热带大西洋对全球变暖的响应

Response of the tropical Atlantic Ocean to global warming in CESM

与太平洋和印度洋不同,全球变暖下热带大西洋变化的研究较少。本文使用地球系统模型CESM(Community Earth System Model),发现全球变暖后热带大西洋在秋季的升温类似大西洋尼诺(Atlantic Ni?o)的正位相,即大西洋西部增暖幅度小于东部;在夏季类似大西洋尼诺的负位相,即大西洋西部增暖幅度大于东部。利用覆盖(overriding)技术,分离了风应力、风速和CO2的直接热效应对海洋升温的作用,探讨了大西洋尼诺本身和全球变暖作用下类似大西洋尼诺正位相(下文简称"类大西洋尼诺升温")的形成机制。结果表明,这两种情况下的形成机制基本相同,风应力的变化是导致大西洋东部暖异常的主要机制。但两者之间也存在区别:1)全球变暖下海表温度的季节变化振幅减小,而大西洋尼诺时变化不大;2)全球变暖下西风异常主要集中在大西洋东部,而大西洋尼诺时主要集中在大西洋中部;3)除风应力外, CO2的热效应对类尼诺升温的变化也有一定影响。

There has been little discussion of the changes in the tropical Atlantic attributable to global warming(GW).Here,we used the Community Earth System Model(CESM),and found that GW induces an Atlantic Nino-like warming pattern in boreal autumn and a cold Atlantic Nino-like warming pattern in boreal summer in the tropical Atlantic Ocean.Applying an overriding technique to the CESM’s ocean component(version 2 of the Parallel Ocean Program),this study isolated the effects of wind stress,wind speed,and thermal warming on the response of the tropical Atlantic Ocean to global warming,and,further,investigated the similarities and differences in formation mechanisms underlying the changes in the tropical Atlantic Ocean between the Atlantic Nino and GW.Results showed that the underlying formation mechanism was quite similar in both cases,with wind-thermocline-SST feedback being the leading mechanism producing the anomalous warming over the eastern tropics in both cases.There were also some significant distinctions between them:1)GW featured an overall reduction in amplitude and phase advance of the seasonal cycle of the mesosphere-lower troposphere(MLT)while the Atlantic Nino caused less disruption of the seasonal cycle;2)westerly wind anomalies were most prominent in the eastern equatorial Atlantic during the warm phase of GW while in the central equatorial Atlantic during the warm Atlantic Nino;3)air-sea interactions made some contribution to GW,however to a lesser degree than the wind stress effect.