Addressing Problems in Tropical Atmospheric Dynamics Using Idealized Global Climate Models

A persistent gap in our knowledge of the climate system occurs in the tropical atmosphere where motions on very small spatial scales play an outsized role in the vertical transport of heat and water. These motions are very difficult to incorporate into global climate models, resulting in uncertainty in climate simulations. This project aims to advance our understanding of key fundamental features of the tropical climate and address how different modeling approaches to incorporate those motions affect these key features. The research strategy entails creating climate models of differing complexity and with realistic interaction between thermal radiation and water vapor. In these simulations, the investigators will examine the time-averaged tropical rainfall distribution and the organization of tropical rainfall on different frequencies and spatial scales, as well as the potential for abrupt reorganization of the tropical winds and rainfall as the climate warms. The research tasks will help train graduate students and early career scientists. The project follows a distinctive approach to climate theory involving the construction and analysis of a systematic hierarchy of climate models by peeling off successive layers of complexity. The examined tropical dynamics include the position and structure of the Hadley Circulation, convectively coupled waves, the Madden-Julian Oscillation, and the susceptibility of the tropics to super-rotate. Deviating from conventional wisdom, the project will initially concentrate on simulations with no additional treatment of vertical heat and moisture fluxes, supplementing what the model can produce on its own based on a horizontal resolution commonly used for climate projections. This strategy will provide a benchmark to facilitate the study of the diversity of model simulations with differing treatments of fluxes or with much smaller grid size. The project will then construct a model with greater flexibility in handling these vertical fluxes than previously possible. The hierarchy approach with accessible results can have great pedagogical values in communicating the fundamental concepts in climate theory and climate change to the public. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.