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Tuesday 01 Dec 2020Using an idealized general circulation model to probe the building blocks of the monsoons and the Quasi-Biennial Oscillation

Prof. Chaim Garfinkel - The Hebrew University

Zoom 13:30-14:30

Monsoons dominate the climate in many regions of the tropics and subtropics, and are characterized by rainy summer and drier winter seasons. This rainfall is crucial for agriculture, among other societal applications, in heavily populated regions of the world. Tropical precipitation also launches a wide variety of waves that propagate upwards, which in turn drives the stratospheric Quasi-Biennial Oscillation, the most predictable and regular phenomena in the atmosphere not directly forced by solar radiation.

An intermediate complexity moist General Circulation Model is used to investigate the forcing of the Asian monsoon and the upper level anticyclone by land-sea contrast, horizontal heat fluxes in the ocean, and topography. The linearity of the response to these building blocks is investigated. The monsoonal pattern is not simply the linear additive sum of the response to each forcing - only when all three forcings are included simultaneously does the monsoonal circulation extend westward to India. Specifically, the response to land-sea contrast and also to topography depends on whether they are added to a model that already includes the other two forcings. The source of the nonlinearity can be diagnosed using gross moist stability. In regions where non-additivity is pronounced, the question of which forcing is most important is ill-posed.

These same integrations are then used to clarify how the Quasi-Biennial Oscillation is forced by tropospheric variability. The downward extension of the Quasi-Biennial Oscillation to the lowermost stratosphere is sensitive to the presence of these building blocks. This sensitivity is associated with differences in Kelvin wave activity among the simulations.

Meeting Access Details:

Meeting ID: 973 5676 8639

Password: 682553

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