24 research outputs found
Morphological study of penumbral formation
Penumbrae are known to be area of mainly horizontal magnetic field
surrounding umbrae of relatively large and mature sunspots. In this paper, we
observationally studied the formation of penumbrae in NOAA10978, where several
penumbral formations were observed in G-band images of SOT/Hinode. Thanks to
the continuous observation by Hinode, we could morphologically follow the
evolution of sunspots and found that there are several paths to the penumbral
formation: (1) Active accumulation of magnetic flux, (2) Rapid emergence of
magnetic field, and (3) Appearance of twisted or rotating magnetic tubes. In
all of these cases, magnetic fields are expected to sustain high inclination at
the edges of flux tube concentration longer than the characteristic growth time
of downward magnetic pumping.Comment: accepted for publication in PAS
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
Spectroscopic Studies of Limb Spicules. I. Radial and Turbulent Velocities
We made high-resolution spectroscopic observations of limb-spicules in
H-alpha using the Vertical Spectrograph of Domeless Solar Telescope at Hida
Observatory. While more than half of the observed spicules have Gaussian
line-profiles, some spicules have distinctly asymmetric profiles which can be
fitted with two Gaussian components. The faster of these components has radial
velocities of 10 - 40 km/s and Doppler-widths of about 0.4 A which suggest that
it is from a single spicule oriented nearly along the line-of-sight. Profiles
of the slower components and the single-Gaussian type show very similar
characteristics. Their radial velocities are less than 10 km/s and the
Doppler-widths are 0.6 - 0.9 A. Non-thermal "macroturbulent" velocities of
order 30 km/s are required to explain these width-values.Comment: 13 pages, 12 figures, to be published in Publications of the
Astronomical Society of Japa
Statistical Study on the Nature of Solar Flux Emergence
We studied 101 flux emergence events ranging from small ephemeral regions to
large emerging flux regions which were observed with Hinode Solar Optical
Telescope filtergram. We investigated how the total magnetic flux of the
emergence event controls the nature of emergence. To determine the modes of
emergences, horizontal velocity fields of global motion of the magnetic patches
in the flux emerging sites were measured by the local correlation tracking.
Between two main polarities of the large emerging flux regions with more than
around 2 \times 10^19 Mx, there were the converging flows of anti-polarity
magnetic patches. On the other hand, small ephemeral regions showed no
converging flow but simple diverging pattern. When we looked into the detailed
features in the emerging sites, irrespective of the total flux and the spatial
size, all the emergence events were observed to consist of single or multiple
elementary emergence unit(s). The typical size of unitary emergence is 4 Mm and
consistent with the simulation results. From the statistical study of the flux
emergence events, the maximum spatial distance between two main polarities, the
magnetic flux growth rate and the mean separation speed were found to follow
the power-law functions of the total magnetic flux with the indices of 0.27,
0.57, and -0.16, respectively. From the discussion on the observed power-law
relations, we got a physical view of solar flux emergence that emerging
magnetic fields float and evolve balancing to the surrounding turbulent
atmosphere. Key words: Sun: magnetic fields - Sun: emerging flux - Sun:
photosphere - Sun: chromospher
Observations of Chromospheric Anemone Jets with Hinode SOT and Hida Ca II Spectroheliogram
We present the first simultaneous observations of chromospheric "anemone"
jets in solar active regions with Hinode SOT Ca II H broadband filetergram and
Ca II K spetroheliogram on the Domeless Solar Telescope (DST) at Hida
Observatory. During the coordinated observation, 9 chromospheric anemone jets
were simultaneously observed with the two instruments. These observations
revealed three important features, i.e.: (1) the jets are generated in the
lower chromosphere, (2) the length and lifetime of the jets are 0.4-5 Mm and
40-320 sec, (3) the apparent velocity of the jets with Hinode SOT are 3-24
km/s, while Ca II K3 component at the jets show blueshifts (in 5 events) in the
range of 2- 6 km/s. The chromospheric anemone jets are associated with mixed
polarity regions which are either small emerging flux regions or moving
magnetic features. It is found that the Ca II K line often show red or blue
asymmetry in K2/K1 component: the footpoint of the jets associated with
emerging flux regions often show redshift (2-16 km/s), while the one with
moving magnetic features show blueshift (around 5 km/s). Detailed analysis of
magnetic evolution of the jet foaming regions revealed that the reconnection
rate (or canceling rate) of the total magnetic flux at the footpoint of the
jets are of order of 10^{16} Mx/s, and the resulting magnetic energy release
rate (1.1-10) x 10^{24} erg/s, with the total energy release (1-13) x 10^{26}
erg for the duration of the magnetic cancellations, 130s. These are comparable
to the estimated total energy, 10^{26} erg, in a single chromospheric anemone
jet. An observation-based physical model of the jet is presented. The relation
between chromospheric anemone jets and Ellerman bombs is discussed.Comment: 22 pages, 27 figures, accepted for Publications of the Astronomical
Society of Japa
Ca II K Spectral Study of an Emerging Flux Region using Domeless Solar Telescope in Hida Observatory
A cooperative observation with Hida observatory and Hinode satellite was
performed on an emerging flux region. The successive Ca II K spectro-heliograms
of the emerging flux region were taken by the Domeless Solar Telescope of Hida
observatory. Hinode observed the emerging flux region with Ca II H and Fe I
Stokes IQUV filtergrams. In this study, detailed dynamics and temporal
evolution of the magnetic flux emergence was studied observationally. The event
was first detected in the photospheric magnetic field signals. 3 minutes later,
the horizontal expansion of the dark area was detected. And then, 7 minutes
later than the horizontal expansion, the emerging loops were detected with the
maximal rise speed of 2.1 km/s at chromospheric heights. The observed dynamics
of emerging magnetic flux from the photosphere to the upper chromosphere is
well consistent with the results of previous simulation works. The gradual
rising phase of flux tubes with a weak magnetic strength was confirmed by our
observation.Comment: 14 pages, 7 figure
Spicule Dynamics over Plage Region
We studied spicular jets over a plage area and derived their dynamic
characteristics using Hinode Solar Optical Telescope (SOT) high-resolution
images. The target plage region was near the west limb of the solar disk. This
location permitted us to study the dynamics of spicular jets without the
overlapping effect of spicular structures along the line of sight.
In this work, to increase the ease with which we can identify spicules on the
disk, we applied the image processing method `MadMax' developed by Koutchmy et
al. (1989). It enhances fine, slender structures (like jets), over a diffuse
background. We identified 169 spicules over the target plage. This sample
permits us to derive statistically reliable results regarding spicular
dynamics.
The properties of plage spicules can be summarized as follows: (1) In a plage
area, we clearly identified spicular jet features. (2) They were shorter in
length than the quiet region limb spicules, and followed ballistic motion under
constant deceleration. (3) The majority (80%) of the plage spicules showed the
cycle of rise and retreat, while 10% of them faded out without a complete
retreat phase. (4) The deceleration of the spicule was proportional to the
velocity of ejection (i.e. the initial velocity).Comment: 12 pages, 9 figures, accepted for publication in PAS
Ellerman Bombs at high resolution: I. Morphological evidence for photospheric reconnection
High-resolution imaging-spectroscopy movies of solar active region NOAA 10998
obtained with the CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish 1-m
Solar Telescope show very bright, rapidly flickering, flame-like features that
appear intermittently in the wings of the Balmer H-alpha line in a region with
moat flows and likely some flux emergence. They show up at regular H-alpha
blue-wing bright points that outline magnetic network, but flare upward with
much larger brightness and distinct "jet" morphology seen from aside in the
limbward view of these movies. We classify these features as Ellerman bombs and
present a morphological study of their appearance at the unprecedented spatial,
temporal, and spectral resolution of these observations. The bombs appear along
magnetic network with footpoint extents up to 900km. They show apparent travel
away from the spot along the pre-existing network at speeds of about 1 km/s.
The bombs flare repetitively with much rapid variation at time scales of
seconds only, in the form of upward jet-shaped brightness features. These reach
heights of 600-1200km and tend to show blueshifts; some show bi-directional
Doppler signature, and some seem accompanied with an H-alpha surge. They are
not seen in the core of H-alpha due to shielding by overlying chromospheric
fibrils. The network where they originate has normal properties. The morphology
of these jets strongly supports deep-seated photospheric reconnection of
emergent or moat-driven magnetic flux with pre-existing strong vertical network
fields as the mechanism underlying the Ellerman bomb phenomenon.Comment: 13pages, 10 figures, 2 tables. Accepted for publication in the
Astrophysical Journa