Measurements and theory of Scattering cross sections of PMSE with the EISCAT VHF and UHF radars

La Hoz, C. and Havnes, O.

University of Tromsų, Tromsų, Norway

Simultaneous and collocated measurements of PMSE and electron density in the D- and E-regions of the ionosphere with the EISCAT radars have allowed to make accurate absolute calibrations of the PMSE scattering cross sections at 224 MHz (Bragg wavelength of 67 cm) and at 930 MHz (Bragg wavelength of 16 cm). These measurements give volume scattering cross sections of 5250x10-18 and 3.5x10-18 m-1 for the VHF and UHF radars respectively. These unprecedented measurements allow to make a crucial test to the theory of PMSE that asserts that electron turbulence induced by neutral air turbulence can be maintained at the necessary scale lengths by an extension of the Kolmogorov spectrum due to the presence of charged nanometer size ice particles which causes an enhancement of the Schmidt number. Using a model of of the Kolmogorov spectrum proposed by Hill that incorporates the Schmidt number, it has been possible to fit to the model the Schmidt number and the dissipation rate of electron density variance, given the two measurements of the volume scattering cross sections. In particular, the Schmidt number turns out to be of the order of a thousand. This number implies charge numbers of the ice particles from the order of ten to several tens, depending on the width of the PMSE spectrum, namely, the intensity of the turbulence. Since reliable models of charged ice in the mesosphere indicate very low charge numbers, of the order of a few charges, it is unlikely that this theory can explain these measurements.