Hale Sector Boundaries.pdf - Leif and Vera Svalgaard's

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Svalgaard et al.Figure 6: The average magnetogramfor a nominal (+) sectorseen ‘face on’ in the northernhemisphere. Appropriate data(WSO 1976-2010) has been mirroredand sign-reversed as describedin section 2.3. The sectorboundary is marked by thesemi-transparent bar. The semitransparentcircle encloses thearea that is mainly contributingto the Sun’s mean field also measuredat WSO (Scherrer et al.,1977).4. DiscussionThe findings of preferential photospheric magnetic fields to heliospheric magneticfield (HMF) sector structures suggests one of a number of possibilities. The mostobvious is that these photospheric structures are responsible for the HMF, andhence a correlation would simply be consistent with the Potential Field SourceSurface models (Schatten et al., 1969; Altschuler and Newkirk, 1969) wherein theHMF was seen as an extension of the solar field, as the solar wind plasma grippedthe field and extended it into the solar wind. This, however, seems insufficient toexplain our findings, since these models are symmetric, with regard to Left-Rightor East-West handedness. So, if the cause were to be a coronal phenomenon, wewould not expect the high degree of asymmetry we find.From our understanding, of the relative high abundance of field orientation(active region formation, going along with Hale’s polarity laws) relative to theHale sector boundaries we show in Figure 1 and the orientation of the subsurfacefield in accordance with, say the Babcock-Leighton dynamo models, it seems thatthe association is more deeply rooted on the Sun, than in the corona. One suchpossible explanation has recently been put forward, and although it seems to beconsistent with our findings, the author was aware of our earlier findings whenhis theory was developed, so this is not any new support for his theory.This involves a recent shallow dynamo model (Schatten, 2009), which usespercolation and clustering to accumulate magnetic flux from ephemeral regionsbelow the photosphere, where they gather together preferentially forming activeregions near the low latitudes of high toroidal magnetic flux. To understand howthis field gathering may relate to our observations, consider the following. Let usconsider a dipole field forming near one of our Hale boundaries, say as oriented inthe Northern hemisphere, as shown. Outward oriented field (ephemeral regionsgathering into sunspots) could gather such field more readily, since the Westernportion of the active region is embedded in an outward polarity background field.SOLA: HaleBx.tex; 21 July 2010; 7:55; p. 8
Hale Sector BoundariesSimilarly the Eastern portion of active regions in these environs can gather fieldpreferentially with these orientations (those orientations which are supported byHale’s laws). In other words, any little instability in this preferential orderingwould grow from pre-existing field with the orientations from their inherentenvironment.The geometry of the modern dynamo has a differing evolution than this shallowmodel: in conventional dynamo models, fields erupt from the Sun’s interioroutwards, whereas in the percolation model, field lines coalesce from small activeregions where field lines are shed from the granulations’ churning of Ephemeralregions. This temporal pattern is thus a difference between the standard dynamotheory and this new model.Aside from these differences, however, the geometry of fields at any time,in the shallow model is similar to the Babcock-Leighton field geometry (bothof course consistent with Hale’s laws), hence either view of the Solar dynamomight equally fit our observations. So, perhaps it is too early to tell whetherthe observations are preferentially supporting which theory. So, although we arefinding out some very important things about how field lines are evolving on andin the Sun, at present, it may be too early to distinguish whether the observationsprovide conclusive evidence on the exact location of the Sun’s dynamo.5. ConclusionAcknowledgementsThe authors thank Ken Schatten for fruitful discussions.SOLA: HaleBx.tex; 21 July 2010; 7:55; p. 9
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