Vertical Velocity Profiles in Convectively Coupled Equatorial Waves and the MJO: New Diagnoses of Vertical Velocity Profiles in the Wavenumber-Frequency Domain

We developed a new diagnostic framework and applied it to the ERA-interim dataset to quantitatively assess vertical velocity (omega) profiles in the wavenumber-frequency domain. Two quantities are defined with the first two EOF-PC pairs of the omega profiles in the tropical ocean: a top-heaviness ratio and a tilt ratio. The top-heaviness and tilt ratios are defined, respectively, as the co-spectrum and quadrature-spectrum of PC1 and PC2 divided by the power spectrum of PC1. They represent how top-heavy the omega profile is at the convective maximum, and how much tilt the omega profiles contain in the spatio-temporal evolution of a wave. The top-heaviness ratio reveals that the omega profiles become top-heavier as the time-scale (spatial scale) becomes longer (larger); and the MJO has the top-heaviest profile, while the EIG and WIG waves have the bottom-heaviest profiles. The tilt ratio reveals that the Kelvin, WIG, EIG, and MRG waves, which belong to waves with fast propagation speeds, have significant tilts in the omega profiles, while the ER wave and MJO, categorized as slow-moving moisture modes, have more vertically stacked profiles. The gross moist stability (GMS), cloud-radiation feedback, and effective GMS were also computed for each wave. The MJO with the top-heaviest omega profile exhibits a relatively high GMS, but has a negative effective GMS due to a strong cloud-radiation feedback. Similarly, the ER wave also exhibits a negative effective GMS. Based on this result, it is speculated that top-heavier systems would be more preferable for the moisture modes.