Influence of the MJO and Extratropical Wavetrains on Intraseasonal Subtropical Gyres over Northeast Africa and Southwest Asia

Analogous to the Gill model’s response to a stationary heat source in the tropics, Madden-Julian Oscillation suppressed convection over the eastern Indian Ocean provokes a Rossby type gyre response which enables intraseasonal enhanced convection over the subtropics of Africa and southwest Asia. However, downstream MJO forcings may not be the only pathway through which these intraseasonal subtropical gyres and associated enhanced convection occur. Composites of the gyres and intraseasonal convection show robust incoming wavetrain signatures from upstream that encroach into the subtropics. Furthermore, these Rossby wavetrains may potentially have been forced or influenced by MJO convection over the Pacific Ocean. Transitions of subtropical gyres are identified through the use of the temporal progression of the latitudinal structure of kinetic energy over the jet region of northeastern Africa and southwest Asia. Events are then separated into groups that are preceded by in phase MJO suppressed convective signals over the eastern Indian Ocean and those that are not, as well as groups that have incoming extratropical wavetrains and those that do not. Composites and comparisons of the subsets may provide insight into which forcings dominate responses and their specific influences.