Using multiple datasets,this paper analyzes the characteristics of winter precipitation over southern China and its association with warm and cold phases of El Nino-Southern Oscillation during 1948-2011.The study proves that El Nino is an important external forcing factor resulting in above-normal winter precipitation in southern China.The study also reveals that the impact of La Nina on the winter precipitation in southern China has a decadal variability.During the winter of La Nina before 1980,the East Asian winter monsoon is stronger than normal with a deeper trough over East Asia,and the western Pacific subtropical high weakens with its high ridge retreating more eastward.Therefore,anomalous northerly winds dominate over southern China,leading to a cold and dry winter.During La Nina winter after 1980,however,the East Asian trough is weaker than normal,unfavorable for the southward invasion of the winter monsoon.The India-Burma trough is intensified,and the anomalous low-level cyclone excited by La Nina is located to the west of the Philippines.Therefore,anomalous easterly winds prevail over southern China,which increases moisture flux from the tropical oceans to southern China.Meanwhile,La Niiia after 1980 may lead to an enhanced and more northward subtropical westerly jet over East Asia in winter.Since southern China is rightly located on the right side of the jet entrance region,anomalous ascending motion dominates there through the secondary vertical circulation,favoring more winter precipitation in southern China.Therefore,a cold and wet winter,sometimes with snowy and icy weathers,would occur in southern China during La Niiia winter after 1980.Further analyses indicate that the change in the spatial distribution of sea surface temperature anomaly during the La Niiia mature phase,as well as the decadal variation of the Northern Hemisphere atmospheric circulation,would be the important reasons for the decadal variability of the La Nina impact on the atmospheric circulation in East Asia and winter precipita
Historical La Nia events since 1950 are divided into Eastern Pacific(EP) type and Central Pacific(CP) type,and the SSTA developing features as well as the different responses of the tropical atmosphere are further analyzed by using multiple datasets.Classification of different types La Nia is based on the normalized Ni o3 and Ni o4 indices and the SSTA distribution pattern during the mature phase.The minimum negative SSTA for CP La Nia is located over the equatorial central Pacific near the dateline,more westward than that of EP La Nia.It has stronger intensity and larger east-west zonal difference of SSTA over the equatorial Pacific than EP La Nia.Influenced by the different SSTA distribution pattern,CP La Nia induces more westward location of the anomalous sinking motion and the anomalous low-level divergent and high-level convergent winds over the equatorial eastern Pacific.The different response of the tropical atmospheric circulation between EP and CP La Nia is more significant in the upper troposphere than in the lower troposphere.However,the tropical precipitation patterns during the mature phase of EP and CP La Nia are much similar,except the less(more) precipitation over the equatorial central Pacific(eastern Indian Ocean-western Pacific) during CP La Nia than during EP La Nia.
