Kenneth G. McCracken
University of Maryland, Visiting Research Scientist is being considered for appointment to Senior Research Scientisit in the Institute for Physical Science and Technology at the University of Maryland, College Park.
The Temporal Variability of the Cosmic Radiation and Solar Activity Over the Past 10,000 Years
The cosmogenic radionuclides, 10Be and 14C, provide a record of the time dependent changes in the intensity of the galactic cosmic radiation at Earth in the past. We now have three independent cosmogenic records, each spanning the past 10,000 years, that allow us to compare the cosmic radiation intensity and solar activity during the modern "space era" with those throughout the past 10 millenia. They show that there have been ~22 occasions similar to that accompanying the Maunder Minimum (1645-1715), when the cosmic radiation intensity in the vicinity of 3GeV was a factor of 2-3 greater than during the "space era". The Grand Minima events exhibit a 2300yr variability, clusters of 3-4 Grand Minima events being separated by intervals of >1000 yr of depressed cosmic ray intensity. While the Grand Minima events in the clusters are typically 150-200 yr apart, shorter periodicities (~110, ~88 and ~60yr) are prominent in the intervening ~1000 yr intervals. It appears likely that the most recent cluster of Grand Minima events ended with the Dalton Minimum of 1800-1820, and that the long-term cosmic ray intensity will remain at or below the present day values for the next 1000yr. The cosmic ray intensity reflects the degree of solar activity; and the cosmogenic data therefore provides the means to study the long-term variability of solar activity, and by inference, the properties of the solar magnetic dynamo. The speaker will conclude by summarising the apparent properties of the solar dynamo, and also briefly discussing the experimental evidence for a correlation between solar activity and the climate of Earth throughout the past 10,000yr.