Model sensitivity runs for Southern Ocean studies

The present generation of global climate models is characterized by insufficient reflection of short-wave radiation over the Southern Ocean due to misrepresentation of clouds. This is a significant concern as it leads to excessive heating of the ocean surface, sea surface temperature biases, and subsequent problems with atmospheric dynamics. Using the recent version of the Met Office's Unified Model, we show that modifying the cloud micro-physics scheme with a more realistic value for the shape parameter of atmospheric ice-crystals suggested by theory and observations, benefits the simulation of short-wave radiation. In the control model, for calculating the growth rate through deposition process, it is assumed that all ice particles are spherical in shape. By approximating the value for plates or aggregates of ice crystals, along with modified ice nucleation temperatures, we show that there is a reduction in the annual-mean short-wave cloud radiative effect over the Southern Ocean.