A statistical survey of electron temperature enhancements in heater modulated polar mesospheric summer echoes at EISCAT

A statistical analysis has been made of 49 Polar Mesospheric Summer Echoes (PMSE) active modulation experiments between 1999 and 2007. PMSE are associated with charged icy dust particles in the polar summer mesopause and can be observed as bands of coherent backscatter in the EISCAT VHF radar. The PMSE signature can be reduced, as seen in the VHF radar, by means of heating the ionosphere with powerful high frequency (HF) radio waves. This technique has long been used to investigate the PMSE phenomenon. However, PMSE modulation experiments sometimes fail. We use a computational model to estimate the enhanced electron temperatures due to ionospheric heating from HF radio waves in the D-region. We show for the first time the statistical relationship between PMSE backscatter reduction with artificial electron temperature enhancement. For the electron temperatures achievable by HF pumping (<3500 K), the PMSE is never completely destroyed. For experiments where the PMSE modulation experiment failed, we show that the PMSE layer was too high in altitude for ionospheric heating by HF waves to have any effect. In addition, we present initial results of the 2008 PMSE modulation campaign where the HF pump power was stepped in order to regulate the electron temperature in a controlled manner.