A conceptual model for self-sustained active-break Indian summer monsoon

[1] The Indian summer monsoon (ISM) exhibits a salient intraseasonal oscillation (ISO), and there have two ISO variability centers that are located at the equatorial Indian Ocean (EIO) and ISM regions, respectively. The prevalence of these two centers indicates that this active-break monsoon cycle has a prominent stationary oscillation. To understand this aspect of the ISM ISO, a two-box model is advanced to represent the ISO in these two variability centers. Linking by the local Hadley circulation, these two boxes can enhance each other's variability, but air-sea interaction is shown to be necessary for producing a sustainable model ISO. Associated with a positive (negative) precipitation dipole anomaly, the reduced (enhanced) short wave radiation cools (warms) the sea surface and leads to an anomalous sea surface temperature dipole, which in turn stimulate development of a reversed precipitation dipole. This leads to a transition from one to the other phase of the monsoon cycle. This model demonstrates that even without the northward propagation, the air-sea interaction, in cooperation with the instability caused by the local Hadley circulation and frictional boundary layer moisture convergence, can produce a self-sustained ISM ISO.