Breaking Down the MJOs Produced by NICAM (Invited Presentation)

The Madden-Julian Oscillation (MJO) materialize as a complex of tropical waves. It is controversial whether the waves are principally passive responses to the latent heat released by the massive convective envelope, or the wave-dynamics are the essential pillars of the mechanics of the MJO. Either way, it is of interest to identify the respective contributions from various waves in a MJO convective envelope. The combined-Fourier-wavelet-transform technique introduced by Kikuchi (2014) enables us to dissolve the MJO convective envelope into different tropical-wave components and quantify their contributions, at any given time and location. We applied this technique to the outward longwave radiation data observed during the CINDY2011 campaign, as well as to those simulated (Miyakawa et al. 2014) by the global cloud-system resolving model NICAM on the K computer. The MJOs in the model were able to propagate eastward at a similar speed with observation although they underestimated the strong Kelvin-wave signals embedded in the observed MJO, supporting that the waves are principally passive responses to the MJO-scale environment. On the other hand, the MJO eastward propagation was delayed in a simulation that overestimated westward cyclonic disturbances and associated surface latent heat flux near the equator, suggesting that the disturbances embedded in the MJO convective envelope can feedback to the MJO-scale features under certain conditions.

Kikuchi, K., 2014: An introduction to combined Fourier-wavelet transform and its application to convectively coupled equatorial waves. Clim. Dyn., 43, 1339-1356.

Miyakawa, T., et al. 2014: Madden-Julian Oscillation prediction skill of a new-generation global model, Nature Commun., 5, 3769, doi:10.1038/ncomms4769.