The Cause And Evolution Analysis Of Rear Inflow In A Squall Line With The Influence Of Trough Wind In Northeast Cold Vortex Generation Period

Using the NCEP analysis data,Doppler radar observation data,conventional meteorological observation data and the numerical simulation results,the evolution and causes of rear inflow during a squall line which in the influence of trough wind in development of Northeast Cold Vortex on July 30,2016.had been investigated.The investigation showed that:(1)Squall line occurred behind of the trough line of mid-latitude new Northeast Cold Vortex,which baroclinic structure is conducive to the accumulation of unstable energy.Vertical wind shear at the low level is easily triggered unstable energy release,and causing convection.(2)There is meso-a-scale westerly wind belt in the middle of the back of the squall line,which results in the opposite horizontal vorticity and trumpet circulation structure in the vertical direction.When horizontal vorticity rotate clockwise in the rniddle-lower layers,the stream is favorable for the formation of the sinking motion,lead to the real inflow and strong wind zone in the lower layer,which format and develop the squall line;meanwhile,when horizontal vorticity clockwise rotated in middle-upper layers,the stream is favorable to the ascending movement,which lead to the development of stratiform clouds in the back of squall line.In the middle of squall line rear edge,there is a strong wind speed area with the development of the squall line.(3)The formation of the strong wind speed area is connection with the convection strength and non-thermal wind vorticity.When convection develop strongly,the larger non-thermal wind vorticity results in the rear westerly acceleration and front westerly deceleration,which is favorable for the strengthening of rear inflow and convergence of airflow in the front of convection system.On the contrary,when the convection is weakened,the non-thermal vorticity and rear inflow are weakened.The conceptual module of formation and evolution of rear inflow has been given in paper.(4)With the development of convection,the convergence of acceleration at the lower level of the convection area and the mid-level rear westerly wind is tronger.The formation of acceleration is mainly related to the latent heat release,which lead to gradient change of pressure(height)field.The development of convective cause latent heat released,though water vapor condensed in the higher level,and case negative temperature change in the lower layer which make inflow sinking in the rear of the squall line.The changes of temperature field make unbalance of pressure(height)field,which affecting the development of the squall line.When the effect of changes in latent heat was removed,the squall line rapidly weakened.