Self-Aggregation of Moist Convection, Radiative-Convective Instability and the Regulation of Tropical Climate

Tropical showers and thunderstorms play an important role in the regulation of Earth's climate. One theory regarding tropical convection is that as sea surface temperatures warm, more clouds form and the atmosphere becomes drier. While the clouds reduce solar radiation from warming the surface, that effect is more than counteracted by a drier atmosphere allowing more outgoing radiation to pass. This could suggest that the tropical climate has a level of self-regulation. To study this idea, the researchers involved in this project have created an idealized computer model to address what they call the "self-aggregation" of convection. This is the tendency for clouds and thunderstorms to move together into clusters. This award will provide funding to enhance the model with more realistic wind and sea surface temperatures. The impact of this research would be through improvements in the representation of tropical convection in weather and climate models. The project would also help to train the next generation of scientists by involving multiple graduate students in the research.

The overarching goal of the project is to understand how aggregation of convection in an environment more realistically representative of the tropics may help regulate tropical climate. The related hypothesis is that aggregation reduces tropical climate sensitivity by providing a powerful negative water vapor feedback that is highly temperature dependent. The researchers will introduce a diurnal cycle and wind shear to their simulations in order to decrease or eliminate the strong aggregation state lock that they found in their prior work. Sea surface temperatures would also be allowed to vary, which will let the researchers test the hypothesis that the existence of aggregation may drive the system's climate toward the critical sea surface temperature for aggregation. The next step will be to use the theoretical model to explore the climate sensitivity of the system by varying the solar constant and CO2. Finally, the researchers will test the hypothesis that the Madden-Julian Oscillation (MJO) results from self-aggregation of convection independent of larger atmospheric waves.