Bibcode
DOI
Lites, B. W.; Socas-Navarro, H.; Skumanich, A.; Shimizu, T.
Bibliographical reference
The Astrophysical Journal, Volume 575, Issue 2, pp. 1131-1143.
Advertised on:
8
2002
Journal
Citations
30
Refereed citations
26
Description
Doppler velocities in the penumbra of a δ-configuration sunspot
observed near the limb indicate flows that converge upon the line
separating locally positive and negative polarity magnetic field (the
polarity inversion line). These flows persist for many hours.
Observations of this region with the Advanced Stokes Polarimeter (ASP)
reveal a convex vector field geometry with magnetic lines of force
arching upward from positive polarity, then downward to negative
polarity. The straightforward interpretation of the combined Doppler
velocity and vector field information leads to an untenable physical
situation: were flows directed from both footpoints toward the tops of
arched magnetic lines of force, mass would rapidly load the tops of the
arches. However, there is no observational evidence of the dynamics that
such a loading would require. To better understand this apparent
contradiction, we perform two-component analyses of the observed Stokes
spectral profiles in the vicinity of the polarity inversion line, in
order to extract information about unresolved structure of the magnetic
field and its associated flows. Fits to the observed profiles, obtained
by use of two different inversion techniques, suggest strongly that, as
in penumbrae of simple sunspots, the field geometry in the convergence
zone is ``fluted.'' However, unlike in simple sunspots, which have only
an outward-directed Evershed flow in the more horizontal of the field
components, at each spatial point our analysis reveals flows in the two
components that are oppositely directed. We interpret these observations
as indicative of an interleaved system of field lines in the vicinity of
the polarity reversal, whereby the convergent streams are able to slip
past one another and return downward into the solar interior.