HR: 1340h
AN: SH43A-1097    [Abstracts]
TI: The effect of the changing solar system environment on galactic cosmic ray propagation through the heliosphere: Consequences for cosmogenic isotope production in the Earth's atmosphere.
AU: Axford, W I
EM: ian@axford.org
AF: University of California, Riverside, Institute of Geophysics and Planetary Physics, University of California, Riverside, CA 92521 United States
AU: * Florinski, V
EM: vflorins@ucr.edu
AF: University of California, Riverside, Institute of Geophysics and Planetary Physics, University of California, Riverside, CA 92521 United States
AU: Zank, G P
EM: zank@ucr.edu
AF: University of California, Riverside, Institute of Geophysics and Planetary Physics, University of California, Riverside, CA 92521 United States
AB: The solar system is traveling through highly inhomogeneous interstellar medium. Our galactic environment (the Local Bubble) is a vast region formed by supernova explosions filled with extremely tenuous fully ionized gas at a temperature of over a million K. Embedded in the Local Bubble are interstellar clouds ranging from cold ($T<100$ K), dense ($n\sim 5000$ cm$^{-3}$) molecular clouds to warm ($T\sim 10^4$ K) and relatively tenuous ($n\sim 0.3$ cm$^{-1}$) partially ionized clouds, such as the Local Cloud where the Sun is currently located. The properties of the cloud control the size and shape of the heliosphere and, consequently, affect the propagation of galactic cosmic rays (GCRs) between the boundary of the modulation region (the heliopause) and Earth. GCRs with energies above several hundred MeV initiate nuclear reactions in the Earth's upper atmosphere producing radioactive isotopes of Beryllium and Carbon that are precipitated on the surface and eventually incorporated into sediments. It is then quite plausible that the history of the variability of the solar environment may be preserved in cosmogenic isotope records available from ice and sea sediment cores dating back more than 100,000 years. Previously, we showed that increasing the density of the cloud surrounding the solar system by a factor of 30 leads to an increase in 1 AU GCR fluxes by a factor of 1.5--3, and that cloud encounters may have been responsible for the observed peaks in $^{10}$Be records 35 and 60 thousand years ago. Extending our early model, we now calculate GCR distribution from the solution of the 2D Parker equation using the global model-calculated plasma and magnetic field parameters as a background to determine the diffusion coefficients. Initial results from a more comprehensive investigation of the global structure of the heliosphere embedded in clouds of varying density, from the present conditions in the Local Cloud to the extreme case of dense molecular clouds, are discussed.
DE: 2104 Cosmic rays
DE: 2124 Heliopause and solar wind termination
DE: 2144 Interstellar gas
DE: 2151 Neutral particles
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2004 AGU Fall Meeting