Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsh52a0436s&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SH52A-0436
Physics
2134 Interplanetary Magnetic Fields, 2169 Sources Of The Solar Wind, 7511 Coronal Holes, 7524 Magnetic Fields
Scientific paper
The magnetic field in the heliosphere originates from a variety of sources on the surface of the Sun, including mature, decaying, and decayed active regions, as well as sunspots. The emergence of new active regions together with the dispersal of flux from older active regions causes the coronal magnetic field topology to continually evolve, allowing previously closed-field regions to open into the heliosphere and previously open-field regions to close. Such evolution of the coronal field, together with the rotation of the Sun, drive space weather through the continually changing conditions of the solar wind and the magnetic field embedded within it. We combine observations and numerical simulations by assimilating SOHO/MDI magnetograms into a surface flux transport model, in order to investigate the origins of the heliospheric field on the solar surface through the rising phase of the current activity cycle. We find that around cycle maximum, the interplanetary magnetic field (IMF) is typically rooted in a dozen disjoint regions on the solar surface. Whereas active regions are sometimes ignored as a source for the IMF, the fraction of the IMF that connects directly to magnetic plage is found to reach up to 30-50%\ at cycle maximum, with even direct connections between sunspots and the heliosphere. We further compare this data assimilation model with a pure simulation model, in which the properties of the emergent active regions were chosen at random from parent distribution functions measured for the sun. The two models show remarkable agreement in the temporal behavior of the sector structure of the IMF, in the magnitude and time-behavior of the heliospheric field, and even in such global properties as the tilt angle of the Sun's large scale dipole. We thus conclude that no additional flux-emergence patterns or field-dispersal properties are required of the solar dynamo beyond those that are included in the model in order to understand the large-scale solar and heliospheric fields.
de Rosa Marc L.
Schrijver Carolus J.
Title Alan M.
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