Dominant Circulation Regimes Of Intra-seasonal Rainfall In South China During Super El Ni(?)o Winter

A super El Ni(?)o took place in the winter of 2015/16 with sequential heavy rainfall events over South China(SC),which caused the local severe winter flooding in historical record.In order to reveal the possible impact of super El Ni(?)o on the sub-seasonal variations of rainfall over SC,we utilized daily in situ rainfall records,NCEP-R2 reanalyzed dataset,NOAA sea surface temperature and the ensemble simulations from the AGCM of MIROC5,and analyzed the dominant circulation regimes with respect to the ISO of rainfall activity during the winter of 2015/16,and compared the historical super El Ni(?)o of 1982/83 and 1997/98.Further,we analyzed the possible influences of super El Ni(?)o on sub-seasonal rainfall over SC based on the model simulations of MIROC5.The main conclusions are summarized as follows:During the 2015/16 super El Ni(?)o event,the sequential heavy rainfall clusters and resultant severe winter flooding occurred over SC were ascribed to the 10-25-and 30-40-day intra-seasonal oscillations(ISOs).The 10-25-day low-frequency rainfall was related to the eastward propagating wave train and the water vapor convergence associated with the tropics.While the 30-40-day ISO was related with the anomalous upper-level divergence,caused by the weakening of the East Asian trough,and the southwesterly surrounding the Tibetan Plateau brought more water vapor into South China to trigger the wet phase.Moreover,the 30-40-day low-frequency westerly anomalies in upper-level provided a better waveguide for the eastward propagation of 10-25-day ISO.The 10-20-and 20-50-day ISOs were all exist during the winter of three super El Ni(?)o events,while in the winter of 1997/98,the precipitation was mostly dominated by the 10-20-day quasi-biweekly oscillation,i.e.,the 20-50-day ISO was relatively weak,causing the precipitation was less than the winter of 1982/83 and 2015/16.And the sub-seasonal variation of rainfall over SC was mainly influenced by the 200-hPa wave train along with the westerly jet.Atmosphere General Circulation Model of MIROC5 can simulate the patterns of climatological precipitation and circulation in winter.And it can also reproduce the ISO wave train related to the sub-seasonal rainfall over SC in the winter of three super El Ni(?)o.However,the model fails to simulate the time phase and amplitude of ISO rainfall in observation.Therefore,further research is needed on the impacts of El Ni(?)o on the ISO of rainfall in SC.