Author name code: clette ADS astronomy entries on 2022-09-14 author:"Clette, Frederic" ------------------------------------------------------------------------ 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 Bibcode: 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. Title: Reconstruction of the Sunspot Number Source Database and the 1947 Zurich Discontinuity Authors: Clette, Frédéric; Lefèvre, Laure; Bechet, Sabrina; Ramelli, Renzo; Cagnotti, Marco Bibcode: 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. Title: Hemispheric sunspot numbers 1874-2020 Authors: Veronig, Astrid M.; Jain, Shantanu; Podladchikova, Tatiana; Pötzi, Werner; Clette, Frederic Bibcode: 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 cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/652/A56 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. Bibcode: 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). Title: VizieR Online Data Catalog: Hemispheric Sunspot Numbers 1874-2020 (Veronig+, 2021) Authors: Veronig, A. M.; Jain, S.; Podladchikova, T.; Poetzi, W.; Clette, F. Bibcode: 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&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). Title: Nonparametric monitoring of sunspot number observations: a case study Authors: Mathieu, Sophie; Lefèvre, Laure; von Sachs, Rainer; Delouille, Véronique; Ritter, Christian; Clette, Frédéric Bibcode: 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. Title: Is the F10.7cm - Sunspot Number relation linear and stable? Authors: Clette, Frédéric Bibcode: 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. Title: Sunspot and Group Number: Recent advances from historical data Authors: Clette, Frédéric; Vaquero, José M.; Cruz Gallego, María; Lefèvre, Laure Bibcode: 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. Title: Sunspot observations by Hisako Koyama: 1945-1996 Authors: Hayakawa, Hisashi; Clette, Frédéric; Horaguchi, Toshihiro; Iju, Tomoya; Knipp, Delores J.; Liu, Huixin; Nakajima, Takashi Bibcode: 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. 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 Bibcode: 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. 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. Bibcode: 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. Title: The Sunspot Number recalibration Authors: Lefevre, Laure; Clette, Frederic; Mathieu, Sophie; Delouille, Veronique; von Sachs, Rainer Bibcode: 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. Title: The Recalibrated Sunspot Number: What It Is and How Will It be Updated? Authors: Clette, Frederic; Pesnell, William Dean; Lefevre, Laure Bibcode: 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. Title: The new Sunspot Number: continuing upgrades and possible impacts Authors: Clette, Frédéric; Lefèvre, Laure Bibcode: 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. Title: The Recalibrated Sunspot Number: Impact on Solar Cycle Predictions Authors: Clette, F.; Lefevre, L. Bibcode: 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. 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. Bibcode: 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. Title: The New Sunspot Number: Assembling All Corrections Authors: Clette, Frédéric; Lefèvre, Laure Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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. Title: The Revised Brussels-Locarno Sunspot Number (1981 - 2015) Authors: Clette, Frédéric; Lefèvre, Laure; Cagnotti, Marco; Cortesi, Sergio; Bulling, Andreas Bibcode: 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 Bibcode: 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 Bibcode: 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; thttp://www.sidc.be/silso/datafiles). 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 & 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 > 20 (compiled into a database at <emph TYPE="46">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. Bibcode: 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<10deg) and high (B>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. Bibcode: 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 > 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1998ASPC..155..389C Altcode: 1998sasp.conf..389C No abstract at ADS Title: Impulsive Coronal Dynamics as Revealed by EIT Authors: Clette, F.; Berghmans, D. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 > 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). Title: Soleil noir dans les Andes: l'éclipse totale de Soleil du 3 novembre 1994. Authors: Clette, F.; Ducuroir, M. Bibcode: 1996C&T...112...57C Altcode: No abstract at ADS Title: Quelques réflexions sur les familles d'éclipses. Authors: Clette, F. Bibcode: 1996C&T...112...54C Altcode: No abstract at ADS 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1995pist.conf..123C Altcode: No abstract at ADS 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Title: The July 11, 1991 solar corona observed in polarized white light. Preliminary results. Authors: Clette, Frederic; Gabryl, J. -R. Bibcode: 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 Bibcode: 1992C&T...108...85C Altcode: No abstract at ADS Title: New thresholds for ground-based photometry of solar intensity oscillations. Authors: Clette, F. Bibcode: 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. Bibcode: 1986C&T...102..160C Altcode: No abstract at ADS Title: Bibliographie: Micro-computer control of Telescopes -- M. Trueblood, R. Genet Authors: Clette, F. Bibcode: 1986C&T...102T..63C Altcode: 1986C&T...102T..63. No abstract at ADS Title: Initiation à la photographic astronomique Authors: Clette, F. Bibcode: 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. Bibcode: 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. Bibcode: 1984C&T...100...32C Altcode: No abstract at ADS