The role of tropical anvil cloud radiative heating in present and a warmer climate

Seminar by Dr. Blaž Gasparini from University of Vienna, Austria

19 June 2023
KST 10:30 – 11:30

The Seminar is being held in Room 1010 (Jasmin) – Integrated mechanical engineering building. Click here for the campus map.

Upper tropospheric clouds, particularly anvil clouds, are the most abundant and radiatively important cloud type in the tropics. Their height is constrained by large-scale climate, while their optical thickness and radiative effects depend on various small-scale microphysical processes, their interaction with radiation, turbulence, and circulation. Such processes are currently poorly understood. Anvil representation in coarse climate models is very crude, and their results should be treated with caution when examining climate projections. Not surprisingly, the tropical anvil cloud feedback is the single largest contributor to the total cloud feedback uncertainty. Kilometer-scale cloud resolving models help us to disentangle these complex interactions. We show examples of how tiny differences in how ice crystals form, grow, and shrink lead to differences in how clouds interact with radiation (cloud radiative heating. These in turn influence the upper tropospheric temperature gradients, circulation, precipitation, and also anvil cloud properties, with large climate impacts. 

Despite the large climatic role of anvil cloud radiative heating, its response to global warming remains unknown. We study changes in cloud radiative heating with surface warming from a multimodel dataset of simulations in radiative-convective-equilibrium, identify physical mechanisms responsible for these changes, and develop a theory to predict them. Our stepwise approach reveals an intensification of cloud radiative heating with ascending clouds, attributed to decreased air density. This mechanism is supported by satellite data. 

The density-mediated increment in cloud radiative heating may increase the role of high clouds in controlling atmospheric flows in a warmer climate. Moreover, a narrowing of the spread in model-simulated cloud radiative heating highlight a path to reduce uncertainties in regional climate change projections.