Previous studies have shown the existence of moist convective-gravity waves. These modes are characterized by intensified convective activity in phase with the large-scale upward motion and out of phase with the temperature perturbation. In this situation, the interaction between moist convection and large-scale flow acts to slow down the wave, which propagates more slowly than a dry gravity wave with a similar vertical structure. The actual propagation speed can be determined from the gross moist static stability and depends on the vertical temperature and moisture profiles of the atmosphere. The tropical atmosphere is not homogeneous but exhibits large-scale variations in convective activity and relative humidity. This paper investigates how such variations can affect the propagation of tropical disturbances, both in the context of simple theoretical models and of an idealized general circulation models with parameterized convection.

A first model is considered in which the gross moist static stability acts as a wave admittance. In this case, horizontal variations of the background relative humidity are associated with accumulation of wave energy in regions of low moist static stability. In addition, sharp transition in relative humidity can produce partial reflection of an incident wave. A more complex model is also discussed. This model allows for both dry and moist modes, and is used to study how a dry perturbation (for example generated in the extra tropics) can propagate into a moist region and excite a convective gravity wave. Finally, these theoretical models are compared to 2 and 3 dimensional simulations with an idealized general circulation model.