熱帶大西洋對夏季西北太平洋副熱帶高壓的影響

Abstract

本研究的目的是分析年際尺度夏季西北太平洋副熱帶高壓 (WNPSH) 與熱帶大西洋海表溫度 (SST) 之間的關係。我們發現年際尺度的WNPSH變異在1980年代初期以後出現顯著增強，也從相關分析中發現WNPSH和SST的相關係數圖也在這時期發生明顯的改變。SST是影響WNPSH的重要因素之一，許多區域如北印度洋、西北太平洋、海洋大陸以及赤道中太平洋SST造成的效應已經被廣泛研究過，但是熱帶大西洋的影響卻較少被討論。 我們透過相關分析找到了與熱太大西洋海溫有顯著關係的太平洋/印度洋四極環流結構。也透過SVD分析，找到包含著四極結構環流場以及與其對應之海溫變異模態，即熱帶大西洋、北印度洋暖海溫，以及西北太平洋冷海溫等特徵。我們認為這和Wang et al. (2013) 透過主成分分析所找到的海氣交互作用模態十分相似，熱帶大西洋可能參與了北印度洋-西北太平洋耦合系統。我們利用ICTP AGCM/slab ocean model (Kucharski et al., 2013) 進行模擬，證實熱帶大西洋可以透過Walker Circulation，一方面使氣流沉降在西北太平洋，另一方面增強北印度洋-西北太平洋耦合系統，於是直接且間接增強WNPSH。

In this study, we target on the interannual relationship between the Western North Pacific Subtropical High (WNPSH) and the Tropical Atlantic sea surface temperature (SST) in the boreal summer. We find that the interannual variance of the WNPSH has become significantly larger after the early 1980s. The interannual correlation between the WNPSH index and global SST is also characterized by a shift on the late 1970s and early 1980s. SST is one of the important factors that affect the WNPSH. The effects of the SST fluctuation in the Northern Indian Ocean (NIO), the Western Pacific (WP), Marine Continent (MC) and the Equatorial Center Pacific (ECP) have been widely examined in recent years. But the effect of the Tropical Atlantic (TA) was hardly explored. The result of correlation analysis with the TA SST shows a quadrupole structure of streamfunction over Pacific and Indian Ocean. Using SVD analysis, we find the variability modes with the circulation patterns associated with the quadrupole structure of streamfunction and the corresponding SST pattern with warm SST in TA and NIO and cold SST in WNP. We think this mode is similar to the air-ocean interaction mode which found by Wang et al. (2013) via Principal Component Analysis. Numerical experiments using the ICTP AGCM/slab ocean model (Kucharski et al., 2013) confirm that the warm TA SST can cause the descending flow by Walker Circulation over the WNP, and also influence the NIO-WNP coupling system in the boreal summer, therefore enhance WNPSH directly and indirectly.