Untitled

Abstract

The global processes that determine cosmic ray modulation are reviewed. The essential elements of the theory which describes cosmic ray behavior in the heliosphere are summarized, and a series of discussions is presented which compare the expectations of this theory with observations of the spatial and temporal behavior of both galactic cosmic rays and the anomalous component; the behavior of cosmic ray electrons and ions; and the 26-day variations in cosmic rays as a function of heliographic latitude. The general conclusion is that the current theory is essentially correct. There is clear evidence, in solar minimum conditions, that the cosmic rays and the anomalous component behave as is expected from theory, with strong effects of gradient and curvature drifts. There is strong evidence of considerable latitude transport of the cosmic rays, at all energies, but the mechanism by which this occurs is unclear. Despite the apparent success of the theory, there is no single choice for the parameters which describe cosmic ray behavior, which can account for all of the observed temporal and spatial variations, spectra, and electron vs. ion behavior.

Record-Setting Cosmic-Ray Intensities in 2009 and 2010

“…Figure 5(a) shows that the 27 day average oxygen intensities are also correlated with the IMF strength three solar rotations earlier (delays of 0, 1, 2, and 4 rotations gave somewhat poorer correlations). The excellent correlation in Figure 5(a) indicates that solar-wind properties have considerable effect out to ∼20 AU, consistent with significant solar modulation occurring in the inner heliosphere at solar minimum (Fisk et al 1998;Cummings & Stone 1999;Fujii & McDonald 2005).…”

“…Although the solar wind takes ∼1 year to reach the termination shock, it requires another year or more to reach the heliopause, often assumed to represent the GCR modulation boundary (e.g., Webber & Higbie 2009). However, solarminimum intensity gradients for <0.5 GeV nucleon −1 GCR ions in the outer heliosphere are small compared to inside ∼20 AU (e.g., Figure 2 in Fisk et al 1998), suggesting that boundarydistance changes have a minor effect on 1 AU GCR intensities.…”

First Observations of Anomalous Cosmic Rays in to 36 Solar Radii

“…In fact, the transport of cosmic rays throughout the heliosphere is highly complex and involves an interplay of many different physical phenomena, including (i) the outwardly expanding solar wind which contributes to adiabatic energy losses and convection, (ii) irregularities in the magnetic field which lead to diffusion, and (iii) the large-scale heliospheric magnetic field that is responsible for gradient and curvature drifts. Although these are well approximated by the Parker transport equation (Parker 1965) and the basic individual processes are, for the most part, well understood, the relative roles that each component plays and how they probe and influence the heliosphere's global structure has yet to be fully untangled (see, e.g., discussions by Fujii & McDonald 1997;Fisk et al 1998). Of these, spatial gradients offer perhaps the most compelling opportunities for insight, particularly as they reflect the longterm variations in the global drift patterns throughout the heliosphere over the solar cycle (Jokipii et al 1977;Fujii & McDonald 1997;Klecker et al 1998; and can be used to derive other terms, such as the diffusion coefficients (e.g., .…”