The solar modulation of cosmic ray electrons 1969–1977

We report cosmic electron spectra obtained on balloon flights in August of the years 1987, 1990, 1992, and 1994 in an extension of the series of observations with the same instrument begun in 1968. Electron fluxes at approximately 6 GeV have returned to levels seen in the decade of the 1980s in spite of the reversal of solar magnetic polarity in 1990, which in some models should have produced a return to the much lower fluxes observed in the 1970s. We know of no satisfactory theoretical interpretation of these results.

Section: Introductionsupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

Cosmic electron spectra 1987–1994

Evenson¹,

Huber²,

Patterson³

et al. 1995

“…Korff [1977, 1979] proposed that the charge sign difference was the cause of the difference in the modulation of protons and electrons. Evenson et al [1979a] studied the simultaneous modulation of protons and electrons through the 1970 solar maximum in a common rigidity interval around 0.4 GV., without finding a correlation between the time variations of the ratio electron/proton and the polarity change of the interplanetary magnetic field. Evenson and Meyer [1984] analyzed proton and electron measurements carried out after the 1980 change in polarity of the polar solar magnetic fields and showed that after the 1981 minimum in cosmic ray intensity • Also at Department of Physics, University of Chicago, Illinois.…”

Section: Introductionmentioning

confidence: 99%

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

Garcia‐Munoz¹,

Meyer²,

Pyle³

et al. 1986

Self Cite

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...

“…Even the added leverage afforded by the difference in drift velocity between electrons and protons has failed to resolve this important issue. Although the hysteresis curves in the ratio of electrons to protons between the 1968 and 1980 maxima of solar activity appear quite divergent, differences in the temporal structure of the two maxima rather than sensitivity to the polarity of the heliospheric field could well be the dominant factor [Evenson et al, 1979;Evenson and Meyer, 1984].…”

Section: Introductionmentioning

confidence: 99%

Variation of cosmic rays and solar wind properties with respect to the heliospheric current sheet: 2. Rigidity dependence of the latitudinal gradient of cosmic rays at 1 AU

Newkirk¹,

Asbridge²,

Lockwood³

et al. 1986

We discuss the role which empirical determinations of the latitudinal variation of cosmic rays with respect to the current sheet may have in illuminating the importance of the cross‐field drift of particles in the large‐scale heliospheric magnetic field. Using K coronameter observations and measured solar wind speeds, we have determined the latitudinal gradients with respect to the current sheet for cosmic rays in four rigidity ranges. Gradients vary between approximately −2 and −50% per astronomical unit. The rigidity dependence of the decrease of cosmic ray flux with distance from the current sheet lies between P−0.72 and P−0.86, with the exact dependence being determined by the definition used for the median rigidity of each monitor.