Joint Seminar: Subseasonal to seasonal drivers of upper Ocean Heat Content in the equatorial Indian Ocean

Subseasonal to seasonal (S2S) mixed layer temperature (MLT) and sea surface temperature (SST) variations in the equatorial Indian Ocean are largely consistent with surface heat fluxes driving temperature variability on these timescales. Recently, interest has been directed to how equatorial wave dynamics, in particular, westward propagating Rossby waves, can have a lagged feedback on atmospheric intraseasonal variability via its modulation of upper Ocean Heat Content (OHC) and mixed layer depth, thereby being important for atmosphere-ocean coupling. With that motivation, this study utilized the fourth release of the Estimating the Circulation and Climate of the Ocean (ECCO) Version 4, an observationally constrained but physically consistent estimate of the ocean’s time evolving state to understand the physical processes driving S2S variations of OHC in the upper 200 m of the equatorial Indian Ocean. This depth is chosen as it is seen to sufficiently capture the maximum signal of S2S temperature variations. The strongest signal of S2S temperature variations (> 0.5°C) occurs below the mixed layer and at depths of between 50 - 150 m. OHC variability along the equator is seen to be consistent with Kelvin wave, while the off-equatorial OHC variability is consistent with westward propagating Rossby waves, demonstrating the important role of equatorial waves in modulating OHC variability in the region. A heat budget analysis composited for the Madden–Julian Oscillation (MJO) phases revealed horizontal advection to be the most important driver of OHC variability. Along the equator, zonal advection was seen to be the most important driver of OHC variations, while in the off-equatorial region, meridional advection dominated the variability.




15:15 h


Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg


Bo Liu

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