Tropical-Extratropical Teleconnections in Boreal Summer: Observed Interannual Variability
Tropical-Extratropical Teleconnections in Boreal Summer: Observed Interannual Variability
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DOI：
10.1175/2011jcli3621.1
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发表时间：
2011-04-01
影响因子：
4.9
通讯作者：
Branstator, Grant
中科院分区：
文献类型：
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作者：
Ding, Qinghua;Wang, Bin;Branstator, Grant
对1948-2009年62年期间记录的北半球夏季、热带降雨和北方200 hPa高度场进行最大协方差分析。领先的模式，它优先出现在夏季前的厄尔尼诺-南方涛动（ENSO）周期的峰值阶段，涉及环全球遥相关（COT）模式在北半球热带外200百帕高度场与印度季风降水异常观察。第二种模式，往往发生在夏季ENSO高峰期后，涉及西太平洋北美（WPNA）遥相关模式的高度场观察到与西北太平洋夏季风降水异常。CGT型主要是沿西风波导沿着纬向波列，而WPNA型则是从西太平洋季风槽发出并沿大圆运动的波列。COT是伴随着一个明显的热带外热带跷跷板在纬向对称的位势高度场和温度场，和WPNA观察与半球均匀异常。这些与厄尔尼诺/南方涛动有关的特征调节热带和热带外的地面气温。ENSO还通过调制印度和西北太平洋季风的强度，间接影响COT和WPNA的波结构。线性正压机制，包括能量传播和正压不稳定的基本状态流，也起到塑造和维持COT。这些研究结果的季节性预测的NH热带外环流的影响进行了讨论。
Maximum covariance analysis is performed on the fields of boreal summer, tropical rainfall, and Northern Hemisphere (NH) 200-hPa height for the 62-yr period of record of 1948-2009. The leading mode, which appears preferentially in summers preceding the peak phases of the El Nino-Southern Oscillation (ENSO) cycle, involves a circumglobal teleconnection (COT) pattern in the NH extratropical 200-hPa height field observed in association with Indian monsoon rainfall anomalies. The second mode, which tends to occur in summers following ENSO peak phases, involves a western Pacific North America (WPNA) teleconnection pattern in the height field observed in association with western North Pacific summer monsoon rainfall anomalies. The CGT pattern is primarily a zonally oriented wave train along the westerly waveguide, while the WPNA pattern is a wave train emanating from the western Pacific monsoon trough and following a great circle. The COT is accompanied by a pronounced tropical extratropical seesaw in the zonally symmetric geopotential height and temperature fields, and the WPNA is observed in association with hemispherically uniform anomalies. These ENSO-related features modulate surface air temperature in both the tropics and extratropics. ENSO also affects the wave structure of the COT and WPNA indirectly, by modulating the strengths of the Indian and western North Pacific monsoons. Linear barotropic mechanisms, including energy propagation and barotropic instability of the basic-state flow, also act to shape and maintain the COT. The implications of these findings for seasonal prediction of the NH extratropical circulation are discussed.