Modulations in the polar mesosphere summer echoes and associated atmospheric gravity waves

Abstract
Mesospheric observations were made by the EISCAT VHF radar. On one occasion a relatively weak Polar Mesosphere Summer Echo (PMSE) was observed with its intensity varying with a period of about 27 minutes. Immediately below the PMSE layer an atmospheric gravity wave was observed, also with a period of about 27 minutes. The maximum intensity of the PMSE corresponded to the maximum upward velocity associated with the wave. Particle precipitation, adiabatic cooling due to the upward velocity and wave steepening and breaking at the mesopause may all play a role in causing PMSEs.