The Characteristics And The Possible Influencing Factors Of The Summer Persistent Rainfall Events Over China

The summer persistent rainfall events over China have a great impact on the society and economics.This study investigates characteristics of the individual-station-based persistent rainfall over the Yangtze-Huaihe River Basin(YHRB)and northern part of China,the associated East Asian jet streams(EAJS)and ocean conditions.Characteristics of the cluster extreme rainfall events(CER)over the southern part of China and the northern part of China have been further investigated.The main conclusions are as follow:(1)The frequency of summer individual-station-based persistent rainfall over the YHRB has increased and the impact stations have also expanded in the recent years(1974-2011).The concurrent variations of the East Asian Subtropical jet(EASJ)and the East Asian Polar Front jet stream(EAPJ)have contributed to the dominant variations based on the EOF analysis.For the EOF1,associated with the polar-ward(equator-ward)shift of the EAPJ(EASJ),the cold-dry air and warm-humid air would converge over YHRB and easily trigger the long-persistent precipitation.For the EOF2,the strengthened EAPJ and weakened EASJ may result in the southern-flood-northern-drought precipitation anomaly,via the water vapor and ascending motion.(2)The frequency of summer individual-station-based persistent rainfall over the northern part of China has experienced a significant decadal shift around 1996,with an enhanced(reduced)anomaly before(after)1996,which is closely associated with a meridional tri-pole sea surface temperature(S ST)anomaly over the central Pacific,a La Nina-like anomaly for the pre-1996 epoch(1971-1996)and an obvious warming over the south Indian Ocean and the western part of south Pacific Ocean in the post-1996 epoch(1997-2014).In the pre-1996 epoch,associated with the typical SSTs,the ascent motion with increasing humidity anomalies are over the northern part of China.Meanwhile,high(low)pressure anomalies are over western Asia and East Asia(Europe and central Asia),which resembles as the positive phase of the Silk Road pattern(SRP).It would be associated with the pole-ward shift of the EAJS and therefore result in the north-ward shift of the rain belt and benefit the occurrence of the individual-station-based persistent rainfall.In the post-1996 epoch,associated with the warming over the specific south oceans,a descend anomaly dominates over the northern part of China,as well as the resembled negative phase of the SRP over mid-high latitudes and equator-ward shift of the EAJS.These would suppress the rainfall over the northern part of China and reduce the individual-station-based persistent rainfall frequency over there after 1996.(3)With the increase of the duration,the affected stations expand and the extreme intensity increase of the cluster extreme rainfall events both over the southern and the northern part of China.The difference is that the event center in the southern part of China moves to the northwest,while the event center in the northern part of China moves to the southwest.It is also found that the 3d-CER over the southern(northern)part of China frequently occurred in the period of 1990-2009(1961-1969).For the 3d-CER over southern part of China during 1990-2009,the impact scope is large,the mean intensity,extreme intensity and composite strength are strong.For the 3d-CER over northern part of China during 1961-1969,the impact scope is small,the mean intensity and extreme intensity are strong,and the event center moves northwest.