Distinct influences of cold vortex over Northeast China on local precipitation in early summer and midsummer

The station observations and reanalysis dataset are utilized to identify the cold vertex over Northeast China (NECV) in early summer (ES) and midsummer (MS) respectively. In this study, we focus on the characteristics of NECV and their distinct influences on local precipitations in ES and MS. The underpinning mechanisms are further inspected in terms of thermodynamic and dynamic processes. Results suggest that in ES (MS) the NECV is mainly located over Northern China-Southeastern Russia (Mongolia) and significantly correlated to the precipitations over the eastern (mid-western) regions of Northeast China. In the strong cases of precipitation, NECV displays northward shift and intensification in ES and MS respectively. Meanwhile, the upper-level wind anomalies suggest a northward displacement of polar front jet and a weakened subtropical jet in ES, and an enhanced polar front jet and a southward shift of subtropical jet in MS. The wind anomalies induced by meridional temperature gradients and the Rossby wave activities transported to Northeast China favor the development of atmospheric circulation vorticity and then promote the variations of NECV. Furthermore, the vorticity and temperature advections are favorable for the enhancement of ascending motion under quasigeostrophic approximation, which is combined with the sufficient water vapor transported from oceanic regions, triggering the regional precipitation. Intriguingly, the pathways of water vapor transport and disturbance energy propagation caused by the diverse external forcings are different in ES and MS, which sheds some fresh light on the insight into the subseasonal variations of NECV and the distinctive contributions to local precipitation.