Statistical study of PMSE response to HF heating in two altitude regions

Abstract

Polar mesospheric summer echoes (PMSE) often show different layers. Artificial electron heating experiments are an important diagnostic tool to investigate the parameters in the PMSE regions. The response of PMSE to high frequency heating in the lower (80-85 km) and upper (85-90 km) PMSE layers is studied by analyzing PMSE observations carried out by the EISCAT VHF radar in July 2007. Different characteristics of modulated PMSE (e.g., PMSE intensity reduction, recovery, overshoot, ratios during the heating-on and heating-off times) are analyzed and compared at different situations such as only in one layer (lower or upper) and in both layers simultaneously without high-energy particle precipitation. Based on statistical results, it is found that in the lower layer all characteristics of modulated PMSE except PMSE recovery are greater than that in the upper layer. Electron temperature enhancement and PMSE modulation index due to ionospheric heating were calculated to show the enhanced electron temperature effect on PMSE. It is found that in both layers usually higher electron temperature enhancement corresponds to higher PMSE modulation index. However, the comparison of statistical results shows that in the lower layer electron temperature enhancement and PMSE modulation index are greater than that in the upper layer. Based on the relation of electron temperature enhancement to the PMSE modulation index, it is concluded that the variability of electron temperature enhancement may be responsible for the variations in different modulated PMSE characteristics between the lower and upper layers.

Modulation of polar mesospheric summer echoes (PMSEs) with high-frequency heating during low solar illumination

“…To summarize, we see only overshoots in less than half of the cycles, with many cycles often more influenced by background ionospheric conditions that might overshadow the heating of the PMSE. Ullah et al (2019) show a more significant occurrence of overshoots in their observations, with around 40 %-70 %, where their observations were during daytime. Havnes et al (2015) observations had a much larger ratio of cycles with decline present and a slightly higher percentage of overshoots present.…”