POAM II/III PMC Research
Although the POAM II and POAM III instruments were not
specifically designed nor their orbits especially suited to observe
Polar Mesospheric Clouds (PMCs), the instruments have proven sensitive enough
to definitively distinguish PMC signatures in the data. So, while PMCs are not
a major research emphasis in the POAM II/III project, analysis has been made in
this area. Since this is the first time that PMCs have been observed in
extinction, the data set and its analysis is quite unique and can add to the
understanding of this atmospheric phenomenon.
PMCs and Noctilucent Clouds (NLCs) are believed to be two different names for the same phenomenon, namely clouds of ice particles which form slightly below the cold summer mesopause where temperatures routinely fall below 140 K. This occurs during an approximately 12 week period centered about two weeks after solstice. This is approximately from mid-November to late-February in the SH and from mid-May to late-August in the NH. Generally these clouds are called PMCs when viewed from space and NLCs when viewed from the ground, whose only differences are due to a diurnal effect on the particle size.
The POAM II instrument aboard the French SPOT3 satellite has observed three seasons of PMCs in each hemisphere. Because of our latitudinal coverage, and the time of the year during which we can observe PMCs, the number of observations of PMCs in the Northern Hemisphere has been extremely small. Therefore, the emphasis on analysis of POAM II data has been in the Southern Hemisphere.
The POAM III instrument has observed one season of PMCs in each hemisphere. As with POAM II, the emphasis on analysis of PMC data has been in the Southern Hemisphere.
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