Dominant role of cold vortices on the precipitation in Northeast China still exists in midsummer

The summer precipitation in Northeast China (NEC) can usually be divided into two stages, namely the Northeast China cold vortex (NECV) influencing stage in early summer (May-June) and the monsoon influencing stage in midsummer (July-August). In this study, the influence of NECV on the precipitation at multi-timescales during different summer periods is studied. The results show that even in midsummer, though the effect of the western Pacific subtropical high is strengthened, the NECV still has the major impact on the precipitation over NEC. High co-variability could be found between the daily precipitation and the NECV index in each month. The running correlation with an 11-day window between precipitation and the NECV index also proves that the NECV has large impact on the precipitation over NEC during the whole summer. Key linkage of NECVs and the precipitation in midsummer can still be detected in synoptic extreme rainfall events. The composite analysis shows that, for the heavy rainfall extremes in NEC, the dominant circulation is an obvious 'negative-positive-negative' vorticity pattern at high latitudes of Asia. The positive vorticity in the pattern corresponds to stronger and more active NECV. That means the NECV is still the most critical factor affecting the NEC precipitation in midsummer. We compared the influences of the NECV on the precipitation during different periods both from seasonal time scale and from extreme synoptic cases. Our results pointed firstly that the NECV is still the most critical factor affecting the NEC precipitation in midsummer.image