THEORY OF QUASI-MONOCHROMATIC WHISTLER WAVE GENERATION IN THE INNER PLASMA SHEET

Nonlinear interactions between plasma sheet electrons and nearly monoc hromatic whistler wave packets are studied. The theory applies to the generation of chorus emissions from quasi-monochromatic wavelets obser ved in the plasma sheet at the top of the ELF/VLF hiss band. The hiss- triggered chorus is produced by step-like deformations that develop in distribution functions at the boundaries between resonant and nonreso nant electrons. Equations are obtained describing the wave amplitudes and frequency-time characteristics for propagation at small angles wit h respect to the geomagnetic field. The linear resonant interactions l eading to wavelet generation are investigated. The resonant wave frequ encies change along the field Lines to compensate for geomagnetic fiel d inhomogeneities. Lf the electric fields exceed the amplitudes of tho se in the background plasmapheric hiss (>> 10(-6) V/m), electrons beco me trapped in phase space and their distribution functions develop pla teaus whose extents are proportional to the square roots of electric f ield amplitudes. Nonlinear currents generated by the trapped electrons are studied to obtain analytical representation of the growth rates a nd frequency spreads. Numerical examplies are presented to illustrate our theoretical analysis.