HR: 14:10h
AN: SA13B-03    [Abstracts]
TI: Long-Term Variations in PMC Frequency as a Function of Latitude from SBUV
AU: * Shettle, E P
EM: shettle@nrl.navy.mil
AF: Naval Research Laboratory, Code 7227, Washington, DC 20375-5351, United States
AU: DeLand, M T
EM: matthew_deland@ssaihq.com
AF: SSAI, Suite 600 10210 Greenbelt Rd, Lanhham, MD 20706, United States
AU: Thomas, G E
EM: thomas@lasp.colorado.edu
AF: LASP, University of Colorado, Boulder, CO 80309-0392, United States
AU: Olivero, J J
EM: oliveroj@erau.edu
AF: Embry-Riddle Aeronautical University, Physical Sciences Dept., Daytona Beach, FL 32114, United States
AB: An earlier analysis of the Polar Mesospheric Cloud (PMC) measurements from the Solar Backscatter Ultraviolet (SBUV & SBUV/2) satellite measurements found that there was a weak long-term increase in the frequency of occurrence of PMCs, which was not statistically significant [DeLand et al. 2003]. Since then, a new Version 3 data set has been developed using an improved PMC detection algorithm which produces more consistent results under all measurement conditions. DeLand et al. [2007] have used this new data set to examine the long-term variations in the PMC brightness. We have utilized this Version 3 data set to examine the corresponding long- term variations in the PMC frequency as a function of latitude. The occurrence frequency data are adjusted for local time effects before merging the overlapping data sets from different SBUV/2 instruments for trend calculations. Preliminary results indicate that while there is a positive trend in all latitude bins, the trend was only about 6% per decade in the lowest latitude bin (50° to 64°) in both hemispheres, and was not statistically significant. At higher latitudes (64° to 74°, and 74° to 82°) the trend was much stronger in both hemispheres (approximately 15% to 25% per decade), and statistically significant. There is also a strong anti-correlation with the long-term variation of solar Lyman-alpha flux, with a peak-to-peak solar cycle variation of approximately a factor of 2 for all latitudes. The weak long-term increase at 50° to 64° N is comparable with that found in the ground based Noctilucent Cloud (NLC) observations for Northern Europe recently updated by Kirkwood et al. [accepted by Ann. Geophys., 2007].
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0340 Middle atmosphere: composition and chemistry
DE: 1610 Atmosphere (0315, 0325)
DE: 1640 Remote sensing (1855)
DE: 1650 Solar variability (7537)
SC: SPA-Aeronomy [SA]
MN: 2007 Fall Meeting