Moisture mode theory: the role of horizontal moisture advection in the MJO

We articulate a theory for low-frequency “moisture modes” with a goal towards explaining the MJO. In this theory column-integrated water vapor is the only prognostic variable, vertical and meridional structure are implicit, and winds are diagnosed as an instantaneous, quasi-static function of precipitation using a Green's function approach. In this presentation, we extend our previous work to consider the role of horizontal moisture advection in more detail. Effects included are meridional moisture advection by the meridional velocity field associated with the planetary-scale disturbance itself; meridional moisture advection by transient, synoptic-scale disturbances (parameterized as diffusive); and zonal advection in the presence of a mean zonal moisture gradient. Some aspects of our development have been motivated by DYNAMO observations.