Summary
Polar Stratospheric Cloud (PSC) composition class information is extracted from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) curtains for four Antarctic PSC seasons (2007 - 2010) and four Arctic PSC seasons (2006/07 - 2009/10). Orographic gravity wave (OGW) active days are defined as those which have either wave-ice PSCs, or large Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) temperature variances. By combining the CALIOP and COSMIC data with temperature and water vapour from the Microwave Limb Sounder (MLS), we investigate the difference in PSC composition class occurrence as a function of the frost point temperature for OGW-active and OGW-quiet days. The regions of direct impacts of OGWs on PSC occurrence are defined using a trajectory model which follows particle movement from the ridge lines over 24 hour periods. In the Arctic, data from Greenland, Scandinavia, Novaya Zemlya and Svalbard are combined, whereas the Antarctic Peninsula is investigated separately. The results show intermittent large wave activity above the mountain regions which is coincident with large increases in water ice PSCs. These ice PSCs advect downstream, where increases in nitric acid trihydrate (NAT) PSCs occur, supporting the mountain wave seeding hypothesis. We quantify the amount of different PSC composition classes in the regions of direct impact due to OGW activity, and then calculate the proportion of total polar-cap PSCs attributable to these mesoscale OGWs.
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