Polar Mesospheric Cloud North/South Hemispheric differences: from SME (1982- present
Abstract
The Ultraviolet Spectrometer (UVS) on the Solar Mesosphere Explorer (SME) mission (1981-86) was designed to measure mesospheric ozone by limb sounding at pairs of UV wavelengths, and to establish its relationship with changes in solar spectral irradiance made by an accompanying solar experiment (Rottman, G. , this meeting). Because of its near-polar sun-synchronous orbit, it was anticipated that the overflights of the polar regions (up to 82 deg) would yield new information on transpolar mesospheric clouds, discovered earlier in 1969 by Donahue and colleagues. Known at lower latitudes as noctilucent clouds (NLC), the extensive ice layer was found in 1969 to grow in scattered brightness and occurrence frequency with latitude. SME was launched at a time when very little was known about the ice properties, their seasonal morphology, north/south differences, etc. SME in its five year lifetime over which atmospheric measurements were made established for the first time the seasonal morphology in the period (1981-86), constrained the particle sizes, described north/south differences, etc. The term PMC originated in the first publication of SME cloud data (Thomas, 1984). This paper describes the SME PMC data base, which has been updated extensively since the first publications. Its focus is on the question of north/south differences in PMC properties, and whether these properties have changed over the 30-year period from the SME era to the present. The quantity of interest is the north/south ratio (NSR) of ice water mass (IWC). The NSR has been reported to be greater than two, on the average, using Solar Backscatter Ultraviolet Spectrometer (SBUV) data by Stevens et al (2007). This earlier study applied to the years of the SME mission, and so provide a good comparison to the present results, with two differences: (1) we deal with the more sensitive SME data and thus a greater fraction of the IWC, and (2) use a new regression analysis which relates IWC to the scattered brightness, as a function of scattering angle. North and South scattering geometries from SME were quite different, but this new method largely eliminates scattering angle dependence. The results for the first six PMC seasons covered by SME (1982-1984) are shown, and compared to the SBUV results, and to present-day results from the Aeronomy of Ice in the Mesosphere (AIM) mission.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMSA41C..01T
- Keywords:
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- 0305 ATMOSPHERIC COMPOSITION AND STRUCTURE / Aerosols and particles;
- 0341 ATMOSPHERIC COMPOSITION AND STRUCTURE / Middle atmosphere: constituent transport and chemistry;
- 0360 ATMOSPHERIC COMPOSITION AND STRUCTURE / Radiation: transmission and scattering;
- 3311 ATMOSPHERIC PROCESSES / Clouds and aerosols