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），MJO 2~4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）处于负位相时，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MSE的变化可能是MJO传播年代际变化的重要原因。
关键词:MJO(Madden-Julian Oscillation)/
年代际变化/
全球变化/
湿静力能(MSE)
Abstract:Characteristics of interdecadal variation of the Madden-Julian Oscillation (MJO) during the boreal winter in the context of global climate change are investigated by using the real-time multivariate MJO (RMM) index, the National Oceanic and Atmospheric Administration (NOAA) daily outgoing longwave radiation data and the National Centers for Environmental Prediction/Nation Center for Atmospheric Research (NCEP/NCAR) reanalysis data, etc. It is found that from the rapid warming period (1985-1997) to the warming hiatus period (2000-2012), the frequencies of MJO in 2-4 phases decreased, while those in 5-7 phases increased obviously. This indicates that the 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 interdecadal fluctuation of global climate change. In negative phases of Pacific Decadal Oscillation (PDO), global warming slows down, and the tropical eastern IO-western Pacific is abnormally warmer than normal, which favors the enhancement of convection and associated ascending motion. Thus, the atmospheric circulation at low-level converges, and moisture and the moist static energy (MSE) increase over the Maritime Continent. When the 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 the tropical IO. However, when the 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 the MJO convective center, and the propagation of MJO slows down. Therefore, the interdecadal variation of MJO propagation is significantly modulated by the PDO in the context of global climate change through the interdecadal changes of atmospheric moisture content and MSE.
Key words:Madden-Julian Oscillation (MJO)/
Interdecadal variation/
Global change/
Moist static energy (MSE)
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