Ocean, Ice, Atmosphere Seminar

Below a certain threshold temperature Polar Stratospheric Clouds (PSCs) can form, thereby providing the surface for heterogenous reactions. These reactions lead to activation of chlorine from its reservoir compounds which in turn leads to the gross loss of ozone during austral spring. Several instruments have been deployed to observe and locate PSCs, and one of these instruments is SCIAMACHY.

SCIAMACHY, the Scanning Imaging Absorption Spectrometer for Atmospheric CHartography is a hyperspectral spectrometer which performs spectroscopic measurements of solar radiation scattered by the Earth's limb, covering a tangent altitude range from about 0 to 100 km. Scattering of solar radiation occurs in the presence of molecular species, but is also due to stratospheric sulphate aerosols and PSCs. Scattering of solar radiation due to PSCs in the Near-InfraRed (NIR) spectral range - where the lower stratosphere can be remotely probed in Limb geometry - is a sensitive indicator of the locations of PSCs. Applying a color index technique, PSCs are detected employing two weakly absorbing NIR wavelengths, i.e, 750 nm and 1090 nm. This presentation describes the PSC detection technique employed, and SCIAMACHY PSC observations during the austral springs 2002 and 2003 are presented. Most of the detected PSCs fall within areas where UKMO temperatures are below 195 K, but with some anomalies. The seasonal evolution of PSC altitude and their geographical distribution were also studied. The derived PSC descent rates are about 2 km/month and are in very good agreement with LIDAR results.