ROLE OF DRIFTS AND GLOBAL MERGED INTERACTION REGIONS IN THE LONG-TERM MODULATION OF COSMIC-RAYS

It is shown that the long-term modulation of 0.2- to 3-GV galactic and anomalous cosmic rays over the 22-year heliomagnetic cycle is principally a combination of two solar related processes, the cumulative effect of long-lived global merged interaction regions (GMIRs) and large-scale particle gradient and curvature drifts 'in the interplanetary magnetic field. This paradigm for cosmic ray modulation is based on the observed changes in cosmic ray intensity from solar minimum to solar maximum over successive solar cycles (21 and 22) using data from 1 AU and from the outer heliosphere. For cycle 21 (when positive ions flow in over the solar pole and out along the heliospheric neutral current sheet; qA > 0), the 1977-1980 modulation is dominated by GMIRs. While drifts may play a role in particle transport in the heliosphere at this time, the changing inclination of the heliospheric neutral sheet has a negligible effect on the intensity of cosmic ray nuclei. In cycle 22 when this flow pattern is reversed, it is shown that drifts are an important but not dominant factor for galactic cosmic ray modulation with the current sheet related drift effects decreasing with increasing rigidity R and heliocentric distance r. Anomalous cosmic rays are much more sensitive to changes in the current sheet inclination. The observed changes in the galactic cosmic ray intensity over the 1987-1988 period due to the increasing inclination of the current sheet, a, are a factor of 3-5 smaller than predicted by the time-dependent model of Potgieter and Le Roux (1992). The latitude variation at Voyager 1 (heliolatitude 32-degrees) of the dependence of galactic cosmic ray intensity on alpha is consistent with theoretical expectations. The strong role of GMIRs and their episodic nature requires a long lifetime (1.5-1.8 years) and a magnetic structure that effectively extends over the solar poles. Such a long GMIR lifetime implies a modulation boundary of the order of approximately 175 AU.