The Analysis On Characteristics Of Cloud And Precipitation Process In Tibet Plateau Experimental Region Based On Constrained Objective Variational Analysis

The method used to build the analysis model is constrained objective variational analysis,which unique feature is the use of domain-averaged surface and TOA observations as constraints to adjust atmospheric state variables from soundings by the smallest possible amount to conserve column-integrated mass,moisture,and static energy so that the final analysis data set is dynamically and thermodynamically consistent.For the test period(August 2014),ERA-Interim reanalysis data,L-band radiosonde data,ground station observations,CERES satellite products,and the boundary layer observations were input into the analysis model to generate the thermal and dynamic coordinated data set for August 2014.By using this dataset,we can analyze the thermodynamic characteristics of the summer cloud and precipitation processes in the Tibetan Plateau.In the deep convection system,CAPE is significantly larger,and there will be more clouds in high level,of which maximum value can reach 100%.In contrast,for shallow convection system,cape is smaller,and there will be fewer clouds in high level,which maximum value will not reach 50%.For deep convection system precipitation period,Q2 can extend to 200 hPa depending on the effect of latent heat release from water vapor,while the Q2 of shallow convection precipitation period only extend about 340 hPa.For both types of precipitation process,Q1 shows the cooling effect on the lower level as the heating effect on the upper level.During the deep convection period,the medium and high level Q1 showed a bimodal structure,the middle layer was affected by latent heat release from the strong condensation of water vapor and the upper layer was mainly affected by the latent heat released when the super-cooled water was condensed into ice crystals to form high-level cloud.In the shallow precipitation period,the medium and high level Q1 showed a unimodal structure in accord with Q2,and the atmospheric heating mainly comes from the latent heat of condensation of water vapor.Long-term sequence heat and dynamic coordination data sets(2013-2016)have been established,by replacing the flux observed in the boundary layer observations with ERA-Interim.We analyzed the atmospheric characteristics throughout the year and compared the dry and wet seasons.The air temperature above the test area showed strong seasonal variability.The mixture ratio of water vapor and precipitation was closely related to precipitation.In the positive relationship,water vapor is mainly concentrated below 300 hPa,and the maximum value can reach over 10 g/kg.In the dry season,the precipitation rate is obviously less,and the relative humidity is mainly concentrated in the mid-level atmosphere between 400-250 hPa.The cloud volume is also mainly concentrated in the middle and lower layers.There is almost no high-level cloud,and the vertical speed is very strong.Ascending movements show as subsidence movements above 300 hPa.The characteristics of Q1 and precipitation processes are not obvious.The cooling effect is mainly below 500 hPa,and most of Q2 is negative.At 22:00 at night,Q2 has the strongest heating effect.In the wet season,the precipitation is intensive.The large relative humidity center is mainly concentrated in the mid-to-lower atmosphere below 300 hPa.And high cloud cloud amount are more closely related to the occurrence of precipitation.During the precipitation process,the entire air column corresponds to a significant upward movement.Q1 acts as a cooling element in the lower atmosphere and warms the atmosphere in the middle and upper atmospheres.At 02:00,the cooling effect in the lower layers becomes more obviously.The correlation between Q2 and precipitation is even more obviously.When there is precipitation,the whole layer is basically positive,with the extreme value at about 450 hPa.When there is no precipitation,the vertical structure of Q2 is the opposite.