256,312 research outputs found
The three-dimensional structure of sunspots II. The moat flow at two different heights
Many sunspots are surrounded by a radial outflow called the moat flow. We
investigate the moat flow at two different heights of the solar atmosphere for
a sunspot whose magnetic properties were reported in the first paper of this
series. We use two simultaneous time series taken with the Transition Region
And Coronal Explorer (TRACE) in white light and in the UV at 170 nm. The
field-of-view is centered on the small sunspot NOAA 10886 located near disk
center. Horizontal velocities are derived by applying two different local
correlation tracking techniques. Outflows are found everywhere in the moat. In
the inner moat, the velocities from the UV series are larger than those from
white light, whereas in the outer part of the moat we find the converse result.
The results imply that the white light velocities represent a general outflow
of the quiet sun plasma in the moat, while UV velocities are dominated by small
bright points that move faster than the general plasma flow.Comment: Manuscript accepted by Astronomy & Astrophysic
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
Characterization of horizontal flows around solar pores from high-resolution time series of images
Though there is increasing evidence linking the moat flow and the Evershed
flow along the penumbral filaments, there is not a clear consensus regarding
the existence of a moat flow around umbral cores and pores, and the debate is
still open. Solar pores appear to be a suitable scenario to test the
moat-penumbra relation as evidencing the direct interaction between the umbra
and the convective plasma in the surrounding photosphere, without any
intermediate structure in between. The present work studies solar pores based
on high resolution ground-based and satellite observations. Local correlation
tracking techniques have been applied to different-duration time series to
analyze the horizontal flows around several solar pores. Our results establish
that the flows calculated from different solar pore observations are coherent
among each other and show the determinant and overall influence of exploding
events in the granulation around the pores. We do not find any sign of
moat-like flows surrounding solar pores but a clearly defined region of inflows
surrounding them. The connection between moat flows and flows associated to
penumbral filaments is hereby reinforced by this work.Comment: 10 pages, 10 figures, Accepted for publication in Astronomy and
Astrophysics
SunPy: Python for Solar Physics. An implementation for local correlation tracking
Python programming language has experienced a great progress and growing use in the scientific community in the last
years as well as a direct impact on solar physics. Python is a very mature language and almost any fundamental feature you
might want to do is already implemented in a library or module. SunPy is a common effort of, using the advantages of Python,
developing tools to be applied for processing and analysis of solar data. In this work we present a particular development,
based on Python, for the analysis of proper motions in time series of images through the local correlation tracking algorithm.
A graphic user interface allows to select different parameters for the computations, visualization and analysis of flow fields
Horizontal flow fields observed in Hinode G-band images. I. Methods
Context: The interaction of plasma motions and magnetic fields is an
important mechanism, which drives solar activity in all its facets. For
example, photospheric flows are responsible for the advection of magnetic flux,
the redistribution of flux during the decay of sunspots, and the built-up of
magnetic shear in flaring active regions. Aims: Systematic studies based on
G-band data from the Japanese Hinode mission provide the means to gather
statistical properties of horizontal flow fields. This facilitates comparative
studies of solar features, e.g., G-band bright points, magnetic knots, pores,
and sunspots at various stages of evolution and in distinct magnetic
environments, thus, enhancing our understanding of the dynamic Sun. Methods: We
adapted Local Correlation Tracking (LCT) to measure horizontal flow fields
based on G-band images obtained with the Solar Optical Telescope on board
Hinode. In total about 200 time-series with a duration between 1-16 h and a
cadence between 15-90 s were analyzed. Selecting both a high-cadence (dt = 15
s) and a long-duration (dT = 16 h) time-series enabled us to optimize and
validate the LCT input parameters, hence, ensuring a robust, reliable, uniform,
and accurate processing of a huge data volume. Results: The LCT algorithm
produces best results for G-band images having a cadence of 60-90 s. If the
cadence is lower, the velocity of slowly moving features will not be reliably
detected. If the cadence is higher, the scene on the Sun will have evolved too
much to bear any resemblance with the earlier situation. Consequently, in both
instances horizontal proper motions are underestimated. The most reliable and
yet detailed flow maps are produced using a Gaussian kernel with a size of 2560
km x 2560 km and a full-width-at-half-maximum (FWHM) of 1200 km (corresponding
to the size of a typical granule) as sampling window.Comment: 12 pages, 8 figures, 4 tables, accepted for publication in Astronomy
and Astrophysic
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