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南太平洋副热带偶极子的时空特征与大气环流变异
Alternative TitleSpatial and Temporal Characteristics of South Pacific Subtropical Dipole and Variability of General Circulation
李琼1,2
Subtype硕士
Thesis Advisor王法明
2016-05
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline气象学
Keyword南太平洋副热带偶极子 南太平洋辐合带 降水 大气环流
Abstract本文利用1948 ~2012年英国气象局Hadley中心的海温数据集HadISST资料以及NCEP-NCAR的大气再分析数据通过经验正交函数分解、合成分析和相关分析等方法,研究了南太平洋副热带偶极子(South Pacific Subtropical Dipole, SPSD)的时空特征以及正负偶极子事件年中南太平洋辐合带(South Pacific Convergence Zone, SPCZ)的大气环流变化。主要结果如下:
(1)南太平洋副热带偶极子的时空特征。南太平洋副热带偶极子是海温去除ENSO(El Niño-Southern Oscillation)后经验正交函数分解的第一模态(方差贡献25%),表现为东北区域与西南区域反位相的海温分布。在时间分布上,南太平洋副热带偶极子有着准四年的周期变化和很强的季节锁相,正偶极子事件期间在南半球春季(9~11月)东北极得热并且西南极失热形成较为稳定的偶极子模态,夏季(12~2月)偶极子达到峰值,之后热量得失情况发生转变,秋季(3~5月)东北极失热并且西南极得热,偶极子强度逐渐减弱。根据EOF第一模态的时间序列,确定正负偶极子事件年,在正负偶极子事件中厄尔尼诺和拉尼娜事件发生频次几乎是相等的,从侧面佐证了偶极子现象独立于ENSO存在。
(2)正负偶极子事件年中南太平洋辐合带区域的大气环流变化。位于峰值期间的南太平洋副热带偶极子(12-2月)与SPCZ区域滞后一个月降水(1-3月)之间的相关性最好,合成分析显示,正事件期间偶极子东北极区域(暖海温)主要受到低压中心控制,水汽辐合上升降水增多;而在偶极子西南极区域(冷海温)水汽辐散下沉降水减少,因此SPCZ降水带偏北。负偶极子事件则相反,东北极降水减少的同时西南极降水增多,从而SPCZ降水带偏南。垂直断面分析显示海温偶极子对大气有着较强的影响,从海表一直延伸到对流层中上层。正事件中降水位置与正海温异常区不完全重合的可能原因是大气对海洋响应的各物理要素从底层到高层向西南倾斜。
(3)对没有ENSO事件只发生正偶极子事件的1983年和只发生负偶极子事件的1990年做个例分析,其结果也很好的验证了偶极子的大气环流变化。在这两年中没有热带太平洋厄尔尼诺和拉尼娜事件的影响,其单独分析的结果与正负偶极子事件合成分析一致,正偶极子事件降水异常偏向东北区域,SPCZ位置偏北;负偶极子事件SPCZ南移。
本研究关于SPSD与SPCZ关系的分析,将有助于更好理解南太平洋的年际气候变异和海气相互作用。
Other AbstractThis study analyses the structure and variability of South Pacific Subtropical Dipole (SPSD) and SPSD general circulation effect in South Pacific Convergence Zone (SPCZ) by using HadISST of Hadley center and atmospheric reanalysis data of NCEP-NCAR from 1948 to 2012. The main results show as follows:
    (1) What is the structure and variability of South Pacific Subtropical Dipole. South Pacific Subtropical Dipole is the first mode of SSTA EOF with ENSO signal removed (variance ratio contribution is 25%) with SSTA outphase from north-east to south-west. South Pacific Subtropical Dipole has four years period and a strong phase locking. During positive dipole events, North-East pole obtains heat and South-West pole loses heat, then matured dipole mode forms in austral spring (September to November). Dipole peaks in austral summer (December to February) and the heat budget reverses, so its North-East pole loses heat and South-West pole obtains heat with strength gradually weakening during autumn (March to May). Dipole events are selected according to time series of EOF’ first mode, and the number of El Niño and La Niña events is equal both in positive and negative dipole events which laterally confirms that dipole events is independent on ENSO.
(2)The influence of SPSD on South Pacific Convergence Zone (SPCZ)  during positive and negative dipole events. The peaking SPSD clearly affects location of SPCZ precipitation. During positive dipole event, composite analyses show that north-east pole (warm SST) is controlled by low pressure center, and convergent moisture moves up, so this area has more precipitation. However, south of south-west pole of dipole(cool SST) is controlled by high pressure center, and divergence moisture moves down, so this area has less precipitation, and the SPCZ moves toward north. Negative dipole event is opposite, north-east pole has less precipitation while south-west has more, so the location of SPCZ precipitation moves south. The analyses of vertical section show SST dipole affects atmosphere strongly from sea surface to middle-upper layer of troposphere. The location of precipitation doesn’t exactly agree with SST variability area, and perhaps because physical variable of atmosphere lean to south-west from under layer to upper layer due to the effect of ocean.
(3)Typical cases without ENSO’s influence of only positive dipole year 1983 and only negative dipole year 1990 also show South Pacific Subtropical Dipole indeed affects SPCZ precipitation. During these two years, there are only dipole events without influence of El Niño and La Niña. The results of typical cases are the same as the composite results of dipole event, and north-east area has more precipitation during positive dipole event, and then SPCZ moves north. The SPCZ moves south during negative dipole event.
The results of this study provide more knowledge of relationship between SPSD and SPCZ, and it’s better to understand climate change and air-sea interaction in south Pacific.
Subject Area 大气科学
Language中文
Document Type学位论文
Identifierhttp://ir.qdio.ac.cn/handle/337002/112529
Collection海洋环流与波动重点实验室
Affiliation1.中国科学院海洋研究所
2.中国科学院大学
Recommended Citation
GB/T 7714
李琼. 南太平洋副热带偶极子的时空特征与大气环流变异[D]. 北京. 中国科学院大学,2016.
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