A study on the impact of tropospheric cloud systems on Antarctic polar stratospheric clouds using NASA A-train CloudSat and CALIPSO measurements

Polar Stratospheric Clouds (PSCs) play important role in ozone-depleting processes in the Polar Regions by providing surface for heterogeneous reactions that convert stable chlorine to highly reactive forms that destroy ozone in sunlit conditions and by denitrification of the stratosphere. Previous studies have shown that PSCs are closely related to tropospheric cloud systems, but the extent to which the tropospheric meteorology or tropospheric cloud systems affect PSCs is not well realized or understood. NASA A-train constellation that includes Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) that carries polarization-capable dual-wavelength lidar and CloudSat that carries 94-GHz cloud profiling radar provide an ideal platform to investigate the association of PSCs with tropospheric cloud systems. In the present study CALIPSO and CloudSat measurements are used to investigate the impact of tropospheric high and deep clouds on the microphysical properties of polar stratospheric clouds (PSCs) over Antarctica during the 2006 and 2007 winters. CALIPSO Level 1B data that has height dependent vertical resolution is averaged to uniform vertical bins of 180 m up to 30 km. Then CALIPSO profiles are collocated to CloudSat footprint (1.4 km cross track × 1.8 km along track) and averaged to a horizontal resolution of 1.1 km. The collocated CALIPSO and CloudSat measurements are used for PSC and tropospheric cloud analyses. Attenuated lidar scattering ratio (ALSR) and PSC depolarization ratios (d) are used to classify PSCs into supercooled ternary solution (STS), Mix 1, Mix 2 and ice classes. Our results show that tropospheric high and deep clouds affect both PSC formation and PSC microphysical properties, especially during September and October, when Antarctic stratosphere starts to get warmer. During the late PSC season, close to 70 % of PSCs are formed in association with high and deep tropospheric cloud systems. The number concentration of PSC particles in each PSC class is larger when they are associated with tropospheric cloud systems, which indicates increased nucleation efficiency in PSCs associated with tropospheric clouds than the PSCs not associated with tropospheric cloud. The effect of tropospheric clouds is more evident in the class of ice PSCs, which require lower temperatures than other PSC classes. Both 2006 and 2007 winters show higher occurrence of ice PSCs associated with tropospheric cloud systems. The strong association between tropospheric clouds and PSCs, especially during the later part of the PSC season, indicates that the interaction between tropospheric meteorology and PSC should be better characterized to understand inter-annual ozone hole variations and ozone hole recovery.