7 research outputs found
On the Moat-Penumbra Relation
Proper motions in a sunspot group with a delta-configuration and close to the
solar disc center have been studied by employing local correlation tracking
techniques. The analysis is based on more than one hour time series of G-band
images. Radial outflows with a mean speed of 0.67 km s^{-1} have been detected
around the spots, the well-known sunspots moats. However, these outflows are
not found in those umbral core sides without penumbra. Moreover, moat flows are
only found in those sides of penumbrae located in the direction marked by the
penumbral filaments. Penumbral sides perpendicular to them show no moat flow.
These results strongly suggest a relation between the moat flow and the
well-known, filament aligned, Evershed flow. The standard picture of a moat
flow originated from a blocking of the upward propagation of heat is commented
in some detail.Comment: 4 pages, 4 figures, To appear in ApJ Letter
Relationships between magnetic foot points and G-band bright structures
Magnetic elements are thought to be described by flux tube models, and are
well reproduced by MHD simulations. However, these simulations are only
partially constrained by observations. We observationally investigate the
relationship between G-band bright points and magnetic structures to clarify
conditions, which make magnetic structures bright in G-band. The G-band
filtergrams together with magnetograms and dopplergrams were taken for a plage
region covered by abnormal granules as well as ubiquitous G-band bright points,
using the Swedish 1-m Solar Telescope (SST) under very good seeing conditions.
High magnetic flux density regions are not necessarily associated with G-band
bright points. We refer to the observed extended areas with high magnetic flux
density as magnetic islands to separate them from magnetic elements. We
discover that G-band bright points tend to be located near the boundary of such
magnetic islands. The concentration of G-band bright points decreases with
inward distance from the boundary of the magnetic islands. Moreover, G-band
bright points are preferentially located where magnetic flux density is higher,
given the same distance from the boundary. There are some bright points located
far inside the magnetic islands. Such bright points have higher minimum
magnetic flux density at the larger inward distance from the boundary.
Convective velocity is apparently reduced for such high magnetic flux density
regions regardless of whether they are populated by G-band bright points or
not. The magnetic islands are surrounded by downflows.These results suggest
that high magnetic flux density, as well as efficient heat transport from the
sides or beneath, are required to make magnetic elements bright in G-band.Comment: 9 pages, 14 figures, accepted for publication in A&