摘要:为了对比分析降水过程中不同表达形式热力学变量和位涡时空分布特点，本文针对2017年7月13～14日吉林省强降水过程，利用模式输出资料对常规位温（θ）、相当位温（θe）、包含凝结概率函数的广义位温（θGao）、包含冻结概率函数的广义位温（θWang）和同时涵盖凝结过程与冻结过程（θGu）五种不同形式位温进行计算，并分析五种对应位涡[PV(θ)、PV(θe)、PV(θGao)、PV(θWang)、PV(θGu)]与降水的关系。结果表明，引入冻结概率函数的广义位温（θWang）和对应的广义湿位涡PV(θWang)与强降水的对应性更好。θWang与θGao差异集中在降水区对流层中高层5～11 km，前者始终高于后者，最大差异达2.5 K，说明冻结概率函数的引入扩大了广义位温的适用范围，更适合描述降水区湿大气非均匀饱和热力状态。五种位涡的差异主要在降水区上空12 km以下，由θGao和θWang定义的位涡PV(θGao)和PV(θWang)的正负异常中心更为明显。相比于PV(θGao)和PV(θWang)异常值更大，差异可达±0.2 PVU，这主要是由于冻结概率函数的引入增大降水区上空广义位温，促使冻结区的湿位涡异常增强。
关键词:凝结/
冻结/
广义位温/
位涡
Abstract:The spatial and temporal distribution characteristics of different types of thermodynamic variables and potential vorticity during precipitation were compared and analyzed in this study. On the basis of the heavy rainfall events in Jilin Province on 13–14 July 2017, the following five types of potential temperature were calculated with model outputs: conventional potential temperature (θ), equivalent potential temperature (θe), generalized potential temperature containing a condensation probability function (θGao), generalized potential temperature containing a freezing probability function (θWang), and potential temperature covering condensation and freezing (θGu). The relationships between five associated types of potential vorticity [PV(θ), PV(θe), PV(θGao), PV(θWang), and PV(θGu)]and precipitation were also analyzed. Results showed that the generalized potential temperature introducing a freezing probability function (θWang) and its potential vorticity [PV(θWang)] corresponded well with heavy rainfall. The differences between θWang and θGao were observed at 5–11 km in the mid-upper troposphere over the rainfall region. θWang was always greater than θGao, with the maximum difference reaching 2.5 K. Hence, the introduction of the freezing probability function extends the application scope of the generalized potential temperature and offers a reliable depiction of the thermodynamic state of nonuniform saturated moist air over rainfall regions. The differences among the five types of potential vorticity were mainly observed under 12 km over the rainfall region. The positive and negative anomaly centers for potential vorticity PV(θGao) and PV(θWang) respectively defined by θGao and θWang were increasingly visible. The anomaly value of PV(θWang) was greater than that of PV(θGao), and the differences could reach ±0.2 PVU. Such difference was due to the enhancement of the generalized potential temperature over the rainfall region resulting from the introduction of the freezing probability function. This condition led to the abnormal enhancement of the moist potential vorticity in the freezing region.
Key words:Condensation/
Freezing/
Generalized potential temperature/
Potential vorticity
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