On the latitudinal extent of chorus emissions as observed by the Polar Plasma Wave Instrument

The statistical distribution of chorus wave power in the off-equatorial region is evaluated using data from the Plasma Wave Instrument (PWI) Sweep Frequency Receiver (SFR) on board the Polar spacecraft. Maps of average wave power in the meridional plane divided into four local time sectors are presented. The geomagnetic dependence of wave power is examined, and substorm activity and enhanced solar wind speed result in distinctly different wave distributions. The maximum latitudinal extent of chorus as a function of latitude and L* is estimated within the orbit constraints of the spacecraft, and on the basis of this the corresponding minimum resonant energy for first-order relativistic cyclotron resonance is calculated using a realistic magnetic field model.