Enhanced whistler instability produced by suprathermal electrons upstream of the Earth's bow shock

Destabilization of the whistler mode by electrons possessing both a temperature anisotropy and a power law tail in particle energy is investigated employing a generalized bi-lorentzian velocity distribution for the electrons. Such a velocity distribution is a good model for the high energy part of the electron distribution upstream of the Earth's bow shock and in the foreshock. It is found that the generalized bi-lorentzian distribution is much more strongly unstable to the generation of parallel whistlers than is a bi-Maxwellian with similar temperature anisotropy. The excited wavenumbers and frequencies are smaller than they are for a bi-Maxwellian. It is suggested that this instability might play a role in the generation of some of the low to intermediate frequency (90 Omega(i) < omega < 400 Omega(i)) whistler bursts observed upstream of the Earth's bow shock and in the foreshock.