The Relationship Between NingalooNi(?)o/Ni(?)a And Winter Precipitation Anomalies In South China

Based on 1961-2017 monthly sea surface temperature data from NOAA_ERSST_V3b,NCEP/NCAR reanalysis data and CN05.1 precipitation data,the change of Ningaloo Ni(?)o/Ni(?)a and its association with winter precipitation anomaly in South China were investigated firstly by observational analysis.Numerical simulations were then conducted with the Community Atmosphere Model version 5.1 from National Center for Atmospheric Research to verify the observational results for revealing the possible mechanism of the influence of Ningaloo Ni(?)o/Ni(?)a on the winter precipitation change in south China.The main conclusions are summarized as follows:(1)Ningaloo Ni(?)o/Ni(?)a is the dominant mode of sea surface temperature anomalies in the Southeast Indian Ocean,with a variance contribution rate is 56 percent.Showing obvious interannual variation characteristics.The area of large sea surface temperature anomalies is located in the west coast of Australia and expands to the northwest.Ningaloo Ni(?)o/Ni(?)a has the characteristics of seasonal phase-locking and reaches the mature phase in winter.Their development process is asymmetric,the development and evolution of Ningaloo Ni(?)a is longer than Ningaloo Ni(?)o.In the 56 years from 1961 to 2016,there are 9 Ningaloo Ni(?)o years and 7 Ningaloo Ni(?)a years.(2)Ningaloo Ni(?)o/Ni(?)a is significantly related to winter precipitation anomaly in South China on the interannual time scale.The Ningaloo Ni(?)o index and the South China Precipitation index are positively correlated.When the Ningaloo Ni(?)o index increases by one standard deviation in winter,the precipitation in South China is compared the multi-year average precipitation has increased by about 15 percent.When the Ningaloo Ni(?)o index decreases by one standard deviation,the precipitation in the eastern part of South China can be reduced by more than 20 percent.(3)Ningaloo Ni(?)o/Ni(?)a can cause abnormal changes in the atmospheric circulation in East Asia.In the winter of Ningaloo Ni(?)o,the anomalous warm sea surface temperature increases the sea-level pressure gradient between the eastern Indian Ocean and the western Pacific,which is conducive to the formation of an abnormal anticyclonic circulation in the western Pacific.The warm shear line in the eastern part of South China at the low level of 850 hPa is conducive to the convergence and rise of warm and humid air.The 500 hPa geopotential height field anomaly on the Eurasian continent is similar to the Eurasian teleconnection type negative phase distribution,and the plateau jet is enhanced at the height of 200 hPa,the weakening of the temperate jet stream provides favorable water vapor and dynamic conditions for the increase of precipitation in South China,which is conducive to the increase of precipitation in South China,and vice versa.(4)Combined with the results of observation analysis and numerical test,the possible mechanism of Ningaloo Ni(?)o/Ni(?)a affecting the winter precipitation anomaly in South China is as follows.An enhanced convection occurs in western Australia during the winter of Ningaloo Ni(?)o,and then results in an anomalous longitudinal circulation cell and anomalous counter-circulation cell in the lower latitudes of the northern hemisphere,which enhances the Southern Branch trough.The intensity of the trough in Southern Branch is positively correlated with the winter precipitation in southern China.When Southern Branch trough is strong,the active disturbance propagates downstream,and the prevailing southwesterly flow in front of the trough makes sufficient water vapor from the Bay of Bengal flowing from southwest to northeast,in favor of more winter precipitation in southern China,and vice versa for Ningaloo Ni(?)a years.