585 research outputs found
A new type of small-scale downflow patches in sunspot penumbrae
A sunspot penumbra is observationally examined to reveal properties of
small-scale flow structures and how they are related to the filamentary
magnetic structures and the Evershed flow. We also study how the photospheric
dynamics is related to chromospheric activities. The study is based on data
analysis of spectro-polarimetric observations of photospheric Fe I lines with
the Solar Optical Telescope aboard Hinode in a sunspot penumbra at different
heliocentric angles. Vector magnetic fields and velocities are derived using
the spectro-polarimetric data and a Stokes inversion technique. An observation
with a Ca II H filtergram co-spatial and co-temporal with the
spectro-polarimetric one is also used to study possible chromospheric
responses. We find small patches with downflows at photospheric layers. The
downflow patches have a size of 0.5" or smaller and have a geometrical
configuration different from that of the Evershed flow. The downflow velocity
is about 1 km/s at lower photspheric layers, and is almost zero in the upper
layers. Some of the downflow patches are associated with brightenings seen in
Ca II H images. The downflows are possible observational signatures of downward
flows driven by magnetic reconnection in the interlaced magnetic field
configuration, where upward flows make brightenings in the chromosphere.
Another possibility is that they are concentrated downward flows of overturning
magnetoconvection.Comment: 9 pages, 7 figures, accepted for publication in Astronomy &
Astrophysic
Magnetic Structure of Umbral Dots Observed with Hinode Solar Optical Telescope
High resolution and seeing-free spectroscopic observation of a decaying
sunspot was done with the Solar Optical Telescope aboard Hinode satellite. The
target was NOAA 10944 located in the west side of the solar surface from March
2 to March 4, 2007. The umbra included many umbral dots (UDs) with size of ~300
km in continuum light. We report the magnetic structures and Doppler velocity
fields around UDs, based on the Milne-Eddington inversion of the two iron
absorption lines at 6302 angstrom.
The histograms of magnetic field strength(B), inclination angle(i), and
Doppler velocity(v) of UDs showed a center-to-limb variation. Observed at disk
center, UDs had (1)slightly smaller field strength (Delta B=-17 Gauss) and
(2)relative blue shifts (Delta v=28 m s-1) compared to their surroundings. When
the sunspot got close to the limb, UDs and their surroundings showed almost no
difference in the magnetic and Doppler values. This center-to-limb variation
can be understood by the formation height difference in a cusp-shaped
magnetized atmosphere around UDs, due to the weakly magnetized hot gas
intrusion. In addition, some UDs showed oscillatory light curves with multiple
peaks around 10 min, which may indicate the presence of the oscillatory
convection. We discuss our results in the frameworks of two theoretical models,
the monolithic model (Schussler & Vogler 2006) and the field-free intrusion
model (Spruit & Scharmer 2006).Comment: 8 pages, 8 figures, accepted for publication in PAS
A Coronal Jet Ejects from Sunspot Light Bridge
Chromospheric brighten and H surge are the evident and common
phenomena along sunspot light bridge. In this paper, a coronal jet ejects from
sunspot light bridge is presented. Using the data from the Solar Dynamics
Observatory (SDO) and Hinode satellites, it is confirmed that the jet has the
root near light bridge, this suggests that the jet may be a result of
reconnection between main sunspot and light bridge. Due to the processing of
jet ejects, the intensity and width of light bridge have some changes at some
extent. This also suggests that jet is related to the interaction between light
bridge and umbra, possibly magnetic reconnection or heat plasma trapped in
light bridge escaping and moving along field line.Comment: It has been accepted for publication in PAS
The properties of penumbral microjets inclination
We investigate the dependence of penumbral microjets inclination on the
position within penumbra. The high cadence observations taken on 10 November
2006 with the Hinode satellite through the \ion{Ca}{ii} H and G--band filters
were analysed to determine the inclination of penumbral microjets. The results
were then compared with the inclination of the magnetic field determined
through the inversion of the spectropolarimetric observations of the same
region. The penumbral microjet inclination is increasing towards the outer edge
of the penumbra. The results suggest that the penumbral microjet follows the
opening magnetic field lines of a vertical flux tube that creates the sunspot.Comment: 4 pages, 4 figures, A&A Letter in pres
Upflows in the central dark lane of sunspot light bridges
We use high spatial and spectral resolution observations obtained with the
CRisp Imaging SpectroPolarimeter at the Swedish 1-m Solar Telescope to analyze
the velocity profile of granular light bridges in a sunspot. We find upflows
associated with the central dark lanes of the light bridges. From bisectors in
the Fe I 630.15 nm line we find that the magnitude of the upflows varies with
height with the strongest upflows being deeper in the atmosphere. Typical
upflow velocities measured from the 70% bisector are around 500 m/s with peaks
above 1 km/s. The upflows in the central dark lane are surrounded by downflows
of weaker magnitude, sometimes concentrated in patches with enhanced velocities
reaching up to 1.1 km/s. A small spatial offset between the upflows and the
continuum dark lane is interpreted as a line-of-sight effect due to the
elevated nature of the dark lane and the light bridge above the umbral
surroundings. Our observations show that the central dark lane in granular
light bridges is not equivalent to the intergranular lanes of normal
photospheric granulation that host convective downflows. These results support
recent MHD simulations of magneto-convection in sunspot atmospheres.Comment: Accepted for publication in Astrophysical Journal Letter
The Solar Internetwork. II. Magnetic Flux Appearance and Disappearance Rates
Small-scale internetwork magnetic fields are important ingredients of the
quiet Sun. In this paper we analyze how they appear and disappear on the solar
surface. Using high resolution Hinode magnetograms, we follow the evolution of
individual magnetic elements in the interior of two supergranular cells at the
disk center. From up to 38 hr of continuous measurements, we show that magnetic
flux appears in internetwork regions at a rate of Mx cm
day ( Mx day over the entire solar
surface). Flux disappears from the internetwork at a rate of Mx
cm day ( Mx day) through fading
of magnetic elements, cancellation between opposite-polarity features, and
interactions with network patches, which converts internetwork elements into
network features. Most of the flux is lost through fading and interactions with
the network, at nearly the same rate of about 50 Mx cm day. Our
results demonstrate that the sources and sinks of internetwork magnetic flux
are well balanced. Using the instantaneous flux appearance and disappearance
rates, we successfully reproduce the time evolution of the total unsigned flux
in the two supergranular cells.Comment: 8 pages, 6 figures. Accepted in ApJ. An animation of the right panel
of Figure 1 is available at
http://spg.iaa.es/pub/downloads/gosic/figure1_right_panel.ta
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