Intraseasonal sea surface warming in the western Indian Ocean by oceanic equatorial Rossby waves. Issue 9 (9th May 2017) - Rydbeck, Adam V.
Abstract: A novel process is identified whereby equatorial Rossby (ER) waves maintain warm sea surface temperature (SST) anomalies against cooling by processes related to atmospheric convection in the western Indian Ocean. As downwelling ER waves enter the western Indian Ocean, SST anomalies of +0.15°C develop near 60°E. These SST anomalies are hypothesized to stimulate convective onset of the Madden‐Julian Oscillation. The upper ocean warming that manifests in response to downwelling ER waves is examined in a mixed layer heat budget using observational and reanalysis products, respectively. In the heat budget, horizontal advection is the leading contributor to warming, in part due to an equatorial westward jet of 80 cm s −1 associated with downwelling ER waves. When anomalous currents associated with ER waves are removed in the budget, the warm intraseasonal temperature anomaly in the western Indian Ocean is eliminated in observations and reduced by 55% in reanalysis. Key Points: Equatorial westward jets in the Indian Ocean develop in response to downwelling equatorial Rossby waves Downwelling equatorial Rossby waves maintain warm SST anomalies after intraseasonal convection begins Intraseasonal SST anomalies substantially cool when ocean currents associated with equatorial Rossby waves are removed