On horizontal wind gradient variability from the stratosphere to the lower troposphere in the Arctic
On horizontal wind gradient variability from the stratosphere to the lower troposphere in the Arctic
复制标题
北极从平流层到对流层低层的水平风梯度变化
DOI：
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
D. Barber
中科院分区：
文献类型：
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作者：
J. Lukovich;D. Barber
[1]以前的研究已经证明了近几十年来垂直风切变的变化，这与向上传播的行星波、平流层极地涡旋和示踪剂运输有关。垂直风切变与水平梯度相结合的变化也被证明有助于示踪场垂直梯度的增加，这对垂直输送具有重要意义。为了探讨垂直风切变的变化在多大程度上反映在水平搅拌的变化中，我们研究了1979 - 2006年从平流层到对流层下层的水平风梯度场。特别研究了相对涡度、散度、应变和Okubo-Weiss准则（监测应变和涡度主导的场之间的竞争）的时空特性和趋势，以说明水平风梯度在过去几十年中是如何变化的。调查结果表明，1998年以后冬季的负涡度和应变异常与近年来平流层突然变暖和极涡扰动的增加有关。秋季和冬季，相对涡度和应变场在对流层顶和平流层中层附近的空间分布呈现出相干结构，这些结构被大久保-魏斯场捕获。趋势分析突出了冬季相对涡度和大久保-魏斯场的统计显著趋势。这次调查的结果表明，从平流层到对流层下部存在统计上显著的趋势。据推测，从对流层下层到高层大气的耦合对于我们理解海冰浓度对气候变率和变化的响应将是重要的。
[1] Previous studies have demonstrated changes in vertical wind shear in recent decades, with implications for upward-propagating planetary waves, the stratospheric polar vortex, and tracer transport. Changes in vertical wind shear combined with horizontal gradients have also been shown to contribute to an increase in vertical gradients in tracer fields, with important implications for vertical transport. In order to explore the extent to which changes in vertical wind shear are reflected in changes to horizontal stirring, we examine horizontal wind gradient fields from the stratosphere to the lower troposphere from 1979 to 2006. Studied in particular are the spatial and temporal properties and trends for relative vorticity, divergence, strain, and the Okubo-Weiss criterion (which monitors the competition between strain- and vorticity-dominated fields) to illustrate how horizontal wind gradients have changed over the last several decades. The results from this investigation show negative vorticity and strain anomalies during winter following 1998 associated with an increase in sudden stratospheric warmings and perturbations to the polar vortex noted in recent years. Spatial distributions for relative vorticity and strain fields exhibit coherent structures near the tropopause and middle stratosphere during fall and winter, which are captured by the Okubo-Weiss fields. Trend analyses highlight statistically significant trends in relative vorticity and Okubo-Weiss fields during winter. The results from this investigation demonstrate that statistically significant trends exist from the stratosphere to the lower troposphere. It is hypothesized that the coupling from the lower troposphere to the upper atmosphere will be important in the development of our understanding of the response of sea ice concentrations to climate variability and change.