodynamic method?V_T?is then compared with the data from ERA-Interim reanalysis(V_ERA-I).The results showed that:?1?V_T and V_ERA-I are quite different in describing the vertical speed in the daytime over the Ali area.In the upper troposphere?below 150 h Pa?,both of them show ascending motion.However,V_T in the lower stratosphere?above 150 h Pa?shows a weak ascending and the ascending rating decreases with height.While V_ERA-I indicates a strong upward movement in this region.?2?Both V_T and V_ERA-I show the same vertical motion characteristics of that ascending below 150 h Pa and describing above 150 h Pa at night,which indicates that there is convergence near 150 h Pa at night in the Ali area.However,in the area above 80 h Pa,V_T shows weak vertical movement and the values concentrate near the 0 line,while V_ERA-I increases significantly.V_T as a whole is smaller than V_ERA-I.?3?When describing the vertical speed in the Ali area,V_T has smaller standard deviation than V_ERA-I,indicating that the changes in daily time series of V_Tare more regular,and it is more reliable to explain the vertical movement in this area.In the daytime,the difference between V_Tand V_ERA-I is statistically significant above 150 h Pa.In the nighttime,the difference between150 h Pa and 80 h Pa is statistically significant.The phenomenon indicates that the ascending motion of V_T at the lower level is weaker than that of V_ERA-I,and the difference between the two at the upper level is significant.But V_T has a better understanding of weak vertical motion in the stratosphere.?4?For the vertical motions over the SAH region,in the daytime,V_T and V_ERA-I both exhibite convergent uplift in the east-west direction,and a simillar upward motion characteristic north-south.However,V_T shows sinking in the west and north,which is not in V_ERA-I.At night,the subsidence motion range of the Western and northern in V_T is enlarged,and the vertical direction is deeper.V_ERA-I sinks only in the lower layers of the west.The results of significance test showed that the ascending motion of V_T was weaker than that of V_ERA-I.?5?The existence of the local Hadley loop subsidence branch will bring sinking airflow to the SAH region.At the same time,the thermal difference between the western Iranian plateau and the eastern Qinghai-Tibet plateau will cause the western ascending to be weak and the eastern acsending strong.Superposed with the sinking branches,it may appear as sinking movement in the West.Meanwhile,there will be a descending motion in the north,caused by the influence of the local Hadley circulation and Brewer-Dobson circulation.V_T is more in line with this interpretation.In addition,the heating rate can be used to determine the direction of vertical movement for that adiabatic heating brings rising,and adiabatic cooling causes sinking.V_Tis closer to the description of the vertical movement by Q_MLS over the SAH region.