关于等熵位涡应用的一点认识

INSIGHTS ON THE APPLICATION OF THE ISENTROPIC POTENTIAL ORTICITY

关键词:  等熵位涡  湿等熵位涡  θ坐标  θse坐标

Key words:  isentropic potential vorticity  moist isentropic potential vorticity  isentropic coordinates  moist isentropic coordinates

摘要:

位涡、湿位涡及其守恒开启了(湿)位涡理论的较广泛应用，使(湿)位涡成为天气系统、天气现象演变的重要诊断物理量，能有效解释一些天气系统、天气现象的演变。为合理应用(湿)位涡及等熵位涡思维，简单分析了气象常用坐标中位涡、湿位涡表达式的限制性条件，强调此条件与(湿)等熵坐标成立的条件相同，指出z 坐标(湿)位涡与p、θ(θse)坐标(湿)位涡存在物理差异。在θ(θse)坐标中，气块的水平速度是相对水平面(地面)的移动速度，而非气块沿着等θ(θse)面的移动。在(湿)等熵位涡分析中，(湿)等熵位涡强度的变化，是平流、垂直输送以及非绝热过程的综合作用，不能简单归因为只由高层的(湿)等熵位涡异常向中低层传输、或中低纬的(湿)等熵位涡异常向高纬传送所造成。

Abstract:

The concept of potential vorticity, (moist)potential vorticity and its conservation equation has been applied widely and the (moist)potential vorticity has become an important diagnostic physical quantity for the evolution process of some synoptic systems and weather events. In this paper, the restrictive condition of the formula of (moist)potential vorticity is discussed. This condition is the same as that of the θ(θse) coordinates. There is physical difference between the (moist)potential vorticity in z coordinates and the one in p, θ(θse) coordinates. The wind does not indicate the air parcel to move along the (moist) isentropic surface in the θ(θse) coordinates. In the (moist)isentropic potential vorticity analyses, it proves to be problematic to assume that the variation of (moist)potential vorticity only results from the downward propagation of (moist) isentropic PV anomaly from the high level or the upward propagation of (moist) isentropic PV anomaly from the low and middle levels.