The radiative impact of Polar Stratospheric Clouds

Polar Stratospheric Clouds (PSCs) are an ubiquitous feature in the stratosphere over the polar regions on the winter hemisphere. Heterogeneous chemistry and microphysics of these clouds play a pivotal role in the formation of the ozone hole. We constrain the radiative impact of these clouds utilizing observations from the space-borne lidar CALIPSO and the state of the art radiative transfer model LBLDIS.In addition to spatial and vertical distribution of PSCs, CALIPSO also provides their composition which is used in LBLDIS to calculate their radiative impact.This analysis focuses on the Antarctic winter season of 2008. Here, CALIPSO shows a distinct maximum in integrated optical depth of PSCs east of the Antarctic peninsula which is present throughout the entire winter season. Under clear-sky conditions PSCs can warm the lower stratosphere by several K/day in this region. However, the radiative impact of PSCs is greatly reduced in the presence of underlying tropospheric clouds. With tropospheric cloud parameters provided by CALIPSO we calculate the radiative impact of PSCs for several tropospheric cloud conditions to constrain the potential impact of PSCs on stratospheric temperatures.We find that high tropospheric clouds reduce the heating effect of PSCs and eventually PSCs have a cooling effect on lower stratospheric temperatures. We investigate how the radiative impact of PSCs changes throughout the winter with changing tropospheric conditions and how these locally forced temperature fluctuations impact the formation of PSCs.