16:30 〜 16:45
[ACG33-11] The mechanisms of the suppressed warming over the subtropical South Pacific Ocean
キーワード：地球温暖化、アトリビューション、大気海洋相互作用、二酸化炭素直接効果
It remains a highly debated issue that GCMs don’t reproduce the observed La Nina-like SST trend in these 45 years in the equatorial Pacific. Some recent studies suggest that cooling in the eastern South Pacific can induce La Nina-like SST pattern in the equator, and Attention is being focused on the role of the South Pacific. Although GCMs don’t reproduce the observed equatorial Pacific SST warming, GCMs reproduce suppressed warming in the South Pacific to some degree. The suppressed warming over the South Pacific is a ubiquitous feature among the observations, CGCM, and even slab ocean model, however, there is too little discussion on the mechanisms of the suppressed warming.
This study investigates the mechanisms of the suppressed warming over the subtropical South Pacific in response to GHGs by using MIROC6 large ensemble dataset of a single-forcing experiment called hist-GHG with 50 members, which enables us to investigate climate change forced solely by historical GHG variations. In addition, the contribution of the GHGs’ direct effect was estimated from an AGCM experiment where the SST is fixed to the piControl climatology, and only the historical GHG concentration variations are provided.
Our mixed-layer heat budget analysis suggests that the suppressed warming over the South Pacific is mainly explained by the enhancement of trade winds and Ekman upwelling driven by GHG’s direct effect rather than WES feedback and Newtonian cooling. GHGs bring anticyclonic anomalies to 40°S in the Pacific Ocean without SST change and enhance trade winds. The anticyclonic anomalies in the Pacific are caused by land-ocean warming contrast due to the smaller heat capacity of land rather than by the climate adjustment process owing to GHGs. This high-pressure anomaly in GHGs’ direct effect is consistent among all CMIP6 models.
This study investigates the mechanisms of the suppressed warming over the subtropical South Pacific in response to GHGs by using MIROC6 large ensemble dataset of a single-forcing experiment called hist-GHG with 50 members, which enables us to investigate climate change forced solely by historical GHG variations. In addition, the contribution of the GHGs’ direct effect was estimated from an AGCM experiment where the SST is fixed to the piControl climatology, and only the historical GHG concentration variations are provided.
Our mixed-layer heat budget analysis suggests that the suppressed warming over the South Pacific is mainly explained by the enhancement of trade winds and Ekman upwelling driven by GHG’s direct effect rather than WES feedback and Newtonian cooling. GHGs bring anticyclonic anomalies to 40°S in the Pacific Ocean without SST change and enhance trade winds. The anticyclonic anomalies in the Pacific are caused by land-ocean warming contrast due to the smaller heat capacity of land rather than by the climate adjustment process owing to GHGs. This high-pressure anomaly in GHGs’ direct effect is consistent among all CMIP6 models.