18.07.2018: FB1-Seminar

11:00 Uhr, Hörsaal, Düsternbrooker Weg 20

Recent decadal variations in subsurface ocean heat content (OHC) in the Indian Ocean (IO) are investigated using ocean reanalyses and a hierarchy of model experiments. We examine how conditions in the tropical Pacific modulate those in the Indian Ocean on decadal time scales through both oceanic and atmospheric pathways, and estimate the contributions of the Pacific relative to those associated with external forcing of the climate system. The spatial pattern of the leading mode of decadal Indian Ocean OHC variability closely matches the regression pattern of OHC on the interdecadal Pacific oscillation, emphasizing the role of the Pacific in determining Indian Ocean OHC decadal variability. Decadal variations of OHC in the eastern IO are attributed in part to western Pacific surface wind anomalies, which trigger oceanic Rossby wave propagating westward through the Indonesian Seas and influence the Indonesian Throughflow transport to impact the eastern IO, and in part to zonal wind anomalies over the central tropical IO, which trigger eastward-propagating Kelvin waves. Decadal variations of OHC in the western IO are linked to conditions in the Pacific via changes in the atmospheric Walker cell, which trigger anomalous wind stress curl and Ekman pumping in the central tropical IO. Westward-propagating oceanic Rossby waves extend the influence of this anomalous Ekman pumping into the western IO. Additional support for these interpretations are provided by a linear Rossby wave model forced by reanalysis-based wind stresses and eastern boundary conditions, OGCM hindcast experiments forced by interannual atmospheric boundary conditions applied only over the Pacific and Indian Oceans, and a paired ensemble of coupled model experiments in which SST anomalies are specified or left free to evolve in the tropical eastern Pacific.

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