American Geophysical Union Become an AGU Member
Subscribe to AGU Journals		 AGU Home AGU Publications

Read Full Article (file size: 127578 bytes)    Cited by

GEOPHYSICAL RESEARCH LETTERS, VOL. 31, L13108, doi:10.1029/2004GL020101, 2004

Evidence for bimodal particle distribution from the spectra of polar mesospheric clouds

J. F. Carbary

Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA


D. Morrison

Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA


G. J. Romick

Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA


Abstract

The spectrographic imagers on the MSX satellite have made the first observations of the middle ultraviolet spectra (200–315 nm) of polar mesospheric clouds (PMCs). Dividing the PMC spectra by the solar spectrum yields a scattering spectrum expressible as a matrix-vector formalism of Mie scattering functions and the particle distribution. Using this formalism, PMC particle distributions are related to the observed scattering spectrum. The scattering spectrum always exhibits a peculiar “hump” at ∼260 nm that cannot be explained by any effect other than the particle distribution. A lognormal distribution of small particles (mode ∼ 50 nm) produces the overall shape of the spectrum but not the “hump.” Although not unique, a simple bimodal distribution of small particles (r ∼ 50 nm) and large particles (r ∼ 200 nm) describes the scattering spectrum and its hump very well. The clouds may therefore consist of two different populations, as suggested by some models of the clouds. Numerically, smaller particles dominate by about 10:1, but the larger particles strongly influence the scattering spectrum.

Received 29 March 2004; accepted 16 June 2004; published 15 July 2004.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0340 Atmospheric Composition and Structure: Middle atmosphere—composition and chemistry; 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation.

Read Full Article (file size: 127578 bytes)    Cited by

Citation: Carbary, J. F., D. Morrison, and G. J. Romick (2004), Evidence for bimodal particle distribution from the spectra of polar mesospheric clouds, Geophys. Res. Lett., 31, L13108, doi:10.1029/2004GL020101.