Radar, Lidar, and Optical Observations in the Polar Summer Mesosphere Shortly After a Space Shuttle Launch

Abstract

In the summer of 2007, a noctilucent cloud (NLC) campaign was organized in Alaska. Radar, lidar, and photographic methods were used. Due to lighting conditions, the campaign was carried out near the end of the NLC season. Sporadic radar and lidar echoes were obtained until the very end of the campaign, when an exceptionally intense event occurred on the local time night of 10–11 August. This late-season event followed the launch of the space shuttle on 8 August. At least twice before, solstice launches of the shuttle have been followed by unique observations of NLC and sporadic iron layers in the polar regions. This was the case here as well. The iron layer increased in altitude and density, the latter by a factor of 20, compared to the previous night. And, for the first time, (1) polar mesospheric summer echoes (PMSE) were recorded by a radar in an event of this nature and (2) an intense sporadic E layer was collocated with the iron atom layer. At the UHF radar frequency used, very large Schmidt numbers are required for PMSE. Indeed, the PMSE was found at and just above the particles responsible for Mie scatter. Such large particles are likely needed to yield large Schmidt numbers. Additionally, similar lidar and sporadic E layers were detected over Greenland on the previous night. Here we consider the ion chemistry that could lead to the collocated atom and iron layers and conclude that considerably enhanced water vapor content was required.