Interdecadal Variation Of MJO During The Boreal Winter In The Context Of Global Climate Change And Its Influence On Precipitation In Southern China

As a prominent atmospheric signal in tropics,Madden-Junlian Oscillation(MJO)exerts great effect on the weather and climate in both tropical and extropical regions.Characteristics of interdecadal variation of MJO during boreal wintertime in the context of global climate change are investigated by using the real-time multi-variate MJO(RMM)index,the National Oceanic and Atmospheric Administration(NOAA)daily long wave radiation data and the National Centers for Environmental Prediction/Nation Center for Atmospheric Research(NCEP/NCAR)reanalysis data,etc.The underlying reason of MJO interdecadal variation and its influence on the southern China precipitation are also discussed.From the rapid warming period(1985–1997)to the warming hiatus period(2000–2012),frequencies of MJO in Phases 2–4 decreased,while those in Phases 5–7 increased obviously.This indicates that MJO convection stays shorter over the tropical Indian Ocean(IO)but stays longer over the tropical western Pacific during the latter episode.Namely,the propagation of MJO slows down over the tropical IO but speeds up over the tropical western Pacific.Further analyses suggest that the interdecadal variation of MJO propagation is closely related to the interdecadal fluctuation of global climate change.In negative phases of Pacific Decadal Oscillation(PDO),when global warming slows down,the tropical eastern IO-western Pacific is abnormally warmer than normal,which favors the enhancement of convection and associated ascending motion,and thus the atmosphere at low-level converges,and moisture and the moist static energy(MSE)increase over the Maritime Continent.When MJO convective center is located over the tropical IO,there are a positive center of mean MSE transport by anomalous MJO circulation to the east of the MJO convective center and a negative one to the west,favorable for the positive MSE tendency to the east and thus speeding up the propagation of MJO over tropical IO.Whereas,when MJO convective center is located over the tropical western Pacific,the mean MSE transport by anomalous MJO circulation leads to a negative MSE tendency to the east of MJO convective center,so that the propagation of MJO slows down.Therefore,the interdecadal variation of MJO propagation is significantly modulated by the PDO in context of global climate change through the interdecadal change of atmospheric moisture content and MSE.Wintertime precipitation in southern China is significantly modulated by the MJO propagation.In Phases 2–4,southern China experiences a wet condition.There are more precipitation and more rainy days than in Phases 5–7,which are relative dry periods of southern China.In the warming hiatus period(2000–2012),decrease in frequencies in 2–4phases and increase in frequencies in 5–7 phases result in corresponding variations of wintertime precipitation in southern China.The rainy days decreased,accompanied by noticeable reduction of precipitation intensity,which may induce less accumulated precipitation.Although no marked interdecadal change of MJO intensity is revealed by RMM index,there are notable difference in MJO convection over Indian Ocean and wetern Pacific Ocean.By affecting the tropical and exropical circulations,the MJO also modulates the daily-mean precipitation anomalies in southern China.Both in Phases 2-4 and 5-7,negative precipitation anomalies appear in southern China.Therefore,the interdecadal variation of MJO plays obvious roles in modulating the interdecadal variations of winter precipitation in southern China.