HF‐Induced Modulation and Electron Temperature Effects in PMSE: VHF Spectral Diagnostics and Dusty Plasma Interpretation

Abstract This study presents the first experimental investigation of Polar Mesospheric Summer Echoes (PMSE) response to high‐frequency (HF) pump power modulation using the EISCAT VHF radar system. Two modulation schemes were employed during a recent campaign: stepped‐power modulation (24 July 2019) and quasi‐continuous power sweeping (26 July 2019). Coherent VHF radar spectra were analyzed to evaluate the impact of HF heating on PMSE characteristics. Results consistently show a contraction in the VHF spectral area with increasing HF pump power (40–80 kW), indicating suppression of small‐scale electron density irregularities. This spectral narrowing is attributed to enhanced diffusion and dust charging processes driven by elevated electron temperatures. The ratio of diffusion to charging timescales is used as a key diagnostic to interpret these changes. Numerical simulations incorporating realistic dust cloud parameters reproduce the observed trends and reveal layer‐specific responses, with lower PMSE layers exhibiting stronger overshoots and higher dust densities. These findings demonstrate that the spectral area under the VHF echo serves as a sensitive proxy for electron temperature enhancements during HF heating, offering a valuable diagnostic tool for studying mesospheric turbulence and dusty plasma dynamics.