Pi2 pulsation polarization patterns on the U.K. sub-auroral magnetometer network (SAMNET)

An array of seven fluxgate magnetometers has been deployed covering mid-latitudes in western Europe. The array is configured to allow simultaneous observations of mid-latitude pulsation characteristics in both latitude and longitude. Here the two-dimensional variations in the horizontal polarization of Pi2 pulsations are related to the substorm current wedge position, deduced from the midtitude bay behaviour, and an estimated plasmapause position. Features of the polarization pattern which are not in agreement with the substorm current wedge model are found. These include unexpected polarization ellipse azimuths and longitudinal phase propagations, and latitudinal variations in polarization ellipse azimuths not associated with ellipticity reversals. An extension of previous travelling wave models to include low latitude effects is considered, which may explain at least some of these discrepancies.