A Summary of Findings on PMCs from WINDII Observations
Abstract
A summary of findings on polar mesospheric clouds (PMCs) from WINDII on UARS is presented. Extensive observations were conducted in January, 1994, 1995, 1996 and 1997 over the southern hemisphere and in July, 1992, 1993, 1994 and 1995 over the northern hemisphere. The WINDII instrument on the UARS satellite has an imaging camera with several filter channels after the interferometer. The limb images cover an area 150 km wide and 30 km high. In the background filter channel at 553 nm, images of scattered sunlight from the earth's atmosphere can be measured in the daytime from 75 km to 95 km. The presence of noctilucent clouds is indicated in most January profiles at southern latitudes above 55S; the occurrence of PMCs was mapped for each day from early January until early February. PMCs were always observed in the SH in January and were apparently brighter than in the northern hemisphere in July. Backscatter ratio versus altitude plots of the clouds indicate that they are very narrow, often with a vertical structure less than 2 km thick; the peak backscatter ratios were often over 10 at 83 km. A statistical analysis was conducted for each day in January. The histogram of the number of occurrences versus backscatter ratio often indicates two peaks, perhaps indicating the presence of two different sizes of ice particles. The diurnal variation of brightness has been investigated using data to cover the local time from 07:00 until 21:00; this analysis indicated only a modest diurnal variation of brightness. Estimates of the particle size were obtained from the 2 fields of view of WINDII; a mean radius of about 25 microns was usual. The intercomparison of WINDII with other satellites by cumulative distributions will be summarised.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2001
- Bibcode:
- 2001AGUSM..SA22A17E
- Keywords:
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- 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0320 Cloud physics and chemistry;
- 1600 GLOBAL CHANGE (New category)