大气季节内振荡对印度洋—西太平洋地区热带低压/气旋生成的影响

MODULATION OF TROPICAL DEPRESSION/CYCLONE OVER THE INDIAN-WES TERN PACIFIC OCEANS BY MADDEN-JULIAN OSCILLATION

文中利用EOF分析大气季节内振荡 (MJO)的时空变化的方法 ,研究了 1996年 9月～ 1997年 6月间的MJO活动对生成在印度洋—西太平洋海域的热带低压 /气旋的影响。结果发现 ,除西北太平洋之外 ,发生在其他区域的热带低压 /气旋有半数以上生成在向东移动的MJO的湿位相中。伴随MJO的向东传播 ,热带低压 /气旋平均生成位置也随之向东移动 ,而生成在西北太平洋的热带低压

The Madden-Julian Oscillation (MJO) is a dominant mode of intraseasonal variabil ity in the tropical atmosphere; it is characterized by an eastward propagating t ropical convective anomalies and associated with circulation anomalies with a ti me period between 30 to 60 days. Since Madden and Julian firstly observed the MJ O (Madden and Julian, 1971), it has been extensively studied in the past decades . Studies suggested that the MJO has a baroclinic mixed Kelvin and Rossby wave s tructure in the Indian and the western Pacific Oceans, where the equatorial wave is strongly coupled to convection with eastward propagation in convection at ro ughly 5 m/s. Kelvin waves propagate eastward out of the convective regions is at phase speeds of 10～12 m/s (Hendon and Salby, 1994), and is generally manifeste d as an eastward propagating, equatorially-trapped, wave number one, baroclinic o scillation in the tropical wind field (Madden and Julian, 1994).A number of observational and modeling studies have suggested that, the MJO stro ngly affects on the tropical cyclogenesis. But fewer works have been found on th e discussion of tropical depression (TD) and tropical cyclone (TC) activities in both equatorial tropical regions, where the tropical cyclogenesis are probably modulated by MJO. In present study, a method used to explore the Madden-Julian o scillation (MJO) by using Empirical Orthogonal Function (EOF) was introduced, an d the modulation of tropical depression/cyclone (TD/TC) over the Indian-western Pacific Oceans by MJO has been addressed for the period of September 1996 to Jun e 1997 on the basis of daily NCAR/NCEP reanalyzed wind vector and Outgoing Longw ave Radiation (OLR) data sets, etc. Analysis has suggested that there are more ( less) TD/TCs, which formed in the wet (dry) phase of MJO convection, except thos e in the western North Pacific sectors, where the TD/TC can be alternatively aff ected by the eastward or westward propagating MJO. Along with the eastward propa gation of MJO convection, the region-averaged position of TD/TC occurrence also appears an eastward shift in spatial.