10 February 2017

The Tropical Rain Belts with an Annual Cycle and a Continent Model Intercomparison Project: TRACMIP

Scientists used an ensemble of idealized modeling experiments to understand what controls the tropical rain belt and its response to climate change.

Science

Simulating tropical rainfall is one of the most stubborn challenges in climate science. Scientists organized the Tropical Rain belts with an Annual cycle and a Continent Model Intercomparison Project (TRACMIP) to study the dynamics (winds) of tropical rain belts using multi-model simulations to bring about a deeper understanding of global and regional climate and past and future climate change.

Impact

Despite general improvements in climate models, a large spread in model simulations of large-scale tropical rainfall has persisted for more than two decades. Uncertainty in projecting tropical rainfall and circulation changes has global consequences. Addressing the question of what controls the tropical rain belts, TRACMIP will shed light on different aspects of the dynamics of tropical rainfall and global climate change.

Summary

In research conducted by a team of scientists, including two at the U.S. Department of Energy’s Pacific Northwest National Laboratory (PNNL), they introduced the Tropical Rain belts with an Annual cycle and a Continent Model Intercomparison Project (TRACMIP) that aimed to study the dynamics of tropical rain belts and their response to past and future perturbations. The experimental design included five idealized modeling experiments: two with an all-ocean planet and three with an idealized tropical continent on an otherwise all-ocean planet. Fourteen models, including one contributed by scientists at PNNL, were involved in the TRACMIP effort. All models included an atmospheric model coupled to a slab ocean model, with seasonally varying solar insolation. The simulations successfully reproduced key features of present-day climate and expected future climate change. When the team quadrupled the concentration of CO2, it led to a northward shift of the tropical rain belt and preferential warming in northern high latitudes. Including an idealized continent modulated both the present-day climate and the response to increased CO2. By using simulations from an ensemble of models under identical conditions, the scientists found climate features that are consistent or scattered across models that are informative in fostering an understanding of the tropical rain belt and its response to climate change.

Contact
L. Ruby Leung
Pacific Northwest National Laboratory
Publications
"The Tropical Rain Belts with an Annual Cycle and a Continent Model Intercomparison Project: TRACMIP." Journal of Advances in Modeling Earth Systems 8, 1868-1891 (2016). [10.1002/2016MS000748].