University of Maryland
Atlantic Building, Room 2400
4:30 PM Monday, April 7, 2014
Coffee, Tea & Snacks 4:15-4:30 PM

Ken McCracken
IPST University of Maryland
A Study of the Cosmic Radiation and the Heliomagnetic Magnetic Fields
during the Maunder Minimum of Solar Activity

Measurements of the cosmogenic radionuclide 10Be in two ice-cores from Greenland provide annual measurements of the paleo-cosmic ray (PCR) intensity from 1391 to the present. Using the cosmic ray propagation equation, they provide annual estimates of the heliomagnetic field (HMF) strength near Earth throughout that interval. They show that the cosmic ray intensities and heliomagnetic fields during the recent long sunspot minimum of 2006-9 were substantially different (PCR lower, HMF higher) than those during the Dalton, Maunder, and Spoerer Grand Minima of solar activity. The data from the Maunder Minimum (MM) will be discussed in detail. While the sunspot number decreased to zero in 1645 and remained at very low values until 1701, the cosmic ray intensity took five solar cycles to reach its maximum value. There was a strong eleven year cycle of PCR intensity throughout the 55 year rising phase. The ratio Bmax / Bmin was computed for all the solar cycles in the MM, where Bmax is the HMF at solar maximum; and Bmin is the HMF at the proceeding solar minimum. The ratios lie in the same range, with an average value that closely approximates those observed by satellites since 1965. This indicates that the solar dynamo operated in a similar manner to the present throughout the MM while the magnetic fields in the active centres was <1500 gauss, with the consequence that sunspots were not detectable with the telescopes of the day. In conclusion, a courageous prediction will be made regarding the cosmic ray intensity, and HMF strength that will be observed in 2020.

Sponsored by: Department of Physics and the Institute for Physical Science and Technology, University of Maryland. For information call Catha Stewart at (301) 405-4811 or go to the UMD Space Physics group seminar web site.

There is free parking after 4:00 PM in lot B (the big parking garage across the street from the ATL building). There are a limited number of spaces in lot Q next to the new ATL wing with free parking after 4PM even when there is a basketball game on campus.