Detection and Tracking of High Altitude Cirrus Clouds With the InfraRed Imaging System of OSIRIS on Odin

The OSIRIS (Optical Spectrograph and InfraRed Imaging System) instrument on the Odin satellite provides a unique data set for the study of near infrared enhanced scattering regions that have been observed near the tropical tropopause. The three infrared channels of the InfraRed Imaging System (IRIS), centered at 1.26, 1.27, and 1.53 microns, provide measurements of brightness, along uniformly spaced lines of sight, of the vertical limb profile of the atmosphere that allow for automated detection and determination of the horizontal and vertical structure of these regions of enhanced scattering. It is believed that these regions are high altitude tropical cirrus clouds that have potentially large climatic warming and cooling effects depending on their extent, duration, thickness, and location. Recent observations with MODIS on TERRA suggest that the extent of these clouds is greater than previously expected, both temporally and spatially. This paper discusses the use of the InfraRed Imaging System data to detect high altitude tropical cirrus clouds and examine their geographic characteristics.