Magnetic field short-period fluctuations ΔB are observed throughout the earth's magnetosheath. We report a study of these fluctuations with frequencies 20<f<1000 Hz in which the turbulence has a broadband spectrum ΔB2(f) varying approximately as f-a, where &agr;~4¿0.5, or consists of a narrowband intermediate frequency peak superimposed on the broadband spectrum. The spectrum is interpreted as due to whistler turbulence in both cases. The broadband fluctuations may arise from the cascade of spectral power from lower-frequency (~0.01 Hz) magnetohydrodynamic modes, while the narrowband peak corresponds to short-period lion roar bursts. The usual whistler cutoff as f approaches fge the electron gyrofrequency, is observed, as well as the polarization of the wave amplitudes perpendicular to the static magnetic field. The frequency of occurrence of whistler turbulence maximizes in the inner regions of the sunward magnetosheath, apparently associated with compressional modes in MHD fluctuations which tend to occur preferentially in the same region. The distribution of fluctuation amplitudes at 200 Hz suggests a tendency for the greatest whistler mode intensities to occur near the magnetopause, a result which contrasts with the intensity distribution of 1-kHz electrostatic waves, which tends to maximize at the bow shock.

These two intensity distributions are thus indicative of the different wave-particle interactions occurring at the inner and outer boundaries of the magnetosheath. The mapping of the magnetosheath in space by the occurrence of whistler turbulence indicates whistlers are at least quasi-trapped in the magnetosheath.