Sun-Earth connection: Boundary layer waves and auroras

Boundary layers are the sites where energy and momentum are exchanged betwe en two distinct plasmas. Boundary layers occurring in space plasmas can sup port a wide spectrum of plasma waves spanning a frequency range of a few mH z to 100 kHz and beyond. The main characteristics of the broadband plasma w aves (with frequencies > 1 Hz) observed in the magnetopause, polar cap, and plasma sheet boundary layers are described. The rapid pitch angle scatteri ng of energetic particles via cyclotron resonant interactions with the wave s can provide sufficient precipitated energy flux to the ionosphere to crea te the diffused auroral oval. The broadband plasma waves may also play an i mportant role in the processes of local heating/acceleration of the boundar y layer plasma.