Cosmic ray modulations related to the interplanetary magnetic field intensity

Journal Article · Fri Apr 01 04:00:00 EST 1983 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JA088iA04p02973· OSTI ID:6036780

Duggal, S P; Pomerantz, M A; Schaefer, R K; Tsao, C H

Data covering a complete solar cycle (1965 1976) have been analyzed in a comprehensive investigation of the nature of transient modulations of relativistic galactic cosmic rays associated with interplanetary magnetic field intensity excursions in the vicinity of the earth. It had been recognized earlier that the correlation coefficient between the cosmic ray intensity and the IMF magnitude is small. In fact, it remains less than 0.5 throughout the solar cycle. In order to understand the nature of field-related modulations and to minimize the complications arising from the effects of other features of solar plasma, the data are here analyzed by the method of superposed epochs. Following newly developed procedures for evaluating the statistical significance of the results obtained with this type of analysis, it is demonstrated that, while the days characterized by high IMF magnitude B are associated with intensity decreases, the IMF rarefactions (low B) cause an increase in the flux. In contrast to the case of geometric disturbances, which respond more rapidly, maximum cosmic ray intensity variations associated with both high and low B occur 1 day after the key days characterized by field departures from average values. This indicates that the modulation mechanism becomes efficient only when the plasma engulfment of the earth extends at least a gyroradius beyond 1 AU. Finally,while the geomagnetic index Ap follows the field changes rather closely, the polar nucleonic intensity shows a prolonged recovery time (7--10 days) following magnetic enhancements as well as rarefactions.

• Research Organization: Bartol Research Foundation of the Franklin Institute, University of Delaware, Newark, Deleware 19711
• OSTI ID: 6036780
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 88:A4; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

640101* -- Astrophysics & Cosmology-- Cosmic Radiation
640107 -- Astrophysics & Cosmology-- Planetary Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMIC RADIATION
COSMIC RAY PROPAGATION
ENERGY RANGE
INTERPLANETARY MAGNETIC FIELDS
IONIZING RADIATIONS
MAGNETIC FIELDS
MODULATION
RADIATIONS
RELATIVISTIC RANGE
SOLAR PARTICLES
SOLAR RADIATION
STELLAR RADIATION