HR: 1330h
AN: SH13A-13    [Abstracts]
TI: Implications of Solar Cycle Dependent Helium Modulation on Source Surface Models of Coronal Fields
AU: * Kasper, J C
EM: jck@space.mit.edu
AF: MIT Center for Space Research, 77 Massachusetts Avenue , Cambridge, MA 02139 United States
AU: Lazarus, A J
EM: ajl@space.mit.edu
AF: MIT Center for Space Research, 77 Massachusetts Avenue , Cambridge, MA 02139 United States
AU: Steinberg, J T
EM: jsteinberg@lanl.gov
AF: Los Alamos National Laboratory , P.O. Box 1663, MS D466 , Los Alamos, NM 87545 United States
AB: Observations of the modulation of the solar wind helium abundance over the solar cycle provide evidence for a physical difference in the mechanism for coronal helium acceleration in the slow solar wind during solar minimum and maximum. During solar minimum, the relative abundance is a linear function of the solar wind speed. This process can be understood in terms of force-free models of the coronal field and the derived expansion factor of the field at the source surface. During solar maximum, however, this linear dependence vanishes. Recent studies of helium modulation using the solar wind measurements of the Faraday Cup instruments on the Wind spacecraft have resulted in additional information about the connection between the in-situ abundance and the coronal field topology. For example, a six-month periodic modulation of the helium abundance - at all solar wind speeds - is related to distance from the heliospheric current sheet. These observations suggest that there are two source regions for slow solar wind in which the coronal magnetic field plays a different role. We will present these observations in the context of source surface calculations and discuss how in-situ data may test coronal field and solar wind acceleration models.
DE: 2162 Solar cycle variations (7536)
DE: 2164 Solar wind plasma
DE: 2169 Sources of the solar wind
DE: 7509 Corona
DE: 7524 Magnetic fields
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2005 Joint Assembly