Origin of transient cosmic ray intensity variations. [Solar flare effects]

Journal Article · Wed Jun 01 04:00:00 EDT 1977 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JA082i016p02170· OSTI ID:7310698

Duggal, S P; Pomerantz, M A

A new approach to determining the solar progenitor of transient cosmic ray intensity variations has revealed that in a statistical sense, solar flares, heretofore regarded as the predominant source of the modulation, actually do not precede the reduction in flux observed at earth. Superposed epoch analysis of the cosmic ray data with respect to the time of occurrence of all 379 solar flares of importance (Imp) < or =2 observed during solar cycle 20 (1964-1974 inclusive) shows that the onset of a decrease in the composite nucleonic intensity at polar stations occurs prior to the zero day (i.e., time of the flare) well before the arrival in the vicinity of earth of the associated solar plasma. The statistical significance of this result is confirmed by comparing the pooled variance determined from Chree analysis of an equal number of random epochs with that of the curve representing the flare epochs. Subdivision of the latter into three groups according to the heliographic longitude of the flares shows that whereas eastern flares might be associated with cosmic ray decreases, central (30degree to -30degree) and western flares cannot be thus related. A similar analysis of all flares of Imp< or =2 that occurred in a selected set of 24 extraordinary flare-rich active centers during 1964--1974 confirms these results and shows that the observed cosmic ray intensity decrease is, in fact, associated with the central meridian passage ( +- 1 day) of the active regions. Thus earlier conclusions concerning relationships between the heliolongitude of flares and their apparent effectiveness in producing Forbush decreases require reevaluation. The specific feature associated with solar active centers that is actually the principal source of transient modulations remanins to be identified.

• Research Organization: Bartol Research Foundation of the Franklin Institute, Swarthmore, Pennsylvania 19081
• OSTI ID: 7310698
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 82:16; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

640101* -- Astrophysics &amp; Cosmology-- Cosmic Radiation
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMIC RADIATION
FORBUSH DECREASE
INTERPLANETARY SPACE
IONIZING RADIATIONS
MAGNETIC STORMS
RADIATIONS
SOLAR ACTIVITY
SOLAR FLARES
SOLAR RADIATION
SPACE