Reciprocity in the Indian Ocean: Intraseasonal Oscillation and Ocean Planetary Waves

During the intraseasonal oscillation (ISO) in the tropical Indian Ocean, a recent study observed an interesting relationship between atmospheric convection and ocean heat content anomalies. Ocean heat content anomalies maximize during periods of enhanced convection. Using that study as motivation, the processes responsible for this behavior are further investigated using satellite observations and a state-of-the-art ocean reanalysis. These data show that ocean dynamics linked to first baroclinic mode equatorial Rossby (ER) waves are responsible for the routine synchronization of anomalous ocean heat content and atmospheric convection during the ISO. Using a novel index to identify oceanic ER waves in the Indian Ocean, we observe the following sequence of events indicative of two-way feedbacks between large-scale intraseasonal modes in the atmosphere and ocean: (a) Westerly wind stress associated with the enhanced convective phase of the ISO piles mass in the eastern Indian Ocean forcing a westward oriented pressure gradient along the equator. (b) The easterly wind stress that immediately follows combines with the pressure gradient forcing to generate downwelling ER waves that slowly propagate westward. (c) The waves maximize in the central Indian Ocean where they depress the isotherms and increase the ocean heat content as the next enhanced convective phase of the ISO passes and intensifies. The entire feedback loop transpires over 90 days.