CALIPSO observations of wave-induced PSCs with near-unity optical depth over Antarctica in 2006-2007

TL;DR

This study uses CALIPSO satellite lidar data to analyze rare, high optical depth polar stratospheric clouds over Antarctica, highlighting the role of gravity wave-induced temperature fluctuations in their formation.

Contribution

It documents a rare type II PSC with high optical depth, explores their distribution and microphysical properties, and links their formation to gravity wave activity.

Findings

Type II PSCs with optical depth up to 0.8 observed from space.

PSC occurrence is concentrated over steep ground slopes with strong winds.

These PSCs are colder and likely ice-based, formed by gravity wave-induced temperature fluctuations.

Abstract

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 farther 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 minima across Antarctica. Lidar and depolarization ratios within these clouds suggest they are most likely ice-based (type II). Similarities between the case study and other PSCs suggest they might share the same formation mechanisms.