Odin/OSIRIS limb observations of polar mesospheric clouds in 2001–2003

Two years of Odin/OSIRIS measurements of the limb-scattered solar radiance are analyzed with respect to polar mesospheric clouds (PMCs) in both the southern hemisphere (SH) and the northern hemisphere (NH). Spatial and temporal distributions, tangent altitudes (TAs) and the brightness of PMCs during two SH summers of 2001/2002 and 2002/2003, and two NH summers of 2002 and 2003 are presented. The Odin/OSIRIS data clearly indicate inter-annual and inter-hemispheric differences in both PMC altitudes and brightness. Most of the SH clouds were detected between 70°S and 82°S, the lowest PMC latitude was 61.4°S in 2001/2002 and 54.7°S in 2002/2003, and only eight clouds were observed equatorward of 70°S in 2001/2002 compared to 33 clouds in 2002/2003. In 2002, NH clouds were observed later (by about 9 days), were in general less frequent and their maximum detection frequency was registered 2 weeks later than in 2003. The number of PMCs observed equatorward of 60°N in 2003 was almost twice as high as in 2002. The inter-annual variability of PMC properties in the NH was generally lower than in the SH. The PMC detection frequency in the SH was about 40% lower than in the NH. The inter-hemispheric difference in the mean PMC TA was between 1.1 and 2.3 km with NH clouds lower than SH clouds. The inter-hemispheric difference in the mean PMC brightness was about ∼35–40% with the NH clouds being brighter.