The heliospheric current sheet and modulation of galactic cosmic rays

Journal Article · Thu Nov 01 00:00:00 EST 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JA095iA11p18731· OSTI ID:5053178

Smith, E J ^[1]

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1. California Inst. of Tech., Pasadena (United States)

The relatively abrupt onset of cosmic ray modulation, observed in May 1987 on Earth and in September 1987 by the Pioneer 10 and 11 spacecraft, enables further investigation of the possible effect of the heliospheric current sheet on modulation. According to the gradient drift theory of cosmic ray transport, modulation is associated with solar cycle changes in the current sheet, whose inclination increases systematically from solar minimum to solar maximum. The measured used in testing this hypothesis is the difference in the maximum latitudinal extent of the current sheet in the northern and souther solar hemispheres. This difference is obtained from contours of the current sheet produced by extrapolating photospheric magnetic field measurements to a solar wind source surface. When the latitude difference, divided by 2 and called the pseudoinclination or pseudotilt angle, is compared with cosmic ray count rates measured on Earth, an excellent correlation is found, as in a previous study of modulation in the years 1976-1986. The abruptness of the onset can be attributed to the greater sensitivity of the cosmic ray intensity to changes in the current sheet when the solar-heliospheric magnetic field is inward in the northern hemisphere as predicted by the model. Thus the observations are found to be consistent with the predictions of the gradient drift model. A preliminary analysis is also carried out to test an alternative, but not necessarily incompatible, hypothesis that large-scale transient solar wind structures (coronal mass ejections, shocks, etc.) form barriers to the inward transport of cosmic rays.

• OSTI ID: 5053178
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:A11; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMIC RADIATION
MODULATION
COMPARATIVE EVALUATIONS
CORRELATIONS
COSMIC RAY PROPAGATION
FORBUSH DECREASE
HELIOSPHERE
MAGNETIC FIELDS
PHOTOSPHERE
PIONEER SPACE PROBES
SENSITIVITY
SOLAR CYCLE
SOLAR WIND
ATMOSPHERES
EVALUATION
IONIZING RADIATIONS
RADIATIONS
SOLAR ACTIVITY
SOLAR ATMOSPHERE
SPACE VEHICLES
VEHICLES
640101* - Astrophysics & Cosmology- Cosmic Radiation