Cirrus Clouds Radiative Effects in the Present Day Climate and in Response to Cirrus Seeding

The global radiative properties of cirrus clouds are, together with their formation mechanisms, associated with a high uncertainty. Moreover, the simulated cirrus net warming effect has driven part of the climate engineering research to suggestions that would decrease the cirrus cloud cover and thus cool Earth in a future warmer world.

Here, we first compare cirrus cloud occurrence and its variability from the ECHAM6-HAM general circulation model with a cirrus cloud occurrence climatology from the 9 years of CALIOP data. CALIOP lidar is part of the Calypso satellite “train”, which is in Earth's orbit since April 2006. Preliminary results show an excellent agreement between the model simulations and the satellite dataset. This gives us confidence that the model correctly captures the main elements of cirrus formation.

We evaluate cirrus clouds radiative properties and their annual cycle. We estimate how these properties change with the shift of ice nucleation mechanisms from homogeneous-only to heterogeneous-only with several intermediate scenarios that enable the competition between homogeneous and heterogeneous ice nucleation.

As a third step we investigate the radiative impacts of cirrus cloud seeding with varying ice nuclei concentrations and seeding strategies. The main idea is to evaluate if cirrus cloud seeding is a feasible way of counteracting global warming in mid and high-latitudes.