Analysis on Thermodynamic Characteristics of Summer Convective Precipitation in the Qinghai-Tibet Plateau Experimental Region Based on Constrained Objective Variational Analysis

Using flux data from the top and bottom of a column to keep the column's mass, moisture and static energy constraint, thermal and dynamic coordinated datasets are generated with the analysis model based on the constrained objective analysis approach. By using this dataset, the authors can analyze thermal characteristics of precipitation process in deep and shallow convection systems in the summer. Vertical velocity is an important indicator of convection strength. The vertical velocity field obtained from the constrained objective analysis can better match the observed convective precipitation process compared to the ERA-Interim reanalysis data. In the deep convective precipitation period, there is more high cloud content, and strong ascending movement prevails in the whole atmosphere. The ascending movement can reach about 100 hPa. During shallow convection period, the high cloud content is small, and the ascending motion can only extend to around 300 hPa. For both types of precipitation process, Q₁ (apparent heating source) has cooling effect in lower layers and heating effect in upper layers. The possible reason is that the evaporation in the near-surface layer absorbs a large amount of heat, which causes the heat content in the lower atmosphere to decrease. During deep convection period, Q₁ in the middle and high levels shows a bimodal structure, i.e., the middle layer is affected by latent heat release from strong condensation of water vapor and the upper layer is mainly affected by the latent heat released when the super-cooled water condenses into ice crystals to form high-level clouds. In shallow convection period, Q₁ in the middle and high levels shows a unimodal structure in accord with Q₂, and the atmospheric heating mainly comes from the latent heat release of condensation of water vapor. In deep convective precipitation period, Q₂ (apparent moisture sink) can extend to 200 hPa depending on the effect of latent heat release from water vapor condensation, while Q₂ can only extend about to 340 hPa in shallow convection precipitation period.