HR: 1400h
AN: SH23C-04    [Abstracts]
TI: Reassessment of Arguments For and Against Open-Flux Conservation in the Heliosphere
AU: * Crooker, N U
EM: crooker@bu.edu
AF: Boston University, Center for Space Physics, 725 Commonwealth Avenue, Boston, MA 02215, United States
AU: Owens, M J
EM: mjowens@bu.edu
AF: Boston University, Center for Space Physics, 725 Commonwealth Avenue, Boston, MA 02215, United States
AU: Schwadron, N A
EM: nathanas@bu.edu
AF: Boston University, Center for Space Physics, 725 Commonwealth Avenue, Boston, MA 02215, United States
AB: Whether or not open magnetic flux from the Sun is conserved in the heliosphere has become a key issue for distinguishing between models of the solar-cycle reversal of magnetic polarity. An argument used in support of open-flux conservation is that dropouts of suprathermal electrons (EDs) that presumably signal a loss of open flux through disconnection from the Sun are rarely observed in the solar wind. On the other hand, coronagraph observations of inflows have been used as support for the argument that disconnection is as common as that predicted by potential field source surface (PFSS) models, which do not conserve open flux. We suggest that neither of these arguments is valid. The argument that rare EDs indicate negligible disconnection leaves open the question of what ED occurrence rate is required to balance the closed flux introduced by coronal mass ejections (CMEs). Recent modeling using observed CME rates indicates that the ED rate should be much lower than expected, consistent with the most recent observations of EDs using high-time-resolution data and thus consistent with no conservation of open flux. Countering this view, however, is the realization that EDs can also be caused by interchange reconnection at the Sun, which conserves open flux. Interchange reconnection can cancel the flux contribution from CMEs by opening them. If it occurs at the foot of a loop that has expanded far out into the heliosphere, the loop will appear to be an open field line at 1 AU, as required for disconnection, because the sunward electrons in the counterstreaming beam will have disappeared owing to scattering along the increasing path length. Regarding the argument concerning coronal inflows, these also can be caused by interchange reconnection with loops that have already expanded into the heliosphere. Moreover, what PFSS models count as disconnection could as well be interchange reconnection with loops that have expanded beyond the source surface. We conclude that observations and models can be viewed as fully consistent with conservation of open flux, attractive for its simplicity; but they cannot exclude the opposing view that the closed flux introduced by CMEs is somehow balanced by disconnection.
DE: 2134 Interplanetary magnetic fields
DE: 2162 Solar cycle variations (7536)
DE: 7524 Magnetic fields
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2007 Joint Assembly