Interseasonal Oscillation Of Precipitation Over South China In Winter And Its Relationship With ENSO

Based on the ERA-Interim and NCEP reanalysis data,this paper analyzed the climatic state,interannual and interdecadal characteristics of low-frequency precipitation in winter(November to April of the following year)and its relationship with Pacific SST.And the main conclusions are given as follows:(1)The average and standard deviation of winter precipitation over East Asian continent is mainly concentrated in the south of China(about 24°N~30°N,108°E~120°E),where the precipitation has significant interannual differences in oscillation intensity,and the dominant period is 10-30-day.The occurrence of low-frequency precipitation is related to the southward propagation of anomalous low-frequency(10-30-day filtering)circulation in mid-high latitudes and the eastward propagation of abnormal circulation in the south of the plateau.(2)The interannual variability of low-frequency precipitation shows that compared to La Ni?a year,typical quasi-biweekly oscillation events of precipitation in El Ni?o year have more frequency with longer period and stronger intensity.The difference of low-frequency precipitation intensity between El Ni?o and La Ni?a years mainly depends on the low-frequency background water vapor((?)).In El Ni?o year,strong low-frequency convergence in active precipitation period provides strong vertical motion,and abundant low-frequency background water vapor provides stronger water vapor conditions for low-frequency precipitation,which makes the intensity of low-frequency precipitation stronger.More kinetic energy transfers toward the background field into the low-frequency field over South China during El Ni?o,which also causes the number of winter precipitation events during El Ni?o to be higher than that during La Ni?a.Moreover,the relationship between the quasi-biweekly oscillation intensity of precipitation and ENSO has significant interdecadal differences.The correlation between ENSO and low-frequency precipitation oscillation intensity over southern China after 1990s is significantly stronger than that in the 1960s-1970s.(3)From the point of the interdecadal variability,the intensity of low-frequency precipitation in winter over southern China shows an increasing trend,the precipitation oscillation isweakwer in 1961/62-1980/81 while is stronger in 1991/92-2010/11.This interdecadal difference is mainly influenced by low-frequency specific humidity(q?).The specifichumidity oscillation over southern China in 1991/92-2010/11 was significantly stronger than that in 1961/62-1980/81,which resulted in stronger low-frequency precipitation in 1991/92-2010/11 under the same convective conditions.