一次典型的平流层爆发性增温中的局地多尺度洛伦兹循环
投稿时间: 2017-06-01  最后修改时间: 2017-06-14  点此下载全文
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作者单位E-mail
徐芬 南京信息工程大学 xu_fly@yeah.net 
梁湘三 南京信息工程大学 san@pacific.harvard.edu 
基金项目:国家自然科学基金项目(面上项目,重点项目,重大项目)
中文摘要:利用一种新的工具,多尺度子空间变换(MWT),以及基于MWT的局地多尺度能量与涡度分析(MS-EVA)与Lorenz循环诊断方法,对2012~2013年冬季平流层发生的爆发性增温(SSW)的内在动力学过程进行了研究。首先,我们用MWT将各个场重构于三个尺度子空间,即平均尺度、爆发性增温尺度(或SSW尺度子空间)和天气尺度子空间上。根据这些重构场,这次强增温事件可被分为三个阶段,即快速增温阶段,增温维持阶段和增温衰退阶段,每一阶段都有不同的动力机制。研究表明,在快速增温阶段(12月28日至1月10日),极地迅速增长的温度是由于SSW尺度子空间上很强的向极的热量通量和极区内的斜压不稳定引起的正则传输(有效位能从平均尺度子空间传输到SSW尺度子空间)共同造成的。在这个过程中,显著增加的有效位能(APE)转换并储存到了SSW尺度子空间的动能(KE)中,导致了极夜急流的反转。在增温维持阶段(1月11——25日),增暖的机制完全不同:先前储存在SSW尺度子空间上的动能又转换回到相同尺度子空间的有效位能中,与此同时,十分重要的是,在这个时间段中,阿拉斯加地区有很强的正压不稳定,使得动能从平均尺度子空间传输到SSW尺度子空间上,维持了增高的温度。平均尺度子空间的动能主要来自对流层,这与经典的波流相互作用中行星波上传理论相一致。增温衰减阶段,温度降低,系统又恢复到了正常的状态。
中文关键词:多尺度子空间变换(MWT)  局地多尺度能量与涡度分析(MS-EVA)  正则传输  正压不稳定  斜压不稳定  平流层爆发性增温
 
The local Lorenz cycle underlying a typical stratospheric sudden warming
Abstract:The Lorenz cycle diagnostic is a powerful approach to the understanding of the internal dynamics within atmospheric events. Local Lorenz cycle diagnoses, however, are mostly restrained from usage by the ambiguity in transport-transfer separation. Recently this issue has been fixed through the introduction of a new functional analysis tool, namely, the multiscale window transform (MWT), and the resulting energy transfer is called canonical transfer. Using an MWT-based localized multiscale energetics analysis, and accordingly the resulting local Lorenz cycle diagnostics, the 2012-2013 sudden stratospheric warming (SSW) is investigated for an understanding of the underlying dynamics. The fields are first reconstructed onto three scale windows, i.e., mean window, sudden warming window or SSW window, and synoptic window. According to the reconstructions the major warming period may be divided into three stages, namely, the stages of rapid warming, maintenance, and decay, each with different mechanisms. It is found that the explosive growth of temperature in the rapid warming stage (December 28 – January 10) is fueled by canonical transfer through several baroclinic instabilities in the polar region, which extract available potential energy (APE) from the mean-scale reservoir. In the course, a portion of the acquired APE is converted to and stored in the SSW-scale kinetic energy (KE), leading to a reversal of the polar night jet. In the stage of maintenance (January 11-25), the mechanism is quite different: Though the baroclinic instabilities are still there, the previously converted energy stored in the SSW-scale KE is converted back, and most importantly in this time a strong barotropic instability happens over Alaska, which extracts the mean-scale KE to maintain the high temperature. That is to say, in this stage, the system is mainly governed by a mixed instability. In the decay stage, the canonical transfers and buoyancy conversions nearly vanish, and the system resumes to its normal state.
keywords:multiscale window transform (MWT)  localized multiscale energy and vorticity analysis(MS-EVA)  canonical transfer  barotropic instability  baroclinic instability  stratospheric sudden warming
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