What favors convective aggregation and why?

Caroline Muller (1) , Sandrine Bony (2)

1 LadHyX - Laboratoire d'hydrodynamique
2 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)

The organization of convection is ubiquitous, but its physical understanding remains limited. One particular type of organization is the spatial self-aggregation of convection, taking the form of cloud clusters, or tropical cyclones in the presence of rotation. We show that several physical processes can give rise to self-aggregation and highlight the key features responsible for it, using idealized simulations. Longwave radiative feedbacks yield a radiative aggregation. In that case, sufficient spatial variability of radiative cooling rates yields a low-level circulation, which induces the upgradient energy transport and radiative-convective instability. Not only do vertically integrated radiative budgets matter but the vertical profile of cooling is also crucial. Convective aggregation is facilitated when downdrafts below clouds are weak (moisture-memory aggregation), and this is sufficient to trigger aggregation in the absence of longwave radiative feedbacks. These results shed some light on the sensitivity of self-aggregation to various parameters, including resolution or domain size.

Domains: Ocean, Atmosphere; Climatology

Caroline Muller, Sandrine Bony. What favors convective aggregation and why?. Geophysical Research Letters, 2015, 42 (13), pp.5626-5634. ⟨10.1002/2015GL064260⟩. ⟨hal-01187680⟩