Inter-hemispheric comparison of PMCs and their environment from SOFIE observations

Observations of polar mesospheric clouds (PMC) and their environment from the Solar Occultation For Ice Experiment (SOFIE) are examined to quantify differences between the Northern Hemisphere (NH) and Southern Hemisphere (SH) during summer. The results indicate that hemispheric differences are smaller when using pressure as the vertical coordinate, instead of altitude. The peak in PMC mass density (Z(max)) was found to exist 1.2 km higher in the SH, but at about the same pressure (similar to 0.0055 hPa) in both hemispheres. This occurs because systematically warmer temperatures in the SH polar summer stratosphere and mesosphere expand the overlying atmosphere to raise the altitudes of pressure levels in the SH mesosphere relative to the NH. For the five southern and five northern PMC seasons observed to date, the primary differences are that PMCs in the Northern Hemisphere are more frequent (24% +/- 32%), have greater ice mass density (65% +/- 26% at Z(max)) and exist for a longer seasonal period (10 +/- 10 days). These differences are attributed primarily to lower temperatures (4 to 9 K) in the north because water vapor differences are small (1.9% +/- 5.4% at Z(max)). 2012 Elsevier Ltd. All rights reserved.