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

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.