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Formation and evolution of small-scale solar magnetic fields

Posted on:2009-03-23Degree:Ph.DType:Thesis
University:University of Colorado at BoulderCandidate:Lamb, D. AFull Text:PDF
GTID:2440390005953788Subject:Physics
Abstract/Summary:
In this thesis I investigate the formation and evolution of small-scale magnetic fields on the surface of the Sun. I observe the magnetic field in quiet sun regions in an effort to further understand the baseline magnetic field that exists throughout the photosphere at all phases of the solar cycle. An automated feature tracking algorithm that I helped develop allows me to systematically analyze datasets containing over 105 evolving magnetic features.;In 1.2"-resolution Michelson Doppler Imager (MDI) magnetograms, I find that 30% of features identified by our algorithm originate without other detectable flux within 2.2 Mm. These features having an apparent unipolar origin account for 94% of the flux newly detected by the algorithm. I infer from their ensemble average that these features are actually previously existing flux, coalesced by surface flows into concentrations large and strong enough to detect. Flux coalescence is at least as important as bipolar ephemeral region emergence for introducing detectable flux into the photosphere, underscoring the importance of small-scale fields to the overall photospheric flux budget.;Using 0.3"-resolution magnetograms from the Narrowband Filter Imager (NFI) on the recently-launched Hinode spacecraft, I confirm that apparent unipolar emergence seen with MDI is indeed flux coalescence. I then demonstrate that apparent unipolar emergence seen in NFI magnetograms also corresponds to coalescence of previously existing weak field. The uncoalesced flux, detectable only in the ensemble average of hundreds of these events, accounts for 30-50% of the total flux within 3 Mm of the detected features.;Finally, I study small-scale fields around intermediate-scale supergranular network concentrations. This is motivated by simulations and observations showing suppression of flux production by background magnetic fields at small and large scales. Within 12 Mm of the network concentrations, I find no evidence that the concentrations systematically affect the local production of weak fields. Rather, the small-scale field usually traces the evolution of the much larger network concentrations, which evolve under the influence of the supergranular flow. These studies show the degree to which the formation and evolution of small-scale magnetic fields is intertwined with surface flows and magnetic fields on both smaller and larger scales.
Keywords/Search Tags:Magnetic fields, Small-scale, Evolution, Surface, Flux
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