| In this paper,we first verify the applicability of NASA MERRA reanalysis data of a plateau shear-line weather process and a plateau shear-line and Tibetan Plateau vortex(TPV)concurrent process.Applying the reanalysis data and the data of Chinese automatic station,CMORPH fusion precipitation data,plateau section sounding and surface observations,this paper studies the precipitation characteristics according to the process of plateau shear-line,and to diagnose and analyze the system’s structure and development by using the relative physical quantity.Finally,this paper analyzes the dry cold air activities intrusion and the characteristics of the baroclinic in the concurrent process of the above plateau shear-line and TPV,and explores the budget characteristics of vorticity,the main results as follows:(1)Comparing the MERRA reanalysis data with the conventional observation data in the two weather processes,it shows that the reanalysis data can perfectly reflect the actual characteristics of height field,wind field and temperature field.To a certain extent to make up for the plateau on the lack of sparse sounding site,and it can be used in the analysis of two plateau weather processes.(2)The analysis of the characteristics of the shear-line precipitation shows that the shear-line precipitation in this plateau had a zonal distribution and its intensity is consistent with the shear-line intensity,and the precipitation center is situated in the south of the shear-line.In dynamics view,the boundary layer in the generation stage is weake convergence rising motion,which is advantageous to the production of dispersed precipitation.During the development and strengthening stage,the positive vorticity is significantly strengthened,the lower convergence and the upper divergence are beneficial to the intense precipitation.In the weakening stage,the range of the positive vorticity band and the convergence field decreases,and the decline of the convergence field in the west section of the shear-line is prior to the eastern segment,at this time,the weak positive vorticity and ascending motion appear on the south of the shear-line,which is beneficial to the precipitation.In the water vapor condition,the plateau shear-line and the 500 h Pa water vapor flux convergence zone are better respond,the water vapor convergence is the strongest in the stage of development,and the water vapor convergence strength at the southeast side of the shear-line is strong,which is beneficial to the precipitation.(3)The diagnosis of shear-line precipitation by using the generalized potential temperature and generalized moist potential vorticity shows that the correlation between the generalized potential temperature and the generalized moist potential vorticity and the water vapor content of the atmosphere can effectively reflect the change trend of the plateau shear-line precipitation.The plateau shear-line precipitation occurs in the positive region of the generalized moist potential vorticity in the boundary layer,and the generalized moist potential vorticity anomaly value is consistent with the cumulative precipitation for next 3-6 hours,the center position of positive anomaly and its evolution also have a good relationship with the large value center of precipitation,and there are obvious characteristics in generalized potential temperature in the large area of precipitation.(4)The diagnosis of the evolution of the shear-line shows that generalized potential temperature and the generalized moist potential vorticity can characterize the actual temperature and humidity distribution of the plateau atmosphere,the anomaly of the generalized moist potential vorticity at lower altitude can be used as a comprehensive index for the development of the shear-line in the plateau.Zero lines between the positive and negative anomalies can better characterize the position of the shear-line in the plateau.The positive and anomaly center strength has certain significance to the occurrence and development of the shear-line.The vortex generation parameter can be used as a dynamic index for the shear-line of the plateau,and the positive size can be used as an obvious precursor signal for the generation and enhancement of the shear-lines in the plateau.The diagnostic advantages of generalized moist potential vorticity and vortex generation parameter can improve the characterization of shear-line progress and movement.(5)An analysis of the dry cold air activities intrusion and the characteristics of the baroclinic in the concurrent process of a plateau shear-line and plateau vortex,it shows that this shear-line occurs in the strong dry cold air intrusion conditions,is a system with oblique pressure,the vortex occurs in the lower-level weak cold air intrusion,the lower to middle layer has weak baroclinic,then the lower level to quasi positive pressure,middle layer to maintain weak baroclinic.The vorticity balance of budget shows,the change of vorticity local before production of the TPV and shear-line and generation phase is "lower layer is plus,the middle and high layers are minus ",it is helpful to increase lower layer vorticity.At the process of developing and strengthening,the feature of vorticity local change "the middle and low layers are minus,high layer is plus" is more prominent,which is conducive to the increase of low layer vorticity and the maintenance and strengthening of upward movement.At the stage of system weaken,the change of vorticity local is "low is minus and high is plus",it is not conducive to the maintenance of the system. |
