| In this study,we analyzed a case of heavy rainfall over the eastern Tibetan Plateau(TP)from July 30,2014 affected by a TP vortex(TPV)and a Southwest China vortex(SCV)to explore their common and individual influence on precipitation.Based on the weather situation,the evolution of synoptic systems,thermodynamic and dynamic diagnosis,water vapor conditions,sources of water vapor in different rainfall centers were also tracked by HYSPLIT model.The results show that: the precipitation is mainly divided into two periods.The first with a weaker precipitation mainly located on TP is caused by the eastward development of the TPV.The second-period rainfall mainly located in the eastern slope of the TP and the western Sichuan Basin increases sharply compared with that in the first stage on the TP,reaching 50 mm in just 6 hours,which is mainly due to that the eastward movement of the TPV and its interaction with the circulation of the early SCV(A)and the later SCV(B)in the basin strengthen the convergence and uplift between the southwest wind in front of TP and the low-level airflow.Water vapor near 1000 m around the first-period rallfall center over the TP is mainly transported through two channels: the first is transported directly from the bay of Bengal over the Himalayas to the TP,and the second is from the South China Sea to the TP along Sichuan and Gansu province.Water vapor below 1000 m around the second-period heavy rainfall center over the eastern slope of the TP and the basin is transported from the bay of Bengal through the South China Sea,while the water vapor around the upper 3000 m comes from the eastern South China Sea.So as to explore the influence of the TPV and the SCV(A)on precipitation and the later new SCV(B),based on Barnes band-pass filter used to separate the TPV and the early SCV(A),sensitivity experiments called NPV and NSV were seperately designed to remove the TPV and the early SCV(A)moreover.It has found that the TPV plays a leading role in the precipitation process,mainly because it provide both dynamic and thermodynamic conditions for the early precipitation on the TP.The subsidence of dry and cold air in front of the TPV promotes the convective movement in the basin,providing dynamic uplift conditions for the late heavy rainfall over the eastern slope of the TP and the basin.The SCV(A),weak in the early stage in the basin,gradually weakens and disappears under the large-scale circulation.It affects little on the early precipation over the TP but affects the early thermal condition and the low-level air flow in the basin,causing the difference of force uplift velocity to the low-level air flow caused by the eastern slope of the TP,and then leads to the difference of early rainfall there and moreover affects the intensity of SCV(B)through the release of condensation latent heat caused by precipitation.Therefore,the SCV(A)affects indirectly on the late heavy rainfall in the basin.Beause of the special topography of the basin and the low-level convergence leading by the increasing low-level jet,the SCV(B)is newly formed in the basin,while the intensity is affected by TPV and the previous SCV(A),however.The SCV(B)continuously transport warm and wet airflow and energy to the basin,combined with the dynamic uplift caused by the TPV,resulting in the late heavy rainfall on the eastern slope of the TP and the basin. |
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