CALIPSO observations of wave-induced PSCs

• Main Authors: Noel V, Hertzog A, Chepfer H, Vincent Noel
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2009
• Subjects: Austral; Antarc*; Antarctica
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.369.3732; http://hal.archives-ouvertes.fr/docs/00/43/96/93/PDF/Opt_Thick_PSC_7.pdf

Ground-based and satellite observations have hinted at the existence of Polar Stratospheric Clouds (PSCs) with relatively high optical depths, even if optical depth values are hard to come by. This study documents a Type II PSC observed from spaceborne lidar, with visible optical depths up to 0.8. Comparisons with multiple temperature fields, including reanalyses and results from mesoscale simulations, suggest that intense small-scale temperature fluctuations due to gravity waves play an important role in its formation; while nearby observations show the presence of a potentially related Type Ia PSC further downstream inside the polar vortex. Following this first case, the geographic distribution and microphysical properties of PSCs with optical depths above 0.3 are explored over Antarctica during the 2006 and 2007 austral winters. These clouds are rare (less than 1 % of profiles) and concentrated over areas where strong winds hit steep ground slopes in the Western hemisphere, especially over the Peninsula. Such PSCs are colder than the general PSC population, and their detection is correlated with daily temperature minimas across Antarctica. Lidar and depolarization ratios within these clouds suggest they are most likely icebased (Type II). Similarities between the case study and other PSCs suggest they might share the same formation mechanisms. 2 2 hal-00439693, version 1- 8 Dec 2009