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Indian Monsoon Depressions: New insights from GFDL's AGCM and Linear Theory

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Wednesday, 04 October 2017, 12:00


Wednesday, October 4, 2017. 12:00PM. Indian Monsoon Depressions: New insights from GFDL's AGCM and Linear Theory. Angel Adames, GFDL. Sponsored by Geophysical Fluid Dynamics Laboratory. More information here.


Summary: The mechanisms that lead to the propagation of moisture and moist static energy in monsoon low and high-pressure systems collectively referred to as synoptic-scale monsoonal disturbances (SMDs), are investigated using daily output fields from GFDL's Atmospheric Model 4 (AM4). Propagation of the moisture anomalies is dominated by vertical moisture advection while the MSE anomalies propagate due to horizontal advection of low-frequency dry static energy by the SMD winds. By combining the budgets, we interpret the propagation of the precipitation anomalies in terms of lifting that is forced by horizontal dry static energy advection. This process moistens the lower free troposphere, producing an environment that is conducive for deep convection. The precipitation anomalies are, in turn, largely maintained by longwave radiative heating. Based on these results, we propose a linear framework where the evolution of moisture plays a central role in SMDs. In this framework, warm air advection by the anomalous northerly winds induces vertical moisture advection, which moistens and destabilizes the column. The moistened lowered troposphere enhances convection which, in turn, causes the low pressure system to intensify through vortex stretching. This instability only occurs if the vorticity tendency from dry processes (such as horizontal vorticity advection) and moist processes (vortex stretching from convection) are of the same polarity.



Location  Smagorinsky Seminar Room, Princeton, NJ.