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ADS astronomy entries on 2022-09-14
author:"Woehl, Hubertus"
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Title: Solar differential rotation in the period 1964-2016 determined
by the Kanzelhöhe data set
Authors: Poljančić Beljan, I.; Jurdana-Šepić, R.; Brajša, R.;
Sudar, D.; Ruždjak, D.; Hržina, D.; Pötzi, W.; Hanslmeier, A.;
Veronig, A.; Skokić, I.; Wöhl, H.
2017A&A...606A..72P Altcode:
Context. Kanzelhöhe Observatory for Solar and Environmental Research
(KSO) provides daily multispectral synoptic observations of the Sun
using several telescopes. In this work we made use of sunspot drawings
and full disk white light CCD images. <BR /> Aims: The main aim of
this work is to determine the solar differential rotation by tracing
sunspot groups during the period 1964-2016, using the KSO sunspot
drawings and white light images. We also compare the differential
rotation parameters derived in this paper from the KSO with those
collected fromf other data sets and present an investigation of the
north - south rotational asymmetry. <BR /> Methods: Two procedures
for the determination of the heliographic positions were applied: an
interactive procedure on the KSO sunspot drawings (1964-2008, solar
cycles Nos. 20-23) and an automatic procedure on the KSO white light
images (2009-2016, solar cycle No. 24). For the determination of the
synodic angular rotation velocities two different methods have been
used: a daily shift (DS) method and a robust linear least-squares fit
(rLSQ) method. Afterwards, the rotation velocities had to be converted
from synodic to sidereal, which were then used in the least-squares
fitting for the solar differential rotation law. A comparison of
the interactive and automatic procedures was performed for the
year 2014. <BR /> Results: The interactive procedure of position
determination is fairly accurate but time consuming. In the case
of the much faster automatic procedure for position determination,
we found the rLSQ method for calculating rotational velocities to
be more reliable than the DS method. For the test data from 2014,
the rLSQ method gives a relative standard error for the differential
rotation parameter B that is three times smaller than the corresponding
relative standard error derived for the DS method. The best fit solar
differential rotation profile for the whole time period is ω(b) =
(14.47 ± 0.01)-(2.66 ± 0.10)sin<SUP>2</SUP>b (deg/day) for the DS
method and ω(b) = (14.50 ± 0.01)-(2.87 ± 0.12)sin<SUP>2</SUP>b
(deg/day) for the rLSQ method. A barely noticeable north - south
asymmetry is observed for the whole time period 1964-2016 in the
present paper. Rotation profiles, using different data sets, presented
by other authors for the same time periods and the same tracer types,
are in good agreement with our results. <BR /> Conclusions: The KSO
data set used in this paper is in good agreement with the Debrecen
Photoheliographic Data and Greenwich Photoheliographic Results and is
suitable for the investigation of the long-term variabilities in the
solar rotation profile. Also, the quality of the KSO sunspot drawings
has gradually increased during the last 50 yr.
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Title: Solar differential rotation in the period 1964 - 2016
determined by the Kanzelhöhe data set
Authors: Poljančić Beljan, I.; Jurdana-Šepić, R.; Brajša, R.;
Sudar, D.; Ruždjak, D.; Hržina, D.; Pötzi, W.; Hanslmeier, A.;
Veronig, A.; Skokić, I.; Wöhl, H.
2017arXiv170707886P Altcode:
The main aim of this work is to determine the solar differential
rotation by tracing sunspot groups during the period 1964-2016, using
the Kanzelhöhe Observatory for Solar and Environmental Research
(KSO) sunspot drawings and white light images. Two procedures for
the determination of the heliographic positions were applied: an
interactive procedure on the KSO sunspot drawings (1964 - 2008, solar
cycles nos. 20 - 23) and an automatic procedure on the KSO white light
images (2009 - 2016, solar cycle no. 24). For the determination of the
synodic angular rotation velocities two different methods have been
used: a daily shift (DS) method and a robust linear least-squares fit
(rLSQ) method. Afterwards, the rotation velocities had to be converted
from synodic to sidereal, which were then used in the least-squares
fitting for the solar differential rotation law. For the test
data from 2014, we found the rLSQ method for calculating rotational
velocities to be more reliable than the DS method. The best fit solar
differential rotation profile for the whole time period is $\omega(b)$
= (14.47 $\pm$ 0.01) - (2.66 $\pm$ 0.10) $\sin^2b$ (deg/day) for the
DS method and $\omega(b)$ = (14.50 $\pm$ 0.01) - (2.87 $\pm$ 0.12)
$\sin^2b$ (deg/day) for the rLSQ method. A barely noticeable north -
south asymmetry is observed for the whole time period 1964 - 2016
in the present paper. Rotation profiles, using different data sets
(e.g. Debrecen Photoheliographic Data, Greenwich Photoheliographic
Results), presented by other authors for the same time periods and the
same tracer types, are in good agreement with our results. Therefore,
the KSO data set is suitable for the investigation of the long-term
variabilities in the solar rotation profile.
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Title: Meridional Motion and Reynolds Stress from Debrecen
Photoheliographic Data
Authors: Sudar, Davor; Brajša, Roman; Skokić, Ivica; Poljančić
Beljan, Ivana; Wöhl, Hubertus
2017SoPh..292...86S Altcode: 2017arXiv170500912S
The Debrecen Photoheliographic Data catalogue is a continuation of
the Greenwich Photoheliographic Results providing daily positions of
sunspots and sunspot groups. We analyse the data for sunspot groups
focussing on meridional motions and transfer of angular momentum towards
the solar equator. Velocities are calculated with a daily shift method
including an automatic iterative process of removing the outliers. Apart
from the standard differential rotation profile, we find meridional
motion directed towards the zone of solar activity. The difference in
measured meridional flow in comparison to Doppler measurements and some
other tracer measurements is interpreted as a consequence of different
flow patterns inside and outside of active regions. We also find a
statistically significant dependence of meridional motion on rotation
velocity residuals confirming the transfer of angular momentum towards
the equator. Analysis of horizontal Reynolds stress reveals that the
transfer of angular momentum is stronger with increasing latitude
up to about 40<SUP>∘</SUP>, where there is a possible maximum in
absolute value.
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Title: A comparison between the observed and predicted amplitude of
the 24<SUP>th</SUP> solar cycle
Authors: Brajša, R.; Verbanac, G.; Sudar, D.; Skokić, I.; Žic,
T.; Hanslmeier, A.; Wöhl, H.; Roth, M.; Mursula, K.; Zhang, L.
2015CEAB...39..135B Altcode:
In present work we compared the measured and predicted amplitudes of
the 24<SUP>th</SUP> solar cycle. The modified minimum--maximum method,
belonging to the precursor class of methods, was applied to the smoothed
monthly sunspot number values (the “old” data set, used before the
change introduced on July 1<SUP>st</SUP>, 2015). The maximum of the
24<SUP>th</SUP> solar cycle occurred in April 2014 with an amplitude of
R=82 and this observed value is very close to our mean predicted value
R=83. The maximum was significantly weaker than in several previous
cycles. Additionally, a curious solar activity minimum of 2008,
between the solar cycles no.~23 and no.~24 was analysed, as well as
the shape of the maximum profile. The maximum of the 24<SUP>th</SUP>
solar cycle had a double-peak, the second one being higher than the
first one. The obtained results represent a strong indication that
the minimum--maximum method is a reliable tool for the solar cycle
prediction, using data available already 3 years before the preceding
minimum of solar activity.
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Title: Validity of the Relations Between the Synodic and Sidereal
Rotation Velocities of the Sun
Authors: Skokić, I.; Brajša, R.; Roša, D.; Hržina, D.; Wöhl, H.
2014SoPh..289.1471S Altcode: 2013arXiv1310.0778S
Existing methods for conversion between synodic and sidereal
rotation velocities of the Sun are tested for validity using
state-of-the-art ephemeris data. We found that some of them agree well
with ephemeris calculations while others show a discrepancy of almost
0.01<SUP>∘</SUP> day<SUP>−1</SUP>. This discrepancy is attributed
to a missing factor and a new corrected relation is given.
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Title: Tracing sunspot groups to determine angular momentum transfer
on the Sun
Authors: Sudar, D.; Skokić, I.; Ruždjak, D.; Brajša, R.; Wöhl, H.
2014MNRAS.439.2377S Altcode: 2014MNRAS.tmp..355S; 2014arXiv1401.5641S
In this paper, our goal is to investigate Reynolds stress and to
check whether it is plausible that this is responsible for angular
momentum transfer towards the solar equator. We have also analysed
meridional velocity, rotation velocity residuals and correlation
between the velocities. We have used the position measurements of
sunspot groups from the Greenwich Photographic Result and the Solar
Observing Optical Network/United States Air Force/National Oceanic
and Atmospheric Administration data bases, covering the period
1878-2011. In order to calculate the velocities, we used the daily
motion of sunspot groups. The sample was also limited to ±58° in the
central meridian distance in order to avoid solar limb effects. We have
mainly investigated velocity patterns depending on the solar cycle phase
and latitude. We have found that the meridional motion of sunspot groups
is towards the centre of activity from all available latitudes and in
all phases of the solar cycle. The range of meridional velocities is
±10 m s<SUP>-1</SUP>. Horizontal Reynolds stress is negative at all
available latitudes and indicates that there is a minimum value (q ≈
-3000 m<SUP>2</SUP> s<SUP>-2</SUP>) located at b ≈ ±30°. In our
convention, this means that angular momentum is transported towards
the solar equator, in agreement with the observed rotational profile
of the Sun.
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Title: A relationship between the solar rotation and activity in the
period 1998-2006 analysed by tracing small bright coronal structures
in SOHO-EIT images
Authors: Jurdana-Šepić, R.; Brajša, R.; Wöhl, H.; Hanslmeier,
A.; Poljančić, I.; Svalgaard, L.; Gissot, S. F.
2011A&A...534A..17J Altcode:
<BR /> Aims: The study aims to find a relationship between the rotation
of the small bright coronal structures (SBCS) described by the solar
rotation parameters and indices of solar activity on monthly and yearly
temporal scales. <BR /> Methods: We analyse precise measurements of
the solar differential rotation determined by tracing SBCS in SOHO-EIT
images and compare the derived solar rotation parameters with the
status of solar activity in the period 1998 - 2006. Full-disc solar
images obtained with the Extreme ultraviolet Imaging Telescope (EIT)
on board the Solar and Heliospheric Observatory (SOHO) were used to
analyse solar differential rotation determined by tracing SBCS. An
automatic method to identify and track the SBCS in EIT full-disc images
with a six hour cadence is applied. We performed a statistical analysis
of the monthly and yearly values of solar sidereal rotation velocity
parameters A and B (corresponding to the equatorial rotation velocity
and the gradient of the solar differential rotation, respectively)
as a function of various solar activity indices. <BR /> Results:
The dependence of the solar rotation on the phase of the solar cycle
was found. It is clearly visible for the solar rotation parameter A,
whilst the results are not conclusive for parameter B. The relationship
between the solar rotation and activity, expressed by the monthly
relative sunspot number, the smoothed monthly relative sunspot number,
the yearly relative sunspot number, and the interdiurnal variability
(IDV) index was investigated. The statistically significant correlation
was found for the solar rotation parameter A, whilst a very low and
insignificant correlation was obtained for the rotation parameter
B. <BR /> Conclusions: During the maximum of the solar cycle 23 and
just after it, the equatorial solar rotation velocity was lower than
in other phases of the cycle, when there was less activity. This is
consistent with other observational findings, obtained by different
tracers and methods.
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Title: Differences in heliographic positions and rotation velocities
of sunspot groups from various observatories
Authors: Poljančić, I.; Brajša, R.; Hržina, D.; Wöhl, H.;
Hanslmeier, A.; Pötzi, W.; Baranyi, T.; Özgüç, A.; Singh, J.;
Ruždjak, V.
2011CEAB...35...59P Altcode:
Measured positions of sunspot groups that differ in format, precision
and observing procedure are collected from various data sets:
GPR (Greenwich Photoheliographic Results), SOON/USAF/NOAA (Solar
Optical Observing Network/United States Air Force/National Oceanic and
Atmospheric Administration), as well as from the Kodaikanal and Debrecen
observatories. Kanzelh&{uml;o}he and Kandilli Observatory currently
provide the digitized sunspot drawings, from which the positions
of selected sunspot groups are determined with a special software
Sungrabber. The rotation velocities are calculated from the position
data. The aim of this work is to compare and to check the precision
of the mentioned data sets using the Kanzelh&{uml;o}he Observatory
data set as the reference basis of sunspot position measurements. The
selected groups (about 40% consist of single sunspots Z&{uml;u}rich
types H and J) are from the years 1972 and 1993 belonging to similar
declining phases of two solar activity cycles. The occurrence of some
systematic differences of the sunspot group positions and rotation
velocities suggests the need for a more detailed analysis of the data
accumulation procedures.
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Title: A Comparison of Sunspot Position Measurments from Different
Data Sets
Authors: Poljancic, I.; Brajsa, R.; Ruzdjak, D.; Hrzina, D.;
Jurdana-Sepic, R.; Wohl, H.; Otruba, W.
2010SunGe...5...52P Altcode:
There are several data sets containing information about the positions
of sunspots and sunspot groups that differ in format and precision,
e.g. GPR (Greenwich Photoheliographic Results) and SOON/USAF/NOAA
(Solar Optical Observing Network/United States Air Force/National
Oceanic and Atmosferic Administration). The aim of this paper is to
check the precision of the SOON/USAF/NOAA data set and compare it with
the GPR data set. For this purpose, we have used a third data set,
the Kanzelhöhe Observatory data set, as a basis of sunspot position
measurments comparison. The positions of selected sunspot groups in the
digitized Solar Observatory Kanzelhöhe drawings were determined with
a special software Sungrabber. The selected groups consisted mostly of
single sunspots (Zürich types H and J) from the years 1972 and 1993
belonging to the similar phases of the solar activity cycles. The
determined Kanzelhöhe sunspot group coordinates were compared with
those from GPR for the year 1972 and SOON/USAF/NOAA for the year
1993. The rotation velocities calculated for sunspot groups observed
at Kanzelhöhe were compared with the ones obtained from the two data
sets mentioned above in the same observing periods. With the assumption
of constant precision of Kanzelhöhe drawings, it was established that
SOON/USAF/NOAA data are somewhat less precise than the GPR ones.
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Title: A precise measurement of the solar differential rotation by
tracing small bright coronal structures in SOHO-EIT images. Results
and comparisons for the period 1998-2006
Authors: Wöhl, H.; Brajša, R.; Hanslmeier, A.; Gissot, S. F.
2010A&A...520A..29W Altcode:
<BR /> Aims: We precisely determine the solar rotation velocity during
most of the 23rd solar cycle, in the years 1998-2006. We measure the
solar differential rotation by tracing small bright coronal structures
(SBCS) in SOHO-EIT images. <BR /> Methods: The 28.4 nm EIT channel was
used and positions of more than 55 000 structures were measured applying
an interactive and improved automatic method of data reduction. <BR />
Results: We achieve the closest representation of the observational
data when all three solar differential rotation parameters are used
and obtain the formula ω (b) = 14.499 (±0.006) - 2.54 (±0.06)
sin<SUP>2</SUP> b - 0.77 (±0.09) sin<SUP>4</SUP>b. This result
represents the sidereal rotation velocity in deg day<SUP>-1</SUP>
and is produced by the automatic method applied in 1998-2006. A
north-south rotational asymmetry and a rigid component of the solar
rotation at high latitudes were found. <BR /> Conclusions: A more
differential rotation profile of SBCS than of sunspots and sunspot
groups was found. The rotation velocity of SBCS is very similar
to those obtained by small photospheric magnetic features. The
north-south rotational asymmetry of SBCS was interpreted with a model
of the relationship between solar rotation and activity. The rigid
component of the solar rotation at high latitudes, identifiable only
from the results of the automatic method, was related to larger
structures mostly identified by that method, in contrast to the
interactive method, which detected smaller structures. <P />Tables
3-11 and Figs. 4, 5 are only available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
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Title: Magnetic loop emergence within a granule
Authors: Gömöry, P.; Beck, C.; Balthasar, H.; Rybák, J.; Kučera,
A.; Koza, J.; Wöhl, H.
2010A&A...511A..14G Altcode: 2009arXiv0910.4449G
<BR /> Aims: We investigate the temporal evolution of magnetic
flux emerging within a granule in the quiet-Sun internetwork at
disk center. <BR /> Methods: We combined IR spectropolarimetry of
high angular resolution performed in two Fe i lines at 1565 nm with
speckle-reconstructed G-band imaging. We determined the magnetic
field parameters by a LTE inversion of the full Stokes vector using
the SIR code, and followed their evolution in time. To interpret
the observations, we created a geometrical model of a rising loop in
3D. The relevant parameters of the loop were matched to the observations
where possible. We then synthesized spectra from the 3D model for a
comparison to the observations. <BR /> Results: We found signatures of
magnetic flux emergence within a growing granule. In the early phases,
a horizontal magnetic field with a distinct linear polarization signal
dominated the emerging flux. Later on, two patches of opposite circular
polarization signal appeared symmetrically on either side of the linear
polarization patch, indicating a small loop-like structure. The mean
magnetic flux density of this loop was roughly 450 G, with a total
magnetic flux of around 3 × 10<SUP>17</SUP> Mx. During the ~12 min
episode of loop occurrence, the spatial extent of the loop increased
from about 1 to 2 arcsec. The middle part of the appearing feature
was blueshifted during its occurrence, supporting the scenario of an
emerging loop. There is also clear evidence for the interaction of
one loop footpoint with a preexisting magnetic structure of opposite
polarity. The temporal evolution of the observed spectra is reproduced
to first order by the spectra derived from the geometrical model. During
the phase of clearest visibility of the loop in the observations,
the observed and synthetic spectra match quantitatively. <BR />
Conclusions: The observed event can be explained as a case of flux
emergence in the shape of a small-scale loop. The fast disappearance
of the loop at the end could possibly be due to magnetic reconnection.
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Title: Comparison of the sidereal angular velocity of subphotospheric
layers and small bright coronal structures during the declining
phase of solar cycle 23
Authors: Zaatri, A.; Wöhl, H.; Roth, M.; Corbard, T.; Brajša, R.
2009A&A...504..589Z Altcode: 2009arXiv0907.4099Z
Context: We compare solar differential rotation of subphotospheric
layers derived from local helioseismology analysis of GONG++
dopplergrams and the one derived from tracing small bright coronal
structures (SBCS) using EIT/SOHO images for the period August
2001-December 2006, which correspond to the declining phase of solar
cycle 23. <BR />Aims: The study aims to find a relationship between
the rotation of the SBCS and the subphotospheric angular velocity. The
north-south asymmetries of both rotation velocity measurements are also
investigated. <BR />Methods: Subphotospheric differential rotation was
derived using ring-diagram analysis of GONG++ full-disk dopplergrams of
1 min cadence. The coronal rotation was derived by using an automatic
method to identify and track the small bright coronal structures in
EIT full-disk images of 6 h cadence. <BR />Results: We find that the
SBCS rotate faster than the considered upper subphotospheric layer
(3 Mm) by about 0.5 deg/day at the equator. This result joins the
results of several other magnetic features (sunspots, plages, faculae,
etc.) with a higher rotation than the solar plasma. The rotation rate
latitudinal gradients of the SBCS and the subphotospheric layers
are very similar. The SBCS motion shows an acceleration of about
0.005°day<SUP>-1</SUP>/month during the declining phase of solar cycle
23, whereas the angular velocity of subsurface layers does not display
any evident variation with time, except for the well known torsional
oscillation pattern. Finally, both subphotospheric and coronal rotations
of the southern hemisphere are predominantly larger than those of the
northern hemisphere. At latitudes where the north-south asymmetry of
the angular velocity increases (decreases) with activity for the SBCS,
it decreases (increases) for subphotospheric layers.
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Title: On solar cycle predictions and reconstructions
Authors: Brajša, R.; Wöhl, H.; Hanslmeier, A.; Verbanac, G.;
Ruždjak, D.; Cliver, E.; Svalgaard, L.; Roth, M.
2009A&A...496..855B Altcode:
Context: Generally, there are two procedures for solar cycle
predictions: the empirical methods - statistical methods based on
extrapolations and precursor methods - and methods based on dynamo
models. <BR />Aims: The goal of the present analysis is to forecast
the strength and epochs of the next solar cycle, to investigate proxies
for grand solar minima and to reconstruct the relative sunspot number
in the Maunder minimum. <BR />Methods: We calculate the asymmetry of
the ascending and descending solar cycle phases (Method 1) and use this
parameter as a proxy for solar activity on longer time scales. Further,
we correlate the relative sunspot numbers in the epochs of solar
activity minima and maxima (Method 2) and estimate the parameters of
an autoregressive moving average model (ARMA, Method 3). Finally,
the power spectrum of data obtained with the Method 1 is analysed
and the Methods 1 and 3 are combined. <BR />Results: Signatures of
the Maunder, Dalton and Gleissberg minima were found with Method 1. A
period of about 70 years, somewhat shorter than the Gleissberg period
was identified in the asymmetry data. The maximal smoothed monthly
sunspot number during the Maunder minimum was reconstructed and found
to be in the range 0-35 (Method 1). The estimated Wolf number (also
called the relative sunspot number) of the next solar maximum is in
the range 88-102 (Method 2). Method 3 predicts the next solar maximum
between 2011 and 2012 and the next solar minimum for 2017. Also, it
forecasts the relative sunspot number in the next maximum to be 90
± 27. A combination of the Methods 1 and 3 gives for the next solar
maximum relative sunspot numbers between 78 and 99. <BR />Conclusions:
The asymmetry parameter provided by Method 1 is a good proxy for solar
activity in the past, also in the periods for which no relative sunspot
numbers are available. Our prediction for the next solar cycle No. 24
is that it will be weaker than the last cycle, No. 23. This prediction
is based on various independent methods.
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Title: Solar Differential Rotation Determined by Tracing Low and
High Brightness Temperature Regions at 8 mm
Authors: Romštajn, I.; Brajša, R.; Wöhl, H.; Benz, A. O.; Temmer,
M.; Roša, D.; Ruždjak, V.
2009CEAB...33...79R Altcode:
At the wavelength of 8 mm absorption features (Low brightness
Temperature Regions, LTRs) and emission features (High brightness
Temperature Regions, HTRs) can be traced for determination of solar
rotation. From earlier studies it is known that about two thirds of LTRs
are associated with Hα filaments. The goal of the present analysis is
to determine the heights of these solar structures and their rotational
velocities. We used the method for the simultaneous determination of
the solar synodic rotation velocity and the height of tracers. The
rotation velocities were determined by the linear least-square fit of
their central meridian distances as a function of time. The mean value
of the low brightness temperature regions' heights is about 45 600
km. The results of solar rotation determined by tracing LTRs and HTRs
are mutually compared and also compared with the results using other
tracers and methods. The method for the simultaneous determination
of the solar synodic rotation velocity and the height of the tracers
could be applied properly only on LTRs, since a wide distribution
over latitudes and central meridian distances of a large data set is
necessary, which was not available for HTRs. Observational findings that
HTRs rotate systematically faster than LTRs and the possibility that
they can be observed at and outside the solar limb are consistent with
relatively high altitudes of HTRs. It was concluded that the radiation
mechanism of HTRs is thermal bremsstrahlung, probably associated with
flaring active regions.
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Title: Measurements of the He I 1083 nm Line on the Sun During
Different Solar Activity Phases: in the Years 1993 and 1995
Authors: Jurdana-Šepić, R.; Brajša, R.; Šaina, B.; Wöhl, H.
2009CEAB...33..337J Altcode:
Latitudinal variations and North--South asymmetry of the He I 1083 nm
line across the solar disc are investigated, based on 69 solar scans
obtained during two observational campaigns in 1993 and 1995. In both
time intervals the He I 1083 nm line was observed in absorption. The
ratio of average intensity in the line and the average intensity of
the nearby quasi-continuum was calculated <P />and cautiously used
as a measure of the line absorption and represented as a function of
position on the solar disc. Results indicate a distinct dependence of
the He I 1083 nm average relative line intensity on the solar latitude,
its North--South asymmetry and well pronounced differences for the two
campaigns belonging to different solar cycle phases. The latitudinal
dependence is analysed with and without discriminating quiet Sun and
active regions. The observed behaviour (the latitudinal dependence
and a North--South asymmetry) is to a large extent a consequence
of the presence/absence of active regions. The differences found
for the two observing campaigns are not only due to decreased solar
activity in 1995 as compared to 1993, but also due to different and
much more pronounced telluric water-vapour contamination during the
second observing interval. Finally, in the Appendix we describe all
He scans used here in more detail and compare the numbers of solar
features identified in other spectral regions along the scans for the
two observational campaigns.
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Title: A Prediction for the 24<SUP>th</SUP> Solar Cycle
Authors: Brajša, R.; Wöhl, H.; Hanslmeier, A.; Verbanac, G.;
Ruždjak, D.; Cliver, E.; Svalgaard, L.; Roth, M.
2009CEAB...33...95B Altcode:
The aim of the present analysis is to forecast the strength of the
next solar maximum of the 24<SUP>th</SUP> cycle. We correlate the
relative sunspot numbers in the epochs of solar activity minima and
maxima. Using this method, the estimated relative sunspot number (also
called the Wolf number) of the next solar maximum is in the range 67-81,
i.e., about 40 % below the peak sunspot number of 121 for cycle No. 23.
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Title: Solar Convection and Oscillation Interaction
Authors: Hanslmeier, A.; Kučera, A.; Rybák, J.; Wöhl, H.;
Gömöry, P.
2009CEAB...33...51H Altcode:
In this paper we investigate bisectors of solar photospheric lines. The
bisectors reflect vertical velocity gradients over the height of line
formation and therefore reveal important information about the dynamics
in these layers. Their shape and shift is influenced by (a) convective
motions, (b) oscillatory motions that can act differently at different
photospheric heights. The bisectors are selected from different
locations that show mainly a granular evolution or an intergranular
evolution. Two selection criteria were applied: continuum intensity
(enhanced for granular bisectors, reduced for intergranular bisectors),
and full width at half maximum values (enhanced for intergranular
bisectors). The results demonstrate how oscillatory motions influence
the bisectors as a whole. In the example given a smaller amplitude of
oscillations over intergranular areas is indicated.
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Title: Heights of solar tracers observed at 8 mm and an interpretation
of their radiation
Authors: Brajša, R.; Romštajn, I.; Wöhl, H.; Benz, A. O.; Temmer,
M.; Roša, D.
2009A&A...493..613B Altcode:
Context: At the wavelength of 8 mm, emissive features (high
brightness-temperatrue regions, HTRs) and absorptive features
(low brightness-temperature regions, LTRs) can be traced for the
determining the solar rotation. From earlier studies it is known
that about two thirds of LTRs are associated with Hα filaments. <BR
/>Aims: Thermal bremsstrahlung and gyromagnetic (cyclotron) radiation
mechanism can be important for explaining the observed phenomena,
so we determine the heights of solar structures and interpret their
radiation mechanism(s). <BR />Methods: We use the method of simultaneous
determination of the solar synodic rotation velocity and the height
of tracers. The rotation velocities were determined by the linear
least-square fit of their central meridian distance as a function of
time. We used a procedure for calculating the brightness temperature for
a given wavelength and model atmosphere, which integrates the radiative
transfer equation for the thermal bremsstrahlung. <BR />Results:
The mean value of the low brightness-temperature regions' heights
is about 45 600 km. This height was used as input for constructing
prominence and coronal condensation models, which, when assuming thermal
bremsstrahlung as the radiation mechanism, yield a decrease in the
brightness temperature of 2-14%, in agreement with observations. If the
same radiation mechanism is considered, the models of the solar corona
above active regions give an increase in the brightness temperature of
5-19%, also in agreement with observations. In this case an indirect
indication (from the rotational analysis) that the HTRs are located
higher in the solar atmosphere than the LTRs was taken into account. <BR
/>Conclusions: The method for simultaneously determining the solar
synodic rotation velocity and the height of tracers could have only
been properly applied on LTRs, since a homogeneous distribution over
latitudes and central meridian distances of a large enough data set is
necessary. Thermal bremsstrahlung can explain both the LTR (prominences
and coronal condensations) and HTR (ordinary active regions) phenomena
observed at 8 mm. At this wavelength, thermal gyromagnetic emission
is almost surely excluded as a possible radiation mechanism.
---------------------------------------------------------
Title: Observational Evidence for Shocks in the Solar Photosphere -
New TESOS/VTT Results
Authors: Rybak, J.; Kucera, A.; Hanslmeier, A.; Woehl, H.;
Wedemeyer-Boehm, S.; Steiner, O.
2008ESPM...12.2.36R Altcode:
High-resolution spectroscopic observations recently acquired with the
TESOS spectrometer at the Vacuum Tower Telescope (VTT, Observatorio
del Teide, Tenerife) are used to test predictions regarding strongly
dynamic events in the photosphere as obtained from three-dimensional
numerical simulations with the CO5BOLD-code. <P />Time series of
two-dimensional maps of the Fe I 543.4 nm spectral line profile at
different centre-to-limb positions are investigated in a statistical
sense by comparing the distributions of individual spectral parameters
derived from observations with the corresponding distributions
from synthesized spectra calculated with the LINFOR3D code from
the simulations. Appropriate degradation of the synthesized spectra
was applied in order to take the limited spatial resolution of the
telescope, seeing effects, and the scattered instrumental light into
account. <P />At the actual spatial resolution of 0.5 arc sec, the
statistics show that signatures of the photospheric dynamics, including
the most dynamical events like occasional supersonic flows of plasma in
the nearly horizontal direction, are very similar in both observations
and simulations. <P />Discrepancies are found only for those spectral
parameters (residual line intensity, Doppler line core shifts), which
are affected by non-LTE effects, since non-LTE effects are not taken
into account in the synthesis of the Fe I 543.4nm spectral line.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: Multi-wavelength Observations of Dynamic Fibrils in the Upper
Photosphere and Chromosphere
Authors: Kucera, A.; Beck, Ch.; Gomory, P.; Koza, J.; Woehl, H.;
Rybak, J.
2008ESPM...12.2.52K Altcode:
Spatial and temporal evolution of dynamic fibrils (DF) as well as
coupling with photospheric features was investigated. <P />The
main target were remnants in the active region 10997 on May 28,
2008. We used about 1 hour series of multi wavelength simultaneous
observations of the DFs and corresponding photospheric features. The
observations were performed with the german Vacuum Tower Telescope
equipped with several post-focus instruments. Namely: TESOS (Triple
Etalon SOlar Spectrometer) instrument was used in polarimetric mode
(VIP=Visual Imaging Polarimeter) to register 2D spectra of the DFs in
H-alpha line and in magnetically sensitive Fe I 630.2 nm line. TIP
(Tenerife Infrared Polarimeter) mounted on the Echelle spectrograph
was used for spectropolarimetric observations of two neutral iron
lines at 1.56 micrometers. We scanned 2D area 80" x 5", producing
thus 2D maps of intensity, velocity and magnetic field of the low
photosphere under the chromospheric fibril field. <P />Additionally
G-band and H-alpha images were registered with high cadence and
the supporting data from the TRACE satellite (17.1 nm, WL, Lyman
alpha line and 160 nm continuum) are also available. After careful
spatial coalignment of 2D maps we first selected numerous DFs in the
H-alpha images. Then we investigated temporal evolution of those DFs
concerning changes of their dimensions, positions and fluctuations
and correlated these characteristics with temporal evolution of the
intensities, velocities and magnetic field characteristics observed in
the spatially corresponding photosphere. The poster demonstrates the
complex observations, data reduction and coalignment and preliminary
results on coupling between DFs and underlying photospheric features.
---------------------------------------------------------
Title: On the Solar Rotation and Activity in the Years 1998 - 2003
Authors: Brajsa, R.; Woehl, H.; Hanslmeier, A.; Gissot, S. F.
2008ESPM...122.114B Altcode:
Full-disc full-resolution solar images obtained by the Extreme
Ultraviolet Imaging Telescope on board the Solar and Heliospheric
Observatory are used to analyse solar differential rotation by tracing
coronal bright points. We applied an interactive and an improved
automatic method of data reduction to process data obtained during
the period 1998 - 2003 with the Fe XV filter (28.4 nm). Using the
interactive method, the data obtained during 8 months of observation
were reduced, while the automatic method was applied to analyse the
whole 57-month period of observations, since the interactive method is
much more time consuming than the automatic one. In the present work we
especially focus on a possible relationship between the solar rotation
(57 monthly values of the solar rotation parameters determined with
the automatic method) and activity (relative sunspot numbers for the
same months) during the maximum phase of the solar cycle 23.
---------------------------------------------------------
Title: Observation of Turbulence in Solar Surface Convection:
I. Line Parameter Correlations
Authors: Hanslmeier, A.; Kučera, A.; Rybák, J.; Wöhl, H.
2008SoPh..249..293H Altcode: 2008SoPh..tmp...88H
By using slit observations of solar photospheric lines shifted by 0.4
arcsec, a 2D field on the Sun was scanned to obtain a 16-minute time
series of 2D line-parameter variations. The aim was to investigate in
detail the occurrence of turbulence that can be measured by line-width
variations extracted from the line profiles. The continuum-intensity
variation served as a proxy for granular (bright) and intergranular
(dark) areas. The results show that turbulence is not limited to
the intergranular space but is also produced by horizontal motions
that may become supersonic, leading to turbulence. These motions
lead to brightenings, as predicted by theoretical models. Thus,
enhanced line-width variations are found to occur in both bright and
dark areas. A Sobel filter served to detect the areas where strong
gradients in the line parameters occur. By applying this filter to the
different line-parameter variations over the 2D field observed, we can
determine whether there exists a similarity of these strong-gradient
patterns with other parameters that characterize granular motions such
as intensity variations or velocity fluctuations.
---------------------------------------------------------
Title: Proper Motions of Coronal Bright Points
Authors: Brajša, R.; Wöhl, H.; Vršnak, B.; Ruždjak, V.; Clette,
F.; Hochedez, J. -F.; Verbanac, G.; Skokić, I.; Hanslmeier, A.
2008CEAB...32..165B Altcode:
Full-field full-resolution solar images obtained by the Extreme
Ultraviolet Imaging Telescope on board the Solar and Heliospheric
Observatory are used to analyse proper motions, velocity distributions,
lifetimes, and diffusion coefficient of coronal bright points. The
results obtained by the interactive method for three tracer subtypes
(point-like structures, small loops, and small active regions)
of coronal bright points for the period 4 June 1998 to 22 May 1999
are presented and compared. Distributions of meridional velocities,
residual azimuthal velocities and velocities of proper motions are
presented for the three tracer subtypes. Lifetimes up to 54 hours
are found for 98% of all observed coronal bright points. Small active
regions last on the average longer than point-like structures and small
loops. The correlation between the absolute velocity of proper motion
and lifetime is investigated and the mean free path (in the range from
3000 km to 15000 km) and the diffusion coefficient (approximately 200
km<SUP>2</SUP>/s) of coronal bright points are estimated. Finally,
characteristics of the random walk process associated to the motions
of coronal bright points are discussed in the Appendix.
---------------------------------------------------------
Title: Coronal Bright Points as Tracers for Solar Rotation in
October-November 1999
Authors: Brajša, R.; Mulec, M.; Hanslmeier, A.; Wöhl, H.; Ruždjak,
V.; Hochedez, J. -F.
2008CEAB...32..117B Altcode:
Whole-disc full-resolution solar images taken in the extreme ultraviolet
part of the spectrum (Fe XV line at 28.4 nm) with the EIT instrument
on board the SOHO spacecraft were used to visually identify coronal
bright points appropriate for solar rotation determination. From the
time differences in successive tracer positions amounting to six hours
the solar rotation velocity was determined tracing coronal bright
points in images obtained in October and November 1999. The resulting
parameters and profiles of the solar rotation are presented.
---------------------------------------------------------
Title: On the solar rotation and activity
Authors: Brajša, R.; Wöhl, H.; Ruždjak, D.; Vršnak, B.; Verbanac,
G.; Svalgaard, L.; Hochedez, J. -F.
2007AN....328.1013B Altcode:
The interaction between differential rotation and magnetic fields in
the solar convection zone was recently modelled by Brun (2004). One
consequence of that model is that the Maxwell stresses can oppose the
Reynolds stresses, and thus contribute to the transport of the angular
momentum towards the solar poles, leading to a reduced differential
rotation. So, when magnetic fields are weaker, a more pronounced
differential rotation can be expected, yielding a higher rotation
velocity at low latitudes taken on the average. This hypothesis
is consistent with the behaviour of the solar rotation during the
Maunder minimum. In this work we search for similar signatures of
the relationship between the solar activity and rotation determined
tracing sunspot groups and coronal bright points. We use the extended
Greenwich data set (1878-1981) and a series of full-disc solar images
taken at 28.4 nm with the EIT instrument on the SOHO spacecraft
(1998-2000). We investigate the dependence of the solar rotation on
the solar activity (described by the relative sunspot number) and
the interplanetary magnetic field (calculated from the interdiurnal
variability index). Possible rotational signatures of two weak solar
activity cycles at the beginning of the 20th century (Gleissberg
minimum) are discussed.
---------------------------------------------------------
Title: An Interpretation of the Coronal Holes' Visibility in the
Millimeter Wavelength Range
Authors: Brajša, R.; Benz, A. O.; Temmer, M.; Jurdana-Šepić, R.;
Šaina, B.; Wöhl, H.
2007SoPh..245..167B Altcode:
Various observations indicate that coronal holes generally appear as low
brightness temperature regions (LTRs) in the centimeter and millimeter
wavelength ranges. However, within their borders local enhancements of
radiation, that is, high brightness temperature regions (HTRs), often
occur. The theory behind the described behavior is not fully understood
and therefore we analyze full-disk solar images obtained at a wavelength
of 8 mm at Metsähovi Radio Observatory and compare them with data
simultaneously taken in other wavelength ranges. The observational
finding that the average brightness temperature of coronal holes is
not much different from the quiet-Sun level (with localized deviations
toward higher and lower intensities on the order of a few percent)
is compared with theoretical models of the thermal bremsstrahlung
radiation originating in the solar chromosphere, transition region,
and corona. Special attention is devoted to the interpretation of the
localized enhancements of radiation observed inside coronal holes at
millimeter wavelengths. The main conclusion is that the most important
contribution to the brightness temperature comes from an increased
density in the transition region and low corona (i.e., at the heights
where the temperature is below 10<SUP>6</SUP> K). This can explain
both the LTRs and HTRs associated with coronal holes.
---------------------------------------------------------
Title: Propagating Waves in the Chromospheric Network
Authors: Gömöry, P.; Rybák, J.; Kučera, A.; Curdt, W.; Wöhl, H.
2007ASPC..368..133G Altcode:
Wave modulation of ultraviolet emissions originated in and above quiet
chromospheric network is studied. In particular, cross-correlation,
wavelet analysis and phase difference analysis of the intensities
as well as the Doppler shifts of emission lines of He I 584.33 Å
(chromosphere), O V 629.73 Å (transition region) and Mg IX 368.07 Å
(corona) are employed to study waves at different heights and their
direction of propagation. The results are interpreted as evidence of
compressive waves that propagate downward from the transition region
to the chromosphere in the observed chromospheric network. Different
scenarios regarding the origin and source localization of these waves
are discussed.
---------------------------------------------------------
Title: Solar Rotation Velocity Determined by Coronal Bright Points -
New Data and Analysis
Authors: Mulec, M.; Brajša, R.; Wöhl, H.; Hanslmeier, A.; Vršnak,
B.; Ruždjak, V.; Hochedez, J. -F.; Engler, J.
2007CEAB...31....1M Altcode:
Full-disc solar images obtained with the Extreme Ultraviolet Imaging
Telescope on board the Solar and Heliospheric Observatory were used
to analyse solar differential rotation determined by tracing coronal
bright points. Rotation velocity residuals, meridional motions and
their relationship are investigated for a new data set from October
1, 1999 to March 31, 2000. Further we take care for the evolution
of the single structures, dividing them into Point-Like-Structures,
Small Loops and Small Active Regions and analysing their variation in
intensity and size.
---------------------------------------------------------
Title: On the Visibility of Coronal Holes in Microwaves
Authors: Brajša, R.; Benz, A. O.; Temmer, M.; Jurdana-Šepić, R.;
Šaina, B.; Wöhl, H.; Ruždjak, V.
2007CEAB...31..219B Altcode:
Previous observations indicate that coronal holes generally appear as
low brightness temperature regions in microwaves. However, within their
borders local enhancements of radiation often occur. This is confirmed
by comparing a full-disc solar image obtained at 37 GHz on 27 May 1993
with full-disc solar images obtained at various wavelengths. Microwave
brightness temperatures of three coronal holes are determined and
interpreted.
---------------------------------------------------------
Title: Round Table Discussion about JIS
Authors: Wöhl, H.
2007CEAB...31..319W Altcode:
After the talks about the CESAR Grid and the Joint Information System
(JIS) a round table discussion was scheduled. The author, who was
the convener of the discussion was asked to summarize the discussion:
The main suggestions are to make access to JIS easier and especially
give all users unlimited access to the personal data.
---------------------------------------------------------
Title: The height dependence of temperature velocity correlation in
the solar photosphere
Authors: Koza, J.; Kučera, A.; Rybák, J.; Wöhl, H.
2007msfa.conf..139K Altcode: 2007arXiv0704.0603K
We derive correlation coefficients between temperature and line-of-sight
velocity as a function of optical depth throughout the solar photosphere
for the non-magnetic photosphere and a small area of enhanced magnetic
activity. The maximum anticorrelation of about -0.6 between temperature
and line-of-sight velocity in the non-magnetic photosphere occurs at
log [tau] 5 = -0.4. The magnetic field is another decorrelating factor
along with 5-min oscillations and seeing.
---------------------------------------------------------
Title: Spectral Characteristics of the Photosphere near a Flare
Authors: Kučera, A.; Wöhl, H.; Rybák, J.; Wu, S. T.; Wang, A. H.
2007CEAB...31...21K Altcode:
We present the temporal evolution of dynamical characteristics of the
solar photosphere in an active region near a flare. Namely, spatial
and temporal variations of Doppler velocities at different heights in
the photosphere mapped by eight photospheric lines are presented for
a time span of 45 minutes. The dynamics of the photosphere before and
during a flare which occurred nearby is discussed. <P />We found that
downward plasma motions are well pronounced up to 300 km height in the
photosphere but did not reach deeper layers. The downward velocities of
the plasma motion caused by the flare are about 1.2 km/s and they are
channelled in a thin structure - flux-tube with diameter less than 0.8
arcseconds. The velocities are better noticeable in the active parts
of the target than in the quiet ones. The magnetic configuration of
the active region is compared with the dynamics behaviour.
---------------------------------------------------------
Title: The Height Dependence of Quiet-Sun Photospheric Temperature
Fluctuations in Observations and Simulations
Authors: Koza, J.; Kučera, A.; Rybák, J.; Wöhl, H.
2006ASPC..354...43K Altcode:
We derive rms temperature fluctuations as a function of height
throughout the solar photosphere for the non-magnetic photosphere and
a small area of enhanced magnetic activity, through semi-empirical
inversion based on response functions of a 15-minute time sequence
of 118 arcsec-long slit spectrograms taken at disk center. While the
observed low photosphere shows small temperature fluctuations (about
≈ 50 K), the sub-photospheric layers and the upper photosphere
show larger fluctuations, with similar gradients as in 3-D radiation
discretionary-hydrodynamics simulations. However, the observed rms
temperature fluctuations are lower than in the simulations at all
depths, which we attribute to smearing by atmospheric seeing.
---------------------------------------------------------
Title: A New Method for Comparing Numerical Simulations with
Spectroscopic Observations of the Solar Photosphere
Authors: Rybák, J.; Kučera, A.; Wöhl, H.; Wedemeyer-Böhm, S.;
Steiner, O.
2006ASPC..354...77R Altcode:
A method for comparing high-resolution spectroscopic observations of
the solar photosphere with numerical simulations of convection in the
solar photosphere is presented. <P />It is based on the comparison of
the granular continuum contrast obtained from both the observations and
the synthetic spectra, when the latter are calculated from numerical
simulations using a particular type of data degradation. This method
can be used post facto when a minimum of auxiliary information on
characteristics of the telescope/spectrograph and on seeing conditions
is available. <P />Here, the method is applied to results of numerical
simulations computed with the CO5BOLD code and high-resolution
spectroscopic observations obtained with the VTT on Tenerife.
---------------------------------------------------------
Title: Photospheric modeling through spectral line
inversion. Temperature and radial velocity stratifications and
fluctuations
Authors: Koza, J.; Kučera, A.; Rybák, J.; Wöhl, H.
2006A&A...458..941K Altcode:
Aims.We aim to determine average radial stratifications of various
physical parameters throughout the solar photosphere at high angular
resolution for non-magnetic and magnetic areas and to compare these
with standard semiempirical 1D modeling and with 3D hydrodynamics (HD)
and magnetohydrodynamics (MHD) simulations.<BR /> Methods: .We analyse
a 15-min sequence of adaptive-optics spectrograms of very high angular
resolution taken at solar disk centre. We split the data between a
quiet area and a magnetic one and derive mean temperature and velocity
stratifications and fluctuations for these separately by applying
LTE inversion based on response functions.<BR /> Results: .The mean
temperature stratifications in the non-magnetic region agree well with
the classical 1D models and the 3D simulations at all heights. However,
the observed rms temperature is much lower than in the simulations,
the observed mean velocities indicate more upflows, and the observed
velocity fluctuations are smaller except in upper layers. Some of
the discrepancies are likely to result from remaining smearing by
atmospheric seeing and instrumental limitations. The magnetic area
shows conspicuous behaviour at large height. We also find evidence of
fast low-photosphere downflows in the magnetic area and of enhanced
temperature above a small pore.<BR />
---------------------------------------------------------
Title: Temporal Variations of the Solar Rotation Determined by
Sunspot Groups
Authors: Brajša, R.; Ruždjak, D.; Wöhl, H.
2006SoPh..237..365B Altcode: 2006SoPh..tmp...37B
The extended Greenwich data set consisting of positions of sunspot
groups is used for the investigation of cycle-related variations of the
solar rotation in the years 1874-1981. Applying the residual method,
which yields a single number for each year describing the average
deviation from the mean value of the solar rotation, the dependence
of the rotation velocity residual on the phase of the solar cycle is
investigated. A secular deceleration of the solar rotation was found:
the slope being statistically significant at the 3σ level. Periods
of 33, 22, 11, 5.2, and 3.5 years can be identified in the power
spectra. The rotation velocity residuals were averaged for all years
with the same solar cycle phase relative to the nearest preceding
sunspot minimum. The variation pattern reveals a higher than average
rotation velocity in the minimum of activity and, to a lesser extent,
also around the maximum of activity. The analysis was repeated with
several changes in the reduction method, such as elimination of the
secular trend, application of statistical weights, different cutoffs of
the central meridian distance, division of the latitude into subregions
and treating data from the years of activity minima separately. The
results obtained are compared with those from the literature, and an
interpretation of the observed phenomena is proposed.
---------------------------------------------------------
Title: Study of a Small-Scale Eruptive Event Observed by SOHO/SUMER
Authors: Tomasz, F.; Régnier, S.; Schwarz, P.; Rybák, J.; Kucera,
A.; Heinzel, P.; Curdt, W.; Wöhl
2006ESASP.617E..79T Altcode: 2006soho...17E..79T
No abstract at ADS
---------------------------------------------------------
Title: Multi-Wavelength Observations with High Resolution of a M5.4
Flare from Ground and Space
Authors: Kucera, A.; Wöhl, H.; Rybák, J.; Gömöry, P.; Veronig, A.
2006ESASP.617E..68K Altcode: 2006soho...17E..68K
No abstract at ADS
---------------------------------------------------------
Title: The Dynamics and Structure of the Solar Atmosphere As Obtained
from Combined SUMER/SOHO and TIP2/VTT Observations
Authors: Tomasz, F.; Régnier, S.; Schwartz, P.; Rybák, J.; Kucera,
A.; Heinzel, P.; Curdt, W.; Wöhl
2006ESASP.617E..78T Altcode: 2006soho...17E..78T
No abstract at ADS
---------------------------------------------------------
Title: SOHO/CDS observations of waves above the network
Authors: Gömöry, P.; Rybák, J.; Kučera, A.; Curdt, W.; Wöhl, H.
2006A&A...448.1169G Altcode:
We analyze temporal variations in the intensities and the Doppler shifts
of He i 584.33 Å (chromosphere), O v 629.73 Å (transition region),
and Mg ix 368.07 Å (corona) measured in and above chromospheric
network near disk center with the Coronal Diagnostic Spectrometer
(CDS) onboard the Solar and Heliospheric Observatory (SOHO). There is
significant correlation between the He i and O v modulations, with O v
intensity leading He i intensity by 27.3 s ± 4.6 s but no significant
time shift in the Doppler shift. Cross-correlation between the O v
and Mg ix intensities reveals multiple maxima without correlation
between their Doppler shifts. Wavelet power analysis gives evidence
of intermittent chromospheric and transition-region oscillations with
periodicities in the 250-450 s range and of coronal oscillations in
the 110-300 s range. Wavelet phase difference analysis shows that
the determined time shift between variations of the He i and O v
intensities is dominated by waves with about 300 s periodicity. We
interpret these results as giving evidence of compressive waves that
propagate downward from the transition region to the chromosphere in
the particular chromospheric network. We discuss different scenarios
regarding origin and source localization of waves, and we speculate
on their role in coronal heating above chromospheric network.
---------------------------------------------------------
Title: Acoustic Flux and Turbulence in the Solar Photosphere
Authors: Hanslmeier, A.; Kučera, A.; Rybák, J.; Wöhl, H.
2006CEAB...30...11H Altcode:
Using slit scans of solar photospheric spectral lines originating in
the middle photosphere a 2-D field on the Sun was obtained and the
occurrence of acoustic flux is investigated. As proxies for acoustic
flux generation enhanced turbulence (measured by fwhm variations) as
well as large continuum intensity values are used. The results show
that acoustic flux is not limited to the intergranular space and is
also produced by horizontal motions that may become supersonic leading
to turbulence. These motions lead to brightenings as it was predicted
by theoretical models.
---------------------------------------------------------
Title: Influence of the 5-min oscillations on solar photospheric
layers. I. Quiet region
Authors: Odert, P.; Hanslmeier, A.; Rybák, J.; Kučera, A.; Wöhl, H.
2005A&A...444..257O Altcode:
Time series of 1D spectrograms are used to study the influence of the
5-min oscillations on intensity and velocity fields of different layers
of the quiet solar photosphere. We study the continuum intensity field
along with intensity and corresponding velocity patterns of the mid and
upper photosphere, obtained from two Fe lines. Oscillations seem to
dominate the intensity and velocity fields of the higher atmospheric
layers. Our results confirm the fast decay of the granular intensity
structure with height. From correlations of temperature structures
at three different photospheric levels we conclude that there are
rapid changes of the structures in the lower photosphere, which are
valid for the duration of the time series, while for the upper levels
changes of the stuctures are fainter and show significant periodic
character. The velocity pattern, on the other hand, shows a periodic
propagation through the photosphere. The tests of the influence of
seeing conditions on the data are considered.
---------------------------------------------------------
Title: Analysis of Dynamics of Loops in AN Active Region Associated
with a Small C-Class Flare
Authors: Gömöry, P.; Rybák, J.; Kucera, A.; Wöhl, H.
2005ESASP.596E..56G Altcode: 2005ccmf.confE..56G
No abstract at ADS
---------------------------------------------------------
Title: Spatial Distribution and North-South Asymmetry of Coronal
Bright Points from Mid-1998 to Mid-1999
Authors: Brajša, R.; Wöhl, H.; Vršnak, B.; Rušdjak, V.; Clette,
F.; Hochedez, J. -F.; Verbanac, G.; Temmer, M.
2005SoPh..231...29B Altcode:
Full-disc full-resolution (FDFR) solar images obtained with the Extreme
Ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric
Observatory (SOHO) were used to analyse the centre-to-limb function and
latitudinal distribution of coronal bright points. The results obtained
with the interactive and the automatic method, as well as for three
subtypes of coronal bright points for the time period 4 June 1998 to 22
May 1999 are presented and compared. An indication of a two-component
latitudinal distribution of coronal bright points was found. The
central latitude of coronal bright points traced with the interactive
method lies between 10<SUP>∘</SUP> and 20<SUP>∘</SUP>. This is
closer to the equator than the average latitude of sunspots in the
same period. Possible implications for the interpretation of the
solar differential rotation are discussed. In the appendix, possible
differences between the two solar hemispheres are analysed. More coronal
bright points were present in the southern solar hemisphere than in
the northern one. This asymmetry is statistically significant for the
interactive method and not for the automatic method. The visibility
function is symmetrical around the central meridian.
---------------------------------------------------------
Title: The Influence of the Evolution of Sunspot Groups on the
Determination of the Solar Velocity Field
Authors: Ruždjak, D.; Brajša, R.; Sudar, D.; Wöhl, H.
2005SoPh..229...35R Altcode:
Meridional motions and differential rotation of stable recurrent
sunspot groups from the Greenwich data set are investigated. Simple
and complex, as well as younger and older sunspot groups are treated
separately. There is no difference in behavior of the meridional
motions for the simple and complex sunspot groups, while complex groups
rotate faster than the simple ones. If we attribute the differences of
rotational velocities to the errors in position determination, it can be
concluded that the rotational velocities determined by using sunspot
groups as tracers are slightly overestimated. Both the meridional
motions and differential rotation show the same dependence on the age,
when simple and complex recurrent sunspot groups are considered.
---------------------------------------------------------
Title: Analysis of Doppler Shifts of Spectral Lines Obtained by the
CDS/SOHO Instrument
Authors: Gömöry, P.; Rybák, J.; Kučera, A.; Curdt, W.; Wöhl, H.
2005ASSL..320..203G Altcode: 2005smp..conf..203G
No abstract at ADS
---------------------------------------------------------
Title: On the Behaviour of a Blinker in Chromospheric and Transition
Region Layers
Authors: Tomasz, F.; Rybák, J.; Kučera, A.; Curdt, W.; Wöhl, H.
2005ASSL..320..207T Altcode: 2005smp..conf..207T
No abstract at ADS
---------------------------------------------------------
Title: Variability and Dynamics of the Outer Atmospheric Layers in
the Quiet Solar Network
Authors: Gömöry, P.; Rybák, J.; Kučera, A.; Curdt, W.; Wöhl, H.
2005HvaOB..29...71G Altcode:
A detailed study of the temporal evolution of the chromospheric He
I 584.33 Å and the transition region O V 629.73 Å emission line
intensities of quiet supergranular network of the Sun near disk centre
observed with Coronal Diagnostic Spectrometer (CDS) is presented. A
wavelet analysis of the 1729 s (28.8 min) long temporal series was
performed in order to derive the duration as well as periods of the
chromospheric and the transition region oscillations. The He I line
intensities show significant power for periods around 300 s (3.3 mHz),
which is relevant only in the second half of the observing sequence
(between 800 -- 1700 s). The temporal evolution corresponding to the
O V line intensities shows strong power around the period of 400 s
(2.5 mHz), which is significant during the whole observing sequence
as well as the oscillation of lower power for periods of around 250 s
(4.0 mHz), which is present only in the middle of the observing sequence
(between 700 -- 1300 s).
---------------------------------------------------------
Title: High Resolution Observations of a M5.4 Flare
Authors: Kučera, A.; Wöhl, H.; Rybák, J.; Gömöry, P.; Tomasz, F.
2005HvaOB..29..177K Altcode:
Hα observations of a M5.4 flare taken in the active region NOAA 10646
with the Vacuum Tower Telescope at Observatório del Teide, Tenerife,
on July 13, 2004 are presented. The temporal evolution of the area
of the flare and its morphological changes are investigated and
discussed. Simultaneous observations of the flare in EUV lines taken
with CDS/SOHO instrument are shown and additional data from GOES-10
instrument are compared.
---------------------------------------------------------
Title: The Old Archives of Solar Images of the Former Frauenhofer
Institut (now: Kiepenheuer-Institut für Sonnenphysik, KIS)
Authors: Wöhl, H.
2005HvaOB..29..319W Altcode:
The inspection of more than 28 000 solar images of the Sun which were
recorded on glass plates 1939 until 1977 for the archives of the former
Fraunhofer Institut (now: Kiepenheuer- Institut für Sonnenphysik,
KIS) is described. Some statistics of inspected and selected images are
given. The digitization and further usage of the integral images, H{_α}
images and Ca II K3 images are discussed. Some examples of digitized
images are also given. Finally the fitting of these reductions in
present scientific projects and the possible storage of digital solar
data are mentioned.
---------------------------------------------------------
Title: Die Archive solarer Integralaufnahmen und von
Spektroheliogrammen des früheren Fraunhofer-Instituts (jetzt:
Kiepenheuer-Institut für Sonnenphysik) in Freiburg und ihre
teilweise Auflösung
---------------------------------------------------------
Title: Die Archive solarer Integralaufnahmen und
von Spektroheliogrammen des früheren Fraunhofer-Instituts (jetzt:
Kiepenheuer-Institut für Sonnenphysik) in Freiburg und ihre teilweise
Auflösung
---------------------------------------------------------
Title: The archives of solar integral exposures and of
spectroheliograms of the former Fraunhofer Institute (now: Kiepenheuer
Institute for Solar Physics) in Freiburg and its partial dissolution
Authors: Wöhl, Hubertus
2005AcHA...25..229W Altcode:
The former Fraunhofer-Institut which was founded about 60 years ago
and since 1978 is named Kiepenheuer-Institut für Sonnenphysik (KIS),
has been for several decades a center to collect information about
solar activity. One of the reasons for interest in solar activity
were in the beginning attempts to forecast disturbances of (military)
radio communication caused by solar eruptions. This would today be
called ‘space weather research’. Later daily maps of the sun -
showing its activity - were edited for many years. The data needed to
describe solar activity were gained mainly from photographic images:
Since 1939 white light images of the full solar disk were collected
and stored in the archive. Since 1943 in addition spectroheliograms of
the full solar disk in H-alpha and in Ca II K3 were collected. These
images were taken on glass plates (some on film) of sizes 9 x 12 cm in
the case of the white light images and of sizes 6 x 12 cm in the case
of the spectroheliograms and were stored in envelopes with additional
information written on them. Several hundred of these plates in their
envelopes were combined in open wooden boxes each. These boxes were
stored in open shelfs in a meeting room of the old solar observatory
on the Schauinsland mountain near Freiburg. Within the last years it
became obvious that the quality of many plates stored was bad and that
the possible scientific usage was becoming very limited. In summer
2002 I started to investigate the quality of the white light images
and prepared a data base in MS ACCESS XP about the plates I found
which were observed at more than 10 different observing places. The
total number of plates checked was 11782. Depending on the quality
and possible later usage for an investigation of proper motions in
sunspot groups I kept several series of them. Most of the plates kept
stem from the years 1945 until 1949 and 1955 until 1959 - when the solar
activity was extremely high. In total about 2000 plates were kept. It is
intended to digitize as many as possible of these selected plates using
a high precision scanner for transparencies. Some examples of digitized
images are already available. More details can be found in a text about
the history of the Fraunhofer-Institut in the WWW pages of the KIS
at: <A href="http://www.kis.uni-freiburg.de/kisgeschichte_e.html">
http://www.kis.uni-freiburg.de/kisgeschichte_e.html</A> In summer
2003 I started to investigate the quality of the spectroheliograms on
glass plates and to prepare another data base of the material I find
in the archive.
---------------------------------------------------------
Title: Die Archive solarer Integralaufnahmen und von
Spektroheliogrammen des früheren Fraunhofer-Instituts (jetzt:
Kiepenheuer-Institut für Sonnenphysik) in Freiburg und ihre teilweise
Auflösung
Authors: Wöhl, Hubertus
2005dsr..conf..229W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Influence of Transition Region Blinker on the Surrounding
Chromospheric and Coronal Plasma
Authors: Tomasz, F.; Rybák, J.; Kučera, A.; Curdt, W.; Wöhl, H.
2005HvaOB..29..197T Altcode:
Results of spectral analysis of a blinker observed in the transition
region O VI 1037.63 Å line and in the chromospheric Ly β 1025.72
Å line which were acquired using the SUMER spectrometer are
presented. Chromospheric and coronal plasma in the vicinity of the
blinker are investigated using also TRACE Ly α, UV continuum and Fe IX
channels. It was found that initial release of energy was localized in
the transition region and plasma has been spreading from transition
region as a bi-directional jet. Energy reached chromosphere ∼60
seconds after primary emission in the o6 line. There were detected
enhanced emissions for about 25-38% in the chromospheric Lyα and UV
continuum. Spatial extent of the blinker response is 6” along the slit
in the Lyα filtergram what is ∼3” less than extent of the blinker
in the o6 line. Maximum extent of the blinker response is 7.5” in
Lyα filtergram. Although, both Lyα and UV continuum reflect physical
conditions in chromosphere, their patterns are completely different:
pattern of the blinker response is compact in the Lyα and UV continuum
shows non-compact structure below the transition region blinker. Coronal
plasma was not influenced by the blinker although plasma moving toward
observer was detected in the final phase of evolution of the blinker.
---------------------------------------------------------
Title: Observational Evidences for Heating of the Solar Corona
by Nanoflares in the Network Derived from the Transition Region
Spectral Lines
Authors: Rybák, J.; Kucera, A.; Curdt, W.; Wöhl, H.
2004ESASP.575..529R Altcode: 2004soho...15..529R
No abstract at ADS
---------------------------------------------------------
Title: Dynamics of the Quiet Upper Solar Atmosphere in the Network
Authors: Gömöry, P.; Rybák, J.; Kucera, A.; Curdt, W.; Wöhl, H.
2004ESASP.575..400G Altcode: 2004soho...15..400G
No abstract at ADS
---------------------------------------------------------
Title: Detection of neutral sodium above Mercury during the transit
on 2003 May 7
Authors: Schleicher, H.; Wiedemann, G.; Wöhl, H.; Berkefeld, T.;
Soltau, D.
2004A&A...425.1119S Altcode:
The extent of the exosphere of Mercury above the planet's limb could
for the first time be observed by detecting an excess absorption
in the solar sodium line D_2 during the transit of Mercury across
the solar disk on 2003 May 7. The <P />observations were performed
with a 2d Fabry-Perot spectrograph of the Vacuum Tower Telescope
at Izaña, Tenerife. The absorption excess, blue-shifted by 13 pm
relative to the solar line, is mainly concentrated near the polar
regions. There, <P />the absorption excess can be traced up to
≈700 km above the limb. Between the two polar regions, along the
eastern limb, a weaker absorption excess can be seen. A possible
streamer-like feature stretches more than 2000 km above the northern
region. Assuming the density to decrease exponentially with height,
we derive for the polar maxima vertical column densities of 3 ×
10<SUP>10</SUP> cm<SUP>-2</SUP>, volume densities at the surface of 2.5
× 10<SUP>3</SUP> cm<SUP>-3</SUP>, and a density scale height of 150 km.
---------------------------------------------------------
Title: Two-dimensional spectroscopic time series of solar granulation
Authors: Hanslmeier, A.; Kucera, A.; Rybák, J.; Wöhl, H.
2004SoPh..223...13H Altcode:
In this paper we investigate the dynamics of the solar granulation
by analyzing time series of 2D spatially highly resolved
spectrograms. These were obtained by spatial scans covering a field
of 12 8″ × 20″. The advantage of this method is a high spectral
resolution, however, the data are not taken simultaneously and to
cover the field described above 50 exposures taken sequentially in
time are necessary. Therefore, to obtain one map about 2 minutes are
required. Plots of the evolution of different line parameters are
given as well as the decay of correlation functions. The correlations
between the first map of line parameters and successive maps (which are
separated by about 2 minutes) were investigated showing a rapid decay
down to a correlation coefficient of 0.4 within 4 minutes, the velocity
pattern in the field observed varies on smaller time scales. The
temporal variation of correlation between the line parameters for the
different lines shows a periodic signal related to 5-min oscillations
which could not be totally filtered. The evolution of the correlation
functions between line parameters is analyzed which gives an error
estimate of all correlation values found in the literature. For
the first time it is explicitly shown how evolution in a selected
photospheric field influences the evolution of granular/intergranular
structures.
---------------------------------------------------------
Title: Indications of shock waves in the solar photosphere
Authors: Rybák, J.; Wöhl, H.; Kučera, A.; Hanslmeier, A.;
Steiner, O.
2004A&A...420.1141R Altcode:
High resolution observations of solar granulation near the solar limb
are used in a search for hydrodynamic shocks caused by an abrupt
braking of the fast (probably supersonic) horizontal flow of the
granular plasma towards the intergranular lane. Shock signatures in
the spectral line of Fe II 6456.38 Åof one particular observed shock
event are investigated in detail. Evolution, amplitude, and spatial
relation of the spectral line characteristics of the shock event are in
agreement with predictions from numerical simulations for such shock
phenomena in the solar photosphere. The dimensions and amplitudes of
the observed shock signatures are comparable to predicted values when
seeing and instrumental effects as well as a possible obliqueness of
the shock front with respect to the observer's line-of-sight are taken
into account. The temporal evolution of such an event is observed for
the first time. The stable and declining phase of the event were studied
for a time period of almost 2 min. A particular relationship was found
between the shock event and a nearby G-band bright point located 2”
from the shock event. It is suggestive that the observed shock is a
causal consequence of the magnetic flux concentration, traced by the
G-band bright point. Such a type of shock can appear outside the flux
concentrations as a consequence of a rapid flux-tube motion.
---------------------------------------------------------
Title: Deceleration of the rotational velocities of sunspot groups
during their evolution
Authors: Ruždjak, D.; Ruždjak, V.; Brajša, R.; Wöhl, H.
2004SoPh..221..225R Altcode:
Using the Greenwich Photoheliographic Results for the years
1874-1976 the daily rotational velocities for 955 recurrent and 13169
non-recurrent sunspot groups from the first day of their appearance and
during their evolution have been determined. The rotational velocities
were divided in six latitude strips with a width of five degrees and
grouped according to the age of the groups. It was established that
the rotational velocities of recurrent and non-recurrent sunspot
groups decrease with time in all studied latitude strips. At their
birth the recurrent spot groups rotate faster by about 0.15°
day<SUP>−1</SUP> than the non-recurrent ones and settle, within
the errors of measurements, to an about 0.5° day<SUP>−1</SUP>
slower velocity value during the second disc passage. A comparison
of our results with helioseismology measurements indicates that in
the frame of the anchoring hypothesis, the recurrent sunspot groups
at their birth could be coupled to the fast rotating layer at about
r=0.93 R<SUB>⊙</SUB>.
---------------------------------------------------------
Title: Height correction in the measurement of solar differential
rotation determined by coronal bright points
Authors: Brajša, R.; Wöhl, H.; Vršnak, B.; Ruždjak, V.; Clette,
F.; Hochedez, J. -F.; Roša, D.
2004A&A...414..707B Altcode:
Full-disc solar images obtained with the Extreme Ultraviolet Imaging
Telescope (EIT) on board the Solar and Heliospheric Observatory
(SOHO) are used to analyse solar differential rotation by tracing
coronal bright points for the period June 4, 1998 to May 22, 1999. A
method for the simultaneous determination of the true solar synodic
rotation velocity and the height of the tracers is applied to data
sets analysed with interactive and automatic methods. The calculated
height of coronal bright points is on average 8000-12000 km above
the photosphere. Corrected rotation velocities are transformed
into sidereal ones and compared with results from the literature,
obtained with various methods and tracers. The differential rotation
profile determined by coronal bright points with the interactive method
corresponds roughly to the profile obtained by correlating photospheric
magnetic fields and the profile obtained from the automatic method
corresponds roughly to the rotation of sunspot groups. This result is
interpreted in terms of the differences obtained in the latitudinal
distribution of coronal bright points using the two methods.
---------------------------------------------------------
Title: On Relations among the Calibrated Parameters of the Transition
Region Spectral Line
Authors: Rybák, J.; Kucera, A.; Curdt, W.; Wöhl, H.
2004ESASP.547..311R Altcode: 2004soho...13..311R
SUMER/SOHO measurements of the O VI 1031.93 Å emission line (280000
K) in the network and internetwork of the transition region of the
quiet solar atmosphere are used for a statistical analysis of the
calibrated spectral parameters: the central line intensity (energetic
units), the line width (m Å) and the Doppler shift (km/s). A detailed
procedure is performed in order to determine the absolute wavelength
calibration of the spectra and Doppler shifts using simultaneously
observed chromospheric O I 1027.44 Å and 1028.15 Å emission lines
(10 000K). The spectral parameters of the O VI line are derived for
both single and double Gaussian fitting of the line according to the
latest findings on the multi-component nature of the transition region
line profiles. Reliability of the absolute wavelength calibration and
effects of two classes of the transition region transient events -
explosive events and blinkers - are discussed in relation to the
overall dependencies of the spectral parameters.
---------------------------------------------------------
Title: Exosphere of Mercury seen as additional absorption in the Na
D2 line during the Transit on 2003 May 7.
Authors: Schleicher, H.; Wiedemann, G.; Woehl, H.; Berkefeld, T.;
Soltau, D.
2004ANS...325...81S Altcode: 2004ANS...325a..81S; 2004ANS...325..P05S
No abstract at ADS
---------------------------------------------------------
Title: On Mutual Relation Among the Outer Atmospheric Layers in
Network: SOHO/CDS Study
Authors: Gömöry, P.; Rybák, J.; Kucera, A.; Curdt, W.; Wöhl, H.
2004ESASP.547..303G Altcode: 2004soho...13..303G
SOHO/CDS measurements of emission in the network of the quiet solar
atmosphere near disk center were used to derive mutual relations
of emission and dynamics in different temperature regimes in/above
supergranular network. Cross-correlation functions of the line
intensities and the Doppler shifts of the chromospheric line He I 584.3
Å, the transition region line O V 629.7 Å and the coronal line Mg
IX 396.1 Å were calculated in order to study relative variability
of different atmospheric layers. Relatively high correlations were
found between the intensities and the Doppler shifts of the He I and
O V lines with two peaks of the intensity correlation function. The
maximum value of the correlation of intensities (CC = 0.86) was reached
for the zero time lag and the second maximum (CC = 0.78) was obtained
for the time lag -190s (O V precedes He I). Only one sharp peak (CC =
0.55) was detected in the Doppler shift correlation function of these
lines for the zero time lag. For the correlation of O V and Mg IX
intensities one peak (CC = 0.57) of the correlation function was also
discovered for the time lag +150s (Mg IX falls behind O V). In contrast,
no correlation was obtained for the Doppler shifts of the O V and Mg
IX lines. Summarizing we can assume clear relation in energy transfer
and/or mass motion between chromosphere and transition region but no
relation was found between corona and the lower parts of the solar
atmosphere above the particular network under study.
---------------------------------------------------------
Title: Velocity field in the intergranular atmosphere
Authors: Kučera, A.; Koza, J.; Bellot Rubio, L. R.; Hanslmeier, A.;
Rybák, J.; Wöhl, H.
2004HvaOB..28...19K Altcode:
The line-of-sight velocity ľand macroturbulent velocity are studied
in the centre of the intergranular space in the solar photosphere. An
inversion method is applied to a 4-min time sequence of Stokes
I spectra of the 5, 6 and 7 lines observed with high spatial and
temporal resolutions at solar disk centre. The results are presented
in the form of the functional dependence of ľ(logτ<SUB>5</SUB>,t)
and (t) on the continuum optical depth τ<SUB>5</SUB> at 500 nm and
time t. A ľof several hundreds of meters per second was found in the
upper photosphere (logτ<SUB>5</SUB>≤-1.5), where the plasma flows
away from the observer. On the contrary, upflows directed toward the
observer were found in deeper layers (logτ<SUB>5</SUB>>-1.5). The
typical value of in the centre of the intergranular space is found to be
∼1.7 kms, which is about 0.5 kms greater than in the adjacent granule.
---------------------------------------------------------
Title: SUMER/SOHO and TRACE Study of the Transition Region Blinker
Authors: Tomasz, F.; Rybák, J.; Kucera, A.; Curdt, W.; Wöhl, H.
2004ESASP.547..307T Altcode: 2004soho...13..307T
The most prominent transient event is presented from an extensive
search for the transition region internetwork activity in the quiet
solar atmosphere performed by SUMER/SOHO spectrometer and TRACE. SUMER
spectra of Ly line (1025.4 Å), two C II lines (1036.3 Å, 1037.0 Å)
and O VI line (1037.61 Å) were used for determination of the spatial
and temporal evolution of the transient event in the transition
region. TRACE images taken in the 1216 Å passband, UV continuum
(1700 Å) and Fe IX line (171 Å) were utilized in order to gain
information about large-scale coronal structures and small-scale
chromospheric variability in the vicinity of the transient event. The
main physical and geometrical parameters of the event were derived
for the transition region O VI line: the spatial extent of 11 000 km,
duration for 9 minutes, intensity enhancement factor of 7 and the
Doppler velocities of both signs up to 15 km/s. According to these
values the event was identified as a transition region blinker. High
deviations of the acquired O VI line profiles from single-Gaussian and
some multi-Gaussian profiles reveal dynamics of the event - occurrence
of the bidirectional jet which is not typical for blinkers. Besides
rapid changes in intensity and in velocity, a rapid increase by a
factor of 4.2 was found in the Gaussian width of O VI line as compared
to the internetwork. Surrounding chromospheric and coronal structures
around the event are discussed on base of the simultaneously taken
TRACE images.
---------------------------------------------------------
Title: One-dimensional spectroscopy of the solar photosphere
Authors: Odert, P.; Hanslmeier, A.; Rybák, J.; Kučera, A.; Wöhl, H.
2004HvaOB..28...37O Altcode:
Data from a time series of spectrograms were used to study
correlative relationships between intensity and velocity in the solar
photosphere. The variations along the slit of the line parameters from
two Fe lines lying in the visible range of the spectrum were used. The
formation height difference of these lines is over 300 km. The temporal
variations of the correlation coefficients were studied, they showed
a strong influence of the 5 min-oscillations.
---------------------------------------------------------
Title: Variation of the solar rotation during the activity cycle
applying the residual method to Greenwich data
Authors: Brajša, R.; Wöhl, H.; Ruždjak, D.; Schawinski-Guiton, K.
2004HvaOB..28...55B Altcode:
The Greenwich data set consisting of positions of sunspot groups was
used for the investigation of possible cycle-related variations of the
solar rotation in the years from 1874 to 1976. The measurements were
extended with the USAF/SOON and NOAA data for the years 1977--1981. The
residual method providing yearly deviations from the mean rotation
velocity (averaged over all years) for each 5-deg latitude band was
applied. These deviations were averaged over latitudes and yearly
residuals were calculated. A dependence of the rotation velocity
residual on the phase of the solar cycle was found and compared with
results from the literature.
---------------------------------------------------------
Title: Proper motions of sunspots - new data and further results
Authors: Wöhl, H.; Brajša, R.; Kučera, A.; Ruždjak, V.; Rybák, J.
2004HvaOB..28...47W Altcode:
The attempts to investigate patterns of motions of main spot components
and small pores in complex sunspot groups were continued. The data
discussed stem mainly from observations at Hvar/HR and Tatranská
Lomnica/SK. Two historic collections of photographic plates are
included: The plate archives of the former Fraunhofer Institute and
that of photographic plates taken at Skalnate Pleso/SK.
---------------------------------------------------------
Title: Extracting the apparent motion from two successive EIT images
Authors: Gissot, Samuel F.; Hochedez, J. -F.; Dibos, F.; Brajša,
R.; Jacques, L.; Berghmans, D.; Zhukov, A.; Clette, F.; Wöhl, H.;
Antoine, J. -P.
2003ESASP.535..853G Altcode: 2003iscs.symp..853G
The EIT observations cover more than seven years of the 23rd solar
cycle. The main synoptic dataset, usually refered to as the "CME
Watch", is a nearly uninterrupted sequence of images taken in the Fe
XII bandpass at a cadence of four images per hour. In this work we
study motion tracking methods in order to estimate displacements from
frame to frame. We have implemented a novel optical flow algorithm,
and tested it on a couple of successive images. We have linked the
apparent motion occurring between two frames to the expected rotation
rate. On this short time scale (20 minutes), we are able to retrieve
the global parameters of the solar differential rotation. A strategy
for the extraction of region with reliable motion will be discussed.
---------------------------------------------------------
Title: Velocity Field of a Complex Sunspot with Light Bridges
Authors: Schleicher, H.; Balthasar, H.; Wöhl, H.
2003SoPh..215..261S Altcode:
For the leading part of sunspot group NOAA 8323, which rapidly changed
its complex structure, a time series of the line-of-sight (LOS)
component of the velocity field was obtained. With a two-dimensional
Fabry-Pérot spectrometer, the magnetically insensitive line Fe i
557.6 nm was scanned. The inclination of the LOS (heliographic angle)
to the vertical was θ=28.5°. The umbra of the observed spot was
divided by a system of light bridges into several parts. The spatial and
temporal velocity field also exhibits a considerable complexity: in one
extended umbral area there is a downward flow of 1 km s<SUP>−1</SUP>
relative to other dark sub-umbrae. At the center-side penumbra,
with a line-of-sight Evershed outflow of 1.5 km s<SUP>−1</SUP>,
a persistent patch, somewhat darker than the average penumbra, has
a LOS velocity of 1.3 km s<SUP>−1</SUP> in opposite direction,
probably a downflow. At the limb-side penumbra, a photosphere-like
area is interspersed, interrupting the Evershed flow which resumes
with typical strength beyond this feature towards the outer penumbral
boundary. Most interesting is the behavior of the light bridges, which
have a slight blue shift, interrupted by short events of strong blue
or red shifts which - within the time resolution of 35 s - instantly
affect a considerable part of a light bridge.
---------------------------------------------------------
Title: Mercury Transit Observed with TESOS at the VTT on Tenerife
Authors: Schleicher, Helmold; Wöhl, Hubertus; Balthasar, Horst
2003ANS...324..114S Altcode: 2003ANS...324..P21S
No abstract at ADS
---------------------------------------------------------
Title: Properties of the solar velocity field indicated by motions
of coronal bright points
Authors: Vršnak, B.; Brajša, R.; Wöhl, H.; Ruždjak, V.; Clette,
F.; Hochedez, J. -F.
2003A&A...404.1117V Altcode:
Full-disc solar images obtained with the Extreme Ultraviolet Imaging
Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO)
are used to analyse properties of the solar velocity field by tracing
coronal bright points from June 4, 1998 to May 22, 1999. Rotation
velocity residuals, meridional motions and their relationship are
investigated. Zones of slow and fast rotation found in motions of
coronal bright points are consistent with the pattern of torsional
oscillations, indicating that the statistical velocity pattern
of bright point motions reflects the large-scale plasma flows. A
complex pattern of meridional motion is deduced: The equatorward
flows are found to dominate at low (B<10<SUP>deg</SUP>) and high
(B>40<SUP>deg</SUP>) latitudes, whereas at mid-latitudes (B~
10<SUP>deg</SUP>-40<SUP>deg</SUP>) a poleward flow is inferred. The
complete data set shows no significant correlation between rotation
residuals and meridional motions. However, when a subsample of
coronal bright points including only the “point-like structures”
(predominantly young bright points) is considered, a statistically
significant correlation is found. On average, faster tracers show
equatorward motion and the slower ones show poleward motion. Such
a segregation is reflected in a statistically significant
covariance of the rotation residuals and meridional velocities
in the order of -1000 m<SUP>2</SUP> s<SUP>-2</SUP>, revealing an
equatorward transport of angular momentum. The negative value of the
covariance is provided by the high velocity tail in the velocity
distribution of point-like structures, representing less than 15%
of the population. The latitude dependence of the covariance can be
expressed as Q=-62 B + 200 m<SUP>2</SUP> s<SUP>-2</SUP> covering the
range B=0<SUP>deg</SUP>-60<SUP>deg</SUP>.
---------------------------------------------------------
Title: Dynamics and turbulence of the chromospheric layers of a
flaring atmosphere
Authors: Brčeková, K.; Kučera, A.; Hanslmeier, A.; Rybák, J.;
Wöhl, H.
2003AN....324..366B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar rotation velocity determined by coronal bright points
Authors: Brajša, R.; Wöhl, H.; Vršnak, B.; Ruždjak, V.; Clette,
F.; Hochedez, J. F.; Roša, D.; Hržina, D.
2003HvaOB..27...13B Altcode:
Full-disc solar images in the extreme ultraviolet part of the spectrum
from the SOHO spacecraft (instrument EIT, data in the spectral line of
Fe XV at a wavelength of 28.4 nm) are used to identify and trace coronal
bright points with the interactive and automatic method. The Solar
rotation was determined for the period June 4, 1998 to May 22, 1999
and a two-step velocity filter was applied. Histograms of latitudinal
and central meridian distance distributions of coronal bright points,
for both solar hemispheres treated together (north and south, east and
west), are presented and compared for different reduction procedures.
---------------------------------------------------------
Title: Transition region blinker - spatial and temporal behaviour
Authors: Tomasz, F.; Rybák, J.; Kučera, A.; Curdt, W.; Wöhl, H.
2003HvaOB..27...75T Altcode:
From an extensive search for transition region internetwork activity
in the quiet Sun atmosphere the most prominent transient event is
presented. The basic physical and geometrical parameters of this event
are derived from the O VI 1037.61 Å emission spectral line. The spatial
extent of 11 000 km, duration for 9 minutes, intensity enhancements
factor of 7 and large Doppler velocities of both signs were estimated
for the event. According to these values this event was identified as
a transition region blinker.
---------------------------------------------------------
Title: Proper motions of sunspot groups
Authors: Wöhl, H.; Brajša, R.; Kučera, A.; Ruždjak, V.; Rybák, J.
2003HvaOB..27....1W Altcode:
Attempts to investigate typical patterns of motions of main spot
components and small pores in complex sunspot groups are described. The
data used up to now stem from observations at Hvar/HR, Tatranská
Lomnica/SK, Izaña/E, Debrecen/H and from the MDI instrument on
SoHO. Preliminary results are presented.
---------------------------------------------------------
Title: Evolution of temperature in granule and intergranular space
Authors: Koza, J.; Bellot Rubio, L. R.; Kučera, A.; Hanslmeier, A.;
Rybák, J.; Wöhl, H.
2003AN....324..349K Altcode:
The temporal evolution of temperature in a dissolving granule and
in an adjacent intergranular space is presented. The semi-empirical
evolutionary models have been calculated using an inversion method
applied to 4-min time series of Stokes I spectral line profiles. The
models are presented in the form of the functional dependence of
temperature T(log tau_5 ,t) on optical depth tau_5 at 500 nm and time
t. The observed disappearance of the granule is accompanied with overall
cooling of the granular photosphere. Temperature changes greater than
100 K have been found in deeper (log tau_5 >=0) and upper layers
(log tau_5 <=-2) whereas the intermediate layers are thermally
stable. The intergranular space, which is 2 arcsec off the granule,
keeps the temperature structure of the layers from log tau_5 =0.5 to
log tau_5 =-2 without global evolutionary changes except short-term
and spatially confined heating. Finally, the significant temperature
changes in the upper layers (log tau_5 <=-2.5) observed during the
time interval of 4 min are found to be typical for the granular and
intergranular photosphere.
---------------------------------------------------------
Title: Observational evidence for a shock event in the solar
granulation
Authors: Kučera, A.; Rybák, J.; Hanslmeier, A.; Wöhl, H.
2003HvaOB..27...25K Altcode:
High resolution spectra of Fe II 6456.39 Å line are used to investigate
a shock in the solar granulation. The changes of the main spectral
characteristics measured in the shock area are in a good agreement with
the characteristics predicted with theory. The analysis of the shock,
made in the past by several authors was extended in this work to the
analysis of a temporal development of the shock event. The 2 minutes
duration of a stable and declining phases of the event was studied. We
conclude that the observed shock belonged to the particular type of
shock generated as a consequence of the swaying motion of the magnetic
flux tube concentrated in the intergranular lane. Such type of shock
was proposed by numerical simulations made by Steiner et al. 1998.
---------------------------------------------------------
Title: Transition region eruptive event observed with SOHO/CDS in
the quiet Sun network
Authors: Gömöry, P.; Rybák, J.; Kučera, A.; Curdt, W.; Wöhl, H.
2003HvaOB..27...67G Altcode:
CDS observations of the quiet Sun network in the chromospheric He I
584.33 Å and transition region O V 629.73 Å emission lines over
a time period of ∼ 29 min are presented. One eruptive event was
detected in this time series of data. The parameters of the network
eruptive event are derived and the type of this small-scale activity
is identified. The lifetime of the event was ∼ 1 min and it was
found only in the transition region emission line. This event had no
chromospheric counterpart. All O V spectral profiles of the eruptive
event were blueshifted and the maximal Doppler shift was -14.7 km
s<SUP>-1</SUP>. During an initial phase of the eruptive event, the
O V intensity enhancement factor was 2.3. These parameters indicate
that the observed event could be a transition region explosive event
but measured with the limited resolution of the CDS instrument.
---------------------------------------------------------
Title: Line intensities of chromospheric and photospheric spectra
of a flare
Authors: Brčeková, K.; Kučera, A.; Hanslmeier, A.; Rybák, J.;
Wöhl, H.
2002ESASP.506..557B Altcode: 2002ESPM...10..557B; 2002svco.conf..557B
In this work we present the intensities of spectral lines determined
from the time series of high resolution spectra obtained during
the relaxing phase of subflare. The spectra were taken in the core
of chromospheric Ca II K line and in two photospheric Fe I 522.5 nm
and Fe I 557.6 nm lines. It is shown, that the energy of the flaring
chromosphere slightly affects the underlying photospheric layers by
heating a small area right under the core of the subflare.
---------------------------------------------------------
Title: Two-dimensional spectroscopic time series of solar granulation:
evolution of individual granules
Authors: Hanslmeier, Arnold; Kučera, Ales; Rybák, Jan; Wöhl,
Hubertus
2002ESASP.506..633H Altcode: 2002svco.conf..633H; 2002ESPM...10..633H
In this paper we investigate the dynamics of the solar granulation by
analyzing time series of 2-D spatially highly resolved spectrograms. The
high quality of the data permitted us to follow the evolution of
individual granular and intergranular areas. We used scans over the
solar surface in order to obtain a 2-D information. This has the
advantage of achieving high spectral and spatial resolution, however
one scan lasted for about 2 min.
---------------------------------------------------------
Title: Line-of-sight velocity in a semiempirical model of a
disappearing granule
Authors: Koza, J.; Bellot Rubio, L. R.; Kučera, A.; Hanslmeier, A.;
Rybák, J.; Wöhl, H.
2002ESASP.506..443K Altcode: 2002svco.conf..443K; 2002ESPM...10..443K
The behaviour of the line-of-sight velocity in the centre of a
disappearing granule is analyzed using an inversion method applied
to a time-series of spectra containing the Fe I 522.5 nm, 557.6
nm and 557.7 nm lines. The temporal evolution of the line-of-sight
velocity v<SUB>LOS</SUB> is presented in the form of the functional
dependence of v<SUB>LOS</SUB>(logτ<SUB>5</SUB>, t) on the optical
depth τ<SUB>5</SUB> at 500 nm and time t. An oscillatory behaviour
is found in the velocity stratification with nearly constant phase
through the photosphere. The amplitude of variations increases from
logτ<SUB>5</SUB> = -0.3 to logτ<SUB>5</SUB> = -2.5 reaching a maximum
of ~1.2 km s<SUP>-1</SUP>. A zero velocity layer is detected in every
instantaneous model of the velocity stratification. The results suggest,
that the zero velocity may occur in a considerable range of the optical
depths from logτ<SUB>5</SUB> ~ -2 to logτ<SUB>5</SUB> ~ -3.5.
---------------------------------------------------------
Title: Precise reduction of solar spectra obtained with large
CCD arrays
Authors: Wöhl, H.; Kučera, A.; Rybák, J.; Hanslmeier, A.
2002A&A...394.1077W Altcode:
A precise procedure suitable for the reduction of solar spectra
taken with large CCD arrays and the retrieval of correct spectral
characteristics is presented. Various effects, which one should take
into account, are considered and several improvements of the standard
reduction are introduced. A special flat-field procedure is suggested
for the reduction of spectra registered in different flat-field
conditions than those when the flat-field matrix was taken. The original
flat-field matrix is split into several components to eliminate the
influence of the drift of the spectrograph and temporal changes of
the flat-field conditions on the reduced spectrum. The importance
of every flat-field matrix component is tested and discussed and the
noise propagation through data reduction is analyzed. It is documented
that the errors of the basic spectral line characteristics, continuum
intensity, line centre intensity and full width at the half maxima
of the line have variations between 0.5% and 15% and the errors of
the line centre Doppler velocity and bisectors fluctuate by up to 200
m s<SUP>-1</SUP>, if derived from imprecise reductions, compared to
precise ones.
---------------------------------------------------------
Title: Temporal evolution of physical parameters in granule
Authors: Koza, J.; Kucera, A.; Hanslmeier, A.; Rybák, J.; Wöhl, H.
2002ESASP.505..457K Altcode: 2002solm.conf..457K; 2002IAUCo.188..457K
The temporal evolution of the physical parameters inside a granule
is presented. This is a step towards a more realistic 1D modeling
of the solar granulation, avoiding the temporal averaging used up
to now. The granulation is treated as a dynamical phenomenon and our
model has been calculated using an inversion method applied to time
series of spectra. The granular evolutionary model is presented in
the form of the functional dependence of temperature T(log τ, t) and
line-of-sight velocity v<SUB>LOS</SUB>(log τ, t) on optical depth τ
and time t. The observed disappearance of the granule is accompanied
with significant temperature changes greater than ~300K in deeper layers
(log τ<SUB>5</SUB> > 0) and upper layers (log τ<SUB>5</SUB> <
-2.5). In contrary, the layers from log τ<SUB>5</SUB> ~= -0.5 to log
τ<SUB>5</SUB> ~= -1.5 are more stable in the sense of temperature
variations, which are less than ~150K. An oscillatory behavior is
found in the line-of-sight velocity stratification from log τ5 ~= 0
upwards with increasing amplitude reaching up to ~= 2 km s<SUP>-1</SUP>
in upper layers.
---------------------------------------------------------
Title: Dynamic coupling of the chromospheric and photospheric
flaring plasma
Authors: Brceková, K.; Kucera, A.; Hanslmeier, A.; Rybák, J.;
Wöhl, H.
2002ESASP.505..357B Altcode: 2002solm.conf..357B; 2002IAUCo.188..357B
The relaxing phase of the subflare observed in the core of chromospheric
Ca II K line and in two photospheric Fe I 522.5 nm and Fe I 557.6 nm
lines was investigated. The temporal evolution of asymmetry in Ca II
K line and the mean bisectors positions of the Fe I line profiles as
well as their correlations are presented. It is documented that the
chromospheric down-flow caused by the subflare strongly affects the
upper layers of the photosphere. As a consequence of relaxation of
the photospheric layers strong down-flows and up-flows were measured
at the end of the subflare relaxing phase.
---------------------------------------------------------
Title: High-resolution CCD spectra reduction: temporal changes of
the flat-field compensation
Authors: Kučera, Aleš; Hanslmeier, Arnold; Rybák, Ján; Wohl,
Hubertus
2002NCimC..25..703K Altcode:
A new method suitable for long-time series of high-resolution CCD
spectra reduction is presented. The method allows to compensate the
temporal changes of the instrument conditions which leads to temporal
changes of the flat-field matrix. Sometimes it is impossible to make
the flat-field measurements during long simultaneous observations with
satellites (SOHO, TRACE). The method splits the flat-field matrix into
two components. The first one, connected with CCD camera is stable in
time and is correct for all spectra. The second one varies and reflects
temporal changes of the conditions in the spectrograph. Description
of the method and its application to real high-resolution CCD spectra
is presented and discussed.
---------------------------------------------------------
Title: Solar differential rotation determined by tracing coronal
bright points in SOHO-EIT images. II. Results for 1998/99 obtained
with interactive and automatic methods
Authors: Brajša, R.; Wöhl, H.; Vršnak, B.; Ruždjak, V.; Clette,
F.; Hochedez, J. -F.
2002A&A...392..329B Altcode:
Full-disc solar images obtained with the Extreme Ultraviolet Imaging
Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO)
were used to analyse solar differential rotation by tracing coronal
bright points. The results obtained with the interactive and the
automatic method for the time period June 4, 1998 to May 22, 1999 are
presented and compared. A possible north-south rotational asymmetry
and differences in the rotation velocity curves for various subtypes
of tracers are investigated.
---------------------------------------------------------
Title: Sunspots as tracers of meridional circulation
Authors: Wöhl, H.
2002AN....323..329W Altcode:
Many sunspots and sunspot groups exhibit only a small amount of change
of their heliographical latitude during their lifetime. This is called
meridional motion and measured in fractions of degrees per day or
meters per second. The fact is demonstrated for sunspots and sunspot
groups selected from several sources and especially for recurrent
sunspots from Debrecen data. There is a tendency of the sunspots and
sunspot groups to move away from the activity belt, which is defined
by all sunspots. The meridional velocities increase with distance to
the activity belt. Since the braking of sunspot rotation velocities by
aging is well known, it is suggested again that the meridional motion
of the solar plasma is comparable to that of the sunspot groups.
---------------------------------------------------------
Title: Differential Rotation of Stable Recurrent Sunspot Groups
Authors: Brajša, R.; Wöhl, H.; Vršnak, B.; Ruždjak, D.; Sudar,
D.; Roša, D.; Hržina, D.
2002SoPh..206..229B Altcode:
Stable recurrent sunspot groups from the Greenwich data set which
were identified in at least two subsequent solar rotations were
traced. The solar rotation was determined by the period method from
the time difference of the two central meridian passages of each of
the 327 identified groups. Sidereal rotation periods were calculated
from the synodic ones by a seasonal-dependent procedure taking into
account the details of the Earth's motion around the Sun. Growing
recurrent sunspot groups rotate on the average faster than decaying
recurrent sunspot groups, while sunspot groups of all types taken
together rotate faster than both growing and decaying recurrent sunspot
groups. A north-south rotational asymmetry and a cycle-dependence of
rotational velocity of recurrent sunspot groups were analyzed. Positive
rotation velocity deviations are larger, but less numerous than the
negative ones. Signatures of torsional oscillations were not found
analyzing the rotation velocity residual of recurrent sunspot groups
as a function of the distance from the average latitude of activity.
---------------------------------------------------------
Title: Transition region dynamics from SUMER/SOHO observations:
shape of the emission spectral lines
Authors: Rybák, J.; Curdt, W.; Kučera, A.; Wöhl, H.
2002ESASP.477..163R Altcode: 2002scsw.conf..163R
The quiet sun network/internetwork transition region line profiles
of C II 1036.34 Å and O VI 1037.61 Å are outlined emphasizing
the temporal/spatial behaviour of their deviations from the
Gaussian shape. Systematic deviations of the line profiles from the
single-Gaussian shape indicate that transition region emission lines
consist of two Gaussian components over almost the whole quiet sun
internetwork except their small innermost parts. This finding is in
qualitative agreement with the transition region model of Peter (2001).
---------------------------------------------------------
Title: Solar differential rotation determined by tracing coronal
bright points in SOHO-EIT images. I. Interactive and automatic
methods of data reduction
Authors: Brajša, R.; Wöhl, H.; Vršnak, B.; Ruždjak, V.; Clette,
F.; Hochedez, J. -F.
2001A&A...374..309B Altcode:
Full-disc solar images obtained with the Extreme Ultraviolet Imaging
Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO)
were used to analyse solar differential rotation determined by tracing
coronal bright points. Two different procedures were developed and
compared: an interactive and an automatic method. The interactive method
is based on the visual tracing of coronal bright points in consecutive
images using computer programs written in the Interactive Data Language
(IDL). The automatic method relies on the IDL procedure “Regions Of
Interest (ROI) segmentation” which is used to detect and follow bright
points in triplets of consecutive images. The test-results obtained
applying both methods by different persons who performed tracing are
presented and compared. The advantages and disadvantages of the two
methods are discussed.
---------------------------------------------------------
Title: On the Rigid Component in the Solar Rotation
Authors: Brajša, R.; Ruždjak, V.; Vršnak, B.; Wöhl, H.;
Pohjolainen, S.; Urpo, S.
2001ASSL..259..263B Altcode: 2001dysu.conf..263B
A rigid component in the rotation velocity determined by tracing low
brightness temperature regions in the microwave regime was found and
interpreted in terms of their association rate (39%) with rigidly
rotating “pivot-points".
---------------------------------------------------------
Title: The Location of Solar Oscillations in the Photosphere
Authors: Hanslmeier, A.; Kučera, A.; Rybák, J.; Wöhl, H.
2001ASSL..259..267H Altcode: 2001dysu.conf..267H
Applying a correlation analysis to time series of granulation it has
been shown that due to the influence of enhanced turbulent motions
near the downflow regions in the intergranular lanes the turbulent
motions predominate.
---------------------------------------------------------
Title: Chromospheric Dynamics as can be Inferred from SUMER/SOHO
Observations
Authors: Rybák, J.; Kučera, A.; Curdt, W.; Schühle, U.; Wöhl, H.
2001ASSL..259..247R Altcode: 2001dysu.conf..247R
Experience with the SUMER/SOHO observations of the chromospheric
dynamics and the reduction of the acquired data is summarized on
base of the SOHO Joint Operation Program 78 which is focused on the
variability of the chromosphere and the transition region to the corona.
---------------------------------------------------------
Title: Meridional Motions of Stable Recurrent Sunspot Groups
Authors: Wöhl, H.; Brajša, R.
2001SoPh..198...57W Altcode:
Stable recurrent sunspot groups from the Greenwich data set which
were identified in at least two subsequent solar rotations were traced
and meridional motions were determined from the two central meridian
passages. In total, 327 meridional velocities were calculated and
the results for the northern and the southern solar hemisphere were
compared. A dependence of the solar meridional velocity vectors on the
development status, latitude and position respectively to the activity
belt of sunspots is investigated. The results indicate that sunspot
groups are moving on the average away from the center of activity. This
was found for sunspot groups growing and decreasing in area.
---------------------------------------------------------
Title: An Analysis of the Solar Rotation Velocity by Tracing Coronal
Features
Authors: Brajsa, R.; Vrsnak, B.; Ruzdjak, V.; Rosa, D.; Hrzina, D.;
Wöhl, H.; Clette, F.; Hochedez, J. -F.
2001IAUS..203..377B Altcode:
Full-disc solar images in the extreme ultraviolet part of the spectrum
from the SOHO spacecraft (EIT) are used to identify various coronal
structures appropriate for the solar rotation determination (e.g. bright
points and coronal holes). From the time differences in tracer positions
(more than 1 image per day) solar rotation velocities are measured,
primarily by well-defined tracers, such as coronal bright points, whose
large number and broad coverage of latitudes may provide an unique
opportunity for a solar rotation analysis. The analysis started using
the SOHO data from 1997-1999 and preliminary experiences obtained
measuring solar rotation from the full-disc images in soft X-rays
from the YOHKOH (SXT) satellite were taken into account. This work is
connected to the SOHO EIT Proposal Brajsas.
---------------------------------------------------------
Title: Determination of the Solar Rotation Tracing EUV Bright Points
with the Automatic Method
Authors: Wöhl, H.; Brajša, R.; Vršnak, B.; Ruždjak, V.; Clette,
F.; Hochedez, J. -F.
2001HvaOB..25...27W Altcode:
Full-disc solar images in the extreme ultraviolet part of the spectrum
from the SOHO spacecraft (instrument EIT, data in the spectral
line of Fe XV at the wavelength of 28.4 nm) are used for the solar
rotation determination tracing coronal bright points. From the time
differences in tracer positions, approximately six hours, the solar
rotation velocity is determined automatically for image sequences in
several time intervals from June 4, 1998 to May 22, 1999. The resulting
rotational profiles are mutually compared.
---------------------------------------------------------
Title: Determination of the Solar Rotation Tracing EUV Bright Points
with the Interactive Method
Authors: Brajša, R.; Wöhl, H.; Schuck, T. J.; Schawinski-Guiton,
K.; Wegner, A.; Vršnak, B.; Ruždjak, V.; Clette, F.; Hochedez, J. -F.
2001HvaOB..25...13B Altcode:
Full-disc solar images in the extreme ultraviolet part of the spectrum
from the SOHO spacecraft (instrument EIT, data in the spectral line of
Fe XV at a wavelength of 28.4 nm) are used to visually identify coronal
bright points appropriate for the solar rotation determination. From the
time differences in successive tracer positions, about six hours, the
solar rotation velocity is determined tracing coronal bright points in
several time intervals from June 4, 1998 to May 22, 1999. The resulting
rotational profiles obtained by five observers are mutually compared.
---------------------------------------------------------
Title: Dynamics of the Upper Photosphere: Coherence and Phase Analysis
(CD-ROM Directory: contribs/hanslmei)
Authors: Hanslmeier, A.; Kučera, A.; Rybák, J.; Wöhl, H.
2001ASPC..223..669H Altcode: 2001csss...11..669H
No abstract at ADS
---------------------------------------------------------
Title: Correlative relationships in an inhomogeneous solar atmosphere
Authors: Gadun, A. S.; Hanslmeier, A.; Kučera, A.; Rybák, J.;
Wöhl, H.
2000A&A...363..289G Altcode:
We analyse the correlative relationships between various quantities
derived from 2-D inhomogeneous and time-dependent model atmospheres
and between selected simulated line parameters to compare them with
height-dependent correlations derived from spectral observations. We
detect three photospheric regions: thermal convection, overshooting
convection and a transition layer. We also show that correlations
found for the model data and those computed within simulated spectral
observations are a good testing tool for line formation depths. As
an example, we examine two criteria, providing heights of line core
formation in LTE, and conclude that the approach which defines
this quantity as geometrical height at line center optical depth
τ<SUB>λ0</SUB> = 1 is likely more suitable for diagnostic purposes
than the method based on depression contribution function.
---------------------------------------------------------
Title: Solar Photosphere: The Limb Effect and Gravitational Redshift
Authors: Wöhl, H.
2000eaa..bookE2256W Altcode:
The `limb effect' is the observational finding that many spectral
absorption lines formed in the photosphere (FRAUNHOFER LINES) show
a REDSHIFT of their mean wavelength when comparing limb observations
with observations from the solar disk center. The magnitude of this
effect is different for each spectral line and equals some 100 m s-1
when explained as a DOPPLER EFFECT....
---------------------------------------------------------
Title: Statistical Weights and Selective Height Corrections in the
Determination of the Solar Rotation Velocity
Authors: Brajša, R.; Ruždjak, V.; Vršnak, B.; Wöhl, H.;
Pohjolainen, S.; Upro, S.
2000SoPh..196..279B Altcode:
Observations of the Sun performed at 37 GHz with the 14-m radio
telescope of the Metsähovi Radio Observatory were analyzed. Rotation
velocities were determined, tracing Low Temperature Regions (LTRs) in
the years 1979-1980, 1981-1982, 1987-1988, and 1989-1991. Statistical
weights were ascribed to the determined rotation velocities of LTRs,
according to the number of tracing days. Measured changes of the
rotation velocity during the solar activity cycle, as well as a
north-south rotation asymmetry, are discussed. The results obtained
with and without the statistical weights procedure are compared, and it
was found that the statistical significance of the solar differential
rotation parameters' changes is higher when the statistical weights
procedure is applied. A selective application of the height correction
on LTR's positions has not removed the cycle-related changes nor the
north-south asymmetry of the solar rotation measured tracing LTRs. So,
projection effects cannot explain these changes. The differential
rotation of LTRs is more rigid than the differential rotation obtained
tracing magnetic features and measuring Doppler shifts, which can be
explained by the association rate of the LTRs' positions with rigidly
rotating `pivot points'. The observed cycle-related changes and the
north-south asymmetry of the rotation velocity of LTRs are consistent
with the cycle-related changes and the north-south asymmetry of the
association rate between LTRs and pivot points.
---------------------------------------------------------
Title: Solar equatorial plasma rotation: a comparison of different
spectroscopic measurements
Authors: Wöhl, H.; Schmidt, W.
2000A&A...357..763W Altcode:
We present solar equatorial rotation velocities measured with two
different spectral lines (Fe I 557.6 nm and Ni I 676.8 nm) and two
different spectrometers at the German Vacuum Tower Telescope (VTT) on
Tenerife. The `classical' sidereal solar equatorial rotation velocity
of about 2000 m/s has been confirmed. The results are compared with
those from velocity data of the Michelson Doppler Imager (MDI) onboard
the Solar Heliospheric Observatory (SOHO) obtained on 10 June 1996 and
27 May 1999. From both data sets of MDI, a rotation velocity about 100
to 200 m/s below the `classical' value cited above was found. Possible
explanations of this discrepancy are discussed.
---------------------------------------------------------
Title: Dynamics of the upper solar photosphere
Authors: Hanslmeier, A.; Kučera, A.; Rybák, J.; Neunteufel, B.;
Wöhl, H.
2000A&A...356..308H Altcode:
The dynamics of the upper solar photosphere was studied by using
1-D photospheric line spectrograms obtained using the VTT of the
Observatorio del Teide. Three spectral lines with line core formation
heights between 250 and 500 km were analyzed. It is clearly seen that at
these levels the velocity and intensity fields are highly correlated
but different from the lower lying zone where convective motions
predominate. This is shown by classical methods (using correlations and
bisectors) as well as by applying the Hurst exponent method to the data.
---------------------------------------------------------
Title: 3-D Tomography of the Solar Photosphere
Authors: Hanslmeier, A.; Kucera, A.; Rybak, J.; Wohl, H.
2000ESASP.463..333H Altcode: 2000sctc.proc..333H
No abstract at ADS
---------------------------------------------------------
Title: Spectral Statistics of Fe I and Ca II K Lines in the Quiet
and Active Solar Atmosphere
Authors: Kucera, A.; Brcekova, A. K.; Hanslmeier, A.; Rybak, J.;
Woehl, H.
2000HvaOB..24..111K Altcode:
Based on two Fe I and Ca II K lines spectra obtained with high spatial
and spectral resolution we investigated some spectral characteristics
of these lines in quiet and active regions. In this paper we present
the behaviour of the central line intensities in different types of
solar activity. We discuss the obtained results and compare them with
the results reported by other authors.
---------------------------------------------------------
Title: Measurements of Solar Rotation Using EUV Bright Points -
Preliminary Results
Authors: Brajsa, R.; Woehl, H.; Kasabasic, M.; Rodmann, J.; Vrsnak,
B.; Ruzdjak, V.; Rosa, D.; Hrzina, D.; Clette, F.; Hochedez, J. -F.
2000HvaOB..24..153B Altcode:
Full-disc solar images in the extreme ultraviolet part of the spectrum
from the SOHO spacecraft (instrument EIT, data in the spectral line
of Fe XV at the wavelength of 28.4 nm) are used to identify visually
various small-scale coronal structures appropriate for the determination
of the solar rotation. From the time differences in tracer positions,
approximately six hours, the solar rotation velocity is determined
tracing coronal bright points in the period June 4-14, 1998 by four
observers. The resulting rotational profiles are mutually compared
and the reduction methods are discussed.
---------------------------------------------------------
Title: Two Dimensional Spectral Time Series
Authors: Hanslmeier, A.; Kucera, A.; Rybak, J.; Woehl, H.
2000HvaOB..24...81H Altcode:
We analyze two dimensional time series of solar photospheric
spectrograms in order to study the dynamics of solar fine structures and
their evolution. The two dimensional images were obtained by scanning
over the photosphere. Spectrographic data of this type include a much
higher information than ordinary images.
---------------------------------------------------------
Title: Interaction of Sunspots with the Surrounding Plasma - a
Progress Report
Authors: Woehl, H.; Rybak, J.; Kucera, A.
2000HvaOB..24..119W Altcode:
The historic development of the search for interactions of sunspots
and solar plasma around them was given in a contribution at the IVth
Hvar Astrophysical Colloquium (Woehl, 1997). It was concentrated on
the results of measurements and their reductions performed by Lustig
and Woehl (1993), showing a dependence of plasma velocity difference
in front and behind stable sunspots depending on their relative speed
within the plasma. Since the result obtained was not significant,
new attempts were started to use MDI/SoHO data and mainly to collect
data ourselves at telescopes and the horizontal spectrometer of the
Astronomical Institute of the Slovak Academy of Sciences in Tatranska
Lomnica, Slovakia. The main difference is that now the plasma velocity
data are gained by a matrix of fiber optics collecting light at several
positions around the sunspot. In addition the sunspot positions are
collected by a different telescope. The reductions of the sunspot
positions give very reliable rotation data and - as expected - very
small meridional motions, while the plasma velocity data are not yet
reliable. Attempts to improve this situation are described.
---------------------------------------------------------
Title: On the Meridional Motions of Recurrent Stable Sunspot Groups
Authors: Brajsa, R.; Woehl, H.
2000HvaOB..24..125B Altcode:
Meridional motions of recurrent stable sunspot groups are analysed as
a function of the distance from the average latitude of activity in
each solar hemisphere. Results were obtained for two data subsets,
consisting of recurrent sunspot groups decreasing and growing in
area respectively, and are compared with the ones published in the
literature. An interpretation of the results in the frame of the model
of magnetic flux-transport on the Sun is discussed.
---------------------------------------------------------
Title: Fe I and Ca II K Lines in Quiet and Active Regions
Authors: Kucera, A.; Brcekova, K.; Hanslmeier, A.; Rybak, J.; Wohl, H.
2000ESASP.463..357K Altcode: 2000sctc.proc..357K
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric and Transition Region Dynamics - Reasons
and Consequences of the Long-period Instrumental Periodicities
of SUMER/SOHO
Authors: Rybák, J.; Curdt, W.; Kucera, A.; Schühle, U.; Wöhl, H.
1999ESASP.448..361R Altcode: 1999mfsp.conf..361R; 1999ESPM....9..361R
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric And Transition Region Dynamics - Reasons
and Consequences of the Short Period Instrumental Periodicities
of SOHO/SUMER
Authors: Rybak, Jan; Curdt, Werner; Kučera, Ales; Schüehle, Udo;
Wöehl, Hubertus
1999ESASP.446..579R Altcode: 1999soho....8..579R
The instrumentally caused oscillations of the spectral lines intensity
and velocity, determined with the SUMER spectrometer onboard SoHO, are
presented. On examples of two long-term measurements of O I, C II and O
VI lines, it is shown that the reason of this instrumental effect was
the insufficient precision of the solar rotation compensation of the
spectrometer slit position. In both observational runs the standard
rotation compensation procedure, performed on-line by the instrument,
was selected for the long-term observations. The minor periodical
motion of the slit position on the solar disk was taking place during
such observations and this effect produced the regular changes of the
measured line intensities and velocities. The significant enhancements
of the oscillations amplitudes around the frequency 2.56 mHz and its
harmonics were detected in the cases of observations, performed at
the disk center. Unfortunately, these frequencies are just in the
range of the typical oscillations determined till now in the upper
solar atmosphere ! Consequences of this instrumental effect for SUMER
measurements of the chromospheric and transition region dynamics
are discussed. Procedures how to exclude the effect from the data
post-facto as well as how to modify the future SUMER oscillations
measurements in order to avoid the effect are proposed
---------------------------------------------------------
Title: Fiber Optics Device for Solar Spectroscopy - First Measurements
Authors: Kucera, A.; Rybák, J.; Wöhl, H.; Hanslmeier, A.
1999ASPC..184..319K Altcode:
In 1996 we introduced the fiber optics device designed for 2D
solar spectroscopy (Kucera et al. 1997). Now we present the first
results obtained within last year. First experiences with wavelength
calibration, light transmission through the fibers, noise reduction,
software for reduction of observations and preliminary results of
reduced scientific data are presented.
---------------------------------------------------------
Title: Der Zyklus der Sonne.
Authors: Schüssler, M.; Wöhl, H.
1999S&WSp...4...56S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Center-to-limb variation of the solar oscillation. New results
from MDI data
Authors: Schmidt, W.; Stix, M.; Wöhl, H.
1999A&A...346..633S Altcode:
{Using 17 hours of full-disk MDI Doppler data we have investigated the
center-to-limb variation of the oscillatory wave spectrum of the solar
photosphere. Power distributions in the k_hnu -plane are calculated
for fields of 20(deg) x 20(deg) on the Sun, centered at every 10(deg)
heliographic latitude. From the center-to-limb variation of the power
in the f mode and the lowest 7 p modes we obtain information about the
mean inclination of the oscillatory velocity vector with respect to
the vertical direction. We find qualitative agreement with a model of
adiabatic waves in an isothermal atmosphere, but generally the solar
oscillations appear to be less inclined than the model oscillations. We
find no indication for the existence of horizontal sound waves on
the Sun.}
---------------------------------------------------------
Title: Height of Tracers and the Correction of the Measured Solar
Synodic Rotation Rate: Demonstration of the Method
Authors: Vršnak, B.; Roša, D.; Božić, H.; Brajša, R.; Ruždjak,
V.; Schroll, A.; Wöhl, H.
1999SoPh..185..207V Altcode:
Two large stable solar filaments were used as test tracers to determine
the apparent synodic rotation rate as a function of the central meridian
distance for several filaments' segments at different heights. An
analytic fitting procedure was applied to determine simultaneously
the real synodic rotation rate and the height of the traced filament
segments. The determined heights were compared with the values obtained
from the widths of filament contours on the solar disk and with the
values obtained by direct measurements at the solar limb. Furthermore,
the obtained rotation rates and heights of the filaments' segments close
to the filaments' pivot points were compared with the values obtained
using two successive central meridian passages. Finally, sources and
scales of errors were investigated and possible implications on the
previous studies of the solar differential rotation were considered.
---------------------------------------------------------
Title: An Estimate of Microwave low-Brightness-Temperature Regions'
Heights Obtained Measuring Their Rotation Velocity
Authors: Brajša, R.; Ruždjak, V.; Vršnak, B.; Wöhl, H.;
Pohjolainen, S.; Urpo, S.
1999SoPh..184..281B Altcode:
Daily full-disk solar maps obtained at 37 GHz in the years 1979,
1980, 1981, 1982, 1987, 1988, 1989, 1990, and 1991 are analysed
and compared with full-disk solar maps in Hα. A search for a
difference in the measured angular rotation velocity for two classes
of microwave low-brightness-temperature regions (LTRs), associated and
not associated with Hα filaments, is performed. Procedures with and
without statistical weights, assigned to angular rotation velocities
according to the tracing time, are applied and the statistical
significance of the results is discussed. A higher angular rotation
velocity is measured for LTRs associated with Hα filaments than for
the not-associated ones. This angular velocity difference is interpreted
as a consequence of a height difference between these two types of LTR
tracers. Changes of the solar differential rotation velocity during
the activity cycle measured using LTRs as tracers are explained by
the measured cycle-dependence of the association rate between LTRs
and Hα filaments. Similarly, the north-south asymmetry in the solar
rotation velocity measured tracing LTRs is explained by the measured
north-south asymmetry in the association rate between LTRs and Hα
filaments. The rotation velocity of LTRs and Hα filaments is on the
average more rigid in comparison with sunspots.
---------------------------------------------------------
Title: SOHO JOP 078 - variability and properties of the quiet sun
supergranular network and internetwork.
Authors: Kučera, A.; Curdt, W.; Fludra, A.; Rybák, J.; Wöhl, H.
1999joso.proc..149K Altcode:
Study of the variability of the quiet solar atmosphere covering as
large as possible range of the temperatures using both the 2D imaging
and 1D spectra was the aim of SOHO JOP 78 observations. Supergranular
cells were the objects of the authors' main interest. This programme is
based on the cooperation of several SOHO instruments (SUMER, CDS, MDI,
EIT) and TRACE. Justification of the JOP, cooperation of instruments
and specially arranged measurements for the post-facto coalignment of
data from different instruments are described in this paper.
---------------------------------------------------------
Title: Correlation of Velocity Fields at Different Heights in the
Solar Photosphere
Authors: Kucera, A.; Rybák, J.; Wöhl, H.
1999ASSL..239..219K Altcode: 1999msa..proc..219K
A simple experimental method for comparison of the line formation
heights in the solar photosphere is presented. Several Fe I lines are
used to test the method.
---------------------------------------------------------
Title: An analysis of the solar rotation velocity determined tracing
microwave features and an estimate of their heights.
Authors: Brajša, R.; Ruždjak, V.; Vršnak, B.; Wöhl, H.;
Pohjolainen, S.; Urpo, S.
1999joso.proc..156B Altcode:
Measurements of the Sun performed at 37 GHz (8 mm) with the 14 m
radio telescope of the Metsähovi Radio Observatory were analysed
and rotation velocities tracing microwave Low brightness Temperature
Regions in the years 1979 - 1980, 1981 - 1982, 1987 - 1988, and 1989 -
1991 were determined. The statistical weights method was applied and
possible changes of the measured rotation velocity values are discussed.
---------------------------------------------------------
Title: Velocity Pulses in a Sunspot with Lightbridges
Authors: Balthasar, H.; Schleicher, H.; Wöhl, H.
1999AGAb...15....7B Altcode: 1999AGM....15..A05B
See splinter meeting SOLAR OBSERVATION WITH HIGH RESOLUTION
---------------------------------------------------------
Title: Velocity Oscillations in Active Sunspot Groups
Authors: Balthasar, H.; Martínez Pillet, V.; Schleicher, H.; Wöhl, H.
1998SoPh..182...65B Altcode:
Time series of two-dimensional spectra were taken with the Göttingen
2D spectrometer at the VTT on Tenerife in 1996. They were investigated
for Doppler velocities and velocity oscillations in small spots and
pores of rapidly evolving sunspot groups. For the present measurements
the magnetically insensitive lines Fe i 557.6 nm and Fe i 709.0 nm
were selected.
---------------------------------------------------------
Title: A Method to Determine the Solar Synodic Rotation Rate and
the Height of Tracers
Authors: Roša, D.; Vršnak, B.; Božić, H.; Brajša, R.; Ruždjak,
V.; Schroll, A.; Wöhl, H.
1998SoPh..179..237R Altcode:
The dependence of the measured apparent synodic solar rotation rate
on the height of the chosen tracer is studied. A significant error
occurs if the rotation rate is determined by tracing the apparent
position of an object above the photospheric level projected on the
solar disc. The centre-to-limb variation of this error can be used to
determine simultaneously the height of the object and the true synodic
rotation rate. The apparent (projected) heliographic coordinates
are presented as a function of the height of the traced object and
the coordinates of its `footpoint'. The relations obtained provide
an explicit expression for the apparent rotation rate as a function
of the observed heliographic coordinates of the tracer, enabling an
analytic least-squares fit expression to determine simultaneously the
real synodic rotation rate and the height of the tracer.
---------------------------------------------------------
Title: Heights of formation of FeI photospheric lines
Authors: Kucera, A.; Balthasar, H.; Rybak, J.; Woehl, H.
1998A&A...332.1069K Altcode:
The determination of the location of spectral line-forming layers
by means of line-depression contribution functions is checked by
observational tests. The method is based on the assumption that the
Doppler velocities derived from line bisectors at a given position in
the profile of a spectral line are related to the actual bulk velocity
at a particular height in the atmosphere. For a set of six magnetically
sensitive and non-sensitive Fe I lines (543.45, 557.61, 630.15, 630.25,
649.50, 649.45 nm) the fluctuations of Doppler velocities along the slit
of the spectrograph were determined at various Delta lambda from the
line centers i.e. at various heights in the photosphere. Correlations
of fluctuations allow us to find those parts in line profiles which
are formed at identical heights in the photosphere. These experimental
results are compared with theoretical estimates based on line depression
contribution functions. The agreement is good and best results are found
for nonmagnetic strong, but still unsaturated lines. The results support
the hypothesis that it is possible to ascribe a single height point
in the solar atmosphere to a given position in a spectral line profile.
---------------------------------------------------------
Title: Oscillations in Chromosphere and Transition Region Based on
SUMER Measurements
Authors: Kucera, A.; Curdt, W.; Rybák, J.; Schühle, U.; Wöhl, H.
1998ASPC..155..351K Altcode: 1998sasp.conf..351K
No abstract at ADS
---------------------------------------------------------
Title: Distribution of sunspot groups from asymmetric rising flux
loops.
Authors: Schuessler, M.; Woehl, H.
1997A&A...327..361S Altcode:
Rising magnetic flux loops in the solar convection zone develop an
asymmetric shape with a flat preceding part and a steeper following
part with respect to the direction of solar rotation. By a statistical
analysis of newly forming sunspot groups we test the conjecture that
this geometrical asymmetry leads to an asymmetric distribution of
secondary spot groups originating from the legs of the same rising flux
loop as the primary group, which develops out of the loop summit. We
find that ~10% of all sunspot groups actually develop secondary
groups within +/-20° longitude distance from the primary group and
within one day after its emergence. Those secondary groups related to
small primary groups (area <100 millionths of the solar hemisphere)
are predominantly located on their eastern (following) side, while for
larger primary groups the secondaries are more numerous on their western
(preceding) side. Both results are consistent with the geometrical
asymmetry developed by rising magnetic flux loops.
---------------------------------------------------------
Title: On the Possible Changes of the Solar Differential Rotation
during the Activity Cycle Determined Using Microwave Low-Brightness
Regions and Hα Filaments as Tracers
Authors: Brajša, R.; Ruždjak, V.; Vršnak, B.; Pohjolainen, S.;
Urpo, S.; Schroll, A.; Wöhl, H.
1997SoPh..171....1B Altcode:
The solar rotation rate obtained using the microwave
Low-brightness-Temperature Regions (LTRs) as tracers in the heliographic
range ± 55° from the years 1979-1980, 1981-1982, 1987-1988, and
1989-1991 varied from 3% to 4% in medium latitudes, and below 1%
at the equator. Using Hα filaments as tracers at higher latitudes
from the years 1979, 1980, 1982, 1984, and 1987, the solar rotation
rate variation was between 2% and 8%. This represents an upper limit
on the rotation rate variation during the solar activity cycle. Such
changes could be caused by short-lived, large-scale velocity patterns
on the solar surface. The Sun revealed a higher rotation rate on the
average during the maxima of the solar activity cycles 21 and 22,
i.e., in the periods 1979-1980 and 1989-1991, respectively, which
differs from the rotation rates (lower on the average) in some years,
1981-1982 and 1987-1988, between the activity maximum and minimum
(LTR data). Simultaneous comparison of rotation rates from LTRs and
Hα filament tracings was possible in very limited time intervals
and latitude bands only, and no systematic relationship was found,
although the rotation rates determined by LTRs were mostly smaller than
the rotation rates determined by Hα filaments. The errors obtained by
applying different fitting procedures of the LTR data were analyzed, as
well as the influence of the height correction. Finally, the north-south
asymmetry in the rotation rate investigated by LTRs indicates that
the southern solar hemisphere rotated slower in the periods under
consideration, the difference being about 1%. The reliability of all
obtained results is discussed and a comparison with other related
studies was performed.
---------------------------------------------------------
Title: Measurement of rotational characteristics of sunspots and
surrounding photospheric plasma.
Authors: Kučera, A.; Rybák, J.; Wöhl, H.
1997joso.proc...68K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Soft X-ray, Microwave and He I Measurements of Coronal Holes
Authors: Brajsa, R.; Ruzdjak, V.; Vrsnak, B.; Pohjolainen, S.; Urpo,
S.; Sakurai, T.; Wohl, H.
1997IAUJD..19E..15B Altcode:
The Poster presents and describes microwave signatures of three
coronal holes that were recorded on May 27, 1993. Differences in the
brightness temperatures between an equatorial and two polar coronal
holes were found. The measurements in the He I 10830 AA absorption
line for that day were also analyzed and compared with the microwave
and soft X-ray data.
---------------------------------------------------------
Title: Investigation of the Dynamics of Chromosphere and Photosphere
from Spectra Obtained by Parallel Observations using SUMER on SOHO
and the VTT on Tenerife
Authors: Curdt, W.; Kucera, A.; Rybak, J.; Schuhle, U.; Wohl, H.
1997ASPC..118..322C Altcode: 1997fasp.conf..322C
This is a preliminary report about parallel observations of
chromospheric and photospheric spectra in the ultraviolet and visible
spectral regions using SUMER on SOHO and the VTT on Tenerife performed
begin of September 1996. The aim is to search for relations of vertical
velocity patterns in the upper photosphere and chromosphere in the
solar disk center. In addition temporal changes in these parts of the
solar atmosphere are investigated.
---------------------------------------------------------
Title: Dynamical Properties of the Chromosphere and Transition Region
in the Supergranular Network: What Precision of the Spectral Line
Characteristics Can be Reached?
Authors: Curdt, W.; Kucera, A.; Rybák, J.; Schühle, U.; Wöhl, H.
1997ESASP.404..307C Altcode: 1997cswn.conf..307C
No abstract at ADS
---------------------------------------------------------
Title: Velocity oscillations in active sunspot groups.
Authors: Balthasar, H.; Martínez Pillet, V.; Schleicher, H.; Wöhl, H.
1997AGAb...13...12B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Interaction of Medium-Scale and Large-Scale Structures in
the Solar Atmosphere
Authors: Woehl, H.
1997HvaOB..21....1W Altcode:
The historic development of the search for interactions of sunspots
and solar plasma around them is given as an example for interactions of
medium-scale and large-scale structures on the sun. This new field of
solar research gained most of its progress from combination of data of
sunspot rotation measurements by tracer techniques with those of the
plasma by Doppler shift measurements of spectral lines. The paper is
concentrated on two main research projects: One was performed mainly
at the German Vacuum Tower Telescope on Tenerife in the beginning of
the nineties and another was started in Slovakia recently. From the
data obtained during the observational program performed from 1990 to
1992 it was found that the rotation velocity difference of the plasma
in front and behind stable sunspots showed a linear dependence on the
difference of the sunspot's rotation velocity as compared with the
mean plasma velocity at the latitude of the sunspot observed. Although
the sample of sunspots used was quite big (22 sunspots), the detected
behavior was just not yet significant on the 3 sigma level. To gain
this significance, and in addition to obtain details about the plasma
flow structure also north and south of the sunspots, the new observing
program was started.
---------------------------------------------------------
Title: On the Determination of the Height of Microwave Low Temperature
Regions from Solar Rotation Measurements
Authors: Brajsa, R.; Ruzdjak, V.; Vrsnak, B.; Pohjolainen, S.; Urpo,
S.; Woehl, H.
1997HvaOB..21...67B Altcode:
A larger angular rotation velocity was measured for microwave LTRs
associated with H-alpha filaments than for the not associated ones. This
implies that LTRs not associated with H-alpha filaments are located
at lower heights above the solar photosphere than LTRs associated with
H-alpha filaments. Data from three intervals were analysed (1979-1980,
1981-1982 and 1987-1988) with different percentages of association
between LTRs and H-alpha filaments.
---------------------------------------------------------
Title: A search for formation-height oscillations in umbrae.
Authors: Berger, B.; Balthasar, H.; Schleicher, H.; Wiehr, E.;
Woehl, H.
1996A&A...310..328B Altcode:
The formation heights of spectral lines and continua in sunspots can be
determined by measuring the apparent distance of the spot relative to
the nearby solar limb. In order to confirm the existence of oscillatory
variations of such limb distances and to exclude possible influences
of differential image motion between the spot and the nearby limb, we
have obtained time series observations of the lines Ca^+^ 8542, Mg b,
and the non-magnetic line Fe 5576 simultaneously on two telescopes. No
indication is found for periodic fluctuations of the spot's apparent
limb distance. Only one of the seven time series shows a significant
40 min period of the line core but not of the continuum in the data
from both telescopes. This variation of the line formation height,
however, may be attributed to parallel guiding corrections of a
spatially inhomogenous umbral chromosphere. The other time series
show different periods for the two telescopes, which must be caused
by unrelated guiding corrections.
---------------------------------------------------------
Title: A New Method for Numerical Data Reduction of Solar Microwave
Measurements
Authors: Brajsa, R.; Ruzdjak, V.; Vrsnak, B.; Woehl, H.; Pohjolainen,
S.; Urpo, S.
1996HvaOB..20...15B Altcode:
Numerical data reduction of full-disk solar measurement taken in
the microwave part of the spectrum (37 GHz) at the Metsahovi Radio
Research Station is described. The basic parameter distinguishing
between various features on the microwave solar maps is the brightness
temperature. Regions on the Sun with a lower brightness temperature
than the quiet Sun level are called Low Temperature Regions (LTRs),
and in the present paper mainly LTRs are considered. On the other
hand, High Temperature Regions (HTRs) have a brightness temperature
higher than the quiet Sun level. The data reduction includes: to
obtain a circular solar picture, to construct twelve radial vectors
from the preliminary solar disk center in order to determinate the
coordinates of the solar limb, to remove "erroneous" limb points,
to determine a circle trough the limb points by the least-squares
method, to obtain corrected coordinates of the solar disk center and
the radius and to repeat the procedures using the obtained results
as input parameters. The quiet Sun level was determined as the mean
value of all data points on the disk for every map separately. Several
numerical criteria were tested, and the minima of relative intensities
for all data points were determined. Taking these minima as centers,
circles of different radii were drawn with criterion that the mean value
inside the circle is less than the quiet Sun level. The latitudinal
distribution of LTRs, as well as the solar rotation rate as determined
by the LTRs, were investigated using automatic numerical procedures. It
was established how the parameters which describe the solar rotation
rate and corresponding errors depend upon various numerical criteria
including: definition of LTR's size, allowing different deviations
of LTR's positions and rotation rate, confining the set of obtained
rotation rates according to each error of the rotation rate and
confining the set of obtained rotation rates according to allowance
of a specific rotation rate at a specific latitude.
---------------------------------------------------------
Title: Helium 10830 Å measurements of the Sun
Authors: Brajša, R.; Pohjolainen, S.; Ruždjak, V.; Sakurai, T.;
Urpo, S.; Vršnak, B.; Wöhl, H.
1996SoPh..163...79B Altcode:
Measurements of the Sun in the near-infrared He I 10830 Å absorption
line were performed using the echelle spectrograph with a dispersion
of 6.71 mÅ per pixel at the Vacuum Tower Telescope (German Solar
Telescopes, Teide Observatory, Izaña, Tenerife, Spain) on May 26,
1993. These measurements were compared with full-disc soft X-ray images
of the Sun (Japanese solar satellite Yohkoh), full-disc solar images
in Hα (Big Bear Solar Observatory), full-disc solar images in the
He I 10830 Å line (National Solar Observatory, Kitt Peak) and with
full-disc microwave solar maps at 37 GHz (Metsähovi Radio Research
Station). In the He 10830 Å line the Sun displays a limb darkening
similar to that in the visible part of the spectrum. Active regions
and Hα filaments show a strong absorption in the He 10830 Å line,
whereas the absorption is weak in coronal holes.
---------------------------------------------------------
Title: Numerical modelling of spectral line asymmetries in
photospheric structures. I. Quiet Sun.
Authors: Marquez, I.; Bonet, J. A.; Vazquez, M.; Woehl, H.
1996A&A...305..316M Altcode:
Modelling of asymmetries in spectral lines with different formation
heights (K I 7699, Fe I 5576 and Fe I 5635A), observed in the quiet Sun
at the disk center, has been performed with the aim of reproducing the
absolute line bisectors obtained from low resolution observations. The
influence of a number of physical and observational factors on the
bisector shape and line shifts, acting together or separately, is
discussed, e.g. mesogranular flows, waves, microturbulence, defective
temporal and spatial averages, etc. The simulations are based on the
VAL-C model (Vernazza et al. 1981) representing the mean photosphere,
and the granular model by Nelson (1978). Following evidence in the
literature, the best match to the observed absolute mean bisectors
is obtained by including in the numerical code a gravity wave and
a strengthening of the microturbulence in the lower layers of the
intergranule.
---------------------------------------------------------
Title: The Relation between the Synodic and Sidereal Rotation Period
of the Sun
Authors: Roša, D.; Brajša, R.; Vršnak, B.; Wöhl, H.
1995SoPh..159..393R Altcode:
The relation between the synodic and sidereal rotation period of
the Sun for an arbitrary date of observation is derived taking into
account details of the Earth's motion. The transformation procedure
between the synodic (apparent) and sidereal rotation period presented
here can be performed without using the annual ephemerides.
---------------------------------------------------------
Title: Observations of Fe I lines in the quiet solar photosphere.
Authors: Kucera, A.; Rybak, J.; Woehl, H.
1995A&A...298..917K Altcode:
We investigate three sets of spectra with high spatial and spectral
resolution. Each set consists of four spectra taken simultaneously
with the Vacuum Tower Telescope at Izana, Tenerife. The main spectral
characteristics (continuum intensity I_c_; full width at half
maximum FWHM; residual intensity I_o_) were computed for 5 magnetic
and non-magnetic Fe I lines (5434.543 A, 5576.099 A, 6301.497 A,
6302.499 A, 6494.994 A). Our results allow a diagnosis of the solar
atmosphere in the vertical (two main levels of line formation)
and horizontal directions (71 arcseconds). The spectra cover both
interior parts of supergranular cells (purely quiet regions, PQR) and
cell boundaries (moderate active regions, MAR). The main results are:
(1) We find a different continuum intensity distribution for PQRs
and MARs, which reflects the existence of different patterns in these
regions. The difference is also evident in the rms residual intensity
fluctuation. (2) A significant minimum of the residual intensity
fluctuations (δI_o_/I_c_)_rms_ occurs at a height of about 300km. (3)
At all heights of the PQRs the line widths FWHM in the intergranular
lanes are larger than the mean line width; those in the granules
are smaller. This variation of the FWHM is influenced by a magnetic
effect near the centres of the intergranular lanes (reduced FWHM),
and by the effect of convection in granules (enhanced FWHM). (4)
The correlation <I_c_, I_o_> reverses its sign at a height of
about 250km. The anticorrelation in the range 300-500km indicates a
non-convective structure, different from the photospheric granular
pattern found earlier.
---------------------------------------------------------
Title: The Growth and Decay of Sunspots: Comparison between the
Greenwich and Mount Wilson Sunspot Data
Authors: Lustig, G.; Wohl, H.
1995SoPh..157..389L Altcode:
The complete sample of theGreenwich Photoheliographic Results (GPR)
for the years 1874-1976 was used for the investigation of the growth
and decay of sunspot groups. The results were compared with similar
findings from the Mt. Wilson sunspot data for the years 1917-1985, which
were recently published by R. F. Howard. The results of the absolute
umbral area changes are about the same for both sets of data. The main
difference between the sets of data occurs for the percentage increase
of the umbral areas as a function of latitude. The mean values from the
Mt. Wilson data are bigger by a factor of 5 to 7 and show a dependence
on the latitude, while the increase of the Greenwich data does not
depend on the latitude. The decrease of sunspot areas as a function of
latitude is only available from the Greenwich data. There occur higher
values for the decrease for higher latitudes from 2.5 up to 42.5 deg
---------------------------------------------------------
Title: Sunspot limb distance variations measured simultaneously with
two telescopes.
Authors: Berger, B.; Balthasar, H.; Schleicher, H.; Wöhl, H.;
Wiehr, E.
1995AGAb...11..142B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Investigation of Cycle-Related Changes of the Solar Rotation
by Tracing Microwave Low Brightness Temperature Regions
Authors: Brajsa, R.; Ruzdjak, V.; Vrsnak, B.; Pohjolainen, S.; Urpo,
S.; Woehl, H.
1995HvaOB..19....1B Altcode:
Indications of possible changes of the solar rotation rate during
several phases of the solar activity cycle (the years analyzed were
1979, 1980, 1981, 1982, 1987, 1988, 1989, 1990 and 1991) were found. The
solar rotation rates were determined by tracing microwave Low brightness
Temperature Regions in the latitude range 55 deg. These changes of the
rotation rate, although of low statistical significance, indicate that
the Sun has nearly equal rotation rates during successive cycle maxima,
which are different from the measured rotation rates in the periods
between the maxima.
---------------------------------------------------------
Title: Meridional motions of sunspot groups during eleven activity
cycles
Authors: Lustig, G.; Woehl, H.
1994SoPh..152..221L Altcode: 1994IAUCo.143..221L; 1994svs..coll..221L
Greenwich data (1874-1976) are used for a time-dependent analysis of
meridional motions of sunspot groups. We obtain the latitude-dependence
of meridional motions of sunspot groups with respect to a mean
latitude determined for half-year intervals. The daily meridional
motions of groups are also given separately for growing and decaying
sunspot groups. The development is determined from changes of sunspot
areas. Our results are compared with the reductions performed by Howard
(1991b) using the Mt. Wilson sunspot data from 1917 until 1985: Although
we have smaller errors, we do not find any significant drift. We also
do not find different trends in the meridional motions of growing as
compared to decreasing sunspots.
---------------------------------------------------------
Title: Solar Centre-to-Limb Functions in Optical and Radio Wavelength
Ranges
Authors: Brajsa, R.; Ruzdjak, V.; Vrsnak, B.; Pohjolainen, S.; Urpo,
S.; Woehl, H.
1994HvaOB..18....9B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Mean magnetic field as a tracer of solar differential rotation
Authors: Hejna, L.; Wöhl, H.
1994smf..conf...65H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Time saeries of the penumbral Evershed effect.
Authors: Schleicher, H.; Wiehr, E.; Balthasar, H.; Wöhl, H.
1994AGAb...10..113S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Problems of solar rotation.
Authors: Wöhl, H.
1994soro.conf..127W Altcode:
Three selected problems of solar rotation are discussed. 1. The solar
rotation elements. 2. Polar rotation structures. 3. Interaction of
sunspots with the surrounding plasma.
---------------------------------------------------------
Title: Magnetic and nonmagnetic line profiles in solar quiet and
active regions
Authors: Kučera, A.; Rybák, J.; Wöhl, H.
1994smf..conf..291K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A comparison of large-scale patterns outlined by low brightness
temperature microwave regions and magnetic fields on the Sun
Authors: Brajša, R.; Pohjolainen, S.; Ruždjak, V.; Teräsranta,
H.; Urpo, S.; Vršnak, B.; Wöhl, H.
1994smf..conf...62B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Comparison of H<SUB>α</SUB> and Microwave Full-Disc
Solar Maps
Authors: Brajša, R.; Ruždjak, V.; Wöhl, H.
1994emsp.conf..125B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Contribution to the Round Table Discussion Concerning Solar
Databases at Catania, May 12, 1993
Authors: Wöhl, H.
1994emsp.conf..217W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Large-scale solar plasma rotation around stable sunspots
Authors: Lustig, G.; Woehl, H.
1993A&A...278..637L Altcode:
Motions of slowly evolving sunspots and the rotation velocity of the
plasma around them were determined within periods of one to three
weeks each year from 1990 until 1992. The sunspots were divided into
two classes depending on the size and number of proceeding and/or
following umbrae. Most of the sunspots were Zuerich type H, too large
and complex sunspots were rejected. The main aim was a determination
of plasma and sunspot velocities within larger fields of activity and
a search for special patterns of plasma flows, which may be caused
by interaction of the magnetized and unmagnetized plasmas. Around a
total of 34 sunspots about 130 plasma velocity fields with sizes of
about 120 by 70 arcseconds could be scanned. Within these fields the
plasma rotation velocity was determined using the non-split solar
spectral line at 5576 A with respect to laboratory iodine lines for
an array of 400 by 240 points. The averaging of sub-fields +5 degrees
in longitude (west) of the sunspots compared with those -5 degrees
(east) of the sunspots showed a difference of 50 m/s to 70 m/s for
the mean values with the same sign and about the same values for
the two classes of sunspots selected. The amount of this determined
asymmetry of the plasma rotation velocities in longitude depends on
the excess rotation velocity of the sunspots as compared to the mean
plasma rotation velocity at the latitudes where the sunspots were
observed. While no dependence on the longitude distribution of the
sunspots could be found, there is for both classes fo sunspots a more
pronounced asymmetry of the plasma rotation velocity in the southern
as compared to the northern hemisphere. Systematic errors are discussed
and excluded. Some attempts are given to explain the new findings.
---------------------------------------------------------
Title: Doppler oscillations in solar prominences simultaneously
observed with two telescopes. Discovery of a 30 S oscillation
Authors: Balthasar, H.; Wiehr, E.; Schleicher, H.; Wohl, H.
1993A&A...277..635B Altcode:
Time series of Doppler shifts are observed simultaneously with two
telescopes in order to separate actual solar velocities from influences
of image motion or unperfect guiding. Several maxima of the power
contours occur only in the data set from one of the two telescopes
and may thus originate from non-solar sources. Considering only those
power maxima which are observed with both telescopes we establish the
solar origin of periods near 20 and 12 min, which may be identified
with `hybrid fast modes' from model calculations. For one prominence a
significant period of 30 5 is detected which theory predicts as a wave
guided by the prominence fine-structures. Our prominence oscillations
are restricted to spatially small areas of a few arc see diameter.
---------------------------------------------------------
Title: Meridional motions of sunspot groups depending on different
activity cycles determined from two independent sets of data.
Authors: Lustig, G.; Wöhl, H.
1993sova.conf...82L Altcode:
A research project to determine the meridional motions of sunspots
from two independent sets of data has been started. The scientific
background, the aims of the reasearch and first results are described.
---------------------------------------------------------
Title: Plasma Motions Around Sunspots
Authors: Lustig, G.; Wohl, H.
1993ASPC...46...40L Altcode: 1993mvfs.conf...40L; 1993IAUCo.141...40L
No abstract at ADS
---------------------------------------------------------
Title: Time series of Doppler velocities in prominences.
Authors: Balthasar, H.; Schleicher, H.; Wöhl, H.; Wiehr, E.
1992AGAb....7..151B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar post-focus instrumentation.
Authors: Woehl, Hubertus
1992soti.book..145W Altcode:
The following lecture includes post-focus instrumentation for solar
observations. The wavelength region covered is mainly the visible,
although most of the equipment will be similar for observations in the
near ultraviolet or near infrared. Complex instrumentation as well as
detectors used in solar observatories are described.
---------------------------------------------------------
Title: The meridional motions of stable recurrent sunspots
Authors: Lustig, G.; Woehl, H.
1991A&A...249..528L Altcode:
The data bases of the Greenwich photoheliographic results and the
similar data from the Kanzelhohe are used to determine meridional
motions of a special sample of identical stable recurrent sunspots
within the period from 1948 until 1976. The motions are determined by
two different methods: from linear fits of the latitudes during the
sunspot disk passage and from mean latitudes at about central meridian
passages of recurrencies. The latter method is more reliable and allows
also to determine an indication for a braking of the meridional motions
with aging of the spots.
---------------------------------------------------------
Title: Asymmetries and shifts of the solar K I 7699 A line and
possible evidence for gravity waves in the quiet photosphere
Authors: Bonet, J. A.; Marquez, I.; Vazquez, M.; Woehl, H.
1991A&A...244..492B Altcode:
A computing code has been developed to simulate the center-to-limb
variation (CLV) of the bisector's shape, and absolute wavelength
shift of the core in strong photospheric lines. Observational results
concerning these aspects are also reported for the K I 7699 line. In
the numerical simulation, granulation is represented, as a first
approximation, by means of the granular model by Nelson (1978). It
appears that granulation alone does not reproduce the observations and
thus some modification has to be implemented in the dynamical model
employed. A good match to the observed CLV of the wavelength shift
of the line core is achieved by adding two 8-min period gravity waves
with horizontal wavelength of the granular scale, the only difference
between them being the sign of their horizontal wavenumber. Changes
in the phase difference between the oscillating parameters have a
decisive influence on the result.
---------------------------------------------------------
Title: State of the art of two-dimensional detector systems for
solar measurements.
Authors: Bin-Xun, Ye; Karud, J.; Wöhl, H.
1991LFTR...47.....B Altcode:
The present report is a review of available two-dimensional detectors
for solar applications with an emphasis on spectroscopy. In a separate
chapter high speed applications are briefly described. CCD-systems for
astronomical applications are in rapid evolution and at present one is
unable to recommend optimum systems for LEST. The goal of this report is
merely a first attempt to describe evolutionary trends of interest for
the project. This report includes a table of two-dimensional detector
systems for solar research actually in use.
---------------------------------------------------------
Title: The Main Component Analysis of the Longitudinal Distribution
of Solar Activity
Authors: Hejna, Ladislav; Wöhl, Hubertus
1991LNP...380..275H Altcode: 1991IAUCo.130..275H; 1991sacs.coll..275H
In this contribution, preliminary results of the main component
analysis of Bartels diagram of time series of daily values of sunspot
group numbers for solar cycles 18, 19 and 20 are presented. The results
obtained suggest that the most significant feature in the longitudinal
distribution of sunspot activity is the existence of preferred solar
hemispheres alternating with a mean period of 2.5 Bartels rotations.
---------------------------------------------------------
Title: The differential rotation of the solar plasma near the poles
Authors: Woehl, H.; Ye, B.
1990A&A...240..511W Altcode:
Based on a large amount of spectra taken from the solar polar regions
in the northern and southern solar hemisphere with a simultaneous
wavelength referencing, the empirical expression for the conventional
global solar differential rotation was checked for its reliability near
the solar poles. After carefully removing the solar limb red shift and
major scattered light effects, the results show a slightly steeper
gradient of the differential rotation law as compared to the Howard
and Harvey (1970) expression, the standard deviation to theirs being
less than 10 m/s. In addition, the reductions indicate a persistent
velocity pattern within 10 deg latitude around the poles: a lower
velocity of about 200 m/s as compared to the Howard and Harvey (1970)
law from 83 to 85 deg and a higher velocity of about 100 m/s from 86
to 89 deg. The pattern existed with very similar details within two
observing periods in summer 1989 and spring 1990.
---------------------------------------------------------
Title: Large-scale convection cells in the solar atmosphere
Authors: Lustig, G.; Wöhl, H.
1990Ap&SS.170...41L Altcode:
The directions and velocities of meridional plasma motions are
investigated using Doppler shifts of the magnetically non-split line
Fe 557.6 nm. Possible drifts of the spectrograph were controlled by
measuring nearly iodine lines from a laboratory source. The scattered
light was kept low by using the Capri Coudé refractor mainly around
local noon. There is a general scatter of about ±20 to ±50 m
s<SUP>-1</SUP> in the yearly mean results. The scatter is up to -200
m s<SUP>-1</SUP> for the year 1985. The results are compared with
published data. Although some systematic meridional plasma motions
could be detected from the average of the meridional flows within the
whole observing period 1982 until 1986, the final analysis suggests,
that all meridional motions averaged over half a solar cycle are below
±10 m s<SUP>-1</SUP>.
---------------------------------------------------------
Title: Die Sonnenrotation vor 100 Jahren.
Authors: Balthasar, H.; Wöhl, H.
1990S&W....29..296B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar meridional plasma motions from 1982 until 1986
Authors: Lustig, G.; Woehl, H.
1990A&A...229..224L Altcode:
The directions and velocities of meridional plasma motions are
investigated using Doppler shifts of the magnetically nonsplit line
Fe 557.6-nm. Possible drifts of the spectrograph were controlled by
measuring nearby iodine lines from a laboratory source. The scattered
light was kept low by using the Capri coude refractor mainly around
local noon. There is a general scatter of about + or - 20-50 m/sec
in the yearly mean results. The scatter is up to -200 m/sec for the
year 1985. The results are compared with published data. Although some
systematic meridional plasma motions could be detected from the average
of the meridional flows within the whole observing period 1982 until
1986, the final analysis suggests that all meridional motions averaged
over half a solar cycle are below + or - 10 m/sec.
---------------------------------------------------------
Title: Comparison of heliographic sunspot coordinates observed with
seven different solar telescopes.
Authors: von Alvensleben, A.; Casas, R.; Csepura, G.; Lustig, G.;
Otruba, W.; Schroll, A.; Vazquez, M.; Wittmann, A. D.; Wöhl, H.
1990AGAb....5...43V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Large-Scale Motions in the Solar Photosphere (Observational
Aspects)
Authors: Wöhl, H.
1990PDHO....7...19W Altcode: 1990ESPM....6...19W; 1990dysu.conf...19W
No abstract at ADS
---------------------------------------------------------
Title: Meridional Motions of Recurrent Sunspots - a Comparison of
Greenwich and Kanzelhöhe Data
Authors: Lustig, G.; Wöhl, H.
1990PDHO....7...53L Altcode: 1990ESPM....6...53L; 1990dysu.conf...53L
No abstract at ADS
---------------------------------------------------------
Title: The Differential Rotation Law of the Solar Plasma nearby
the Poles
Authors: Wöhl, H.; Ye, B.
1990PDHO....7...52W Altcode: 1990dysu.conf...52W; 1990ESPM....6...52W
No abstract at ADS
---------------------------------------------------------
Title: Equatorial rotation velocity of the Sun from 1983 to 1986
(poster)
Authors: Lustig, G.; Wöhl, H.
1989hsrs.conf..540L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar equatorial plasma rotation from 1983 until 1986
Authors: Lustig, G.; Woehl, H.
1989A&A...218..299L Altcode:
The plasma rotation velocity at the solar equator is investigated
using Doppler shifts of the magnetically nonsplit line Fe 557.6 nm. The
results are compared with data from Stanford and from Mt. Wilson. There
is a comparable scatter in all these data of about 10 to 50 m/s. Since
no systematic correlations of variations can be found, it is assumed
that such variations are caused by instrumental effects and by
small-scale solar fluctuations rather than by large-scale solar
velocity fields.
---------------------------------------------------------
Title: The solar rotation 1883 until 1893 as inferred from the
Greenwich Photoheliographic Results and observations published by
G. Spoerer
Authors: Woehl, H.; Balthasar, H.
1989A&A...219..313W Altcode:
The finding that the solar rotation velocity inferred from the
Greenwich Photoheliographic Results (GPR) as compared to that from
observations published by G. Spoerer for the years 1883 until 1893
shows a difference of the order of 0.1 deg/day is investigated in
some details. An analysis of rotation velocities of stable sunspots,
which are covered sufficiently by observations in both sets of data,
yields no significant differences. The mean difference is nearly two
orders of magnitude below the above cited value. The explanation of the
difference is the presence of more short-living sunspots in the GPR,
which show a more rapid rotation velocity. There are about twice as
many days without any spot observations in the publications of Spoerer
as compared to the GPR. Some indications are presented, that the solar
behavior changed after the begining of our century.
---------------------------------------------------------
Title: Pole-equator-difference of the size of the chromospheric CA
II-K-network in quiet and active solar regions
Authors: Muenzer, H.; Schroeter, E. H.; Woehl, H.; Hanslmeier, A.
1989A&A...213..431M Altcode:
The dependence of the size of chromospheric network cells on latitude
was investigated for quiet and active solar regions. Calibrated
photographic Ca II K-filtergrams were used and a Fast Fourier Transform
analysis was performed to obtain the cell size. Among other reductions
the results had to be corrected for seeing effects. A significant
decrease of the cell size toward higher latitudes and an increase with
locally increasing magnetic activity was found.
---------------------------------------------------------
Title: A thinned CCD camera for solar spectroscopic investigations -
testing and first applications
Authors: Schleicher, H.; Wittman, A. D.; Wöhl, H.; Ye, B.
1989AGAb....3...18S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Pole-Equator Difference of the Size of the Chromospheric Ca
II-K Network in Quiet and Active Solar Regions
Authors: Münzer, H.; Hanslmeier, A.; Schröter, E. H.; Wöhl, H.
1989ASIC..263..217M Altcode: 1989ssg..conf..217M
No abstract at ADS
---------------------------------------------------------
Title: Temporal and center-to-limb variations of the K I 769.9 NM
line profiles in quiet and active solar regions
Authors: Bonet, J. A.; Marquez, I.; Vazquez, M.; Woehl, H.
1988A&A...198..322B Altcode:
The temporal and spatial behaviour of the K I 769.9 nm solar line are
investigated using several series of high spectral resolution low-noise
photoelectric scans obtained at Kitt Peak National Observatory in
quiet and active (plages and sunspots) regions. Corrections due
to the instrumental profile were applied to yield the best line
shape. A systematic center-to-limb investigation of the behaviour
of the line shape was performed in quiet regions. Power and phase
spectra of the main parameters defining the line shape have also
been determined. Within several umbrae at different cos θ positions,
an inverse C-shape or even an "S"-shape of the bisectors was found.
---------------------------------------------------------
Title: On the Age Dependence of the Asymmetry of Penumbrae of Sunspots
Authors: Collados, M.; del Toro Iniesta, J. C.; Vazquez, M.; Woehl, H.
1988SoPh..117..199C Altcode:
The age dependence of the recently described asymmetry of penumbrae
of large stable sunspots was analyzed. Young sunspots showed shorter
eastern penumbrae, which differed by a maximum of ± 10 % from their
mean width. For older sunspots the western penumbrae became smaller
than the mean penumbra reaching differences of 20 % for spots of two
months age.
---------------------------------------------------------
Title: On the possible detection of large-scale solar meridional
motions by analyzing A-type spots from the Greenwich photoheliographic
results
Authors: Woehl, H.
1988SoPh..116..199W Altcode:
Young A-type sunspots taken from the Greenwich Photoheliographic
Results (1940-1976) were used to search for systematic meridional
motions. No indication for a systematic pattern of meridional motions
could be found.
---------------------------------------------------------
Title: Solar radiation and solar differential rotation
Authors: Wöhl, H.
1988SoPh..114..181W Altcode:
Areas of sunspots and their positions taken from the Greenwich
Photoheliographic Results (1874-1976) and typical intensities of the
umbrae and penumbrae are used to calculate daily values of the solar
flux at a wavelength of about 500 nm. Using overlapping time series
of 512 days each solar rotation periods are determined by Fourier
transformation. The periods found depend on the phase of the solar
activity cycle, as expected from the solar differential rotation. This
method may be used for solar type stars to determine relations between
activity and rotation too. The problems of errors - e.g. by faculae
or the variation of the umbral intensity within the activity cycle -
are explained.
---------------------------------------------------------
Title: The solar rotation elements i and Omega derived from recurrent
single sunspots
Authors: Balthasar, H.; Woehl, H.; Stark, D.
1987A&A...174..359B Altcode:
Using the data of recurrent single sunspot observations obtained at
Greenwich 1874 to 1976 the solar rotation elements were determined. The
results confirm earlier results, where a smaller i-value and a slightly
bigger Ω-value as compared to the well known Carrington rotation
elements was found. No indication was found for a systematic difference
between solar rotation elements determined from recurrent single
sunspots as compared with results using all sunspot group positions.
---------------------------------------------------------
Title: Solar radiation and solar differential rotation
Authors: Woehl, H.
1987SoPh..114..181W Altcode:
Sunspot areas and positions obtained from the Greenwhich
Photoheliographic Results for 1874-1976, and typical intensities of
the umbrae and penubrae, have been used to determined daily values
of the solar flux at 500 nm wavelength. Overlapping time series of
512 days each are used to obtain solar rotation periods by Fourier
transformation, and the periods are shown to depend upon the phase
of the solar activity cycle. Sources of error involving the faculae
or the variation of the umbral intensity within the activity cycle
are considered.
---------------------------------------------------------
Title: Center-to-Limb Variation of the Asymmetries of the K 7699 Å
line in Solar Quiet and Active Regions
Authors: Bonet, J. A.; Marquez, I.; Vázquez, M.; Wöhl, H.
1987rfsm.conf...32B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Die Sonnenachsenlage - wie bekannt!?
Authors: Wöhl, H.
1987Sonne..11....4W Altcode:
The latest results in determining the solar rotation elements are given.
---------------------------------------------------------
Title: Solares Aktivitätsminimum erst 1989/90?
Authors: Landscheidt, T.; Wöhl, H.
1986S&W....25..584L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The solar rotation elements i and omega derived from sunspot
groups
Authors: Balthasar, H.; Lustig, G.; Woehl, H.; Stark, D.
1986A&A...160..277B Altcode:
Greenwich Photoheliographic results from 1874 to 1976 are completed
to reduce the mean value errors of the i and Omega determination, and
results are verified with independent data obtained between 1947 and
1984 at the Kanzelhohe observatory. The data-reduced i value of 7.137 +
or - 0.017 deg is much less than the Carrington (1863) value, while
the Omega(1850) vlkue of 73.75 + or - 0.15 deg is not significantly
different than the Carrington Value.
---------------------------------------------------------
Title: Zum Pol-Äquator Unterschied des Chromosphärischen
Ca<SUP>+</SUP>- Netzwerks und des supergranularen
Geschwindigkeitsfeldes
Authors: Münzer, H.; Rimmele, T.; Schröter, E. H.; Wöhl, H.
1986MitAG..67..281M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solare Strahlung und Sonnenrotation
Authors: Wöhl, H.
1986MitAG..67..277W Altcode:
Der Autor untersucht, ob die differentielle Rotation der Sonne aus
den Strahlungsmessungen ermittelt werden kann.
---------------------------------------------------------
Title: Rotation und meridionale Strömungen auf der Sonne
Authors: Hanslmeier, A.; Lustig, G.; Wöhl, H.
1986MitAG..67..285H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Differential rotation of sunspot groups in the period from
1874 through 1976 and changes of the rotation velocity within the
solar cycle
Authors: Balthasar, H.; Vazquez, M.; Woehl, H.
1986A&A...155...87B Altcode:
An effort is made to determine the differential rotation of the sun
on the basis of the complete sample (1874-1976) of the Greenwich
Photoheliographic Results. In order to improve the representation
of differential rotation, a modified fit formula whose constant
lies at 15 deg latitude (where sunspots nearly always occur) is
introduced. Rotation is noted to strongly depend on sunspot type,
with C-groups exhibiting high velocities and H- and J-spots the lowest
ones. The new fit formula indicates that the highest velocity is found
around the minima; at the beginning of an activity maximum, there
is a secondary velocity maximum. The lowest velocities lie between
the activity maximum and minimum. The braking of recurrent sunspots
is confirmed.
---------------------------------------------------------
Title: Eine Jahrhundertarbeit über Sonnenfleckengruppen.
Authors: Balthasar, H.; Vázquez, M.; Wöhl, H.
1985S&W....24..634B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Comparison of Artificial Solar Granules with Real Solar
Granules
Authors: Woehl, H.; Nordlund, A.
1985SoPh...97..213W Altcode:
The lifetimes, characteristics of the shapes as well as lengths and
perimeters of artificial solar granules (Nordlund, 1982, 1984a) are
compared with data from the literature and parameters determined from
two different sets of observed granules. No significant differences
of the parameters for these sets of granules are detectable.
---------------------------------------------------------
Title: Westdeutsche experimentelle Sonnenforschung bis zum
Jahrtausendende.
Authors: Wöhl, H.
1985Sonne...9...94W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The response of the line KI 7699 to the solar oscillations
Authors: Marmolino, C.; Roberti, G.; Severino, G.; Vazquez, M.;
Woehl, H.
1984ESASP.220..191M Altcode: 1984ESPM....4..191M
The time behavior of the KI 7699 line profile in presence of
acoustic-gravity waves with periods of 300, 180, and 30 sec was
studied. The response of the line to the waves depends strongly on
the period and is not linear for the 30 sec wave. The height increase
of the amplitude in the longer period waves explains the observed
anticorrelation between line asymmetry and line core shift. The time
averaged profile for the 30 sec wave has a red shifted line core. This
could account for the lowest part of the C shaped solar bisectors.
---------------------------------------------------------
Title: On the determination of the solar rotation and indications of
the solar differential rotation from an analysis of solar integrated
light.
Authors: Drescher, T.; Woehl, H.; Kueveler, G.
1984ESASP.220...29D Altcode: 1984ESPM....4...29D
The rotation modulation of the emission measure of the Ca<SUP>+</SUP>K
line within the integrated solar light is used to determine the solar
rotation period. Attempts are made to determine changes of this period
due to the differential rotation and the different latitude regions
of the activity.
---------------------------------------------------------
Title: The use of molecular iodine absorption lines as wavelength
references for solar Doppler shift measurements
Authors: Koch, A.; Woehl, H.
1984A&A...134..134K Altcode:
Molecular iodine absorption lines are used as wavelength references for
solar Doppler shift measurements near 5576 Å and 5612 Å. The possible
shifts of these wavelength references caused by weak lines in the solar
continuum used as the light source, are investigated by measurements and
numerical model calculations. Within the solar spectrum from 5000 Å to
6000 Å optimum windows are given for the use of iodine reference lines.
---------------------------------------------------------
Title: On the Determination of Heliographic Positions and Rotation
Velocities of Sunspots - Part Three - Effects Caused by Wrong Solar
Image Radii and Their Corrections
Authors: Balthasar, H.; Lustig, G.; Woehl, H.
1984SoPh...91...55B Altcode:
In an earlier paper of this series it was shown how the Wilson
depression influences the determination of sunspot rotation
velocities. Using this finding and the fact that stable recurrent
sunspots show a very constant rotation velocity it is possible to
determine the effect of wrong solar image radii on the determination
of sunspot rotation velocities and correct them.
---------------------------------------------------------
Title: New information about solar rotation
Authors: Woehl, H.; Balthasar, H.; Koch, A.; Kueveler, G.; Roca-Cortes,
T.; Schmidt, W.; Vazquez, M.
1984S&W....23...73W Altcode:
It is pointed out that the phenomenon of solar rotation is known
since the introduction of the telescope into astronomy by Galilei in
1610. Regular measurements concerning the positions of sunspots were
conducted with the aid of photographic plates at the Royal Greenwich
Observatory during the time from 1874 to 1976. The obtained data
provide an excellent basis for statistical analysis. Information
obtained as a result of such analyses is discussed. Attention is given
to the determination of the Wilson depression, details regarding
solar differential rotation, plans for an evaluation of data with
the aid of a computer, the rotation of the solar plasma, a comparison
of sunspots and plasma, the theory of differential rotation, and new
information concerning solar rotation partly obtained with the aid of
solar telescopes in a Spanish observatory on the island of Tenerife.
---------------------------------------------------------
Title: Profile Variations of the Solar KI 7699 Line In Quiet and
Active Regions
Authors: Bonnet, J. A.; Marquez, T.; Roca-Corks, T.; Vasquez, M.;
Wohl, H.; Wittman, A.
1984ssdp.conf..323B Altcode:
The authors have investigated the time behaviour of the K I 7699 line
profile in quiet and active regions and measured the line asymmetries
by the bisector method. In the mean bisectors a red asymmetry was found
in the magnetic plages in contrast to the typical blue one of the quiet
regions. The anticorrelation, reported by Roca-Cortes at al. (1983),
between the asymmetry and the 5-min oscillation seems to be confirmed.
---------------------------------------------------------
Title: Gibt es meridionale Strömungen des solaren Plasmas?
Authors: Lustig, G.; Wöhl, H.
1984MitAG..62..217L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Atlas of Spectral Line Asymmetries and Their CLV From
Solar FTS Spectra
Authors: Balthasar, H.; Wohl, H.
1984ssdp.conf..317B Altcode:
Preliminary informations are given on the CLV of solar spectral line
asymmetries in quiet regions. The results are based on FTS spectra with
high spectral resolution and a S/N of about 3000. Three main classes of
the CLVs of solar spectral lines are introduced and their dependences on
the excitation potentials of the lines and their heights of formation
are given. In addition shifts of lines depending on their formation
depths, equatorial rotation velocities and limb-effect results are
given.
---------------------------------------------------------
Title: Recommendations on post focus instrumentation for LEST.
Authors: Wöhl, H.; Huber, M. C. E.; Mein, P.; Smaldone, L.
1984LFTR....5.....W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Neues über die Sonnenrotation.
Authors: Balthasar, H.; Koch, A.; Küveler, G.; Roca-Cortes, T.;
Schmidt, W.; Vázquez, M.; Wöhl, H.
1984S&W....23...73B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Determination of Heliographic Positions and Rotation
Velocities of Sunspots - Part Two - Systematic Effects Caused by
the Wilson Depression
Authors: Balthasar, H.; Woehl, H.
1983SoPh...88...71B Altcode:
Using sunspot positions of small sunspots observed at Debrecen and
Locarno as well as positions of recurrent sunspots taken from the
Greenwich Photoheliographic Results (1940-1976) the influence of the
Wilson depression on the rotation velocities was investigated. It
was found that the Wilson depression can be determined by minimizing
errors of the rotation velocities or minimizing the differences of
rotation velocities determined from disk passages and central meridian
passages. The Wilson depressions found were between 765 km and 2500
km for the first sample while they were between 0 km and several
1000 km for the second sample. The averaged Wilson depression for the
second sample is between 500 km and 965 km depending on the reduction
method. A dependence of the Wilson depression on the age of the spots
investigated seems not to exist.
---------------------------------------------------------
Title: Space and time variations of KI 7699 solar line profile
Authors: Roca-Cortes, T.; Vazquez, M.; Woehl, H.
1983SoPh...88....1R Altcode:
The temporal and spatial behaviour of the KI7699 line profile is
investigated. In particular we have measured the asymmetries of the line
profile at several residual intensities using the bisector method. We
find, in the bisector of the mean line profile, similar shapes as those
obtained before for different positions on the solar disk. However the
strong variations of the bisector found with time and geometry of input
aperture, warns us against the use of the mean or integrated profiles
(either in time or space). Moreover, we find an anticorrelation between
the asymmetry in the line profile at different residual intensities
and the shift, found as the distance to a terrestrial line, for any
position observed on the solar disk. No limb effect for this line is
found, within errors.
---------------------------------------------------------
Title: On the Determination of Heliographic Positions and Rotation
Velocities of Sunspots - Part One - Comparison of Results from
Different Observatories and Different Observing Procedures
Authors: Woehl, H.
1983SoPh...88...65W Altcode:
Heliographic coordinates of several small but stable sunspots,
which were determined at five different observatories in 1979, are
compared. Some systematic differences within these results are found,
which suggest a more detailed analysis of the data accumulation
procedures and the physical interpretation. The same holds for the
rotation velocities derived from the position data.
---------------------------------------------------------
Title: Daily variations of the photospheric equatorial rotation
velocity of the sun and its absolute values in 1981 and 1982 as
determined from measurements using a two-dimensional photodiode array
Authors: Kueveler, G.; Woehl, H.
1983A&A...123...29K Altcode:
Doppler velocity measurements using the solar spectral line Fe I 6301.5
Å and the terrestrial O<SUB>2</SUB> line at 6302.0 Å as a reference
were used to determine the equatorial rotation velocity of the solar
photosphere. The spectral lines were recorded by a two-dimensional
photodiode array. <P />The absolute values of the rotation velocity
were 1988 m/s in April 1981 and 1953 m/s in May 1982. The daily
variations did not exceed 10 m/s when time averages of several hours
existed. <P />The comparison with results from other observes and other
observatories shows the same behaviour from 1981 to 1982: a decrease of
the rotation velocity by about 35 m/s. But neither the absolute values
nor the daily changes are in good agreement with other observations.
---------------------------------------------------------
Title: A matrix photodiode array to measure Doppler shifts of solar
spectral lines
Authors: Kueveler, G.; Woehl, H.
1983A&A...122...69K Altcode:
A 100×100 photodiode array of the Reticon type is used to measure
velocity fields in the solar atmosphere at the Locarno Observatory of
the University of Göttingen. A 16 bit microprocessor serves to control
the array and the telescope. Several tests were performed to determine
the properties of the new measurement system. After correction for
the dark current and the flat field the fixed pattern noise is less
than 1%. Averaging over 5 rows of the array, which corresponds to a
spatial averaging over 2arcsec.5, allows to determine velocities with
a precision of ±25 m/s.
---------------------------------------------------------
Title: Possibilities and attempts to determine the differential
rotation on F-type main-sequence stars
Authors: Woehl, H.
1983IAUS..102..155W Altcode:
The differential rotation upper limits have been determined for 11
F-type stars, mostly from the main sequence, by means of a Fourier
transformation analysis of their spectral lines. No indication is found
of steep differential rotation for stars of this type, as claimed
by Belvedere et al. (1980). The present results are in keeping with
those obtained by Gray (1982) for other spectral lines of largely
different stars.
---------------------------------------------------------
Title: Differentielle Rotation der Sonne - Nachweis aus
Integralmessungen
Authors: Drescher, Th.; Küveler, G.; Wöhl, H.
1983MitAG..60..238D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rotationsgeschwindigkeit des photosphärischen Sonnenplasmas
Authors: Küveler, G.; Wöhl, H.
1983MitAG..60..237K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Erratum - Differential Rotation and Meridional Motions of
Sunspots from 1874 TO 1902
Authors: Arevalo, M. J.; Gomez, R.; Vazquez, M.; Balthasar, H.;
Wohl, H.
1983A&A...117..170A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Absorption Lines of Feh in a Sunspot Spectrum
Authors: Wohl, H.; Engvold, O.; Brault, J. W.
1983itab.rept....1W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rotationsgeschwindigkeiten von Sonnenflecken - mögliche
Fehler und ihre Korrektion
Authors: Balthasar, H.; Lustig, G.; Wöhl, H.
1983MitAG..60..236B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Absorption lines of FeH in a sunspot spectrum.
Authors: Wöhl, H.; Engvold, O.; Brault, J. W.
1983ITABO..56.....W Altcode:
The strengths of the 8690 Å and 9890 Å bands of the FeH molecule
are measured in the spectrum of a large sunspot. The strongest lines
attain central depths of about 20% of the continuum intensity.
---------------------------------------------------------
Title: Terrestrial O2 lines used as wavelength references - Comparison
of measurements and model computations
Authors: Balthasar, H.; Thiele, U.; Woehl, H.
1982A&A...114..357B Altcode:
High precision spectral measurements of the wavelength of terrestrial
O2 lines within solar spectra using the Kitt Peak 1-m Vacuum Fourier
Transform Spectrometer are compared with model computations of the
shifts of these lines due to wind up to 20 km. Although the wind data
available existed only from radio sonde measurements about 65 km away
and only from two launches per day, the shifts observed during two days
could be explained well. Maximum shifts of terrestrial O2 lines of +
or - 0.3 mA at about 6300 A were observed. It is shown that it may
be possible to correct a general trend of the observed shifts with a
precision of + or - 3 m/sec during a day.
---------------------------------------------------------
Title: Wie rotieren Sterne?
Authors: Woehl, H.
1982S&W....21..299W Altcode:
Theories of stellar rotation are discussed. The discovery of sunspots
and their use in determining rotation rates is explained along with
use of spectroscopy, in particular the Doppler effect, in determining
rates, and the differential rotation of the sun is discussed with
some mathematics. The most important theories of differential solar
rotation are presented: differential viscosity in the convection zone,
interaction of convective cells with rotating gas, and the influence
of the Coriolis force. The relationship of stellar rotational velocity
to spectral type is shown and explained, and methods of determining
stellar rotation are discussed, including relating variations in
stellar activity to variations in starspot spectra, and analyzing
spectral profiles with Fourier transforms.
---------------------------------------------------------
Title: Differential rotation and meridional motions of sunspots from
1874 to 1902
Authors: Arevalo, M. J.; Gomez, R.; Vazquez, M.; Balthasar, H.;
Woehl, H.
1982A&A...111..266A Altcode:
Position data of sunspot groups from the period 1874-1902 are used to
investigate the differential rotation of the Sun and the meridional
motions of the sunspots. The equatorial velocity is higher than in
the period 1940-1968 investigated by Balthasar and Wöhl (1980), while
differences between the northern and southern hemispheres are less. For
cycle 12 we find meridional motions towards north while in cycle 13 the
motions are directed towards south like in the period 1940-1968. Our
other results are comparable to those of Balthasar and Wöhl (1980)
for the period 1940-1968.
---------------------------------------------------------
Title: Solar site-testing campaign of JOSO on the Canary Islands
in 1979
Authors: Brandt, P. N.; Woehl, H.
1982A&A...109...77B Altcode:
Results of the campaign of testing undertaken by the European JOSO
(Joint Organization for Solar Observations) in order to find an
excellent site for solar observations are presented. Measurements
with telescopes of 40 and 45 cm aperture and photoelectric
seeing measurements were made at the sites of Izana and Roche
de los Muchachos on the Canary Islands of Tenerife and La Palma,
respectively. Observations obtained on 160 days between April and
November, 1979 demonstrate the superiority of Izana in the area of
image sharpness, although both sites offer an increase of one order
of magnitude in the duration of good seeing compared to existing
European stations. Photographs of the solar granulation taken from
July to November confirm the superiority of Izana, where 4.5% of the
exposures exhibit very high quality compared to 1.4% at Roche de los
Muchachos. Analysis of meteorological records indicates that Izana
is capable of providing 3000 hour/year of usable solar observations,
and suggest an explanation for the higher quality of the Izana site.
---------------------------------------------------------
Title: Book Reviews
Authors: Shaviv, G.; de Jager, C.; De Loore, C.; Fricke, W.; Kleczek,
J.; van Zolingen, R. J. C.; Vardya, M. S.; Wöhl, H.; Tauber, G.;
de Jong, T.; de Graaff, W.
1982SSRv...31..119S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On changes of the rotation velocities of stable, recurrent
sunspots and their interpretation with a flux tube model
Authors: Balthasar, H.; Schuessler, M.; Woehl, H.
1982SoPh...76...21B Altcode:
The angular rotation velocities of stable, recurrent sunspots
were investigated using data from the Greenwich Photoheliographic
Results 1940 until 1968. We found constant rotation velocities
during the passages on the solar disk with errors of about ±4 m
s<SUP>−1</SUP>. During their lifetime these spots show a decreasing
braking of their rotation velocities from 0.8 to 0.3 m s<SUP>−1</SUP>
per day. A plausible interpretation is found by assuming the spots
to be coupled to a slowly rising subsurface flux tube and a rotation
velocity which increases with depth.
---------------------------------------------------------
Title: A model for constructing artificial integrated spectral lines
and their Fourier transform properties relevant to the search for
differential rotation of stars
Authors: Garcia-Alegre, M. C.; Vazquez, M.; Woehl, H.
1982A&A...106..261G Altcode:
A model is given for constructing artificial integrated spectral lines
which allows the inclusion of all effects relevant to the synthesis
of these lines by numerical methods. Among the effects included are
noise, limb darkening, the centre-to-limb variation of the shapes and
wavelength positions of the spectral line profiles, different laws
of the differential rotation and a tilting of the rotating star. <P
/>Fourier transformation of the artificial integrated spectral lines
is applied to decide whether the different effects may influence the
possibility of detecting stellar differential rotation by the method
of Gray (1977).
---------------------------------------------------------
Title: Sonnenrotation des photosphärischen und umbralen Plasmas
Authors: Koch, A.; Wöhl, H.
1982MitAG..55...91K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book Review: The Ancient Sun - Fossil Record in the Earth,
Moon, and Meteorites
Authors: Pepin, R. O.; Eddy, J. A.; Merrill, R. B.; Wöhl, H.
1982SSRv...31R.121P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Limb-Effekte und Asymmetrien solarer Spektrallinien zwischen
4800 und 6500 Angström in Fouriertransformspektren
Authors: Balthasar, H.; Wöhl, H.
1982MitAG..55...71B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Messung des Geschwindigkeitsfeldes der solaren
Super-granulation mit einem 100 x 100 Photodiodenarray
Authors: Küveler, G.; Wöhl, H.
1982MitAG..55...92K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Untersuchung von Referenzlinien zur solaren Doppler-messung
Authors: Thiele, U.; Wöhl, H.
1982MitAG..55...93T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Motions and Lifetimes of the Penumbral Bright Grains in
Sunspots
Authors: Toenjes, K.; Woehl, H.
1982SoPh...75...63T Altcode:
It is confirmed that the penumbral bright grains are moving towards
the sunspots umbra. We find different proper motions of 0.08 to 0.33
km s<SUP>−1</SUP> for different penumbrae and different reduction
methods. The lifetimes of these bright grains are about 1.5 to 3 hr
depending on the position in the penumbra.
---------------------------------------------------------
Title: On the size and structure of bright solar
Ca<SUP>+</SUP>-network cells depending on the heliographic position
Authors: Brune, R.; Woehl, H.
1982SoPh...75...75B Altcode:
From photographic recordings of some hundred bright
Ca<SUP>+</SUP>-network cells on the solar disk we find evidence for
a smaller size of polar cells as compared to equatorial cells by a
factor of about 0.9. We do not find an indication of a dependence of
the structure of the cells on the heliographic position.
---------------------------------------------------------
Title: Der Einsatz eines zwei-dimensionalen Photodioden-arrays zur
spektroskopischen Erfassung solarer Geschwindigkeitsfelder.
Authors: Kueveler, G.; Woehl, H.
1981S&W....20..452K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On Diurnal Variations of the Solar Rotation Rate as Derived
from Sunspot Tracings
Authors: Koch, A.; Woehl, H.; Schroeter, E. H.
1981SoPh...71..395K Altcode:
The heliographic positions of more than 100 sunspots were accurately
measured several times a day from 1974 until 1979 by means of the
computer-controlled tracing method described by Schröter and Wöhl
(1975). A striking degree of constancy of the solar rotation rate (about
0.15% or 3 m s<SUP>−1</SUP>) is found, when east-west proper motion
components of each individual stable sunspot is considered. However,
large differences of the rotation rate are observed (up to 7% or 130
m s<SUP>−1</SUP>) when comparing different sunspots. We found no
significant correlation of these fluctuations with characteristics of
the sunspots (age, evolution, etc.).
---------------------------------------------------------
Title: Erratum - Differential Rotation and Meridional Motions of
Sunspots in the Years 1940-1968
Authors: Balthasar, H.; Wohl, H.
1981A&A....98..422B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Rotation Velocity as Determined from Sunspot Drawings
of Hevelius, J. in the 17TH-CENTURY
Authors: Abarbanell, Claudia; Wöhl, Hubertus
1981SoPh...70..197A Altcode:
Using two original copies of Hevelius' `Selenographia' and reducing
spot positions with two different methods, we found that the solar
angular rotation velocity at the beginning of the Maunder minimum was
about the same as today. The gradient of the differential rotation was
slightly steeper than given in modern reductions, but not significantly
different. These findings are in contradiction to those published by
Eddy et al. (1976).
---------------------------------------------------------
Title: Giant Cells? why are they Expected? what can BE done to
Find Them?
Authors: Wöhl, H.
1981siwn.conf..128W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Die Rotationselemente i und OMEGA der Sonne.
Authors: Stark, D.; Woehl, H.
1981S&W....20...61S Altcode:
Values of i and Omega for 1940 to 1968 have been obtained from sunspot
observations. It is shown that the present values of the rotation
elements do not deviate significantly from those obtained by Carrington
(1863) and agree well with those of Clark et al. (1979).
---------------------------------------------------------
Title: Zum Nachweis der differentiellen Rotation auf Sternen der
Hauptreihe
Authors: Garcia-Alegre, M. C.; Vázquez, M.; Wöhl, H.
1981MitAG..52...67G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Einsatz eines 100 x 100 Photodiodenarrays zur Messung solarer
Geschwindigkeitsfelder
Authors: Küuveler, G.; Wöhl, H.
1981MitAG..52S.106K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Einsatz eines 100×100 Photodiodenarrays zur Messung solarer
Geschwindigkeitsfelder.
Authors: Küveler, G.; Wöhl, H.
1981MitAG..52..106K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Großräumige Strömungszellen in der Photosphäre der Sonne -
spektroskopisch gemessen mit einem linearen Photodiodenarray
Authors: Perez Garde, M.; Vázquez, M.; Wöhl, H.; Schwan, H.
1981MitAG..52..119P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the solar rotation elements as determined from sunspot
observations
Authors: Stark, D.; Woehl, H.
1981A&A....93..241S Altcode:
The solar rotation elements Omega and i have been determined from
sunspot observations in the years 1940 to 1968 given in the 'Greenwich
Photoheliographic results'. The result based on 2134 groups with at
least 8 observations is: Omega (1980) 75.8 plus or minus 0.27 deg,
i 7.15 plus or minus 0.034 deg. The results, though not significantly
different from Carrington's rotation elements, are characterized by
a smaller i and a larger Omega, in agreement with other authors
---------------------------------------------------------
Title: Differentielle Rotation und meridionale Bewegungen von
Sonnenflecken in den Jahren 1940 bis 1968
Authors: Balthasar, H.; Wöhl, H.
1981MitAG..52...26B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Large-Scale Solar Motions as Determined by Doppler Shift
Measurements Using a Linear Photodiode Array
Authors: Perez Garde, M.; Vazquez, M.; Schwan, H.; Woehl, H.
1981A&A....93...67P Altcode: 1981MiABB..96...67P
Doppler shifts of the solar Fe line 630.15 nm relative to the
terrestrial O2 line 630.2 nm were determined at many positions on
the solar disk to investigate the rotation of the solar plasma and
locate large-scale plasma motions. The spectrum was measured by a
self-scanning linear photodiode array with 128 diodes; and average
rotation velocity of (2.881 plus or minus 0.027) microrad/s was found at
the solar equator in September 1978, and large-scale velocity pattern
occurred between plus 40 and minus 30 deg in latitude with a period
of 45 deg in longitude during Sept. 6 to 13, 1978.
---------------------------------------------------------
Title: Die Rotationselemente i und Ω der Sonne
Authors: Stark, D.; Wöhl, H.
1981MitAG..52Q.145S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Zur Rotationsgeschwindigkeit stabiler Sonnenflecken.
Authors: Wöhl, H.
1981Sonne...5...46W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Site-Untersuchungen für ein neues Sonnenobservatorium auf
den Kanarischen Inseln.
Authors: Brandt, P. N.; Wöhl, H.
1981S&W....20..359B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Computergesteuerte Tracermessungen an Sonnenflecken
Authors: Koch, A.; Wöhl, H.; Schröter, E. H.
1981MitAG..52..105K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the variability of the solar diameter
Authors: Wittmann, A. D.; Bonet Navarro, J. A.; Woehl, H.
1981phss.conf..424W Altcode:
In an attempt to elucidate the daily fluctuations seen in the 1980
drift time data (August 30-September 13) and to monitor the solar
diameter for an interval as long as possible, visual drift timing
observations were made on 46 consecutive days, from May 16 to June 30,
1981. A total of 2091 visual drift times (including 11 doubtful ones)
was obtained. From the observations, R(vis) is found to be 960.2 +
or - 0.1 arcsec, that is, the standard value of 961.18 arcsec derived
from Greenwich transits is much too large. With due weight assigned
to the photoelectric observations, it is concluded that the correct
value of R is 960.0 + or - 0.1 arcsec.
---------------------------------------------------------
Title: Differential rotation and meridional motions of sunspots in
the years 1940-1968
Authors: Balthasar, H.; Woehl, H.
1980A&A....92..111B Altcode:
Using positions of sunspots from the Greenwich Photoheliographic
Results from 1940 to 1968 equations for the differential rotation and
meridional motions of sunspot groups are determined. The differential
rotation depends on the phase in the solar cycle and on the type of the
groups. The meridional motions show a general southdrift of the spots,
but they are not significantly different from zero. The significance
of the equatorward motion near the equator found by Ward (1965) seems
to be due to an effect of selection. Changes of the meridional motions
with time are not in good agreement with former publications, but they
are also not significant. A dependence of the meridional motions on
the local activity is not detectable.
---------------------------------------------------------
Title: Solar observations at the Göttingen University Observatory
Authors: Wiehr, E.; Wittmann, A.; Wöhl, H.
1980SoPh...68..207W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Identification of the CrH molecule in a sunspot spectrum.
Authors: Engvold, O.; Woehl, H.; Brault, J. W.
1980A&AS...42..209E Altcode:
The <SUP>6</SUP>Σ<SUP>+</SUP> - <SUP>6</SUP>Σ<SUP>+</SUP> infrared
system of the CrH molecule has been identified in the spectrum of a
large sunspot.
---------------------------------------------------------
Title: Änderungen der differentiellen Rotation und meridionale
Bewegungen von Sonnenflecken 1940 bis 1968.
Authors: Balthasar, H.; Woehl, H.
1980S&W....19..385B Altcode:
Various methods of measuring solar activity are discussed with
emphasis given to following identifiable objects such as sunspots over
a period of time. A formula describes the rotation of sunspots for the
period between 1940 and 1968, and the data for each year are divided
within a seven year cycle. Mathematical formulas of rotation are also
presented for the northern and southern hemispheres. Latitudinal
movement of sunspots is investigated and compared to the method of
Ward (1965). Differences in northern and southern hemisphere movement
are considered.
---------------------------------------------------------
Title: Reconstruction of the Locarno Telescope before shifting to
the Canary Islands site
Authors: Wiehr, E.; Wöhl, H.
1980fsoo.conf...63W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Reconstruction of the Locarno telescope before shifting to
the Canary Islands site.
Authors: Wiehr, E.; Wöhl, H.
1979MmArc.106...63W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An attempt to compare the differential rotation of the
Ca<SUP>+</SUP>-network with that of the photospheric plasma.
Authors: Schroeter, E. H.; Woehl, H.; Soltau, D.; Vazquez, M.
1978SoPh...60..181S Altcode:
In this third paper of a series we report on results obtained
from almost simultaneous observations of the differential
rotation of the Ca<SUP>+</SUP>-chromosphere and the photospheric
plasma. The observations (tracings of Ca<SUP>+</SUP>-mottles,
Doppler-shift-measurements in a photospheric line) were performed
at the Locarno station during two extended periods in 1976. Both
data sets were used to search for a large scale circulation
pattern. A regular long-lived pattern could not be detected, but a
single cell with radial outflow (∼40 ms<SUP>-1</SUP>) extending
over more than 50° in longitude has been found. Statistically
significant temporal changes of the differential rotation law of the
Ca<SUP>+</SUP>-chromosphere correlated with changes of meridional
motions and differences in the rotation of the two hemispheres
were observed. The data of 1976 show no significant difference in
the equatorial velocity of the Ca<SUP>+</SUP>-chromosphere and the
photosphere. A comparison of temporal variations of the rotation
velocity of the Ca<SUP>+</SUP>-mottles and the photospheric plasma
yielded no significant correlation. Finally, we correlated the
measurements of the photospheric rotation performed within the
equatorial belts at Locarno with those obtained at Mt. Wilson by a
different method during the same periods. The Locarno data show small
temporal variations (±50 m<SUP>-1</SUP>s) with no correlation between
the two hemispheres, while from the Mt. Wilson data larger variations
(±100 m s<SUP>-1</SUP>) with a very high correlation between the two
hemispheres have been found. A comparison of both sets of data yielded
no correlation at all demonstrating the need for further coordinated
observations and a drastic increase of internal accuracy.
---------------------------------------------------------
Title: On Possible Giant Cell Circulations of the Solar CA
hoch+-Network
Authors: Schwan, H.; Woehl, H.
1978A&A....70..297S Altcode: 1978MiABB..76..297S
An attempt is made to detect large-scale circulation patterns within
the solar Ca(+) network with the aid of a method of representing the
systematic parts of the motions of Ca(+) mottles analytically by a
series expansion in spherical harmonics. The significant terms of the
series are determined by using the statistical F-test. It is shown that
the proposed method of analyzing motions of Ca(+) mottles gives mostly
the same results as those reported by Schroeter and Woehl (1975, 1976)
and Schroeter et al. (1978). Furthermore, the large-scale circulation
patterns can be represented by vector flow diagrams.
---------------------------------------------------------
Title: Bestimmungen der Radioelemente i und OMEGA der Sonne.
Authors: Woehl, H.
1978S&W....17..126W Altcode:
A description is presented concerning the approaches used for the
determination of the position of the solar axis in space. This position
is defined by means of the inclination of the axis relative to the
perpendicular on the ecliptic (i) and the angle between the point of
intersection of the solar equatorial plane with the ecliptic and the
vernal equinox (Omega). Historical developments related to the study of
seasonal changes of the orbital forms of sunspots during their east-west
motion over the solar disk are considered and details are provided
regarding the determination of the solar rotational elements on the
basis of the Doppler velocity measurements of the solar plasma. The
significance of these measurements for current solar studies is also
discussed.
---------------------------------------------------------
Title: On the solar rotation elements i and OMEGA as determined by
Doppler velocity measurements of the solar plasma.
Authors: Woehl, H.
1978A&A....62..165W Altcode:
Two methods of deriving the solar rotation elements are discussed. The
procedures rely on Doppler velocity measurements of the solar plasma
for determining the angle between the ecliptic and the solar equator
and the angle between the crosspoint of the solar equator with the
ecliptic and the equinox point. Both methods are mainly based on
the solar differential rotation. The first method depends on the
determination of the maximum of the differential rotation velocity as
well as on recently detected humps in the shape of the differential
rotation velocity. The second method makes use of the full shape
of the differential rotation velocity. The derived solar rotation
elements are i equals (6.77 plus or minus 0.31) deg and Omega equals
(76.31 plus or minus 0.65) deg for 1976. It is suggested that these
results do not indicate a difference of the mean plasma rotation as
compared with the mean rotation of sunspots but that the values of
i and Omega derived from motions of sunspots more than 100 years ago
(Carrington, 1863) should be corrected.
---------------------------------------------------------
Title: Erstmalige Bestimmung der Sonnenachsenlage im Raum aus
Dopplermessungen der solaren Plasmabewegungen
Authors: Wöhl, H.
1978MitAG..43..141W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Reconstruction of the Locarno Telescope before shifting to
the Canary Islands site
Authors: Wiehr, E.; Wöhl, H.
1978fsoo.conf...63W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Gab es Änderungen der Solarkonstanten in historischer Zeit?
Authors: Wöhl, H.
1978S&W....17...25W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Großräumige Plasmabewegungen auf Sternen.
Authors: Woehl, H.
1977S&W....16..363W Altcode:
A description is presented of the observed motions of fine structures
and homogeneous gas masses in the visible layers of the sun and
other stars. Attention is given to the historical results of solar
observations, theoretical explanations regarding the differential
rotation, the search for solar flow systems, approaches used for the
determination of the rotational velocities of stars, studies conducted
by Gray (1977), and the possibility to obtain the pictures of large
stars with the aid of speckle interferometry.
---------------------------------------------------------
Title: On velocity oscillations in sunspot umbrae.
Authors: Soltau, D.; Schroeter, E. H.; Woehl, H.
1976A&A....50..367S Altcode:
We report results from a power spectrum analysis of photographic
measurements of velocity oscillations in two sunspot umbrae. We find
oscillations with 3 regimes, of periods: 470-300 s, 196-164 s and
123-110 s with a peak to peak amplitude of about 0.6 km/sec. Whereas
the two long period oscillations agree well with the findings of
previous authors the detection of the short period oscillations is
new. We find significant power for the 300 s oscillations in a purely
umbral molecular line, 6496.2 A (TiO), which establishes the umbral
origin of this oscillation mode.
---------------------------------------------------------
Title: Differential rotation and giant cell circulation of solar
Ca<SUP>+</SUP>-network.
Authors: Schroeter, E. H.; Woehl, H.
1976SoPh...49...19S Altcode:
We report new results obtained from high precision computer controlled
tracings of ca. 400 bright Ca<SUP>+</SUP>-mottles made during summer
1975 in continuation of our 1974 program (Schröter and Wöhl, 1975). In
particular, we looked in 1975 for the existence of a giant circulation
pattern in the equatorial zone. We find for the differential rotation:
ω = 13.93 − 2.90 sin<SUP>2</SUP>B (deg/day, sidereal) when combining
the new measurements with those obtained in 1974. Observations from
26th April until June 19th give strong evidence that at that time
four giant circulation cells, crossing the solar equator, (i.e. a
nonaxisymmetric velocity field pattern with respect to the solar
equator) did exist. This yields two more rapid and two slower rotating
sectors with Δv = ±80 m s<SUP>−1</SUP>. These giant cells transport
angular momentum towards the equator.
---------------------------------------------------------
Title: Large-Scale Solar Motions
Authors: Wöhl, H.
1976IAUTB..16..247W Altcode: 1976IAUT...16B.247W
No abstract at ADS
---------------------------------------------------------
Title: Differentielle Rotation und meridionale Bewegungen des solaren
Ca<SUP>+</SUP>-Netzwerkes
Authors: Wöhl, H.; Schröter, E. H.
1976MitAG..38..208W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Differential Rotation and Giant Cell Circulation of the Solar
CA^{+}- Network
Authors: Schröter, E. H.; Wöhl, H.
1976IAUS...71...37S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Die Bewegungen des solaren Kalzium-Netzwerkes.
Authors: Wöhl, H.
1976Umsch..76..222W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Differentielle Rotation der solaren Kalzium-Mottles und
großräumige Strömungszellen auf der Sonne.
Authors: Wöhl, H.
1976S&W....15..239W Altcode:
No abstract at ADS
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Title: Scattered Light - A Comparison between Theory and Experiments
during the 1973 Transit of Mercury
Authors: Wittmann, A.; Woehl, H.
1975SoPh...44..231W Altcode:
We check the formalism used to derive stray light corrections from
measured aureole intensities and correct an error in the pertinent
literature. We solve the alledged problem of appropriately normalizing
the spread function by treating blurring and scattering separately. We
test the method by comparing stray light corrections derived from both
the aureole and from intensity profiles across Mercury's disc obtained
during the transit of November 10, 1973.
---------------------------------------------------------
Title: On the center-to-limb variation of infrared photospheric
carbon lines and the infrared continuum intensity around 1.75 μ M
Authors: Woehl, H.
1975SoPh...43..285W Altcode:
The center-to-limb variation (CLV) of several infrared carbon lines
and the infrared continuum intensity around 1.75 μm were measured. The
results were compared with theoretical predictions using four different
photospheric models. It was found that the model by Holweger and Müller
(1974) describes the observations best.
---------------------------------------------------------
Title: On Line Blanketing in Solar Spectra
Authors: Woehl, H.
1975A&A....40..343W Altcode:
Summary. We have obtained spectra in the range 7000-11000 A of the
nuclei of the Seyfert galaxies NGC1068, NGC3516, NGC4051, NGC4t5t
and of the nucleus of NGC 3031 (M 81). The spectra of NGC 1068 and
NGC 4151 are caracterized by the high intensity of the lines' [S III]
9069 and 9532 and He 110830, while these lines are absent or weak in
the other spectra. An interpretation is given in terms of a higher
continuum contribution in these latter spectra, probably due to stellar
emission. Key words: spectres infrarouge noyaux de galaxies de Seyfert
---------------------------------------------------------
Title: Differential rotation, meridional and random motions of the
solar Ca<SUP>+</SUP> network
Authors: Schroeter, E. H.; Woehl, H.
1975SoPh...42....3S Altcode:
From high precision computer controlled tracings of bright
Ca<SUP>+</SUP>-mottles we investigated differential rotation, meridional
and random motions of these chromospheric fine structures. The
equatorial angular velocity of the Ca<SUP>+</SUP>-mottles agrees well
with that of sunspots (14°.50 per day, sidereal) and is 5 % higher than
for the photosphere. The slowing down with increasing latitude is larger
than for sunspots. Hence in higher latitudes Ca<SUP>+</SUP>-mottles
rotate as fast as the photospheric plasma. A systematic meridional
motion of about 0.1 km s<SUP>−1</SUP> for latitudes around 10° was
found. The Ca<SUP>+</SUP>-mottles show horizontal random motions due
to the supergranular flow pattern with an rms velocity of about 0.15
km s<SUP>−1</SUP>. We finally investigated the correctness of the
solar rotation elements i and Ω derived by Carrington (1863).
---------------------------------------------------------
Title: Zur Streulichtbehandlung solarer Intensitätsmessungen
Authors: Wittmann, A.; Wöhl, H.
1975MitAG..36..138W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Differentielle Rotation und meridionale Strömungen des
solaren Ca<SUP>+</SUP>-networks
Authors: Schröter, E. H.; Wöhl, H.
1975MitAG..36..141S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solare Spektralmessungen im infraroten Bereich
Authors: Wöhl, H.
1975MitAG..36..131W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Solar Boron Abundance
Authors: Wohl, H.
1974A&A....34...41W Altcode:
Summary. Low-noise infrared photo spheric spectra around the
wavelength of a proposed Boron i-line at 16244.66 A were obtained
with the new infrared spectral scanning system of the Institute for
Solar Research of the DFG at Locarno/Switzerland: No absorption line
was detectable. Comparisons of this result with predicted Boron line
intensities give a new upper limit of the solar Boron abundance: l0gN
<2.3. Key words: infrared photospheric spectrum Boron absorption
line solar Boron abundance
---------------------------------------------------------
Title: The Center-to-Limb Variation of the Photospheric Wave Spectrum
Authors: Stix, M.; Wöhl, H.
1974SoPh...37...63S Altcode:
Using photoelectric observations in the Fe 5576 Å line we obtained
line-of-sight velocities at nine different positions on the solar disk,
as functions of one horizontal co-ordinate and time. With the help of
the Fast Fourier Transform algorithm we calculated two-dimensional power
spectra (horizontal wave number and frequency). Special attention was
given to the possible existence of horizontal sound waves. We find
only very little power in these waves; thus the excitation of the
solar atmosphere to oscillations by locally overshooting granules,
which should be accompanied by horizontal sound waves with large
amplitudes, can play only a minor role.
---------------------------------------------------------
Title: Der Merkurdurchgang vom 10. November 1973.
Authors: Wittmann, A.; Wöhl, H.
1974S&W....13...41W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Polfelder der Sonne.
Authors: Rossbach, M.; Woehl, H.
1974S&W....13..157R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Göttinger Beiträge zum Skylab-Projekt.
Authors: Rossbach, M.; Wöhl, H.
1974S&W....13..227R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Prozeßrechner-gesteuerte Sonnenbeobachtung.
Authors: Woehl, H.
1973S&W....12...51W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Transit of Mercury.
Authors: Wittmann, A.; Woehl, H.
1973IAUC.2598....1W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Instrumentelle Verbesserungen im Locarno-Observatorium
Authors: Wöhl, H.
1973MitAG..32..164W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Neuer Atlas des Sonnenspektrums auf Magnetband.
Authors: Wöhl, H.
1973Umsch..73..606W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On C<SUB>2</SUB> Lines in Sunspot Spectra
Authors: Wöhl, Hubertus
1972SoPh...24..342W Altcode:
The questionable existence of C<SUB>2</SUB> absorption lines in spectra
of sunspots was checked: In two umbral spectra of large single sunspots
evidence for the presence of lines of the (0, 0) band and of the (0,
1) band was found.
---------------------------------------------------------
Title: Über die große Sonneneruption Anfang August 1972.
Authors: Born, R.; Brandt, P.; Mattig, W.; Wöhl, H.
1972S&W....11..339B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Das neue Göttinger Photometer - ein prozeßrechnergesteuertes
Mikrophotometer.
Authors: Wöhl, H.
1972S&W....11..187W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On Molecules in Sunspots
Authors: Wöhl, H.
1971SoPh...16..362W Altcode:
Spectra of umbrae of several sunspots in the wavelength region 4000-8000
Å scanned photoelectrically at the Göttingen Locarno Observatory were
used in order to search for absorption lines of molecules. Several
thousands of lines of known molecules were reidentifled (see Table
II and Table III). Newly identified molecules are CoH, NiH and
H<SUB>2</SUB>O (see Table IV and Wöhl (1969a)). The Zeemann effect
on molecular lines (of MgH and CaH; see Table V and Wöhl (1969b))
in spectra of umbrae was detected.
---------------------------------------------------------
Title: Die Göttinger Spektralaufnahmen der Umbra und Penumbra
Authors: Wöhl, H.
1971MitAG..30..137W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Wasser auf extraterrestrischen Objekten.
Authors: Woehl, H.
1971S&W....10...93W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On Rotational Temperatures of Umbrae
Authors: Wöhl, H.
1970SoPh...15..342W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Continuum windows in spectra of umbrae (4000 8000 Å)
Authors: Wöhl, H.
1970SoPh...15..338W Altcode:
A list of continuum windows in umbral spectra is given and briefly
discussed.
---------------------------------------------------------
Title: A complete photoelectric sunspot spectrum: An atlas from 3900
8000 Å
Authors: Wöhl, H.; Wittmann, A.; Schröter, E. H.
1970SoPh...13..104W Altcode:
Complete photoelectric spectra of the photosphere as well as of both
umbra and penumbra of a typical sunspot, ranging from 3900-8000 Å, have
been obtained at the Locarno observatory. An automatic scanning device,
a high precision electronic divider and an on-line Oscillomink penless
recorder enabled us to eliminate the noise produced by image distortion
and to scan the entire visible spectrum within just 5 h. The recordings
have a linear dispersion of about 50 mm/Å and a spectral resolution of
40 mÅ or better. Simultaneously with these observations the momentary
continuous spot intensity and its fast variation with time due to seeing
variations have been recorded with a frequency resolution up to 100
Hz. In order to provide as much data as possible for the correction
of the umbral spectrum for parasitic light, we also measured the limb
profile and the aureola intensity at several wavelengths.
---------------------------------------------------------
Title: Erratum; On the Magnetic Splitting of Molecular Lines in
Sunspot Spectra
Authors: Wohl, H.
1969A&A.....3..487W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Magnetic Splitting of Molecular Lines in Sunspot Spectra
Authors: Wohl, H.
1969A&A.....3..378W Altcode:
In sunspot spectra, MgH lines show Zeeman splitting which can be used
for magnetic field measurements.
---------------------------------------------------------
Title: On H<SUB>2</SUB>O in sunspots
Authors: Wöhl, H.
1969SoPh....9..394W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Moleküle in Sonnenflecken.
Authors: Wöhl, H.
1969Umsch..69..845W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Kurzberichte aus der Forschung.
Authors: Wöhl, H.; Lemke, D.; Herrmann, J.
1969S&W.....8...15W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Moleküle in Sonnenflecken
Authors: Wöhl, H.
1969MitAG..27..206W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Kurzberichte aus der Forschung.
Authors: Wöhl, H.; Ackermann, G.; Herrmann, J.; Brosche, P.; Köhler,
H. W.
1969S&W.....8...61W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Das Institut für Sonnenforschung der Deutschen
Forschungsgemeinschaft (DFG) in Locarno.
Authors: Wöhl, H.
1969S&W.....8..155W Altcode:
No abstract at ADS
