| 摘要: |
| 采用复经验正交函数展开（CEOF）等方法研究了热带海洋海表温度异常（SSTA）和北半球500hPa高度场异常（H500）的甚低频（LF）和准两年（QB）两种低频振荡的空间振幅和位相变化，发现SSTA变化信号在热带西太平洋最先出现，其后是热带中东太平洋，最后是热带印度洋和南海。副热带中西太平洋H500滞后于热带中东太平洋SSTA1-2月，H500的LF分量从副热带中西太平洋经西北太平洋至北美洲呈正负相间的驻波型振荡，而从H500的QB分量在该区域则呈现由低纬度向中高纬度传播的行进波特征。H500和SSTA的LF和QB分量极值位相都呈现一定的季节锁定特征，极端异常事件的出现与两种低频振荡的位相季节锁定的共性有关。 |
| 关键词: CEOF 甚低频振荡 准两年振荡 位相锁定 |
| DOI： |
| 分类号: |
| 基金项目:国家自然科学基金资助项目，49276250号;国家气候中心开放实验室96-6LCS-02课题资助项目 |
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| THE CHARACTER OF LOW-FREQUENCY OSCILLATION IN THE TROPIC OCEAN SST AND NORTHERN HEMISPHERE ATMOSPHERE CIRCULATION |
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LI Yong-ping1, DUAN Yi-hong1, LIU Qin-yu2, QIN Zeng-hao2
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1.Shanghai Typhoon Institute,Shanghai,200030;2.The Institute of Physical Oceanography,Ocean university of Qingdao,Qingdao,266003
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| Abstract: |
| The time series of Fourier expansion and a weights filter are used in this paper to separate two bands of low frequency. i.e. the quasi-biennial oscillation (QB) and 3-7 years low frequency (LF). It is shown that both LF and QB widely exist in the both fields of tropical sea surface temperature anomalies (SSTA) and atmosphere geopotential height at 500hPa level (H500) in the Northern Hemisphere. And that the fraction of total variance for LF is generally larger than that of the QB constituent.
The leading spatial structure and the phase relation as concisely described by a set of complex empirical orthogonal functions (CEOF), revealed that the SSTA anomalies in the tropical West Pacific varies out of phase, leading by 1 to 3 months those in the tropical Central and Ease Pacific and Indian Oceans. The subtropical West Pacific H500 signals lag 1-2 months those of SSTA anomalies in the Central Pacific. The variation of H500’s LF component in the subtropical West and Central Pacific become opposite in phase with the counterpart over the Northwest Pacific, but the H500’s QB signals in this region have a slight tendency to propagate northward.
The variation in phase of the low frequency oscillations, LF and QB, of SSTA in tropics and H500 in the Northern Hemisphere are closely related to annual cycles. As to the LF constituent, for example, most positive / negative extremes of SSTA in the tropical West Pacific are locked in from July to August and from November to December. While the negative / positive extremes of SSTA in the tropical Central and East Pacific and Indian Oceans are respectively locked in the time lagging behind from one to two months and two to three months to the appearance of extremes of SSTA in the tropical West Pacific. As well as the associated negative / positive extremes of H500 over the subtropical Central and West Pacific appear in the time lagging behind from one to two months to the appearance of extremes of SSTA in the tropical Central and East Pacific. However, the extremes of the QB constituent of the tropical SSTA and H500 are locked in relatively fixed months, for examples, most positive / negative extremes of SSTA in the tropical West Pacific are locked in from July to August, while those in the tropical Central and East Pacific and Indian Oceans are locked in from September to October and from October to November, as well as most negative / positive extremes of H500 are locked in from November to December.
Since both LF and QB constituents possess seasonal phase locking, a certain relationship has been found between these two kinds of low frequency oscillations which plays an important role in the happenings of El Nino. La Nina and anomalous atmospheric general circulation. |
| Key words: CEOF, Low-frequency oscillation, Quasi-biennial oscillation, Phase locking |
