The dependence of solar modulation on the sign of the cosmic ray particle charge

Abstract

We compare the solar modulation of galactic cosmic ray helium and electrons at 1AU, within the 600-1000 MV magnetic rigidity interval, from 1965 through 1984. The time-intensity variatlons during the two solar maxima around 1970 and 1981 show that after 1970 the helium intensity recovers earlier than that of the electrons, whereas after 1981 the electron intensity recovers earlier than that of helium. The flux ratio of helium to electrons (He/e) undergoes a major increase during the 1969-1971 period and a major decrease during 1979-83.These experimental results can be interpreted as due to a dependence of the solar modulation of galactic cosmic rays on the sign of the particle charge, possibly as a consequence of drifts due to gradients and curvatures in the interplanetary magnetic field. However, the comparison of the shapes of the intensitytime curves of helium and electrons in the period 1970-1981 does not support a major specific prediction of the drift model. I.Introduction. The perception that the interplanetary magnetic field is a distorted dipole, coherent in large scale, suggests that drifts due to field gradients and curvatures may play a significant role in solar modulation .Because the drifts of particles of opposite charge move in opposite directions, the modulation effects on nuclei at a given point in the interplanetary space will be different from those on electrons.This paper addresses the problem of the importance of drifts -trying to detect differences in the modulation of nuclear and electron cosmic rays that could be in principle attributed to the presence of drlfts. We study the modulation of 70-95 MeV/n (739-866 MV) cosmic ray helium-4 and 600-1000 MeV cosmic ray electrons from 1965 through 1984 with special emphasis on the intervals around the two consecutive solar maxima in 1970 and 1981 in which the interplanetary magnetic field changed polarity. 2.The Experimental Data.Most of the experimental data used in this work have been obtained with the University of Chicago cosmic ray telescopes flown on balloons or aboard satellites. ABSTRACTWe compare the solar modulation of galactic cosmic ray helium and electrons at 1 AU, within the 600-1000 MV magnetic rigidity interval, from 1965 through 1984. The time-intensity variat10ns during the two solar maxima around 1970 and 1981 show that after 1970 the helium intensity recovers earlier than that of the electrons, whereas after 1981 the electron intensity recovers earlier than that of helium. The flux ratio of helium to electrons (He/e) undergoes a major increase during the 1969-1971 period and a major decrease during 1979-83.These experimental results can be interpreted as due to a dependence of the solar modulation of galactic cosmic rays on the sign of the particle charge, possibly as a consequence of drifts due to gradients and curvatures in the interplanetary magnetic field. However, the comparison of the shapes of the intensitytime curves of helium and electrons in the period 1970-1981 does not support a major specific prediction...

Solution of Heliospheric Propagation: Unveiling the Local Interstellar Spectra of Cosmic-ray Species

“…In addition, according to the original formulation by Parker (1958), the heliospheric magnetic field (HMF) follows an Archimedean spiral that causes charged particles (i.e., CRs) to experience a combination of gradient, curvature and current sheet drifts (see e.g. Jokipii et al 1977), whose experimental evidence was provided, for instance, by Garcia-Munoz et al (1986) and Boella et al (2001). The overall effect of heliospheric propagation on the spectra of Galactic CRs is called solar modulation.…”

“…With the development of sophisticated Galactic propagation models, the force-field approximation became the Achilles' hill of CR astrophysics. More advanced mod-els did exist -including those accounting for the so-called "charge drift effect" (e.g., Jokipii et al 1977;Burger 2012), whose experimental evidence was provided, for instance, by Garcia-Munoz et al (1986) and Boella et al (2001), -but they were not as "user friendly" and their wide practical application was suppressed by the high "threshold" demand of an expertise in the heliospheric physics.…”

Latitude Survey Investigation of Galactic Cosmic Ray Solar Modulation During 1994-2007

“…In other words, 11 yr periods with opposite magnetic polarity exhibit distinct GCR variations. These effects are associated with a variety of interesting phenomena, such as guiding center drifts, latitudinal GCR gradients, particle charge sign dependence, and changing diffusion coefficients (e.g., Jokipii et al 1977;Garcia-Munoz et al 1986;Bieber & Chen 1991). These phenomena depend on the sign of qA, where q is the particle charge and A is the solar magnetic polarity.…”

Charge sign dependence of cosmic ray modulation near a rigidity of 1 GV

“…Many modulation phenomena have different patterns in solar cycles of opposite polarity. Possibly, the most striking of these is the change in the flux of electrons relative to that of protons and helium when the solar polarity reverses [Evenson and Meyer, 1984;Garcia-Munoz et al, 1986;Ferrando et al, 1996].…”