Heliocentric distance dependence of the interplanetary magnetic field

Journal Article · Wed Feb 01 04:00:00 EST 1978 · Rev. Geophys. Space Phys.; (United States)

DOI:https://doi.org/10.1029/RG016i001p00125· OSTI ID:7075391

Behannon, K W

Recent and ongoing planetary missions have provided and are continuing to provide extensive observations of the variations of the interplanetary magnetic field (IMF) both in time and with heliocentric distance from the sun. Large time variations in both the IMF and its fluctuations are observed. These are produced predominantly by dynamical processes in the interplanetary medium associated with stream interactions. Magnetic field variations near the sun are propagated to greater heliocentric distances, a process also contributing to the observed variability of the IMF. Temporal variations on a time scale comparable to or less than the corotation period complicate attempts to deduce radial gradients of the field and its fluctuations from the various observations. However, recent measurements inward to 0.46 AU and outward to 5 AU suggest that the radial component of the field on average decreases approximately as r/sup -2/, as was predicted by Parker, while the azimuthal component decreases more rapidly than the r/sup -1/ dependence predicted by simple theory. Three sets of observations are consistent with r/sup -1.3/ dependence for vertical-barB/sub phi/vertical-bar. The temporal variability of solar wind speed is most likely the predominant contributor to this latter observational result. The long-term average azimuthal component radial gradient is probably consistent with the Parker r/sup -1/ dependence when solar wind speed variations are taken into account. The observations of the normal component magnitude vertical-barB/sub theta/vertical-bar are roughly consistent with a heliocentric distance dependence of r/sup -1.4/. The observed radial distance dependence of the total magnitude of the IMF is well described by the Parker formulation. There is observational evidence that amplitudes of fluctuations of the vector field with periods less than 1 day vary with heliocentric distance as approximately r/sup -3/2/, in agreement with theoretical models.

• Research Organization: Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771
• OSTI ID: 7075391
• Journal Information: Rev. Geophys. Space Phys.; (United States), Journal Name: Rev. Geophys. Space Phys.; (United States) Vol. 16:1; ISSN RGPSB
• Country of Publication: United States
• Language: English

Related Subjects

640107* -- Astrophysics & Cosmology-- Planetary Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
DISTRIBUTION
INTERPLANETARY MAGNETIC FIELDS
MAGNETIC FIELDS
POWER
SHOCK WAVES
SOLAR ACTIVITY
SOLAR WIND
SPACE VEHICLES
SPATIAL DISTRIBUTION
VARIATIONS