Polar mesosphere summer echoes and noctilucent clouds: Simultaneous and common‐volume observations by radar, lidar and CCD camera

Abstract

Simultaneous and common‐volume VHF radar and lidar measurements of polar mesospheric summer echoes (PMSEs) and noctilucent clouds (NLCs) have been successfully performed during August 10/11 and 13/14, 1997 from Esrange in northern Sweden (68°N, 21°E). There was no one‐to‐one correlation of PMSEs and NLCs in the observed volume during these observations. Rather, regions of PMSE, separated in altitude and time, showed an apparent evolution from PMSE alone to NLC alone to combined PMSE/NLC. A CCD camera observed the night sky above Esrange at the same time from Lycksele, 372km south of Esrange. While the first lidar NLC on August 10/11 was also detected by the camera, the second lidar NLC remained invisible to the camera in spite of clear skies. For the first NLC the altitude and the optical thickness are anticorrelated, showing a periodicity of 20.5±2.5 min. We associate this modulation with the NLC band structure seen on the camera images. We can show that the modulation, the radar winds, and the band orientation form a consistent data set. The change in orientation of the visual NLC bands during this night, the two distinct lidar NLCs, in combination with the change in mesospheric winds give evidence for advection of different airmasses over our volume of measurements.