冬季北半球风暴轴的多尺度能量变化特征及其可能机制

基于1971—2016年NCEP/NCAR(美国环境预报中心和国家大气研究中心)的逐日再分析资料及NCPC(美国国家海洋和大气管理局气候预报中心)的海温、大气环流及海洋指数等资料通过多尺度能量分析(MS-EVA)等方法,把冬季北半球风暴轴看做一整体,分析了风暴轴区域多尺度的能量变化特征及其可能机制。主要结论概括如下:(1)多年气候平均状态下,风暴轴的动能来源主要表现为在风暴轴中上游先由低频尺度向天气尺度输送有效位能,随后在风暴轴主体区再由天气尺度有效位能转换为天气尺度动能,其中风暴轴西端可直接由低频尺度向天气尺度输送动能。(2)北半球三大风暴轴联合EOF结果表明:第一模态下,主要体现了北西伯利亚风暴轴与北太平洋风暴轴强度的减弱(增强),同时伴随着北大西洋风暴轴位置北抬(南压);第二模态下,主要体现了北西伯利亚风暴轴强度减弱(增强),同时北太平洋风暴轴位置北抬(南压)中东部强度增强(减弱),而北大西洋风暴轴位置南压(北抬)。(3)回归分析表明:北半球风暴轴异常在不同模态下与低频尺度环流联系密切。低频尺度波动可通过海温及西风急流等异常变化先影响风暴轴区域多尺度间的能量转换,进而影响风暴轴整体的异常变化。

Multiscale energy change characteristics of storm tracks in the Northern Hemisphere and its possible mechanism during winter

Based on the daily reanalysis data of National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), the sea surface temperature data, atmospheric circulation and oceanic index data of National Climate Prediction Center (NCPC) from 1971 to 2016, this paper recognizes storm tracks in the Northern Hemisphere as a whole, and analyzes the characteristics of multi-scale energy variation and its possible mechanism using the multi-scale energy and vorticity analysis (MS-EVA). The results are summarized as follows. (1) The mean state of climate of many years shows that the kinetic energy source of storm tracks manifests as the available potential energy transmission from large scale to synoptic scale on the middle and upper reaches of storm tracks, and the subsequent energy conversion from potential to kinetic energy on the synoptic scale in the main areas of storm tracks. Besides, there is directly energy transmission from large scale to synoptic scale in the western part of storm tracks. (2) The first mode of EOF shows that with the weakening (intensification) of Siberian storm track and the northern Atlantic storm track, the Pacific storm track shifts northward (southward), and the second mode shows that with the weakening (intensification) of Siberian storm track, the Northern Atlantic storm track shifts northward (southward), and intensifies (weakens) in its middle-eastern part, together with southward (northward) shift of the Pacific storm track. (3) Regression analysis shows that the abnormality of the storm tracks in the northern hemisphere has a close association with the large-scale circulation in different modes. The large-scale fluctuation can affect the multi-scale energy conversion in the area of storm tracks by changing sea temperature and westerly jet, and then affect the anomaly characteristics of the overall storm track.