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2024年2月湖北省两次雨雪冰冻天气特征及海温影响分析

Analysis of weather characteristics and sea surface temperature impact on rainfall/snowfall and freezing events in Hubei Province in February 2024

  • 摘要: 2024年2月湖北省连续发生两次雨雪冰冻天气,其中冻雨造成的灾害尤其严重,为深入分析这两次雨雪冰冻天气的成因,利用湖北省82个国家气象站1961年以来逐日观测、再分析及海温和环流指数资料,基于改进的持续低温雨雪冰冻强度综合指数,将这两次过程与2008年最强雨雪冰冻天气特征进行比较,并分析了这两次过程的环流异常特征及海温的影响,结果表明:(1) 2024年2月两次过程雨雪相态更复杂、冻雨范围和极端性均强于2008年,但持续时间和积雪深度不及2008年;(2) 500 hPa位势高度距平场为有利于降水的典型 “西低东高”分布,西太平洋副热带高压(简称西太副高)异常增强,配合东路冷空气,形成持续低温雨雪冰冻天气过程;第一次过程具有更深厚的暖层条件和更强的西南水汽,以降冻雨为主;第二次过程冷空气相对更强,但西南水汽减弱,以冰粒和霰为主,期间夹杂冻雨,雨雪相态更为复杂;(3) 2024年2月两次过程发生于一次中等偏强厄尔尼诺事件达到峰值并开始衰减的海温背景下,印度洋异常增暖且呈“西暖东冷”分布,导致后冬西太副高异常增强、南方水汽充足;(4)我国黄海至日本海附近异常暖海温在日本海上空强迫出异常反气旋环流,阻挡西风带气流东移,冷空气南下与增强的西太副高输送的南方水汽交汇,形成持续雨雪冰冻天气。

     

    Abstract: In February 2024, Hubei Province experienced two low temperature, rainfall/snowfall and freezing events. Particularly, the damage caused by freezing rain was especially severe. To analyze the causes of the two rainfall/snowfall and freezing events, the reanalysis, the sea temperature and circulation index, the daily observation data from 82 national meteorological stations in Hubei Province since 1961 were used. Based on the improved composite index of persistent low temperature, rainfall/snowfall and freezing intensity, these two events characteristics were compared with the strongest rainfall/snowfall and freezing weather in 2008. Then the circulation anomalies and the influence of sea surface temperature (SST) of these two events was analyzed. The results are as follows. (1) During the two events in February 2024, the rain and snow phases were more complex, with a larger freezing rain range and stronger extremity compared to those in 2008. But the duration and snow depth were less severe than those in 2008. (2) The 500 hPa geopotential height anomaly was a typical “low in the west and high in the east” distribution, which is favorable for precipitation. The anomaly of the western Pacific subtropical high (WPSH) was enhanced, combined with the cold air from the east, forming persistent low temperature, rainfall/snowfall and freezing weather. The first event had deeper warm layer conditions and stronger southwest water vapor, mainly dominated by freezing rain. The second event featured stronger cold air but weakened southwest water vapor, which was dominated by a mix of ice particles, graupel, and freezing rain, with more complex precipitation phases. (3) The two events in February 2024 occurred under the background of a moderately strong El Niño event reaching its peak and beginning to weaken. The Indian Ocean was abnormally warming and exhibited a distribution pattern of "warm in the west and cold in the east", which played an important role in the abnormal enhancement of the WPSH and the abnormal enhancement of water vapor in the south in the late winter. (4) The abnormally warm SST near the Yellow Sea to the Sea of Japan forced an anomalous anticyclonic circulation over the Sea of Japan, blocking the eastward movement of the westerly wind belt. The southward movement of cold air converged with the enhanced WPSH transporting southern water vapor, resulting in sustained rainfall/snowfall and freezing weather.

     

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