Association of Alfvén waves and proton cyclotron waves with electrostatic bipolar pulses: magnetic hole events observed by Polar
- 1Indian Institute of Geomagnetism, Colaba, Mumbai, India
- 2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
- 3Department of Physics and Astronomy, University of Iowa, Iowa City, IA, USA
Abstract. Two magnetic hole events observed by Polar on 20 May 1996 when it was in the polar cap/polar cusp boundary layer are studied. Low-frequency waves, consisting of nonlinear Alfvén waves and large amplitude (±14nT peak-to-peak) obliquely propagating proton cyclotron waves (with frequency f~0.6 to 0.7 fcp), accompanied by electric bipolar pulses (electron holes) and electron heating have been observed located within magnetic holes. It is shown that low-frequency waves can provide free energy to drive some high frequency instabilities which saturate by trapping electrons, thus, leading to the generation of electron holes.