北大西洋高纬度海区湍流热通量对全球增暖的响应

The response of high-latitude North Atlantic surface turbulence heat flux to global warming

大西洋经向翻转环流(the Atlantic Meridional Overturning Circulation,AMOC)由低纬输送大量热量至高纬度北大西洋海区,并通过热通量由海洋输送给大气,主导了附近区域的气候形态,并对北半球尺度的气候变化产生显著影响。本文根据CMIP5多模式多增暖情景的预估模拟结果,通过与增暖前控制试验的对比发现,全球增暖可导致该海区湍流热通量的减小,且减小的幅度随增暖强度增大,模拟结果与观测一致。进一步研究发现,热通量的减小存在季节差异,冬季的减小幅度远大于夏季。结合淡水扰动试验的分析表明,全球增暖下AMOC强度的减弱导致大西洋经向热输送减少,进而导致高纬度北大西洋海洋向大气的热输送减小。

Immense heat of about1PW(1PW=1015W)is transported by Atlantic Meridional Overturning Circulation(AMOC)from the low latitude to high latitude North Atlantic(HNA),and then released to the local atmosphere through surface turbulent heat flux,thus dominating the pattern of the local climate and climate changes over the Northern Hemisphere on multiple scales.Based on limited observations,previous works have observed a weakening trend in the turbulent heat flux of the HNA over the last part of20th century,and have proposed that it is a result of global warming.To confirm these findings,in this study we investigate the response of HNA turbulent heat flux to global warming based on four warming scenario experiments of13CMIP5models.The results show that the HNA turbulent heat flux significantly decreases under a warming climate,and that its weakening magnitude is larger under warmer scenarios.For the strongest warming scenario of Rcp85,the multi model averaged reduced magnitude of the HNA turbulent heat flux reaches about40W·m2,which is nearly1/3of the value before warming.Furthermore,the results of multi model consistently show a stronger weakening of the HNA turbulent heat flux in winter.The multi model averaged reduced magnitude of the HNA turbulent heat flux in winter is close to about43W·m-2,but the value in summer is only about10W·m-2,signifying that its magnitude in summer is less than1/4that in summer.The weakened HNA turbulent heat flux under warming is attributed to the weakened AMOC and its related reduced oceanic heat transport to the HNA.The results of a water hosing experiment,using a fully coupled climate model of CCSM3,confirm the dominant contributions of weakened AMOC to reduced HNA turbulent heat flux under warming.The reduced turbulent heat flux of the HNA is a key factor to understanding the climate changes of the Northern Hemisphere under warming.