Title: Solar Variability as Deduced from 400 Years of Large Fluence Solar
Proton events
Author: M.A. Shea
Affil: CSPAR, University of Alabama, Huntsville, AL 35899
Email: sssrc@msn.com
Authors: M.A. Shea
D.F. Smart
, K.G. McCracken
, and G.A.M. Dreschhoff
Affils: CSPAR, University of Alabama, Huntsville, AL 35899,
Institute for Physical Science and Technology, University of
Maryland, College Park, MD 20742,
Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045
Abstract: We have used satellite measurements of the > 10 MeV solar proton events and nitrates deposited
in polar ice as a proxy to identify large solar proton fluence events back to 1561 to investigate
solar proton event variability. From the spacecraft measurements we have found that the number
of > 10 MeV solar proton events with peak flux exceeding 10 (cm-sec-ster)
was remarkably
constant for solar cycles 19-22 even though the total integrated fluence experienced at the earth
per solar cycle varied by a factor of four. From the nitrate measurements we find that the
frequency of occurrence of large fluence solar proton events (> 30 MeV omni-directional fluence
> 10
cm) has varied by a factor >10 in the interval 1561-1994. We also find that the rate of
occurrence of solar proton events during Schwabe cycle 1698-1711, at the end of the Maunder
Minimum, was one of the highest in the period 1561-1994. There is a well defined "Gleissberg"
(80-85 year) periodicity in the ice core/nitrate data, with six well defined minima, two in close
association with the Maunder and Dalton minima in sunspot numbers. Furthermore, the present
"satellite" era is a recurrence of this series of minima.