摘要
切变线风场除伴随温度锋区出现以外，也可以在夏季副热带大尺度弱环境风场中伴随狭窄、深厚的强对流加热带而出现。后者的结构是相当正压的（本文称为ＥＢｔＳＬ）。除ＲＯｓｓｂｙ数Ｒ０＝０（ｄｕ／ｄｔ）／ｆ０Ｕ以外，决定带状准二维运动系统性质的另一个重要参数是Ｈ＝（ＣＺ／ｆ０ｌ）２，ＥＢｔＳＬ的特点是在跨带水平尺度ｌ收缩的同时，铅直尺度Ｚ（无量纲）并不随之收缩，因而Ｈ～１０（斜压锋面，Ｈ≤１）。在这种情况下，即使非绝热加热率比温度平流大一个量级，且Ｒ０＝１０－１／２；Ｏ（｜ｄｖａ／ｄｔ｜）＝１０－１／２０（｜ｄｖｇ／ｄｔ｜）已不符合经典的地转动量近似，但仍旧能够成为排除重力一惯性波的准平衡运动系统。变化的欧拉时间尺度仍取决于平流，即ＥＢｔＳＬ能持续地容纳特大的潜热释放（和降水）。本文给出ＥＢｔＳＬ的发展方程和次级环流方程，讨论了ＥＢｔＳＬ的基本动力学性质。这些结果把关于典型ＥＢｔＳＬ的一系列观测事实逻辑地联系起来，并给予理论解释，表明ＥＢｔＳＬ是一种特别有利于持续大暴雨的动力学结构。典型的ＥＢｔＳＬ是长江流域梅雨晚期自由大气层的切变线。其初生机制是低层干一湿气团界带紧南侧２θｅ／ｙ２负值最大轴附近的带状ＣＩＳＫ。自由大?
The characteristic wind fields of shear--line can occur not only along the thermal frontal zones, but also along the narrow and deep zones with intensively convective heating in the background of weak large--scale wind field in summer subtropics. The structure of the latter is equivalentbarotropical (abbreviated as EBtSL in this paper). The extraordinarily strong release of latent heat (and precipitation) can be continuously tolerated in EBtSL. The development equation and the secondary circulation equation are given in this paper, and the basic dynamical characters of EBtSL are discussed.Having the aid of these results, a number of observational facts relevant to the typical EBtSL can be stringed logically together and explained theoretically. It is indicated that EBtSL, as a kind of dynamic structure, is especially favourable to the continuous unusual intense precipitation.
出处
《大气科学》
CSCD
北大核心
1996年第3期326-336,共11页
Chinese Journal of Atmospheric Sciences
关键词
夏季
副热带
相当正压
切变线
动力学性质
summer subtropical belt equivalent--barotropic shear line dynamic characters
