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Title: Heliospheric modulation of high-energy cosmic rays: II. Deformation of the neutral surface

Abstract

Analysis of neutron monitor data in the periods of negative and positive polarities of the general solar magnetic field has revealed a dependence of the long-term cosmic-ray modulation on both deformation of the neutral surface of the interplanetary magnetic field and solar activity level. The effects of solar activity and neutral surface deformation dominate at positive and negative polarities, respectively. The magnetic drift of cosmic rays with different trajectories in the epochs of positive and negative polarities is responsible for this behavior of the 11-year and annual density modulations.

Authors:
; ; ;  [1]
  1. Russian Academy of Sciences, Shafer Institute of Cosmophysical Research and Aeronomy, Siberian Branch (Russian Federation), E-mail: s.k.gerasimova@ikfia.ysn.ru
Publication Date:
OSTI Identifier:
21072536
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Experimental and Theoretical Physics; Journal Volume: 104; Journal Issue: 2; Other Information: DOI: 10.1134/S1063776107020045; Copyright (c) 2007 Nauka/Interperiodica; Article Copyright (c) 2007 Pleiades Publishing, Inc; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; COSMIC RADIATION; DEFORMATION; INTERPLANETARY MAGNETIC FIELDS; MODULATION; NEUTRON MONITORS; SOLAR ACTIVITY; SURFACES; TRAJECTORIES

Citation Formats

Krymsky, G. F., Krivoshapkin, P. A., Mamrukova, V. P., and Gerasimova, S. K. Heliospheric modulation of high-energy cosmic rays: II. Deformation of the neutral surface. United States: N. p., 2007. Web. doi:10.1134/S1063776107020045.
Krymsky, G. F., Krivoshapkin, P. A., Mamrukova, V. P., & Gerasimova, S. K. Heliospheric modulation of high-energy cosmic rays: II. Deformation of the neutral surface. United States. doi:10.1134/S1063776107020045.
Krymsky, G. F., Krivoshapkin, P. A., Mamrukova, V. P., and Gerasimova, S. K. Sun . "Heliospheric modulation of high-energy cosmic rays: II. Deformation of the neutral surface". United States. doi:10.1134/S1063776107020045.
@article{osti_21072536,
title = {Heliospheric modulation of high-energy cosmic rays: II. Deformation of the neutral surface},
author = {Krymsky, G. F. and Krivoshapkin, P. A. and Mamrukova, V. P. and Gerasimova, S. K.},
abstractNote = {Analysis of neutron monitor data in the periods of negative and positive polarities of the general solar magnetic field has revealed a dependence of the long-term cosmic-ray modulation on both deformation of the neutral surface of the interplanetary magnetic field and solar activity level. The effects of solar activity and neutral surface deformation dominate at positive and negative polarities, respectively. The magnetic drift of cosmic rays with different trajectories in the epochs of positive and negative polarities is responsible for this behavior of the 11-year and annual density modulations.},
doi = {10.1134/S1063776107020045},
journal = {Journal of Experimental and Theoretical Physics},
number = 2,
volume = 104,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • We have constructed a greatly simplified theory for the heliospheric modulation of high-energy cosmic rays in which no adjustable parameters are used. The only parameter k, which characterizes the degree of regularity of the interplanetary magnetic field, varies in the model in a definite way with solar cycle phase. The approximations used lead to solutions expressed in terms of elementary functions. The role of the magnetic drift of particles has been revealed. Quantitative agreement with the observed cosmic-ray variations has been achieved.
  • The relatively abrupt onset of cosmic ray modulation, observed in May 1987 on Earth and in September 1987 by the Pioneer 10 and 11 spacecraft, enables further investigation of the possible effect of the heliospheric current sheet on modulation. According to the gradient drift theory of cosmic ray transport, modulation is associated with solar cycle changes in the current sheet, whose inclination increases systematically from solar minimum to solar maximum. The measured used in testing this hypothesis is the difference in the maximum latitudinal extent of the current sheet in the northern and souther solar hemispheres. This difference is obtainedmore » from contours of the current sheet produced by extrapolating photospheric magnetic field measurements to a solar wind source surface. When the latitude difference, divided by 2 and called the pseudoinclination or pseudotilt angle, is compared with cosmic ray count rates measured on Earth, an excellent correlation is found, as in a previous study of modulation in the years 1976-1986. The abruptness of the onset can be attributed to the greater sensitivity of the cosmic ray intensity to changes in the current sheet when the solar-heliospheric magnetic field is inward in the northern hemisphere as predicted by the model. Thus the observations are found to be consistent with the predictions of the gradient drift model. A preliminary analysis is also carried out to test an alternative, but not necessarily incompatible, hypothesis that large-scale transient solar wind structures (coronal mass ejections, shocks, etc.) form barriers to the inward transport of cosmic rays.« less
  • We discuss the role which empirical determinations of the latitude 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 observation and measured solar wind speeds, we have determined the latitude 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/sup -0.72/ and P/sup -0.86/, withmore » the exact dependence being determined by the definition used for the median rigidity of each monitor.« less