Microstructure of the interplanetary magnetic field near 4 and 5 AU

Journal Article · Fri Aug 01 04:00:00 EDT 1980 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JA085iA08p04275· OSTI ID:5096594

Parker, G D

Seventy-two days of vector magnetic field measurements from Pioneer 10 and 11 are analyzed for information about magnetic field fluctuations in the quiet solar wind near 4 and 5 AU. Calculated as functions of frequency over the range 4 x 10/sup -5/ to 9 x 10/sup -3/ Hz, directional properties of magnetic field fluctuations are presented and are discussed with reference to theoretical predictions for MHD plane waves. The distributions of maximum variance directions computed from approx. =500 spectral matrices for each spacecraft are peaked along the normal to the plane of the minimum variance direction and the mean magnetic field. This orientation is expected for a planar, small-amplitude Alfven wave with a minimum variance direction close to the wave vector. Noting also that magnetic fluctuations tend to conserve field magnitude, as is required for Alfvenic fluctuations, we infer that single small-amplitude Alfven waves are occasionally present in the temporal and frequency bands analyzed. However, statistics of the relative spatial orientations of the mean field and the minimum and maximum variance directions permit that waves with wave vectors not well approximated by the minimum variance direction, Alfven wave ensembles, finite-amplitude waves, and nonplanar fluctuations may also be present. Assuming that the minimum variance direction approximates the wave vector when a small-amplitude wave is present, we note that (1) among those data in which the field fluctuations behave in accord with theoretical predictions for single, planar, small-amplitude MHD waves, observations suggest the predominance of the Alfven mode over the fast and slow modes and (2) there is a general lack of observational support for theoretical models of outward propagating plane Alfven waves of solar origin.

• Research Organization: Department of Physics, Norwich University, Northfield, Vermont 05663
• OSTI ID: 5096594
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 85:A8; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

640107* -- Astrophysics & Cosmology-- Planetary Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALFVEN WAVES
DISTURBANCES
HYDROMAGNETIC WAVES
INTERPLANETARY MAGNETIC FIELDS
INTERPLANETARY SPACE
JUPITER PLANET
MAGNETIC FIELDS
MORPHOLOGY
PIONEER SPACE PROBES
PLANETS
SOLAR ACTIVITY
SOLAR WIND
SPACE
SPACE VEHICLES