Magnetic fluctuations in the frequency range 0.1 to 1 hertz observed upstream from the earth's bow shock

An investigation of variations in the magnetic field as observed upstream from the earth's bow shock is reported. The data upon which this study is based were obtained with the UCLA triaxial fluxgate magnetometer experiment on OGO 5 during its traversals into the upstream region in 1968 to 1969. Power spectra of upstream fields undisturbed by bow-shock-associated effects are presented for the frequency range 10-2 less than or equal to f approx. < 1 Hz. The interplanetary power spectrum thus obtained is shown to be devoid of spectral peaks, in general, and to have a power law dependence of f, P(f) proportional f-/sup α/, with 1.5 approx. < α approx. < 2. No significant coherences among the field vector components are found, and no definite preference for the radial, i.e., the sun-probe, component to be the least active component is evident. Magnetic fields disturbed by bow-shock-related effects measured in the upstream region on both sides of the sun-earth direction are found to have similar power spectra over the range 1number 10-2 less than or equal to f approx. < 1 Hz. The salient spectral characteristic of these fields is a strong peak in the range 0.01 to 0.05 Hz, marked by significant coherences among the vector components at the peak frequency. The spatial distribution of the upstream field fluctuations in the range 0.07 less than or equal to f approx. < 1 Hz is presented. For the afternoon side of the sun-earth direction no unambiguous radial dependence of the total field rms amplitudes deltaB/sub T/ can be derived. The morning-side fields display a definite radial dependence, and contours for deltaB/sub T/, ranging from 0.4γ to 0.9γ, are presented