Abstract/Summary

The composite effect of intraseasonal sea surface temperature (SST) variability on the Madden-Julian Oscillation (MJO) is studied in the context of the column integrated moist static energy (MSE) budget using data from the European Centre for Medium-Range Weather Forecasts Interim Reanalysis (ERA-I). SST fluctuations influence the Delta-q and Delta-T parts of the bulk surface latent and sensible heat flux calculations, respectively, each of which influence column MSE. Reynolds decomposition of latent and sensible heat fluxes (LH and SH) reveal that the thermodynamic perturbations modestly offset the equatorial wind-driven perturbations and MSE, but strongly offset the subtropical wind-driven perturbations and MSE. Column moistening east of MJO convection is opposed by wind-driven perturbations and supported by thermodynamic perturbations. Impacts of intraseasonal SST fluctuations are analyzed by recomputing surface flux component terms using 61-day running-mean SST. Differences between "full SST" and "smoothed SST" projections onto MSE and its tendency yield the "SST effect" on the MJO MSE budget. Particularly in the Indian Ocean, intraseasonal SST fluctuations maintain equatorial MSE anomalies at a rate of 1%-2% per day, and damp subtropical MSE anomalies at a similar rate. Vertical advection exports 10%-20% of MSE per day, implying that the SST modulation of surface fluxes offsets roughly 10% of equatorial MSE export and amplifies by 10% the subtropical MSE export by vertical advection. SST fluctuations support MJO propagation by encouraging on-equator convection and the circulation anomalies that drive MJO propagation, and by contributing up to 10% of MSE tendencies across the Warm Pool.