Recent Investigations of Polar Mesospheric Summer Echoes (PMSE) Subject to RF Modification with the MORRO and the EISCAT Radars

An investigation of Polar Mesospheric Summer Echoes (PMSE) subject to RF modification has been carried out with the MST MORRO radar operating at 56 MHz and the EISCAT radars at VHF 224 and UHF 930 MHz. MORRO is deployed at the EISCAT installation near Tromso in northern Norway home of the two other large incoherent scatter radars and an RF heating facility. It is known that under appropriate cycling of RF modification PMSE at the EISCAT VHF radar frequency shows an overshoot effect that is a result of the control of PMSE by charged dust particles. At the lower frequency of MORRO a different characteristic overshoot has been predicted by Chen and Scales (2005). In July 2008 a three-radar campaign was conducted involving MORRO the EISCAT VHF and UHF radars and the RF heater. Only weak effects of the heater on the PMSE measured by the 224 MHz radar were observed and a nearly absence of any effects on the PMSE measured by the 56 MHz radar. We investigate whether absorption of the heater wave in the lower D-region may have depleted the heater wave in the lower part of the D-region thus explaining the near absence of the expected heater effects on PMSE, that is, the overshoot effect with different characteristics for the MORRO and EISCAT VHF radars.