Atmosphere Ocean Science Colloquium

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Clouds, Circulation, and Climate Sensitivity in Cloud-Resolving Model Simulations of Self-Aggregation of Convection

Speaker: Allison Wing, Columbia University

Location: Warren Weaver Hall 1302

Date: Wednesday, October 5, 2016, 3:30 p.m.

Synopsis:

Large-scale atmospheric circulation, and its interaction with organized moist convection across many scales, sets the patterns of tropical cloud cover and relative humidity and their sensitivity to climate change. Possible changes in the amount of organized convection with warming therefore may modulate climate sensitivity. We explore changes in clouds and circulation and the degree of self-aggregation of convection in response to uniform SST change in a set of radiative-convective equilibrium simulations with the System for Atmospheric Modeling (SAM) cloud resolving model. We use a non-rotating, highly elongated three-dimensional channel domain of length >104 km, with interactive radiation and surface fluxes and fixed sea-surface temperature varying from 280-310 k. Convection self-aggregates into multiple moist and dry bands across this full range of temperatures; we describe the time and length scale of the aggregation and explain the physical mechanisms that cause it. We discuss how large-scale overturning circulations, cloud fraction, and cloud feedbacks change in response to warming, and compare these results to the responses in small-domain RCE (which does not have organized convection or large-scale circulation).