Interplanetary magnetic field power spectra: Mean field radial or perpendicular to radial
Abstract
Power spectral, correlation, and coherency analyses have been made for selected periods of Pioneer 6 interplanetary magnetic field data for the frequency range of 5×10^{4} to 1.6×10^{2} Hz. The periods are chosen for times when the mean field was either radial or perpendicular to the heliocentric radius. At such times, some of the interpretive ambiguities which arise from the convection of the magnetic field by the solar wind are removed, and the field fluctuations can be understood in terms of the spatial dependence of wave or static structures. Results from the power spectral and coherency analyses for the radial field periods indicate the existence of constantmagnitude Alfvén waves propagating along the field as well as magnetosonic waves propagating obliquely to the mean field. No evidence for a significant component of circularly polarized Alfvén waves is found. Our results also rule out some magnetic field models which have been widely used in cosmic ray studies. Differences in the spectral slopes and power levels for magnetic field fluctuations parallel and transverse to the mean field indicate that the radial field indicate that the radial periods cannot be approximated by isotropic magnetic field fluctuations while the perpendicular periods are not fit by the 'slab' model. All periods are consistent with a superposition of Alfvén waves and magnetosonic waves with less than one quarter of the power in the magnetosonic waves as in Alfvén waves. Finally, autocorrelation analysis for the radial periods indicates that the correlation length for transverse magnetic fluctuations between discontinuities is 26 ×10^{10} cm.
 Publication:

Journal of Geophysical Research
 Pub Date:
 November 1976
 DOI:
 10.1029/JA081i031p05489
 Bibcode:
 1976JGR....81.5489S
 Keywords:

 Interplanetary Magnetic Fields;
 Magnetic Field Configurations;
 Pioneer 6 Space Probe;
 Power Spectra;
 Autocorrelation;
 Coherent Radiation;
 Frequency Measurement;
 Frequency Ranges;
 Magnetic Flux;
 Magnetoacoustic Waves;
 Phase Velocity;
 Radial Distribution;
 Solar Wind Velocity;
 Spatial Distribution;
 Wave Propagation;
 Astrophysics