Investigation of the Mesospheric PMSE Conditions by Use of the New Overshoot Effect

Abstract

We present a model for the recently discovered PMSE overshoot effect. The overshoot effect is created during radar observations of the mesospheric Polar Mesospheric Summer Echoes (PMSE), when the PMSE strength is modified by artificial electron heating over a short period which in our cases were 20 s. Thereafter the heater is switched off for a long period (160 s) so the plasma and dust charges are allowed to relax back to their undisturbed values. This heater cycling is then repeated throughout the observing run. This results in a series of what we have called overshoot characteristic curves (OCC) which contain information on the state of the PMSE dusty plasma. The form of the OCC strongly support a model where the radar scattering is controlled by many small dust structures within the PMSE region, each of which will produce an electron gradient, with a strength which will depend mainly on the density and size of the dust, the electron density and temperature. It is the electron gradients which cause the PMSE radar scattering. With this model, and assuming an average dust structure to represent the PMSE dust structures, we follow the changes of the dust charging and the electron density through one cycle where the heater is switched on and off, and show how the resulting relative scattering efficiency reproduce observed OCC. We show that we can obtain values for the increase of electron temperature as the heater is switched on, the dust content, and from the relaxation time of the OCC the photodetachment rate or an upper limit to it. Other information may possibly also be obtained from the OCC, such as the electron density from electron heating calculations when the temperature is known, and information on to what degree absorption of plasma during the electron heating phase is important.