Pc1 propagation in the ionopsheric duct: dispersion relation and source structure

Pc1 geomagnetic pulsations (Pc1) observed on the ground at subauroral latitudes are signatures of ion cyclotron waves at frequencies between 0.2 and 5.0Hz in the inner magnetosphere. When the waves reach the ionosphere, they induce time-varying Pedersen and Hall currents that generate both Alfven and fast mode waves in the ionospheric duct. The fast mode waves propagate horizontally and are observed in distant areas at lower latitudes from the wave entrance region. Previous theoretical studies have shown attenuation rates, polarizations, and dispersion relations of those waves. So far no observational study found a Pc1 dispersion relation and compared with theoretical results. We have investigated wave vectors of Pc1 pulsations both with the 2D Wave Telescope technique and with the minimum variance analysis. We also have investigated the spatial power distribution of Pc1 pulsations. For our study, we used ground-based measurements of Pc1 pulsations from 27 May 2011, observed at 17 different stations of the Canadian magnetometer network CARISMA (www.carisma.ca). We identified the frequency-wave number relation that shows a behavior of fast mode waves. Furthermore, we found that the attenuation rates of Pc1 wave power are larger along the meridian than normal it, in contrast to theoretical results. The possible source structure of incident Alfven waves will be discussed using power distributions of Pc1 pulsations by considering both effects of attenuation and conversion to fast mode waves.