Investigation of Polar Mesospheric Summer Echoes observed with the EISCAT VHF radar

Polar mesospheric summer echoes (PMSE) are strong radar echoes that can be observed in the mesosphere. They form at altitudes between 80 and 90 kilometres during summer in high and middle latitudes, when temperatures are low enough for ice particles to form. PMSE come from coherent scattering from irregularities in the electron density and are observed when the spatial structures of the electron density are at half the radar wavelength. It is assumed that ice particles are spatially structured by the neutral air turbulence and that via their surface charge they influence the electron density. The formation of PMSE depends on atmospheric characteristics such as turbulence, electron density and electron diffusivity. The size and lifetime of the ice particles which are involved in the formation of PMSE vary with height.

We investigate the properties of PMSE using selected data of EISCAT VHF observations made between 2010 and 2021. The observations were made using the Manda experiment, which is suitable for observing the mesosphere and the lower ionosphere; the observations have a time resolution of several seconds. The EISCAT real-time graphics software is used to determine the spectra at altitudes of 80-90 km.

Using a Gaussian fit, we determine the spectral width, Doppler shift and received echo strength and use thresholds for these parameters to classify PMSE. We present an analysis of these properties, their variation with the height, the characteristics of gravity waves seen in PMSE, and the correlation between spectral width and amplitude.