Kilometer-scale global warming simulations and active sensors reveal changes in tropical deep convection

Different types of clouds affect climate and weather in different ways. Credit: NOAA

Under global warming, changes in the location and structure of the deep convection in the tropics have profound consequences for tropical climate. The tropics are characterized by the ubiquitous presence of high ice clouds formed by detrainment from precipitating deep convection. The bulk of these clouds are so-called anvil clouds in extensive formations that shield the convective centers.  These can persist for several hours after the decay of active convection and they carry low to moderate ice loads.

The centers of active convection, on the other hand, correspond to a small fraction of the cloudy region and are typically of kilometric scale. Ice loads in the convective centers are very high, reaching tens of kilograms of ice per square meter, and can only be maintained by the strong convective velocities existing at these locations. Changes in ice loading in active convection thus have the potential to shed light on changes of convective velocities with warming.

Tropical deep convection is one of the leading sources of uncertainty in future projections of the Earth’s temperature. In particular, there remain major uncertainties in the radiative response of convective clouds, which can have negative or positive radiative effects depending on their optical depth, and on the response of convective velocities with warming. This response, the focus of this paper, is particularly difficult to quantify due to the small scales involved.