Unstable growth of unducted whistlers propagating at an angle to the geomagnetic field

Abstract

The local growth rate for whistler waves propagating at an angle to the geomagnetic field is combined with model ray path calculations to estimate the wave growth along the whistler path. This growth rate depends critically upon the equatorial plane distribution of electrons in the few hundreds of electron volt energy range. When the electron energy spectrum between 10² ev and ∼104 kev is sufficiently hard, ∼1/E², there exists a narrow region, |λ| ≈ 15°, of whistler growth near the equatorial plane sufficient to make a whistler mode unstable over-all as it bounces back and forth across the equatorial plane between reflection points. The region of cyclotron growth shrinks for softer energy spectra. Only unducted whistlers generated by resonant particle instabilities are treated.