Movies of Earth from space show beautiful and intricate patterns. Specifically, IR images show water vapor and clouds as they change in time, revealing a variety of patterns evolving on a range of spatial and temporal scales, as part of the atmospheric circulation. This talk is focused on understanding the aggregation patterns formed by deep tropical convective clouds, which appear in the satellite images as distinct cold regions.

The organization of convection into coherent large-scale structures is a feature of moist tropical systems, which by diverse means play a major role in shaping tropical weather and are responsible for much of the extreme weather in the tropics. Spectral analysis of the cloud signature reveals peaks along linear dispersion relation curves for planetary scale waves, alongside a red noise spectrum. Attributing the red-noise spectrum to turbulence, we study the coexistence of waves and turbulence in the tropics.

The talk will give a brief introduction to tropical waves, turbulence theory in the tropics, and the simplest model which can represent them- a moist shallow water model. We will then show that planetary scale waves can be excited via an upscale turbulent cascade from mesoscale convective systems, if anomalies of vorticity (a measure of local angular momentum of the flow) is excited strongly enough.

Lieu
École normale supérieure – PSL
24 rue Lhomond – aile Erasme
Salle Claude Froidevaux – E314