skip to main content

Title: Latitude survey investigation of galactic cosmic ray solar modulation during 1994-2007

The Galactic cosmic ray spectrum exhibits subtle variations over the 22 yr solar magnetic cycle in addition to the more dramatic variations over the 11 yr sunspot cycle. Neutron monitors are large ground-based detectors that provide accurate measurements of variations in the cosmic ray flux at the top of the atmosphere above the detector. At any given location the magnetic field of the Earth excludes particles below a well-defined rigidity (momentum per unit charge) known as the cutoff rigidity, which can be accurately calculated using detailed models of the geomagnetic field. By carrying a neutron monitor to different locations, e.g., on a ship, the Earth itself serves as a magnet spectrometer. By repeating such latitude surveys with identical equipment, a sensitive measurement of changes in the spectrum can be made. In this work, we analyze data from the 1994 through 2007 series of latitude surveys conducted by the Bartol Research Institute, the University of Tasmania, and the Australian Antarctic Division. We confirm the curious 'crossover' in spectra measured near solar minima during epochs of opposite solar magnetic polarity, and show that it is directly related to a sudden change in the spectral behavior of solar modulation at the time ofmore » the polarity reversal, as revealed from contemporaneous variations in the survey data and a fixed station. We suggest that the spectral change and crossover result from the interaction of effects due to gradient/curvature drifts with a systematic change in the interplanetary diffusion coefficient caused by turbulent magnetic helicity.« less
Authors:
; ;  [1] ; ; ; ;  [2] ; ;  [3]
  1. Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400 (Thailand)
  2. Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States)
  3. School of Physical Sciences, University of Tasmania, Hobart, Tasmania 7001 (Australia)
Publication Date:
OSTI Identifier:
22370349
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 795; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; COSMIC GAMMA SOURCES; COSMIC RADIATION; COSMIC RAY FLUX; DIFFUSION; EQUIPMENT; GEOMAGNETIC FIELD; HELICITY; INTERACTIONS; MAGNETIC SPECTROMETERS; MODULATION; NEUTRON MONITORS; SPECTRA; SUNSPOTS