Diagnosing Air-Sea Interactions on Intraseasonal Timescales (Invited Presentation)

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Wednesday, 7 January 2015: 4:00 PM
224A (Phoenix Convention Center - West and North Buildings)
Charlotte DeMott, Colorado State University, Fort Collins, CO

What is the role of ocean coupling in the Madden Julian Oscillation (MJO)? Consensus thinking holds that the essential physics of the MJO involve various interactions between convection, atmospheric wave dynamics, and boundary layer and free troposphere moisture. However, many modeling studies have demonstrated improvement in the simulation of the MJO when an atmosphere-only general circulation model (AGCM) is coupled to an ocean model, so feedbacks from the ocean are probably not negligible.

Assessing the importance and processes of these feedbacks is challenging for at least two reasons. First, observations of the MJO can only sample the fully coupled ocean-atmosphere system; there is no "uncoupled" MJO in nature. The practice of analyzing the MJO in uncoupled and coupled GCMs (CGCMs) points to the second challenge, which involves using imperfect tools to study the problem. Although MJO simulation is improving in many models, shortcomings remain in both AGCMs and CGCMs, making it difficult to determine if changes brought about through coupling reflect critical air-sea interactions or are simply part of the collective idiosyncracies of a given model.

From the point of view of the atmosphere, ocean feedbacks from sea surface temperature (SST) variations are communicated through their effects on surface fluxes of heat and moisture. The SST can therefore interact with the atmosphere via its impact on surface fluxes. This talk presents a set of analysis tools for diagnosing the impact of an interactive ocean on surface latent and sensible heat fluxes, including their mean, variance, and relative phasing with respect to MJO convection. The analyses are demonstrated with application to several models from the CMIP5 archive, and reveal a variety of responses to coupled ocean feedbacks.