Does the clustering of convective clouds matter for climate?

ICAS External Seminar

Abstract

Tropical convection often organizes into convective cloud clusters, which are responsible for most of rainfall and cloudiness over the Tropics. This organization of convective systems is usually thought to be rooted in external influences such as large-scale surface temperature gradients, wind shear or rotation. However, simulations using cloud-resolving models run with high resolution under conditions of radiative-convective equilibrium have shown that convection can organize spontaneously even in the absence of external influences, a behaviour called `self-aggregation’. These simulations further suggest that the aggregation of convection depends on mean surface temperature, and that it dramatically alters the large-scale state of the atmosphere, including its humidity and cloudiness. The question thus arises as to how much convective aggregation matters for climate, and whether climate models are able to represent this fundamental interaction between convection, circulation and eventually climate. It will be shown that the impact of convective aggregation on the large-scale state of the atmosphere is also evident in observational data, and that the phenomenon of self-aggregation also occurs in General Circulation Models. The physical mechanisms underlying this behaviour will be explained, and the role that convective aggregation may play in large-scale circulations, climate variability and climate sensitivity will be discussed.

Biography

I am a CNRS Director of Research at LMD (Laboratoire of Dynamical Meteorology) in Paris. My main research interest is advancing understanding of the role of clouds and cloud processes in climate sensitivity and in the large-scale circulation of the atmosphere, using a combination of modeling, observational and conceptual approaches. Two of my hobbies these days consist in exploring the role of convective organization in climate, and in preparing a field experiment named EUREC4A (Elucidating the role of clouds-circulation coupling in climate, www.eurec4a.eu) that will take place in 2020 over the tropical Atlantic near Barbados.