A numerical technique is introduced for the solution of the time‐dependent equation for the solar modulation of galactic cosmic rays, in which transport in heliographic latitude is ignored. We illustrate this method with a model for the solar cycle variation in cosmic ray intensity. The variation is assumed to result from changes in the number of enhanced cosmic ray scattering regions, which are produced by flare‐generated shock waves in the solar wind. The model can account for the observed solar cycle variation in intensity at different energies as well as the observed spatial gradients. This model also provides a natural explanation for the cosmic ray hysteresis effect.

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A solution of the time-dependent, spherically symmetric cosmic ray transport equation, with a defensible diffusion coefficient and a natural model for an ll-year cycle of diffusive scattering disturbances that originate on the sun and travel through interplanetary space, accounted simultaneously for the spectral changes of both galactic protons and electrons, for the time and phase lag of high-versus low-energy protons, and for the integral radial gradients of protons > 100 MeV over most of the solar cycle and over large distances in the heliosphere. Each individual disturbance caused a sudden particle intensity decrease as it passed a point in space; recovery of intensity began immediately afterward. The characteristic recovery time at 1 AU was in the range found in neutron monitor and satellite data, except that the recovery time constant was rigidity-dependent, contrary to these same data. Also, spectral changes over successive solar minima in 1965 and 1977, heretofore linked to drifts, can be explained as an adjunct to the hysteresis effect. Overall, the primary galactic cosmic ray flux over the l 1-year solar cycle is dominated in the ecliptic plane by turbulent scattering regions emitted by the sun and at best only secondarily affected by gradient and curvature drifts, effects which may be confined near 1 AU.

We present new evidence to support the hypothesis that the l 1-year solar cycle modulation of galactic cosmic rays is caused by strong particle diffusion inside long-lived, merged interaction regions. These regions are represented by local enhancements in the heliospheric magnetic field strength. To test this hypothesis, we solved the one-dimensional, force field approximation of the cosmic ray modulation equation. The only variables were the strength of the local magnetic field and the position of the spacecraft, both taken directly from Voyager 2 data. We assume that a constant solar wind speed convects magnetic field compressions and rarefactions unchanged through a model heliosphere. The result is a reasonable simulation of the integrated, high-energy cosmic ray intensity profile from about 1982 to mid-1989. This period encompasses both the full recovery portion of the last 11-year cosmic ray cycle and the first year and a half of the new cycle. In particular, this model responds to the Voyager 2 magnetic field data by correctly timing the beginning of the new modulation cycle in late 1987. We conclude that our hypothesis is consistent with the results of this simulation.

We have formally confirmed that galactic cosmic ray intensity variations measured by Voyager 2 during recovery from solar maximum are caused by traveling compressions and rarefactions in the mean interplanetary magnetic field. We used Voyager's magnetic field data as input to a time‐independent, spherically symmetric, cosmic ray transport equation in the force field approximation. The solutions closely followed the count rate of cosmic rays greater than 75 MeV/nucleon over 4 years, during the recovery phase of the 11‐year solar‐driven cosmic ray cycle. This strongly supports prior theoretical assertions that turbulent interaction regions traveling with the solar wind are the major cause of the solar cycle variation of galactic cosmic rays in the ecliptic region.