Computer Science – Sound
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsa41a1598s&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SA41A-1598
Computer Science
Sound
[0340] Atmospheric Composition And Structure / Middle Atmosphere: Composition And Chemistry, [0360] Atmospheric Composition And Structure / Radiation: Transmission And Scattering, [1610] Global Change / Atmosphere, [3360] Atmospheric Processes / Remote Sensing
Scientific paper
Polar Mesospheric Clouds (PMC) form in the upper mesosphere (~ 80 to 86 km) at latitudes greater than 50° during the summer season in each hemisphere. These clouds are formed of water ice particles, and thus can form only in regions where the temperatures are cold enough for water vapor to be saturated relative to ice. We can verify this assumption by comparing observations of PMCs made by the Ozone Monitoring Instrument (OMI) with coincident measurements of atmospheric temperature and water vapor made by the Microwave Limb Sounder (MLS) instrument, both of which fly on the Aura satellite. The large cross-track swath of the OMI measurements with sampling every 13 km along track ensures that there will be several OMI pixels (~13 km x 48 km) overlapping with the footprint of each MLS measurement (200 km x 12 km for temperature and 300 km x 6 km for water vapor). We calculate the saturation ratio with respect to ice from the MLS measurements of temperature and water vapor at a nominal PMC altitude of 0.006 mb (or about 83 km). The probability of OMI detecting a PMC and the brightness of these PMCs increases with decreasing temperatures and with increasing saturation ratio, as expected. The PMC events occurred at higher saturation ratios than the non-PMC events, and nearly all PMCs corresponded to MLS temperatures less than 160 K. The temperatures tend to be warmer in the Southern Hemisphere (SH) with correspondingly lower saturation ratios, resulting in fewer PMCs than in the NH. However, even for given temperature or saturation ratio there is still a greater probability of detecting PMCs and they are brighter in the NH than the SH. Possible explanations for this North/South asymmetry include hemispheric differences in the availability of ice nuclei, differences in gravity wave activity, differences in the local time of the measurements in each hemisphere and any tidal forcing.
DeLand Matthew T.
Levelt Pieternel
Nedoluha Gerald E.
Olivero John J.
Shettle Eric P.
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