GENERATION MECHANISM OF POLAR MESOSPHERE SUMMER ECHOES

A generation mechanism of short-scale charge density fluctuations is c onsidered, which is based on the interaction between charged aerosol p articles and an updrafting airflow. The mechanism is analogous to that of the resistive beam-plasma instability. It is shown that the most f avorable conditions for the instability are realized at the height of mesospheric temperature minimum, h similar to 87 km, in the regions wh ere the electron density is relatively low and heavy ions are predomin ant. An attempt is undertaken to apply this mechanism for explanation of some types of polar mesosphere summer echoes (PMSE), which correlat e with atmospheric convective cells and intense gravity waves. The ins tability threshold can be achieved if an ionized air component include s a group of charged aerosol particles with the radius r(alpha) = 0.2 mu m and charge number \Z\ similar to 10(3), or two groups of light (r (alpha 1) similar to 10(-2)-10(-3) mu m, \Z(alpha 1) similar to 1) and heavy (r(alpha 2) similar to 0.1 mu m, \Z(alpha 2)\ similar to 10-10( 2)) particles with a small addition of electrons and ions.