2002 Annual

Tuesday, 15 January 2002
Interactions of monsoons and subtropical anticyclones
Todd D. Ringler, Colorado State University, Fort Collins, CO; and D. A. Randall
This work uses a coupled ocean-atmosphere climate model with highly idealized boundary conditions to better understand the manner in which monsoons and subtropical highs interact. We use the model to test various hypotheses regarding the factors that control the amplitude to the monsoon-anticyclone system.

The first mechanism we will test is the longwave radiative cooling feedback mechanism. Hoskins et al. have hypothesized that the relatively dry air associated with subtropical anticyclones leads to enhanced radiative cooling that, in turn, amplifies the strength of the anticyclone. In addition to testing the extent to which this mechanism modifies the anticyclone, we will try to determine the influence of this mechanism on the monsoonal heating located to the east.

We will also test two feedback mechanism related to the occurrence of stratocumulus clouds. Marine stratocumulus clouds are commonly found in the region between the monsoon and subtropical anticyclone, such as off the west coast of North America, South America, Africa, and Australia. The presence of these clouds lead to enhance shortwave reflection and a cooling of the ocean surface. This cooling may lead to an amplification of the anticyclone. Also, these cloud occur in the presence of descending equatorward flow. This leads to coast upwelling that cools the surface and may also amplify the anticyclonic flow.

While these mechanisms appear to emphasize the study of the subtropical anticyclones, a primary purpose of this work is to understand how changes in either part of the monsoon-anticyclone system alters the system as a whole. Our finding should be directly applicable to both the South American Monsoon and the North American Monsoon.

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