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湖北冬季极端低温特征及其与大气环流的关系

Characteristics of Winter Extreme Low Temperatures in Hubei Province and Their Relationship with Atmospheric Circulation

  • 摘要: 利用湖北省1971~2020年冬季逐日最低气温观测资料和NCEP/NCAR大气环流资料,采用百分位阈值法、线性分析以及合成分析等方法,对湖北省冬季极端低温的年际变化特征和环流特征进行了分析,并进一步研究了2024年2月湖北极端低温冻雨的环流特征。结果表明:近50年来,湖北极端低温共出现460次,整体呈显著减小趋势,冬季季节尺度极端低温频次也逐月减少,12月减少趋势最快达−1.37(10 a)−1。湖北极端低温事件强度呈西南—东北向递减,总体趋于减弱,但近10年来有所增强。500 hPa中高纬环流距平呈“北高南低”,湖北处于槽前正涡度平流中,850 hPa上西北风引导冷平流南下,有利于湖北12月出现极端低温;中层中高纬经向环流度的加大和冷涌的偏强,有利于冷空气南下,低层冷空气以偏东路径进入湖北,容易造成湖北1月极端低温事件;欧亚大陆“西高东低”的高度距平场配置,有利于加强乌拉尔山阻塞形势,大陆高压与鄂霍次克海高压对峙,在西北路+东路回流冷空气共同影响下,湖北2月极易发生极端低温。500 hPa阻塞高压减弱引导冷空气南下,其中南支槽与异常偏强的西太平洋副热带高压在110°E附近交汇,低层西南暖湿气流沿锋区持续爬升,地面气压场呈东高西低的形势,使得冷空气路径偏东,造成了湖北2024年2月同时出现极端低温和雨雪冰冻事件。

     

    Abstract: Based on daily minimum temperature observations data and NCEP/NCAR atmospheric circulation data from 1971 to 2020, this study analyzes the interannual variation and circulation characteristics of winter extreme low temperatures in Hubei Province using the percentile threshold method, linear analysis, and synthetic analysis. The characteristics of extreme low-temperature freezing rain circulation in Hubei in February 2024 were further studied. The findings indicate that within the past 50 years, Hubei Province experienced 460 instances of extreme low temperatures, exhibiting a marked decline in frequency. The frequency of extreme low temperatures at the sub-seasonal scale in winter has also decreased month by month, with the most rapid decrease occurring in December at a rate of −1.37 (10 a)−1. The intensity of extreme low-temperature events in Hubei exhibited a decrease from southwest to northeast, with a general tendency to weaken; however, these events have increased in frequency over the past decade. The 500-hPa mid-high latitude circulation anomaly is high in the Northern Hemisphere and low in the Southern Hemisphere. Hubei Province is situated within the positive vorticity advection in front of the trough. The northwestern wind at 850 hPa directs cold advection toward the south, thereby fostering the potential for extreme low temperatures in Hubei during December. The increase of meridional circulation in the middle and high latitudes, in conjunction with a robust cold surge, fosters the southward movement of cold air. This results in the entry of low-level cold air into Hubei via an easterly trajectory, a phenomenon that suggests the likelihood of extreme low-temperature events in Hubei during January. The height anomaly field configuration, characterized by “high in the west and low in the east” in Eurasia, is conducive to the strengthening of the blocking situation over the Ural Mountains. The continental high pressure and the Okhotsk Sea high pressure systems are in relative opposition. The state of Hubei Province is susceptible to extreme low temperatures in February, primarily due to the combined influence of northwest and east return cold air. The weakening of the blocking high at 500 hPa results in the southward movement of the cold air. The southern branch trough intersects with the abnormally strong western Pacific subtropical high near 110°E. The ongoing progression of the low-level southwest warm and humid airflow along the frontal zone has been observed. The surface pressure field exhibited high values in the eastern region and low values in the western region. Consequently, the cold air mass propagated eastward, leading to the extreme low temperature rain and snow freezing events that occurred in Hubei in February 2024.

     

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