Author name code: robbrecht ADS astronomy entries on 2022-09-14 author:"Robbrecht, Eva" ------------------------------------------------------------------------ Title: Verification of space weather forecasting at the Regional Warning Center in Belgium Authors: Devos, Andy; Verbeeck, Cis; Robbrecht, Eva Bibcode: 2014JSWSC...4A..29D Altcode: The Solar Influences Data analysis Center (SIDC) in Brussels at the Royal Observatory of Belgium (ROB) has been providing daily space weather forecasts for more than a decade. A verification analysis was applied to evaluate the performance of the SIDC forecasts of fundamental space weather parameters such as the F10.7 radio flux, solar flare activity, and local geomagnetic index. Strengths and weaknesses are determined compared to common numerical models. Descriptive model statistics, common verification measures, error analysis and conditional plots related to forecasts and observations are presented. The verification analysis methods have been designed such that future improvements and additions can easily be included, for example with new forecasting models. The SIDC forecast (together with the persistence model) achieves the best performance for forecasting F10.7 on day 1, but has potential for improvement for a larger lead time mainly by applying estimates from the persistence and corrected recurrence models. The persistence model is superior for the forecast of flares, though corrected recurrence models are slightly better in foreseeing M- and X-class flares and the SIDC forecast estimates B- and C-class flares very well. The SIDC forecast scores better than all models in forecasting the local K-index. It best reproduces observations in the range of K = 2-4, but underestimates larger K values. The SIDC forecast provides a distribution that best matches the observations of the K-index. The analysis presented here demonstrates the influence of solar activity on the confidence level of the forecasts, as well as the hinted influence of the forecaster on duty due to the subjective nature of forecasting. The output aids to identify the strong and weak points of the SIDC forecast as well as those of the models considered. Though the presented analysis needs further extension, it already illustrates the opportunity to regularly reevaluate space weather forecasts and to stimulate ideas for improvement and increase the reliability of space weather forecasting. Title: Determining the North-South Displacement of the Heliospheric Current Sheet from Coronal Streamer Observations Authors: Robbrecht, E.; Wang, Y. -M. Bibcode: 2012ApJ...755..135R Altcode: Inferences based on interplanetary field measurements have suggested a statistical tendency for the heliospheric current sheet (HCS) to be displaced southward of the heliographic equator during the past four solar cycles. Here, we use synoptic maps of white-light streamer structures to determine more directly the longitudinally averaged latitude of the HCS, after separating out the contribution of streamers without magnetic polarity reversals ("pseudostreamers"). We find a strong tendency for the HCS to be shifted southward by a few degrees during 2007-2011, but no significant shift during the 1996-1997 sunspot minimum. Fluctuations in the magnitude and direction of the north-south shifts often occur on timescales as short as one or two Carrington rotations, as a result of changes in the streamer structures due to active region emergence. The largest shifts occurred during 2010-2011 and were on the order of -6°. Such southward displacements are consistent with the overwhelming dominance of northern-hemisphere sunspot activity during the rising phase of the current solar cycle 24, resulting in a strong axisymmetric quadrupole component whose sign at the equator matched that of the north polar field; the symmetry-breaking effect of the quadrupole was further enhanced by the weakness of the polar fields. Title: Forecasting Geomagnetic Storms and Solar Energetic Particle Events: the COMESEP Project Authors: Crosby, N.; Veronig, A.; Robbrecht, E.; Vrsnak, B.; Vennerstrøm, S.; Malandraki, O.; Dalla, S.; Srivastava, N.; Hesse, M.; Odstrcil, D. Bibcode: 2012EGUGA..1412544C Altcode: COMESEP (COronal Mass Ejections and Solar Energetic Particles), funded by the European Union Framework 7 programme, is a three-year collaborative project that has been running for one year. Tools for forecasting geomagnetic storms and solar energetic particle (SEP) radiation storms are being developed under the project. By analysis of historical data, complemented by the extensive data coverage of solar cycle 23, the key ingredients that lead to magnetic storms and SEP events and the factors that are responsible for false alarms are being identified. To enhance our understanding of the 3D kinematics and interplanetary propagation of coronal mass ejections (CMEs), the structure, propagation and evolution of CMEs are being investigated. In parallel, the sources and propagation of SEPs are being examined and modeled. Based on the insights gained, and making use of algorithms for the automated detection of CMEs, forecasting tools for geomagnetic and SEP radiation storms are being developed and optimised. Validation and implementation of the produced tools into an operational Space Weather Alert system will be performed. Geomagnetic and SEP radiation storm alerts will be based on the COMESEP definition of risk. COMESEP is a unique cross-collaboration effort and bridges the gap between the SEP and CME scientific communities. For more information about the project, see the COMESEP website http://www.comesep.eu/ . This work has received funding from the European Commission FP7 Project COMESEP (263252). Title: On the Nature of the Solar Wind from Coronal Pseudostreamers Authors: Wang, Y. -M.; Grappin, R.; Robbrecht, E.; Sheeley, N. R., Jr. Bibcode: 2012ApJ...749..182W Altcode: Coronal pseudostreamers, which separate like-polarity coronal holes, do not have current sheet extensions, unlike the familiar helmet streamers that separate opposite-polarity holes. Both types of streamers taper into narrow plasma sheets that are maintained by continual interchange reconnection with the adjacent open magnetic field lines. White-light observations show that pseudostreamers do not emit plasma blobs; this important difference from helmet streamers is due to the convergence of like-polarity field lines above the X-point, which prevents the underlying loops from expanding outward and pinching off. The main component of the pseudostreamer wind has the form of steady outflow along the open field lines rooted just inside the boundaries of the adjacent coronal holes. These flux tubes are characterized by very rapid expansion below the X-point, followed by reconvergence at greater heights. Analysis of an idealized pseudostreamer configuration shows that, as the separation between the underlying holes increases, the X-point rises and the expansion factor f ss at the source surface increases. In situ observations of pseudostreamer crossings indicate wind speeds v ranging from ~350 to ~550 km s-1, with O7 +/O6 + ratios that are enhanced compared with those in high-speed streams but substantially lower than in the slow solar wind. Hydrodynamic energy-balance models show that the empirical v-f ss relation overestimates the wind speeds from nonmonotonically expanding flux tubes, particularly when the X-point is located at low heights and f ss is small. We conclude that pseudostreamers produce a "hybrid" type of outflow that is intermediate between classical slow and fast solar wind. Title: Asymmetric Sunspot Activity and the Southward Displacement of the Heliospheric Current Sheet Authors: Wang, Y. -M.; Robbrecht, E. Bibcode: 2011ApJ...736..136W Altcode: Observations of the interplanetary magnetic field (IMF) have suggested a statistical tendency for the heliospheric current sheet (HCS) to be shifted a few degrees southward of the heliographic equator during the period 1965-2010, particularly in the years near sunspot minimum. Using potential-field source-surface extrapolations and photospheric flux-transport simulations, we demonstrate that this southward displacement follows from Joy's law and the observed hemispheric asymmetry in the sunspot numbers, with activity being stronger in the southern (northern) hemisphere during the declining (rising) phase of cycles 20-23. The hemispheric asymmetry gives rise to an axisymmetric quadrupole field, whose equatorial zone has the sign of the leading-polarity flux in the dominant hemisphere; during the last four cycles, the polarity of the IMF around the equator thus tended to match that of the north polar field both before and after polar field reversal. However, large fluctuations are introduced by the nonaxisymmetric field components, which depend on the longitudinal distribution of sunspot activity in either hemisphere. Consistent with this model, the HCS showed an average northward displacement during cycle 19, when the "usual" alternation was reversed and the northern hemisphere became far more active than the southern hemisphere during the declining phase of the cycle. We propose a new method for determining the north-south displacement of the HCS from coronal streamer observations. Title: The Evolution of Dark Canopies Around Active Regions Authors: Wang, Y. -M.; Robbrecht, E.; Muglach, K. Bibcode: 2011ApJ...733...20W Altcode: 2011arXiv1103.4373W As observed in spectral lines originating from the chromosphere, transition region, and low corona, active regions are surrounded by an extensive "circumfacular" area which is darker than the quiet Sun. We examine the properties of these dark moat- or canopy-like areas using Fe IX 17.1 nm images and line-of-sight magnetograms from the Solar Dynamics Observatory. The 17.1 nm canopies consist of fibrils (horizontal fields containing extreme-ultraviolet-absorbing chromospheric material) clumped into featherlike structures. The dark fibrils initially form a quasiradial or vortical pattern as the low-lying field lines fanning out from the emerging active region connect to surrounding network and intranetwork elements of opposite polarity. The area occupied by the 17.1 nm fibrils expands as supergranular convection causes the active-region flux to spread into the background medium; the outer boundary of the dark canopy stabilizes where the diffusing flux encounters a unipolar region of opposite sign. The dark fibrils tend to accumulate in regions of weak longitudinal field and to become rooted in mixed-polarity flux. To explain the latter observation, we note that the low-lying fibrils are more likely to interact with small loops associated with weak, opposite-polarity flux elements in close proximity, than with high loops anchored inside strong unipolar network flux. As a result, the 17.1 nm fibrils gradually become concentrated around the large-scale polarity inversion lines (PILs), where most of the mixed-polarity flux is located. Systematic flux cancellation, assisted by rotational shearing, removes the field component transverse to the PIL and causes the fibrils to coalesce into long PIL-aligned filaments. Title: Validation of CME Detection Software (CACTus) by Means of Simulated Data, and Analysis of Projection Effects on CME Velocity Measurements Authors: Bonte, K.; Jacobs, C.; Robbrecht, E.; De Groof, A.; Berghmans, D.; Poedts, S. Bibcode: 2011SoPh..270..253B Altcode: 2011SoPh..tmp...52B; 2011SoPh..tmp...72B In the context of space weather forecasting, an automated detection of coronal mass ejections (CMEs) becomes more and more important for efficiently handling a large data flow which is expected from recently-launched and future solar missions. In this paper we validate the detection software package "CACTus" by applying the program to synthetic data from our 3D time-dependent CME simulations instead of observational data. The main strength of this study is that we know in advance what should be detected. We describe the sensitivities and strengths of automated detection, more specific for the CACTus program, resulting in a better understanding of CME detection on one hand and the calibration of the CACTus software on the other hand, suggesting possible improvements of the package. In addition, the simulation is an ideal tool to investigate projection effects on CME velocity measurements. Title: The Evolution of Dark Canopies Around Active Regions Authors: Muglach, Karin; Wang, Y. M.; Robbrecht, E. Bibcode: 2011SPD....42.1718M Altcode: 2011BAAS..43S.1718M As observed in spectral lines originating from the chromosphere, transition region, and low corona, active regions are surrounded by an extensive 'circumfacular' area which is darker than the quiet Sun. We examine the properties of these dark moat- or canopy-like areas using Fe IX 17.1 nm images and line-of-sight magnetograms from the Solar Dynamics Observatory. The 17.1 nm canopies consist of fibrils (horizontal fields containing EUV-absorbing chromospheric material) clumped into featherlike structures. The dark fibrils initially form a quasiradial or vortical pattern as the low-lying field lines fanning out from the emerging active region connect to surrounding network and intranetwork elements of the opposite polarity. The area occupied by the 17.1 nm fibrils expands as supergranular convection causes the active region flux to spread into the background medium; the outer boundary of the dark canopy stabilizes where the diffusing flux encounters a unipolar region of the opposite sign. The dark fibrils tend to accumulate in regions of weak longitudinal field and to become rooted in mixed-polarity flux. To explain the latter observation, we note that the low-lying fibrils are more likely to interact with small loops associated with weak, opposite-polarity flux elements in close proximity, than with high loops anchored inside strong unipolar network flux. As a result, the 17.1 nm fibrils gradually become concentrated around the large-scale polarity inversion lines (PILs), where most of the mixed-polarity flux is located. Systematic flux cancellation, assisted by rotational shearing, removes the field component transverse to the PIL and causes the fibrils to coalesce into long PIL-aligned filaments. Title: The Temperature-dependent Nature of Coronal Dimmings Authors: Robbrecht, Eva; Wang, Yi-Ming Bibcode: 2010ApJ...720L..88R Altcode: 2010arXiv1007.5191R The opening-up of the magnetic field during solar eruptive events is often accompanied by a dimming of the local coronal emission. From observations of filament eruptions recorded with the Extreme-Ultraviolet Imager on STEREO during 2008-2009, it is evident that these dimmings are much more pronounced in 19.5 nm than in the lower-temperature line 17.1 nm, as viewed either on the disk or above the limb. We conclude that most of the cooler coronal plasma is not ejected but remains gravitationally bound when the loops open up. This result is consistent with Doppler measurements by Imada and coworkers, who found that the upflow speeds in a transient coronal hole increased dramatically above a temperature of 1 MK it is also consistent with the quasistatic behavior of polar plumes, as compared with the hotter interplume regions that are the main source of the fast solar wind. When the open flux reconnects and closes down again, the trapped plasma is initially heated to such high temperatures that it is no longer visible at Fe IX 17.1 nm. Correspondingly, 17.1 nm images show a dark ribbon or "heat wave" propagating away from the polarity inversion line and coinciding with the brightened Fe XV 28.4 nm and Fe XII 19.5 nm post-eruptive loops and their footpoint areas. Such dark ribbons provide a clear example of dimmings that are not caused by a density depletion. The propagation of the "heat wave" is driven by the closing-down, not the opening-up, of the flux and can be observed both off-limb and on-disk. Title: Sun to 1 AU propagation and evolution of a slow streamer-blowout coronal mass ejection Authors: Lynch, B. J.; Li, Y.; Thernisien, A. F. R.; Robbrecht, E.; Fisher, G. H.; Luhmann, J. G.; Vourlidas, A. Bibcode: 2010JGRA..115.7106L Altcode: 2010JGRA..11507106L We present a comprehensive analysis of the evolution of the classic, slow streamer-blowout CME of 1 June 2008 observed by the STEREO twin spacecraft to infer relevant properties of the pre-eruption source region which includes a substantial portion of the coronal helmet streamer belt. The CME was directed ∼40° East of the Sun-Earth line and the Heliospheric Imager observations are consistent with the CME propagating essentially radially to 1 AU. The elongation-time J-map constructed from the STEREO-A HI images tracks the arrival of two density peaks that bound the magnetic flux rope ICME seen at STEREO-B on 6 June 2008. From the STEREO-A elongation-time plots we measure the ICME flux rope radial size Rc(t) and find it well approximated by the constant expansion value Vexp = 24.5 km/s obtained from the STEREO-B declining velocity profile within the magnetic cloud. The flux rope spatial orientation, determined by forward modeling fits to the STEREO COR2 and HI1 data, approaches the observed 1 AU flux rope orientation and suggests large-scale rotation during propagation, as predicted by recent numerical simulations. We compare the ICME flux content to the PFSS model coronal field for Carrington Rotation 2070 and find sufficient streamer belt flux to account for the observed ICME poloidal/twist flux if reconnection during CME initiation process is responsible for the conversion of overlying field into the flux rope twist component in the standard fashion. However, the PFSS model field cannot account for the ICME toroidal/axial flux component. We estimate the field strength of the pre-eruption sheared/axial component in the low corona and the timescales required to accumulate this energized pre-eruption configuration via differential rotation and flux cancelation by supergranular diffusion at the polarity inversion line. We show that both mechanisms are capable of generating the desired shear component over time periods of roughly 1-2 months. We discuss the implications for slow streamer-blowout CMEs arising as a natural consequence of the corona's re-adjustment to the long term evolutionary driving of the photospheric fields. Title: On the "Extended" Solar Cycle in Coronal Emission Authors: Robbrecht, E.; Wang, Y. -M.; Sheeley, N. R., Jr.; Rich, N. B. Bibcode: 2010ApJ...716..693R Altcode: Butterfly diagrams (latitude-time plots) of coronal emission show a zone of enhanced brightness that appears near the poles just after solar maximum and migrates toward lower latitudes; a bifurcation seems to occur at sunspot minimum, with one branch continuing to migrate equatorward with the sunspots of the new cycle and the other branch heading back to the poles. The resulting patterns have been likened to those seen in torsional oscillations and have been taken as evidence for an extended solar cycle lasting over ~17 yr. In order to clarify the nature of the overlapping bands of coronal emission, we construct butterfly diagrams from green-line simulations covering the period 1967-2009 and from 19.5 nm and 30.4 nm observations taken with the Extreme-Ultraviolet Imaging Telescope during 1996-2009. As anticipated from earlier studies, we find that the high-latitude enhancements mark the footpoint areas of closed loops with one end rooted outside the evolving boundaries of the polar coronal holes. The strong underlying fields were built up over the declining phase of the cycle through the poleward transport of active-region flux by the surface meridional flow. Rather than being a precursor of the new-cycle sunspot activity zone, the high-latitude emission forms a physically distinct, U-shaped band that curves upward again as active-region fields emerge at midlatitudes and reconnect with the receding polar-hole boundaries. We conclude that the so-called extended cycle in coronal emission is a manifestation not of early new-cycle activity, but of the poleward concentration of old-cycle trailing-polarity flux by meridional flow. Title: Formation and Evolution of Coronal Holes Following the Emergence of Active Regions Authors: Wang, Y. -M.; Robbrecht, E.; Rouillard, A. P.; Sheeley, N. R., Jr.; Thernisien, A. F. R. Bibcode: 2010ApJ...715...39W Altcode: The low level of solar activity over the past four years has provided unusually favorable conditions for tracking the formation and evolution of individual coronal holes and their wind streams. Employing extreme-ultraviolet images recorded with the Solar Terrestrial Relations Observatory during 2007-2009, we analyze three cases in which small coronal holes first appear at the edges of newly emerged active regions and then expand via flux transport processes, eventually becoming attached to the polar holes. The holes form gradually over timescales comparable to or greater than that for the active regions to emerge, without any obvious association with coronal mass ejections. The evolving hole areas coincide approximately with the footpoints of open field lines derived from potential-field source-surface extrapolations of the photospheric field. One of these coronal-hole systems, centered at the equator and maintained by a succession of old-cycle active regions emerging in the same longitude range, persists in one form or another for up to two years. The other two holes, located at midlatitudes and originating from new-cycle active regions, become strongly sheared and decay away after a few rotations. The hole boundaries and the small active-region holes, both of which are sources of slow wind, are observed to undergo continual short-term (lsim1 day) fluctuations on spatial scales comparable to that of the supergranulation. From in situ measurements, we identify a number of plasma sheets associated with pseudostreamers separating holes of the same polarity. Title: Heatwaves on the Sun Authors: Robbrecht, Eva; Wang, Yi-Ming; Vourlidas, Angelos; Patsourakos, Spiros Bibcode: 2010cosp...38.1791R Altcode: 2010cosp.meet.1791R Dimmings have been observed for several years now, but their interpretation is still problematic. A dimming is an observational effect of diminished brightness with respect to pre-event images, which is usually interpreted as a density depletion. But not all dimmings are what they appear to be. In this paper we report on an unusual "dimming wave" which is not a density depletion but rather a heat wave. Thanks to the stereoscopic view from the SECCHI/EUVI imagers we are able not only to uncover the nature of the wave, but also to understand its three dimensional evolution and its relationship to a quiet sun CME. Title: Sun to 1 AU Propagation of a Slow Streamer-Blowout Coronal Mass Ejection Authors: Lynch, B. J.; Li, Y.; Thernisien, A. F.; Robbrecht, E.; Luhmann, J. G.; Vourlidas, A. Bibcode: 2009AGUFMSH41A1635L Altcode: We present the time history and evolution of the 3-dimensional size, shape, and orientation of the slow, classic streamer blowout CME of 2008 Jun 01 by combining STEREO-A remote imaging of its interplanetary propagation with in situ STEREO-B plasma and field measurements at 1~AU. The STEREO-A HI coverage allows unambigious identification of the CME white light front-cavity structure and the resulting ICME flux rope boundaries in running difference images. The elongation-time tracks predict the arrival of the ICME at STEREO-B on 2008 June 06 remarkably well. Starting from the simplest in situ flux rope model for the coherent magnetic cloud field structure, we utilize the unprecedented coverage of the coronal and heliospheric imaging observations to obtain important corrections for the ICME flux rope geometry. MHD modeling results obtained from the NASA Community Coordinated Modeling Center for the ambient heliopsheric solar wind stream structure and a simple CME-like density-pulse propagation are used to verify the overall propagation direction and characterize some of the observed evolutionary properties. The ICME radial expansion, i.e. the time evolution of the flux rope radius Rc(t) from the STEREO-A elongation-time plots, is well approximated by the standard treatment of constant radial expansion Vexp = 24.5 km/s measured from the in situ bulk velocity profile. The 3-dimensional spatial orientation of the ICME flux rope determined by forward modeling in the inner heliosphere shows excellent agreement with the observed 1~AU flux rope orientation and evidence for large scale rotation of the ICME flux rope during its propagation, as predicted by recent numerical simulations. In addition, measurements of the CME's latitudinal angular width allows us to improve the estimate the actual flux rope cross-sectional area and measurements of the CME's longitudinal extent allows us to estimate a more realistic CME ``loop length". These geometric quantities are used to improve the estimates of the ICME in situ toroidal and poloidal magnetic fluxes, ΦT and ΦP. The in situ flux values are then compared to the magnetic fluxes inferred from this event's source region, which includes a substantial portion of the large scale coronal helmet streamer belt. We conlude by discussing our results in the context of both CME initiation and the physical mechanism(s) that energize the pre-eruption configuration. Support for this work was provided by NASA HGI NNX08AJ04G. Title: On the Weakening of the Polar Magnetic Fields during Solar Cycle 23 Authors: Wang, Y. -M.; Robbrecht, E.; Sheeley, N. R., Jr. Bibcode: 2009ApJ...707.1372W Altcode: The Sun's polar fields are currently ~40% weaker than they were during the previous three sunspot minima. This weakening has been accompanied by a corresponding decrease in the interplanetary magnetic field (IMF) strength, by a ~20% shrinkage in the polar coronal-hole areas, and by a reduction in the solar-wind mass flux over the poles. It has also been reflected in coronal streamer structure and the heliospheric current sheet, which only showed the expected flattening into the equatorial plane after sunspot numbers fell to unusually low values in mid-2008. From latitude-time plots of the photospheric field, it has long been apparent that the polar fields are formed through the transport of trailing-polarity flux from the sunspot latitudes to the poles. To address the question of why the polar fields are now so weak, we simulate the evolution of the photospheric field and radial IMF strength from 1965 to the present, employing a surface transport model that includes the effects of active region emergence, differential rotation, supergranular convection, and a poleward bulk flow. We find that the observed evolution can be reproduced if the amplitude of the surface meridional flow is varied by as little as 15% (between 14.5 and 17 m s-1), with the higher average speeds being required during the long cycles 20 and 23. Title: No Trace Left Behind: STEREO Observation of a Coronal Mass Ejection Without Low Coronal Signatures Authors: Robbrecht, Eva; Patsourakos, Spiros; Vourlidas, Angelos Bibcode: 2009ApJ...701..283R Altcode: 2009arXiv0905.2583R The availability of high-quality synoptic observations of the extreme-ultraviolet (EUV) and visible corona during the SOHO mission has advanced our understanding of the low corona manifestations of coronal mass ejections (CMEs). The EUV imager/white light coronagraph connection has been proven so powerful, it is routinely assumed that if no EUV signatures are present when a CME is observed by a coronagraph, then the event must originate behind the visible limb. This assumption carries strong implications for space weather forecasting but has not been put to the test. This paper presents the first detailed analysis of a frontside, large-scale CME that has no obvious counterparts in the low corona as observed in EUV and Hα wavelengths. The event was observed by the SECCHI instruments onboard the STEREO mission. The COR2A coronagraph observed a slow flux-rope-type CME, while an extremely faint partial halo was observed in COR2B. The event evolved very slowly and is typical of the streamer-blowout CME class. EUVI A 171 Å images show a concave feature above the east limb, relatively stable for about two days before the eruption, when it rises into the coronagraphic fields and develops into the core of the CME. None of the typical low corona signatures of a CME (flaring, EUV dimming, filament eruption, waves) were observed in the EUVI B images, which we attribute to the unusually large height from which the flux rope lifted off. This interpretation is supported by the CME mass measurements and estimates of the expected EUV dimming intensity. Only thanks to the availability of the two viewpoints we were able to identify the likely source region. The event originated along a neutral line over the quiet-Sun. No active regions were present anywhere on the visible (from STEREO B) face of the disk. Leaving no trace behind on the solar disk, this observation shows unambiguously that a CME eruption does not need to have clear on-disk signatures. Also it sheds light on the question of "mystery" geomagnetic storms, storms without clear solar origin (formerly called problem storms). We discuss the implications for space weather monitoring. Preliminary inspection of STEREO data indicates that events like this are not uncommon, particularly during the ongoing period of deep solar minimum. Title: No trace left behind: STEREO Observation of a Coronal Mass Ejection Lacking Low Coronal Signatures Authors: Vourlidas, Angelos; Robbrecht, E.; Patsourakos, S. Bibcode: 2009SPD....40.2104V Altcode: The availability of high quality synoptic observations of the EUV and visible corona during the SOHO mission has advanced our understanding of the low corona manifestations of CMEs. The EUV imager/White light coronagraph connection has been proven so powerful, it is routinely assumed that if no EUV signatures are present when a CME is observed by a coronagraph, then the event must originate behind the visible limb. This assumption carries strong implications for space weather forecasting but has not been put to the test. This paper presents the first detailed analysis of a frontside, large-scale CME that has no obvious counterparts in the low corona. The event was observed by the SECCHI instruments on the STEREO mission. The COR2A coronagraph observed the event as a typical flux-rope type CME, while an extremely faint partial halo was observed in COR2B. The event evolved very slowly and is typical of the streamer-blowout CME class. EUVI-A 171A images show a concave feature above the east limb, relatively stable for about two days before the eruption, when it rises into the coronagraphic fields and develops into the core of the CME. None of the typical low corona signatures of a CME (flaring, EUV dimming, filament eruption, waves) were observed. Thanks to the two STEREO viewpoints we were able to identify the likely source region. The event originated along a quiet sun neutral line. No active regions were present anywhere on the visible face of the disk. Leaving no trace behind, this observation shows unambiguously that a CME eruption does not need to have clear on-disk signatures. Also it sheds light on the question of `mystery' geomagnetic storms; storms without clear solar origin. Preliminary inspection of STEREO data indicates that events like this are not uncommon, particularly during the ongoing period of deep solar minimum. Title: Automated LASCO CME Catalog for Solar Cycle 23: Are CMEs Scale Invariant? Authors: Robbrecht, E.; Berghmans, D.; Van der Linden, R. A. M. Bibcode: 2009ApJ...691.1222R Altcode: 2008arXiv0810.1252R In this paper, we present the first automatically constructed LASCO coronal mass ejection (CME) catalog, a result of the application of the Computer Aided CME Tracking software (CACTus) on the LASCO archive during the interval 1997 September-2007 January. We have studied the CME characteristics and have compared them with similar results obtained by manual detection (CDAW CME catalog). On average, CACTus detects less than two events per day during solar minimum, up to eight events during maximum, nearly half of them being narrow (<20°). Assuming a correction factor, we find that the CACTus CME rate is surprisingly consistent with CME rates found during the past 30 years. The CACTus statistics show that small-scale outflow is ubiquitously observed in the outer corona. The majority of CACTus-only events are narrow transients related to previous CME activity or to intensity variations in the slow solar wind, reflecting its turbulent nature. A significant fraction (about 15%) of CACTus-only events were identified as independent events, thus not related to other CME activity. The CACTus CME width distribution is essentially scale invariant in angular span over a range of scales from 20° to 120° while previous catalogs present a broad maximum around 30°. The possibility that the size of coronal mass outflows follow a power-law distribution could indicate that no typical CME size exists, i.e., that the narrow transients are not different from the larger well defined CMEs. Title: First STEREO observation of a quiet sun CME Authors: Robbrecht, E.; Patsourakos, S.; Vourlidas, A. Bibcode: 2008AGUFMSH13B1560R Altcode: Streamer-blowouts form a particular class of CMEs characterized by a slow rise and swelling of the streamer that can last for days. While they are more massive than the average CME, their slow development complicates their association with features/activity in the low corona and hampers studies on their initiation mechanism(s). This paper reports on the first observation from 2 viewpoints of a streamer blowout CME. The event was observed by the SECCHI/COR2 A instrument as a typical flux-rope type CME, while a very faint partial halo was observed in COR2-B. The CME erupted from the east limb in the COR2 A field of view. EUVI-171 A images show a bright feature above the limb, traveling from the southern hemisphere towards the equator after which it slowly rises into the coronagraphic fields of view developing into the flux-rope structure CME. At the time of eruption the separation between the two STEREO spacecraft is sufficiently large (54 deg) to observe the source region face-on in STEREO-B. However, inspection of EUVI B data didn't reveal any particular source region, other than the quiet sun. No flaring activity could be related to the eruption. This observation shows unambiguously that a CME eruption does not necessarily have clear on-disk signature. Also it sheds light on the long-standing question of the necessity of having a flare for producing a CME. This result supplies strong constraints for CME initiation models. This type of observation could not have been achieved without the multi-viewpoint observations by STEREO. Title: Preface: SOHO 20 - Transient events on the Sun and in the heliosphere Authors: Robbrecht, E.; Hochedez, J. -F.; Fleck, B.; Gurman, J.; Forsyth, R. Bibcode: 2008AnGeo..26.2953R Altcode: No abstract at ADS Title: New techniques for the characterisation of dynamical phenomena in solar coronal images Authors: Robbrecht, E. Bibcode: 2007PhDT........11R Altcode: During a total solar eclipse, a narrow strip of the Earth's surface is shielded completely by the Moon from the disk of the Sun. In this strip, the corona appears crown-like around the shade of the Moon. It was uncertain until the middle of the 20th century whether the corona was a solar phenomenon or if it was related to the Moon or whether it represented an artifact produced by the Earth's atmosphere. The answer to this question was provided by Grotrian (1939) and Edlèn (1942). Based on studies of iron emission lines, they suggested that the surface of the Sun is surrounded by a hot tenuous gas having a temperature of million degrees Kelvin and thus in a state of high ionization. This discovery was a result from spectroscopy, a field of research which started in 1666 with Sir Isaac Newton's observations of sunlight, dispersed by a prism.

It is now clear that the hot solar corona is made of a low density plasma, highly structured by the magnetic field on length scales ranging from the Sun's diameter to the limit of angular resolution (e.g. Démoulin and Klein 2000). The need to resolve and study the corona down to such scales has determined a vigorous scientific and technological impulse toward the development of solar Ultraviolet (UV) and X-ray telescopes with high spatial and temporal resolution. With the advent of the satellite SOHO (Solar and Heliospheric Observatory, see chapter 1), the picture of a quiet corona was definitely sent to the past. EUV (Extreme UV) image sequences of the lower solar corona revealed a finely structured medium constantly agitated by a wide variety of transients (e.g. Harrison 1998). Active regions consisting of large magnetic loops with enhanced temperature and density are observed, as well as "quiet" areas, coronal holes and numerous structures of different scales such as plumes, jets, spicules, X-ray bright points, blinkers, all structured by magnetic fields. Launched in 1998, the Transition Region And Coronal Explorer (TRACE) was an important step on the way to subarcsecond telescopes. It allows a spatial resolution of 1" in the EUV and UV bands and, simultaneously, a temporal resolution of the order of a few seconds.

Coronal physics studies are dominated by two major and interlinked problems: coronal heating and solar wind acceleration. Above the chromosphere there is a thin transition layer in which the temperature suddenly increases and density drops. How can the temperature of the solar corona be three orders of magnitude higher than the temperature of the photosphere? In order for this huge temperature gradient to be stationary, non-thermal energy must be transported from below the photosphere towards the chromosphere and corona and converted into heat to balance the radiative and conductive losses. This puzzle of origin, transport and conversion of energy is referred to as the "coronal heating problem". Due to its fundamental role in the structuring of the corona, the magnetic field is supposed to play an important role in the heating.

In this dissertation we describe two aspects of solar coronal dynamics: waves in coronal loops (Part I) and coronal mass ejections (Part II). We investigate the influence of (semi-) automated techniques on solar coronal research. This is a timely discussion since the observation of solar phenomena is transitioning from manual detection to "Solar Image Processing". Our results are mainly based on images from the Extreme UV Imaging Telescope (EIT) and the Large Angle and Spectrometric Coronagraph (LASCO), two instruments onboard the satellite SOHO (Solar and Heliospheric Observatory) of which we recently celebrated its 11th anniversary. The high quality of the images together with the long timespan created a valuable database for solar physics research.

Part I reports on the first detection of slow magnetoacoustic waves in transequatorial coronal loops observed in high cadence image sequences simultaneously produced by EIT and TRACE (Transition Region And Coronal Explorer). Ten years of EUV observations made it clear that these disturbances are a widespread phenomenon in active region loops. The existence of these waves in the corona had been predicted by the theory of magnetohydrodynamics (MHD), which we revise briefly. Just like in helioseismology, coronal seismology uses observations of oscillations to derive physical parameters which are not directly measurable, such as the Alfvén speed or the magnetic field strength. The comparison with helioseismology does not fully hold in the sense that the dense photosphere does not allow any seeing inside. Instead, for the corona we do have direct observations, but because of its optical thinness these observations leave space for many interpretations.

At the end of the forties, it was suggested that the corona could be heated by the dissipation of acoustic waves (sound waves) driven by the p-mode oscillations, generated by turbulence in the convection zone. While they travel upwards, these waves form shocks and heat the plasma by viscous dissipation. Nowadays, they are believed to be only important for lower chromospheric heating. By the time the upper chromosphere is reached, the acoustic waves are heavily damped and what rests is reflected by the steep temperature and density gradients in the transition zone. As such, they cannot deposit enough energy in the corona to sufficiently heat it to the observed temperatures. Dissipation of magnetic energy by Alfvén waves or directly by the reconnection process in current sheets are considered to be more likely to heat the corona.

Part II addresses the question of detecting coronal mass ejections (CMEs) in coronagraphic white light data. The study of CMEs is a rather young (≲ 30 years) field of research. Coronal mass ejections are sudden expulsions of mass and magnetic field from the solar corona into the interplanetary medium. A classical CME carries away some 10^15 g of coronal mass and can liberate energies of 10^23-10^25 J. They are often observed n association with low coronal activity, such as flares and filament eruptions. During the first years of CME observation, it was believed that a flare was a necessary condition for CME occurrence. The widely accepted picture today is that flares and CMEs are both different manifestations of magnetic field restructuring through reconnection (flare) and the expulsion of mass (CME). Up till now, the SOHO mission has been the best mission for CME studies because of the increased resolution, cadence, sensitivity and dynamic range of the LASCO instruments, but also because of the large array of ground-based instruments (Howard 2006). The complexity of the CME-picture grew likewise. The next mission with a coronagraph is the NASA STEREO mission (Solar Terrestrial Relations Observatory), launched on 26 Oct. 2006.

In chapter 4 we test the possibility of automatically detecting CMEs in LASCO data. We describe the algorithm CACTus (Computer Aided CME Tracking) and test its validity on a short period of 6 days. In chapter 5 we present our newly constructed CME catalog based on our automated detection scheme. It is the first automatically generated catalog which runs over a complete solar cycle (cycle 23). It required no human interaction, which implies it is totally objective. It includes all transients obeying the observational definition of CME as a "new, discrete, bright, white-light feature in the coronagraph field-of-view moving radially outward" (Hundhausen et al. 1984). As a result, our catalog contains much more events, mostly narrow, than are included in the classical CDAW CME catalog (Yashiro et al. 2004) which is assembled manually. We discuss the CME rate over the solar cycle and present important new statistics on the CACTus CME parameters (size, latitude, speed).

CME research has gained an increased interest due to their strong space weather impact. Space weather is defined by the European Space Agency (ESA) 1 as the "conditions on the Sun and in the solar wind, magnetosphere, ionosphere and thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems and can endanger human life or health." The significance of space weather lies in its potential impact on man-made technologies on Earth and in space, for example, on satellites and spacecraft, electricity power grids, pipelines, radio and telephone communications and on geophysical exploration. Space weather also has implications for manned space flight, both in Earth orbit and further out into space. Solar activity is the main source of space weather. It is now well established that CMEs are the primary cause of geomagnetic storms and that their associated shocks accelerate high energetic particles. These particles can directly and indirectly influence the operation of spacecraft and affect communication and navigation. In order to protect systems and people that might be at risk from space weather effects, we need to understand the causes of space weather and try to predict its impact on the heliosphere as soon as possible. A growing field in this respect is Solar mage Processing (SIP). It allows continuous monitoring and interpretation of new incoming data. This is not only interesting for space weather forecasting, but it is also needed to be able to handle efficiently the large data flow which is expected from recently launched and future missions. In chapter 6 we revise the current capabilities for automated detection of CMEs and related phenomena. Title: Current and future space weather services and products from the SIDC- Brussels Authors: Lawrence, G.; Kretzschmar, M.; Berghmans, D.; Clete, F.; Hochedez, J.; van der Linden, R.; Delouille, V.; Gissot, S.; Marque, C.; Nicula, B.; Patoul, J.; Podladchikova, E.; Robbrecht, E.; Vanlommel, P.; Dehant, V. Bibcode: 2006AGUFMSA51A..04L Altcode: The SIDC-Brussels, as WDC for the sunspot index and European RWC of the ISES, is the European hub for solar data and forecasts. Its services and products, while long established and widely recognised and used, are continuously being enhanced and supplemented. We present in detail the current status and outline the imminent improvements and additions. The Solar Weather Browser (SWB) is a free, downloadable, multi-platform visualisation package for real-time browsing of processed solar images from a variety of space and ground based sources, combined with context information (events, regions IDs, etc.) via a wide choice of overlay combinations. The Estimated International Sunspot Number (EISN) has been produced and distributed daily since January 2006 by the SIDC. Intended to support operational model predictions of ionospheric radio propagation, we present some early statistical results. CACTus, the operational Computer-Aided CME Tracking algorithm, now freely available to the community via the SSW software framework, is being tested for its real-time application to the STEREO/SECCHI COR-2 "space weather beacon" coronagraph telemetry stream. Also NEMO, a software package for the automated detection and morphological analysis of EIT waves presently being tested, details the relation between coronal EUV wave fronts and dimmings and characterizes their evolution; we present sample results of both developments. The Velociraptor software processes and interprets movies of the EUV solar corona, an algorithm identifying outstanding motions such as loop openings that are associated to space weather events. Sample results using EIT and TRACE data will be shown. A new flare catalog called B2X is presented, compliled via a method to detect automatically, and characterise according to time, localization, size, EUV flares belonging to classes B to X anywhere on the solar disc and at the limb. In addition we present a summary of the full range of products available from SIDC which can be chosen in any combination tailored to the individual, or group's needs. All products are available via the revamped SIDC website, http://www.sidc.be Title: A Broad Perspective on Automated CME Tracking: Towards Higher Level Space Weather Forecasting Authors: Robbrecht, Eva; Berghmans, David Bibcode: 2006GMS...165...33R Altcode: We discuss our current capabilities to deliver the CME parameters required for the space weather forecasting process. The ever growing importance of space weather has lead to new requirements on the timeliness and objectiveness of CME detection. It has become indispensable to report the occurrence of Earth-directed CMEs and to predict their possible impact on the geospace environment. Early 2005, we are on the eve of a new era in space weather forecasting. We point out the restricted accuracy on the current forecasts and discuss a chance for amelioration. This invokes data-driven models (empirical and numerical), triggered by a real-time CME disturbance, simulating the propagation and interaction of the ejection with the ambient solar wind. We discuss the link between the direct observable parameters (like the CME projected speed and angle around the occulter) and the required input parameters (like radial speed, direction, …). The only way to guarantee the real-time value of the simulations is by employing software which autonomously detect CME parameters in a variety of data. This paper focusses on the automated CME detection algorithms that are currently available. Automated CME tracking is yet in its infancy, therefore this `review' will be an outlook on the potential of this field rather than looking back on already achieved milestones. Title: A broad Perspective on Automated CME Tracking: towards higher level space weather forecasting Authors: Robbrecht, E.; Berghmans, D. Bibcode: 2006GMS...165.....R Altcode: We discuss our current capabilities to deliver the CME parameters required for the space weather forecasting process. The ever growing importance of space weather has lead to new requirements on the timeliness and objectiveness of CME detection. It has become indispensable to report the occurrence of Earth-directed CMEs and to predict their possible impact on the geospace environment. Early 2005, we are on the eve of a new era in space weather forecasting. We point out the restricted accuracy on the current forecasts and discuss a chance for amelioration. This invokes data-driven models (empirical and numerical), triggered by a real-time CME disturbance, simulating the propagation and interaction of the ejection with the ambient solar wind. We discuss the link between the direct observable parameters (like the CME projected speed and angle around the occulter) and the required input parameters (like radial speed, direction, ...). The only way to guarantee the real-time value of the simulations is by employing software which autonomously detect CME parameters in a variety of data. This paper focusses on the automated CME detection algorithms that are currently available. Automated CME tracking is yet in its infancy, therefore this `review' will be an outlook on the potential of this field rather than looking back on already achieved milestones. 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: Objective CME detection over the solar cycle: A first attempt Authors: Robbrecht, E.; Berghmans, D.; van der Linden, R. A. M. Bibcode: 2006AdSpR..38..475R Altcode: We recently developed a software package to autonomously detect coronal mass ejections (CMEs) in image sequences from large angle spectrometric coronagraph (LASCO). The detection is not done in the original images, instead we detect bright ridges in (time, height) plots using a modified version of the Hough transform. Experimental results on real-time data have shown that the developed technique can achieve excellent results in measuring starting time and principal angle and good results for the angular width and velocity measurement compared to the CMEs listed in the manually assembled catalog. The real-time output of the software can be found online at www.sidc.oma.be/cactus. With the present paper, we report on the first large scale application of the software to the LASCO archive. In an ongoing work, we have applied the software on a first sample of 29 months selected from archive data in the period July 1997 to December 2002. The results in this paper show that relevant characteristics of CMEs over the solar cycle are successfully recovered with the automated procedure. This proves that a completely automatically produced CME catalog is within reach. Title: A Complete LASCO CME-Catalog based on Automated Detection Authors: Robbrecht, E.; Berghmans, D.; van der Linden, R. A. M. Bibcode: 2006cosp...36.3564R Altcode: 2006cosp.meet.3564R We present our new CME catalog a result of the large scale application of our software CACTus on the LASCO archive We recently improved the algorithm and upgraded the test-version of the catalog available online at www sidc be cactus The automatic detection of a CME is done in two steps and is applied simultaneously on c2 and c3 running difference images 1 detection of bright features moving radially outward 2 clustering detections into CMEs The recent improvements are undertaken in the second step of this process Unique for our detection method is that we use the condition moving radially outward as part of the detection criterion The detection itself is done using the stroboscopic method i e in height time slices where height means radial distance from the sun An outwardly moving feature appears then as a bright ridge extracted by a modified version of the Hough transform Per month the output consists of a table containing the CME characteristics and an overview map in a angle time -coordinate system that clearly shows all detected CMEs As a result of our method we also have for each CME a linear speed profile along the angular width of the CME We studied the characteristics of the CMEs detected with CACTus over the solar cycle and compared them with results obtained from other catalogs This paper shows that relevant characteristics of CMEs over the solar cycle are successfully recovered with the automated procedure Recent tests prove that in general automated procedures detect far more small features than human 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: Entering The Era Of Automated Cme Recognition: A Review Of Existing Tools Authors: Robbrecht, E.; Berghmans, D. Bibcode: 2005SoPh..228..239R Altcode: We consider the problem of the observational identification of CMEs. The ever growing importance of space weather has led to new requirements on the timeliness and objectiveness of CME detection. It is not sufficient any more to simply detect CMEs, a complete set of characteristics (speed, direction, mass, chirality) must be reported as soon as possible to estimate its geoeffectiveness. Recent developments in (solar) feature recognition greatly improved the ability to address these new needs. Progress was achieved in automating the detection of CMEs in coronagraphic data. This has led to near-real-time messages alerting the space weather community day and night. In attempting to generate ever-prompter alerts, we can employ a far broader set of solar observations than coronagraphic data alone. At present an extensive set of automatic recognition tools exists for a number of CME-related phenomena occurring in the lower corona. This paper deals with detection techniques for disappearing filaments in Hα images, dimmings, EIT waves and erupting prominences in radio data. We believe that incorporating all automatically generated alerts into one report per CME can provide valuable CME information, especially when no coronagraphic images are available. This paper is thus a quest to reach a maximal success rate with the help of an integrated system of tools acting on a variety of data. Future grid-technology systems will greatly facilitate this. Title: Automated recognition of coronal mass ejections (CMEs) in near-real-time data Authors: Robbrecht, E.; Berghmans, D. Bibcode: 2004A&A...425.1097R Altcode: This paper presents a new method and first applications of software that we have developed to autonomously detect CMEs in image sequences from LASCO (Large Angle Spectrometric Coronagraph). The crux of the software is the detection of CMEs as bright ridges in (time, height) maps using the Hough transform. The next step employs clustering and morphological closing operations to mark out different CMEs. The output is a list of events, similar to the classic catalogs, with starting time, principle angle, angular width and velocity estimation for each CME. In addition we present a new type of CME overview map that clearly shows all detected CMEs in a (principal angle, time of occurrence) coordinate system. In contrast to catalogs assembled by human operators, these CME detections can be done without any human interference on real-time data 24 h per day (see http://sidc.oma.be/cactus for the real-time output with data covering the last 4 days). Therefore the detection is not only more immediate, but, more importantly, also more objective. In this paper we describe the software and validate its performance by comparing its output with the SOHO LASCO CME catalog. Experimental results on real-time data show that the developed technique can achieve excellent results in measuring starting time and principal angle and good results for the angular width and velocity measurement compared to the CMEs listed in the catalog. Its overall success rate is presently about 94%. The software also reveals CMEs or other features that have not been listed in the catalog. Such unreported cases might influence CME statistics and they demonstrate that also the present catalogs do not have a 100% success rate. This inevitably leads to a discussion on the definition of a CME. Prospects for improvement and exploitation are discussed. 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: Objective CME detection over the solar cycle Authors: Robbrecht, E.; Berghmans, D. Bibcode: 2004cosp...35.2702R Altcode: 2004cosp.meet.2702R We have developed a software package for 'Computer Aided CME Tracking' (CACTus), that autonomously detects CMEs in image sequences from LASCO. The crux of the CACTus software is the detection of CMEs as bright ridges in [height, time] maps using the Hough transform. The output is a list of events, similar to the classic catalogs, with principle angle, angular width and velocity estimation for each CME. In contrast to catalogs assembled by human operators, these CME detections by software can be faster and possibly also more objective, as the detection criterion is written explicitly in a program. Especially on the timescale of a solar cycle, it is questionnable whether human, visual CME detection is stable, as the operator gains experience or personnel is replaced. In this paper we overview the latest improvements of CACTUS and validate its performance by comparing the CACTus output with the classical, visually assembled CME catalogs. Discrepancies between the classical catalogs and the CACTUS catalogs are discussed. Such discrepancies highlight not only the performance of CACTUS but also the caveats of the classical catalogs. Indeed, CACTUS sometimes finds CMEs that are not listed in the catalogs or interpreted differently (eg halo CME or not). It is important to know these caveats when using the CME catalogs as input for statistical CME studies over the solar cycle. The near realtime output of the software is available on the web(http://sidc.oma.be/cactus) and is updated daily. Title: Spectroscopic Monitoring of 10 Northern SPB Candidates Authors: Mathias, P.; Le Contel, J. -M.; Aerts, C.; De Cat, P.; van Winckel, H.; Robbrecht, E.; Briquet, M.; Cuypers, J. Bibcode: 2002ASPC..259..232M Altcode: 2002rnpp.conf..232M; 2002IAUCo.185..232M No abstract at ADS Title: Slow magnetoacoustic waves in coronal loops: EIT and TRACE Authors: Robbrecht, E.; Verwichte, E.; Berghmans, D.; Hochedez, J. F.; Poedts, S.; Nakariakov, V. M. Bibcode: 2001A&A...370..591R Altcode: On May 13, 1998 the EIT (Extreme ultraviolet Imaging Telescope) on board of SoHO (Solar and Heliospheric Observatory) and TRACE (Transition Region And Coronal Explorer) instruments produced simultaneous high cadence image sequences of the same active region (AR 8218). TRACE achieved a 25 s cadence in the Fe Ix (171 Å) bandpass while EIT achieved a 15 s cadence (operating in ``shutterless mode'', SoHO JOP 80) in the Fe Xii (195 Å) bandpass. These high cadence observations in two complementary wavelengths have revealed the existence of weak transient disturbances in an extended coronal loop system. These propagating disturbances (PDs) seem to be a common phenomenon in this part of the active region. The disturbances originate from small scale brightenings at the footpoints of the loops and propagate along the loops. The projected propagation speeds roughly vary between 65 and 150 km s-1 for both instruments which is close to and below the expected sound speed in the coronal loops. The measured slow magnetoacoustic propagation speeds seem to suggest that the transients are sound (or slow) wave disturbances. This work differs from previous studies in the sense that it is based on a multi-wavelength observation of an entire loop bundle at high cadence by two EUV imagers. The observation of sound waves along the same path shows that they propagate along the same loop, suggesting that loops contain sharp temperature gradients and consist of either concentric shells or thin loop threads, at different temperatures. Title: Slow magnetoacoustic waves in coronal loops Authors: Nakariakov, V. M.; Verwichte, E.; Berghmans, D.; Robbrecht, E. Bibcode: 2000A&A...362.1151N Altcode: A theoretical model interpreting propagating disturbances of EUV emission intensity, recently observed in coronal loops, is constructed in terms of slow magnetoacoustic waves. The model is one-dimensional and incorporates effects of nonlinearity, dissipation due to finite viscosity and thermal conduction, and gravitational stratification of plasma in the loop. It has been found that, for the observationally detected parameters of the waves, the main factors influencing the wave evolution are dissipation and stratification. The upwardly propagating waves of observed periods (5-20 min) are found to decay significantly in the vicinity of the loop apex, explaining the rarity of observational detection of downwardly propagating waves. The model provides a theoretical basis for development of MHD seismology of the coronal loops. Title: Slow magnetoacoustic waves in coronal loops: EIT vs TRACE Authors: Robbrecht, E.; Verwichte, E.; Berghmans, D.; Hochedez, J. F.; Poedts, S. Bibcode: 2000AIPC..537..271R Altcode: 2000wdss.conf..271R On May 13, 1998 the EIT (Extreme-Ultraviolet Imaging Telescope) and TRACE (Transition Region And Coronal Explorer) instruments produced simultaneous high cadence image sequences of the same active region (AR 8218). TRACE achieved a 25 sec cadence in the Fe IX/X (171 Å) bandpass while EIT achieved a 15 sec cadence (operating in `shutterless mode,' SOHO JOP 80) in the Fe XII (195 Å) bandpass. These high cadence observations in two complementary wavelengths have revealed the existence of weak transient disturbances in an extended coronal loop system. These propagating disturbances (PDs) seem to be a common phenomenon in this part of the active region. The disturbances originate from small scale brightenings at the footpoints of the loops and propagate along the loops. The apparent propagation speeds roughly vary between 65 and 150 km s-1 which is close to the expected sound speed of the coronal loops. The measured propagation speeds seem to suggest that the transients are sound (or slow) wave disturbances. . 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: Slow Magnetoacoustic Waves in Coronal Loops? Authors: Robbrecht, E.; Berghmans, D.; Nakariakov, V.; Poedts, S. Bibcode: 1999ESASP.446..575R Altcode: 1999soho....8..575R On May 13, 1998 the EIT and TRACE instruments produced simultaneous high cadence image sequences of the same active region (AR 8218). TRACE achieved a 25 sec cadence in the 171 deg passband while EIT achieved a 15 sec cadence (operating in 'shutterless mode', SOHO JOP 80) in the 195 deg passband. These high cadence observations in two complementary wavelengths have revealed the existence of weak disturbances in an extended coronal loop system. The disturbances originate from small scale brightenings at the footpoints of the loops and propagate along the loops at an apparant speed of the order of 150 km/s which is close to the expected sound speed. To conclude whether these propagating disturbances should be interpreted as slow magnetoacoustic waves or as mass motions ('microflows'), we compare our observational findings with theoretical models. Our results suggest that the recent discovery of DeForest and Gurman (1998) of slow MHD waves in polar plumes, are in fact not typical of polar plumes but occur also in extended coronal structures elsewhere.