Local and Remote Influences on the Intertropical Convergence Zone in a Hierarchy of Models

University Of Washington, Seattle WA

Investigators

Abstract

A new and fruitful line of research has developed over the last decade, which has shown that tropical rainfall is sensitive to influences even far away from the tropics. Even heating anomalies in high latitudes spread equatorward with ease via changes in extratropical eddy energy transports. In the tropics, an anomalous Hadley circulation develops in response to heating, fluxing heat out of the hemisphere that is warmed more in its upper branch, but moisture into the warmed hemisphere by the circulation in its lower branch. Recent results undertaken by the research group has used a new attribution procedure based on the idea of extratropical influence on tropical precipitation to uncover a surprising potential primary cause of the double intertropical convergence zone (ITCZ) problem, to develop a new theory for why the ITCZ is in the Northern Hemisphere and to discover and attribute a late 20th century southward shift in precipitation in part due to aerosol forcing. In this project, this line of work will be extended to study several more important issues involving local and remote influences on the ITCZ. First, precipitation in the Indian Ocean is unique in that it peaks south of the equator. Climate models will be used to test whether this is due to local ocean heat transport, continental interactions over the seasonal cycle, or other factors. Second, the effect of absorbing aerosols on ITCZ shifts will be studied in a series of idealized model experiments. Finally, the impact of tropical radiation anomalies on ITCZ shifts induced from the tropics and extratropics will be examined, via simulations that fix clouds and water vapor impacts on radiation in the tropics.