Origin of low-frequency (intraseasonal) oscillations in the tropical atmosphere. Part II: structure and propagation of mobile wave-CISK modes and their modification by lower boundary forcings

Abstract

The convective heating in the model is parameterized by a simple one-dimensional cloud model which takes into account the available moisture supply in the lower troposphere and the mean thermodynamic states for the entire troposphere. Consequently, the spatial distribution of convective heating in the model can be determined internally as a function of the sea surface temperature. The periods of low-frequency oscillations excited in the numerical simulations range from 20 to 50 days depending primarily on the vertical distribution of heating through condensation-moisture-convergence feedback of "mobile wave-CISK'. It is found that boundary forcing plays an important role in sustaining the propagation of intraseasonal oscillations around the globe, especially over the eastern part of ocean where SST is cold and deep convection is strongly inhibited. -from Authors