Abstract
AbstractAtmosphere‐ocean feedbacks often improve the Madden‐Julian oscillation (MJO) in climate models, but these improvements are balanced by mean state biases that can degrade the MJO through changing the basic state on which the MJO operates. The Super‐Parameterized Community Atmospheric Model (SPCAM3) produces perhaps the best representation of the MJO among contemporary models, which improves further in a coupled configuration (SPCCSM3) despite considerable mean state biases in tropical sea surface temperatures and rainfall. We implement an atmosphere‐ocean‐mixed‐layer configuration of SPCAM3 (SPCAM3‐KPP) and use a flux‐correction technique to isolate the effects of coupling and mean state biases on the MJO. When constrained to the observed ocean mean state, air‐sea coupling does not substantially alter the MJO in SPCAM3, in contrast to previous studies. When constrained to the SPCCSM ocean mean state, SPCAM3‐KPP fails to produce an MJO, in stark contrast to the strong MJO in SPCCSM3. Further KPP simulations demonstrate that the MJO in SPCCSM3 arises from an overly strong sensitivity to El Niño–Southern Oscillation events. Our results show that simulated interannual variability and coupled‐model mean state biases affect the perceived response of the MJO to coupling. This is particularly concerning in the context of internal variability in coupled models, as many previous MJO sensitivity studies in coupled models used relatively short (20‐ to 50‐year) simulations that undersample interannual‐decadal variability. Diagnosing the effects of coupling on the MJO requires simulations that carefully control for mean state biases and interannual variability.
Highlights
The Madden-Julian oscillation (MJO; Madden & Julian, 1971) is a quasiperiodic (30- to 70-day), eastward propagating (≈5 m/s) mode of variability in the tropical climate system
This suggests that in SPC fewer MJO events propagate from the Indian Ocean to the Maritime Continent, but more events propagate across the Maritime Continent to the far western Pacific
Our study suggests that these comparisons are flawed because they do not account for changes in interannual variability between the CGCM and AGCM, either in the phenomena themselves (e.g., CGCM biases in the representation of El Niño–Southern Oscillation (ENSO) or the Indian Ocean Dipole (IOD)) or in their teleconnections to the MJO
Summary
The Madden-Julian oscillation (MJO; Madden & Julian, 1971) is a quasiperiodic (30- to 70-day), eastward propagating (≈5 m/s) mode of variability in the tropical climate system. Convective anomalies associated with the MJO are a key cause of rainfall variability throughout the tropics, including in the major monsoon regions (e.g., Lawrence & Webster, 2002; Lorenz & Hartmann, 2006; Wheeler et al, 2009). Anomalous westerly winds are associated with the “active” (enhanced convection) phase of the MJO, while easterly anomalies are KLINGAMAN AND DEMOTT. The passage of the MJO active phase enhances tropical cyclogenesis in all basins (e.g., Maloney & Hartmann, 2000; Camargo et al, 2008; Vitart, 2009). Teleconnections from MJO convective heating in the West Pacific extend into the midlatitudes, influencing the Pacific and Atlantic storm tracks (e.g., Cassou, 2008; Lin et al, 2009; Vitart & Molteni, 2010)
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