22,644 research outputs found
A coronal wave and an asymmetric eruptive filament in SUMER, CDS, EIT, and TRACE co-observations
The objectives of the present study is to provide a better physical
understanding of the complex inter-relation and evolution of several solar
coronal features comprising a double-peak flare, a coronal dimming caused by a
CME, a CME-driven compression, and a fast-mode wave. For the first time, the
evolution of an asymmetric eruptive filament is analysed in simultaneous SUMER
spectroscopic and TRACE and EIT imaging data. We use imaging observations from
EIT and TRACE in the 195A channel and spectroscopic observations from the CDS
in a rastering and SUMER in a sit-and-stare observing mode. The SUMER spectra
cover spectral lines with formation temperatures from logT(K) ~ 4.0 to 6.1.
Although the event was already analysed in two previous studies, our analysis
brings a wealth of new information on the dynamics and physical properties of
the observed phenomena. We found that the dynamic event is related to a complex
flare with two distinct impulsive peaks, one according to the GOES
classification as C1.1 and the second - C1.9. The first energy release triggers
a fast-mode wave and a CME with a clear CME driven compression ahead of it.
This activity is related to, or possibly caused, by an asymmetric filament
eruption. The filament is observed to rise with its leading edge moving at a
speed of ~300 km/s detected both in the SUMER and CDS data. The rest of the
filament body moves at only ~150 km/s while untwisting. No signature is found
of the fast-mode wave in the SUMER data, suggesting that the plasma disturbed
by the wave had temperatures above 600 000 K. The erupting filament material is
found to emit only in spectral lines at transition region temperatures. Earlier
identification of a coronal response detected in the Mg X 609.79 A line is
found to be caused by a blend from the O IV 609.83 A line.Comment: 10 pages, 8 figures, A&A, in pres
Can coronal hole spicules reach coronal temperatures?
We aim with the present study to provide observational evidences on whether
coronal hole spicules reach coronal temperatures. We combine multi-instrument
co-observations obtained with the SUMER/SoHO and with the EIS/SOT/XRT/Hinode.
The analysed three large spicules were found to be comprised of numerous thin
spicules which rise, rotate and descend simultaneously forming a bush-like
feature. Their rotation resembles the untwisting of a large flux rope. They
show velocities ranging from 50 to 250 km/s. We clearly associated the red- and
blue-shifted emissions in transition region lines with rotating but also with
rising and descending plasmas, respectively. Our main result is that these
spicules although very large and dynamic, show no presence in spectral lines
formed at temperatures above 300 000 K. The present paper brings out the
analysis of three Ca II H large spicules which are composed of numerous dynamic
thin spicules but appear as macrospicules in EUV lower resolution images. We
found no coronal counterpart of these and smaller spicules. We believe that the
identification of phenomena which have very different origins as macrospicules
is due to the interpretation of the transition region emission, and especially
the He II emission, wherein both chromospheric large spicules and coronal X-ray
jets are present. We suggest that the recent observation of spicules in the
coronal AIA/SDO 171 A and 211 A channels is probably due to the existence of
transition region emission there.Comment: 4 pages, 4 figures, accepted for publication in A&
Diagnostic reasoning techniques for selective monitoring
An architecture for using diagnostic reasoning techniques in selective monitoring is presented. Given the sensor readings and a model of the physical system, a number of assertions are generated and expressed as Boolean equations. The resulting system of Boolean equations is solved symbolically. Using a priori probabilities of component failure and Bayes' rule, revised probabilities of failure can be computed. These will indicate what components have failed or are the most likely to have failed. This approach is suitable for systems that are well understood and for which the correctness of the assertions can be guaranteed. Also, the system must be such that changes are slow enough to allow the computation
Coronal hole boundaries at small scales: IV. SOT view Magnetic field properties of small-scale transient brightenings in coronal holes
We study the magnetic properties of small-scale transients in coronal hole.
We found all brightening events are associated with bipolar regions and caused
by magnetic flux emergence followed by cancellation with the pre-existing and
newly emerging magnetic flux. In the coronal hole, 19 of 22 events have a
single stable polarity which does not change its position in time. In eleven
cases this is the dominant polarity. The dominant flux of the coronal hole form
the largest concentration of magnetic flux in terms of size while the opposite
polarity is distributed in small concentrations. In the coronal hole the number
of magnetic elements of the dominant polarity is four times higher than the
non-dominant one. The supergranulation configuration appears to preserve its
general shape during approximately nine hours of observations although the
large concentrations in the network did evolve and were slightly displaced, and
their strength either increased or decreased. The emission fluctuations seen in
the X-ray bright points are associated with reoccurring magnetic cancellation
in the footpoints. Unique observations of an X-ray jet reveal similar magnetic
behaviour in the footpoints, i.e. cancellation of the opposite polarity
magnetic flux. We found that the magnetic flux cancellation rate during the jet
is much higher than in bright points. Not all magnetic cancellations result in
an X-ray enhancement, suggesting that there is a threshold of the amount of
magnetic flux involved in a cancellation above which brightening would occur at
X-ray temperatures. Our study demonstrates that the magnetic flux in coronal
holes is continuously recycled through magnetic reconnection which is
responsible for the formation of numerous small-scale transient events. The
open magnetic flux forming the coronal-hole phenomenon is largely involved in
these transient features.Comment: 19 pages, 18 figures, A&A in pres
Calculating effective resistances on underlying networks of association schemes
Recently, in Refs. \cite{jsj} and \cite{res2}, calculation of effective
resistances on distance-regular networks was investigated, where in the first
paper, the calculation was based on stratification and Stieltjes function
associated with the network, whereas in the latter one a recursive formula for
effective resistances was given based on the Christoffel-Darboux identity. In
this paper, evaluation of effective resistances on more general networks which
are underlying networks of association schemes is considered, where by using
the algebraic combinatoric structures of association schemes such as
stratification and Bose-Mesner algebras, an explicit formula for effective
resistances on these networks is given in terms of the parameters of
corresponding association schemes. Moreover, we show that for particular
underlying networks of association schemes with diameter such that the
adjacency matrix possesses distinct eigenvalues, all of the other
adjacency matrices , can be written as polynomials of ,
i.e., , where is not necessarily of degree . Then, we use
this property for these particular networks and assume that all of the
conductances except for one of them, say , are zero to give a
procedure for evaluating effective resistances on these networks. The
preference of this procedure is that one can evaluate effective resistances by
using the structure of their Bose-Mesner algebra without any need to know the
spectrum of the adjacency matrices.Comment: 41 page
Data users note: Apollo 17 lunar photography
The availability of Apollo 17 pictorial data is announced as an aid to the selection of the photographs for study. Brief descriptions are presented of the Apollo 17 flight, and the photographic equipment used during the flight. The following descriptions are also included: service module photography, command module photography, and lunar surface photography
Small-scale flows in SUMER and TRACE high-cadence co-observations
We report on the physical properties of small-scale transient flows observed
simultaneously at high cadence with the SUMER spectrometer and the TRACE imager
in the plage area of an active region. Our major objective is to provide a
better understanding of the nature of transient phenomena in the solar
atmosphere by using high-cadence imager and spectrometer co-observations at
similar spatial and temporal resolution. A sequence of TRACE Fe IX/X 171 A and
high-resolution MDI images were analysed together with simultaneously obtained
SUMER observations in spectral lines covering a temperature range from 10 000 K
to 1 MK. We reveal the existence of numerous transient flows in small-scale
loops (up to 30 Mm) observed in the plage area of an active region. These flows
have temperatures from 10 000 K (the low temperature limit of our observations)
to 250 000 K. The coronal response of these features is uncertain due to a
blending of the observed coronal line Mg X 624.85 A. The duration of the events
ranges from 60 s to 19 min depending on the loop size. Some of the flows reach
supersonic velocities. The Doppler shifts often associated with explosive
events or bi-directional jets can actually be identified with flows (some of
them reaching supersonic velocities) in small-scale loops. Additionally, we
demonstrate how a line-of-sight effect can give misleading information on the
nature of the observed phenomena if only either an imager or a spectrometer is
used.Comment: 7 pages, 6 figures, accepted by A&
Jets or high velocity flows revealed in high-cadence spectrometer and imager co-observations?
We report on active region EUV dynamic events observed simultaneously at
high-cadence with SUMER/SoHO and TRACE. Although the features appear in the
TRACE Fe ix/x 171A images as jets seen in projection on the solar disk, the
SUMER spectral line profiles suggest that the plasma has been driven along a
curved large scale magnetic structure, a pre-existing loop. The SUMER
observations were carried out in spectral lines covering a large temperature
range from 10^4 K to 10^6 K. The spectral analysis revealed that a sudden
heating from an energy deposition is followed by a high velocity plasma flow.
The Doppler velocities were found to be in the range from 90 to 160 km/s. The
heating process has a duration which is below the SUMER exposure time of 25 s
while the lifetime of the events is from 5 to 15 min. The additional check on
soft X-ray Yohkoh images shows that the features most probably reach 3 MK
(X-ray) temperatures. The spectroscopic analysis showed no existence of cold
material during the events
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