Chorus observations by the Polar spacecraft near the mid-altitude cusp

Observations of whistler-mode emission, including chorus, were made frequently by mid-altitude satellites such as Polar. In this study we examine an example of such emission when the high-frequency waveform receiver on board Polar was operating allowing direction-finding and polarization measurements in the low-altitude cusp. The results reveal at least two and possibly three distinct groups of narrow-banded chorus emission with a primary source region at the magnetic equator. The groups include emission propagating near the resonance cone angle, emission propagating along a density duct, and possibly emission reflected from the low-altitude cusp. The results indicate that the mid- and low-altitude cusp, perhaps unlike the high-altitude cusp, is not a significant source of narrowband chorus emission.