Tropical deep convection produces a wide range of cloud types. Different parts of these cloud systems exert strong positive and negative radiative effects, but the climatological radiative effect of tropical convection is near zero. This balance results from a very specific distribution of convective cloud types, and we are unsure of how it will be affected by climate change. If the radiative balance of tropical convection shifts in the future, it could constitute an important climate feedback.

My work has used satellite observations and cloud-resolving models to study the evolution of convective cloud populations. This has shown that the most common anvil clouds found in the Tropics are those with the strongest climate-warming effect. Using a radiative transfer model and satellite observations of cloud microphysics, we find that these clouds are selectively maintained by radiative heating. Check out our paper on this in JGR-Atmospheres.

We have also found that anvil clouds produced during the daytime have a longer lifetime and a different climate impact than those produced at night. Read the paper here.

More recently, we've studied how convective clouds respond to surface warming in a large ensemble of cloud-resolving models. Our findings suggest that the anvil cloud area feedback is near zero and that the optical depth feedback is slightly positive—which has some important implications for estimates of climate sensitivity. Check out my climate sensitivity symposium talk on this work or our paper in Nature Geoscience.

Interactions between sea surface temperature (SST), deep convection, and the large-scale tropical circulation shape weather and climate across the globe. I am working on understanding these interactions in an idealized modeling setup, in which we run a cloud-resolving model with an interactive ocean for over 20 years. So far, these simulations have produced some very interesting results about the stability of the troposphere, convective organization, and the vertical structure of the tropical overturning circulation. Publications are in prep.

The gif to the right shows some of this internal variability. Blue shading is relative humidity, black shading shows clouds, and the red line is SST. Watch for the regime shift around day 7100.

I've examined how surface warming affects the balance between radiative cooling and latent heating in the tropical upper troposphere. Our main finding was that increases in the average amount of cloud ice are much smaller than increases in the rate of radiative cooling. This means that the residence time of cloud ice in the upper troposphere decreases, i.e., that ice is cycled through the atmosphere at a faster rate. Read the paper here.

Tropical convection has three distinct "modes": deep (thunderstorms), shallow (trade cumulus), and congestus (something in between). Many convection-resolving models reproduce these three modes in radiative-convective equilibrium, but many do not. My work has looked at intermodel variability in the congestus mode as well as congestus dynamics in idealized simulations. We found that the strength of the congestus mode is affected by the large-scale convective aggregation via feedbacks involving moisture and radiative cooling. When present, congestus convection has a large impact on tropospheric stability and mean climate. For this reason, it is important to understand the balance between the three modes of convection, both in the real tropics and in the models that are so heavily relied on in atmospheric research. Read our JAMES paper here.