关于业务上应用条件对称不稳定相关问题的讨论  

A discussion on conditional symmetric instability in operational application

作　　者：章丽娜[1] 周小刚[1] 夏扬 ZHANG Lina;ZHOU Xiaogang;XIA Yang(China Meteorological Administration Training Center,Beijing 100081,China)

机构地区：[1]中国气象局气象干部培训学院,北京100081

出　　处：《气象学报》2018年第5期824-832,共9页Acta Meteorologica Sinica

基　　金：国家自然科学基金项目(41475042;41705031);国家科技支撑计划项目(2015BAC03B06)

摘　　要：条件对称不稳定(CSI)理论常常被用来作为倾斜对流的发展机制之一,在业务上常用来解释与锋面相联系的一条或多条中尺度雨带、雷达图像上观测到的带状雨带的成因等。条件对称不稳定的诊断包括CSI斜率判据、斜升对流有效位能(SCAPE)、湿对称不稳定(MSI)、相当位涡(EPV)等判据。业务预报人员存疑较多的问题是这些方法是否具有一致性并在业务上如何使用。针对上述问题,首先通过与业务预报人员较熟悉的条件不稳定类型作类比,来说明条件对称不稳定两种判据与条件不稳定两种判据的相似性。但在业务使用上,判别条件对称不稳定时多使用CSI斜率判据,即等动量面的坡度大于等位温面坡度而小于等湿球位温面坡度。由于条件对称不稳定通常出现在大气处于几乎饱和的情况下,此时的CSI斜率判据则演变为湿对称不稳定判据,即等动量面坡度小于等湿球位温面坡度。为判别相当位涡与湿对称不稳定判据是否具有一致性,文中的推导和实例分析均表明,二维相当位涡实际上是湿对称不稳定判据的另一种表现形式,但是湿对称不稳定判据需主观去比较等相当位温面与等动量面斜率大小,而二维相当位涡则可通过其是否小于0进行客观判断。需注意的是,在与推导条件对称不稳定斜率判据相同的二维坐标下,相当位涡与湿对称不稳定判据才具有一致性,将相当位涡扩展到常规坐标下使用三维相当位涡作为湿对称不稳定判据是不可取的。Conditional symmetric instability（CSI）is considered to be one of the mechanisms for the development of slantwise convection,and it is often used to explain mesoscale precipitation bands associated with fronts or rainbands observed on weather radar image.Many instability criteria can be used to diagnose conditional symmetric instability,such as the CSI slope criterion,the slantwise Convective Available Potential Energy（SCAPE）,the moist symmetric instability（MSI）,and the equivalent potential vorticity（EPV）.However,forecasters are not sure whether these criteria are consistent and how to use them in operation.Aiming at the confusions mentioned above,the similarities between two criteria of conditional symmetric instability and two criteria of conditional instability are illustrated first in this paper because weather forecasters are more familiar with conditional instability.In operational application,the slope criterion is used more often,i.e.the slope of geostrophic momentum surface is steeper than the isentropic surface but more gradual than the surface of constant wet-bulb pseudo potential temperature.Since the environment that is conducive to slantwise convection is nearly saturated in a deep layer,the instability criterion of CSI is equivalent to MSI.Derivation and case study all indicate that the criteria of EPV and MSI are consistent and the two dimensional EPV is another expression of MSI.Comparing to subjective judgment of the slopes between constant geostrophic momentum surface and constant equivalent potential temperature surface,the EPV criterion solely based on its sign is more objective.It is important to note that the criteria of EPV and MSI are only consistent when they are under the same two-dimensional coordinate.It is wrong when using EPV as the criterion of MSI in three-dimensional coordinate.

关 键 词：条件对称不稳定斜率判据 斜升对流有效位能 湿对称不稳定 相当位涡 

分 类 号：P445[天文地球—大气科学及气象学]