The role of corotating interaction regions in cosmic‐ray modulation

Abstract

We present the first global simulations of the modulation of galactic cosmic rays by a three‐dimensional solar wind with corotating interaction regions. The cosmic‐ray transport equation is solved in a computed wind and magnetic‐field model. The results show both the previously‐neglected small‐scale response to CIR's and global, drift‐dominated, effects which are similar to previous models. Our model predicts a correlation between the local magnetic field and the rate of decrease of the cosmic‐ray intensity which is similar to that observed. This is found to be due to inhibited diffusion. We suggest that such small‐scale variations are local and that they do not change significantly the global cosmic‐ray structure except, perhaps, near sunspot maximum.

Cosmic ray modulation by different types of solar wind disturbances

“…Richardson et al (1996) pointed out that the SWD speed might be the most important parameter, favoring a diffusion-convection model for this behavior. On the other hand, Čalogović et al (2009) found a statistically significant correlation between the depression amplitude and the SWD magnetic field strength, which is more in favor of the diffusiondrift model proposed by Kota & Jokipii (1991). Similar inconsistencies were found in studies of ICMEs.…”

“…It opposes modeling based on the propagating region of the enhanced scattering and reduced drift (Kota & Jokipii 1991) or enhanced convection , since no correlations were found between the amplitude of the depression and magnetic field strength/fluctuations/speed. But the time profile of SWDs, which we found to be very important for CR exclusion in general, was not regarded within these models.…”

“…Indeed, most of the theoretical models for transport of CRs emphasize the importance of pitch angle scatter and the magnetic field fluctuations, both for galactic cosmic rays (based on the Parkers transport equation, see e.g. Le Roux & Potgieter 1991;Kota & Jokipii 1991;Richardson et al 1996;Potgieter 1998, and references therein) and also solar cosmic rays (based on the Roelof equation of focused transport, see e.g. Dröge 2000;Verkhoglyadova et al 2010, and references therein).…”

On the Relationship of the 27-day Variations of the Solar Wind Velocity and Galactic Cosmic Ray Intensity in Minimum Epoch of Solar Activity

“…At the same time, the role of different ranges of the heliolongitudinal changes of the solar wind velocity in the A>0 and A<0 epochs was not considered. The 3-D models with heliolongitudinal dependent solar wind velocity with consequent changes of the frozen interplanetary magnetic field (IMF) were presented by Kota and Jokipii (1991; followed after the first 3-D model (Kota and Jokipii, 1983). Model of Kota and Jokipii (1991) was the first global simulations of the modulation of GCR by 3-D solar wind with corotating interaction regions (CIR), though there was not considered an expected difference of the amplitudes of the 27-day variations of the GCR intensity in the A>0 and A<0 polarity epochs.…”

“…The 3-D models with heliolongitudinal dependent solar wind velocity with consequent changes of the frozen interplanetary magnetic field (IMF) were presented by Kota and Jokipii (1991; followed after the first 3-D model (Kota and Jokipii, 1983). Model of Kota and Jokipii (1991) was the first global simulations of the modulation of GCR by 3-D solar wind with corotating interaction regions (CIR), though there was not considered an expected difference of the amplitudes of the 27-day variations of the GCR intensity in the A>0 and A<0 polarity epochs. Later, Kota and Jokipii (2001) developed new time dependent 3-D model including multiple heliospheric neutral sheet (HNS) characterizing high solar activity to cover more complex structures of the HNS and CIRs.…”