HR: 11:00h
AN: SH32A-03    [Abstracts]
TI: The Decay of Interplanetary Coronal Mass Ejections and Forbush Decrease Recovery Times
AU: * Penna, R F
EM: rpenna@pas.rochester.edu
AF: University of Rochester, Department of Physics and Astronomy, Rochester, NY 14627 United States
AU: * Penna, R F
EM: rpenna@pas.rochester.edu
AF: University of Rochester, CPU Box 274450, Rochester, NY 14627 United States
AU: Quillen, A C
EM: aquillen@pas.rochester.edu
AF: University of Rochester, Department of Physics and Astronomy, Rochester, NY 14627 United States
AB: We investigate the relationship between Forbush cosmic ray decrease recovery time and coronal mass ejection transit time between the Sun and the L1 Lagrange point. We identify 17 Forbush decreases from ground based neutron count rates between 1978 and 2003 that occur during at same phase in the solar cycle and can be associated with single coronal mass ejections (CMEs) in the SOHO LASCO CME Catalog and specific interplanetary coronal mass ejections (ICMEs) crossing the vicinity of Earth. We find a negative correlation between Forbush recovery times and CME transit times that contradicts the predictions of simple diffusive barrier models. The anti-correlation suggests that the decay rate of ICMEs is anti-correlated with their travel speed. Forbush recovery times range from five times the transit time for the fastest disturbance to a fifth the Sun-Earth transit time for the slowest. To account for the large range of measured recovery times we infer that the slowest disturbances must decay rapidly with radius whereas the fastest events must remain strong. The longest recovery times suggest that the fastest disturbances in our sample decayed less rapidly with radius than the ambient solar wind magnetic field strength.
DE: 2104 Cosmic rays
DE: 2111 Ejecta, driver gases, and magnetic clouds
DE: 2139 Interplanetary shocks
DE: 7513 Coronal mass ejections
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2005 Joint Assembly