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Author name code: staiger
ADS astronomy entries on 2022-09-14
author:"Staiger, Joachim"
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Title: Frequency Distribution of Acoustic Oscillation in the Solar
Atmosphere During Flare Event
Authors: Wiśniewska, A.; Chmielewska, E.; Radziszewski, K.; Roth,
M.; Staiger, J.
2019ApJ...886...32W Altcode: 2022arXiv220302420W
We present a study of multi-wavelength observations, of a C 2.3 solar
flare in Active Region NOAA 12353, observed on 2015 May 23, which
reveal new properties of acoustic waves in the flaring region. The
space-, and ground-based data measured by the HELioseismological
Large Regions Interferometric Device, operating at the Vacuum Tower
Telescope, the Atmospheric Imaging Assembly (AIA), and Helioseismic
and Magnetic Imager on board the Solar Dynamic Observatory, were used
in this paper. First, using power spectra of solar oscillations,
we identified the dominant frequencies and their location at seven
different atmospheric levels before and after the flare event. Second,
based on AIA observations taken in six Extreme Ultraviolet filters, we
derived Differential Emission Measure (DEM) profiles and DEM maps of the
flare. Finally, we confirm the sigma shape of the magnetic field in the
active area, directly related to the flare. Our results are as follows:
the high-frequency waves (ν > 5 mHz) in the photosphere, in both
cases, before and after the flare, are generated at the footpoints of
the chromospheric loop, while in the chromosphere (Hα line), before
the event the power enhancement exhibits the maximum of flare emission,
and after the eruption the enhancement by all frequencies is observed
only in the post-flare loop area. Moreover, the power of oscillation in
the pores surrounding the area before the flare has a random character,
while after the flare oscillation power is concentrated in the pore,
and weakened outside of. We conclude that accurate detection of
high-frequency acoustic waves in active regions can lead to faster
and easier prediction of high-energy events.
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Title: Observational Evidence for Variations of the Acoustic Cutoff
Frequency with Height in the Solar Atmosphere
Authors: Wiśniewska, A.; Musielak, Z. E.; Staiger, J.; Roth, M.
2016ApJ...819L..23W Altcode:
Direct evidence for the existence of an acoustic cutoff frequency in
the solar atmosphere is given by observations performed by using the
HELioseismological Large Regions Interferometric DEvice operating on the
Vacuum Tower Telescope located on Tenerife. The observational results
demonstrate variations of the cutoff with atmospheric heights. The
observed variations of the cutoff are compared to theoretical
predictions made by using five acoustic cutoff frequencies that
have been commonly used in helioseismology and asteroseismology. The
comparison shows that none of the theoretical predictions is fully
consistent with the observational data. The implication of this finding
is far reaching as it urgently requires either major revisions of the
existing methods of finding acoustic cutoff frequencies or developing
new methods that would much better account for the physical picture
underlying the concept of cutoff frequencies in inhomogeneous media.
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Title: Multi-height spectroscopy for probing the solar atmosphere
Authors: Wiśniewska, A.; Roth, M.; Staiger, J.
2015CEAB...39..101W Altcode:
We present preliminary results from multi-height observations,
taken with the HELLRIDE (HELioseismic Large Region Interferometric
DEvice) instrument at the VTT (Vacuum Tower Telescope) in Izaña,
Tenerife. The goal of this work is to study solar oscillations at
different atmospheric heights. The data was obtained in May 2014 for
10 different wavelengths with high spatial, spectral and temporal
resolution. In this paper we discuss the results from quiet sun
measurements. The region was selected in such a way to be near to the
disk center. Using spectral and cross-spectral analysis methods we
derive phase differences of waves propagating between the atmospheric
layers. The formation heights of the photospheric spectral lines were
calculated by τ^c_{5000} = 1 in agreement with an LTE approximation
and chromospheric lines with an NLTE method, respectively. We find
that the acoustic cut-off frequency is a function of height in the
solar atmosphere.
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Title: Using SDO and GONG as Calibration References for a New
Telescope Pointing Algorithm
Authors: Staiger, J.
2013ASPC..478..109S Altcode:
Long duration observations are a basic requirement for most types
of helioseismic measurements. Pointing stability and the quality of
guiding is thus an important issue with respect to the spatio-temporal
analysis of any velocity datasets. Existing pointing tools and
correlation-tracking devices will help to remove most of the spatial
deviations building up during an observation with time. Yet most ground-
and space-based high-resolution solar telescopes may be subject to
slow image-plane drift that cannot be compensated for by guiding and
which may accumulate to displacements of 10″ or more during a 10-hour
recording. We have developed a new pointing model for solar telescopes
that may overcome these inherent guiding-limitations. We have tested
the model at the Vacuum Tower Telescope (VTT), Tenerife. We are using
SDO and GONG full-disk imaging as a calibration reference. We describe
the algorithms developed and used during the tests. We present our first
results. We describe possible future applications as to be implemented
at the VTT. So far, improvements over classical limb-guider systems
by a factor of 10 or more seem possible.
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Title: On the co-alignment of solar telescopes. A new approach to
solar pointing
Authors: Staiger, J.
2013JPhCS.440a2004S Altcode:
Helioseismological measurements require long observing times and
thus may be adversely affected by lateral image drifts as caused
by pointing instabilities. At the Vacuum Tower Telescope VTT,
Tenerife we have recorded drift values of up to 5" per hour under
unstable thermal conditions (dome opening, strong day-to-day thermal
gradients). Typically drifts of 0.5" - 1.0" per hour may be encountered
under more favorable conditions. <P />Past experience has shown that
most high-resolution solar telescopes may be affected by this problem
to some degree. This inherent shortcoming of solar pointing is caused
by the fact that the guiding loop can be closed only within the guiding
beam but not within the telescope's main beam. <P />We have developed
a new approach to this problem. We correlate continuum brightness
patterns observed from within the telescope main beam with patterns
originating from a full disk telescope. We show that brightness patterns
of sufficient size are unique with respect to solar location at any
instant of time and may serve as a location identifier. We make use
of the fact that averaged location information of solar structures is
invariant with respect to telescope resolution. We have carried out
tests at the VTT together with SDO. We have used SDO as a full disk
reference. We were able to reduce lateral image drifts by an order
of magnitude.
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Title: HELLRIDE: A New Multiline Spectrometer for the Vacuum Tower
Telescope, Tenerife
Authors: Staiger, J.
2012ASPC..463..445S Altcode:
HELLRIDE stands for HELioseismological Large Regions Interferometric
DEvice. It is a new Fabry-Pérot based spectrometer specifically
designed to record the Doppler shifts of a large number of solar
spectral lines in a quasi-simultaneous and multitarget mode. It will
be used primarily at the VTT to carry out helioseismic investigations
of the solar atmosphere and to analyze footpoint flows of coronal
loops. Solar flares may be a further target in a future upgraded mode.
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Title: High precision pointing with a multiline spectrometer at
the VTT
Authors: Staiger, J.
2012AN....333.1092S Altcode:
We are investigating the pointing quality of the VTT, Tenerife
under the aspect of suitability for long-term heliosesimological
observations. Tests have shown that thermal and mechanical loads within
the telescope may create spurious image drifts with shift rates of
up to 5 arcsec per hour. During daylong recordings this will reduce
significantly the effective size of the field-of-view and may infer
artificial lateral movements into the data. The underlying problem
that not all image position offsets developing during a measurement may
be compensated for is common to most high-resolution solar telescopes
independently of the type of pointing system used. We are developing
new approaches to address this problem which are to be tested in the
near future at the VTT. The simulations established so far show that
the problem may be reduced by more than 90 %.
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Title: HELLRIDE: a new interferometric multiline instrument for the
analysis of the solar atmosphere
Authors: Staiger, J.
2012SPIE.8446E..75S Altcode:
We are developing a new etalon-based spectrometer 'HELLRIDE' for
the Vacuum Tower Telescope (VTT), Tenerife. It will offer improved
performance over existing devices in a number of operational
aspects. Primary development goal has been increasing the number
of spectral lines for the simultaneous recording of solar Doppler
shifts. Observations may cover a large field-of-view at high spatial
and temporal resolution. New electromagnetic drive technologies are to
be implemented. A focus will be set to achieve thermal stability with
respect to spectroscopic drifts and pointing precision. All aspects of
device operation are to be covered by a numerical model allowing for
offline testing and offline observations simulation. Remote operation
options will be available for dedicated observational programs. The
new instrument is foreseen to be used for the analysis of energy
transfers within the solar atmosphere. The helioseismological and
kinetic aspects of chromospheric and coronal heating are here of special
interest. To allow for synchronized observations of photospheric and
coronal phenomena new procedures are under development to improve
co-alignment of ground-based and space-based telescopes. HELLRIDE
stands for HELioseismological Large Regions Interferometric DEvice.
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Title: HTTP-based remote operational options for the Vacuum Tower
Telescope, Tenerife
Authors: Staiger, J.
2012SPIE.8448E..28S Altcode:
We are currently developing network based tools for the Vacuum Tower
Telescope (VTT), Tenerife which will allow to operate the telescope
together with the newly developed 2D-spectrometer HELLRIDE under remote
control conditions. The computational configuration can be viewed as a
distributed system linking hardware components of various functionality
from different locations. We have developed a communication protocol
which is basically an extension of the HTTP standard. It will serve as
a carrier for command- and data-transfers. The server-client software
is based on Berkley-Unix sockets in a C++ programming environment. A
customized CMS will allow to create browser accessible information
on-the-fly. Java-based applet pages have been tested as optional
user access GUI's. An access tool has been implemented to download
near-realtime, web-based target information from NASA/SDO. Latency
tests have been carried out at the VTT and the Swedish STT at La Palma
for concept verification. Short response times indicate that under
favorable network conditions remote interactive telescope handling
may be possible. The scientific focus of possible future remote
operations will be set on the helioseismology of the solar atmosphere,
the monitoring of flares and the footpoint analysis of coronal loops
and chromospheric events.
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Title: A multiline spectrometer for the analysis of solar atmospheric
oscillations and flows at the VTT, Tenerife
Authors: Staiger, J.
2011A&A...535A..83S Altcode:
Context. Despite longstanding observational efforts, the origins of
the chromospheric temperature rise and the coronal heating are still
not well understood. There is reason to believe that the limitations
of existing observational devices might be contributing to this lack of
experimental evidence. <BR /> Aims: We intended to develop a multiline
spectrometer capable of observing velocity fields simultaneously at more
height levels of the solar atmosphere than previously possible. System
design and handling would be optimized for the 3D-analysis of
atmospheric waves and flows. <BR /> Methods: The number of optical
components was kept to a minimum in order to achieve high optical
throughput and short scanning times. A new type of bandpass preselection
unit was developed. We successfully tested this Fabry-Perot based
multiline device at the Vacuum Tower Telescope (VTT). <BR /> Results:
During a proof-of-concept run we were able to observe 16 spectral lines
at a cadence of 60 s sustained over several hours. The field of view was
100-by-100 arcsecs. Multiple diagnostic diagrams from closely spaced
height levels were derived. <BR /> Conclusions: A new instrument of
this type will be installed permantently at the VTT. We expect to be
able to collect new 3D-information about atmospheric waves and flows.
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Title: A Ground Based Multiline Spectrometer for the Analysis of
Solar Atmospheric Waves
Authors: Staiger, J.
2011JPhCS.271a2023S Altcode:
The presence of magnetic fields may influence the propagation
characteristics of acoustic waves in the solar atmosphere. Investigating
amplitude and phase properties may thus help to reveal the 3D geometry
of magnetic fields above sunspots and activity regions. The height
resolution of this type of measurements was limited in the past by
the limitations of existing spectrometers. <P />We have developed
a double-etalon based spectrometer allowing us to observe solar
velocities with an unprecedented number of spectral lines. A test
version of this instrument has been installed at the Vacuum Tower
Telescope of the Kiepenheuer-Institut at Tenerife in July 2009 for
the first time. 16 spectral lines were observed at a cadence of 60
secs over a period of 4 hours. The field of view was 100"x100". <P
/>The multiple diagnostic diagrams resulting from these observations
clearly reveal the simultaneous p-mode ridge structure at every height
level from the deep photosphere (538.0 nm C I) to the chromosphere
(656.3 nm H-alpha). We are confident that individual acoustic modes
may be vertically traced through the atmosphere at yet unsurpassed
height resolution in the future.
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Title: Local Helioseismology with GFPI at the Vacuum Tower Telescope,
Tenerife
Authors: Staiger, J.; Roth, M.; Wöhl, H.; Schleicher, H.; Puschmann,
K.
2008ESPM...12..2.3S Altcode:
Local Helioseimology has recently become an important tool to
investigate the Solar Interior in the vicinity of localized
phenomena like sunspots. It possibly holds the promise to give
informations about subsurface magnetic fields and material flows. We
are currently modifying the GFPI Instrument at the VTT which will
also be a First Light Instrument at GREGOR Telescope to the needs of
ground-based helioseismologic observations (GFPI: Göttingen Fabry
Perot Interferomer). <P />The upgrade consists of a CCD-camera with a
larger Field-of-View (100"-by-100"), a modified Interfacing Hardware and
dedicated Control- and Recording-Software. Direct Interfacing to the
VTT's telescope control system allows for mosaic type patching of the
observations field. Cadence times of below 1 Minute for a 300"-by-300"
field at the telescope's resolution limit of 0.2" are possible. Data
are stored to USB-based external harddisks. An of-the-shelf beamer
allows for optical adjustments with an artificial light source. <P
/>Available Preprocessing Tools allow to immediately visualize the
quality of the observational data. This includes a prelimary Ringdiagram
Analysis. Future Online Preprocessing Capabilities are to further
reduce the achievable cycle times. <P />We will present some details
of the instrumental setup and some prelimiary observational results.
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Title: Plio-Pleistocene history of Ferrar Glacier, Antarctica:
Implications for climate and ice sheet stability
Authors: Staiger, J. W.; Marchant, D. R.; Schaefer, J. M.; Oberholzer,
P.; Johnson, J. V.; Lewis, A. R.; Swanger, K. M.
2006E&PSL.243..489S Altcode:
The areal distribution and elevation of glacial drifts in Vernier
Valley, southern Victoria Land, are used to reconstruct the
Plio-Pleistocene history of upper Ferrar Glacier. <SUP>21</SUP>Ne
cosmogenic-nuclide analyses of surface cobbles on four moraines, Ferrar
1, 2, 3, and 4, provide age control. A minimum-age estimate for Ferrar
Drifts calculated by assuming zero surface erosion indicates that
the oldest moraine, Ferrar 4, was deposited at least ∼ 3400 ka. Our
preferred age model, which applies a very conservative erosion rate
of 5 cm Ma <SUP>- 1 </SUP> in age calculations, suggests that Ferrar
4 is ∼ 4000 ka; Ferrar 3 is ∼ 1200 ka; and Ferrar 2 is ∼ 700
ka. Based on glacial geologic data, Ferrar 1 is modern; cosmogenic ages
for cobbles on this moraine suggest a value for nuclide inheritance
of ∼ 50 ka. The Ferrar drifts are most easily interpreted in terms
of a progressive reduction in the ice-surface elevation of upper
Ferrar Glacier during Plio-Pleistocene time. Relative to today, the
surface of upper Ferrar Glacier was ∼ 100 to 125 m higher during
the Pliocene Climatic Optimum and ∼ 50 m higher during early to mid
Quaternary time. Conversely, during MIS 2, the ice-surface elevation
of upper Ferrar Glacier was likely no larger than today and may have
stood below modern levels. The texture and sedimentology of all Ferrar
drifts indicate that during ice recession from Vernier Valley the upper
Ferrar Glacier lacked surface-melting ablation zones, even during the
Pliocene Climatic Optimum. Results from a simple 2-D glaciological
flow-band model demonstrate that upper Ferrar Glacier also lacked
basal-melting zones during ice recession. We show that the development
of weathering pits and desert varnish on cobbles exposed at the surface
of Ferrar drifts varies in accord with cosmogenic age. The mean width
and depth of the largest surface pits on boulders from Ferrar drifts
increases by ∼ 10 mm Ma <SUP>- 1 </SUP> and ∼ 6.7 mm Ma <SUP>-
1 </SUP>, respectively; the maximum thickness of desert varnish on
surface boulders increases by ∼ 1.5 mm Ma <SUP>- 1 </SUP>. These
rates may be used to help calculate ages for dolerite-rich drifts
elsewhere in the western Dry Valleys region. The general stability of
the ice-surface elevation of upper Ferrar Glacier, and of the landscape
in Vernier Valley, suggests minimal climatic amelioration in the upland
region of the Dry Valleys during the last ∼ 4 Ma.
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Title: Magnetic changes observed in the formation of two filaments
in a complex active region: TRACE and MSDP observations
Authors: Schmieder, Brigitte; Mein, Nicole; Deng, Yuanyong; Dumitrache,
Cristiana; Malherbe, Jean-Marie; Staiger, Joachim; Deluca, E. E.
2004SoPh..223..119S Altcode:
This paper is focused on the formation of two filaments in a complex
center of decaying active regions (AR 8329 and AR 8326), located in
the northern hemisphere. The observations were obtained in Hα by
the Multi-channel Subtractive Double Pass spectrograph (MSDP mounted
on the German telescope VTT in Tenerife) and EUV lines with TRACE
(Transition Region And Corona Explorer). High Doppler shifts are found
to be related to the ends of filament segments where canceling magnetic
fields are also located (as seen on magnetograms from Big Bear Solar
Observatory). At these locations, velocities along the line of sight,
derived by using a cloud model method reach −20 km s<SUP>−1</SUP>,
the segments of filaments merge and frequently a time-related sub-flare
is observed by TRACE. The chirality of the filament segments has been
determined by different methods: the segments of dextral chirality
join together and form a long dextral filament, and a single filament
of sinistral chirality forms end to end with the dextral filament
but does not merge with it. Assuming a model of twisted flux tube for
filament material, we suggest that the dextral filament has negative
helicity and a relationship between its formation and the close by
sunspot with the same sign of helicity.
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Title: Multi-Wavelength Observations of an M1.0 Flare on 22 October
2002
Authors: Berlicki, A.; Schmieder, B.; Vilmer, N.; Mein, P.; Mein,
N.; Heinzel, P.; Staiger, J.; Deluca, E. E.
2004IAUS..219..669B Altcode:
No abstract at ADS
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Title: A Study of Hydrogen Density in Emerging Flux Loops from
a Coordinated Transition Region and Coronal Explorer and Canary
Islands Observation Campaign
Authors: Mein, N.; Schmieder, B.; DeLuca, E. E.; Heinzel, P.; Mein,
P.; Malherbe, J. M.; Staiger, J.
2001ApJ...556..438M Altcode:
During an international ground-based campaign in the Canary Islands
coordinated with space instruments (i.e., Transition Region and Coronal
Explorer [TRACE]), we observed an active region on 1998 September
10 with high spatial and temporal resolution. New emerging flux in
the central part of the active region was observed in magnetograms
of the Swedish Vacuum Solar Telescope, La Palma. Emerging loops
(arch-filament systems [AFSs]) are well developed in Hα and Ca II
according to the observations made at the Vacuum Tower Telescope (VTT)
and THEMIS telescope in Tenerife with the Multichannel Subtractive
Double Pass (MSDP) spectrographs. The TRACE images obtained at 171
and 195 Å show low-emission regions that are easily identified as
the individual AFS. They are due to absorption by hydrogen and helium
continua in the cool filament plasma. We compare two techniques of
measuring the hydrogen density in the cool dense fibrils of AFSs. The
first method based on TRACE observations derived the neutral hydrogen
column density of the plasma absorbing coronal lines. The second one
using Hα line profiles provided by the MSDP spectrographs is based on
the cloud model. The results are consistent. We derive also electron
density values using Hα lines that are in good agreement with those
derived from the 8542 Å Ca II line observed with THEMIS (Mein et
al.). The three types of observations (TRACE, VTT, THEMIS) are well
complementary: absorption of coronal lines giving a good approximation
for the maximum value of the neutral hydrogen column density, the Hα
line giving a good determination of n<SUB>e</SUB>, and the 8542 Å Ca
II line a good determination of the electronic temperature.
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Title: Dynamics of the solar granulation - On the Time Variation of
the Granular Flow
Authors: Nesis, A.; Hammer, R.; Roth, M.; Schleicher, H.; Soltau,
D.; Staiger, J.
2001SoPh..200...11N Altcode:
The emergence and evolution of large granules shows thegranular dynamics
particularly well. We therefore investigate the time dependence of
the convective flows within a regular and an exploding granule. The
observational material for this study was taken at the center of the
solar disk with the German VTT in Izaña (Tenerife, Spain) during
an observing campaign in the year 1994. It consists of series of
spectrograms of high spatial resolution, which were digitized and
processed with wavelet techniques. Among other features, our data show
the dynamical portrait of a regular and an exploding granule. We can
follow their temporal evolution over more than 12 min. Using absorption
lines of different strength we are able to see the dynamical change
of both granules at several heights within the first 200 km above
τ<SUB>5000</SUB>=1. The observations reveal significant changes of
the convective flow of both granules over time as well as over height,
which are discussed in detail.
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Title: A Study of Hydrogen Density in Emerging Flux Loops from a
Coordinated TRACE and Canary Islands Observation Campaign
Authors: Schmieder, B.; Deluca, E.; Mein, N.; Mein, P.; Malherbe,
J. M.; Wilken, V.; Staiger, J.; Engvold, O.; Hanssen, I.
1999ESASP.448..653S Altcode: 1999mfsp.conf..653S; 1999ESPM....9..653S
No abstract at ADS
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Title: Dynamics of the solar granulation. VI. Time variation of the
granular shear flow
Authors: Nesis, A.; Hammer, R.; Kiefer, M.; Schleicher, H.; Sigwarth,
M.; Staiger, J.
1999A&A...345..265N Altcode:
Excellent spectrograms can yield observational insight in the dynamics
of the solar surface not yet accessible to numerical simulations. We
present results of the elaboration of a series of spectrograms taken at
the center of the solar disk. Each of the spectrograms includes more
than 250 granules, while the series covers a time of 12 min. Our main
emphasis is to study the dynamics of the visible solar layers not only
as a function of height but also as a function of time. We investigated
the temporal and spatial behavior of the turbulent concentration at the
granular borders and its spreading-out into the intergranular space. In
the deep photosphere, enhanced turbulence is concentrated predominantly
near granular borders, while at higher layers the turbulence spreads
out over the entire intergranular space. Remarkable is the decay of the
turbulence with the height in the photosphere. There was no significant
variation of the turbulence over the 12 min. We also determined the rms
turbulent pressure at the granulation layers near tau_ {5000}=1. The
average ratio of turbulent to gas pressure is of the order of 0.1;
values of this size are also discussed in recent theoretical works. In
order to take the intermittency into account, we traced the peak to
peak variations of the turbulent velocity, which turn out to be ~
4 km sec(-1) . The corresponding ratio of turbulent to gas pressure
may thus reach locally significant values up to about 0.3. We did not
find either a correlation or an anticorrelation between turbulence
and convective flow, although the turbulence is presumably generated
by granular shear flow. We suggest that the intermittent turbulence
in the visible layers and the convective flow constitutes a dynamical
system. This turbulence-granulation-dynamical system exhibits a cyclic
behavior corresponding to the dynamical time of the granules, i.e. the
growth and decay of their velocity profile. The power spectra of the
turbulent and granular velocity show a two-component character, which
presumably reflects the action of two different processes determining
the dynamics of the solar convective boundary layers and above.
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Title: ACE Spacecraft
Authors: Chiu, M. C.; von-Mehlem, U. I.; Willey, C. E.; Betenbaugh,
T. M.; Maynard, J. J.; Krein, J. A.; Conde, R. F.; Gray, W. T.; Hunt,
J. W., Jr.; Mosher, L. E.; McCullough, M. G.; Panneton, P. E.; Staiger,
J. P.; Rodberg, E. H.
1998SSRv...86..257C Altcode:
The Johns Hopkins University Applied Physics Laboratory (JHU/APL)
was responsible for the design and fabrication of the ACE spacecraft
to accommodate the ACE Mission requirements and for the integration,
test, and launch support for the entire ACE Observatory. The primary
ACE Mission includes a significant number of science instruments -
nine - whose diverse requirements had to be factored into the overall
spacecraft bus design. Secondary missions for monitoring space weather
and measuring launch vibration environments were also accommodated
within the spacecraft design. Substantial coordination and cooperation
were required between the spacecraft and instrument engineers, and
all requirements were met. Overall, the spacecraft was kept as simple
as possible in meeting requirements to achieve a highly reliable and
low-cost design.
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Title: Evolution of the Magnetic Field and Chromospheric Fine
Structure in a Filament Channel
Authors: van Driel-Gesztelyi, L.; Mein, P.; Mein, N.; Schmieder,
B.; Malherbe, J. -M.; Aulanier, G.; Démoulin, P.; Deforest, C.;
Staiger, J.
1998ASPC..155..321V Altcode: 1998sasp.conf..321V
No abstract at ADS
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Title: Velocity Fields of a Filament Region Observed with Ground-Based
Telescopes and from SOHO
Authors: Mein, P.; Schmieder, B.; Malherbe, J. -M.; Wiik, J. E.;
Engvold, O.; Brekke, P.; Zirker, J. B.; Poland, A. I.; Delaboudiniere,
J. -P.; Staiger, J.
1998ASPC..150..135M Altcode: 1998npsp.conf..135M; 1998IAUCo.167..135M
No abstract at ADS
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Title: Dynamics of the solar granulation. IV. Granular shear flow.
Authors: Nesis, A.; Hammer, R.; Hanslmeier, A.; Schleicher, H.;
Sigwarth, M.; Staiger, J.
1997A&A...326..851N Altcode:
Strong velocity gradients at granular borders appear to be the source
of unresolved velocity fluctuations detectable as line broadening
variations of magnetically and thermally insensitive absorption
lines. Based on spectrograms of high spatial and spectral resolution
taken with the German Vacuum Tower Telescope(VTT) in Izana (Tenerife) we
study the strong velocity gradients and the unresolved velocity field as
well as their mutual interaction. We also investigate the variation of
these quantities with the height in the photosphere, for both a regular
and an exploding granule. By means of a coherence analysis we study,
furthermore, the extension of the convective and turbulent fluctuation
field of the granulation layers into the overlying overshoot layers as
a function of the wavenumber. The results of the coherence analysis
are consistent with, and complementary to, those obtained from the
investigation of regular and exploding granules. The small and large
scales of the convective and unresolved velocity field behave clearly
different as far as their penetration into the overlying photospheric
layers is concerned. One pressure scale height above the continuum we
find an unresolved velocity field that does not show any resemblance
to the same velocity field at the continuum level. We find that the
symmetry behavior of the unresolved velocity field with respect to
the granular flow varies with the height in the photosphere. The
unresolved velocity field could be of oscillatory, convective, or
turbulent character. However, the fact that the unresolved velocity
field is more prominent at the granular border, which is also the
location of strong shear flow, favors its turbulent character. In
this sense the granules can be seen as quasi-laminar convective flows
emerging in the turbulent field of the overshoot layers.
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Title: Flare Multi-Line 2D-SPECTROSCOPY
Authors: Mein, P.; Mein, N.; Malherbe, J. -M.; Heinzel, P.; Kneer,
F.; von Uexkull, M.; Staiger, J.
1997SoPh..172..161M Altcode: 1997ESPM....8..161M
A small flare was observed at the Teide Observatory on October 5,
1994. Simultaneous data were obtained at the German Vacuum Tower
Telescope (VTT) with the MSDP spectrograph providing high-resolution
imaging spectroscopy in two chromospheric lines, and the Gregory Coudé
Telescope (GCT) providing information about the magnetic field. Basic
flare characteristics are:
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Title: Dynamics of the solar granulation. V. The intergranular space.
Authors: Nesis, A.; Hammer, R.; Hanslmeier, A.; Schleicher, H.;
Sigwarth, M.; Staiger, J.
1996A&A...310..973N Altcode:
This investigation is based on a spectrogram of extraordinary spatial
resolution selected from a series of 80 spectrograms taken with the
vacuum tower telescope at Izana (Tenerife) in May 1994. The wavelength
range was λλ: 491.00-491.40nm and includes both magnetically sensitive
and insensitive spectral lines. The spectrograph slit intersected parts
of the border and interior of CaII network cells, thus permitting a
comparative study of the granular dynamics at varying, but moderate,
levels of magnetic activity. As diagnostic tools we use the Doppler
shift variation of line cores, which is associated with spatially
resolved velocity structures, and the line broadening variation,
which is a signature of unresolved velocity fluctuations. We discuss
in particular the granular dynamics and the intermittency of the
line broadening within the intergranular space as functions of height
and position relative to network cells. Our results suggest that the
magnetic field in the network is not only located preferentially in
the intergranular space, but furthermore coincides with regions of
enhanced line broadening. We confirm that the Doppler shift variation
is reduced in regions of enhanced magnetic field, but we find that this
reduction affects the entire range of granular scales. The slopes of
the velocity power spectra are independent of the magnetic activity
level. This result is surprising, since on the basis of classical MHD
turbulence theory one would have expected shallower power spectra in
magnetically active regions. The line broadening variation is much
less sensitive to the magnetic field than the line shift variation.
---------------------------------------------------------
Title: Cloud model with variable source function for solar Hα
structures.
Authors: Mein, N.; Mein, P.; Heinzel, P.; Vial, J. -C.; Malherbe,
J. M.; Staiger, J.
1996A&A...309..275M Altcode:
The "cloud model" used to derive the physical parameters of solar
chromospheric features is extended to the cases of non-constant
source function and of velocity gradients. This model assumes a given
relationship between the source function and the opacity of the cloud
which is derived from non-LTE modelling. An algorithm using 4 points
of the H<SUB>alpha</SUB>_ profile is proposed to derive the optical
thickness, the line-of-sight velocity and the dopplerwidth. The
results are compared with a 5-points inversion which does not use the
given relationship between source function and opacity. Effects of the
uncertainty about the radiation coming from the underlying chromosphere,
as well as effects of data noise, are discussed. The inversion method
is illustrated by some examples of observed profiles obtained with
the MSDP spectrograph of the VTT telescope (Teide Observatory).
---------------------------------------------------------
Title: X-Ray Bright Point Flares Due to Magnetic Reconnection
Authors: Van Driel-Gesztelyi, L.; Schmieder, B.; Cauzzi, G.; Mein,
N.; Hofmann, A.; Nitta, N.; Kurokawa, H.; Mein, P.; Staiger, J.
1996SoPh..163..145V Altcode:
Ground-based optical observations coordinated with Yohkoh/SXT X-ray
observations of an old, disintegrating bipolar active region AR NOAA
7493 (May 1, 1993) provided a multiwavelength data base to study
a flaring `active region' X-ray bright point (XBP) of about 16 hr
lifetime, and the activity related to it in different layers of the
solar atmosphere. The XBP appeared to be related to a new minor bipole
of about 10<SUP>20</SUP> Mx. Superposed on a global evolution of soft
X-ray brightness, the XBP displayed changes of brightness, lasting for
1-10 min. During the brightenings the XBP apparently had a spatial
structure, which was (tiny) loop-like rather than point-like. The
X-ray brightenings were correlated with chromospheric activity: (i)
brightenings of underlying chromospheric faculae, and (ii) appearance
of strong turbulent velocities in the arch filament system. We propose
that the XBP brightenings were due to reconnection of the magnetic
field lines (sketched in 3D) between the new bipole and a pre-existing
plage field induced by the motion of one of the new pores (v = 0.2
km s<SUP>−1</SUP>) towards the plage, and that the XBP itself was
a reconnected hot loop between them.
---------------------------------------------------------
Title: High resolution flare observations with multi-line imaging
spectroscopy.
Authors: Mein, P.; Heinzel, P.; Malherbe, J. -M.; Staiger, J.
1996joso.proc...68M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Dynamics of the solar granulation. III. Fractional diffusion.
Authors: Nesis, A.; Hammer, R.; Hanslmeier, A.; Staiger, J.; Westendorp
Plaza, C.; Grabowski, U.
1995A&A...296..210N Altcode:
In most papers dealing with random motions and diffusion of small
magnetic elements in the photosphere, the convective flows and
in particular the granulation are considered as drivers of these
motions. The results of these works have been discussed in terms
of the fractal dimension of the granulation as seen in intensity
pictures. So far neither a fractal dimension associated with the
granular velocity field nor the nature of the random walks in the
granular intergranular space have been determined. Using spectrograms
of high spatial resolution taken with the VTT at Izana (Tenerife,
Spain) we investigated the granular velocity field in terms of its
fractal nature and its diffusion properties. We applied the rescaled
range analysis to both the velocity and intensity fields, thus enabling
us to calculate a fractal dimension as well as a "diffusion" exponent
which together characterize the diffusion properties of the granulation
layers. We found a fractal dimension of the granular velocity of the
same order as the fractal dimensions of the distribution of the magnetic
elements in the photosphere, and the fractal dimension corresponding
to the diffusion of the magnetic elements in a fractal geometry. The
diffusion processes in the granulation layers show a subdiffusive
nature characteristic of anomalous diffusion rather than the classical
Fickian diffusion. Anomalous diffusion is often found in stochastic
transport in spatially heterogeneous media. The velocity field of the
granulation can be thought of as a heterogeneous turbulent medium:
the granules show less turbulence than the intergranular space.
---------------------------------------------------------
Title: Dynamics of the solar granulation.
Authors: Nesis, A.; Hanslmeier, A.; Hammer, R.; Komm, R.; Mattig,
W.; Staiger, J.
1993A&A...279..599N Altcode:
This investigation is based on a series of spectrograms of extraordinary
spatial resolution taken with the vacuum tower telescope (VTT) at Izana
(Tenerife) in 1990. The quantitative analysis of these spectrograms
reveals an asymmetrical character of the granular flow (non-Benard like
convection). We suggest that a typical granule consists of a region
of high intensity and low turbulence in its interior and a region of
high turbulence and moderate intensity at its border. In other words,
we surmise that reigons of enhanced turbulence outline the borders
of granules. By means of power and coherence analyses we found two
different scaling laws for the small scale range: both the velocity
and intensity power as well as various cross-correlation functions
change their behavior near log k approximately = 0.8.
---------------------------------------------------------
Title: Rapid Variations in the Intergranular Space
Authors: Nesis, A.; Hanslmeier, A.; Hammer, R.; Komm, R.; Mattig,
W.; Staiger, J.
1993ASPC...46..222N Altcode: 1993mvfs.conf..222N; 1993IAUCo.141..222N
No abstract at ADS
---------------------------------------------------------
Title: What are the Boundaries of Solar Granules?
Authors: Nesis, A.; Hanslmeier, A.; Hammer, R.; Komm, R.; Mattig,
W.; Staiger, J.
1992AAS...180.5109N Altcode: 1992BAAS...24..814N
This investigation is based on a series of spectrograms of extraordinary
spatial resolution taken with the vacuum tower telescope(VTT) at Iza\
na (Tenerife) in 1990. The quantitative analysis of these spectrograms
revealed an asymmetrical character of the granular flow (non-Benard
like convection). The intensity maximum and the maximum of the upward
line-of-sight velocity do not coincide. In most cases the maximum of
the velocity lies near the border of the granule and falls rapidly to
the adjacent intergranular lane(from 1.5 to 0.2kmsec(-1) over 200km),
but moderately towards the other intergranular lane. In some granules
the position with zero velocity coincides with the position of highest
intensity, whereas maxima of velocities with different signs lie at
their border, thus reflecting a typical velocity profile of a rotating
eddy. The low correlation(of less than 0.5) between intensity and
Doppler velocity fluctuations along the spectrograph slit reflects
the asymmetric character of the solar granular flow. Concerning
the border of granules we find that bright regions often exhibit
downward, instead of the expected upward velocity. Moreover, by
investigating the broadening of a non-magnetically sensitive line,
we were able to localize regions with enhanced turbulence within the
intergranular space. We find that these regions do not always cover
the whole intergranular lane, but are concentrated at the border of
the granules, especially where the steep decrease of the velocity
takes place. On the basis of these findings we suggest that a typical
granule consists of a region of high intensity and low turbulence in
its interior and a region of high turbulence and moderate intensity
at its border. In other words, we surmise that regions of enhanced
turbulence outline the borders of granules. Using our time series
of spectrograms, which were taken every 15sec over a total of 5min,
we followed the dynamics of these properties and the evolution of the
steep intensity and velocity changes along the slit. These changes
are connected with shear instabilities and turbulence production. The
findings from non-active regions will be compared with those from
active regions based on magnetically sensitive lines.
---------------------------------------------------------
Title: Solar Granulation Spectroscopy: Dynamics of the Intergranular
Space
Authors: Nesis, A.; Hanslmeier, A.; Hammer, R.; Mattig, R. Komm W.;
Staiger, J.
1992ASPC...26..181N Altcode: 1992csss....7..181N
No abstract at ADS
---------------------------------------------------------
Title: Dynamics of the solar granulation. I - A phenomenological
approach
Authors: Nesis, A.; Hanslmeier, A.; Hammer, R.; Komm, R.; Mattig,
W.; Staiger, J.
1992A&A...253..561N Altcode:
High-spatial-resolution spectrograms taken with the vacuum tower
telescope in Tenerife were used to investigate the dynamics of the deep
photospheric layers by tracing the motions of small-scale structures
such as granulation. Based on a time series of these spectrograms,
traces of line Doppler shifts were detected which show strong
asymmetries within solar granules. The results are discussed within
the framework of different granulation flow models.
---------------------------------------------------------
Title: Granulation Spectroscopy: First Results from VTT-Tenerife
Authors: Nesis, A.; Hanslmeier, A.; Hammer, R.; Komm, R.; Mattig,
W.; Staiger, J.
1991BAAS...23R1048N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of oscillatory phase-shifts with diode arrays
Authors: Staiger, J.
1987A&A...175..263S Altcode:
Several problems related to the oscillations of the Sun's atmosphere are
not yet understood completely, such as the vertical energy transfer,
the formation of gravity waves by granulation and their propagation,
chromospheric oscillations, the radiative dissipation of oscillations
etc. In a series of papers the author wants to investigate some of
these problems from the experimental point of view. He used three
linear diode arrays to observe the phase-propagation characteristics
within the solar atmosphere at different height levels. In this first
paper he mainly describes the measuring-device, the observations and
the way of data-reduction. Some new experimental results presented are
related to the vertical oscillatory energy transfer and the existence
of running acoustic waves.
