Physics
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmsa51a..05s&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SA51A-05
Physics
0300 Atmospheric Composition And Structure, 0305 Aerosols And Particles (0345, 4801, 4906), 0320 Cloud Physics And Chemistry, 0341 Middle Atmosphere: Constituent Transport And Chemistry (3334), 0360 Radiation: Transmission And Scattering
Scientific paper
The POAM (Polar Ozone and Aerosol Measurement) II and III solar occultation instruments were designed primarily for stratospheric measurements. However, they demonstrated sufficient sensitivity to detect Polar Mesospheric Clouds (PMCs), [Debrestian et al. 1997]. While all POAM measurements are made at high latitudes, they are not optimized for PMC observation since POAM is measuring furthest away from the poles at the summer solstices, 63° S in the Southern Hemisphere (SH) and 54° N in the Northern Hemisphere (NH). Because of the hemispheric asymmetry in the measurement latitudes there are very few PMC observations in the NH, so our analysis has been focused on the SH. POAM II operated from October 1993 to November 1996, and POAM III from April 1998 to December 2005, providing a total of ten seasons of PMC measurements. The 0.8 km vertical field-of-view of POAM allows us to determine the altitude and vertical extent of the PMCs. The seasonally averaged altitude varies between 82 and 84 km, and the vertical thickness is between 2 and 3 km. While this latter value is much larger than the lidar measurements give, it should be recognized that the several hundred kilometer horizontal line-of-sight (LOS) of the limb-viewing geometry means any variation in the PMC altitude along the LOS would increase the apparent vertical thickness of the PMC. The POAM instruments measure atmospheric transmission at nine wavelengths ranging from 354 nm to 1018 nm. The spectral dependence of the PMC optical depth, obtained by subtracting the Rayleigh background from the measured total optical depth, can be used to determine the characteristic particle size of the PMCs. Using the four shortest wavelengths (354 to 603 nm), we find the mean effective radius of PMC particles is about 43 nm, with the densest clouds generally having the largest particles.
Alfred J. M.
Lumpe J. D.
Shettle Eric P.
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