Opposite phases of the antarctic oscillation and relationships with intraseasonal to interannual activity in the tropics during the austral summer
Opposite phases of the antarctic oscillation and relationships with intraseasonal to interannual activity in the tropics during the austral summer
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DOI：
10.1175/jcli-3284.1
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发表时间：
2005-03-01
影响因子：
4.9
通讯作者：
Ambrizzi, T
中科院分区：
文献类型：
--
作者：
Carvalho, LMV;Jones, C;Ambrizzi, T
南极涛动（AAO）是在南半球中高纬度地区观测到的一种深层涛动。在本研究中，AAO模式被定义为从1979年至2000年逐日700 hPa高度距平获得的经验正交函数（EOF-1）的主导模式。这里的目标是确定每日的正和负AAO阶段和与热带季节内活动的关系以及南方夏季[12月-1月-2月（DJF）]期间厄尔尼诺-南方涛动（ENSO）阶段。正和负AAO阶段被定义为当每日的时间系数高于（或低于）DJF平均值的一个标准差时。低频海表温度变化，200百帕纬向风，和向外长波辐射（OLR）的复合材料表明，负（正）阶段的AAO占主导地位时，SST，对流和环流异常的模式类似厄尔尼诺（拉尼娜）阶段的ENSO。从南（北方）半球的热带到热带外的季节内活动增强与AAO的负（正）相位有关。此外，有迹象表明，AAO的负相位的开始与Madden-Julian振荡（MJO）的传播有关。印尼上空的季节内对流活动在AAO正位相时受到抑制。据推测，深对流在热带太平洋中部，这是有关厄尔尼诺或向东传播的MJO，或两者的结合现象，调制南半球环流，有利于负AAO阶段在DJF。AAO相位的交替似乎与副热带高空急流的纬向迁移和极地急流强度的变化有关。这反过来又会影响热带气旋的性质，如起源、最小/最大中心气压及其向赤道的传播。
The Antarctic Oscillation (AAO) has been observed as a deep oscillation in the mid- and high southern latitudes. In the present study, the AAO pattern is defined as the leading mode of the empirical orthogonal function (EOF-1) obtained from daily 700-hPa geopotential height anomalies from 1979 to 2000. Here the objective is to identify daily positive and negative AAO phases and relationships with intraseasonal activity in the Tropics and phases of the El Nino-Southern Oscillation (ENSO) during the austral summer [December-January-February (DJF)]. Positive and negative AAO phases are defined when the daily EOF-1 time coefficient is above (or below) one standard deviation of the DJF mean. Composites of low-frequency sea surface temperature variation, 200-hPa zonal wind, and outgoing longwave radiation (OLR) indicate that negative (positive) phases of the AAO are dominant when patterns of SST, convection, and circulation anomalies resemble El Nino (La Nina) phases of ENSO. Enhanced intraseasonal activity from the Tropics to the extratropics of the Southern (Northern) Hemisphere is associated with negative (positive) phases of the AAO. In addition, there is indication that the onset of negative phases of the AAO is related to the propagation of the Madden-Julian oscillation (MJO). Suppression of intraseasonal convective activity over Indonesia is observed in positive AAO phases. It is hypothesized that deep convection in the central tropical Pacific, which is related to either El Nino or eastward-propagating MJO, or a combination of both phenomena, modulates the Southern Hemisphere circulation and favors negative AAO phases during DJF. The alternation of AAO phases seems to be linked to the latitudinal migration of the subtropical upper-level jet and variations in the intensity of the polar jet. This, in turn, affects extratropical cyclone properties, such as origin, minimum/maximum central pressure, and their equatorward propagation.