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全球变化背景下冬季MJO传播的年代际变化及其对中国南方冬季降水的影
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摘要
利用1979～2013年实时多要素MJO（Madden-Julian Oscillation）监测（RMM）指数，美国NOAA逐日长波辐射资料和NCEP/NCAR的再分析资料等，分析了全球变化背景下北半球冬季MJO传播的年代际变化特征。从全球平均气温快速增暖期（1985～1997）到变暖趋缓期（2000～2012），MJO2～4位相频次减少，5～7位相频次增多，即MJO对流活跃区在热带印度洋地区停留时间缩短、传播速度加快，而在热带西太平洋停留时间加长、传播明显减缓。进一步分析发现，以上MJO的年代际变化特征与全球变化年代际波动有关。当太平洋年代际涛动（PDO）处负位相时，全球变暖趋缓，热带东印度洋～西太平洋海温异常偏暖，使其上空对流加强，垂直上升运动加强，对流层低层辐合，大气中的水汽含量增多，该区域的湿静力能（MSE）为正异常。当MJO对流活跃区位于热带印度洋地区时，MJO异常环流对季节平均MSE的输送在强对流中心东侧为正、西侧为负，有利于东侧MSE扰动增加，使得MJO对流扰动东移加快；而当MJO对流活跃区在热带西太平洋地区，MJO异常环流对平均MSE的输送形成东负西正的形势，东侧MSE扰动减小，不利于MJO快速东传。因此，全球变化背景下PDO 引起的大气中水汽含量及湿静力能（MSE）的变化可能是调制MJO传播年代际变化的重要原因。
speculation
MJO传播的年代际变化对中国南方地区冬季降水也有一定的调制作用。我们利用中国台站逐日降水资料分析了MJO的不同位相与中国南方地区冬季降水的关系。在MJO 2～4位相，对应着我国南方地区降水偏多、雨日偏多、雨强偏强，呈偏湿状态；而在MJO5～7位相，南方地区降水偏少，雨强偏弱，呈偏干状态。我们对全球变暖趋缓前后的MJO位相频次的年代际变化与中国南方降水的关系进行了研究发现，2000年之后，2～4位相的频次减少，5～7位相的频次增加使得南方地区的雨日减少，降水强度减弱，故而累计降水量减少。虽然RMM指数中表示的MJO的强度在2000年前后并没有明显的年代际差别，但是由于受到了年代际背景的影响，OLR显示的对流强度在印度洋地区和西太平洋地区还是有一定的年代际变化出现，因此我们也对全球变暖趋缓前后的MJO 强度的差异与中国南方冬季平均降水强度的关系以及其对应的环流场的变化情况进行了分析研究，发现在变暖趋缓期南方地区日平均降水有减弱的趋势，在MJO2-4位相和5-7位相时，中国南方地区均出现了降水负异常。由此，MJO的年代际变化对我国南方冬季降水的年代际变化起到了明显的调制作用。
关键词：MJO，年代际变化，全球变化，湿静力能（MSE），冬季降水
Interdecadal Variation of MJO During the Boreal Winter in the Context of Global Climate Change and its influence on Precipitation in Southern
China
willandgrace
mr yin
Xiu Junyi(Meteorology)
neea edu cn
Directed by Wen Min
Abstract
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 Rearch (NCEP/NCAR)reanalysis data,etc.The underlying reason of MJO interdecadal variation and its influence on the southern China precipitation are also discusd.
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From the rapid warming period(1985–1997)to the warming hiatus period(2000–2012), frequencies of MJO in Phas2–4decread,while tho in Phas5–7incread 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 analys suggest that the interdecadal variation of MJO propagation is cloly related to the interdecadal fluctuation of global climate change.In negative phas 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)increa 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.
全球变化背景下冬季MJO传播的年代际变化及其对中国南方冬季降水的影响
感谢信 英文Wintertime precipitation in southern China is significantly modulated by the MJO propagation.In Pha
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s2–4,southern China experiences a wet condition.There are more precipitation and more rainy days than in Phas5–7,which are relative dry periods of southern China.In the warming hiatus period(2000–2012),decrea in frequencies in2–4 phas and increa in frequencies in5–7phas result in corresponding variations of wintertime precipitation in southern China.The rainy days decread,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 Phas2-4and5-7,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.
Keywords:MJO,Interdecadal variation,Global change,Moist static energy(MSE), Wintertime precipitation
