The seasonal variation of auroral ion beams

We present observations of a seasonal variation in the occurrence frequency of upflowing ions beams near 1 RE altitude in the 1800-2400 local time sector. These observations were obtained from the Toroidal Imaging Mass-Angle Spectrograph (TIMAS) instrument during POLAR satellite perigee passes from March 1996 to September 1997. We show that the observed variation is most simply interpreted as a variation in the magnitude of the auroral acceleration process responsible for creating upflowing ion beams and precipitating energetic electrons. These observations, the first to find a seasonal effect in the occurence of ion beams, also confirm previous reports which examined related phenomena and provide further evidence that changes in ionospheric conductivity have a measurable effect in the strength of the interaction between the Earth's magnetosphere and ionosphere.