Diagnosing ocean feedbacks to the MJO: SST‐modulated surface fluxes and the moist static energy budget. Issue 14 (28th July 2016)

• Record Type: Journal Article
• Authors: DeMott, Charlotte A.; Benedict, James J.; Klingaman, Nicholas P.; Woolnough, Steven J.; Randall, David A.
• Is Part Of: Journal of geophysical research. Volume 121:Issue 14(2016)
• Page Start: 8350
• Page End: 8373
• Publication Date: 2016-07-28
• Subjects: surface fluxes -- ocean coupling -- tropical convection -- Indian Ocean -- Warm Pool; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1002/2016JD025098
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: 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 (〈 m 〉) budget using data from the European Centre for Medium‐Range Weather Forecasts Interim Reanalysis (ERA‐I). SST fluctuations influence the Δ q and Δ T 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., Δ q ′ | V | ¯ for LH) modestly offset the equatorial wind‐driven perturbations ( Δq ¯ | V | ′ ) and 〈 m 〉, but strongly offset the subtropical Δq ¯ | V | ′ and 〈 m 〉. Column moistening east of MJO convection is opposed by Δq ¯ | V | ′ and supported by Δ q ′ | V | ¯ . 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. Key Points: SST variations reduce wind‐driven fluxes SST offset of wind‐driven flux maximizes in the subtropics SST fluctuations support on‐equator convection and MJO propagation