Ten years of Southern Hemisphere polar mesospheric cloud observations from the Polar Ozone and Aerosol Measurement instruments

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Abstract

[1] Polar mesospheric clouds (PMCs) were observed in the Southern Hemisphere by both the Polar Ozone and Aerosol Measurement (POAM) II and III instruments. POAM II operated from 1993 to 1996 and its three seasons of Southern Hemisphere PMC observations were previously reported by Debrestian et al. (1997a, 1997b). POAM III operated from 1998 to 2005 and thus observed PMCs during seven Southern Hemisphere seasons. The two POAM instruments are in identical orbits and are very similar in design and measurement capability. These similarities allow for the application of a common PMC detection algorithm to generate a consistent long-term data record by combining the two POAM data sets. In this paper we present an analysis of this combined data set, which consists of approximately 670 PMC observations. The seasonally averaged PMC occurrence frequency, when adjusted for differences in detection sensitivity of the instruments, is found to be strongly anticorrelated with the solar Lyman-α flux. The POAM PMC profiles were analyzed using a geometrical cloud model to determine cloud height, vertical thickness, and wavelength-dependent extinction. Seasonally averaged cloud altitudes range from 82.6 to 83.5 km and the thickness varies between approximately 2 and 3 km. The multiwavelength capability of the POAM III instrument has been used to derive information on PMC particle sizes using the spectral dependence of the measured slant path optical depth. The results of this analysis indicate a mean value of 52 nm for the PMC optically effective radius, which is consistent with a variety of other observations.

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