Polar Mesospheric Clouds as Seen by the Halogen Occultation Experiment

Data from the Halogen Occultation Experiment (HALOE) are being used to study Polar Mesospheric Clouds (PMCs), their long-term variations with time, northern and southern hemispheric asymmetries, and variations with latitude. HALOE has been observing the polar summer region since the end of 1991, which has provided 12 northern and 12 southern seasons of data. HALOE typically makes 2-3 sweeps through the high latitudes each summer that provide approximately 600 polar observing opportunities each PMC season. These observations can vary with latitude and time for each summer season, and since PMC occurrence frequency will depend on latitude and time, the HALOE PMC observations are normalized to the SME climatology as described by Shettle et. al. (2002) so that interannual comparisons can be made. We will present the seasonal PMC occurrence frequency and extinction, and the seasonally averaged temperature and water vapor at PMC altitudes for both the northern and southern hemisphere. PMC altitude distributions for each hemisphere and occurrence frequency with latitude and time in a season will be shown. Occurrence frequency results versus time show good agreement with the SME distribution.