HR: 14:55h
AN: SA42A-05    [PDF]
TI: The Hump in the Ultraviolet Spectra of Polar Mesospheric Clouds
AU: Morrison, D
EM: danny.morrison@jhuapl.edu
AF: Daniel Morrison, Johns Hopkins University Applied Physics Laboratory 11100 Johns Hopkins Rd, Laurel, MD 20723 United States
AU: * Carbary, J
EM: james.carbary@jhuapl.edu
AF: Daniel Morrison, Johns Hopkins University Applied Physics Laboratory 11100 Johns Hopkins Rd, Laurel, MD 20723 United States
AU: Yee, J
EM:
AF: Daniel Morrison, Johns Hopkins University Applied Physics Laboratory 11100 Johns Hopkins Rd, Laurel, MD 20723 United States
AB: The scattering spectrum of polar mesospheric clouds (PMC) can be defined as the ratio of the scattered spectrum to the incident solar spectrum. Ultraviolet PMC spectra (200-315 nm) were accurately measured during the northern summer of 1999 by spectrographic imagers on the Midcourse Space Experiment (MSX) satellite. These spectra differ from a pure Rayleigh spectrum (which has a $\lambda^-4$ dependence) and from the background dayglow spectrum (which itself is non-Rayleigh). To first order, the PMC spectra can be represented as the spectra of Mie scatterers with a log-normal distribution having modes of $\sim$50-70 nm and dispersions of $\sim$1.15-1.20. However, the PMC spectrum exhibits a peculiar (anomalous?) "hump" near $\lambda$=250 nm. This hump cannot be explained as an instrumental effect or a background contamination effect. The existence of this hump casts some shadow on the usual assumption of a lognormal distribution of Mie scatterers. The implications of this hump for the scattering distribution will be discussed.
DE: 0320 Cloud physics and chemistry
DE: 0340 Middle atmosphere--composition and chemistry
DE: 1610 Atmosphere (0315, 0325)
DE: 3334 Middle atmosphere dynamics (0341, 0342)
DE: 6952 Radar atmospheric physics
SC: SPA - Aeronomy [SA]
MN: 2003 Fall Meeting