Scattering by Cirrus: from Microphysics to Climate Change

Ice clouds, which can cover 20-35% of the Earth’s surface at any time, make a major contribution to radiative forcing in the atmosphere, both trapping IR (terrestrial) radiation and reflecting solar radiation. The balance between these processes determines whether the cloud has a net warming or cooling effect. This range of possibilities in the net radiative effect of cirrus is one of the causes of the range in climate sensitivity (i.e., the mean equilibrium surface temperature response to a doubling of CO2) reported across differing climate models. Cirrus must be represented in a simplified form in climate models, but one of the difficulties with these parameterisations is lack of understanding of how the cirrus microphysical properties (size, shape, roughness of the ice particles) interact with radiation.

There is an opportunity for a student to work alongside NERC-funded researchers exploring the backscatter from ice particles representative of real cirrus in the Manchester Ice Cloud Chamber, to enable improved and verified modelling of such backscatter. The results will input to development and testing of a new scheme for representing cirrus that will be used in the Met Office UKV forecast model and in the Met Office Earth System Model.