75 research outputs found
Dynamic Ly alpha jets
The solar chromosphere and transition region are highly structured and
complex regimes. A recent breakthrough has been the identification of dynamic
fibrils observed in H alpha as caused by field-aligned magnetoacoustic shocks.
We seek to find whether such dynamic fibrils are also observed in Ly alpha. We
used a brief sequence of four high-resolution Ly alpha images of the solar limb
taken by the Very high Angular resolution ULtraviolet Telescope (VAULT), which
displays many extending and retracting Ly alpha jets. We measured their top
trajectories and fitted parabolas to the 30 best-defined ones. Most jet tops
move supersonically. Half of them decelerate, sometimes superballistically, the
others accelerate. This bifurcation may arise from incomplete sampling of
recurrent jets. The similarities between dynamic Ly alpha jets and H alpha
fibrils suggest that the magnetoacoustic shocks causing dynamic H alpha fibrils
also affect dynamic Ly alpha jets.Comment: 5 pages, 7 figures; changed title and content; accepted in Astronomy
and Astrophysics; eps figures in full resolution are available at
http://www.astro.sk/~koza/publications/vault/figs
Observations of quasi-periodic phenomena associated with a large blowout solar jet
A variety of periodic phenomena have been observed in conjunction with large
solar jets. We aim to find further evidence for {(quasi-)}periodic behaviour in
solar jets and determine what the periodic behaviour can tell us about the
excitation mechanism and formation process of the large solar jet. Using the
304 {\AA} (He-II), 171 {\AA} (Fe IX), 193 {\AA} (Fe XII/XXIV) and 131 {\AA} (Fe
VIII/XXI) filters on-board the Solar Dynamic Observatory (SDO) Atmospheric
Imaging Assembly (AIA), we investigate the intensity oscillations associated
with a solar jet. Evidence is provided for multiple magnetic reconnection
events occurring between a pre-twisted, closed field and open field lines.
Components of the jet are seen in multiple SDO/AIA filters covering a wide
range of temperatures, suggesting the jet can be classified as a blowout jet.
Two bright, elongated features are observed to be co-spatial with the large
jet, appearing at the jet's footpoints. Investigation of these features reveal
they are defined by multiple plasma ejections. The ejecta display
(quasi-)periodic behaviour on timescales of 50 s and have rise velocities of
40-150 km\,s along the open field lines. Due to the suggestion that the
large jet is reconnection-driven and the observed properties of the ejecta, we
further propose that these ejecta events are similar to type-II spicules. The
bright features also display (quasi)-periodic intensity perturbations on the
timescale of 300 s. Possible explanations for the existence of the
(quasi-)periodic perturbations in terms of jet dynamics and the response of the
transition region are discussed.Comment: Astronomy and Astrophysics - In Prin
EUV jets, type III radio bursts and sunspot waves investigated using SDO/AIA observations
Images from the Solar Dynamics Observatory (SDO) at 211A are used to identify
the solar source of the type III radio bursts seen in WIND/WAVES dynamic
spectra. We analyse a 2.5 hour period during which six strong bursts are seen.
The radio bursts correlate very well with the EUV jets coming from the western
side of a sunspot in AR11092. The EUV jet emission also correlates well with
brightening at what looks like their footpoint at the edge of the umbra. For
10-15 min after strong EUV jets are ejected, the footpoint brightens at roughly
3 min intervals. In both the EUV images and the extracted light curves, it
looks as though the brightening is related to the 3-min sunspot oscillations,
although the correlation coefficient is rather low. The only open field near
the jets is rooted in the sunspot. We conclude that active region EUV/X-ray
jets and interplanetary electron streams originate on the edge of the sunspot
umbra. They form along a current sheet between the sunspot open field and
closed field connecting to underlying satellite flux. Sunspot running penumbral
waves cause roughly 3-min jet footpoint brightening. The relationship between
the waves and jets is less clear.Comment: 4 pages, 7 figures, Accepted by A&A Letters. For associated gif
movie, see http://www.mps.mpg.de/data/outgoing/innes/jets/losb_304_211_rd.gi
Chromospheric jets around the edges of sunspots
Aims. Evidence is beginning to be put forward that demonstrates the role of the chromosphere in supplying energy and mass to the corona. We aim to asses the role of chromospheric jets in active region dynamics.
Methods. Using a combination of the Hinode/SOT Ca II H and TRACE 1550 Å and 1600 Å filters we examine chromospheric jets situated at the edge of a sunspot.
Results. Analysis reveals a near continuous series of jets, that raise chromospheric material into the low corona above a sunspot. The jets have average rise speeds of 30 km/s
and a range of 10−100 km/s. Enhanced emission observed at the jets leading edge suggests the formation of a shock front. Increased emission in TRACE bandpasses above the sunspot and the disappearance of the jets from the Ca II filter suggests that some of the chromospheric jet material is at least heated to ∼ 0.1 MK. The evidence suggests that the jets could be a mechanism which provides a steady, low-level heating for active region features
Oscillations and waves in solar spicules
Since their discovery, spicules have attracted increased attention as energy/mass bridges between the dense and dynamic photosphere and the tenuous hot solar corona. Mechanical energy of photospheric random and coherent motions can be guided by magnetic field lines, spanning from the interior to the upper parts of the solar atmosphere, in the form of waves and oscillations. Since spicules are one of the most pronounced features of the chromosphere, the energy transport they participate in can be traced by the observations of their oscillatory motions. Oscillations in spicules have been observed for a long time. However the recent high-resolutions and high-cadence space and ground based facilities with superb spatial, temporal and spectral capacities brought new aspects in the research of spicule dynamics. Here we review the progress made in imaging and spectroscopic observations of waves and oscillations in spicules. The observations are accompanied by a discussion on theoretical modelling and interpretations of these oscillations. Finally, we embark on the recent developments made on the presence and role of Alfven and kink waves in spicules. We also address the extensive debate made on the Alfven versus kink waves in the context of the explanation of the observed transverse oscillations of spicule axes
Non-homogeneous Behaviour of the Spatial Distribution of Macrospicules
In this paper the longitudinal and latitudinal spatial
distribution of macrospicules is examined. We found a statistical
relationship between the active longitude determined by
sunspot groups and the longitudinal distribution of macrospicules.
This distribution of macrospicules shows an inhomogeneity and
non-axysimmetrical behaviour in the time interval from June
2010 until December 2012 covered by observations of the Solar
Dynamic Observatory (SDO) satellite. The enhanced positions
of the activity and its time variation has been calculated. The
migration of the longitudinal distribution of macrospicules shows
a similar behaviour as that of the sunspot groups
Spectroscopy at the solar limb: I. Average off-limb profiles and Doppler shifts of Ca II H
We present constraints on the structure of the chromosphere from observations
of the Ca II H line profile near and off the solar limb. We obtained a data set
of the Ca II H line in a field of view extending 20" across the limb. We
analyzed the spectra for the properties of off-limb spectra. We used tracers of
the Doppler shifts, such as the location of the absorption core, the ratio of
the two emission peaks H2V and H2R, and intensity images at a fixed wavelength.
The average off-limb profiles show a smooth variation with increasing limb
distance. The line width increases up to a height of about 2 Mm above the limb.
The profile shape is fairly symmetric with nearly identical H2V and H2R
intensities; at a height of 5 Mm, it changes into a single Gaussian without
emission peaks. We find that all off-limb spectra show large Doppler shifts
that fluctuate on the smallest resolved spatial scales. The variation is more
prominent in cuts parallel to the solar limb than on those perpendicular to it.
As far as individual structures can be unequivocally identified at our spatial
resolution, we find a specific relation between intensity enhancements and
Doppler shifts: elongated brightenings are often flanked all along their
extension by velocities in opposite directions. The average off-limb spectra of
Ca II H present a good opportunity to test static chromospheric atmosphere
models because they lack the photospheric contribution that is present in
disk-center spectra. We suggest that the observed relation between intensity
enhancements and Doppler shifts could be caused by waves propagating along the
surfaces of flux tubes: an intrinsic twist of the flux tubes or a wave
propagation inclined to the tube axis would cause a helical shape of the
Doppler excursion, visible as opposite velocity at the sides of the flux tube.Comment: 11 pages, 11 figures + 3 pages Appendix, accepted by A&
Increased fluid flow activity in shallow sediments at the 3 km Long Hugin Fracture in the central North Sea
The North Sea hosts a wide variety of seafloor seeps that may be important for transfer of chemical species, such as methane, from the Earth's interior to its exterior. Here we provide geochemical and geophysical evidence for fluid flow within shallow sediments at the recently discovered, 3-km long Hugin Fracture in the Central North Sea. Although venting of gas bubbles was not observed, concentrations of dissolved methane were significantly elevated (up to six-times background values) in the water column at various locations above the fracture, and microbial mats that form in the presence of methane were observed at the seafloor. Seismic amplitude anomalies revealed a bright spot at a fault bend that may be the source of the water column methane. Sediment porewaters recovered in close proximity to the Hugin Fracture indicate the presence of fluids from two different shallow (<500m) sources: (i) a reduced fluid characterized by elevated methane concentrations and/or high levels of dissolved sulfide (up to 6 mmol L−1), and (ii) a low-chlorinity fluid (Cl ∼305 mmol L−1) that has low levels of dissolved methane and/or sulfide. The area of the seafloor affected by the presence of methane-enriched fluids is similar to the footprint of seepage from other morphological features in the North Sea
Effects on and transfer across the blood-brain barrier in vitro—Comparison of organic and inorganic mercury species
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