Maintenance Mechanisms of the Madden-Julian Oscillation

We analyze the behavior of a Madden-Julian oscillation (Madden and Julian 1971, 1972) (MJO)-like feature in an intermediate-complexity atmospheric model, and some of the proposed maintenance mechanisms for the oscillation. Specifically, we examine the evaporation-wind feedback (EWF) mechanism (Emanuel 1987, Neelin et al. 1987, Xie et al. 1993) and the influence of tropospheric extratropical excitation (e.g. Liebmann and Hartmann 1984, Hsu et al. 1990, Ferranti et al. 1990). Although the EWF mechanism has been examined by a variety of other models, including GCMs, we conduct a self-consistent modeling study of the relative importance of each of these mechanisms on maintaining the MJO using a model of moderately realistic complexity. In particular, we present a new way of testing the influence of extratropical excitation by suppressing baroclinic instability. The model experiments conducted suggest that both the EWF and tropospheric extratropical excitation play a role in maintaining the MJO, and that of the two mechanisms, extratropical excitation provides the greater variance to the system.

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