Dynamic effects of electron heating on Polar Mesospheric Clouds

Summary form only given. Polar Mesospheric Clouds (PMCs) are composed of dust grains (aerosols) of submicron size at altitudes 80-90 kilometers. The dust grains acquire electric charges and they may change significantly the properties of the surrounding D-region ionosphere plasma. The PMCs are believed to be the major cause of Polar Mesosphere Summer Echoes (PMSE) whose nature is not yet fully understood. The dust charge is determined by grain sizes, dust material composition, and ionospheric parameters. It fluctuates due to the discrete nature of the attaching or detaching ionospheric particles (free electrons and ions). The average aerosol charge is determined by the balance between the thermal fluxes of free electrons and ions and possible photoionization caused by Solar radiation and determined by the properties of the dust material. Rapid heating of free electrons by strong HF heating should modify the average dust charge and accordingly the density of free electrons. Monitoring dynamical variations of free-electron density during specially arranged pulsed HF heating may provide some useful information about the dust properties. Free-electron density variations could be measured by sensitive UHF or VHF radars. Radar-observed PMSE can also serve as a proxy of such variations. A recently discovered effect of the HF heating on PMSE is not connected directly with the dust charge variations, but the underlying experiment sets a proper way for future observations.