Dynamics of Large-scale Monsoons and their Response to Climate Changes

点击翻译按钮获取中文摘要

Monsoons are prominent features of the large-scale circulation of the Earth's atmosphere, sustaining densely populated, rapidly growing and socially vulnerable regions in the tropics and subtropics. This project seeks to improve understanding of the essential processes that are involved in monsoons and that mediate their response to climate change. The premise of the project is that monsoons can be viewed as seasonal migrations of zones of tropical convection and their associated large-scale overturning circulations, and that the fundamental dynamics of such convectively-driven overturning can be understood in terms of angular momentum and energy balance constraints. Under this premise the research begins by examining the behavior of seasonally migrating convection zones in simplified "aquaplanet" simulations in which the earth's surface is entirely covered by oceans and there are no land-sea contrasts. These model simulations are followed by further simulations with idealized continents, and finally results from these simulations are compared with realistic climate simulations from the Climate Model Intercomparison Project version 5 (CMIP5). Specific issues to be addressed include the relatively sudden onset of the monsoon, the delay of monsoon onset with increasing global mean temperature found in model simulations, and the relationship between global mean temperature and the strength of the overturning circulation. Goals of the project are to 1) investigate how monsoons change in a wide range of climates, in order to place past, present and future changes in a broad context; 2) determine how monsoons change in simulations in which complexity is progressively increased; starting from aquaplanet simulations with no land-masses to simulations with idealized continental geometries; and 3) use the conceptual understanding emerging from the idealized simulations to evaluate state-of-the-art general circulation models, and better constrain future projections.The work has broader impacts due to the importance of monsoons for agriculture and water resources in densely populated regions of the world. Understanding how monsoons change with changing climate is both a priority and a major challenge in climate science, and the present work may contribute both by improving our ability to interpret and evaluate projections of monsoon change from climate models, and in improving the models used for such projections. In addition, the project will support and train a graduate student, thereby providing for the next generation of researchers in this area, and three undergraduate students will be hosted for summer research.