Seminars

The Sensitivity of the Tropical Atmosphere to Changes in Mixed-Layer Depth and Ocean Heat Flux Convergence Over the Indian Ocean

Wed., 1pm, via Webex [contact bklinger@gmu.edu for link)

The Madden-Julian Oscillation (MJO) is a tropical phenomenon that influences high-impact events such as hurricane activity and Asian monsoons on intraseasonal (2-8 week) time scales.  However, the essential dynamical mechanisms responsible for the MJO are highly debated. Specifically, the role of the ocean on the MJO is unclear. Ocean dynamics has a negligible impact on atmospheric intraseasonal variability. Therefore, to gain insight into MJO-ocean interactions, we conduct climate model experiments where the ocean is replaced by a motionless slab whose thickness, called the mixed-layer-depth (MLD), varies in space but not in time. This slab-model configuration allows the atmosphere and ocean to communicate through surface fluxes of heat and moisture while suppressing interactive ocean currents. Consistent with previous studies, the MJO is nearly indistinguishable between the fully-coupled and slab-models. However, drastic changes in the MLD and ocean heat convergence over the Indian Ocean had no discernible impact on MJO propagation, predictability, or variability. This suggests that atmosphere-ocean coupling may not be critical to the MJO over the Indian Ocean.  A discriminant analysis technique used to optimize the differences between experiments reveals that differences caused by changing Indian Ocean MLD were restricted mostly to surface fluxes and could be explained by simple physics. Despite precautions to preserve the climate, the control slab has a warmer climate than the fully coupled model.  Generally,  differences between fully coupled and slab models were consistent with changes associated with global warming, particularly the ``wet-gets-wetter" mechanism in a warmer climate.