Ionospheric conductivity modulation in ULF pulsations

Using incoherent scatter radar and magnetometer measurements, we report tha t during terrestrial magnetic Pc5 pulsations in the afternoon sector, a mod ulation of particle precipitation and ionospheric conductivities by a facto r of 2 occurs in addition to high-amplitude variations of electric and magn etic fields. The event thus seems to be considerably more complicated than previously studied ones where information about conductivities was mostly n ot available. Our ground-based data set gives us several clues about magnet ospheric processes. The origin of the conductivity variations seems to be p eriodically modulated diffusion of hot electrons into the loss cone that is in turn caused by a ring current instability. The direction of the phase p ropagation of the observed disturbances is also consistent with the hypothe sis of a ring current source. From the ionospheric electron densities we ca n roughly estimate the equatorial phase space diffusion rate which seems re latively high. In addition, strong electric field and Poynting flux variati ons suggest that intense coupling to shear Alfven modes happens in the magn etosphere. The latitudinal variation of power and wave polarization shows f eatures of a field line resonance. Furthermore, power spectral analysis of conductivities, electric and magnetic fields, reveals that there is a turbu lent-like background in all three parameters, which is of magnetospheric or igin but modified by the ionosphere. The power law slope of the conductivit y spectra is comparable to that of the electric field, while the ground mag netic field shows a steeper decrease with frequency because of the shieldin g of small-scale current structures. A clear anticorrelation between conduc tivities and the eastward electric field is interpreted as an ionospheric p olarization effect, which transmits Alfven waves from the ionosphere upward . Finally, we show that due to the time-varying conductivities only the han dedness (ratio of left- and right-handed components) of the Hall current is very close to that of the magnetic field, while the electric field has a s ignificantly different polarization.