2,944 research outputs found
Fine structures in the atmosphere above a sunspot umbra
We present simultaneous photospheric and chromospheric observations of the
trailing sunspot in NOAA 10904, obtained with the Swedish Solar Telescope (SST)
La Palma, Canary Islands. Time series of high resolution \ion{Ca}{ii}\,
images show transient jet-like structures in sunspot umbrae are elongated,
which we call umbral microjets. These jets are directed roughly parallel to
nearby penumbral microjets, suggesting that they are aligned with the
background magnetic field. In general, first a bright dot-like structure
appears, from which a jet later emerges, although some jets appear without an
associated chromospheric dot. Bright photospheric umbral dots are associated
with umbral microjets arising in the outer umbra. Nevertheless, a one-to-one
correspondence between jet-like events and underlying umbral dots is not seen.
They are typically less than 1\arcsec ~long and less than 0\farcs3 wide. The
typical lifetime of umbral microjets is around one minute. The brightness of
these structures increases from the center of the umbra towards the
umbra-penumbra boundary along with the brightness of the local background.Comment: 5 pages, 6 figures. Accepted for publication in A&A Lette
Waves as the source of apparent twisting motions in sunspot penumbrae
The motion of dark striations across bright filaments in a sunspot penumbra
has become an important new diagnostic of convective gas flows in penumbral
filaments. The nature of these striations has, however, remained unclear. Here
we present an analysis of small scale motions in penumbral filaments in both
simulations and observations. The simulations, when viewed from above, show
fine structure with dark lanes running outwards from the dark core of the
penumbral filaments. The dark lanes either occur preferentially on one side or
alternate between both sides of the filament. We identify this fine structure
with transverse (kink) oscillations of the filament, corresponding to a
sideways swaying of the filament. These oscillations have periods in the range
of 5-7 min and propagate outward and downward along the filament. Similar
features are found in observed G-band intensity time series of penumbral
filaments in a sunspot located near disk center obtained by the Broadband
Filter Imager (BFI) on board {\it Hinode}. We also find that some filaments
show dark striations moving to both sides of the filaments. Based on the
agreement between simulations and observations we conclude that the motions of
these striations are caused by transverse oscillations of the underlying bright
filaments.Comment: Accepted for publication in Astrophysical Journal on 8th April 201
Downflows in sunspot umbral dots
We study the velocity field of umbral dots at a resolution of 0.14". Our
analysis is based on full Stokes spectropolarimetric measurements of a pore
taken with the CRISP instrument at the Swedish 1-m Solar Telescope. We
determine the flow velocity at different heights in the photosphere from a
bisector analysis of the Fe I 630 nm lines. In addtion, we use the observed
Stokes Q, U, and V profiles to characterize the magnetic properties of these
structures. We find that most umbral dots are associated with strong upflows in
deep photospheric layers. Some of them also show concentrated patches of
downflows at their edges, with sizes of about 0.25", velocities of up to 1000
m/s, and enhanced net circular polarization signals. The downflows evolve
rapidly and have lifetimes of only a few minutes. These results appear to
validate numerical models of magnetoconvection in the presence of strong
magnetic fields.Comment: Final published version. For best quality figures, please download
the PS versio
Enhanced Joule Heating in Umbral Dots
We present a study of magnetic profiles of umbral dots (UDs) and its
consequences on the Joule heating mechanisms. Hamedivafa (2003) studied Joule
heating using vertical component of magnetic field. In this paper UDs magnetic
profile has been investigated including the new azimuthal component of magnetic
field which might explain the relatively larger enhancement of Joule heating
causing more brightness near circumference of UD.Comment: 8 pages, 1 figure, accepted in Solar Physic
Growth and Development of Health science Colleges in Rajasthan: A Study
Health science education may be a general application of science to the effective utilization of human resources for healthy and loaded society. it's received wider attention because of its urgency in securing prosperity for the folks and even additional relationship to social order. Medical Education may be a challenge to drugs and education in the context of universal declaration of human rights of individuals to Social Security which coated the risks of illness, invalidity, maternity, old age, death, education and opportunities to induce health data for a stronger and healthy living. Health is the one amongst the basic rights of individual while not discrimination of race, religion, political, economic and social condition. Key words: Health Science, Medical Education, Ayurveda, Unani, Homeopathy, Allopathy
Properties of simulated sunspot umbral dots
Realistic 3D radiative MHD simulations reveal the magneto-convective
processes underlying the formation of the photospheric fine structure of
sunspots, including penumbral filaments and umbral dots. Here we provide
results from a statistical analysis of simulated umbral dots and compare them
with reports from high-resolution observations. A multi-level segmentation and
tracking algorithm has been used to isolate the bright structures in synthetic
bolometric and continuum brightness images. Areas, brightness, and lifetimes of
the resulting set of umbral dots are found to be correlated: larger umbral dots
tend to be brighter and live longer. The magnetic field strength and velocity
structure of umbral dots on surfaces of constant optical depth in the continuum
at 630 nm indicate that the strong field reduction and high velocities in the
upper parts of the upflow plumes underlying umbral dots are largely hidden from
spectro-polarimetric observations. The properties of the simulated umbral dots
are generally consistent with the results of recent high-resolution
observations. However, the observed population of small, short-lived umbral
dots is not reproduced by the simulations, possibly owing to insufficient
spatial resolution.Comment: Accepted for publication in A&
Searching for overturning convection in penumbral filaments: slit spectroscopy at 0.2 arcsec resolution
Recent numerical simulations of sunspots suggest that overturning convection
is responsible for the existence of penumbral filaments and the Evershed flow,
but there is little observational evidence of this process. Here we carry out a
spectroscopic search for small-scale convective motions in the penumbra of a
sunspot located 5 deg away from the disk center. The position of the spot is
very favorable for the detection of overturning downflows at the edges of
penumbral filaments. Our analysis is based on measurements of the Fe I 709.0 nm
line taken with the Littrow spectrograph of the Swedish 1 m Solar Telescope
under excellent seeing conditions. We compute line bisectors at different
intensity levels and derive Doppler velocities from them. The velocities are
calibrated using a nearby telluric line, with systematic errors smaller than
150 m/s. Deep in the photosphere, as sampled by the bisectors at the 80%-88%
intensity levels, we always observe blueshifts or zero velocities. The maximum
blueshifts reach 1.2 km/s and tend to be cospatial with bright penumbral
filaments. In the line core we detect blueshifts for the most part, with small
velocities not exceeding 300 m/s. Redshifts also occur, but at the level of
100-150 m/s, and only occasionally. The fact that they are visible in high
layers casts doubts on their convective origin. Overall, we do not find
indications of downflows that could be associated with overturning convection
at our detection limit of 150 m/s. Either no downflows exist, or we have been
unable to observe them because they occur beneath tau=1 or the spatial
resolution/height resolution of the measurements is still insufficient.Comment: Accepted for publication in Ap
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