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EP: Fachverband Extraterrestrische Physik
EP 12: Heliophysics II
EP 12.1: Talk
Thursday, April 2, 2009, 14:00–14:15, Zahnklinik
Modulation of galactic cosmic ray protons and electrons during an unusual solar minimum — •Bernd Heber1, Andreas Kopp1, Jan Gieseler1, Reinhold Müller-Mellin1, Horst Fichtner2, and Klaus Scherer2 — 1Christian-Albrechts-Universität Kiel — 2Ruhr-Universität Bochum
During the latest Ulysses out-of-ecliptic orbit the solar wind density, its pressure and the magnetic field strength have been lowest ever observed in the history of space exploration. Since cosmic ray particles respond to the heliospheric magnetic field variations in the expanding solar wind and its turbulence, a weak heliospheric magnetic field, low plasma density, and pressure is expected to cause the smallest modulation since the 1970’s. In contrast to this expectation the galactic cosmic ray proton flux measured in 2008 at the Ulysses spacecraft and Earth does not exceed the one observed in the 1960’s and 1980’s significantly. In contrast to the protons flux, that of galactic cosmic ray electrons exceeds those measured during the 1990’s by 10% after having corrected the data for Ulysses’ latitude and radial distance. Although solar activity, as indicated by the Sunspot number, has been low, the tilt angle remained at intermediate values. Therefore, so far, current sheet, gradient and curvature drifts prevent the galactic cosmic ray flux to rise to real solar minimum values. The observed galactic cosmic ray intensities at 2.5 GV should increase by a factor of 1.25±0.05 if the tilt angle would reach values below 10 degrees.