clette

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Author name code: clette
ADS astronomy entries on 2022-09-14
author:"Clette, Frederic"

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Title: Maximal growth rate of the ascending phase of a sunspot cycle
for predicting its amplitude
Authors: Podladchikova, Tatiana; Jain, Shantanu; Veronig, Astrid M.;
Sutyrina, Olga; Dumbović, Mateja; Clette, Frédéric; Pötzi, Werner
2022A&A...663A..88P Altcode: 2022arXiv220612606P
Context. Forecasting the solar cycle amplitude is important for a
better understanding of the solar dynamo as well as for many space
weather applications. Different empirical relations of solar cycle
parameters with the peak amplitude of the upcoming solar cycle have
been established and used for solar cycle forecasts, as, for instance,
the Waldmeier rule relating the cycle rise time with its amplitude,
the polar fields at previous minimum, and so on. Recently, a separate
consideration of the evolution of the two hemispheres revealed even
tighter relations. Aims: We aim to introduce the maximal growth
rate of sunspot activity in the ascending phase of a cycle as a new
and reliable precursor of a subsequent solar cycle amplitude. We also
intend to investigate whether the suggested precursor provides benefits
for the prediction of the solar cycle amplitude when using the sunspot
indices (sunspot numbers, sunspot areas) derived separately for the
two hemispheres compared to the total sunspot indices describing the
entire solar disc. Methods: We investigated the relationship
between the maximal growth rate of sunspot activity in the ascending
phase of a cycle and the subsequent cycle amplitude on the basis
of four data sets of solar activity indices: total sunspot numbers,
hemispheric sunspot numbers from the new catalogue from 1874 onwards,
total sunspot areas, and hemispheric sunspot areas. Results:
For all the data sets, a linear regression based on the maximal
growth rate precursor shows a significant correlation. Validation of
predictions for cycles 1-24 shows high correlations between the true
and predicted cycle amplitudes reaching r = 0.93 for the total sunspot
numbers. The lead time of the predictions varies from 2 to 49 months,
with a mean value of 21 months. Furthermore, we demonstrated that the
sum of maximal growth rate indicators determined separately for the
north and the south hemispheric sunspot numbers provides more accurate
predictions than that using total sunspot numbers. The advantages reach
27% and 11% on average in terms of rms and correlation coefficient,
respectively. The superior performance is also confirmed with
hemispheric sunspot areas with respect to total sunspot areas. Conclusions: The maximal growth rate of sunspot activity in the
ascending phase of a solar cycle serves as a reliable precursor of
the subsequent cycle amplitude. Furthermore, our findings provide
a strong foundation for supporting regular monitoring, recording,
and predictions of solar activity with hemispheric sunspot data,
which capture the asymmetric behaviour of the solar activity and solar
magnetic field and enhance solar cycle prediction methods.

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Title: Reconstruction of the Sunspot Number Source Database and the
1947 Zurich Discontinuity
Authors: Clette, Frédéric; Lefèvre, Laure; Bechet, Sabrina; Ramelli,
Renzo; Cagnotti, Marco
2021SoPh..296..137C Altcode:
The recalibration of the sunspot number series, the primary long-term
record of the solar cycle, requires the recovery of the entire
collection of raw sunspot counts collected by the Zurich Observatory
for the production of this index between 1849 and 1980.

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Title: Hemispheric sunspot numbers 1874-2020
Authors: Veronig, Astrid M.; Jain, Shantanu; Podladchikova, Tatiana;
Pötzi, Werner; Clette, Frederic
2021A&A...652A..56V Altcode: 2021arXiv210700553V
Context. Previous studies show significant north-south asymmetries
for various features and indicators of solar activity. These findings
suggest some decoupling between the two hemispheres over the solar
cycle evolution, which is in agreement with dynamo theories. For the
most important solar activity index, the sunspot numbers, so far only
limited data are available for the two hemispheres independently. Aims: The aim of this study is to create a continuous series of
daily and monthly hemispheric sunspot numbers (HSNs) from 1874 to
2020, which will be continuously expanded in the future with the
HSNs provided by SILSO. Methods: Based on the available daily
measurements of hemispheric sunspot areas from 1874 to 2016 from
Greenwich Royal Observatory and National Oceanic and Atmospheric
Administration, we derive the relative fractions of the northern and
southern activity. These fractions are applied to the international
sunspot number (ISN) to derive the HSNs. This method and obtained
data are validated against published HSNs for the period 1945-2004
and those provided by SILSO for 1992 to 2016. Results: We
provide a continuous data series and catalogue of daily, monthly
mean, and 13-month smoothed monthly mean HSNs for the time range
1874-2020 -fully covering solar cycles 12 to 24- that are consistent
with the newly calibrated ISN (Clette et al., 2014). Validation of the
reconstructed HSNs against the direct data available since 1945 reveals
a high level of consistency, with Pearson correlation coefficients
of r = 0.94 (0.97) for the daily (monthly mean) data. The cumulative
hemispheric asymmetries for cycles 12-24 give a mean value of 16%,
with no obvious pattern in north-south predominance over the cycle
evolution. The strongest asymmetry occurs for cycle no. 19, in which
the northern hemisphere shows a cumulated predominance of 42%. The
phase shift between the peaks of solar activity in the two hemispheres
may be up to 28 months, with a mean absolute value over cycles 12-24
of 16.8 months. The phase shifts reveal an overall asymmetry of the
northern hemisphere reaching its cycle maximum earlier (in 10 out of
13 cases), with a mean signed phase shift of −7.6 months. Relating
the ISN and HSN peak growth rates during the cycle rise phase with
the cycle amplitude reveals higher correlations when considering the
two hemispheres individually, with r ≈ 0.9. Conclusions:
Our findings provide further evidence that to some degree the solar
cycle evolves independently in the two hemispheres, and demonstrate
that empirical solar cycle prediction methods can be improved by
investigating the solar cycle dynamics in terms of the HSN evolution. The catalogue is only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr/">cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/652/A56">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/652/A56</A>

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Title: A Modern Reconstruction of Richard Carrington's Observations
(1853-1861)
Authors: Bhattacharya, S.; Teague, E. T. H.; Fay, S.; Lefèvre, L.;
Jansen, M.; Clette, F.
2021SoPh..296..118B Altcode: 2021arXiv210305353B
The focus of this article is a re-count of Richard Carrington's original
sunspot observations from his book drawings (Carrington in Observations
of the Spots on the Sun from November 9, 1853, to March 24, 1861 Made
at Redhill, Williams and Norgate, London, 1863) by an observer from
the World Data Center-SILSO (WDC-SILSO, http://www.sidc.be/silso/home)
network, Thomas H. Teague (UK). This modern re-count will enable the
recomputation of the entire Sunspot Number series in a way Carrington's
original counts (Casas and Vaquero in Solar Phys. 289(1), 79, 2014)
did not. Here we present comparison studies of the new re-counted
series with contemporary observations, new data extracted from the
Journals of the Zürich Observatory and other sources of Carrington's
own observations and conclude that Carrington's group counting is
very close to the modern way of counting while his method for counting
individual spots lags significantly behind modern counts. We also test
the quality and robustness of the new recount with methods developed
in Mathieu et al. (Astrophys. J. 886(1), 7, 2019).

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Title: VizieR Online Data Catalog: Hemispheric Sunspot Numbers
1874-2020 (Veronig+, 2021)
Authors: Veronig, A. M.; Jain, S.; Podladchikova, T.; Poetzi, W.;
Clette, F.
2021yCat..36520056V Altcode:
We provide a catalogue that contains hemispheric sunspot numbers (HSN)
from 1874 until 2020. Catalogue A contains the daily data. Catalogue
B contains the monthly mean and 13-month smoothed monthly data. This
series will be continuously expanded in the future with the HSN
provided by the SILSO World Data Center (http://www.sidc.be/silso/). The
long-term HSN catalogue provided here was created using the available
daily measurements of hemispheric sunspot areas from 1874-2016 from
Greenwich Royal Observatory and NOAA, from which we derived the
relative fractions of the Northern and Southern activity. These
fractions were subsequently applied to the International Sunspot
Numbers (ISN) to derive the HSN. This method and obtained data have
been validated against the HSN available for the period 1945-2004
from Temmer et al. (2006A&amp;A...447..735T, Cat. J/A+A/447/735)
and 1992-2020 by SILSO. The 13-month smoothed data presented in the
catalogue uses the optimized smoothing method described in Podladchikova
et al. (2017ApJ...850...81P). (2 data files).

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Title: Nonparametric monitoring of sunspot number observations:
a case study
Authors: Mathieu, Sophie; Lefèvre, Laure; von Sachs, Rainer;
Delouille, Véronique; Ritter, Christian; Clette, Frédéric
2021arXiv210613535M Altcode:
Solar activity is an important driver of long-term climate trends
and must be accounted for in climate models. Unfortunately, direct
measurements of this quantity over long periods do not exist. The
only observation related to solar activity whose records reach back
to the seventeenth century are sunspots. Surprisingly, determining
the number of sunspots consistently over time has remained until
today a challenging statistical problem. It arises from the need
of consolidating data from multiple observing stations around the
world in a context of low signal-to-noise ratios, non-stationarity,
missing data, non-standard distributions and many kinds of errors. The
data from some stations experience therefore severe and various
deviations over time. In this paper, we propose the first systematic
and thorough statistical approach for monitoring these complex and
important series. It consists of three steps essential for successful
treatment of the data: smoothing on multiple timescales, monitoring
using block bootstrap calibrated CUSUM charts and classifying of
out-of-control situations by support vector techniques. This approach
allows us to detect a wide range of anomalies (such as sudden jumps or
more progressive drifts), unseen in previous analyses. It helps us to
identify the causes of major deviations, which are often observer or
equipment related. Their detection and identification will contribute
to improve future observations. Their elimination or correction in
past data will lead to a more precise reconstruction of the world
reference index for solar activity: the International Sunspot Number.

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Title: Is the F10.7cm - Sunspot Number relation linear
and stable?
Authors: Clette, Frédéric
2021JSWSC..11....2C Altcode:
The F10.7cm radio flux and the Sunspot Number are the
most widely used long-term indices of solar activity. They are
strongly correlated, which led to the publication of many proxy
relations allowing to convert one index onto the other. However,
those existing proxies show significant disagreements, in particular
at low solar activity. Moreover, a temporal drift was recently found
in the relative scale of those two solar indices. Our aim is to bring
a global clarification of those many issues. We compute new polynomial
regressions up to degree 4, in order to obtain a more accurate proxy
over the whole range of solar activity. We also study the role of
temporal averaging on the regression, and we investigate the issue of
the all-quiet F10.7 background flux. Finally, we check for
any change in the F10.7-Sunspot Number relation over the
entire period 1947-2015. We find that, with a 4th-degree polynomial,
we obtain a more accurate proxy relation than all previous published
ones, and we derive a formula giving standard errors. The relation is
different for daily, monthly and yearly mean values, and it proves
to be fully linear for raw non-averaged daily data. By a simple
two-component model for daily values, we show how temporal averaging
leads to non-linear proxy relations. We also show that the quiet-Sun
F10.7 background is not absolute and actually depends
on the duration of the spotless periods. Finally, we find that the
F10.7cm time series is inhomogeneous, with an abrupt 10.5%
upward jump occurring between 1980 and 1981, and splitting the series
in two stable intervals. Our new proxy relations bring a strong
improvement and show the importance of temporal scale for choosing
the appropriate proxy and the F10.7 quiet-Sun background
level. From historical evidence, we conclude that the 1981 jump is
most likely due to a unique change in the F10.7 scientific
team and the data processing, and that the newly re-calibrated sunspot
number (version 2) will probably provide the only possible reference
to correct this inhomogeneity.

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Title: Sunspot and Group Number: Recent advances from historical data
Authors: Clette, Frédéric; Vaquero, José M.; Cruz Gallego, María;
Lefèvre, Laure
2020IAUGA..30..156C Altcode:
Due to its unique 400-year duration, the sunspot number is a central
reference for understanding the long-term evolution of solar activity
and its influence on the Earth environment and climate. Here, we
outline current data recovery work. For the sunspot number, we find
historical evidence of a disruption in the source observers occurring
in 1947-48. For the sunpot group number, recent data confirm the
clear southern predominance of sunspots during the Maunder Minimum,
while the umbra-penumbra ratio is similar to other epochs. For the
Dalton minimum, newly recovered historical observations confirm a
higher activity level than in a true Grand Minimum.

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Title: Sunspot observations by Hisako Koyama: 1945-1996
Authors: Hayakawa, Hisashi; Clette, Frédéric; Horaguchi, Toshihiro;
Iju, Tomoya; Knipp, Delores J.; Liu, Huixin; Nakajima, Takashi
2020MNRAS.492.4513H Altcode: 2019MNRAS.tmp.3114H; 2019arXiv191112702H
Sunspot records are the only observational tracer of solar activity
that provides a fundamental, multicentury reference. Its homogeneity
has been largely maintained with a succession of long-duration visual
observers. In this article, we examine observations of one of the
primary reference sunspot observers, Hisako Koyama. By consulting
original archives of the National Museum of Nature and Science of Japan
(hereafter, NMNS), we retrace the main steps of her solar-observing
career, from 1945 to 1996. We also present the reconstruction of a
full digital data base of her sunspot observations at the NMNS, with
her original drawings and logbooks. Here, we extend the availability
of her observational data from 1947-1984 to 1945-1996. Comparisons
with the international sunspot number (Version 2) and with the
group sunspot number series show a good global stability of Koyama's
observations, with only temporary fluctuations over the main interval
1947-1982. Identifying drawings made by alternate observers throughout
the series, we find that a single downward baseline shift in the record
coincides with the partial contribution of replacement observers
mostly after 1983. We determine the correction factor to bring the
second part (1983-1996) to the same scale with Koyama's main interval
(1947-1982). We find a downward jump by 9 per cent after 1983, which
then remains stable until 1995. Overall, the high quality of Koyama's
observations with her life-long dedication leaves a lasting legacy
of this exceptional personal achievement. With this comprehensive
recovery, we now make the totality of this legacy directly accessible
and exploitable for future research.

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Title: Historical astronomical data: urgent need for preservation,
digitization enabling scientific exploration
Authors: Pevtsov, Alexei; Griffin, Elizabeth; Grindlay, Jonathan;
Kafka, Stella; Bartlett, Jennifer; Usoskin, Ilya; Mursula, Kalevi;
Gibson, Sarah; Pillet, Valentín; Burkepile, Joan; Webb, David; Clette,
Frédéric; Hesser, James; Stetson, Peter; Muñoz-Jaramillo, Andres;
Hill, Frank; Bogart, Rick; Osborn, Wayne; Longcope, Dana
2019BAAS...51c.190P Altcode: 2019arXiv190304839P; 2019astro2020T.190P
This white paper emphasizes critical importance of preservation,
digitization and scientific exploration of historical astronomical
data. It outlines the rationale, provides examples of new science
with such data, and reviews the potential losses to science if nothing
it done.

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Title: A Sunspot Catalog for the Period 1952 - 1986 from Observations
Made at the Madrid Astronomical Observatory
Authors: Aparicio, A. J. P.; Lefèvre, L.; Gallego, M. C.; Vaquero,
J. M.; Clette, F.; Bravo-Paredes, N.; Galaviz, P.; Bautista, M. L.
2018SoPh..293..164A Altcode: 2018arXiv181201733A
Sunspot catalogs are very useful for studying the solar activity of the
recent past. In this context, a catalog covering more than three solar
cycles made by the astronomers of the Madrid Astronomical Observatory
in Spain (nowadays, the National Astronomical Observatory) from 1952
until 1986 has been recovered. Moreover, a machine-readable version
of this catalog has been made available. We have recovered abundant
metadata and studied the reliability of this dataset by comparing it
with other sunspot catalogs.

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Title: The Sunspot Number recalibration
Authors: Lefevre, Laure; Clette, Frederic; Mathieu, Sophie; Delouille,
Veronique; von Sachs, Rainer
2018csc..confE...2L Altcode:
We will present here the revision of the Sunspot Numbers undertaken
by the whole solar community since 2010 that led to the publication
of a new series in 2015 (http://www.sidc.be/silso/newdataset). This
well-known index of solar activity had not been revised since
its creation by Rudolf Wolf in 1849. For the Sunspot Number, the k
scaling coefficients of individual observers were recomputed using new
statistical methodologies while the last 50 years were fully recomputed,
using all original data from the 270 stations archived by the World
Data Center - SILSO in Brussels. For the Sunspot Group Numbers, most
corrections rely entirely on original sunspot data, using various
approaches. Newly recovered historical sunspot records were added and
a critical data selection was applied for the 17th and 18th century,
confirming the low solar activity during the Maunder Minimum. The new
Sunspot Number series definitely exclude a progressive rise in average
solar activity between the Maunder Minimum and an exceptional Grand
Maximum in the late 20th century. Residual differences between the Group
and Sunspot Numbers over the past 250 years confirm that they reflect
different properties of the solar cycle. We also present preliminary
results obtained in the context of the VALUSUN (BELSPO-BRAIN)
project concerning the statistical modelling of the Sunspot Numbers:
this includes constant quality control of the most recent part of
the series and the inclusion of significant error bars. We conclude
on the implications for solar cycle and Earth climate studies and on
important new conventions adopted for the new series: new unit scales,
new SN and GN symbols and a new version-tracking scheme implemented
at the WDC-SILSO, as a framework open to future improvements of those
unique data series.

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Title: The Recalibrated Sunspot Number: What It Is and How Will It
be Updated?
Authors: Clette, Frederic; Pesnell, William Dean; Lefevre, Laure
2018tess.conf30288C Altcode:
Recently, and for the first time since their creation, the definition
of the sunspot number and group number series were revisited. A fully
recalibrated version was officially released in July 2015 by the World
Data Center SILSO (Brussels). Those long-term reference series are
widely used as input data or as a calibration reference by many research
projects in solar physics and space weather. To clarify the nature of
the applied changes, we describe the different corrections applied to
the sunspot and group number series, which affect extended time periods
and can reach up to 40%. While some changes simply involve constant
scale factors, other corrections vary with time or are modulated by
the solar cycle. Depending on the research project and the selected
time interval, this can lead to different responses and biases. For
example, predictions of solar activity based on the sunspot number
should be redone using the new sunspot series, and methods already
used for predicting Solar Cycle 24 will require adaptations before
attempting predictions of the next cycles. In addition, the revised
sunspot series includes standard error estimates, which may help
in deriving more accurate uncertainties for predicted activity
indices. We conclude with the new round of recalibration that is
now undertaken in the framework of a broad multi-team collaboration
articulated around upcoming ISSI workshops. We outline the future
corrections that can still be expected in the future, as part of a
permanent upgrading process and quality control. From now on, future
sunspot-based predictive models should thus be made more adaptable,
and regular updates of such models should become common practice in
order to track periodic upgrades of the sunspot number series, just
like it is done when using other modern solar observational series.

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Title: The new Sunspot Number: continuing upgrades and possible
impacts
Authors: Clette, Frédéric; Lefèvre, Laure
2018IAUS..340...17C Altcode:
The first-ever revision of the sunspot number was released in 2015
by the World Data Center (WDC) SILSO. We describe the main diagnosed
corrections to the sunspot and group number series, and also review
newly published alternate reconstructions. We show the convergence
of the determinations of the 1947 scale jump in the sunspot number
around a value of 1.18 for cycle maxima. We also assess new proposed
reconstructions of the group number, like the “backbone” and
“active-day fraction” methods. No agreement was reached yet for this
series. We highlight the main impacts of those recent upgrades on
different scientific applications. As this first revision also marks
a transition towards a dynamical series open to future improvements,
we finally introduce the ongoing collaborative process for preparing
the next upgrade (Version 3). From now on, our scientific users must
be prepared for a flexible integration of an evolving sunspot number
series.

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Title: The Recalibrated Sunspot Number: Impact on Solar Cycle
Predictions
Authors: Clette, F.; Lefevre, L.
2017AGUFMSH11C..04C Altcode:
Recently and for the first time since their creation, the sunspot
number and group number series were entirely revisited and a first
fully recalibrated version was officially released in July 2015 by
the World Data Center SILSO (Brussels). Those reference long-term
series are widely used as input data or as a calibration reference by
various solar cycle prediction methods. Therefore, past predictions
may now need to be redone using the new sunspot series, and methods
already used for predicting cycle 24 will require adaptations before
attempting predictions of the next cycles.In order to clarify the nature
of the applied changes, we describe the different corrections applied
to the sunspot and group number series, which affect extended time
periods and can reach up to 40%. While some changes simply involve
constant scale factors, other corrections vary with time or follow
the solar cycle modulation. Depending on the prediction method and
on the selected time interval, this can lead to different responses
and biases. Moreover, together with the new series, standard error
estimates are also progressively added to the new sunspot numbers,
which may help deriving more accurate uncertainties for predicted
activity indices. We conclude on the new round of recalibration that
is now undertaken in the framework of a broad multi-team collaboration
articulated around upcoming ISSI workshops. We outline the future
corrections that can still be expected in the future, as part of a
permanent upgrading process and quality control. From now on, future
sunspot-based predictive models should thus be made more adaptable,
and regular updates of predictions should become common practice in
order to track periodic upgrades of the sunspot number series, just
like it is done when using other modern solar observational series.

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Title: Multi-instrument observations of the solar eclipse on 20
March 2015 and its effects on the ionosphere over Belgium and Europe
Authors: Stankov, Stanimir M.; Bergeot, Nicolas; Berghmans,
David; Bolsée, David; Bruyninx, Carine; Chevalier, Jean-Marie;
Clette, Frédéric; De Backer, Hugo; De Keyser, Johan; D'Huys, Elke;
Dominique, Marie; Lemaire, Joseph F.; Magdalenić, Jasmina; Marqué,
Christophe; Pereira, Nuno; Pierrard, Viviane; Sapundjiev, Danislav;
Seaton, Daniel B.; Stegen, Koen; Van der Linden, Ronald; Verhulst,
Tobias G. W.; West, Matthew J.
2017JSWSC...7A..19S Altcode:
A total solar eclipse occurred on 20 March 2015, with a totality
path passing mostly above the North Atlantic Ocean, which resulted
in a partial solar eclipse over Belgium and large parts of Europe. In
anticipation of this event, a dedicated observational campaign was set
up at the Belgian Solar-Terrestrial Centre of Excellence (STCE). The
objective was to perform high-quality observations of the eclipse and
the associated effects on the geospace environment by utilising the
advanced space- and ground-based instrumentation available to the STCE
in order to further our understanding of these effects, particularly on
the ionosphere. The study highlights the crucial importance of taking
into account the eclipse geometry when analysing the ionospheric
behaviour during eclipses and interpreting the eclipse effects. A
detailed review of the eclipse geometry proves that considering the
actual obscuration level and solar zenith angle at ionospheric heights
is much more important for the analysis than at the commonly referenced
Earth's surface or at the plasmaspheric heights. The eclipse occurred
during the recovery phase of a strong geomagnetic storm which certainly
had an impact on (some of) the ionospheric characteristics and perhaps
caused the omission of some "low-profile" effects. However, the analysis
of the ionosonde measurements, carried out at unprecedented high rates
during the eclipse, suggests the occurrence of travelling ionospheric
disturbances (TIDs). Also, the high temporal and spatial resolution
measurements proved very important in revealing and estimating
some finer details of the delay in the ionospheric reaction and the
ionospheric disturbances.

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Title: The New Sunspot Number: Assembling All Corrections
Authors: Clette, Frédéric; Lefèvre, Laure
2016SoPh..291.2629C Altcode: 2016SoPh..tmp..183C
Based on various diagnostics and corrections established in the
framework of several Sunspot Number Workshops and described by
Clette et al. (Space Sci. Rev.186, 35, 2014), we now assembled all
separately derived corrections to produce a new standard version of the
reference sunspot-number time series. We explain here the three main
corrections and the criteria used to choose a final optimal version of
each correction factor or function, given the available information
and published analyses. We then discuss the differences between the
new corrected series and the original sunspot number, including the
disappearance of any significant rising secular trend in the solar-cycle
amplitudes after this recalibration. We also introduce the new version
management scheme now implemented at the World Data Center Sunspot
Index and Long-term Solar Observations (WDC-SILSO), which reflects a
major conceptual transition: beyond the rescaled numbers, this first
revision of the sunspot number also transforms the former static data
archive into a living observational series open to future improvements.

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Title: Preface to Topical Issue: Recalibration of the Sunspot Number
Authors: Clette, F.; Cliver, E. W.; Lefèvre, L.; Svalgaard, L.;
Vaquero, J. M.; Leibacher, J. W.
2016SoPh..291.2479C Altcode: 2016SoPh..tmp..184C
This topical issue contains articles on the effort to recalibrate
the sunspot number (SN) that was initiated by the Sunspot Number
Workshops. These workshops led to a revision of the Wolf sunspot number
(WSN) and a new construction of the group sunspot number (GSN),
both published herein. In addition, this topical issue includes
three independently proposed alternative SN time series (two Wolf
and one group), as well as articles providing historical context,
critical assessments, correlative analyses, and observational data,
both historical and modern, pertaining to the sunspot-number time
series. The ongoing effort to understand and reconcile the differences
between the various new sunspot number series is briefly discussed.

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Title: A Revised Collection of Sunspot Group Numbers
Authors: Vaquero, J. M.; Svalgaard, L.; Carrasco, V. M. S.; Clette, F.;
Lefèvre, L.; Gallego, M. C.; Arlt, R.; Aparicio, A. J. P.; Richard,
J. -G.; Howe, R.
2016SoPh..291.3061V Altcode: 2016arXiv160904882V; 2016SoPh..tmp..152V
We describe a revised collection of the number of sunspot groups from
1610 to the present. This new collection is based on the work of Hoyt
and Schatten (Solar Phys. 179, 189, 1998). The main changes are the
elimination of a considerable number of observations during the Maunder
Minimum (hereafter, MM) and the inclusion of several long series of
observations. Numerous minor changes are also described. Moreover,
we have calculated the active-day percentage during the MM from this
new collection as a reliable index of the solar activity. Thus, the
level of solar activity obtained in this work is greater than the
level obtained using the original Hoyt and Schatten data, although
it remains compatible with a grand minimum of solar activity. The new
collection is available in digital format.

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Title: The Revised Brussels-Locarno Sunspot Number (1981 - 2015)
Authors: Clette, Frédéric; Lefèvre, Laure; Cagnotti, Marco; Cortesi,
Sergio; Bulling, Andreas
2016SoPh..291.2733C Altcode: 2015arXiv150707803C; 2016SoPh..tmp...54C
In 1981, the production of the international sunspot number moved from
the Zürich Observatory to the Royal Observatory of Belgium, with a
new pilot station: the Specola Solare Ticinese Observatory in Locarno,
Switzerland. This marked a profound transition in the history of the
sunspot number. Those recent decades are particularly important as they
provide the link between recent modern solar indices and the entire
sunspot-number series extending back to the eighteenth century. However,
large variations have recently been identified in the scale of the
sunspot number during this recent time period. Here, we refine the
determination of those recent inhomogeneities by reconstructing a
new average sunspot-number series [SN] from a subset
of long-duration stations between 1981 and 2015. We also extend
this reconstruction by gathering long time series from 35 stations
over 1945 - 2015, thus straddling the critical 1981 transition. In
both reconstructions, we also derive a parallel group number series
[GN] built by the same method from exactly the same data
set. Our results confirm the variable trends associated with drifts
of the Locarno pilot station, which start only in 1983. They lead
to a fully uniform SN-series over the entire 1945 - 2015
interval. By comparing the new SN- and GN-series,
we find that a constant quadratic relation exists between those two
indices over Cycles 19 to 23. Comparisons with a few other solar indices
additionally validate this and reveal some possible undetected problems
in those series. Using this new reference SN, we find that
observing stations are surprisingly grouped among distinct subsets
that share similar personal k -scaling coefficients. These various
results also open the way to implementing a more advanced method for
producing the sunspot number in the future.

---------------------------------------------------------
Title: Uncertainties in the Sunspot Numbers: Estimation and
Implications
Authors: Dudok de Wit, Thierry; Lefèvre, Laure; Clette, Frédéric
2016SoPh..291.2709D Altcode: 2016SoPh..tmp..142D; 2016arXiv160805261D
Sunspot number series are subject to various uncertainties that are
still poorly known. The need to understand these better was recently
highlighted by the major revision of the international Sunspot Number
(Clette et al., in Space Sci. Rev.186, 35, 2014). We present the first
thorough estimation of these uncertainties, which behave as Poisson-like
random variables with a multiplicative coefficient that is time-
and observatory-dependent. We provide a simple expression for these
uncertainties, and reveal how their evolution in time coincides with
changes in the observations and processing of the data. Knowing their
value is essential for properly building composites out of multiple
observations, and for preserving the stability of the composites
in time.

---------------------------------------------------------
Title: Comparison of New and Old Sunspot Number Time Series
Authors: Cliver, Edward W.; Clette, Frédéric; Lefévre, Laure;
Svalgaard, Leif
2016SPD....47.1101C Altcode:
As a result of the Sunspot Number Workshops, five new sunspot series
have recently been proposed: a revision of the original Wolf or
international sunspot number (Lockwood et al., 2014), a backbone-based
group sunspot number (Svalgaard and Schatten, 2016), a revised group
number series that employs active day fractions (Usoskin et al., 2016),
a provisional group sunspot number series (Cliver and Ling, 2016) that
removes flaws in the normalization scheme for the original group sunspot
number (Hoyt and Schatten,1998), and a revised Wolf or international
number (termed SN) published on the SILSO website as a
replacement for the original Wolf number (Clette and Lefèvre, 2016; <A
href="http://www.sidc.be/silso/datafiles">thttp://www.sidc.be/silso/datafiles</A>).
Despite quite different construction methods, the five new series
agree reasonably well after about 1900. From 1750 to ~1875, however,
the Lockwood et al. and Usoskin et al. time series are lower than the
other three series. Analysis of the Hoyt and Schatten normalization
factors used to scale secondary observers to their Royal Greenwich
Observatory primary observer reveals a significant inhomogeneity
spanning the divergence in ~1885 of the group number from the original
Wolf number. In general, a correction factor time series, obtained
by dividing an annual group count series by the corresponding yearly
averages of raw group counts for all observers, can be used to assess
the reliability of new sunspot number reconstructions.

---------------------------------------------------------
Title: Detailed Analysis of Solar Data Related to Historical Extreme
Geomagnetic Storms: 1868 - 2010
Authors: Lefèvre, Laure; Vennerstrøm, Susanne; Dumbović, Mateja;
Vršnak, Bojan; Sudar, Davor; Arlt, Rainer; Clette, Frédéric;
Crosby, Norma
2016SoPh..291.1483L Altcode: 2016SoPh..tmp...64L
An analysis of historical Sun-Earth connection events in the context
of the most extreme space weather events of the last ∼150 years
is presented. To identify the key factors leading to these extreme
events, a sample of the most important geomagnetic storms was selected
based mainly on the well-known aa index and on geomagnetic parameters
described in the accompanying paper (Vennerstrøm et al., Solar Phys. in
this issue, 2016, hereafter Paper I). This part of the analysis focuses
on associating and characterizing the active regions (sunspot groups)
that are most likely linked to these major geomagnetic storms.

---------------------------------------------------------
Title: Extreme Geomagnetic Storms - 1868 - 2010
Authors: Vennerstrom, S.; Lefevre, L.; Dumbović, M.; Crosby, N.;
Malandraki, O.; Patsou, I.; Clette, F.; Veronig, A.; Vršnak, B.;
Leer, K.; Moretto, T.
2016SoPh..291.1447V Altcode: 2016SoPh..tmp...73V
We present the first large statistical study of extreme geomagnetic
storms based on historical data from the time period 1868 - 2010. This
article is the first of two companion papers. Here we describe how the
storms were selected and focus on their near-Earth characteristics. The
second article presents our investigation of the corresponding solar
events and their characteristics. The storms were selected based
on their intensity in the aa index, which constitutes the longest
existing continuous series of geomagnetic activity. They are analyzed
statistically in the context of more well-known geomagnetic indices,
such as the Kp and Dcx/Dst index. This reveals that neither Kp nor
Dcx/Dst provide a comprehensive geomagnetic measure of the extreme
storms. We rank the storms by including long series of single magnetic
observatory data. The top storms on the rank list are the New York
Railroad storm occurring in May 1921 and the Quebec storm from March
1989. We identify key characteristics of the storms by combining
several different available data sources, lists of storm sudden
commencements (SSCs) signifying occurrence of interplanetary shocks,
solar wind in-situ measurements, neutron monitor data, and associated
identifications of Forbush decreases as well as satellite measurements
of energetic proton fluxes in the near-Earth space environment. From
this we find, among other results, that the extreme storms are very
strongly correlated with the occurrence of interplanetary shocks (91 -
100 %), Forbush decreases (100 %), and energetic solar proton events
(70 %). A quantitative comparison of these associations relative to less
intense storms is also presented. Most notably, we find that most often
the extreme storms are characterized by a complexity that is associated
with multiple, often interacting, solar wind disturbances and that they
frequently occur when the geomagnetic activity is already elevated. We
also investigate the semiannual variation in storm occurrence and
confirm previous findings that geomagnetic storms tend to occur less
frequently near solstices and that this tendency increases with storm
intensity. However, we find that the semiannual variation depends on
both the solar wind source and the storm level. Storms associated
with weak SSC do not show any semiannual variation, in contrast to
weak storms without SSC.

---------------------------------------------------------
Title: Active Latitude Oscillations Observed on the Sun
Authors: Kilcik, A.; Yurchyshyn, V.; Clette, F.; Ozguc, A.; Rozelot,
J. -P.
2016SoPh..291.1077K Altcode: 2016SoPh..tmp...62K; 2016arXiv160400831K
We investigate periodicities in the mean heliographic latitudes of
sunspot groups, called active latitudes, for the past six complete
solar cycles (1945 - 2008). For this purpose, the multitaper method
and Morlet wavelet analysis were used. We found that solar rotation
periodicities (26 - 38 days) are present in active latitudes of both
hemispheres for all the investigated cycles (18 to 23). Both in the
northern and southern hemispheres, active latitudes drifted toward the
equator from the beginning to the end of each cycle and followed an
oscillating path. These motions are well described by a second-order
polynomial. There are no meaningful periods of between 55 and about
300 days in either hemisphere for all cycles. A periodicity of 300
to 370 days appears in both hemispheres for Cycle 23, in the northern
hemisphere for Cycle 20, and in the southern hemisphere for Cycle 18.

---------------------------------------------------------
Title: Thomas Cragg Proves to Be a Good Observer (Abstract)
Authors: Howe, R.; Clette, F.
2015JAVSO..43..257H Altcode:
(Abstract only) Thomas Cragg proves to be a good observer, enough
to be included in the restricted club of 21 long-duration stations
without major stability problems over the interval 1945-2015. Although,
his counts seem to make a slight downward jump in 1983, and there
is a sharp decline in the last two years of his observing career
(aging?). Cragg's observations will be used for the equivalent
comparison with the new reconstructed sunspot number that is produced
from the 21 stations showing the same features in the past six solar
cycles. This reconstructed number is fully independent from the
original Zürich sunspot number. It actually confirms the corrections
being applied to the original sunspot number series (a more simple
approach simply multiplying the original series by the correction factor
established for the Locarno Observatory's drift), as published in the
2014 paper, by Frédéric Clette, SILSO, Royal Observatory of Belgium.

---------------------------------------------------------
Title: The new Sunspot Number: assembling all corrections
Authors: Frédéric; Clette; Lefèvre, Laure
2015arXiv151006928F Altcode:
The Sunspot Number, created by R.Wolf in 1849, provides a direct
long-term record of solar activity from 1700 to the present. In spite
of its central role in multiple studies of the solar dynamo and of the
past Sun-Earth relations, it was never submitted to a global critical
revision. However, various discrepancies with other solar indices
recently motivated a full re-calibration of this series. Based on
various diagnostics and corrections established in the framework of
several Sunspot Number Workshops and described in Clette et al. 2014,
we assembled all corrections in order to produce a new standard version
of this reference time series. In this paper, we explain the three main
corrections and the criteria used to choose a final optimal version of
each correction factor or function, given the available information and
published analyses. We then discuss the good agreement obtained with the
Group sunspot Number derived from a recent reconstruction. Among the
implications emerging from this re-calibrated series, we also discuss
the absence of a rising secular trend in the newly-determined solar
cycle amplitudes, also in relation with contradictory indications
derived from cosmogenic radionuclides. As conclusion, we introduce
the new version management scheme now implemented at the World Data
Center - SILSO, which reflects a major conceptual transition: beyond
the re-scaled numbers, this first revision of the Sunspot Number also
transforms the former locked data archive into a living observational
series open to future improvements.

---------------------------------------------------------
Title: The new Sunspot and Group Numbers: a full recalibration
Authors: Clette, Frédéric; Svalgaard, Leif; Cliver, Edward W.;
Vaquero, José M.; Lefèvre, Laure
2015IAUGA..2249591C Altcode:
After a 4-year research effort, we present here the first end-to-end
revision of the Sunspot Number since the creation of this reference
index of solar activity by Rudolf Wolf in 1849 and the simultaneous
re-calibration of the Group Number, which leads to the elimination of
the past incompatibility between those two independent data sets.Most
corrections relied entirely on original sunspot data, using various
approaches. Newly recovered historical sunspot records were added
and a critical data selection was applied for the 17th
and 18th century, confirming the low solar activity
during the Maunder Minimum. Over the 19th century, the k
scaling coefficients of individual observers were recomputed using
new statistical methodologies, like the "backbone" method resting on
a chain of long-duration observers. After identifying major changes
in the observing methods, two major inhomogeneities were corrected
in 1884 in the Group Number (~40% upward drift) and in 1947 in the
Sunspot Number (~20% overestimate). Finally, a full re-computation of
the group and sunspot numbers was done over the last 50 years, using
all original data from the 270 stations archived by the World Data
Center - SILSO in Brussels.The new Sunspot Number series definitely
exclude a progressive rise in average solar activity between the Maunder
Minimum and an exceptional Grand Maximum in the late 20th
century. Residual differences between the Group and Sunspot Numbers over
the past 250 years confirm that they reflect different properties of
the solar cycle and that the average number of spots per group varies
over time, as it just happened in the recent unexpected evolution of
cycles 23 and 24. We conclude on the implications for solar cycle and
Earth climate studies and on important new conventions adopted for
the new series: new unit scales (constant "heritage" factors 0.6 and
12.08 dropped for the Sunspot and Group Numbers respectively), new
SN and GN symbols and a new version-tracking
scheme implemented at the WDC-SILSO, as a framework open to future
improvements of those unique data series.

---------------------------------------------------------
Title: The new Sunspot Number: re-calibration, re-computation and
implications for the solar cycle
Authors: Clette, Frédéric; Lefèvre, Laure
2015IAUGA..2256393C Altcode:
Our knowledge of the long-term behaviour of the solar cycle and the
occurrence of Grand Minima rest largely on the 400-year sunspot
record, currently in the form of two time series: the Sunspot
Number and the Group Number. Recently, a full revision of those two
series allowed to identify and correct various inhomogeneities,
thereby also eliminating most of the discrepancies between those
two parallel series.We report here about the changes in those two
series and one of the main implications: the absence of a progressive
rise of solar activity from the Maunder Minimum to a modern maximum
in the 20th century. We also focus in particular on the
important corrections applied over the last 50 years, in particular
a variable drift in the scale of the Specola Solare station (Locarno)
that defined the long-term scale of the International Sunspot Number
over the last 35 years, i.e. over the period when modern measurements
of solar irradiance and solar wind particles can be correlated with
the Sunspot Number for building long-term backward reconstructions
of those physical parameters. Taking advantage of the archive of the
World Data Center SILSO (270 stations, 550,000 observations), we could
entirely re-compute the Sunspot Number. We describe the properties of
the new resulting series and the new method developed to build a more
stable multi-station reference for the Sunspot Number.We conclude on
the release of the new reference Sunspot Number and the simultaneous
adoption of new conventions and standards (error estimates, version
tracking and documenting). We also consider the next steps that will
allow future progresses in the characterisation of the solar cycle:
the digitisation of historical drawings and the creation of image-based
sunspot indices that will allow adding spatial information, to extend
the one-dimensional information brought by the Sunspot Number.

---------------------------------------------------------
Title: Recalibrating the Sunspot Number (SN): The 3rd
and 4th SN Workshops
Authors: Cliver, E. W.; Clette, F.; Svalgaard, L.; Vaquero, J. M.
2015CEAB...39....1C Altcode:
At the XIIth Hvar Astrophysical Colloquium in 2012, we reviewed the
progress of an effort begun in 2011 to recalibrate the sunspot number
(SN). That work is now nearing completion and we review the motivation,
approach, and results of this process which was conducted via a series
of four international workshops. Previously we discussed the principal
results of workshops at Sunspot in 2011 and Brussels in 2012. These
involved the identification of discontinuities circa 1885 in the Hoyt
and Schatten Group SN and 1945 in the International SN. Subsequently,
workshops were held in Tucson (2013) and Locarno (2014). Key results
during the time of these two workshops included: (1) development of
an independent ”backbone” method for determining the Group sunspot
number; (2) identification of post-1970 inhomogeneities in the
Group SN and the International SN; (3) construction of preliminary
revisions of the Group SN from 1610-present and the International
SN from 1700--present; (4) reassessment (ongoing) of the Hoyt and
Schatten Group SN data base from 1610-present; and (5) establishment
of a SN archive at the University of Extremadura. The release of the
new International and Group SN series is anticipated during the second
half of 2015 and procedures are being put in place both to maintain the
calibration of these two series and to produce subsequent revisions
should more historical data be unearthed or new inhomogeneities in
the series be uncovered or arise.

---------------------------------------------------------
Title: Revisiting the Sunspot Number
Authors: Clette, Frédéric; Svalgaard, Leif; Vaquero, José M.;
Cliver, Edward W.
2015sac..book...35C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Revisiting the Sunspot Number. A 400-Year Perspective on the
Solar Cycle
Authors: Clette, Frédéric; Svalgaard, Leif; Vaquero, José M.;
Cliver, Edward W.
2014SSRv..186...35C Altcode: 2014SSRv..tmp...38C; 2014arXiv1407.3231C
Our knowledge of the long-term evolution of solar activity and of
its primary modulation, the 11-year cycle, largely depends on a
single direct observational record: the visual sunspot counts that
retrace the last 4 centuries, since the invention of the astronomical
telescope. Currently, this activity index is available in two main
forms: the International Sunspot Number initiated by R. Wolf in 1849
and the Group Number constructed more recently by Hoyt and Schatten
(Sol. Phys. 179:189-219, 1998a, 181:491-512, 1998b). Unfortunately,
those two series do not match by various aspects, inducing confusions
and contradictions when used in crucial contemporary studies of the
solar dynamo or of the solar forcing on the Earth climate. Recently,
new efforts have been undertaken to diagnose and correct flaws and
biases affecting both sunspot series, in the framework of a series of
dedicated Sunspot Number Workshops. Here, we present a global overview
of our current understanding of the sunspot number calibration.

---------------------------------------------------------
Title: Survey and Merging of Sunspot Catalogs
Authors: Lefevre, Laure; Clette, Frédéric
2014SoPh..289..545L Altcode: 2012SoPh..tmp..305L
In view of the construction of new sunspot-based activity indices and
proxies, we conducted a comprehensive survey of all existing catalogs
providing detailed parameters of photospheric features over long time
intervals. Although there are a fair number of such catalogs, a global
evaluation showed that they suffer from multiple limitations: finite
or fragmented time coverage, limited temporal overlap between catalogs,
and, more importantly, a mismatch in contents and conventions. Starting
from the existing material, we demonstrate how the information from
parallel catalogs can be merged to form a much more comprehensive record
of sunspots and sunspot groups. To do this, we use the uniquely detailed
Debrecen Photoheliographic Data (DPD), which is already a composite of
several ground-based observatories and of SOHO data, and the USAF/Mount
Wilson catalog from the Solar Observing Optical Network (SOON). We also
outline our cross-identification method, which was needed to match
the non-overlapping solar active-region nomenclature. This proved
to be the most critical and subtle step when working with multiple
catalogs. This effort, focused here first on the last two solar cycles,
should lead to a better central database that collects all available
sunspot group parameters to address future solar-cycle studies beyond
the traditional sunspot-index time series [Ri].

---------------------------------------------------------
Title: Towards a first detailed reconstruction of sunspot information
over the last 150 years
Authors: Lefevre, Laure; Clette, Frédéric
2013EGUGA..1511461L Altcode:
With four centuries of solar evolution, the International Sunspot Number
(SSN) forms the longest solar time series currently available. It
provides an essential reference for understanding and quantifying
how the solar output has varied over decades and centuries and thus
for assessing the variations of the main natural forcing on the Earth
climate. For such a quantitative use, this unique time-series must be
closely monitored for any possible biases and drifts. This is the main
objective of the Sunspot Workshops organized jointly by the National
Solar Observatory (NSO) and the Royal Observatory of Belgium (ROB)
since 2010. Here, we will report about some recent outcomes of past
workshops, like diagnostics of scaling errors and their proposed
corrections, or the recent disagreement between the sunspot sumber
and other solar indices like the 10.7cm radio flux. Our most recent
analyses indicate that while part of this divergence may be due to
a calibration drift in the SSN, it also results from an intrinsic
change in the global magnetic parameters of sunspots and solar
active regions, suggesting a possible transition to a new activity
regime. Going beyond the SSN series, in the framework of the SOTERIA,
TOSCA and SOLID projects, we produced a survey of all existing catalogs
providing detailed sunspot information and we also located different
primary solar images and drawing collections that can be exploitable
to complement the existing catalogs (COMESEP project). These are first
steps towards the construction of a multi-parametric time series of
multiple sunspot group properties over at least the last 150 years,
allowing to reconstruct and extend the current 1-D SSN series. By
bringing new spatial, morphological and evolutionary information, such
a data set should bring major advances for the modeling of the solar
dynamo and solar irradiance. We will present here the current status of
this work. The catalog now extends over the last 3 cycles (Lefevre &amp;
Clette 2011,doi:10.1007/s11207-012-0184-5). A partially complete version
extends back to 1965, and will soon reach 1940 thanks to the data from
the Uccle Solar Equatorial Table (USET) operated by the ROB. We will
also present initial applications derived from the present version of
the catalog, such as new sunspot-based solar fluxes and proxies that
should ultimately help refine our knowledge of the influence of the Sun
on our environment, now and throughout the ages. This work has received
funding from the European Commission FP7 Project COMESEP (263252).

---------------------------------------------------------
Title: Recalibrating the Sunspot Number (SSN): The SSN Workshops
Authors: Cliver, E. W.; Clette, F.; Svalgaard, L.
2013CEAB...37..401C Altcode:
The sunspot number (SSN) is the primary time series in solar and
solar-terrestrial physics. Currently there are two widely-used
sunspot numbers, the International SSN and the Group SSN, which
differ significantly before ∼1885. Thus the SSN is potentially a
free-parameter in models of climate change or solar dynamo behavior. To
reconcile the International and Group SSNs, we have organized a series
of workshops. The end goal of this effort is a community-vetted time
series of sunspot numbers for use in long-term studies. We are about
half way through the process, with the International and Group SSN time
series reconciled back to 1826. We hope to have the reconciliation
completed back to the beginning of the SSN time series (1610) by
mid-2014. We have learned or relearned some interesting things along the
way: (1) the International or Wolf SSN time series is not based solely
on sunspots; (2) the simple formula from Wolf for the SSN that is found
in all solar physics textbooks is not used in practice (all sunspots
are not equal); and (3) the Group SSN appears to be too low before
1885. When completed, the reconciled ∼400-yr SSN time series will
serve as a bridge to the millennia-scale record of solar variability
from cosmogenic nuclide concentrations in tree rings and ice cores.

---------------------------------------------------------
Title: Are the sunspots really vanishing?. Anomalies in solar cycle
23 and implications for long-term models and proxies
Authors: Clette, Frédéric; Lefèvre, Laure
2012JSWSC...2A..06C Altcode:
Context: The elapsed solar cycle (23) ended with an exceptionally long
period of low activity and with unprecedented low levels for various
series of solar irradiance and particle flux measurements. This
unpredicted evolution of solar activity raised multiple questions
about a future decline of the solar cycles and launched a quest for
precursor signs of this possible deep solar transition over the last
decade. Aim: We present here a review and overall interpretation
of most current diagnostics of solar cycle 23, including the recent
disagreements that appeared among solar reference indices and standard
solar-based geo-indices, the indication of a changed pattern of
internal torsional waves (helioseismology) or the announced fading
and magnetic weakening of sunspots. Methods: Based on a statistical
analysis of detailed sunspot properties over the last 24 years, we
complete the picture with new evidence of a strong global deficit
of the smallest sunspots starting around 2000, in order to answer
the question: are all sunspots about to disappear? Results: This
global scale-dependent change in sunspot properties is confirmed to
be real and not due to uncontrolled biases in some of the indices. It
can also explain the recent discrepancies between solar indices by
their different sensitivities to small and weak magnetic elements
(small spots). The International Sunspot Index Ri, based
on unweighted sunspot counts, proved to be particularly sensitive to
this particular small-scale solar evolution. Conclusions: Our results
and interpretation show the necessity to look backwards in time, more
than 80 years ago. Indeed, the Sun seems to be actually returning to a
past and hardly explored activity regime ending before the 1955-1995
Grand Maximum, which probably biased our current space-age view of
solar activity.

---------------------------------------------------------
Title: A global small sunspot deficit at the base of the index
anomalies of solar cycle 23
Authors: Lefèvre, L.; Clette, F.
2011A&A...536L..11L Altcode:
Context. The variability of the 11-year cycle of solar activity on
secular timescales is well established through the sunspot record,
but it remains unpredictable. Indeed, the duration of the last solar
cycle 23 was exceptionally long and took the solar physics community
by surprise. The long minimum was marked by particularly low and often
unprecedented levels of the international sunspot index Ri
and most other solar indices. Earlier in the course of cycle 23,
discrepancies appeared between several of those indices, raising a
new issue: is there something wrong in the recent index values or
is a real physical change occurring inside the Sun? Aims:
By exploiting detailed sunspot information, we look for independent
evidence of a concrete and significant global change in sunspot
properties appearing in the course of cycle 23. Methods:
To achieve this goal, we compared existing sunspot indices, such as
the international sunspot number (Ri), and exploited the
most complete information currently available on individual sunspots,
obtained by merging two recent and complementary catalogs. Detailed
statistics were obtained according to group type and spot size. 
Results: We find that the Sun has shown an important deficit in small
spots since the last activity maximum around 2000. While the number
of large-scale spots remained largely unaffected, the occurrence rate
of the smallest sunspots, and among them the ones with the shortest
lifetimes, was more than halved during cycle 23. This explains the
divergence between indices, weighted in favor of the largest active
regions/magnetic structures, and sunspot counts that do not include
such a weighting. It also confirms an actual intrinsic transition in
the magnetic field generation inside the Sun, arising years before
the exceptional activity minimum. Conclusions: Our results
thus reveal the potential of such detailed sunspot analyses for
understanding and predicting future trends in the solar cycle. The
change found here in the small individual sunspots suggests that solar
and solar-terrestrial proxies should be redefined for the current state
of the Sun, replacing the present ones. This scale-dependent change
also provides support to dynamo models involving the coexistence of
a deep and a superficial dynamo.

---------------------------------------------------------
Title: In-depth survey of sunspot and active region catalogs
Authors: Lefèvre, Laure; Clette, Frédéric; Baranyi, Tunde
2011IAUS..273..221L Altcode:
When consulting detailed photospheric catalogs for solar activity
studies spanning long time intervals, solar physicists face multiple
limitations in the existing catalogs: finite or fragmented time
coverage, limited time overlap between catalogs and even more
importantly, a mismatch in contents and conventions. In view of a
study of new sunspot-based activity indices, we have conducted a
comprehensive survey of existing catalogs. In a first approach,
we illustrate how the information from parallel catalogs can be merged
to form a much more comprehensive record of sunspot groups. For this,
we use the unique Debrecen Photoheliographic Data (DPD), which is
already a composite of several ground observatories and SOHO data, and
the USAF/Mount Wilson catalog from the Solar Optical Observing Network
(SOON). We also describe our semi-interactive cross-identification
method, which was needed to match the non-overlapping solar active
region nomenclature, the most critical and subtle step when working
with multiple catalogs. This effort, focused here first on the last
two solar cycles, should lead to a better central database collecting
all available sunspot group parameters to address future solar cycle
studies beyond the traditional sunspot index time series Ri.

---------------------------------------------------------
Title: Past and future sunspot indices: New goals for SoTerIA
Authors: Clette, Frédéric
2011JASTP..73..182C Altcode:
Sunspot drawings and images are the base material at our disposal to
derive more detailed information about the long-term evolution of the
solar cycle, beyond the classical total sunspot index Ri. In
the context of the new SoTerIA project, the SIDC World Data Center
“Sunspot” will pursue two complementary goals. We will develop tools
to digitize and encode the largely unexploited information recorded in
sunspot drawing collections, starting with the Uccle station. Turning
towards the future, we will define and evaluate possible global activity
indices based on full-disk sunspot CCD imagery. As a support, we will
also provide such CCD images from the Uccle solar telescopes. Here, we
describe the main steps of this work and the available data sets. We
also outline the prospects and resulting products in the 3-year
framework of the SoTerIA project.

---------------------------------------------------------
Title: Correlation between solar activity and Earth's ionospheric
electron content during the 23rd solar cycle
Authors: Bergeot, N.; Legrand, J.; Burston, R.; Bruyninx, C.;
Defraigne, P.; Chevalier, J.; Clette, F.; Marque, C.; Lefevre, L.
2010AGUFMSA33B1774B Altcode:
The beginning of the 23rd solar cycle (May 1996 to December 2008)
coincided with the start of the catalogue of global ionospheric
modeling using GPS data. Comparison between solar activity parameters
and GPS-derived Total Electron Content (TEC) is now possible for
the whole of solar cycle 23. In this study, we compared the daily
sunspot number and F10.7 cm flux with the daily mean global TEC values
during the entire last solar cycle. In order to better understand the
ionization response, we show correlations between the daily F10.7cm
delivered by NGDC-NOAA (National Geophysical Data Center - National
Oceanic and Atmospheric Administration) and the daily sunspot number
from SIDC (Solar Influences Data Analysis Center) with the daily
mean latitudinal TEC values extracted from CODE (Center for Orbit
Determination in Europe) GPS-based global ionospheric maps for the
period 1995-2009. The correlations were investigated for different
daily mean latitudinal ionospheric TEC: (1) expressed in geographic and
geomagnetic coordinates; (2) with respect to the seasons and; (3) with
respect to the different phases of the solar cycle. In general, results
show in the north and south hemispheres a different ionospheric response
(TEC) to solar activity (F10.7cm). Moreover, the switch from geographic
to geomagnetic coordinates does not change the observed correlation
between TEC and solar parameters. Finally, a larger correlation is
observed at N20°-30° during the transition phase in the solar cycle.

---------------------------------------------------------
Title: Space Weather data and services at SIDC / RWC Belgium
Authors: van der Linden, Ronald; Ben Moussa, Ali; Berghmans, David;
Boulvin, Olivier; Boyes, David; Cabanas Parada, Carlos; Callebaut,
Benoit; Clette, Frédéric; Dammasch, Ingolf; Delouille, Veronique;
D'Huys, Elke; Dolla, Laurent; Dominique, Marie; Dufond, Jean-Luc;
Ergen, Aydin; Giordanengo, Boris; Gissot, Samuel; Goryaev, Farid;
Hochedez, Jean-Francois; Lemaâtre, Olivier; Lisnichenko, Pavel;
Magdalenic, Jas-Mina; Mampaey, Benjamin; Marque, Christophe; Nicula,
Bogdan; Podladchikova, Elena; Pylyser, Erik; Raynal, Sophie; Rodriguez,
Luciano; Seaton, Daniël; van der Linden, Ronald; Vandersyppe, Anne;
Vanlommel, Petra; Vanraes, Stéphane; Verbeeck, Cis; Verdini, Andrea;
Wauters, Laurence; West, Matthew; Willems, Sarah; Zhukov, Andrei
2010cosp...38.4202V Altcode: 2010cosp.meet.4202V
The SIDC of the Royal Observatory of Belgium is a very active center
for solar physics research, but also provides an operational service
for data and services related to solar activity and space weather. In
this poster we present the currently available data sets and products,
with a focus on recent additions and new developments.

---------------------------------------------------------
Title: Du nombre de Wolf á l'indice international des taches
solaires: 25 ans de SIDC (2e partie)
Authors: Clette, Frédéric; Berghmans, David; Vanlommel, Petra;
van der Linden, Ronald A. M.; Koeckelenbergh, André; Wauters, Laurence
2008C&T...124...98C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Du nombre de Wolf á l'indice international des taches
solaires: 25 ans de SIDC (1e partie)
Authors: Clette, Frédéric; Berghmans, David; Vanlommel, Petra;
van der Linden, Ronald A. M.; Koeckelenbergh, André; Wauters, Laurence
2008C&T...124...66C Altcode:
No abstract at ADS

---------------------------------------------------------
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
km2/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: From the Wolf number to the International Sunspot Index:
25 years of SIDC
Authors: Clette, Frédéric; Berghmans, David; Vanlommel, Petra;
Van der Linden, Ronald A. M.; Koeckelenbergh, André; Wauters, Laurence
2007AdSpR..40..919C Altcode:
By encompassing four centuries of solar evolution, the sunspot number
provides the longest available record of solar activity. Nowadays,
it is widely used as the main reference solar index on which hundreds
of published studies are based, in various fields of science. In this
review, we will retrace the history of this crucial solar index, from
its roots at the Zürich Observatory up to the current multiple indices
established and distributed by the Solar Influences Data Analysis Center
(SIDC), World Data Center for the International Sunspot Index, which
was founded in 1981, exactly 25 years ago. We describe the principles
now in use for the statistical processing of input data coming from
the worldwide observing network (∼80 stations). Among the various
SIDC data products and innovations, we highlight some recent ones,
including the daily Estimated International Sunspot Number. Taking a
wider perspective, we show how the sunspot index stands the test of
time versus more recent quantitative indices, but we also consider
the prospects and possible options for a future transition from
the visual sunspot index heritage towards an equivalent global
activity index. Based on past historical flaws, we conclude on the
key requirements involved in the maintenance of any robust long-term
solar activity index.

---------------------------------------------------------
Title: History of the Sunspot Index: 25 years SIDC
Authors: Berghmans, D.; van der Linden, R. A. M.; Vanlommel, P.;
Clette, F.; Robbrecht, E.
2006BGGKP...7..288B Altcode:
The sunspot number is the oldest solar activity index. For a long time,
it was the only index representative of the solar cycle, and many
studies on the cyclical behavior of the Sun were performed using the
sunspot number. The Sunspot Index Data Center (SIDC) was founded in
January 1981 to continue the work of the Swiss Federal Observatory ,
when this institution decided to stop computing and publishing the
sunspot number. The SIDC now also provides daily activity reports and
forecasts of the status of the space environment. This 'space weather'
activity is part of the International Space Environment Services (ISES,
a permanent service of the FAGS) that co-ordinates 10 regional warning
centers (RWC). In this paper we will give an overview of the history
of the sunspot number, as well as a short overview of the 25-year
history of the SIDC.

---------------------------------------------------------
Title: LYRA, a solar UV radiometer on Proba2
Authors: Hochedez, J. -F.; Schmutz, W.; Stockman, Y.; Schühle, U.;
Benmoussa, A.; Koller, S.; Haenen, K.; Berghmans, D.; Defise, J. -M.;
Halain, J. -P.; Theissen, A.; Delouille, V.; Slemzin, V.; Gillotay, D.;
Fussen, D.; Dominique, M.; Vanhellemont, F.; McMullin, D.; Kretzschmar,
M.; Mitrofanov, A.; Nicula, B.; Wauters, L.; Roth, H.; Rozanov, E.;
Rüedi, I.; Wehrli, C.; Soltani, A.; Amano, H.; van der Linden, R.;
Zhukov, A.; Clette, F.; Koizumi, S.; Mortet, V.; Remes, Z.; Petersen,
R.; Nesládek, M.; D'Olieslaeger, M.; Roggen, J.; Rochus, P.
2006AdSpR..37..303H Altcode:
LYRA is the solar UV radiometer that will embark in 2006 onboard
Proba2, a technologically oriented ESA micro-mission. LYRA is
designed and manufactured by a Belgian Swiss German consortium (ROB,
PMOD/WRC, IMOMEC, CSL, MPS and BISA) with additional international
collaborations. It will monitor the solar irradiance in four UV
passbands. They have been chosen for their relevance to Solar Physics,
Aeronomy and Space Weather: (1) the 115 125 nm Lyman-α channel,
(2) the 200 220 nm Herzberg continuum range, (3) the Aluminium
filter channel (17 70 nm) including He II at 30.4 nm and (4) the
Zirconium filter channel (1 20 nm). The radiometric calibration will
be traceable to synchrotron source standards (PTB and NIST). The
stability will be monitored by onboard calibration sources (LEDs),
which allow to distinguish between potential degradations of the
detectors and filters. Additionally, a redundancy strategy maximizes
the accuracy and the stability of the measurements. LYRA will benefit
from wide bandgap detectors based on diamond: it will be the first space
assessment of a pioneering UV detectors program. Diamond sensors make
the instruments radiation-hard and solar-blind: their high bandgap
energy makes them insensitive to visible light and, therefore, make
dispensable visible light blocking filters, which seriously attenuate
the desired ultraviolet signal. Their elimination augments the effective
area and hence the signal-to-noise, therefore increasing the precision
and the cadence. The SWAP EUV imaging telescope will operate next to
LYRA on Proba2. Together, they will establish a high performance solar
monitor for operational space weather nowcasting and research. LYRA
demonstrates technologies important for future missions such as the
ESA Solar Orbiter.

---------------------------------------------------------
Title: SWAP onboard PROBA 2, a new EUV imager for solar monitoring
Authors: Berghmans, D.; Hochedez, J. F.; Defise, J. M.; Lecat, J. H.;
Nicula, B.; Slemzin, V.; Lawrence, G.; Katsyiannis, A. C.; van der
Linden, R.; Zhukov, A.; Clette, F.; Rochus, P.; Mazy, E.; Thibert,
T.; Nicolosi, P.; Pelizzo, M. -G.; Schühle, U.
2006AdSpR..38.1807B Altcode:
SWAP (Sun Watcher using Active Pixel system detector and image
processing) is a solar imager in the extreme ultraviolet (EUV)
that has been selected to fly in 2007 on the PROBA 2 technological
platform, an ESA program. SWAP will use an off-axis Ritchey Chrétien
telescope equipped with an EUV enhanced active pixel sensor detector
(coated APS). This type of detector has advantages that promise to
be very profitable for solar EUV imaging. SWAP will provide solar
coronal images at a 1-min cadence in a bandpass centered on 17.5
nm. Observations with this specific wavelength allow detecting
phenomena, such as solar flares or EIT-waves, associated with the
early phase of coronal mass ejections. Image processing software will
be developed that automatically detects these phenomena and sends out
space weather warnings. Together with its sister instrument LYRA, also
onboard PROBA 2, SWAP will serve as a high performance solar monitoring
tool to be used in operational space weather forecasting. The SWAP
data will complement the solar observations provided by instruments
like SOHO-EIT, and STEREO-SECCHI.

---------------------------------------------------------
Title: Solar weather monitoring
Authors: Hochedez, J. -F.; Zhukov, A.; Robbrecht, E.; van der Linden,
R.; Berghmans, D.; Vanlommel, P.; Theissen, A.; Clette, F.
2005AnGeo..23.3149H Altcode:
Space Weather nowcasting and forecasting require solar observations
because geoeffective disturbances can arise from three types of solar
phenomena: coronal mass ejections (CMEs), flares and coronal holes. For
each, we discuss their definition and review their precursors in terms
of remote sensing and in-situ observations. The objectives of Space
Weather require some specific instrumental features, which we list
using the experience gained from the daily operations of the Solar
Influences Data analysis Centre (SIDC) at the Royal Observatory of
Belgium. Nowcasting requires real-time monitoring to assess quickly and
reliably the severity of any potentially geoeffective solar event. Both
research and forecasting could incorporate more observations in order
to feed case studies and data assimilation respectively. Numerical
models will result in better predictions of geomagnetic storms
and solar energetic particle (SEP) events. We review the data types
available to monitor solar activity and interplanetary conditions. They
come from space missions and ground observatories and range from
sequences of dopplergrams, magnetograms, white-light, chromospheric,
coronal, coronagraphic and radio images, to irradiance and in-situ
time-series. Their role is summarized together with indications about
current and future solar monitoring instruments.

---------------------------------------------------------
Title: Solar activity: nowcasting and forecasting at the SIDC
Authors: Berghmans, D.; van der Linden, R. A. M.; Vanlommel, P.;
Warnant, R.; Zhukov, A.; Robbrecht, E.; Clette, F.; Podladchikova,
O.; Nicula, B.; Hochedez, J. -F.; Wauters, L.; Willems, S.
2005AnGeo..23.3115B Altcode:
The Solar Influences Data analysis Center (SIDC) is the World Data
Center for the production and the distribution of the International
Sunspot Index, coordinating a network of about 80 stations
worldwide. From this core activity, the SIDC has grown in recent years
to a European center for nowcasting and forecasting of solar activity
on all timescales. This paper reviews the services (data, forecasts,
alerts, software) that the SIDC currently offers to the scientific
community. The SIDC operates instruments both on the ground and in
space. The USET telescope in Brussels produces daily white light and
Hα images. Several members of the SIDC are co-investigators of the
EIT instrument onboard SOHO and are involved in the development of the
next generation of Europe's solar weather monitoring capabilities. While
the SIDC is staffed only during day-time (7 days/week), the monitoring
service is a 24 h activity thanks to the implementation of autonomous
software for data handling and analysis and the sending of automated
alerts. We will give an overview of recently developed techniques for
visualization and automated analysis of solar images and detection of
events significant for space weather (e.g. CMEs or EIT waves). As part
of the involvement of the SIDC in the ESA Pilot Project for Space
Weather Applications we have developed services dedicated to the
users of the Global Positioning System (GPS). As a Regional Warning
Center (RWC) of the International Space Environment Service (ISES),
the SIDC produces daily forecasts of flaring probability, geomagnetic
activity and 10.7 cm radio flux. The accuracy of these forecasts will
be investigated through an in-depth quality analysis.

---------------------------------------------------------
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∘ and 20∘. 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: Pierre Cugnon: une vie au soleil
Authors: Clette, Frédéric
2005C&T...121...21C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Sidc: World Data Center for the Sunspot Index
Authors: Vanlommel, P.; Cugnon, P.; Linden, R. A. M. Van Der;
Berghmans, D.; Clette, F.
2004SoPh..224..113V Altcode: 2005SoPh..224..113V
Since January 1981, the Royal Observatory of Belgium (ROB) has operated
the Sunspot Index Data Center (SIDC), the World Data Center for the
Sunspot Index. From 2000, the SIDC obtained the status of Regional
Warning Center (RWC) of the International Space Environment Service
(ISES) and became the "Solar Influences Data analysis Center". As a
data analysis service of the Federation of Astronomical and Geophysical
data analysis Services (FAGS), the SIDC collects monthly observations
from worldwide stations in order to calculate the International Sunspot
Number, Ri. The center broadcasts the daily, monthly, yearly
sunspot numbers, with middle-range predictions (up to 12 months). Since
August 1992, hemispheric sunspot numbers are also provided.

---------------------------------------------------------
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: MAGRITTE: an instrument suite for the solar atmospheric
imaging assembly (AIA) aboard the Solar Dynamics Observatory
Authors: Rochus, Pierre L.; Defise, Jean-Marc; Halain, Jean-Philippe;
Jamar, Claude A. J.; Mazy, Emmanuel; Rossi, Laurence; Thibert,
Tanguy; Clette, Frederic; Cugnon, Pierre; Berghmans, David; Hochedez,
Jean-Francois E.; Delaboudiniere, Jean-Pierre; Auchere, Frederic;
Mercier, Raymond; Ravet, Marie-Francoise; Delmotte, Franck; Idir,
Mourad; Schuehle, Udo H.; Bothmer, Volker; Fineschi, Silvano; Howard,
Russell A.; Moses, John D.; Newmark, Jeffrey S.
2004SPIE.5171...53R Altcode:
The Solar Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics
Observatory will characterize the dynamical evolution of the solar
plasma from the chromosphere to the corona, and will follow the
connection of plasma dynamics with magnetic activity throughout the
solar atmosphere. The AIA consists of 7 high-resolution imaging
telescopes in the following spectral bandpasses: 1215Å. Ly-a,
304 Å He II, 629 Å OV, 465 Å Ne VII, 195 Å Fe XII (includes Fe
XXIV), 284 Å Fe XV, and 335 Å Fe XVI. The telescopes are grouped
by instrumental approach: the MAGRITTE Filtergraphs (R. MAGRITTE,
famous 20th Century Belgian Surrealistic Artist), five multilayer EUV
channels with bandpasses ranging from 195 to 1216 Å, and the SPECTRE
Spectroheliograph with one soft-EUV channel at OV 629 Å. They will be
simultaneously operated with a 10-second imaging cadence. These two
instruments, the electronic boxes and two redundant Guide Telescopes
(GT) constitute the AIA suite. They will be mounted and coaligned on a
dedicated common optical bench. The GTs will provide pointing jitter
information to the whole SHARPP assembly. This paper presents the
selected technologies, the different challenges, the trade-offs to be
made in phase A, and the model philosophy. From a scientific viewpoint,
the unique combination high temporal and spatial resolutions with the
simultaneous multi-channel capability will allow MAGRITTE / SPECTRE
to explore new domains in the dynamics of the solar atmosphere, in
particular the fast small-scale phenomena. We show how the spectral
channels of the different instruments were derived to fulfill the
AIA scientific objectives, and we outline how this imager array will
address key science issues, like the transition region and coronal waves
or flare precursors, in coordination with other SDO experiments. We
finally describe the real-time solar monitoring products that will be
made available for space-weather forecasting applications.

---------------------------------------------------------
Title: The expanding space weather services of the SIDC at the Royal
Observatory of Belgium
Authors: van der Linden, R. A. M.; Berghmans, D.; Vanlommel, P.;
Robbrecht, E.; Cugnon, P.; Clette, F.; Wauters, L.; Zhukov, A.
2004cosp...35.2781V Altcode: 2004cosp.meet.2781V
Originally founded in 1981 as the World Data Centre for the Sunspot
Index, the SIDC (Solar Influences Data analysis Centre) shifted to
a higher gear in 2000, when it became a Regional Warning Centre of
the ISES (taking over this activity from Meudon). The obvious link
between space weather and solar activity - a prime research topic of
the solar physics department of the Royal Observatory of Belgium -
and the equally obvious relevance of continuous long-term monitoring
of solar activity have made the SIDC well-placed to embark on this new
future. Thanks to becoming one of the Service Development Activities in
the Space Weather Applications Pilot Project recently set up by ESA, the
SIDC has been able to further improve and expand these activities. In
this paper we discuss some of the new tools, models and data that have
been or will be developed to this purpose. It will also be detailed how
the scientific and operational involvement of the Royal Observatory of
Belgium in many future space missions oriented towards solar physics
and solar monitoring will help the SIDC become an independent European
space weather monitoring and forecasting centre.

---------------------------------------------------------
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: Solar Wind Disturbances and Their Sources in the EUV Solar
Corona
Authors: Zhukov, A. N.; Veselovsky, I. S.; Clette, F.; Hochedez,
J. -F.; Dmitriev, A. V.; Romashets, E. P.; Bothmer, V.; Cargill, P.
2003AIPC..679..711Z Altcode:
We investigate possible links between the activity manifestations in the
solar corona and conditions in the solar wind. For the reduction of this
immense task we have selected 206 events in the solar wind in 1997 -
2000 corresponding to geomagnetic events with Ap &gt; 20 (compiled into
a database at &lt;emph TYPE="46"&gt;http://alpha.sinp.msu.ru/apev). Up
to now, 24 events during the epoch of low solar activity (January 1997 -
January 1998) are investigated. The solar wind conditions monitored by
ACE and WIND spacecraft were traced back to the solar corona observed
by SOHO/EIT. The search for coronal signatures which are probably
associated with the disturbed solar wind conditions was performed. The
coronal sources of these 24 events are identified, namely: eruptions in
active regions, filament eruptions and coronal holes. It is shown that
halo and partial halo CMEs observed within the SOHO/LASCO sensitivity
limits are not necessary indicators of Earth-directed eruptions, and
coronal EUV dimmings can be used as a complementary indicator. We also
found that a structure now conventionally called a “sigmoid” cannot
be represented as a single S-shaped loop (flux tube), but exhibits an
assembly of many smaller structures. It could be formed and destroyed
via eruptions.

---------------------------------------------------------
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&lt;10deg) and high
(B&gt;40deg) latitudes, whereas at mid-latitudes (B~
10deg-40deg) 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 m2 s-2, 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 m2 s-2 covering the
range B=0deg-60deg.

---------------------------------------------------------
Title: Solar wind disturbances and their sources in the EUV solar
corona
Authors: Zhukov, A.; Veselovsky, I.; Bothmer, V.; Dmitriev, A.;
Clette, F.; Romashets, E.; Cargill, P.
2003EAEJA.....2682Z Altcode:
We investigate possible links between the activity manifestations in
the solar corona and conditions in the solar wind. For the reduction
of this immense task we have selected 206 events in the solar wind
in 1997 -- 2000 corresponding to geomagnetic events with Ap &gt; 20
(compiled into a database at http://alpha.sinp.msu.ru/apev). The solar
wind conditions monitored by ACE and WIND spacecraft were traced back to
the solar corona observed by SOHO/EIT. The search for coronal signatures
that are probably associated with the disturbed solar wind conditions
was performed. The coronal sources of the events are identified, namely:
eruptions in active regions, filament eruptions and coronal holes. It is
shown that halo and partial halo CMEs observed within the SOHO/LASCO
sensitivity limits are not necessary indicators of Earth-directed
eruptions, and coronal EUV dimmings can be used as a complementary
indicator. We also found that a structure now conventionally called a
”sigmoid” cannot be represented as a single S-shaped loop (flux tube),
but exhibits an assembly of many smaller structures. It could be formed
and destroyed via eruptions.

---------------------------------------------------------
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: MAGRITTE / SPECTRE : the Solar Atmospheric Imaging Assembly
(AIA) aboard the Solar Dynamics Observatory
Authors: Rochus, P.; Defise, J. M.; Halain, J. P.; Mazy, E.; Jamar, C.;
Clette, F.; Cugnon, P.; Berghmans, D.; Hochedez, J. F.; Delaboudiniere,
J. P.; Artzner, G.; Auchere, F.; Mercier, R.; Ravet, M. F.; Delmotte,
M.; Idir, M.; Fineschi, S.; Antonucci, E.; Harrison, R. A.; Howard,
R. A.; Moses, J. D.; Newmark, J. S.
2002AGUFMSH21C..05R Altcode:
The Solar Atmospheric Imaging Assembly (AIA) aboard the Solar
Dynamics Observatory will characterize the dynamical evolution of
the solar plasma from the chromosphere to the corona, and will follow
the connection of plasma dynamics with magnetic activity throughout
the solar atmosphere. The AIA consists of 7 high resolution imaging
telescopes in the following spectral bandpasses: 1215 \x8F Ly-a, 304
\x8F He II, 629 \x8F OV, 465 \x8F Ne VII, 195 \x8F Fe XII (includes Fe
XXIV), 284 \x8F Fe XV, and 335 \x8F Fe XVI. The telescopes are grouped
by instrumental approach: the Magritte Filtergraphs (R. Magritte,
famous 20th Century Belgian Surrealistic Artist), five multilayer EUV
channels with bandpasses ranging from 195 to 1216 \x8F, and the SPECTRE
Spectroheliograph with one soft-EUV channel at OV 629 \x8F. They will
be simultaneously operated with a 10-second imaging cadence. These two
instruments, the electronic boxes and two redundant Guide Telescopes
(GT) constitute the AIA suite. They will be mounted and coaligned on a
dedicated common optical bench. The GTs will provide pointing jitter
information to the whole SHARPP assembly. This poster presents the
selected technologies, the different challenges, the trade-offs to be
made in phase A, and the model philosophy. From a scientific viewpoint,
the unique combination high temporal and spatial resolutions with the
simultaneous multi-channel capability will allow Magritte/SPECTRE
to explore new domains in the dynamics of the solar atmosphere, in
particular the fast small-scale phenomena. We show how the spectral
channels of the different instruments were derived to fulfill the
AIA scientific objectives, and we outline how this imager array will
address key science issues, like the transition region and coronal waves
or flare precursors, in coordination with other SDO experiments. We
finally describe the real-time solar monitoring products that will be
made available for space-weather forecasting applications.

---------------------------------------------------------
Title: The Solar Influences Data Analysis Center: current status of
expanding activities
Authors: Clette, F.; van der Linden, R.; Cugnon, P.; Berghmans,
D.; Foullon, C.; Wouters, L.; Verwichte, E.; Hochedez, J. -F.;
Vanlommel, P.
2002ESASP.506..125C Altcode: 2002ESPM...10..125C; 2002svco.conf..125C
Over the last 24 months, the activities of the SIDC, which is the
European Regional Warning Center of the ISES, have steadily expanded. A
7-day/week service has been implemented, the SIDC Web interface has
been reworked and expanded and the number of registered users increased
further. New image data have been added, including new photospheric
and chromospheric CCD images from the Uccle Station. We summarize here
the new services provided to the community and some statistics about
the success rate of our forecasts. We also outline the orientations
of the future SIDC development.

---------------------------------------------------------
Title: The new instrumentation of the SIDC/Uccle station
Authors: Clette, F.; Cugnon, P.; Berghmans, D.; van der Linden, R.;
Wauters, L.
2002ESASP.506..935C Altcode: 2002svco.conf..935C; 2002ESPM...10..935C
New digital 1K×1K CCD cameras have been installed on the solar
telescope of the Royal Observatory of Belgium (ROB, Uccle, Brussels),
in addition to the visual telescope used for the classical sunspot
observations. One camera provides full-disk images of the photosphere
and uses an image-selection algorithm to compensate the effects
of the seeing. The other camera produces full-disk images of the
chromosphere in the Hα line, and will be used for an automated flare
patrol work. After completion of the instrument commissioning (August
2002), those images will be made available in near real-time through
the SIDC Regional Warning Center web pages (http://sidc.oma.be) and
in the form of a FITS file archive. We describe here the instruments
and their capabilities.

---------------------------------------------------------
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: Small features in the EIT-SOHO images
Authors: Hochedez, J. -F.; Jacques, L.; Zhukov, A.; Clette, F.;
Antoine, J. -P.
2002ESASP.508..295H Altcode: 2002soho...11..295H
The Extreme ultraviolet Imaging Telescope (EIT) of SoHO incessantly
observed small coronal and transition region features: EUV bright
points, ephemeral regions, brightenings, network enhancements, loop
segments, etc. In this work, the small objects are extracted and
characterized automatically in terms of their scale, location, peak and
background intensities. We correct for the visibility bias introduced
by the expansion of bright regions that develops with the solar cycle,
and we plot the resulting instantaneous densities over the 1996-2001
period. The four time-series exhibit dissimilar trends. The 171 Å
and 195 Å channels are found to show a moderate anti-cyclic behaviour.

---------------------------------------------------------
Title: Global asymmetry of the Sun observed in the extreme ultraviolet
radiation
Authors: Zhukov, A. N.; Veselovsky, I. S.; Hochedez, J. -F.; Clette,
F.; Panasenco, O. A.; Cugnon, P.
2002ESASP.508..189Z Altcode: 2002soho...11..189Z
We report on the observations of the solar luminosity variations in
four SOHO/EIT bandpasses over the period 1996 - 2001. Contributions
of coronal holes, intermediate brightness features, active regions
and bright points are evaluated. We find that during the epoch of low
activity a significant contribution to the longitudinal asymmetry, and
thus to the 27-day variability of the solar EUV radiation, is produced
by the numerous intermediate brightness elements that are globally
distributed over large areas (up to 2/3 of the whole surface of the Sun)
and generally correspond to the "quiet Sun". During the activity minimum
the contribution of this component is comparable to the active regions
contribution. The "quiet Sun" average brightness exhibits rotational
modulation throughout half of the solar cycle observed by SOHO.

---------------------------------------------------------
Title: Multiscale activity observed by EIT/SoHO
Authors: Hochedez, J. -F.; Jacques, L.; Verwichte, E.; Berghmans,
D.; Wauters, L.; Clette, F.; Cugnon, P.
2002ESASP.477..115H Altcode: 2002scsw.conf..115H
The Extreme ultraviolet Imaging Telescope (EIT) of SoHO provides a
high-resolution and large sampling of the solar corona in time, space
and brightness. To extract the wealth of its physics, it is valuable to
adopt a multiscale approach. The Mexican Hat (MH) Continuous Wavelet
Transform (CWT) is used for the first time to derive statistically
the distribution of scales over 4 Mm. The global behaviour of the
small scales offers a powerful way to monitor coronal activity. This
is demonstrated with the May 1998 "CME Watch" data. This benefit
is of space weather relevance and could improve forecasting of the
solar activity.

---------------------------------------------------------
Title: The solar influences data analysis centre
Authors: Berghmans, D.; Clette, F.; Cugnon, P.; Gabryl, J. -R.;
Hochedez, J. -F.; Van der Linden, R. A. M.; Verwichte, E.
2002JASTP..64..757B Altcode: 2002JATP...64..757B
Since 1981, the Royal Observatory of Belgium has operated the
Sunspot Index Data Centre, the World Data Centre for the Sunspot
Index. Recently, the Space Weather Forecast Centre of Paris-Meudon
was transferred and added to the activities of the SIDC. Moreover,
a complete archive of all images of the SOHO instrument EIT has
become available at the SIDC. Given all these extensions, the new
style SIDC has become a `Solar Influences Data Centre' that analyses
solar activity and provides services on three different time scales:
1. Fast warnings and real time monitoring. As the Regional Warning
Centre (RWC) for Western Europe of the International Space Environment
Service (ISES), the SIDC collects and redistributes solar, geomagnetic,
and ionospheric data in Western Europe. Short-term predictions (3 days)
and alerts are produced on a daily basis. 2. Forecasts and middle term
analysis. The SIDC takes care of the calculation of a sunspot index,
called the International Sunspot Number. We compute and broadcast the
daily, monthly, yearly international sunspot numbers, with middle range
predictions (up to 12 months). 3. Post-event analysis and long-term
solar cycle analysis. Since the launch of SOHO, EIT offers a global view
of the EUV corona over the whole rising phase of the solar activity
cycle. Such a long-duration data series is unprecedented and allows
the study of the evolution over the solar cycle of objects classes
such as active regions, coronal holes, coronal mass ejections or flares.

---------------------------------------------------------
Title: The Radiometric Calibration of the Extreme Ultraviolet
Imaging Telescope
Authors: Clette, F.; Hochedez, J. -F.; Newmark, J. S.; Moses, J. D.;
Auchère, F.; Defise, J. -M.; Delaboudinière, J. -P.
2002ISSIR...2..121C Altcode: 2002ESASR...2..121C; 2002rcs..conf..121C
After a five-year effort, the analysis of the pre-flight and in-flight
calibrations of EIT is finally yielding firm results. In this
introductory overview, we will summarize what we learned "internally"
from EIT itself. This includes the interpretation of the pre-flight
calibrations, the original flat-field components (CCD, grid), the
in-flight determination of the point-spread function and straylight and
the compensation of the in-orbit response degradation. Based on this
experience, we conclude with some suggestions of possible improvements
to future calibrations, on SOHO and other planned missions.

---------------------------------------------------------
Title: JOSO national report 2000-2001 - Belgium
Authors: Clette, F.
2002joso.book...32C Altcode:
Much of the solar-related research in Belgium is now concentrated in
Brussels, with a few other dynamical teams or individual researchers
working in various universities.

---------------------------------------------------------
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: Global Asymmetry of the Sun Observed in the Extreme Ultraviolet
Radiation
Authors: Veselovsky, I. S.; Zhukov, A. N.; Dmitriev, A. V.; Tarsina,
M. V.; Clette, F.; Cugnon, P.; Hochedez, J. F.
2001SoPh..201...27V Altcode:
We report on observations of the solar luminosity variations in the
Fe xii line (195 Å) over the period 1996-1999, which corresponds
to the minimum and rising phase of the current 23rd solar cycle. The
relatively or rather high temporal cadence and spatial resolution of
the Extreme-ultraviolet Imaging Telescope (EIT) on board the Solar
and Heliospheric Observatory (SOHO) allowed a nearly continuous
measurement of intensity of different structures on the Sun. We
find that a significant contribution to the longitudinal asymmetry,
and thus to the 27-day variability of the solar EUV radiation,
is produced by the numerous intermediate brightness elements that
are globally distributed over large areas (up to about of the whole
surface of the Sun). When activity is low, this component even becomes
dominant over the contribution from localized active regions and bright
points. This suggests that weak magnetic field areas outside active
regions constitute an important factor through which solar activity
modulates the solar EUV luminosity.

---------------------------------------------------------
Title: In-flight Calibration of SOHO EIT
Authors: Newmark, J. S.; Cook, J. W.; Auchere, F.; Moses, J. D.;
Clette, F.
2001AGUSM..SP21B06N Altcode:
The SOHO EIT response has varied both temporally and spatially
throughout the mission. A large effort has been put forth into
understanding instrument responsivity changes, the spectral response
and absolute calibration. The latter two have been completed (Dere et
al. 2000, Newmark 2000). The response degradation process consists of
several components which are difficult to separate in detail. The two
basic processes contributing to the degradation are 1) the absorption
of EUV before it interacts with the CCD by a surface contaminant plus
possible blackening of the entrance filter and 2) the reduction of
charge collection efficiency (CCE) in the CCD due to EUV induced device
damage. A method utilizing the in-flight calibration lamps has been
developed which accurately characterizes the sensitivity changes. We
present absolutely calibrated SOHO EIT data from 1996 - 2000.

---------------------------------------------------------
Title: Active region transient brightenings. A simultaneous view by
SXT, EIT and TRACE
Authors: Berghmans, D.; McKenzie, D.; Clette, F.
2001A&A...369..291B Altcode:
This paper reports on a qualitative study on the weakest flarelike
brightenings in active region that can be observed with current
coronal imagers. Specificallly, we investigate the correspondence of
the “active region transient brightenings” (ARTB) first observed
almost a decade ago with SXT with similar brightenings in the EUV
that are now observed by EIT and TRACE. For this goal, exceptionally
high cadence image sequences were acquired of a small but rapidly
evolving active region (NOAA 8218), simultaneously by SXT, EIT, and
TRACE. Within the timeframe of this coordinated campaign, we detected
41 soft X-ray brightenings and 373 EUV brightenings. We find that the
strongest brightenings observed by EIT are indeed the EUV counterparts
of the ARTBs seen by SXT. Weaker brightenings seen by EIT often do not
have an X-ray counterpart. Among the brightenings detected with SXT we
discover a new subpopulation, consisting of events that brighten in soft
X-rays only, at a footpoint of a pre-existing SXT loop shortly after
an ARTB occurred at the other footpoint. The propagation speed of the
perturbation suggests an interpretation in terms of slow mode MHD waves.

---------------------------------------------------------
Title: TECONet: un réseau de polarimétrie d'éclipse
Authors: Clette, F.; Gabryl, J. -R.
2001C&T...117...16C Altcode:
No abstract at ADS

---------------------------------------------------------
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: Long Term Variations in the Extreme UV Corona: the EIT/SoHO
perspective
Authors: Hochedez, J. -F.; Clette, F.; Verwichte, E.; Berghmans, D.;
Cugnon, P.
2001IAUS..203..501H Altcode:
Since the start of the SOHO mission, EIT offered a global view of
the extreme ultraviolet corona constinuously over the whole rising
phase of the solar activity cycle. Such a long-duration data serie
is unprecedented. We present here the current results of an ongoing
investigation of the entire EIT data set. In this process, numerous
classes of magnetic regions of all sizes (active regions, coronal
holes, bright points, plumes, transition region network, filaments)
as well as many different classes of dynamic events (CME's, flares,
jets, blinkers, macrospicules) will be identified in EIT images made
in its four bandpasses. The changes in the class properties (location,
size, area, topology, lifetime, integrated flux) or in the relationship
between different object classes can then be monitored over the fast
rise of magnetic activity towards the current maximum. We describe here
the image processing techniques developed for this search as well as
early results.

---------------------------------------------------------
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: Calibration and flight of the NRL EIT CalRoc
Authors: Newmark, Jeffrey S.; Moses, J. Daniel; Cook, John W.;
Delaboudiniere, Jean-Pierre; Song, Xueyan; Carabetian, Charles;
Bougnet, Marie; Brunaud, Jacqueline; Defise, Jean-Marc; Clette,
Frederic; Hochedez, Jean-Francois E.
2000SPIE.4139..328N Altcode:
The ability to derive physical parameters of the Sun from observations
by the Solar and Heliospheric Observatory (SOHO) Extreme Ultraviolet
Imaging Telescope (EIT) greatly increases the scientific return of the
mission. The absolute and time variable calibration of EIT therefore is
of extreme interest. The NRL EIT Calibration Sounding Rocket (CalRoc)
program was initiated to provide well calibrated, contemporaneous
observations in support of SOHO EIT. These observations provide
three benefits to the SOHO EIT data, absolute calibration points,
temporal and spatial information of the EIT EUV response variability
in flight via flat field information and clues to the physics of the
degradation. Details of the bandpasses of the multilayered optics and
the total telescope photometry are presented. Comparisons are shown
with the contemporaneous images from SOHO EIT. Plans for the second
CalRoc flight are discussed. Loss of reflectivity in the multilayer
mirrors has been identified as a new component to the SOHO EIT and
CalRoc degradation.

---------------------------------------------------------
Title: The Preflight Photometric Calibration of the
Extreme-Ultraviolet Imaging Telescope EIT
Authors: Dere, K. P.; Moses, J. D.; Delaboudinière, J. -P.; Brunaud,
J.; Carabetian, C.; Hochedez, J. -F.; Song, X. Y.; Catura, R. C.;
Clette, F.; Defise, J. -M.
2000SoPh..195...13D Altcode:
This paper presents the preflight photometric calibration of the
Extreme-ultraviolet Imaging Telescope (EIT) aboard the Solar and
Heliospheric Observatory (SOHO). The EIT consists of a Ritchey-Chrétien
telescope with multilayer coatings applied to four quadrants of the
primary and secondary mirrors, several filters and a backside-thinned
CCD detector. The quadrants of the EIT optics were used to observe
the Sun in 4 wavelength bands that peak near 171, 195, 284, and 304
Å. Before the launch of SOHO, the EIT mirror reflectivities, the filter
transmissivities and the CCD quantum efficiency were measured and these
values are described here. The instrumental throughput in terms of an
effective area is presented for each of the various mirror quadrant
and filter wheel combinations. The response to a coronal plasma as
a function of temperature is also determined and the expected count
rates are compared to the count rates observed in a coronal hole,
the quiet Sun and an active region.

---------------------------------------------------------
Title: Mid-Term Variations in the Extreme UV Corona: the EIT/SOHO
Perspective
Authors: Hochedez, J. F.; Clette, Frederic; Verwichte, Erwin;
Berghmans, David; Cugnon, Pierre
2000ESASP.463...79H Altcode: 2000sctc.proc...79H
No abstract at ADS

---------------------------------------------------------
Title: The TECONet Project One Year after Totality
Authors: Clette, F.; Gabryl, J. -R.
2000ESASP.463..581C Altcode: 2000sctc.proc..581C
No abstract at ADS

---------------------------------------------------------
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: Early Results from TECONet
Authors: Clette, F.; Gabryl, J. -R.
1999ESASP.448.1273C Altcode: 1999ESPM....9.1273C; 1999mfsp.conf.1273C
No abstract at ADS

---------------------------------------------------------
Title: Multi-Imager Study of Transients and Propagating Disturbances
in Active Region Loops (SOHO JOP80 Campaign)
Authors: Berghmans, D.; Clette, F.; Robbrecht, E.; McKenzie, D.
1999ESASP.448..575B Altcode: 1999ESPM....9..575B; 1999mfsp.conf..575B
No abstract at ADS

---------------------------------------------------------
Title: Active Region Transient Brightenings : EIT Versus SXT
Authors: Berghmans, D.; McKenzie, D.; Clette, F.
1999ESASP.446..173B Altcode: 1999soho....8..173B
On May 13, 1998, the Extreme-Ultraviolet Imaging Telescope (EIT,
on board SOHO) has produced a unique image sequence operating in
'shutterless mode' (SOHO JOP 80). In JOP 80, EIT is the leading
instrument, followed by several space born instruments (SXT, TRACE,
MDI, CDS, SUMER), as well as two observatories on the ground (in La
Palma and Sac Peak). The target of the campaign was a relatively small
but rapidly evolving active region (AR 8218). For the EIT contribution,
a 15 s cadence was achieved in the Fe XII bandpass at 195 deg by leaving
EIT's shutter open for 1 hour and operating the CCD in frame transfer
mode. We have started the analysis of the huge data set, by making an
inventory of the transients observed in the EIT image sequence. These
transients range from a B3.5 flare producing a large plasma flow along
pre-existing loops, to smaller EUV brightenings of active region
loops. In addition, a new class of weaker footpoint brightenings
was discovered that produce wave-like disturbances propagating along
quasi-open field lines (see the presentation by Eva Robbrecht at this
workshop). In this paper we take the opportunity provided by JOP 80,
to investigate the correspondence of the transient brightenings observed
by EIT in this active region, with the ARTB previously observed by SXT
and studied by Shimizu (1992). Within the simultaneous high cadence
SOHO JOP 80 image sequences, both EIT and SXT accummulated a few tens
of brightening events. At the time of the writing of this abstract,
we can say that most of the SXT events have indeed 1 or more EIT
counterparts. Typically the SXT events are somewhat bigger than the EIT
events where the latter are ussualy located toward the point of origin
of the SXT events. Whereas a few brightenings exist in one dataset
without any trace in the other dataset (in both directions), we have
additionally for a few brightenings in the SXT data, a corresponding
EIT darkening as if the plasma is suddenly heated and dissappears from
the EIT passband.

---------------------------------------------------------
Title: Working Group 6: Activity on all Scales
Authors: Clette, F.; Poletto, G.; Ŝvestka, Z.
1999ESASP.446..103C Altcode: 1999soho....8..103C
No abstract at ADS

---------------------------------------------------------
Title: In-flight characterization and compensation of the optical
properties of the EIT instrument
Authors: Defise, Jean-Marc; Clette, Frederic; Auchere, Frederic
1999SPIE.3765..341D Altcode:
Onboard the SOHO spacecraft, the Extreme UV Imaging Telescope
(EIT) is imagin successfully the EUV solar corona since January
96. EIT is a normal incidence telescope, segmented in 4 separate
quadrants. Each of those quadrants reflects extreme UV (EUV) light
in a narrow bandpass defined by multilayer coatings deposited on
the mirrors and by aluminum filters used to reject the visible and
IR part of the solar irradiance. The specific configuration of the
optical system is generating artifacts that must be compensated in the
raw solar images. However, the only information available to improve
image quality comes from the continuous survey of the solar corona
accomplished in flight by EIT. In-flight image characteristics and
instrumental aspects are discussed in this paper, showing how methods
can be derived to clean up the EIT data. The current investigations
are addressing the internal vignetting, the shadow pattern of grids
supporting the focal filters, the determination of the instrumental
point spread function and the assessment of the telescope focusing,
as well as the relation between those factors.

---------------------------------------------------------
Title: EIT Micro-Variability Studies : Preliminary Results from the
SOHO JOP 80 Campaign
Authors: Clette, F.; Berghmans, D.
1999ASPC..184..217C Altcode:
The first results from the high-cadence imaging campaign run in May 98,
by several space-based instruments with ground support (SOHO JOP80), are
presented. General properties and scaling laws are deduced for a fairly
large sample of small-amplitude short-lived impulsive brightenings
occuring locally in active region loops. From these, we derive some
conclusions about similarities with soft-X ray microflares. Several
classes of minor transients are distinguished, such as loop-like and
twin brightenings. We find also evidence for propagating compressive
waves in extended field lines rooted near one magnetic pole of the
active region. This study provides a first inventory of small-scale
variabilities in view of the full analysis of this huge and rich
data set.

---------------------------------------------------------
Title: Past Achievements and Prospects 10 Months before Totality Day
Authors: Clette, F.
1999ASPC..184..339C Altcode:
The present status of JOSO Working Group 7 (WG7) activities is
summarized, including the support for coordination between scientific
teams, as well as the educational project. Although the practical
organisation of professional expeditions took off only slowly in the
course of 1998, often by direct contacts between institutes, the WG7
leader could serve as a central relay point, helping scientists in their
search of local contact addresses. We also report about the progresses
accomplished in the edition of an information booklet and the support we
could get for this task. The prospects for a multi-station coordinated
campaign, involving primarily basic observations by amateur astronomers,
will be discussed, starting from the pioneering effort of the Groupement
Français pour l'Observation et l'Etude du Soleil (GFOES).

---------------------------------------------------------
Title: Polarization observations and results of the 1998 February
26th solar eclipse
Authors: Gabryl, J. -R.; Cugnon, P.; Clette, F.
1999AIPC..471..749G Altcode: 1999sowi.conf..749G
Following our long-term solar corona study program, we organized an
expedition to the Curacao island (Dutch Antillas) to observe the total
solar eclipse of February 26th, 1998. As the duration of this totality
was quite short, our polarized white-light CCD imaging experiment
was redesigned in order to increase the number of recorded images,
thereby increasing the number of sampled polarization angles and
exposures. This was made possible by upgrading to a new PC system,
with fast hard disc and data transfer port. This allowed us to finally
record 7 series of different exposures, each containing 24 images taken
at 12 polarization angles, i.e. with 8-time oversampling. The data
were processed to derive global maps of brightness and polarization,
and from these, to build electron density models. In those maps,
the shape of the corona is highly flattened, with extended polar
holes filled with numerous wide plumes. All large streamers are
essentially aligned along the solar equatorial plane. Moreover,
the measured degree of polarization indicates that these structures
are located in the vicinity of the plane of the sky. Unfortunately,
the unusually high sky brightness hid the faint extensions of coronal
structures. This limited their visibility to less than 3 solar radii,
implying a corresponding limitation in the radial extent of our global
model. The results presented here are also briefly compared with our
earlier eclipse observations.

---------------------------------------------------------
Title: Active region EUV transient brightenings - First Results by
EIT of SOHO JOP 80
Authors: Berghmans, D.; Clette, F.
1999SoPh..186..207B Altcode:
On 13 May 1998, the Extreme-Ultraviolet Imaging Telescope (EIT, on board
SOHO) has produced a unique image sequence operating in 'shutterless
mode' (SOHO JOP 80). In JOP 80, EIT is the lead instrument, followed by
several space-born instruments (SXT, TRACE, MDI, CDS, SUMER), as well
as two observatories on the ground (in La Palma and Sac Peak). The
target of the campaign was a relatively small but rapidly evolving
active region (AR 8218). For the EIT contribution, a 15 s cadence was
achieved in the Fe xii bandpass at 195 Å by leaving EIT's shutter open
for 1 h and operating the CCD in frame-transfer mode. In this paper, we
start the analysis of the huge data set, by making an inventory of the
transients observed in the EIT image sequence. Besides scatter plots of
duration, size and radiative output of the detected EUV brightenings,
we discuss in full detail the morphology and evolution of several
typical events. These transients range from a B3.5 flare producing a
large plasma flow along pre-existing loops, to EUV versions of active
region transient brightenings as previously observed by SXT on board
Yohkoh. In addition, a new class of weaker footpoint brightenings
is discussed that produce wave-like disturbances propagating along
quasi-open field lines. This new class of propagating disturbances
extends the wide variety of transient phenomena that we discovered in
the EIT data, and makes the potential for inter-instrumental studies of
the JOP 80 data all the more exciting. We stress the necessity of such
forthcoming studies to reach an instrument-independent classification
of small-scale solar transients.

---------------------------------------------------------
Title: Images d'éclipse: technique photographique et vidéo.
Authors: Clette, F.
1999C&T...115...92C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: JOSO Working Group 7: Preparation of the August 1999 Solar
Eclipse
Authors: Clette, F.; Cugnon, P.
1999CoSka..28..243C Altcode:
As an European association of professional solar observers, JOSO (Joint
Organisation for Solar Observations) has organised a working group
(WG7) in order to contribute to the preparation of scientists for this
`European' eclipse event. We present here the main projects of this
small group: diffusion of practical information to scientific teams
(planning support, contact addresses in welcoming countries, with an
emphasis on Eastern Europe), promotion of collaborations, coordination
of a basic experiment by amateurs and professionals along the totality
band, and diffusion of an educational reference publication to help
local non-specialised scientists and authorities across the continent
to provide reliable information to the public.

---------------------------------------------------------
Title: The program of the Royal Observatory of Belgium for the total
solar eclipse of August 11th 1999
Authors: Clette, F.; Cugnon, P.; Gabryl, J. -R.
1999CoSka..28..251C Altcode:
This paper briefly describes the solar physics program of the Royal
Observatory of Belgium, for the total solar eclipse of 1999 August
11. We intend to set up similar experiments at two sites close to the
center line, respectively in France and in Romania. In this purpose,
close collaborations with local organizations are being established. The
observing program will consist in two main experiments: - Fast CCD
imaging of the corona in polarized white-light, up to 2 to 4 R_Sun,
using fully automated 24-position rotating polarizing filters and
powerful computers. - photographic observations, also in polarized
white-light, using a six-position manual polarizing filter at the prime
focus of 1 meter refractors. The program may also include infrared
photography of the far corona.

---------------------------------------------------------
Title: Polarization observations and results of the 1998 February
26th solar corona
Authors: Gabryl, J. -R.; Cugnon, P.; Clette, F.
1999CoSka..28..216G Altcode:
In the frame of the long-term study program of the solar corona, we have
organized an expedition in Curacao (Dutch Antillas) to observe the total
solar eclipse of February 26th, 1998. As the totality duration was quite
short, we had to improve again the CCD experiment layout in order to
record a sample of images as wide as possible in both polarization and
brightness ranges. This was made possible by the acquisition of a new PC
with fast hard disc and data transfer port. We managed then to record 7
series of different exposures, each containing polarization measurements
of 24 images (thus 8 times oversampled). The data processing led to
accurate brightness and polarization maps as well as electron density
models. The shape of the corona is highly flattened with large polar
holes filled by numerous wide plumes. Large streamers are also observed
and are essentially aligned along the solar equatorial plane. Moreover,
the polarization indicates that these structures are located in the
vicinity of the plane of the sky. Unfortunately, the unusually high
sky brightness hid the faintest coronal structures and limited the
visibility up to 3 solar radii implying a similar limitation in our
modelling. We present here these results and give a brief comparison
with our previous eclipse observation.

---------------------------------------------------------
Title: Observations of Coronal Structures Above an Active Region by
EIT and Implications for Coronal Energy Deposition
Authors: Neupert, W. M.; Newmark, J.; Delaboudinière, J. -P.;
Thompson, B. J.; Catura, R. C.; Moses, J. D.; Gurman, J. B.;
Portier-Fozzani, F.; Gabriel, A. H.; Artzner, G.; Clette, F.; Cugnon,
P.; Maucherat, A. J.; Defise, J. M.; Jamar, C.; Rochus, P.; Dere,
K. P.; Howard, R. A.; Michels, D. J.; Freeland, S.; Lemen, J. R.;
Stern, R. A.
1998SoPh..183..305N Altcode:
Solar EUV images recorded by the EUV Imaging Telescope (EIT) on SOHO
have been used to evaluate temperature and density as a function of
position in two largescale features in the corona observed in the
temperature range of 1.0-2.0 MK. Such observations permit estimates
of longitudinal temperature gradients (if present) in the corona and,
consequently, estimates of thermal conduction and radiative losses
as a function of position in the features. We examine two relatively
cool features as recorded in EIT's Fe ix/x (171 Å) and Fe xii (195 Å)
bands in a decaying active region. The first is a long-lived loop-like
feature with one leg, ending in the active region, much more prominent
than one or more distant footpoints assumed to be rooted in regions of
weakly enhanced field. The other is a near-radial feature, observed
at the West limb, which may be either the base of a very high loop
or the base of a helmet streamer. We evaluate energy requirements to
support a steady-state energy balance in these features and find in
both instances that downward thermal conductive losses (at heights
above the transition region) are inadequate to support local radiative
losses, which are the predominant loss mechanism. The requirement that a
coronal energy deposition rate proportional to the square of the ambient
electron density (or pressure) is present in these cool coronal features
provides an additional constraint on coronal heating mechanisms.

---------------------------------------------------------
Title: In-orbit performances of the EIT instrument on board SOHO
and intercalibration with the EIT Calroc Sounding Rocket program
Authors: Defise, Jean-Marc; Moses, John Daniel; Clette, Frederic
1998SPIE.3442..126D Altcode:
The Extreme UV Imaging Telescope (EIT) instrument is operating
on-board the SOHO spacecraft since January 1996. EIT is providing EUV
observations of the solar corona in four narrow channels: 171, 195,
284 and 304 angstrom. Due to continuous exposure to the EUV solar
irradiation, the instrument performance is continuously evolving. The
backside thinned detector is showing important changes in its overall
response and local damage of EUV highly exposed areas. These performance
modifications can be characterized through several observation analyses
that are discussed in this paper. Two major effects are identified:
contamination on the detector surface and charge mobility changes in the
CCD produced by the EUV irradiation. To restore the instrument response,
bakeouts are regularly planned as well as specific observation sequences
that are used to characterize the detector damages. An overview of
the instrument response behavior is presented in this paper.

---------------------------------------------------------
Title: JOSO Working Group 7: Preparation of teh Augiust 1999 Eclipse
Authors: Clette, F.; Cugnon, P.
1998jena.conf....5C Altcode:
As an European association of professional solar observers, the Joint
Organisation for Solar Observations (JOSO) has organized a working
group in order to contribute to the preparation of scientists for
this "European" event. We present here the main projects of this small
group: diffusion of practical information to scientific teams (planning
support, contact addresses in welcoming countries, with an emphasis on
Eastern Europe), promotion of collaborations, coordination of a basic
experiment by amateurs and professionals along the totality band,
and diffusion of an educational reference publication to help local
non-specialized scientists and authorities across Europe to provide
reliable information to the public.

---------------------------------------------------------
Title: The program of the Royal Observatory of Belgium for the Total
Eclipse of August 1999
Authors: Clette, F.; Cugnon, P.; Gabryl, J. -R.
1998jena.conf....4C Altcode:
This paper describes only tentatively the program of the Solar Physics
department of the Royal Observatory of Belgium, as some elements of
this program are not yet firmly settled. We intend essentially to set
up similar experiments at two different sites. The first one will be
located in France (probably Alsace) and the second one in Romania, not
far from the maximum duration point, both as close as possible to the
centerline. In both cases, close collaborations with local organizations
are being established. The observing program will consist in two main
experiments: * CCD imaging of the corona in polarized white light, up
to two 4 solar radii, with increased capabilities compared to previous
expeditions. Namely, two or even three CCD cameras will be used, with
fully authomated 24 position rotating polarizing filters and powerful
PC'st. Fast image acquisition is indeed indspensable due to the very
short duration of the totality. * Photographic observations, also in
polarized white light, using a six -position manual polarizing filter
at the prime focus of 1 meter refractors. This older observing setup,
which was used many times since 1973, is kept in service to ensure the
long-term continuity of our polarimetric observations. This program
may also include infrared photography of the far corona, depending on
the available manpower

---------------------------------------------------------
Title: Quiet Sun EUV transient brightenings and turbulence. A
panoramic view by EIT on board SOHO
Authors: Berghmans, D.; Clette, F.; Moses, D.
1998A&A...336.1039B Altcode:
Since January 1996, the Extreme-Ultraviolet Imaging Telescope (EIT,
onboard SOHO) has produced unique image sequences covering a wide field
of view with a high temporal resolution, in the He Ii transition region
line and in several Fe coronal emission lines. Using two sequences
acquired with cadences of the order of one minute and with durations
ranging from one hour to several hours, we analyse the dynamical
properties of the transition region and corona. We find evidence of
turbulence both in spatial and in temporal power spectra suggesting
that the plasma of the quiet solar atmosphere is in a permanent state
of turbulence. As predicted by numerical simulations, this turbulence
has an highly intermittent nature. We find an unexpectedly large number
of small-scale brightenings. The coronal brightenings are identified as
the low energy counterparts of “X-ray network flares” observed with
SXT on board Yohkoh. The thousands of brightenings observed by EIT in
the transition region include many that are similar to “blinkers”
observed with CDS, though we find a larger variety. Thanks to EIT's
wide spatial coverage, we can perform a large scale statistical study,
complementing spectroscopic studies which give access to only a very
small subsample of events. We present occurrence distributions of
duration, size and radiative output of the brightenings as well as
various correlations between these parameters. The energy injected by
the brightenings into the solar atmosphere is insufficient to be in
itself responsible for coronal heating. We discuss the importance of
the ubiquitous small brightenings as perhaps the most visible aspect
of yet undetected heating events higher up in the quiet corona.

---------------------------------------------------------
Title: Working Group 7 Activities in 1997: Still one Eclipse to GO !
Authors: Clette, F.
1998ASPC..155..389C Altcode: 1998sasp.conf..389C
No abstract at ADS

---------------------------------------------------------
Title: Impulsive Coronal Dynamics as Revealed by EIT
Authors: Clette, F.; Berghmans, D.
1998ASPC..155..356C Altcode: 1998sasp.conf..356C
No abstract at ADS

---------------------------------------------------------
Title: Quiet Sun EUV Transient Brightenings and Turbulence
Authors: Berghmans, D.; Clette, F.; Moses, D.
1998ESASP.417..229B Altcode: 1998cesh.conf..229B
No abstract at ADS

---------------------------------------------------------
Title: EIT Observations of Small-Scale Dynamics in the Transition
Region and Corona
Authors: Clette, F.; Berghmans, D.
1997ESASP.415...95C Altcode: 1997cpsh.conf...95C
No abstract at ADS

---------------------------------------------------------
Title: EIT Observations of the Extreme Ultraviolet Sun
Authors: Moses, D.; Clette, F.; Delaboudinière, J. -P.; Artzner,
G. E.; Bougnet, M.; Brunaud, J.; Carabetian, C.; Gabriel, A. H.;
Hochedez, J. F.; Millier, F.; Song, X. Y.; Au, B.; Dere, K. P.; Howard,
R. A.; Kreplin, R.; Michels, D. J.; Defise, J. M.; Jamar, C.; Rochus,
P.; Chauvineau, J. P.; Marioge, J. P.; Catura, R. C.; Lemen, J. R.;
Shing, L.; Stern, R. A.; Gurman, J. B.; Neupert, W. M.; Newmark,
J.; Thompson, B.; Maucherat, A.; Portier-Fozzani, F.; Berghmans, D.;
Cugnon, P.; Van Dessel, E. L.; Gabryl, J. R.
1997SoPh..175..571M Altcode:
The Extreme Ultraviolet Imaging Telescope (EIT) on board the SOHO
spacecraft has been operational since 2 January 1996. EIT observes
the Sun over a 45 x 45 arc min field of view in four emission line
groups: Feix, x, Fexii, Fexv, and Heii. A post-launch determination
of the instrument flatfield, the instrument scattering function, and
the instrument aging were necessary for the reduction and analysis
of the data. The observed structures and their evolution in each
of the four EUV bandpasses are characteristic of the peak emission
temperature of the line(s) chosen for that bandpass. Reports on the
initial results of a variety of analysis projects demonstrate the range
of investigations now underway: EIT provides new observations of the
corona in the temperature range of 1 to 2 MK. Temperature studies of
the large-scale coronal features extend previous coronagraph work
with low-noise temperature maps. Temperatures of radial, extended,
plume-like structures in both the polar coronal hole and in a low
latitude decaying active region were found to be cooler than the
surrounding material. Active region loops were investigated in detail
and found to be isothermal for the low loops but hottest at the loop
tops for the large loops.

---------------------------------------------------------
Title: In-orbit diagnostics of EIT EUV CCD radiation-induced aging
Authors: Defise, Jean-Marc; Clette, Frederic; Moses, John Daniel;
Hochedez, Jean-Francois E.
1997SPIE.3114..598D Altcode:
The extreme UV imaging telescope (EIT) on-board SOHO is performing a
global survey of the extreme ultraviolet (EUV) solar corona. Operating
since January 96, EIT has been producing tens thousands of images of the
Sun in four narrow channels (171, 195, 284 and 304 angstrom). orbiting
around the L1 Lagrangian point and oriented permanently towards the
Sun, the EIT mission is a unique opportunity to study an instrument
continuously exposed to solar EUV radiations. The backside thinned
CCD detector is showing significant changes in its overall signal
and in local 'burn in' regions. Periodic bakeouts allowed to
restore a good efficiency. However, a specific observation program
has been set up to diagnose the origin of the signal decay. In this
framework, photon transfer analyses are performed on solar EUV images,
providing good indications on the local charge collection efficiency
status. Calibration lamp images are also used to eluate the signal
recovery in the visible range. The signal degradation seems to be the
result of two competing effects: periodic deposition of a contamination
layer, and charge mobility change in the CCD Si layer as a function
of the accumulated EUV dose. In this paper, the CCD quantum properties
evolution is discussed, as well as the contamination issue. Preliminary
diagnostics on the CCD aging under EUV radiations are exposed.

---------------------------------------------------------
Title: EIT and LASCO Observations of the Initiation of a Coronal
Mass Ejection
Authors: Dere, K. P.; Brueckner, G. E.; Howard, R. A.; Koomen, M. J.;
Korendyke, C. M.; Kreplin, R. W.; Michels, D. J.; Moses, J. D.;
Moulton, N. E.; Socker, D. G.; St. Cyr, O. C.; Delaboudinière, J. P.;
Artzner, G. E.; Brunaud, J.; Gabriel, A. H.; Hochedez, J. F.; Millier,
F.; Song, X. Y.; Chauvineau, J. P.; Marioge, J. P.; Defise, J. M.;
Jamar, C.; Rochus, P.; Catura, R. C.; Lemen, J. R.; Gurman, J. B.;
Neupert, W.; Clette, F.; Cugnon, P.; Van Dessel, E. L.; Lamy, P. L.;
Llebaria, A.; Schwenn, R.; Simnett, G. M.
1997SoPh..175..601D Altcode:
We present the first observations of the initiation of a coronal mass
ejection (CME) seen on the disk of the Sun. Observations with the EIT
experiment on SOHO show that the CME began in a small volume and was
initially associated with slow motions of prominence material and a
small brightening at one end of the prominence. Shortly afterward,
the prominence was accelerated to about 100 km s-1 and
was preceded by a bright loop-like structure, which surrounded an
emission void, that traveled out into the corona at a velocity of
200-400 km s-1. These three components, the prominence,
the dark void, and the bright loops are typical of CMEs when seen at
distance in the corona and here are shown to be present at the earliest
stages of the CME. The event was later observed to traverse the LASCO
coronagraphs fields of view from 1.1 to 30 R⊙. Of particular interest
is the fact that this large-scale event, spanning as much as 70 deg in
latitude, originated in a volume with dimensions of roughly 35" (2.5
x 104 km). Further, a disturbance that propagated across
the disk and a chain of activity near the limb may also be associated
with this event as well as a considerable degree of activity near the
west limb.

---------------------------------------------------------
Title: Association of Extreme-Ultraviolet Imaging Telescope (EIT)
Polar Plumes with Mixed-Polarity Magnetic Network
Authors: Wang, Y. -M.; Sheeley, N. R.; Dere, K. P.; Duffin, R. T.;
Howard, R. A.; Michels, D. J.; Moses, J. D.; Harvey, J. W.; Branston,
D. D.; Delaboudinière, J. -P.; Artzner, G. E.; Hochedez, J. F.;
Defise, J. M.; Catura, R. C.; Lemen, J. R.; Gurman, J. B.; Neupert,
W. M.; Newmark, J.; Thompson, B.; Maucherat, A.; Clette, F.
1997ApJ...484L..75W Altcode:
SOHO EIT spectroheliograms showing the polar coronal holes during the
present sunspot minimum are compared with National Solar Observatory
(Kitt Peak) magnetograms taken in Fe I λ8688 and Ca II λ8542. The
chromospheric λ8542 magnetograms, obtained on a routine, near-daily
basis since 1996 June, reveal the Sun's strong polar fields with
remarkable clarity. We find that the Fe IX λ171 polar plumes occur
where minority-polarity flux is in contact with flux of the dominant
polarity inside each polar hole. Moreover, the locations of “plume
haze” coincide approximately with the patterns of brightened He
II λ304 network within the coronal hole. The observations appear
to be consistent with mechanisms of plume formation involving
magnetic reconnection between unipolar flux concentrations and nearby
bipoles. The fact that minority-polarity fields constitute only a small
fraction of the total magnetic flux within the polar holes suggests
that plumes are not the main source of the high-speed polar wind.

---------------------------------------------------------
Title: Observations of Coronal Features by EIT above an Active Region
by EIT and Implications for Coronal Heating
Authors: Neupert, W. M.; Newmark, J.; Thompson, B. J.; Catura, R.;
Moses, J. D.; Portier-Fozzani, F.; Delaboudiniere, J. P.; Gabriel, A.;
Artzner, G.; Clette, F.; Cugnon, P.; Maucherat, A.; Defise, J. M.;
Jamar, C.; Rochus, P.; Howard, R.; Michels, D.; Dere, K.; Freeland,
S.; Lemen, J.; Stern, R.; Gurman, J.
1997SPD....28.0115N Altcode: 1997BAAS...29..881N
The EUV Imaging Telescope (EIT) on the SOHO provides the capability
for multi-wavelength imaging of the corona in four spectral bands,
centered at 171, 195, 284, and 304 Angstroms, using multilayer telescope
technology. These bands encompass coronal temperatures from 1 MK
to 2.5 MK as well as the upper chromosphere, at about 60,000 K. In
particular, nearly simultaneous imaging in the 171 and 195 Angstrom
bands, the former including major Fe IX and Fe X emission lines, the
latter including a strong Fe XII line, provides a capability to infer
the morphology and characteristics of the corona at temperatures of
1.0 - 1.7 MK. We have examined the corona in this temperature range
over an active region observed from SOHO from May - September, 1996 and
find that low-lying loops (below a density scale height of 75,000 km,
characteristic of Fe X) vary little in brightness and temperature along
their length. For features extending to greater heights, however, both
brightness gradients and temperature gradients are observed. Preliminary
analysis of the observations when the region was on the West limb
on September 30 indicates a small positive temperature gradient of
approximately 0.5 K/km in one loop system that extended above 100,000
km. On the other hand, a nearly radial feature extending to the edge of
the EIT FOV was isothermal or had at most a slight negative temperature
gradient. Such measurements may have application to the modeling of
coronal loops and streamers and the processes of coronal heating and
solar wind acceleration.

---------------------------------------------------------
Title: Imaging the solar corona in the EUV
Authors: Delaboudiniere, J. -P.; Stern, R. A.; Maucherat, A.;
Portier-Fozzani, F.; Neupert, W. M.; Gurman, J. B.; Catura, R. C.;
Lemen, J. R.; Shing, L.; Artzner, G. E.; Brunaud, J.; Gabriel, A. H.;
Michels, D. J.; Moses, J. D.; Au, B.; Dere, K. P.; Howard, R. A.;
Kreplin, R.; Defise, J. M.; Jamar, C.; Rochus, P.; Chauvineau, J. P.;
Marioge, J. P.; Clette, F.; Cugnon, P.; van Dessel, E. L.
1997AdSpR..20.2231D Altcode:
The SOHO (SOlar and Heliospheric Observatory) satellite was launched on
December 2nd 1995. After arriving at the Earth-Sun (L1) Lagrangian point
on February 14th 1996, it began to continuously observe the Sun. As
one of the instruments onboard SOHO, the EIT (Extreme ultraviolet
Imaging Telescope) images the Sun's corona in 4 EUV wavelengths. The
He II filter at 304 A˚ images the chromosphere and the base of the
transition region at a temperature of 5 - 8 x 10^4 K; the Fe IX-X
filter at 171 A˚ images the corona at a temperature of ~ 1.3 x 10^6 K;
the Fe XII filter at 195 A˚ images the quiet corona outside coronal
holes at a temperature of ~ 1.6 x 10^6 K; and the Fe XV filter at 284
A˚ images active regions with a temperature of ~ 2.0 x 10^6 K. About
5000 images have been obtained up to the present. In this paper,
we describe also some aspects of the telescope and the detector
performance for application in the observations. Images and movies
of all the wavelengths allow a look at different phenomena present in
the Sun's corona, and in particular, magnetic field reconnection.

---------------------------------------------------------
Title: JOSO and the 1999 Solar Eclipse in Europe
Authors: Clette, F.
1997ASPC..118..402C Altcode: 1997fasp.conf..402C
An introduction to JOSO Working Group 7 is presented, outlining its
aims and activities. This European group was created one year ago
in order to prompt scientific collaboration around the August 11,
1999 total solar eclipse. All scientific teams involved in eclipse
observation programs are invited to join this new community.

---------------------------------------------------------
Title: SOHO EIT Carrington Maps from Synoptic Full-Disk Data
Authors: Thompson, B. J.; Newmark, J. S.; Gurman, J. B.;
Delaboudiniere, J. P.; Clette, F.; Gibson, S. E
1997ESASP.404..779T Altcode: 1997cswn.conf..779T
No abstract at ADS

---------------------------------------------------------
Title: Comparing the large-scale coronal electron density distribution
of the 1991 and 1994 solar eclipses.
Authors: Gabryl, J. -R.; Cugnon, P.; Clette, F.
1997ASIC..494...73G Altcode: 1997topr.conf...73G
The observational determination of the electron density and velocity
distributions in the solar corona is a basis to any physical
modelling. In this context, the author's program, started in 1973,
consists in deriving the large-scale electron density distribution
from photographic observations of the polarized white-light corona
during total solar eclipses. Since 1991, this program makes use of CCD
technologies. The authors present here results of their 2D descriptive
model of the electron density distribution.

---------------------------------------------------------
Title: Wave and Small-Scale Dynamics Study Using High-Cadence EIT
Image Sequences
Authors: Clette, F.; Berghmans, D.
1997ESASP.404..283C Altcode: 1997cswn.conf..283C
No abstract at ADS

---------------------------------------------------------
Title: JOSO working group 7. A focal point for collaboration around
the 1999 solar eclipse.
Authors: Clette, F.
1997ASIC..494..215C Altcode: 1997topr.conf..215C
A new working group dedicated to the preparation of the August 11,
1999 total solar eclipse was created recently as part of the JOSO
(Joint Organisation for Solar Observations). This European group
was created in order to prompt scientific collaboration around this
event. The aims and future actions of JOSO WG7 are outlined here. All
research groups who are planning to set up a scientific programme at
this occasion are invited to join this new community.

---------------------------------------------------------
Title: Reconstruction of the large-scale distribution of coronal
electrons from eclipse data.
Authors: Clette, F.
1997ASIC..494..103C Altcode: 1997topr.conf..103C
Mathematical models of the global electron density distribution
in the corona were first constructed from solar eclipse images at
the end of the last century. Since then, the complexity of these
density models has increased steadily, as additional free parameters
and new mathematical tools were incorporated. The ultimate goal of
this effort has always been to improve the representation of the
inhomogeneous coronal structure, while maintaining a restricted set
of parameters. This review puts the sucessive steps of this maturation
process in a general perspective. A recent model, developed at the Royal
Observatory of Belgium for the 1991 and 1994 eclipses, is described
to illustrate the modeling techniques and some current issues.

---------------------------------------------------------
Title: First Results from EIT
Authors: Clette, F.; Delaboudiniere, J. -P.; Artzner, G. E.; Brunaud,
J.; Gabriel, A. H.; Hochedez, J. -F.; Millier, F.; Song, X. Y.; Au, B.;
Dere, K. P.; Howard, R. A.; Kreplin, R.; Michels, D. J.; Moses, J. D.;
Defise, J. -M.; Jamar, C.; Rochus, P.; Chauvineau, J. -P.; Marioge,
J. -P.; Catura, R. C.; Lemen, J. R.; Shing, L.; Stern, R. A.; Gurman,
J. B.; Neupert, W. M.; Maucherat, A.; Cugnon, P.; van Dessel, E. L.
1997ASPC..118..268C Altcode: 1997fasp.conf..268C
The Extreme-UV Imaging telescope has already produced more than 15000
wide-field images of the corona and transition region, on the disk
and up to 1.5R_⊙ above the limb, with a pixel size of 2.6\arcsec. By
using four different emission lines, it provides the global temperature
distribution in the quiet corona, in the range 0.5 to 3*E(6) K. Its
excellent sensitivity and wide dynamic range allow unprecedented views
of low emission features, even inside coronal holes. Those so-called
“quiet” regions actually display a wide range of dynamical phenomena,
in particular at small spatial scales and at time scales going down
to only a few seconds, as revealed by all EIT time sequences of
full- or partial-field images. The initial results presented here
demonstrate the importance of this wide-field imaging experiment for
a good coordination between SOHO and ground-based solar telescopes,
as well as for science planning.

---------------------------------------------------------
Title: Observations of the South coronal hole from EIT and YOHKOH
Authors: Handy, B. N.; Catura, R.; Freeland, S.; Lemen, J.; Stern,
R.; Gurman, J. B.; Delaboudiniere, J. P.; Artzner, G.; Gabriel, A.;
Maucherat, A.; Defise, J. M.; Jamar, C.; Rochus, P.; Clette, F.;
Cugnon, P.; Howard, R.; Michels, D.; Moses, J. D.; Dere, K.; Cyr,
O. C. St.; Catura, R.; Freeland, S.; Lemen, J.; Stern, R.; Neupert,
W.; Einfalt, E.; Newmark, J.
1996AAS...188.0206H Altcode: 1996BAAS...28..821H
The Extreme ultraviolet Imaging Telescope (EIT) on board the
SOHO spacecraft is capable of studying solar transition region,
chomospheric and coronal plasmas over bandpasses optimized for He II
304 Angstroms (0.08 MK), Fe IX/X 171, 173 Angstroms (0.8 - 1.0 MK),
Fe XII 195 Angstroms (1.5 MK), and Fe XV 284 Angstroms (2.0 - 2.5
MK) with 2.5 arcsecond spatial resolution. This telescope in concert
with the Yohkoh/SXT instrument allows us to simultaneously observe
solar structures at temperatures ranging from less than 0.1MK in the
transition region to over 3MK in the solar corona. EIT has had several
opportunities to observe the South coronal hole with high spatial and
temporal resolution. We compare observations from EIT and SXT with
an eye towards correlating temporal variations over the range of
wavelengths, activity of polar crown filament systems and relating
large-scale morphology of the X-ray corona to the transition region
in He II.

---------------------------------------------------------
Title: There's No Such Thing as the Quiet Sun: EUV Movies from SOHO
Authors: Gurman, J. B.; Delaboudiniere, J. P.; Artzner, G.; Gabriel,
A.; Maucherat, A.; Defise, J. M.; Jamar, C.; Rochus, P.; Clette, F.;
Cugnon, P.; Howard, R.; Michels, D.; Moses, J. D.; Dere, K.; Cyr,
O. C. St.; Catura, R.; Freeland, S.; Lemen, J.; Stern, R.; Neupert,
W.; Einfalt, E.; Newmark, J.
1996AAS...188.3718G Altcode: 1996BAAS...28..880G
We present unique time series of high-resolution solar images from the
normal-incidence Extreme ultraviolet Imaging Telescope (EIT) on board
the SOHO spacecraft. With a pixel scale of 2.6 arc sec and a detector
dynamic range of &gt; 10(4) , the EIT can be used to study the dynamics
of chromospheric and coronal features in multilayer bandpasses optimized
for He II 304 Angstroms (0.08 MK), Fe IX/X 171, 173 Angstroms (0.8 -
1.0 MK), Fe XII 195 Angstroms (1.5 MK), and Fe XV 284 Angstroms (2.0 -
2.5 MK). Among the most striking features of the digital movies we will
display are: the dynamic nature of small-scale loop features in the
polar coronal holes, the constant activity of the polar crown filament
systems, the locations of the bases of polar plumes, the presence
of dark (scattering) filament material in the coronal emission line
images, and the evolution of a unique, linear, dark feature in a young
active region. The latter feature is suggestive of the “coronal void”
observed in the electron scattering corona by Macqueen et al./ (1983).

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Title: Soleil noir dans les Andes: l'éclipse totale de Soleil du
3 novembre 1994.
Authors: Clette, F.; Ducuroir, M.
1996C&T...112...57C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Quelques réflexions sur les familles d'éclipses.
Authors: Clette, F.
1996C&T...112...54C Altcode:
No abstract at ADS

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Title: Observations of the south coronal hole from EIT and Yohkoh.
Authors: Handy, B. N.; Catura, R.; Freeland, S.; Lemen, J.; Stern,
R.; Gurman, J. B.; Delaboudinière, J. P.; Artzner, G.; Gabriel,
A.; Maucherat, A.; Defise, J. M.; Jamar, C.; Rochus, P.; Clette, F.;
Cugnon, P.; Howard, R.; Michels, D.; Moses, J. D.; Dere, K.; St. Cyr,
O. C.; Neupert, W.; Einfalt, E.; Newmark, J.
1996BAAS...28Q.821H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: EIT Images of the EUV Solar Atmosphere
Authors: Portier-Fozzani, F.; Moses, J. D.; Delaboudiniere, J. P.;
Gurman, J. B.; Clette, F.; Maucherat, A.
1996ASPC..111..402P Altcode: 1997ASPC..111..402P
The Extreme-ultraviolet Imaging Telescope (EIT) was one of several
instruments launched on board SOHO on 1995 Dec 2. It has already
produced thousands of wide-field images of the low corona at 4
wavelengths (171, 195, 284 and 304 Å). These wavelengths correspond
to different emission lines, formed over a wide range of plasma
temperatures. The first EIT images and movies reveal how this sensitive
instrument will provide unprecedented information about the dynamics
of small scale phenomena in the quiet solar corona and inside coronal
holes. Results of a local deconvolution method, used to correct a grid
pattern present in raw EIT images, are also presented.

---------------------------------------------------------
Title: EIT: Extreme-Ultraviolet Imaging Telescope for the SOHO Mission
Authors: Delaboudinière, J. -P.; Artzner, G. E.; Brunaud, J.; Gabriel,
A. H.; Hochedez, J. F.; Millier, F.; Song, X. Y.; Au, B.; Dere, K. P.;
Howard, R. A.; Kreplin, R.; Michels, D. J.; Moses, J. D.; Defise,
J. M.; Jamar, C.; Rochus, P.; Chauvineau, J. P.; Marioge, J. P.;
Catura, R. C.; Lemen, J. R.; Shing, L.; Stern, R. A.; Gurman, J. B.;
Neupert, W. M.; Maucherat, A.; Clette, F.; Cugnon, P.; Van Dessel,
E. L.
1995SoPh..162..291D Altcode:
The Extreme-ultraviolet Imaging Telescope (EIT) will provide wide-field
images of the corona and transition region on the solar disc and up to
1.5 R⊙ above the solar limb. Its normal incidence multilayer-coated
optics will select spectral emission lines from Fe IX (171 å), Fe
XII (195 å), Fe XV (284 å), and He II (304 å) to provide sensitive
temperature diagnostics in the range from 6 × 104 K to 3
× 106 K. The telescope has a 45 x 45 arcmin field of view
and 2.6 arcsec pixels which will provide approximately 5-arcsec spatial
resolution. The EIT will probe the coronal plasma on a global scale,
as well as the underlying cooler and turbulent atmosphere, providing
the basis for comparative analyses with observations from both the
ground and other SOHO instruments. This paper presents details of the
EIT instrumentation, its performance and operating modes.

---------------------------------------------------------
Title: Calibration of the EIT instrument for the SOHO mission
Authors: Defise, Jean-Marc; Song, Xueyan Y.; Delaboudiniere,
Jean-Pierre; Artzner, Guy E.; Carabetian, Charles; Hochedez,
Jean-Francois E.; Brunaud, Jacqueline; Moses, John D.; Catura,
Richard C.; Clette, Frederic; Maucherat, Andre J.
1995SPIE.2517...29D Altcode:
Optical characteristics in the wavelength range 15 - 75 nm of the
EUV imaging telescope to be launched soon on the SOHO mission are
discussed. Bandpasses and photometric sensitivity of the multilayered
optics telescope have been measured by a dedicated synchrotron light
source at Orsay, France.

---------------------------------------------------------
Title: Summary of the Belgian Experiments at Putre
Authors: Clette, F.
1995pist.conf..123C Altcode:
No abstract at ADS

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Title: EIT: The Extreme Ultraviolet Imaging Telescope. Synoptic
Observations of Small and Large-Scale Coronal Structures
Authors: Clette, F.; Delaboudinière, J. P.; Dere, K. P.; Cugnon,
P.; EIT Science Team
1995LNP...444..251C Altcode: 1995cmer.conf..251C
The EIT will provide wide-field images of the corona and transition
region, on the solar disc and up to 1 R⊙ above the
limb. Its normal incidence multilayer-coated optics will select the
spectral emission lines of four ions (Fe IX, 171 Å; Fe XII, 195
Å; Fe XV, 284 Å; Hell, 304 Å), providing a sensitive temperature
diagnostic in the range 6.104 to 3.106K. This
SOHO instrument will thus probe the coronal plasma on a global scale,
as well as the underlying cooler and turbulent atmosphere. The EIT's
characteristics and performances are presented, and prospects for
coordinated observations with ground-based radio observatories are
outlined.

---------------------------------------------------------
Title: Modelling the Electron Density Distribution in the July 1991
Solar Corona
Authors: Clette, F.; Cugnon, P.; Gabryl, J. -R.
1994scs..conf..535C Altcode: 1994IAUCo.144..535C
Using intensity and polarization maps computed from white-light
observations of the July 11, 1991 solar eclipse, the authors present
axisymmetrical models of the large-scale electron density distribution
in the corona. They consider two plausible configurations, aligned
on the rotation axis or the mean bipolar magnetic field axis. Their
respective abilities to reproduce a strongly non-spherical global
magnetic structure are then compared.

---------------------------------------------------------
Title: Properties of the atmospheric noise in full-disk photometric
observations of solar oscillations - Implications for asteroseismology
from the ground
Authors: Clette, F.
1993A&A...267..577C Altcode:
By using solar irradiance measurements made at Jungfraujoch and
Pic-du-Midi, we were able to detect the strongest solar global p-modes
in noisy power spectra, which can be compared directly with those
obtained from asteroseismological data. In order to facilitate
the interpretation of such periodograms, a practical method is
introduced that allows the significance of features to be estimated
simultaneously at all frequencies in a spectrum with nonuniform noise
distribution. When working with multisite networks, a cross-spectral
analysis, based on simultaneous data obtained from two locations,
is proposed as a means for distinguishing solar or stellar signals
from the contribution of local perturbations. In addition, changing
properties of the observed noise induced by the variable transparency
contribution are analyzed, and a relationship is derived between the
horizontal coherence scale of atmospheric fluctuations and the time
scale of the local instabilities. By combining these results with
other photometric data, we provide estimates of the limits for future
ground-based observations of stellar intensity oscillations.

---------------------------------------------------------
Title: Plans for a new radioheliograph in Belgium
Authors: Cugnon, Pierre; Gonze, Roger; Clette, Frederic
1992SoPh..142..391C Altcode:
The existence of "spikes" with very short time scales (1 to 10 ms)
in the decimetric radio spectrum emphasizes the necessity of building
radio instruments with very high time resolution. Therefore, we are
planning to build a multi-frequency decimetric radioheliograph at
the radioastronomical station of the Observatoire Royal de Belgique
(Humain, Belgium). The existing array primarily devoted to observe at
408 MHz will constitute the starting structure of the project.

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Title: The July 11, 1991 solar corona observed in polarized white
light. Preliminary results.
Authors: Clette, Frederic; Gabryl, J. -R.
1992ESASP.348..351C Altcode: 1992cscl.work..351C
During the July 91 total solar eclipse, the polarized K-corona
was observed from two sites in Baja California (Mexico) using two
techniques: photography with a 6 position polarizing filter (30°
steps) and a CCD camera using 12 positions (15° steps). A total of
36 CCD images were combined to produce intensity and polarization
maps of the corona from 1.1 to 3.0 solar radii with 10″spatial
resolution. Several characteristics of the corona can already be deduced
from those data, which are now processed to compute the global electron
density distribution.

---------------------------------------------------------
Title: Eclipse totale de Soleil du 11 juillet 1991: les observations
photographiques et CCD de la polarisation coronale
Authors: Clette, Frédéric
1992C&T...108...85C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: New thresholds for ground-based photometry of solar intensity
oscillations.
Authors: Clette, F.
1988ESASP.286..189C Altcode: 1988ssls.rept..189C
The analysis of new whole-disc intensity observations realized
from Pic-du-Midi and Jungfraujoch reveals the presence of the
solar p-modes. With a 10 hours (single day) integration time and
a 10 nm optical bandpass, the resolved groups of modes show a peak
amplitude between 10-5 (red channel) and 3×10-5
(blue channel), while the observed background noise power is of the
order of 1×10-6/Hz at 3 mHz. The authors also apply a
cross-spectrum analysis to their solar data. The less than optimum data
available prevent nevertheless any firm conclusion here. Considering
the possibility to transpose this technique to stars, they conclude
that intensity oscillations of solar-like stars are within reach of
ground-based instruments, assuming atmospheric transparency fluctuations
as low as those encountered in the present work.

---------------------------------------------------------
Title: Observation de l'éclipse totale de Lune du 17 octobre 1986
Authors: Clette, F.
1986C&T...102..160C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Bibliographie: Micro-computer control of Telescopes --
M. Trueblood, R. Genet
Authors: Clette, F.
1986C&T...102T..63C Altcode: 1986C&T...102T..63.
No abstract at ADS

---------------------------------------------------------
Title: Initiation à la photographic astronomique
Authors: Clette, F.
1986C&T...102....3C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations of the solar corona in polarized white light
during the total solar eclipse of February 16, 1980: Preliminary
results
Authors: Clette, F.; Cugnon, P.; Koeckelenbergh, A.
1985SoPh...98..163C Altcode:
Photographic observations of the corona were made by a Belgian
expedition to Kenya during the eclipse of 1980, February 16, using
a polaroïd filter oriented in three directions 60 ° apart. The
preliminary results of the reduced data are presented here; these
results consist in the analysis of the three following parameters:
total intensity, degree of polarization, direction of the electric
vector. The local variation of these parameters reveals, among other
features, a deep coronal hole at the south pole and peculiar streamer
(P.A. 280 °) associated to a transient, (the so-called `tennis racket')
also observed by other teams, and a density enhancement at P.A. 200 °,
possibly associated with a transient observed with the K-coronameter
of the High Altitude Observatory 12 hr before the eclipse.

---------------------------------------------------------
Title: Croquis planétaires
Authors: Clette, F.
1984C&T...100...32C Altcode:
No abstract at ADS