7. Convectively Coupled Equatorial Waves in the Multicloud Model

As we saw in the previous chapter, the multicloud model exhibits a new kind of instability of moist gravity waves that are self-sustained, in the sense that these waves amplify naturally during nonlinear simulation without the need of an artifact such as WISHE; this wasn’t the case for the stratiform instability in Chapter 5. We also demonstrated that the multicloud instability is a combination of the stratiform instability and congestus preconditioning through low-level convergence. The latter mechanism should not be confused with congestus moistening through detrainment which may not be effective in sustaining and organizing the propagation of convectively coupled equatorial waves (CCEWs) but can indeed be important during the initiation phase [40, 268, 82, 100]. To demonstrate that the moist gravity waves seen in the previous chapter are indeed the analogs of CCEWs as observed in nature (c.f. Chapter 3), here we consider the effect of rotation and the background wind shear in the multicloud model (MCM) and show that under this combined effect, the MCM is able to capture the observed spectrum of CCEWs.