东亚—西北太平洋地区夏季季节内振荡的年代际变化

本文重点分析对比热带夏季季节内振荡(Boreal Summer Intraseasonal Oscillation,BSISO)1987—1995年(P1),1996—2007年(P2)和2008—2017年(P3)三阶段东亚—西北太平洋地区(East Asian-Western North Pacific,EAWNP)5—9月BSISO年代际变化的季节内差异特征。结果表明,在P1和P3两阶段,5—7月EAWNP BSISO强度几乎相同,但P2中每个月均显著增强,表明5—7月EAWNP BSISO经历了P1—P2增强和P2—P3减弱的年代际变化。8月,EAWNP BSISO强度从P1到P3逐渐增强,P3阶段比P1有显著增强,孟加拉湾和东亚副热带区域的BSISO活动增强。和P1相比,南海地区BSISO活动在P2阶段异常活跃,在5—7月强度增强,并且北传显著。在P2阶段,负位相的太平洋年代际(Interdecadal Pacific Oscillation,IPO)对应的赤道西太平洋和印度洋海温增暖,及Walker环流的增强为5—7月BSISO活动提供了水汽和对流发展的有利条件,而南海地区北传对流的叠加作用以及南海海温增暖进一步加强了BSISO的强度和北传。在P3阶段,8月孟加拉湾BSISO活动增强,除了热带印度洋一致增暖和太平洋ENSO型海温为BSISO活动提供水汽和对流发展的条件外,70°~90°E区域局地Hadley环流引起的上升运动也对BSISO的强度增强和北传有贡献。

Decadal change in the boreal summer intraseasonal oscillation over the East Asian-Western North Pacific

This study instead focuses on the intraseasonal diversity of Boreal Summer Intraseasonal Oscillation (BSISO) decadal changes over the East Asia-Western North Pacific region (EAWNP) based on the comparisons between the three periods such as 1987-1995(P1),1996-2007(P2)and 2008-2017(P3)from May to September. Results indicate that a significant decadal enhanced (weakened) shift of EAWNP BSISO on May, June and July were detected from P1 to P2 (P2 to P3). Convection in the BSISO was active and propagated further northward in P2 over the South China Sea (SCS) during May-July. In August, EAWNP BSISO has enhanced from P1 to P2 and from P2 to P3, and the BSISO is most active over the subtropical area of East Asia in P3. During P2, the Sea Surface Temperature (SST) warming over the equatorial western Pacific and Indian Ocean associated with the negative phase of the Interdecadal Pacific Oscillation (IPO) and enhanced Walker circulation supplies favorable condition as moisture and the growth of the convection, and the merging process of the convection over SCS and the warmer SST in this region lead to the further enhancement and north-ward propagation of the BSISO. During P3, the BSISO is most active over the Bay of the Bengal on August. The Basin wide scale warming of SST in tropical Indian and western Pacific Oceans is benefit for the moisture supply and convective activity, and the ascending anomalies associated with the local Hadley circulation between 70°-90°E contributes to the growth of the BSISO and its northward propagation.