Electrostatic plasma instabilities in the daytime lower ionosphere

Using a model collision operator we derive the dispersion relation for high frequency electrostatic waves in the lower ionosphere for daytime, midlatitude conditions. We find that the suprathermal electrons near 5 eV can excite unstable electron cyclotron and upper hybrid waves. The possible role of these instabilities in determining the shape of the photoelectron energy spectrum from 2 to 6 eV is briefly discussed.