Time evolution of artificial electron heating in polar mesosphere summer echo layers

Abstract

Artificial electron heating by the use of high‐energy transmitters can have a strong effect on the observed strength of the radar polar mesospheric summer echoes (PMSE). This heating can make PMSE go through a sequence where it nearly disappears as the heater is turned on and can also cause PMSE to overshoot its preheating strength by a large factor as the heater is switched off. Modeling the effect of heating on the PMSE scattering has shown that the form of the variation in PMSE intensity during the heater cycling is crucially dependent on the amount of electron heating and on the dust and plasma conditions. In the present paper we examine if and when the model assumption that the electron temperature Te stays constant during the heating after the first sudden rise when the heater is switched on is correct. We find that this is valid for low values of the ratio between the charge density of dust and electron charge density throughout the PMSE layer since dust has little effect on the electron density. However, when this ratio is not small compared to 1, so we have an electron bite‐out, the increased electron temperature and collision rate of electrons and dust particles can now lead to a significant reduction in the electron density. This will lead to a reduction in the absorption of heater wave energy in the bite‐out, and more wave energy will become available in its upper parts and in the PMSE above it where the electron temperature now will increase. This situation does, however, require that a substantial fraction of the heater wave energy reach the PMSE layer so that at least the lower parts of it are strongly heated.