与不同El Nino相伴的IOD事件的季节演变特征对比

Contrasting seasonal evolution features of Indian Ocean Dipole accompanied with two-type El Nino

基于1951—2012年逐月海洋和大气多种要素的再分析资料,分析了与两类El Nino相伴的IOD(Indian Ocean Dipole,印度洋偶极子)事件盛期的海洋和大气异常特征,并进一步对比了与不同类型El Nino相伴的IOD事件的季节演变及对应的海气耦合过程。结果表明:两类IOD事件盛期时,暖海温强度和位置有显著差异。发生在东部型El Nino期间的IOD事件(简称EP-IOD)盛期,正(负)SSTA中心出现在热带西北(赤道东南)印度洋,强度相当,对应的热带印度洋—海洋大陆异常Walker环流强度较强、范围较大;与中部型CP El Nino相伴的IOD事件(简称CP-IOD)的正SSTA相对较弱,且偏于南印度洋,异常Walker环流较弱、较窄。在季节演变中,两类IOD事件期间的局地海气过程差异显著,伴随着西印度洋西南季风减弱和东印度洋异常东风加强,EP-IOD事件的发展以西正东负的偶极型异常海温的出现及加强为主要特征;而CP-IOD事件的发生发展则与西北印度洋异常冷海温的生消及南印度洋暖水的堆积相伴,表现为"-+-"三极型SSTA的出现并转为西正东负偶极型的过程,夏季时出现在东印度洋的异常东风以及赤道中印度洋低层负涡度异常水平环流对其发展具有重要作用。

The differences in the seasonal evolution features of Indian Ocean Dipole（IOD） accompanied with two-type E1 Nino have been investigated based on the observed dataset from 1951 to 2012.Here, this paper focuses on the ocean-atmosphere coupled processes over the tropical Indian Ocean during the evolution of IOD.Results show that, when IOD peaks, the intensity and location of the war- ming SST anomalies （SSTAs） are different between the IOD co-occurred with EP and CP E1 Nino. When IOD peaks during EP E1 Nino, tropical northwestern Indian Ocean warms up and the equatorial southeastern Indian Ocean cools off with a similar intensity, associated with a strong anomalous Walkercirculation rising over the western Indian Ocean and sinking over the Maritime Continent.But the warm SSTA locates southward over the central Indian Ocean at the peak of the IOD during CP E1 Nino, asso- ciated with weaker anomalous rising over central Indian Ocean.As to the seasonal evolution of the IOD co-occurred with EP E1 Nino, the warm and cool SSTAs develop intensely in summer then peak in au- tumn, which is resulted from the weak southwest summer monsoon over western Indian Ocean and the strong anomalous easterly over eastern Indian Ocean.By comparison, the evolution of IOD during CP E1 Nino is associated with the strong anomalous easterly over eastern Indian Ocean and anomalous negative vorticity winds in the low troposphere over the central Indian Ocean.The dipole SSTA develops when the west pole of the triple pattern SSTA decays, which is different from the IOD co-occurred with EP E1 Nino.