PLANETARY-SCALE CIRCULATIONS FORCED BY INTRASEASONAL VARIATIONS OF OBSERVED CONVECTION

Interhemispheric differences of the Madden-Julian oscillation (MJO) ar e investigated in a linearized primitive equation model. Heating is pr escribed from the observed life cycle of the MJO, in which anomalous c onvection is concentrated in the Eastern Hemisphere. The dynamical res ponse in the Eastern Hemisphere has the form of a forced disturbance t hat involves Kelvin and Rossby components. These dynamical components propagate eastward along with the prescribed heating and have zonal wa venumber-2 structure, in accord with observed behavior. The behavior i n the Eastern Hemisphere also resembles that emerging from frictional wave-CISK, in which heating follows autonomously from the circulation. When the prescribed heating collapses near the date line, the Rossby component dissipates. The Kelvin component, however, continues to adva nce across the Western Hemisphere, where it propagates at more than tw ice the speed of the disturbance in the Eastern Hemisphere. The distur bance in the Western Hemisphere, which likewise is in accord with the observed behavior, can be understood as the radiating response to tran sient heating confined to the Eastern Hemisphere.