Idealized numerical experiments are conducted to investigate the evolution of equatorial Mixed Rossby Gravity (MRG) waves in MJO type environments. The shallow water equations for a single layer of fluid, linearized about a basic state, are employed for the simulations. The steady state response of the tropical atmosphere in the presence of a mass sink and frictional damping is used to define the basic state representative of the convective phase of the MJO. The resulting basic state is inhomogeneous in space, but invariant in time. The initial perturbation fields, i.e., the MRG waves, are analytically obtained. All numerical experiments are conducted on an equatorial beta-plane. The domain is continuous along the zonal direction and confined to a channel along the meridional direction.

Preliminary results illustrate the growth of the MRG wave and development of a localized wave packet in regions associated with convergence in the basic state. The amplification of the MRG wave appears to occur as a result of accumulation of wave energy. Consistent with this process, reduction in the wavelength and decrease in the eastward group speed of the wavepacket are seen. A notable aspect of this evolution is that even the off-equatorial (around 10 degrees) parts of the wave experience considerable amplification. These results are significant in light of past studies that have documented the role of the MJO in creating a favorable environment for tropical cyclogenesis. The reduction in scale and amplification of the MRG wave may provide a mechanism through which seed disturbances for tropical cyclones may be created. This process may be particularly relevant to the tropical western Pacific, a region that is influenced by the MJO and where MRG waves have been frequently observed.

Numerical experiments are being performed to examine the role of basic state asymmetries in the evolution of the MRG waves. Sensitivity to the strength and structure of the basic states are also being studied, the results of which will be reported during the conference.