Conductivity profiles of the disturbed polar ionosphere from VLF reflection data

Two independent techniques are used to determine conductivity profiles of the lower polar ionosphere during a strong solar proton event (SPE). The first method inverts reflection coefficients measured with a groundbased VLF sounder; the second uses proton fluxes measured on board satellites to calculate ion-pair production rates, which, in turn, are input to lumped-parameter de-ionization equations. Conductivities determined by the two methods exceed ambient by two or more orders of magnitude, but disagree by up to an order of magnitude at altitudes between fifty and sixty kilometers. Full-wave calculations are used to predict the effect of the SPE-disturbed profiles on long range VLF propagation in the earth-ionosphere waveguide. The SPE is found to suppress the geomagnetically converted transverse electric field radiated by a groundbased vertical electric dipole.