基于变分客观分析方法的青藏高原试验区夏季对流降水过程热动力特征分析

本文利用基于变分客观分析方法的物理协调大气分析模型，构建了青藏高原试验区大气热力—动力相互协调的数据集，并通过该数据集对青藏高原试验区夏季深厚及浅薄对流降水过程的热动力特征进行分析，结果表明:变分客观分析后的垂直速度场能更好地与实际观测的对流降水过程相吻合；深厚对流降水期高云含量多，整层大气为较强的上升运动，上升运动可达100 hPa左右，浅薄期高云含量少，上升运动仅能延伸到300 hPa左右；两种对流降水过程中视热源Q₁在低层为冷却作用，高层为加热作用，在深厚期中高层Q₁存在两个加热中心，中层受较强的水汽凝结释放潜热加热所影响，高层主要受过冷云水凝结成冰晶形成高云时释放的热量所影响；在浅薄期中高层Q₁只存在一个加热中心，大气的加热主要来源于水汽的凝结潜热释放；深厚对流降水期视水汽汇Q₂的加热作用可以延伸到200 hPa，而浅薄期仅到340 hPa左右。

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.