全球变暖背景下春季Hadley环流与东亚夏季风环流年际对应关系的多模式预估

摘要

观测事实揭示,春季Hadley环流在年际时间尺度上与东亚夏季风环流和降水具有密切联系.在未来全球变暖背景下,春季Hadley环流与东亚夏季风环流和降水的这种年际关系是否会发生变化?针对该问题,本文在评估的基础上选取五个气候模式,分析了AlB排放情景下春季北半球Hadley环流年际变率的未来变化及其与东亚夏季风环流和降水的年际关系.多模式集合(MME)预估结果表明,在全球变暖背景下,与20世纪末期(1970-1999年)相比,到21世纪末期(2070-2099年),春季北半球Hadley环流的年际变率强度将减弱,减弱幅度达32％.随着春季Hadley环流年际变率的减弱,其与夏季西太平洋副热带高压和东亚夏季风强度的联系将变弱.MME模拟结果还显示,春季Hadley环流与夏季东亚西风急流和降水的关系也降低,但各单个模式间存在较大差异.%Observations indicate that spring Hadley circulation is tightly linked to East Asian summer circulations and precipitation on the interannual timescale. Whether does such a relationship as in the observation tend to change under the background of global warming in the future? To answer this question, five climate models (GFDL_CM2_0, GFDL_CM2_ 1, IAP_ FGOALS_1. Og, NCAR_CCSM, UKMO_HADCM3) , which can well reproduce the observed interannual variability of spring Hadley circulation in the Northern Hemisphere and its linkage to East Asian summer atmospheric circulations and precipitation are firstly chosen based on overall assessment of models' simulation ability. Then, the potential change of the interannual variability of spring Hadley circulation and its interannual connection with East Asian summer circulations and precipitation under the A1B scenario are projected by using the outputs of these five climate models. To facilitate quantitative estimation of their change, five indices are exploited in this study. The Northern Hemispheric Hadley circulation index (HCI) is defined as the maximum value of the zonal mean mass stream function occurring within the latitudinal zone of 0°-30°N, and the western Pacific subtropical high index (WPSHI) as the 850 hPa geopotential height anomalies averaged over the region (10°N-30°N,110°E-150°E). The difference of zonal wind anomalies at 850 hPa between the region (10°N-20°N,100°E-150°E) and (25°N-35°N,100°E-150°E) and that at 200 hPa between the region (25°N-35°N,80°E-150°E) and (40°N-50°N,80°E-150°E) are used to define the East Asian summer monsoon index (EASMI) and the East Asian Jet index (EAJI) , respectively. The East Asian rainfall index is represented by mean precipitation over the region (27°N-32°N, 110°E- 130°E). The multi-model ensemble (MME) results show that the interannual variability of the Northern Hemispheric Hadley circulation in spring tends to decrease by 23% in the late 21s' century (2070-2099) compared to the late 20th century (1970-1999). Concurrent with the decreased interannual variability of spring Hadley circulation, its linkage to summer western Pacific subtropical high and East Asian summer monsoon is also projected to be weakened. The correlation coefficients between spring HCI and summer WPSHI (EASMI) decrease from 0. 44 ( - 0. 46) in the late 20th century to 0. 19 ( - 0. 15) in the late 21st century. Such a change can be simulated consistently by individual models. In addition, the MME results suggest that the association of spring Hadley circulation with summer East Asian jet and precipitation will also be weakened. However, there are discrepancies in the change of their relationship between individual models.