东北冷涡气候特征及其对海河流域夏季降水的影响

Climatic characteristics of northeast cold vortex and its impact on summer precipitation in the Haihe river basin

  • 摘要: 东北冷涡是对流层发生在东北亚区域深厚的冷性低压系统,它的活动异常往往会给夏季降水预测带来很大的不确定性。为改进降水预测技术,使用1961—2021年中国2400多站降水数据和NCEP/NCAR再分析环流数据等资料,采用机器自动识别、相关分析和回归重构等方法,分析了东北冷涡气候特征及其对海河流域夏季降水的影响。主要结果如下:(1)东北冷涡发生时间和地理位置具有明显的气候特征。东北冷涡一年四季均可出现,夏季冷涡天数最多。月份上,5—9月冷涡过程明显偏多,其中6月过程和天数最多。夏季,冷涡中心位置在6月最偏南,7月最偏西,8月最偏东北。(2)海河流域夏季降水与全年或夏季的东北冷涡天数整体上不存在明显相关,但与夏季西涡(<120°E)天数存在显著的正相关,与夏季东涡(≥120°E)天数存在显著的负相关。夏季西涡活动多,有利于海河流域夏季降水偏多;夏季东涡活动多,可能会造成海河流域夏季降水偏少。(3)东北冷涡可通过动力环流异常和水汽输送异常影响海河流域夏季降水。西涡出现时,会造成200 hPa层西风急流在海河流域上空显著增强,500 hPa层海河流域处于“东高西低”环流型槽前的上升区,850 hPa层东亚地区出现偏南风异常,增强了向海河流域的水汽输送。东涡出现时,200 hPa层西风急流在海河流域上空无明显异常,500 hPa层海河流域处于 “东低西高”环流型高压脊前的辐散区,850 hPa东亚地区无明显水汽输送异常。

     

    Abstract: Northeast Cold Vortex (NECV) is a deep cold low-pressure system occurring in the troposphere over Northeast Asia, and anomalies of its activity can often bring great uncertainty to summer precipitation prediction. To improve precipitation prediction technology, this article analyzes climatological characteristics of NECV and its influence on summer precipitation in the Haihe river basin based on precipitation data collected at more than 2400 stations in China and NCEP/NCAR reanalysis circulation data for the period 1961−2021. Machine automatic recognition, correlation analysis and regression reconstruction are employed in this study. Major results are as follows: (1) The occurrence time and geographical location of NECV have obvious climatological characteristics. It can appear all year round, and the number of cold vortex days is the largest in summer. From May to September, there are more cold vortex processes, especially in June. In summer, the center of cold vortex is located further south in June, further west in July, and further northeast in August. (2) There is no significant correlation between summer precipitation in the Haihe river basin and the overall number of days of NECV throughout the year or in summer. However, there is a significant positive correlation with the number of days of summer Western Vortex (<120°E) and a significant negative correlation with the number of days of summer Eastern Vortex (≥120°E). The frequent activities of the Western Vortex in summer are conducive to higher summer precipitation in the Haihe river basin, while the frequent activities of the Eastern Vortex in summer may result in less summer precipitation in the Haihe river basin. (3) NECV can affect summer precipitation in the Haihe river basin through anomalies of dynamic circulation and water vapor transport. Corresponding to the Western Vortex, the westerly jet at 200 hPa is significantly stronger over Haihe river basin, and Haihe river basin at 500 hPa is located in the rising zone in front of the low pressure trough in the blocking circulation pattern of "high in the east and low in the west". Meanwhile, anomalous southerly winds at 850 hPa over East Asia enhance water vapor transport to Haihe river basin. Corresponding to the Eastern Vortex, the westerly jet at 200 hPa shows no obvious anomalies over Haihe river basin, while Haihe river basin at 500 hPa is in the divergence area in front of the high pressure ridge of "low in the east and high in the west" circulation pattern, and there is no obvious water vapor transport anomaly at 850 hPa over East Asia.

     

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