5:15 PM - 7:15 PM
[ACG43-P07] Importance of the Western Boundary Component of the Subtropical Cells on Ocean Heat Content Variability associated with Tropical Pacific Decadal Variability
Keywords:Subtropical Cells, Tropical Pacific Decadal Variability
The decadal to interdecadal climate variability in the tropical Pacific, referred to as the Tropical Pacific Decadal Variability (TPDV), is known to have significant global climate impacts, and better understanding of their underlying mechanisms is a crucial task. It is believed that such decadal variability in the heat content anomaly in the tropical Pacific is regulated by the changes of the heat transport across the subtropics-tropics boundaries through shallow meridional overturning circulation called the Subtropical Cells (STCs).
The variation of the STCs includes the horizontal component, consisting of the transport within the interior ocean far from the boundaries (IN) and the western boundary currents (BC) other than the meridional overturning component, consisting of the surface Ekman transport (EKM) and the IN. Although most of the studies evaluated the role of the STCs by focusing on the IN, the variation of the BC, which is known to compensate that of the IN, could have significant impacts on the heat transport across the subtropics-tropics boundaries.
In this study, the role of the STCs in the TPDV is revisited in detail using outputs from an eddy resolving OGCM, with a particular focus on the contribution of the BC in terms of the meridional heat transport across 10N/S. The decadal variations of the meridional heat transport convergence by the STCs largely explain those of the ocean heat content in the tropical Pacific. Comparison of the heat transport variations among branches of the STCs, i.e. the EKM, IN and BC shows that a significant part of the IN is compensated by the BC in the Northern Hemisphere and about a half of the IN in the Southern Hemisphere. It turns out that the rate of compensation greatly varies over the study period depending on the compensation among the overturning components, particularly in the Northern Hemisphere. These results clearly demonstrate the importance of the BC for the quantitative assessment of the role of STCs in the TPDV.
The variation of the STCs includes the horizontal component, consisting of the transport within the interior ocean far from the boundaries (IN) and the western boundary currents (BC) other than the meridional overturning component, consisting of the surface Ekman transport (EKM) and the IN. Although most of the studies evaluated the role of the STCs by focusing on the IN, the variation of the BC, which is known to compensate that of the IN, could have significant impacts on the heat transport across the subtropics-tropics boundaries.
In this study, the role of the STCs in the TPDV is revisited in detail using outputs from an eddy resolving OGCM, with a particular focus on the contribution of the BC in terms of the meridional heat transport across 10N/S. The decadal variations of the meridional heat transport convergence by the STCs largely explain those of the ocean heat content in the tropical Pacific. Comparison of the heat transport variations among branches of the STCs, i.e. the EKM, IN and BC shows that a significant part of the IN is compensated by the BC in the Northern Hemisphere and about a half of the IN in the Southern Hemisphere. It turns out that the rate of compensation greatly varies over the study period depending on the compensation among the overturning components, particularly in the Northern Hemisphere. These results clearly demonstrate the importance of the BC for the quantitative assessment of the role of STCs in the TPDV.