Long Term Modulation of the Galactic Cosmic Radiation

University Of Maryland, College Park, College Park MD

Investigators

Abstract

The investigators will determine which physical processes are responsible for temporal variations in galactic cosmic radiation with time scales greater than 22 years, with particular emphasis on periods of order 100 years and greater. A subsidiary goal will be to establish limits for the "space weather" that has occurred throughout the period 1200-2000 AD. The main effort is to use the cosmogenic records of the time variation of the galactic cosmic radiation over the period 1200-2000 AD, together with the neutron monitor and satellite measurements over the past 50 years, to investigate the physical properties of the long term (100 year time scale) modulation. This study comprises several components. The investigators will set limits on the changes in beryllium-10 and carbon-14 due to changes in the geomagnetic cutoff, as a consequence of changes in the geomagnetic moment, and its vector direction, 1200-2000 AD, and developing a means to correct the data for these effects. They will use the known occurrence of very large solar cosmic ray events in the interval 1561-1994 to investigate the contributions they have made to the beryllium and carbon data, and to develop a method to remove such contributions. Using these results, they will remove geomagnetic cutoff and solar cosmic ray effects from the cosmogenic data, leaving a more accurate representation of the long-term modulation of the galactic cosmic rays. This will allow them to deduce what temporal changes in the energy spectrum of the galactic cosmic radiation are consistent with the observed long-term changes in cosmic ray intensity from 1200 AD to the present. Synthesizing the work with satellite data from near earth and from the far heliosphere, the investigators will set bounds on the nature of the mechanisms that produce the long-term modulation of the galactic cosmic radiation. They will explore the astrophysical implications of the results and establish benchmarks for space weather 1200- 2000.