Bonn 2010 – scientific programme
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EP: Fachverband Extraterrestrische Physik
EP 1: Near Earth Space I
EP 1.3: Talk
Monday, March 15, 2010, 09:45–10:00, AKM
Prediction of GCR proton intensities from simultaneous proton and electron measurements during an A<0 solar minimum — •B. Heber1, J. Gieseler1, K. Herbst1, A. Kopp1, R. Müller-Mellin1, H. Fichtner2, K. Scherrer2, F. Steinhilber3, M. Potgieter4, and S. Ferreira4 — 1IIEAP, CAU, Kiel — 2TP-4, RUB — 3Eawag, Dübendorf, CH — 4NWU, Potchefstroom, SA
The intensity of GCRs is modulated as they traverse the turbulent heliospheric magnetic field (HMF) embedded in the solar wind. To describe this modulation the so called force-field approximation is often used. This handy approximation depends on two quantities only: the modulation parameter Φ and the local interstellar spectrum outside the heliosphere. However, the modulation parameter Φ can not take into account the differences between positive and negative solar magnetic epochs or the difference over the Hale cycle. Although the HMF strength in the current solar minimum is the lowest observed since the 1960’s, the intensity as measured by neutron monitors (NMs, mid 2009) is about the same as in the 1960’s. While the 2.5 GV KET proton measurements confirm the NM measurements, 2.5 GV GCR electrons exceed the intensity of protons by more than 30%. Using Φ from Usoskin et al. (2005) the proton time profile could be reproduced reasonably well from 1990 to 2004, spanning values from Φ=400 MV in 1997 and Φ = 1100 MV at solar maximum. The latest KET proton measurements result in a modulation potential of about Φ = 350 MV. Since electrons and protons at these rigidities have the same modulation amplitude, Φ is expected to decrease to 290 MV.