Regime shifts found in the Northern Hemisphere SST field
Regime shifts found in the Northern Hemisphere SST field
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DOI：
10.2151/jmsj.80.119
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发表时间：
2002-02
影响因子：
3.1
通讯作者：
S. Yasunaka;K. Hanawa
中科院分区：
文献类型：
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作者：
S. Yasunaka;K. Hanawa
“状态转移”的特征是从一种准稳定的气候状态突然过渡到另一种气候状态，其过渡期远短于每个气候状态的个别时期的长度。本文利用北半球冬季海表温度场，研究了气候变化发生的时间以及变化前后气候状态的差异。研究了海温场变化与大气环流变化的关系。为了检测海温变化的有组织模式，我们采用了经验正交函数（EOF）分析。结果表明，第一模态与厄尔尼诺/南方涛动（ENSO）和所谓的太平洋年代际涛动（PDO）相同，与太平洋/北美（PNA）模态相对应。第二个模态与北极涛动（AO）有关，在北大西洋和北太平洋都有纬向拉长的信号。分别对各大洋盆地进行了EOF分析，并验证了这些模型的鲁棒性。在本研究中，我们将政权转移定义为两个准稳定状态之间的“显著”和“系统”变化，持续时间超过5年。然后，为了识别海温场发生变化的年份，我们仔细检查了原始网格化海温数据和EOF模态的时间序列。因此，在20世纪10年代至90年代的研究期间发现了6次变化：1925/26年、1945/46年、1957/58年、1970/71年、1976/77年和1988/89年。可以确定，几乎所有电网的转换都在一年内完成。所有的状态变化都具有相似的海温和大气环流型，包括阿留申低压（AL）强度的变化，以及相应的北太平洋中部海温变化。所有的态移都可以用第一模态和第二模态的组合来描述。每次体制转变之间的间隔时间约为10年，与PDO相同。第一和第二EOF模式的同时变化，暗示与PNA模式相关的AL活动的变化可能与AO的变化有某种联系。
A 'regime shift' is characterized by an abrupt transition from one quasi-steady climatic state to another, and its transition period is much shorter than the lengths of the individual epochs of each climatic state. In the present study, we investigate when regime shifts occurred and what was the difference in climatic states before and after the shifts, using the wintertime sea surface temperature (SST) field in the Northern Hemisphere. The relationship between changes in the SST field, and those in the atmospheric circulation, is also investigated. In order to detect organized patterns of the SST variations, we apply an empirical orthogonal function (EOF) analysis. As the results, the first mode is identical to El Nino/Southern Oscillation (ENSO) and so-called Pacific Decadal Oscillation (PDO), and corresponds to the Pacific/North American (PNA) pattern. The second mode, which relates to the Arctic Oscillation (AO), has a zonally elongated signal in both the North Atlantic, and North Pacific. EOF analyses to each oceanic basin are made separately, and the robustness of these modes is confirmed. In the present study, we define the regime shifts as the 'significant' and 'systematic' changes between the two quasi-steady states, continuing more than 5 years. Then, in order to identify the years when regime shifts occurred in the SST field, we carefully inspect the time series of original gridded SST data and those of the EOF modes. As a result, six regime shifts are detected in the study period from the 1910s to the 1990s: 1925/26, 1945/46, 1957/58, 1970/71, 1976/77 and 1988/89. It is ascertained that the shifts at almost all grids are completed within one year. All regime shifts having similar SST and atmospheric circulation pattern, including the changes in an intensity of the Aleutian Low (AL), and the corresponding SST changes in the central North Pacific. All regime shifts can be well described by the combination of the first and the second EOF modes. The duration between each regime shift is about 10 years, which are identical to the PDO. The simultaneous shifts in the first, and the second EOF modes, imply that the change in the AL activity associated with the PNA pattern, might have some connection with that of the AO.