ELECTRON HEATING EFFECTS ON POLAR MESOSPHERIC CLOUDS - A COMPARISON BETWEEN OBSERVATIONS AND MODELLING

We discuss simultaneous and collocated radar observations at 56 and 224 MHz, of polar mesospheric clouds modulated by artificial electron heating. While the backscatter at 56 MHz often increases when the heating is turned on, the 224 MHz radar nearly always sees the "normal" overshoot behavior with an initial rapid reduction of backscatter. However, in some few heater cycles we see the same rapid and strong increase of both the 56 MHz and 224 MHz, to levels several times above that just before the heater was switched on. In higher layers, both radars see a clear reduction of the backscatter as the heater is switched on with little recovery during the heater on time. The reaction when the heater was switched off was a clear overshoot for nearly all VHF cases but less so for MORRO. We discuss the different results in comparison with modeling.