TRANS-POLAR PROPAGATION OF Pi1 WAVE BURST AS OBSERVED BY AN ANTARCTIC ARRAY DURING THE THEMIS 2007/03/23 SUBSTORM

We have analyzed bursty Pi1 emissions that occurred during an interval of substorm activity on March 23, 2007. Magnetometer observations from the multi-spacecraft Themis mission and from the search- coil magnetometers in Antarctica are augmented by UVI images from the Polar satellite. Dynamic spectra from high-latitude stations reveal that Pi1 bursts can propagate poleward, even across the polar cap. Surprisingly, Pi1 propagation at high latitudes is more efficient than that of Pi2 pulsations. We infer that the propagation mechanism for Pi1 is the partial wave energy trapping in the ionospheric waveguide. The band-limited spectral structure of Pi1 burst can arise owing to the combination of a cutoff at lower frequency, and a weaker excitation and stronger attenuation at higher frequencies.