32 research outputs found
Non-LTE hydrogen-line formation in moving prominences
The behavior of hydrogen-line brightness variations, depending on the prominence-velocity changes were investigated. By solving the NON-Local thermodynamic equilibrium (LTE) problem for hydrogen researchers determine quantitatively the effect of Doppler brightening and/or Doppler dimming (DBE, DDE) in the lines of Lyman and Balmer series. It is demonstrated that in low-density prominence plasmas, DBE in H alpha and H beta lines can reach a factor of three for velocities around 160 km/sec, while the L alpha line exhibits typical DDE. L beta brightness variations follow from a combined DBE in the H alpha and DDE in L alpha and L beta itself, providing that all relevant multilevel interlocking processes are taken into account
Estimation of solar prominence magnetic fields based on the reconstructed 3D trajectories of prominence knots
We present an estimation of the lower limits of local magnetic fields in
quiescent, activated, and active (surges) promineces, based on reconstructed
3-dimensional (3D) trajectories of individual prominence knots. The 3D
trajectories, velocities, tangential and centripetal accelerations of the knots
were reconstructed using observational data collected with a single
ground-based telescope equipped with a Multi-channel Subtractive Double Pass
imaging spectrograph. Lower limits of magnetic fields channeling observed
plasma flows were estimated under assumption of the equipartition principle.
Assuming approximate electron densities of the plasma n_e = 5*10^{11} cm^{-3}
in surges and n_e = 5*10^{10} cm^{-3} in quiescent/activated prominences, we
found that the magnetic fields channeling two observed surges range from 16 to
40 Gauss, while in quiescent and activated prominences they were less than 10
Gauss. Our results are consistent with previous detections of weak local
magnetic fields in the solar prominences.Comment: 14 pages, 12 figures, 1 tabl
Explosive events - swirling transition region jets
In this paper, we extend our earlier work to provide additional evidence for
an alternative scenario to explain the nature of so-called `explosive events'.
The bi-directed, fast Doppler motion of explosive events observed
spectroscopically in the transition region emission is classically interpreted
as a pair of bidirectional jets moving upward and downward from a reconnection
site. We discuss the problems of such a model. In our previous work, we focused
basically on the discrepancy of fast Doppler motion without detectable motion
in the image plane. We now suggest an alternative scenario for the explosive
events, based on our observations of spectral line tilts and bifurcated
structure in some events. Both features are indicative of rotational motion in
narrow structures. We explain the bifurcation as the result of rotation of
hollow cylindrical structures and demonstrate that such a sheath model can also
be applied to explain the nature of the puzzling `explosive events'. We find
that the spectral tilt, the lack of apparent motion, the bifurcation, and a
rapidly growing number of direct observations support an alternative scenario
of linear, spicular-sized jets with a strong spinning motion.Comment: 9 pages, 3 figures, accepted for publication in Solar Physic
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
Formation of a White-Light Jet within a Quadrupolar Magnetic Configuration
We analyze multi-wavelength and multi-viewpoint observations of a large-scale
event viewed on 7 April 2011 originating from an active region complex. The
activity leads to a white-light jet being formed in the outer corona. The
topology and evolution of the coronal structures were imaged in high resolution
using the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics
Observatory (SDO). In addition, large field-of-view images of the corona were
obtained using the Sun Watcher using Active Pixel System detector and Image
Processing (SWAP) telescope onboard the PRoject for Onboard Autonomy (PROBA2)
microsatellite, providing evidence for the connectivity of the coronal
structures with outer coronal features that were imaged with the Large Angle
Spectrometric Coronagraph (LASCO) C2 on Solar and Heliospheric Observatory
(SOHO). The data-sets reveal an Eiffel-tower type jet configuration extending
into a narrow jet in the outer corona. The event starts from the growth of a
dark area in the central part of the structure. The darkening was also observed
in projection on the disk by the Solar TErrestrial RElations Observatory-Ahead
(STEREO-A) spacecraft from a different point of view. We assume that the dark
volume in the corona descends from a coronal cavity of a flux rope that moved
up higher in the corona but still failed to erupt. The quadrupolar magnetic
configuration corresponds to a saddle-like shape of the dark volume and
provides a possibility for the plasma to escape along the open field lines into
the outer corona, forming the white-light jet.Comment: 15 pages, 10 figure
Observations of the Sun at Vacuum-Ultraviolet Wavelengths from Space. Part II: Results and Interpretations
Radio Emission Associated with Mass Ejection Events from Active Regions of the Sun - Event of 1992 August 5
Search for 1-10 Hz modulations in coronal emission with SECIS during the August 11, 1999 eclipse
Results of the search of the periodic changes of the 530.3 nm line
intensity emitted by selected structures of the solar corona in the frequency
range 1–10 Hz are presented. A set of 12 728 images of the section of
the solar corona extending from near the north pole to the south-west were
taken simultaneously in the 530.3 nm (“green”) line and white–light
with the Solar Eclipse Coronal Imaging System (SECIS) during the 143–seconds–long
totality of the 1999 August 11 solar eclipse observed in Shabla, Bulgaria. The time
resolution of the collected data is better than 0.05 s and the pixel size is
approximately 4 arcsec.
Using classical Fourier spectral analysis tools, we investigated temporal changes
of the local 530.3 nm coronal line brightness in the frequency range
1–10 Hz of thousands of points within the field of view. The various
photometric and instrumental effects have been extensively considered. We did not
find any indisputable, statistically significant evidence of periodicities in
any of the investigated points (at significance level )