Impact Of Victoria Mode In North Pacific On ENSO And South China Winter Extreme Precipitation

The El Ni?o-Southern Oscillation(ENSO)phenomenon is the strongest signal in the interannual climate change in the tropical Pacific region,and its occurrence and development mechanism and prediction have been one of the most important points of research.At the same time,under the background of global warming,the frequent occurrence of extreme weather and climate events has become one of the major concerns of human beings.In East Asia,especially China,with a dense population and inadequate disaster prevention and reduction infrastructure,it is more vulnerable to extreme events.The extreme winter rainfall in South China in China occupies an important position in the country.Therefore,in order to solve the problems in the previous research,the analysis of the climatic factors in the tropical and northern Pacific to ENSO and the extreme precipitation events in southern China in winter is of great significance to make timely plans to avoid risks and avoid loss of personal and property.This paper uses 1950-2017 HadISST sea surface temperature data,SODA data set,NCEP-NCAR atmospheric reanalysis data,Chinese ground station data,and model simulation data.Through empirical orthogonal function decomposition,singular value decomposition,correlation analysis,regression analysis and a series of methods,such as synthetic analysis,are mainly used to study the two SST modes of the Victorian mode(VM)and Pacific meridional mode(PMM)in the tropical North Pacific Ocean.The analysis of its spatiotemporal changes and its impact on ENSO aims to explore the connection and differences between the two,and at the same time analyze the relationship between VM and winter extreme precipitation in South China,as well as the potential impact mechanism,so as to further supplement the external tropical signals to ENSO and extremes.The impact of the event and provide a certain reference for the prediction of ENSO and extreme events.The following main conclusions were reached:(1)Unlike the PMM local-scale SST model located in the subtropical northeast Pacific,VM,as a SST model in the tropical North Pacific basin,has its own unique SST structure.The most significant difference in the spatial distribution of sea surface temperature anomalies between the two lies in the sea surface temperature anomaly structure located in the northwest Pacific along the coast of East Asia.VM has its own independent time variability characteristics.The regression reconstruction method is used to show that the SST anomaly distribution in the Northwest Pacific and the subtropical Northeast Pacific is an important component of the North Pacific SST mode related to VM.The classification of VM events and PMM events shows that the occurrence of VM events is not completely accompanied by the occurrence of PMM events.Therefore,VMs have their own time-varying characteristics.(2)The relationship between VM and ENSO is closer than that between PMM and ENSO.Through the combined effect of the negative anomaly of the SST in the northwest Pacific and the positive anomaly of the subtropical northeast Pacific,VM increases the zonal SST anomaly gradient in the tropical Pacific,thereby strengthening the abnormal westerly winds over the western equatorial Pacific and triggering the airsea process of positive feedback The interaction promoted the sustained growth of these anomalies,and eventually produced significant warming in the equatorial Middle East and Pacific Ocean,affecting the development of ENSO.The negative SST anomalies in the Northwest Pacific region associated with the VM played a key role in this process.(3)VM may be used as a more effective predictor than PMM to affect ENSO events,thereby improving the predictability of ENSO.VM may trigger ENSO through two main processes: the thermodynamic process of the ocean surface associated with PMM occurring in the subtropical Northeast Pacific;and the thermocline-sea surface temperature feedback process related to the SST in the Northwest Pacific along the equator.Statistically,VM often results in a mixed mode of CP-type and EP-type ENSO events.However,the positive sub-sea surface temperature anomalies associated with PMM are basically limited to the equatorial central Pacific,and the ability to propagate eastward is weak,so PMM tends to cause CP-type ENSO events.This is also one of the possible reasons why the impact of VM on ENSO events is stronger than that of PMM.In addition,the coupled model intercomparison project phase 5(CMIP5 for short)model data can basically simulate the correlation between VM and PMM and ENSO and the seasonal evolution of the element fields related to the two modes.(4)The VM in the early spring season is likely to be a precursor signal about three seasons in advance,which will have a strong impact on the subsequent changes in the frequency of extreme winter precipitation in southern China.The potential mechanism of VM affecting winter extreme precipitation frequency in South China shows that VM affects the development of winter extreme precipitation frequency in South China by affecting the development of ENSO,which provides a reference for improving the predictability of winter extreme precipitation in South China.The distribution of VM through the SST negative anomaly in the northwest Pacific and the SST positive anomaly in the subtropical northeast Pacific strengthens the abnormal zonal westerly winds along the equator,which in turn triggers the equatorial ocean Kelvin waves and affects the development of ENSO.As a result,anticyclones in the northwest Pacific strengthened,which enhanced water vapor transmission from the South China Sea and the Indian Ocean.At the same time,the negative anomalies of outward long wave radiation(OLR)in South China are significant,eventually leading to an abnormal increase in the frequency of winter extreme precipitation in South China.