藏北地区强降温分布特征与预报方法

Distribution Characteristics and Prediction Methods of Strong Cooling in Northern Tibet

  • 摘要: 本文选取1991—2024年藏北地区地面观测、探空、MICAPS资料及ERA5再分析资料,按照Ⅰ级、Ⅱ级、Ⅲ级强降温等级标准,应用Mann—Kenddall检验、Morlet小波分析、相关分析、阈值分析等方法,通过分析藏北地区强降温时空分布特征,在制定强降温判定指标的基础上,构建强降温预报模型并检验其预报效果。结果表明:(1)近30 a藏北地区共出现了660次强降温事件,集中发生在10月—次年5月,其中1月、2月、12月尤为多发,且呈中部多、东西部少的空间分布特征。(2)Ⅰ级、Ⅱ级、Ⅲ级强降温事件年均频次分别为22次、10次、4次,均呈减少趋势,气候倾向率分别为−1.2/10 a、−0.5/10 a、−0.04/10 a。(3)Ⅰ级和Ⅲ级强降温事件均存在气候突变特征,前者发生在2004年,突变后频次减少,后者发生在2002年与2018年,2002年突变后频次减少,2018年突变后频次增加;三类强降温事件均存在准6 a振荡周期。(4)藏北地区强降温事件发生发展的环流背景可分为三类,分别是大型槽东移型、短波槽波动型和脊前型。(5)利用强降温预报指数(Y)可判别强降温天气及降温强度,6≤Y<8对应Ⅰ级强降温事件,8≤Y<10对应Ⅱ级强降温事件,Y≥10对应Ⅲ级强降温事件,其预报准确率可达88%。

     

    Abstract: Selecting ground observation data, sounding data, MICAPS data and ERA5 reanalysis data from 1991 to 2024 in northern Tibet. According to the strong cooling grade standards of Grade I, II, and III, the Mann Kendall test, Morlet wavelet analysis, correlation analysis, threshold analysis and other methods are used to analyze the spatiotemporal distribution characteristics of strong cooling in northern Tibet. A strong cooling prediction model and indicators are constructed and the predictive performance is tested. The results show that: (1) In the past 30 years, a total of 660 strong cooling events have occurred in the northern Tibetan Plateau, concentrated from October to May of the following year, with particularly high frequencies in January, February, and December. Spatially, these events are more common in the central region and less frequent in the eastern and western areas. (2) The annual average frequencies of Grade I, Grade II, and Grade III strong cooling events are 22, 10, and 4 times, respectively. All show a decreasing trend, with climate tendency rates of−1.2/10 a, −0.5/10 a, and −0.04/10 a, respectively. (3) Both Grade I and Grade III strong cooling events exhibit characteristics of climate abrupt changes. The former occurred in 2004, with a decrease in frequency after the abrupt change, while the latter occurred in 2002 and 2018, with a decrease in frequency after 2002 and an increase after 2018. All three types of strong cooling events exhibit a quasi-6-year oscillation cycle. (4) The circulation backgrounds for the development of strong cooling events in the northern Tibetan Plateau can be divided into three types: large trough eastward movement, short-wave trough fluctuation, and ridge-front type. (5) The strong cooling forecast index (Y) can be used to distinguish strong cooling weather and cooling intensity. 6 ≤ Y < 8 corresponds to Grade I strong cooling events, 8 ≤ Y < 10 corresponds to Grade II strong cooling events, and Y ≥ 10 corresponds to Grade III strong cooling events, with a forecasting accuracy of up to 88%.

     

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