HR: 11:50h
AN: SH12B-07 [Abstracts]
TI: Modulation of galactic cosmic rays by global merged interaction region near the solar wind termination shock and in the heliosheath
AU: Rassoul, H K
EM: rassoul@fit.edu
AF: Department of Physics and Space Science,
Florida Institute of Technology, 150 W. University Blvd., Melbourne, FL 32901, United States
AU: * Zhang, M
EM: mzhang@fit.edu
AF: Department of Physics and Space Science,
Florida Institute of Technology, 150 W. University Blvd., Melbourne, FL 32901, United States
AU: Richardson, J D
EM: jdr@space.mit.edu
AF: Center for Space Research,
Massachusetts Institute of Technology, 77 Mass Ave., Cambridge, MA 02139, United States
AB:
Measurements from Voyager spacecraft at distant heliosphere show that cosmic rays are still modulated near the
termination shock and even in the heliosheath. The September 2005 solar event propagated to the outer
heliosphere, resulting in a very noticeable global merged interaction region (GMIR) at both Voyager 2 (still in the
solar wind slightly insider the termination shock) and Voyager 1 (in the heliosheath). Decreases of galactic
cosmic ray fluxes were observed in correlation with the GMIR. After the passage of GMIR, galactic cosmic ray
fluxes have been recovering towards the solar minimum level, but cosmic ray flux at Voyager 2 is changing at a
faster rate than at Voyager 1. The cosmic ray decreases in 2006 are definitely produced by the GMIR, but the
cause of different rates of cosmic ray recovery after the GMIR is less certain. We use stochastic simulation of
cosmic ray transport to investigate how the particle drift pattern and the GMIR, as a propagating diffusion barrier,
can affect cosmic ray modulation in outer heliosphere. In this paper, we present calculation results of cosmic ray
flux and its radial gradients when a GMIR passes the spacecraft near the termination shock or in the heliosheath.
The results will be compared with observations to find out major causes of modulation under the current
conditions in the outer heliosphere. We will also demonstrate how sensitive the cosmic ray modulation level and
their recovery at the Voyager locations depend on the properties of GMIR in the heliosheath.
DE: 2104 Cosmic rays
DE: 2114 Energetic particles (7514)
DE: 2124 Heliopause and solar wind termination
DE: 2126 Heliosphere/interstellar medium interactions
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2007 Fall Meeting