743 research outputs found
Detection of Small-Scale Granular Structures in the Quiet Sun with the New Solar Telescope
Results of a statistical analysis of solar granulation are presented. A data
set of 36 images of a quiet Sun area on the solar disk center was used. The
data were obtained with the 1.6 m clear aperture New Solar Telescope (NST) at
Big Bear Solar Observatory (BBSO) and with a broad-band filter centered at the
TiO (705.7 nm) spectral line. The very high spatial resolution of the data
(diffraction limit of 77 km and pixel scale of 0.0375) augmented by the very
high image contrast (15.50.6%) allowed us to detect for the first time a
distinct subpopulation of mini-granular structures. These structures are
dominant on spatial scales below 600 km. Their size is distributed as a power
law with an index of -1.8 (which is close to the Kolmogorov's -5/3 law) and no
predominant scale. The regular granules display a Gaussian (normal) size
distribution with a mean diameter of 1050 km. Mini-granular structures
contribute significantly to the total granular area. They are predominantly
confined to the wide dark lanes between regular granules and often form chains
and clusters, but different from magnetic bright points. A multi-fractality
test reveals that the structures smaller than 600 km represent a multi-fractal,
whereas on larger scales the granulation pattern shows no multi-fractality and
can be considered as a Gaussian random field. The origin, properties and role
of the newly discovered population of mini-granular structures in the solar
magneto-convection are yet to be explored.Comment: 13 pages, 5 figure
Magnetic Energy Spectra in Active Regions
Line-of-sight magnetograms for 217 active regions (ARs) of different flare
rate observed at the solar disk center from January 1997 until December 2006
are utilized to study the turbulence regime and its relationship to the flare
productivity. Data from {\it SOHO}/MDI instrument recorded in the high
resolution mode and data from the BBSO magnetograph were used. The turbulence
regime was probed via magnetic energy spectra and magnetic dissipation spectra.
We found steeper energy spectra for ARs of higher flare productivity. We also
report that both the power index, , of the energy spectrum, , and the total spectral energy are comparably
correlated with the flare index, , of an active region. The correlations are
found to be stronger than that found between the flare index and total unsigned
flux. The flare index for an AR can be estimated based on measurements of
and as , with and . We found that the regime of the fully-developed turbulence occurs in
decaying ARs and in emerging ARs (at the very early stage of emergence).
Well-developed ARs display under-developed turbulence with strong magnetic
dissipation at all scales.Comment: 14 pages, 4 figure
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