Abstract
The interactions of clouds with radiation influence climate. Many of
these impacts appear to be related to the radiative heating and cooling
from high-level clouds in the upper troposphere, but few studies have
explicitly tested this. Here, we use simulations with the ICON-ESM
global atmosphere model to understand how high-level clouds through
their radiative heating and cooling of the atmosphere, influence the
large-scale atmospheric circulation and precipitation in the present-day
climate. We introduce a new method to diagnose the radiative heating of
high-level clouds: we use a temperature threshold of -35°C to define
high-level clouds and also include the lower parts of these clouds at
warmer temperatures. The inclusion of the lower cloud parts circumvents
the creation of artificial cloud boundaries and strong artificial
radiative heating at the temperature threshold. To isolate the impact of
high-level clouds, we analyze simulations with active cloud-radiative
heating, with the radiative heating from high-level clouds set to zero,
and with the radiative heating from all clouds set to zero. We show that
the radiative interactions of high-level clouds warm the troposphere and
strengthen the eddy-driven jet streams, but have no impact on the
strength of the Hadley circulation and the latitude of the Intertropical
Convergence Zone. Consistent with their positive radiative heating and
energetic arguments, high-level clouds reduce precipitation throughout
the tropics and lower midlatitudes. Overall, our results confirm that
the radiative interactions of high-level clouds have important impacts
on climate and highlight the need for better representing their
radiative interactions in models.