Diagnosing ocean feedbacks to the MJO: SST‐modulated surface fluxes and the moist static energy budget

Abstract

AbstractThe 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 (〈m〉) budget using data from the European Centre for Medium‐Range Weather Forecasts Interim Reanalysis (ERA‐I). SST fluctuations influence the Δq and ΔT parts of the bulk surface latent and sensible heat flux calculations, respectively, each of which influence column 〈m〉. Reynolds decomposition of latent and sensible heat fluxes (LH and SH) reveal that the thermodynamic perturbations (e.g., for LH) modestly offset the equatorial wind‐driven perturbations ( ) and 〈m〉, but strongly offset the subtropical and 〈m〉. Column moistening east of MJO convection is opposed by and supported by . 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 〈m〉 and its tendency (∂〈m〉/∂t) yield the “SST effect” on the MJO 〈m〉 budget. Particularly in the Indian Ocean, intraseasonal SST fluctuations maintain equatorial 〈m〉 anomalies at a rate of 1%–2% d−1 and damp subtropical 〈m〉 anomalies at a similar rate. Vertical advection (−〈ω∂m/∂p〉) exports 10%–20% of 〈m〉 per day, implying that the SST modulation of surface fluxes offsets roughly 10% of equatorial 〈m〉 export and amplifies by 10% the subtropical 〈m〉 export by −〈ω∂m/∂p〉. 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 ∂〈m〉/∂t across the Warm Pool.