太平洋沃克环流近几十年来的加强

摘要

太平洋沃克环流的强度随全球变暖而减弱, 但有研究表明近几十年太平洋沃克环流呈增强趋势, 两者是否矛盾?文章用 1979 年至 2014 年的再分析数据资料分析了近几十年来太平洋沃克环流强度的变化特征, 各要素场均表明太平洋沃克环流的强度在过去几十年呈显著的增强趋势, 且太平洋沃克环流的强度在年际变化尺度上与 ENSO 相关性很强.之前有关太平洋沃克环流的研究多局限于太平洋海盆内部, 文章通过印太三极模态理论对太平洋沃克环流的年代际变化进行解释.研究发现, 印度洋沃克环流与太平洋沃克环流存在同样的增强趋势.印太暖池海温、印度洋?太平洋沃克环流及海洋性大陆区域上升运动组成了一个简单的反馈系统, 暖池海温的升高使海洋性大陆区域大气辐聚上升运动增强, 两沃克环流随之增强; 底层纬向风的增强使暖池区域的暖水堆积增多, 从而使暖池区海温进一步升高, 两沃克环流也进一步增强.同时近几十年太平洋年代际振荡(PDO)由暖位相到冷位相的转换导致中东太平洋海温降低, 暖池增暖及中东太平洋变冷使太平洋海温梯度增加, 最终导致太平洋沃克环流过去几十年的增强.%There is evidence showing a long-term weakened trend of the tropical Pacific Walker Circulation under global warming condition, consistent with the expectation that the circulation will be weakened further. But recent research shows that the Walker Circulation has intensified over the recent decades. Is there any contradiction between the two? We analyzed the strength change of the Walker Circulation during the last decades using the reanalysis data of the tropical Pacific over the 36-year period from 1979 to 2014. The result showed an overall trend towards a stronger La Ni?a-like Walker Circulation. On the interannual timescale, the El Ni?o-Southern Oscillation (ENSO) accounts for much of the variability in the Pacific Walker Circulation; but the strengthening of the Pacific Walker Circulation in the recent decades cannot be explained by global warming or ENSO. The Indo-West Pacific sea surface temperature (SST), the Indian Ocean-Pacific Walker Circulation, the SST over the Indo-Pacific region, and Maritime Continent area's upward movement constituted a simple positive feedback system: stronger Walker Circulation accelerates more warm water to the warm pool area. Warmer SST in the warm pool region strengthens the convergence and upward motion over the Maritime Continent, which makes the Walker Circulation stronger. Besides, the Pacific Decadal Oscillation (PDO) was in the transition from cold phase to warm phase over the past decades, which intensified Pacific zonal SST gradient. The tropical Indo-West Pacific warming, tropical central eastern Pacific cooling and a closer connection between the two basins were the reasons of enhancement of Pacific Walker Circulation over the past decades.