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南海地区大气30~60天低频振荡及其对南海夏季风的可能影响
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国家重点基础研究发展规划项目2009CB421405, 国家自然科学基金资助项目41025017、 40921160379


Tropical Low Frequency Oscillations with 30-60 Day Period and Its Possible Influence on the South China Sea Summer Monsoon
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    摘要:

    本文利用1979~2008 年美国国家环境预报中心(NCEP)和美国国家大气研究中心(NCAR)第二套再分析资料、美国国家海洋和大气管理局(NOAA)的向外长波辐射(OLR)资料及1979~2007年全球降水资料(CMAP), 分析了南海地区热带大气的低频振荡及其对南海夏季风的可能影响。结果表明, 夏半年南海地区存在显著的30~60天的周期振荡。当30~60天低频振荡处于活跃位相时, 南海及其周围地区的低层大气为低频西南风, 南海和菲律宾北部为低频气旋流场且为正的位涡度, 对应着增强的南海夏季风槽和南海夏季风; 当 30~60天低频振荡处于不活跃位相时, 情形正好相反。进一步的研究揭示出, 夏半年30~60天低频振荡变化的空间型与夏半年平均场的年际变化的空间分布非常相似, 并且南海及其附近地区的 30~60天低频振荡活动的年际变化对夏半年平均场的年际变化有显著的贡献。强、弱南海夏季风年30~60天低频振荡活动的比较也说明, 强的南海夏季风年30~60天低频振荡活跃状态发生的概率大于不活跃状态发生的概率, 而弱的南海夏季风年则是不活跃状态发生的概率大于活跃状态发生的概率。因此, 南海地区30~60天低频振荡对南海夏季风很可能有重要影响, 当30~60天低频振荡的活跃状态处于主导时, 南海夏季风往往会偏强; 反之, 如果不活跃状态处于主导时, 南海夏季风往往会偏弱。

    Abstract:

    The tropical low frequency oscillation and its possible influence on the South China Sea (SCS) summer monsoon are studied by using the daily NCEP/NCAR-2 (National Centers for Environmental Prediction and National Center for Atmospheric Research) reanalysis data and the outgoing long-wave radiation (OLR) data from NOAA (National Oceanic and Atmospheric Administration) for the time period of 1979-2008, and the CPC Merged Analysis of Precipitation (CMAP) data for the time period of 1979-2007. Results reveal that there are significant low frequency oscillations with 30-60 day period over the SCS region. When the 30-60 day oscillation is in an active state, the low frequency components of southwesterly prevail over the SCS and the cyclonic circulation appears in northern SCS. Hence, in the active state the low frequency oscillation tends to strengthen the South China Sea summer monsoon (SCSSM) trough and the SCS summer monsoon. In the inactive state of the low frequency oscillation, the situation tends to be opposite. Further researches indicate that the spatial pattern for the variability of the low frequency oscillation is analogous to that for the interannual variations of the SCS summer monsoon. Particularly the variance of low frequency oscillation activity in the SCS region can account for nearly half of that for the interannual variations of the SCS summer monsoon. The comparison between strong and weak SCS summer monsoon years presents that the occurrence probability of active state is higher than that of inactive state for the low frequency oscillation in strong monsoon years. However, in weak monsoon years the occurrence probability of inactive state is higher than that of active state. Therefore, the low frequency oscillation with 30-60 day period likely has an important influence on the SCS summer monsoon. When the active state is dominant for the low frequency oscillation, the SCS summer monsoon tends to be strong. On the contrary, the SCS summer monsoon tends to be weak when the inactive state is dominant for the low frequency oscillation.

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陈尚锋,温之平,陈文.南海地区大气30~60天低频振荡及其对南海夏季风的可能影响.大气科学,2011,35(5):982~992 CHEN Shangfeng, WEN Zhiping, CHEN Wen. Tropical Low Frequency Oscillations with 30-60 Day Period and Its Possible Influence on the South China Sea Summer Monsoon. Chinese Journal of Atmospheric Sciences (in Chinese),2011,35(5):982~992

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