Author name code: bloomfield ADS astronomy entries on 2022-09-14 author:"Bloomfield, D. Shaun" ------------------------------------------------------------------------ Title: The high-energy Sun - probing the origins of particle acceleration on our nearest star Authors: Matthews, S. A.; Reid, H. A. S.; Baker, D.; Bloomfield, D. S.; Browning, P. K.; Calcines, A.; Del Zanna, G.; Erdelyi, R.; Fletcher, L.; Hannah, I. G.; Jeffrey, N.; Klein, L.; Krucker, S.; Kontar, E.; Long, D. M.; MacKinnon, A.; Mann, G.; Mathioudakis, M.; Milligan, R.; Nakariakov, V. M.; Pesce-Rollins, M.; Shih, A. Y.; Smith, D.; Veronig, A.; Vilmer, N. Bibcode: 2021ExA...tmp..135M Altcode: As a frequent and energetic particle accelerator, our Sun provides us with an excellent astrophysical laboratory for understanding the fundamental process of particle acceleration. The exploitation of radiative diagnostics from electrons has shown that acceleration operates on sub-second time scales in a complex magnetic environment, where direct electric fields, wave turbulence, and shock waves all must contribute, although precise details are severely lacking. Ions were assumed to be accelerated in a similar manner to electrons, but γ-ray imaging confirmed that emission sources are spatially separated from X-ray sources, suggesting distinctly different acceleration mechanisms. Current X-ray and γ-ray spectroscopy provides only a basic understanding of accelerated particle spectra and the total energy budgets are therefore poorly constrained. Additionally, the recent detection of relativistic ion signatures lasting many hours, without an electron counterpart, is an enigma. We propose a single platform to directly measure the physical conditions present in the energy release sites and the environment in which the particles propagate and deposit their energy. To address this fundamental issue, we set out a suite of dedicated instruments that will probe both electrons and ions simultaneously to observe; high (seconds) temporal resolution photon spectra (4 keV - 150 MeV) with simultaneous imaging (1 keV - 30 MeV), polarization measurements (5-1000 keV) and high spatial and temporal resolution imaging spectroscopy in the UV/EUV/SXR (soft X-ray) regimes. These instruments will observe the broad range of radiative signatures produced in the solar atmosphere by accelerated particles. Title: The flare likelihood and region eruption forecasting (FLARECAST) project: flare forecasting in the big data & machine learning era Authors: Georgoulis, Manolis K.; Bloomfield, D. Shaun; Piana, Michele; Massone, Anna Maria; Soldati, Marco; Gallagher, Peter T.; Pariat, Etienne; Vilmer, Nicole; Buchlin, Eric; Baudin, Frederic; Csillaghy, Andre; Sathiapal, Hanna; Jackson, David R.; Alingery, Pablo; Benvenuto, Federico; Campi, Cristina; Florios, Konstantinos; Gontikakis, Constantinos; Guennou, Chloe; Guerra, Jordan A.; Kontogiannis, Ioannis; Latorre, Vittorio; Murray, Sophie A.; Park, Sung-Hong; von Stachelski, Samuelvon; Torbica, Aleksandar; Vischi, Dario; Worsfold, Mark Bibcode: 2021JSWSC..11...39G Altcode: 2021arXiv210505993G The European Union funded the FLARECAST project, that ran from January 2015 until February 2018. FLARECAST had a research-to-operations (R2O) focus, and accordingly introduced several innovations into the discipline of solar flare forecasting. FLARECAST innovations were: first, the treatment of hundreds of physical properties viewed as promising flare predictors on equal footing, extending multiple previous works; second, the use of fourteen (14) different machine learning techniques, also on equal footing, to optimize the immense Big Data parameter space created by these many predictors; third, the establishment of a robust, three-pronged communication effort oriented toward policy makers, space-weather stakeholders and the wider public. FLARECAST pledged to make all its data, codes and infrastructure openly available worldwide. The combined use of 170+ properties (a total of 209 predictors are now available) in multiple machine-learning algorithms, some of which were designed exclusively for the project, gave rise to changing sets of best-performing predictors for the forecasting of different flaring levels, at least for major flares. At the same time, FLARECAST reaffirmed the importance of rigorous training and testing practices to avoid overly optimistic pre-operational prediction performance. In addition, the project has (a) tested new and revisited physically intuitive flare predictors and (b) provided meaningful clues toward the transition from flares to eruptive flares, namely, events associated with coronal mass ejections (CMEs). These leads, along with the FLARECAST data, algorithms and infrastructure, could help facilitate integrated space-weather forecasting efforts that take steps to avoid effort duplication. In spite of being one of the most intensive and systematic flare forecasting efforts to-date, FLARECAST has not managed to convincingly lift the barrier of stochasticity in solar flare occurrence and forecasting: solar flare prediction thus remains inherently probabilistic. Title: Validation of Global EUV Wave MHD Simulations and Observational Techniques Authors: Downs, Cooper; Warmuth, Alexander; Long, David M.; Bloomfield, D. Shaun; Kwon, Ryun-Young; Veronig, Astrid M.; Vourlidas, Angelos; Vršnak, Bojan Bibcode: 2021ApJ...911..118D Altcode: Global EUV waves remain a controversial phenomenon more than 20 yr after their discovery by SOHO/EIT. Although consensus is growing in the community that they are most likely large-amplitude waves or shocks, the wide variety of observations and techniques used to identify and analyze them have led to disagreements regarding their physical properties and interpretation. Here, we use a 3D magnetohydrodynamic (MHD) model of the solar corona to simulate an EUV wave event on 2009 February 13 to enable a detailed validation of the various commonly used detection and analysis techniques of global EUV waves. The simulated event exhibits comparable behavior to that of a real EUV wave event, with similar kinematic behavior and plasma parameter evolution. The kinematics of the wave are estimated via visual identification and profile analysis, with both approaches providing comparable results. We find that projection effects can affect the derived kinematics of the wave, due to the variation in fast-mode wave speed with height in the corona. Coronal seismology techniques typically used for estimates of the coronal magnetic field are also tested and found to estimate fast-mode speeds comparable to those of the model. Plasma density and temperature variations of the wave front are also derived using a regularized inversion approach and found to be consistent with observed wave events. These results indicate that global waves are best interpreted as large-amplitude waves and that they can be used to probe the coronal medium using well-defined analysis techniques. Title: The Spectrometer/Telescope for Imaging X-rays (STIX) Authors: Krucker, Säm; Hurford, G. J.; Grimm, O.; Kögl, S.; Gröbelbauer, H. -P.; Etesi, L.; Casadei, D.; Csillaghy, A.; Benz, A. O.; Arnold, N. G.; Molendini, F.; Orleanski, P.; Schori, D.; Xiao, H.; Kuhar, M.; Hochmuth, N.; Felix, S.; Schramka, F.; Marcin, S.; Kobler, S.; Iseli, L.; Dreier, M.; Wiehl, H. J.; Kleint, L.; Battaglia, M.; Lastufka, E.; Sathiapal, H.; Lapadula, K.; Bednarzik, M.; Birrer, G.; Stutz, St.; Wild, Ch.; Marone, F.; Skup, K. R.; Cichocki, A.; Ber, K.; Rutkowski, K.; Bujwan, W.; Juchnikowski, G.; Winkler, M.; Darmetko, M.; Michalska, M.; Seweryn, K.; Białek, A.; Osica, P.; Sylwester, J.; Kowalinski, M.; Ścisłowski, D.; Siarkowski, M.; Stęślicki, M.; Mrozek, T.; Podgórski, P.; Meuris, A.; Limousin, O.; Gevin, O.; Le Mer, I.; Brun, S.; Strugarek, A.; Vilmer, N.; Musset, S.; Maksimović, M.; Fárník, F.; Kozáček, Z.; Kašparová, J.; Mann, G.; Önel, H.; Warmuth, A.; Rendtel, J.; Anderson, J.; Bauer, S.; Dionies, F.; Paschke, J.; Plüschke, D.; Woche, M.; Schuller, F.; Veronig, A. M.; Dickson, E. C. M.; Gallagher, P. T.; Maloney, S. A.; Bloomfield, D. S.; Piana, M.; Massone, A. M.; Benvenuto, F.; Massa, P.; Schwartz, R. A.; Dennis, B. R.; van Beek, H. F.; Rodríguez-Pacheco, J.; Lin, R. P. Bibcode: 2020A&A...642A..15K Altcode:
Aims: The Spectrometer Telescope for Imaging X-rays (STIX) on Solar Orbiter is a hard X-ray imaging spectrometer, which covers the energy range from 4 to 150 keV. STIX observes hard X-ray bremsstrahlung emissions from solar flares and therefore provides diagnostics of the hottest (⪆10 MK) flare plasma while quantifying the location, spectrum, and energy content of flare-accelerated nonthermal electrons.
Methods: To accomplish this, STIX applies an indirect bigrid Fourier imaging technique using a set of tungsten grids (at pitches from 0.038 to 1 mm) in front of 32 coarsely pixelated CdTe detectors to provide information on angular scales from 7 to 180 arcsec with 1 keV energy resolution (at 6 keV). The imaging concept of STIX has intrinsically low telemetry and it is therefore well-suited to the limited resources available to the Solar Orbiter payload. To further reduce the downlinked data volume, STIX data are binned on board into 32 selectable energy bins and dynamically-adjusted time bins with a typical duration of 1 s during flares.
Results: Through hard X-ray diagnostics, STIX provides critical information for understanding the acceleration of electrons at the Sun and their transport into interplanetary space and for determining the magnetic connection of Solar Orbiter back to the Sun. In this way, STIX serves to link Solar Orbiter's remote and in-situ measurements. Title: 2D and 3D Analysis of a Torus-unstable Quiet-Sun Prominence Eruption Authors: Rees-Crockford, T.; Bloomfield, D. S.; Scullion, E.; Park, S. -H. Bibcode: 2020ApJ...897...35R Altcode: The role of ideal-MHD instabilities in a prominence eruption is explored through 2D and 3D kinematic analysis of an event observed with the Solar Dynamics Observatory and the Solar Terrestrial Relations Observatory between 22:06 UT on 2013 February 26 and 04:06 UT on 2013 February 27. A series of 3D radial slits are used to extract height-time profiles ranging from the midpoint of the prominence leading edge to the southeastern footpoint. These height-time profiles are fit with a kinematic model combining linear and nonlinear rise phases, returning the nonlinear onset time (tnl) as a free parameter. A range (1.5-4.0) of temporal power indices (I.e., β in the nonlinear term ${(t-{t}_{\mathrm{nl}})}^{\beta }$ ) are considered to prevent prescribing any particular form of nonlinear kinematics. The decay index experienced by the leading edge is explored using a radial profile of the transverse magnetic field from a PFSS extrapolation above the prominence region. Critical decay indices are extracted for each slit at their own specific values of height at the nonlinear phase onset (h(tnl)) and filtered to focus on instances resulting from kinematic fits with ${\chi }_{\mathrm{red}}^{2}\lt 2$ (restricting β to 1.9-3.9). Based on this measure of the critical decay index along the prominence structure, we find strong evidence that the torus instability is the mechanism driving this prominence eruption. Defining any single decay index as being "critical" is not that critical because there is no single canonical or critical value of decay index through which all eruptions must succeed. Title: A Comparison of Flare Forecasting Methods. IV. Evaluating Consecutive-day Forecasting Patterns Authors: Park, Sung-Hong; Leka, K. D.; Kusano, Kanya; Andries, Jesse; Barnes, Graham; Bingham, Suzy; Bloomfield, D. Shaun; McCloskey, Aoife E.; Delouille, Veronique; Falconer, David; Gallagher, Peter T.; Georgoulis, Manolis K.; Kubo, Yuki; Lee, Kangjin; Lee, Sangwoo; Lobzin, Vasily; Mun, JunChul; Murray, Sophie A.; Hamad Nageem, Tarek A. M.; Qahwaji, Rami; Sharpe, Michael; Steenburgh, R. A.; Steward, Graham; Terkildsen, Michael Bibcode: 2020ApJ...890..124P Altcode: 2020arXiv200102808P A crucial challenge to successful flare prediction is forecasting periods that transition between "flare-quiet" and "flare-active." Building on earlier studies in this series in which we describe the methodology, details, and results of flare forecasting comparison efforts, we focus here on patterns of forecast outcomes (success and failure) over multiday periods. A novel analysis is developed to evaluate forecasting success in the context of catching the first event of flare-active periods and, conversely, correctly predicting declining flare activity. We demonstrate these evaluation methods graphically and quantitatively as they provide both quick comparative evaluations and options for detailed analysis. For the testing interval 2016-2017, we determine the relative frequency distribution of two-day dichotomous forecast outcomes for three different event histories (I.e., event/event, no-event/event, and event/no-event) and use it to highlight performance differences between forecasting methods. A trend is identified across all forecasting methods that a high/low forecast probability on day 1 remains high/low on day 2, even though flaring activity is transitioning. For M-class and larger flares, we find that explicitly including persistence or prior flare history in computing forecasts helps to improve overall forecast performance. It is also found that using magnetic/modern data leads to improvement in catching the first-event/first-no-event transitions. Finally, 15% of major (I.e., M-class or above) flare days over the testing interval were effectively missed due to a lack of observations from instruments away from the Earth-Sun line. Title: Feature Ranking of Active Region Source Properties in Solar Flare Forecasting and the Uncompromised Stochasticity of Flare Occurrence Authors: Campi, Cristina; Benvenuto, Federico; Massone, Anna Maria; Bloomfield, D. Shaun; Georgoulis, Manolis K.; Piana, Michele Bibcode: 2019ApJ...883..150C Altcode: 2019arXiv190612094C Solar flares originate from magnetically active regions (ARs) but not all solar ARs give rise to a flare. Therefore, the challenge of solar flare prediction benefits from an intelligent computational analysis of physics-based properties extracted from AR observables, most commonly line-of-sight or vector magnetograms of the active region photosphere. For the purpose of flare forecasting, this study utilizes an unprecedented 171 flare-predictive AR properties, mainly inferred by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory (SDO/HMI) in the course of the European Union Horizon 2020 FLARECAST project. Using two different supervised machine-learning methods that allow feature ranking as a function of predictive capability, we show that (i) an objective training and testing process is paramount for the performance of every supervised machine-learning method; (ii) most properties include overlapping information and are therefore highly redundant for flare prediction; (iii) solar flare prediction is still—and will likely remain—a predominantly probabilistic challenge. Title: Which Photospheric Characteristics Are Most Relevant to Active-Region Coronal Mass Ejections? Authors: Kontogiannis, Ioannis; Georgoulis, Manolis K.; Guerra, Jordan A.; Park, Sung-Hong; Bloomfield, D. Shaun Bibcode: 2019SoPh..294..130K Altcode: 2019arXiv190906088K We investigate the relation between characteristics of coronal mass ejections and parameterizations of the eruptive capability of solar active regions widely used in solar flare-prediction schemes. These parameters, some of which are explored for the first time, are properties related to topological features, namely, magnetic polarity-inversion lines (MPILs) that indicate large amounts of stored non-potential (i.e. free) magnetic energy. We utilize the Space Weather Database of Notifications, Knowledge, Information (DONKI) and the Large Angle and Spectrometric Coronograph (LASCO) databases to find flare-associated coronal mass ejections and their kinematic characteristics, while properties of MPILs are extracted from Helioseismic and Magnetic Imager (HMI) vector magnetic-field observations of active regions to extract the properties of source-region MPILs. The correlation between all properties and the characteristics of CMEs ranges from moderate to very strong. More significant correlations hold particularly for fast CMEs, which are most important in terms of adverse space-weather manifestations. Non-neutralized currents and the length of the main MPIL exhibit significantly stronger correlations than the rest of the properties. This finding supports a causal relationship between coronal mass ejections and non-neutralized electric currents in highly sheared, conspicuous MPILs. In addition, non-neutralized currents and MPIL length carry distinct, independent information as to the eruptive potential of active regions. The combined total amount of non-neutralized electric currents and the length of the main polarity-inversion line, therefore, reflect more efficiently than other parameters the eruptive capacity of solar active regions and the CME kinematic characteristics stemming from these regions. Title: A Comparison of Flare Forecasting Methods. III. Systematic Behaviors of Operational Solar Flare Forecasting Systems Authors: Leka, K. D.; Park, Sung-Hong; Kusano, Kanya; Andries, Jesse; Barnes, Graham; Bingham, Suzy; Bloomfield, D. Shaun; McCloskey, Aoife E.; Delouille, Veronique; Falconer, David; Gallagher, Peter T.; Georgoulis, Manolis K.; Kubo, Yuki; Lee, Kangjin; Lee, Sangwoo; Lobzin, Vasily; Mun, JunChul; Murray, Sophie A.; Hamad Nageem, Tarek A. M.; Qahwaji, Rami; Sharpe, Michael; Steenburgh, Robert A.; Steward, Graham; Terkildsen, Michael Bibcode: 2019ApJ...881..101L Altcode: 2019arXiv190702909L A workshop was recently held at Nagoya University (2017 October 31-November 2), sponsored by the Center for International Collaborative Research, at the Institute for Space-Earth Environmental Research, Nagoya University, Japan, to quantitatively compare the performance of today’s operational solar flare forecasting facilities. Building upon Paper I of this series, in Paper II we described the participating methods for this latest comparison effort, the evaluation methodology, and presented quantitative comparisons. In this paper, we focus on the behavior and performance of the methods when evaluated in the context of broad implementation differences. Acknowledging the short testing interval available and the small number of methods available, we do find that forecast performance: (1) appears to improve by including persistence or prior flare activity, region evolution, and a human “forecaster in the loop” (2) is hurt by restricting data to disk-center observations; (3) may benefit from long-term statistics but mostly when then combined with modern data sources and statistical approaches. These trends are arguably weak and must be viewed with numerous caveats, as discussed both here and in Paper II. Following this present work, in Paper IV (Park et al. 2019) we will present a novel analysis method to evaluate temporal patterns of forecasting errors of both types (i.e., misses and false alarms). Hence, most importantly, with this series of papers, we demonstrate the techniques for facilitating comparisons in the interest of establishing performance-positive methodologies. Title: A Comparison of Flare Forecasting Methods. II. Benchmarks, Metrics, and Performance Results for Operational Solar Flare Forecasting Systems Authors: Leka, K. D.; Park, Sung-Hong; Kusano, Kanya; Andries, Jesse; Barnes, Graham; Bingham, Suzy; Bloomfield, D. Shaun; McCloskey, Aoife E.; Delouille, Veronique; Falconer, David; Gallagher, Peter T.; Georgoulis, Manolis K.; Kubo, Yuki; Lee, Kangjin; Lee, Sangwoo; Lobzin, Vasily; Mun, JunChul; Murray, Sophie A.; Hamad Nageem, Tarek A. M.; Qahwaji, Rami; Sharpe, Michael; Steenburgh, Robert A.; Steward, Graham; Terkildsen, Michael Bibcode: 2019ApJS..243...36L Altcode: 2019arXiv190702905L Solar flares are extremely energetic phenomena in our solar system. Their impulsive and often drastic radiative increases, particularly at short wavelengths, bring immediate impacts that motivate solar physics and space weather research to understand solar flares to the point of being able to forecast them. As data and algorithms improve dramatically, questions must be asked concerning how well the forecasting performs; crucially, we must ask how to rigorously measure performance in order to critically gauge any improvements. Building upon earlier-developed methodology of Paper I (Barnes et al. 2016), international representatives of regional warning centers and research facilities assembled in 2017 at the Institute for Space-Earth Environmental Research, Nagoya University, Japan to, for the first time, directly compare the performance of operational solar flare forecasting methods. Multiple quantitative evaluation metrics are employed, with the focus and discussion on evaluation methodologies given the restrictions of operational forecasting. Numerous methods performed consistently above the “no-skill” level, although which method scored top marks is decisively a function of flare event definition and the metric used; there was no single winner. Following in this paper series, we ask why the performances differ by examining implementation details (Leka et al. 2019), and then we present a novel analysis method to evaluate temporal patterns of forecasting errors in Paper IV (Park et al. 2019). With these works, this team presents a well-defined and robust methodology for evaluating solar flare forecasting methods in both research and operational frameworks and today’s performance benchmarks against which improvements and new methods may be compared. Title: Solar Flare Forecasting from Magnetic Feature Properties Generated by the Solar Monitor Active Region Tracker Authors: Domijan, Katarina; Bloomfield, D. Shaun; Pitié, François Bibcode: 2019SoPh..294....6D Altcode: We study the predictive capabilities of magnetic-feature properties (MF) generated by the Solar Monitor Active Region Tracker (SMART: Higgins et al. in Adv. Space Res.47, 2105, 2011) for solar-flare forecasting from two datasets: the full dataset of SMART detections from 1996 to 2010 which has been previously studied by Ahmed et al. (Solar Phys.283, 157, 2013) and a subset of that dataset that only includes detections that are NOAA active regions (ARs). The main contributions of this work are: we use marginal relevance as a filter feature selection method to identify the most useful SMART MF properties for separating flaring from non-flaring detections and logistic regression to derive classification rules to predict future observations. For comparison, we employ a Random Forest, Support Vector Machine, and a set of Deep Neural Network models, as well as lasso for feature selection. Using the linear model with three features we obtain significantly better results (True Skill Score: TSS = 0.84) than those reported by Ahmed et al. (Solar Phys.283, 157, 2013) for the full dataset of SMART detections. The same model produced competitive results (TSS = 0.67) for the dataset of SMART detections that are NOAA ARs, which can be compared to a broader section of flare-forecasting literature. We show that more complex models are not required for this data. Title: Solar flare forecasting from magnetic feature properties generated by Solar Monitor Active Region Tracker Authors: Domijan, Katarina; Bloomfield, D. Shaun; Pitie, Francois Bibcode: 2018arXiv181202652D Altcode: We study the predictive capabilities of magnetic feature properties (MF) generated by Solar Monitor Active Region Tracker (SMART) for solar flare forecasting from two datasets: the full dataset of SMART detections from 1996 to 2010 that has been previously studied by Ahmed et al. (2011) and a subset of that dataset which only includes detections that are NOAA active regions (ARs). Main contributions: we use marginal relevance as a filter feature selection method to identify most useful SMART MF properties for separating flaring from non-flaring detections and logistic regression to derive classification rules to predict future observations. For comparison, we employ a Random Forest, Support Vector Machine and a set of Deep Neural Network models, as well as Lasso for feature selection. Using the linear model with three features we obtain significantly better results (TSS=0.84) to those reported by Ahmed et al.(2011) for the full dataset of SMART detections. The same model produced competitive results (TSS=0.67) for the dataset of SMART detections that are NOAA ARs which can be compared to a broader section of flare forecasting literature. We show that more complex models are not required for this data. Title: Photospheric Shear Flows in Solar Active Regions and Their Relation to Flare Occurrence Authors: Park, Sung-Hong; Guerra, Jordan A.; Gallagher, Peter T.; Georgoulis, Manolis K.; Bloomfield, D. Shaun Bibcode: 2018SoPh..293..114P Altcode: 2018arXiv180707714P Solar active regions (ARs) that produce major flares typically exhibit strong plasma shear flows around photospheric magnetic polarity inversion lines (MPILs). It is therefore important to quantitatively measure such photospheric shear flows in ARs for a better understanding of their relation to flare occurrence. Photospheric flow fields were determined by applying the Differential Affine Velocity Estimator for Vector Magnetograms (DAVE4VM) method to a large data set of 2548 coaligned pairs of AR vector magnetograms with 12-min separation over the period 2012 - 2016. From each AR flow-field map, three shear-flow parameters were derived corresponding to the mean («S »), maximum (Smax) and integral (Ssum) shear-flow speeds along strong-gradient, strong-field MPIL segments. We calculated flaring rates within 24 h as a function of each shear-flow parameter and we investigated the relation between the parameters and the waiting time (τ ) until the next major flare (class M1.0 or above) after the parameter observation. In general, it is found that the larger Ssum an AR has, the more likely it is for the AR to produce flares within 24 h. It is also found that among ARs which produce major flares, if one has a larger value of Ssum then τ generally gets shorter. These results suggest that large ARs with widespread and/or strong shear flows along MPILs tend to not only be more flare productive, but also produce major flares within 24 h or less. Title: Flare forecasting using the evolution of McIntosh sunspot classifications Authors: McCloskey, Aoife E.; Gallagher, Peter T.; Bloomfield, D. Shaun Bibcode: 2018JSWSC...8A..34M Altcode: 2018arXiv180500919M Most solar flares originate in sunspot groups, where magnetic field changes lead to energy build-up and release. However, few flare-forecasting methods use information of sunspot-group evolution, instead focusing on static point-in-time observations. Here, a new forecast method is presented based upon the 24-h evolution in McIntosh classification of sunspot groups. Evolution-dependent ≥C1.0 and ≥M1.0 flaring rates are found from NOAA-numbered sunspot groups over December 1988-June 1996 (Solar Cycle 22; SC22) before converting to probabilities assuming Poisson statistics. These flaring probabilities are used to generate operational forecasts for sunspot groups over July 1996-December 2008 (SC23), with performance studied by verification metrics. Major findings are: (i) considering Brier skill score (BSS) for ≥C1.0 flares, the evolution-dependent McIntosh-Poisson method (BSSevolution = 0.09) performs better than the static McIntosh-Poisson method (BSSstatic = - 0.09); (ii) low BSS values arise partly from both methods over-forecasting SC23 flares from the SC22 rates, symptomatic of ≥C1.0 rates in SC23 being on average ≈80% of those in SC22 (with ≥M1.0 being ≈50%); (iii) applying a bias-correction factor to reduce the SC22 rates used in forecasting SC23 flares yields modest improvement in skill relative to climatology for both methods (BSSstaticcorr = 0.09 and BSSevolutioncorr = 0.0.20) and improved forecast reliability diagrams. Title: Forecasting Solar Flares Using Magnetogram-based Predictors and Machine Learning Authors: Florios, Kostas; Kontogiannis, Ioannis; Park, Sung-Hong; Guerra, Jordan A.; Benvenuto, Federico; Bloomfield, D. Shaun; Georgoulis, Manolis K. Bibcode: 2018SoPh..293...28F Altcode: 2018arXiv180105744F We propose a forecasting approach for solar flares based on data from Solar Cycle 24, taken by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) mission. In particular, we use the Space-weather HMI Active Region Patches (SHARP) product that facilitates cut-out magnetograms of solar active regions (AR) in the Sun in near-realtime (NRT), taken over a five-year interval (2012 - 2016). Our approach utilizes a set of thirteen predictors, which are not included in the SHARP metadata, extracted from line-of-sight and vector photospheric magnetograms. We exploit several machine learning (ML) and conventional statistics techniques to predict flares of peak magnitude >M1 and >C1 within a 24 h forecast window. The ML methods used are multi-layer perceptrons (MLP), support vector machines (SVM), and random forests (RF). We conclude that random forests could be the prediction technique of choice for our sample, with the second-best method being multi-layer perceptrons, subject to an entropy objective function. A Monte Carlo simulation showed that the best-performing method gives accuracy ACC =0.93 (0.00 ), true skill statistic TSS =0.74 (0.02 ), and Heidke skill score HSS =0.49 (0.01 ) for >M1 flare prediction with probability threshold 15% and ACC =0.84 (0.00 ), TSS =0.60 (0.01 ), and HSS =0.59 (0.01 ) for >C1 flare prediction with probability threshold 35%. Title: Active Region Photospheric Magnetic Properties Derived from Line-of-Sight and Radial Fields Authors: Guerra, J. A.; Park, S. -H.; Gallagher, P. T.; Kontogiannis, I.; Georgoulis, M. K.; Bloomfield, D. S. Bibcode: 2018SoPh..293....9G Altcode: 2017arXiv171206902G The effect of using two representations of the normal-to-surface magnetic field to calculate photospheric measures that are related to the active region (AR) potential for flaring is presented. Several AR properties were computed using line-of-sight (Blos) and spherical-radial (Br) magnetograms from the Space-weather HMI Active Region Patch (SHARP) products of the Solar Dynamics Observatory, characterizing the presence and features of magnetic polarity inversion lines, fractality, and magnetic connectivity of the AR photospheric field. The data analyzed correspond to ≈4 ,000 AR observations, achieved by randomly selecting 25% of days between September 2012 and May 2016 for analysis at 6-hr cadence. Results from this statistical study include: i) the Br component results in a slight upwards shift of property values in a manner consistent with a field-strength underestimation by the Blos component; ii) using the Br component results in significantly lower inter-property correlation in one-third of the cases, implying more independent information as regards the state of the AR photospheric magnetic field; iii) flaring rates for each property vary between the field components in a manner consistent with the differences in property-value ranges resulting from the components; iv) flaring rates generally increase for higher values of properties, except the Fourier spectral power index that has flare rates peaking around a value of 5 /3 . These findings indicate that there may be advantages in using Br rather than Blos in calculating flare-related AR magnetic properties, especially for regions located far from central meridian. Title: The Next Level in Automated Solar Flare Forecasting: the EU FLARECAST Project Authors: Georgoulis, M. K.; Bloomfield, D.; Piana, M.; Massone, A. M.; Gallagher, P.; Vilmer, N.; Pariat, E.; Buchlin, E.; Baudin, F.; Csillaghy, A.; Soldati, M.; Sathiapal, H.; Jackson, D.; Alingery, P.; Argoudelis, V.; Benvenuto, F.; Campi, C.; Florios, K.; Gontikakis, C.; Guennou, C.; Guerra, J. A.; Kontogiannis, I.; Latorre, V.; Murray, S.; Park, S. H.; Perasso, A.; Sciacchitano, F.; von Stachelski, S.; Torbica, A.; Vischi, D. Bibcode: 2017AGUFMSA21C..07G Altcode: We attempt an informative description of the Flare Likelihood And Region Eruption Forecasting (FLARECAST) project, European Commission's first large-scale investment to explore the limits of reliability and accuracy achieved for the forecasting of major solar flares. We outline the consortium, top-level objectives and first results of the project, highlighting the diversity and fusion of expertise needed to deliver what was promised. The project's final product, featuring an openly accessible, fully modular and free to download flare forecasting facility will be delivered in early 2018. The project's three objectives, namely, science, research-to-operations and dissemination / communication, are also discussed: in terms of science, we encapsulate our close-to-final assessment on how close (or far) are we from a practically exploitable solar flare forecasting. In terms of R2O, we briefly describe the architecture of the FLARECAST infrastructure that includes rigorous validation for each forecasting step. From the three different communication levers of the project we finally focus on lessons learned from the two-way interaction with the community of stakeholders and governmental organizations. The FLARECAST project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 640216. Title: Understanding the Physical Nature of Coronal "EIT Waves" Authors: Long, D. M.; Bloomfield, D. S.; Chen, P. F.; Downs, C.; Gallagher, P. T.; Kwon, R. -Y.; Vanninathan, K.; Veronig, A. M.; Vourlidas, A.; Vršnak, B.; Warmuth, A.; Žic, T. Bibcode: 2017SoPh..292....7L Altcode: 2016arXiv161105505L For almost 20 years the physical nature of globally propagating waves in the solar corona (commonly called "EIT waves") has been controversial and subject to debate. Additional theories have been proposed over the years to explain observations that did not agree with the originally proposed fast-mode wave interpretation. However, the incompatibility of observations made using the Extreme-ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory with the fast-mode wave interpretation was challenged by differing viewpoints from the twin Solar Terrestrial Relations Observatory spacecraft and data with higher spatial and temporal resolution from the Solar Dynamics Observatory. In this article, we reexamine the theories proposed to explain EIT waves to identify measurable properties and behaviours that can be compared to current and future observations. Most of us conclude that the so-called EIT waves are best described as fast-mode large-amplitude waves or shocks that are initially driven by the impulsive expansion of an erupting coronal mass ejection in the low corona. Title: Solar Magnetic Data Analysis for the FLARECAST Project Authors: Guerra, J. A.; Park, S. H.; Kontogiannis, I.; Bloomfield, D.; Gallagher, P.; Georgoulis, M. K. Bibcode: 2016AGUFMSH11C2234G Altcode: The Flare Likelihood And Region Eruption foreCASTing (FLARECAST) project is an EU H2020-funded consortium project aiming to develop an advanced solar flare forecasting system by implementing state-of-the-art solar data analysis and flare prediction algorithms. The Solar Physics Group at Trinity College Dublin is in charge of the analysis of observational data to extract solar active region properties that serve as input for the prediction algorithms. The calculated active region properties correspond to a non-exhaustive list of parameters that have demonstrated a strong flare association, such as Schrijver's R-value, the Fourier power spectrum exponent, the effective connected magnetic field (Beff), the horizontal field decay index, and the weighted length of strong-gradient polarity inversion lines (WLSG). Parameters were calculated from Spaceweather HMI Active Region Patch (SHARP) magnetograms, a data product of the Helioseismic and Magnetic Imager (HMI) magnetograph on the Solar Dynamics Observatory (SDO). SHARPs provide photospheric vector-magnetic field (B) images in near-realtime. For this study, results from a statistical study performed on a robust subsample of the entire SHARP dataset will be presented. In the framework of the FLARECAST predictor component, this study focuses, for the first time, on differences between parameter values found when the radial magnetic field component, Br, is used instead of the line-of-sight component, Blos. The effect of active region longitudinal position is discussed, as well as the flare association of the properties. Title: Community-wide space weather Scoreboards: Facilitating the Validation of Real-time CME, Flare, and SEP Forecasts Authors: Mullinix, R.; Mays, M. L.; Kuznetsova, M. M.; Andries, J.; Bingham, S.; Bloomfield, D.; Boblitt, J. M.; Crosby, N. B.; Dierckxsens, M.; Guerra, J. A.; Leka, K. D.; Marsh, M. S.; Murray, S.; Wiegand, C. Bibcode: 2016AGUFMSH11C2256M Altcode: Confidence assessment of predictive space weather models ultimately determines the value of forecasts for end users. Testing predictive capabilities before event onset is important and especially relevant for validating space weather models. This poster presents three real-time forecast validation projects facilitated by the CCMC via forecast collection "scoreboards": (1) CME arrival time and geomagnetic storm strength, (2) flare occurrence probability, and (3) SEP onset, duration, peak flux, probability, and overall profile. The CME, Flare, and SEP scoreboards enable world-wide community involvement in real-time predictions, foster community validation projects, and ultimately help researchers improve their CME, flare, and SEP forecasts. All CME, Flare, SEP forecast modelers and experts worldwide are invited to advise or participate in this effort. The flare and SEP systems are automated such that model developers can routinely upload their predictions to an anonymous ftp and the data is accessible to anyone via an API. The "CME arrival time scoreboard" (https://kauai.ccmc.gsfc.nasa.gov/CMEscoreboard/) provides a central location for the community to: submit their CME arrival time forecast in real-time, quickly view all forecasts at once in real-time, and compare forecasting methods when the event has arrived. There are currently 19 registered CME arrival time prediction methods. The "Flare Scoreboard" (http://ccmc.gsfc.nasa.gov/challenges/flare.php) project is led by the UK Met Office.The full disk and active region flare forecasts can currently be viewed on an interactive display overlaid on an SDO/AIA or HMI image of the Sun and will be dynamically paired with a display of flare probability time series (coming soon). The "SEP Scoreboard" (http://ccmc.gsfc.nasa.gov/challenges/sep.php) project is led by BIRA-IASB and the UK Met Office. SEP forecasts can be roughly divided into three categories: continuous/Probabilistic, solar event triggered, non near real-time. The SEP scoreboard will focus on real-time forecasts, however the SEP scoreboard team can also coordinate a set of historical events for a "SEP challenge" with different models, particularly those physics-based models in the third category that are not ready or relevant for real-time modeling. Title: Exploring Coronal Dynamics: A Next Generation Solar Physics Mission white paper Authors: Morton, R. J.; Scullion, E.; Bloomfield, D. S.; McLaughlin, J. A.; Regnier, S.; McIntosh, S. W.; Tomczyk, S.; Young, P. Bibcode: 2016arXiv161106149M Altcode: Determining the mechanisms responsible for the heating of the coronal plasma and maintaining and accelerating the solar wind are long standing goals in solar physics. There is a clear need to constrain the energy, mass and momentum flux through the solar corona and advance our knowledge of the physical process contributing to these fluxes. Furthermore, the accurate forecasting of Space Weather conditions at the near-Earth environment and, more generally, the plasma conditions of the solar wind throughout the heliosphere, require detailed knowledge of these fluxes in the near-Sun corona. Here we present a short case for a space-based imaging-spectrometer coronagraph, which will have the ability to provide synoptic information on the coronal environment and provide strict constraints on the mass, energy, and momentum flux through the corona. The instrument would ideally achieve cadences of $\sim10$~s, spatial resolution of 1" and observe the corona out to 2~$R_{\sun}$. Such an instrument will enable significant progress in our understanding of MHD waves throughout complex plasmas, as well as potentially providing routine data products to aid Space Weather forecasting. Title: A Comparison of Flare Forecasting Methods. I. Results from the “All-Clear” Workshop Authors: Barnes, G.; Leka, K. D.; Schrijver, C. J.; Colak, T.; Qahwaji, R.; Ashamari, O. W.; Yuan, Y.; Zhang, J.; McAteer, R. T. J.; Bloomfield, D. S.; Higgins, P. A.; Gallagher, P. T.; Falconer, D. A.; Georgoulis, M. K.; Wheatland, M. S.; Balch, C.; Dunn, T.; Wagner, E. L. Bibcode: 2016ApJ...829...89B Altcode: 2016arXiv160806319B Solar flares produce radiation that can have an almost immediate effect on the near-Earth environment, making it crucial to forecast flares in order to mitigate their negative effects. The number of published approaches to flare forecasting using photospheric magnetic field observations has proliferated, with varying claims about how well each works. Because of the different analysis techniques and data sets used, it is essentially impossible to compare the results from the literature. This problem is exacerbated by the low event rates of large solar flares. The challenges of forecasting rare events have long been recognized in the meteorology community, but have yet to be fully acknowledged by the space weather community. During the interagency workshop on “all clear” forecasts held in Boulder, CO in 2009, the performance of a number of existing algorithms was compared on common data sets, specifically line-of-sight magnetic field and continuum intensity images from the Michelson Doppler Imager, with consistent definitions of what constitutes an event. We demonstrate the importance of making such systematic comparisons, and of using standard verification statistics to determine what constitutes a good prediction scheme. When a comparison was made in this fashion, no one method clearly outperformed all others, which may in part be due to the strong correlations among the parameters used by different methods to characterize an active region. For M-class flares and above, the set of methods tends toward a weakly positive skill score (as measured with several distinct metrics), with no participating method proving substantially better than climatological forecasts. Title: Understanding the Physical Nature of Coronal "EIT Waves" Authors: Long, D. M.; Bloomfield, D. S.; Chen, P. -F.; Downs, C.; Gallagher, P. T.; Kwon, R. -Y.; Vanninathan, K.; Veronig, A.; Vourlidas, A.; Vrsnak, B.; Warmuth, A.; Zic, T. Bibcode: 2016usc..confE..24L Altcode: For almost 20 years the physical nature of globally-propagating waves in the solar corona (commonly called "EIT waves") has been controversial and subject to debate. Additional theories have been proposed throughout the years to explain observations that did not fit with the originally proposed fast-mode wave interpretation. However, the incompatibility of observations made using the Extreme-ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observatory with the fast-mode wave interpretation have been challenged by differing viewpoints from the Solar Terrestrial Relations Observatory spacecraft and higher spatial/temporal resolution data from the Solar Dynamics Observatory. In this paper, we reexamine the theories proposed to explain "EIT waves" to identify measurable properties and behaviours that can be compared to current and future observations. Most of us conclude that "EIT waves" are best described as fast-mode large-amplitude waves/shocks, which are initially driven by the impulsive expansion of an erupting coronal mass ejection in the low corona. Title: Flaring Rates and the Evolution of Sunspot Group McIntosh Classifications Authors: McCloskey, Aoife E.; Gallagher, Peter T.; Bloomfield, D. Shaun Bibcode: 2016SoPh..291.1711M Altcode: 2016arXiv160700903M; 2016SoPh..tmp..116M Sunspot groups are the main source of solar flares, with the energy to power them being supplied by magnetic-field evolution (e.g. flux emergence or twisting/shearing). To date, few studies have investigated the statistical relation between sunspot-group evolution and flaring, with none considering evolution in the McIntosh classification scheme. Here we present a statistical analysis of sunspot groups from Solar Cycle 22, focusing on 24-hour changes in the three McIntosh classification components. Evolution-dependent ≥C 1.0 , ≥M 1.0 , and ≥X 1.0 flaring rates are calculated, leading to the following results: i) flaring rates become increasingly higher for greater degrees of upward evolution through the McIntosh classes, with the opposite found for downward evolution; ii) the highest flaring rates are found for upward evolution from larger, more complex, classes (e.g. Zurich D- and E-classes evolving upward to F-class produce ≥C 1.0 rates of 2.66 ±0.28 and 2.31 ±0.09 flares per 24 hours, respectively); iii) increasingly complex classes give higher rates for all flare magnitudes, even when sunspot groups do not evolve over 24 hours. These results support the hypothesis that injection of magnetic energy by flux emergence (i.e. increasing in Zurich or compactness classes) leads to a higher frequency and magnitude of flaring. Title: Enabling Solar Flare Forecasting at an Unprecedented Level: the FLARECAST Project Authors: Georgoulis, Manolis K.; Pariat, Etienne; Massone, Anna Maria; Vilmer, Nicole; Jackson, David; Buchlin, Eric; Csillaghy, Andre; Bommier, Veronique; Kontogiannis, Ioannis; Gallagher, Peter; Gontikakis, Costis; Guennou, Chloé; Murray, Sophie; Bloomfield, D. Shaun; Alingery, Pablo; Baudin, Frederic; Benvenuto, Federico; Bruggisser, Florian; Florios, Konstantinos; Guerra, Jordan; Park, Sung-Hong; Perasso, Annalisa; Piana, Michele; Sathiapal, Hanna; Soldati, Marco; Von Stachelski, Samuel; Argoudelis, Vangelis; Caminade, Stephane Bibcode: 2016cosp...41E.657G Altcode: We attempt a brief but informative description of the Flare Likelihood And Region Eruption Forecasting (FLARECAST) project, European Commission's first large-scale investment to explore the limits of reliability and accuracy for the forecasting of major solar flares. The consortium, objectives, and first results of the project - featuring an openly accessible, interactive flare forecasting facility by the end of 2017 - will be outlined. In addition, we will refer to the so-called "explorative research" element of project, aiming to connect solar flares with coronal mass ejections (CMEs) and possibly pave the way for CME, or eruptive flare, prediction. We will also emphasize the FLARECAST modus operandi, namely the diversity of expertise within the consortium that independently aims to science, infrastructure development and dissemination, both to stakeholders and to the general public. Concluding, we will underline that the FLARECAST project responds squarely to the joint COSPAR - ILWS Global Roadmap to shield society from the adversities of space weather, addressing its primary goal and, in particular, its Research Recommendations 1, 2 and 4, Teaming Recommendations II and III, and Collaboration Recommendations A, B, and D. The FLARECAST project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 640216. Title: Conditions for electron-cyclotron maser emission in the solar corona Authors: Morosan, D. E.; Zucca, P.; Bloomfield, D. S.; Gallagher, P. T. Bibcode: 2016A&A...589L...8M Altcode: 2016arXiv160404788M Context. The Sun is an active source of radio emission ranging from long duration radio bursts associated with solar flares and coronal mass ejections to more complex, short duration radio bursts such as solar S bursts, radio spikes and fibre bursts. While plasma emission is thought to be the dominant emission mechanism for most radio bursts, the electron-cyclotron maser (ECM) mechanism may be responsible for more complex, short-duration bursts as well as fine structures associated with long-duration bursts.
Aims: We investigate the conditions for ECM in the solar corona by considering the ratio of the electron plasma frequency ωp to the electron-cyclotron frequency Ωe. The ECM is theoretically possible when ωp/ Ωe< 1.
Methods: Two-dimensional electron density, magnetic field, plasma frequency, and electron cyclotron frequency maps of the off-limb corona were created using observations from SDO/AIA and SOHO/LASCO, together with potential field extrapolations of the magnetic field. These maps were then used to calculate ωp/Ωe and Alfvén velocity maps of the off-limb corona.
Results: We found that the condition for ECM emission (ωp/ Ωe< 1) is possible at heights <1.07 R⊙ in an active region near the limb; that is, where magnetic field strengths are >40 G and electron densities are >3 × 108 cm-3. In addition, we found comparatively high Alfvén velocities (>0.02c or >6000 km s-1) at heights <1.07 R⊙ within the active region.
Conclusions: This demonstrates that the condition for ECM emission is satisfied within areas of the corona containing large magnetic fields, such as the core of a large active region. Therefore, ECM could be a possible emission mechanism for high-frequency radio and microwave bursts. Title: Performance of Major Flare Watches from the Max Millennium Program (2001 - 2010) Authors: Bloomfield, D. S.; Gallagher, P. T.; Marquette, W. H.; Milligan, R. O.; Canfield, R. C. Bibcode: 2016SoPh..291..411B Altcode: 2015arXiv151204518B; 2016SoPh..tmp....1B The physical processes that trigger solar flares are not well understood, and significant debate remains around processes governing particle acceleration, energy partition, and particle and energy transport. Observations at high resolution in energy, time, and space are required in multiple energy ranges over the whole course of many flares to build an understanding of these processes. Obtaining high-quality, co-temporal data from ground- and space- based instruments is crucial to achieving this goal and was the primary motivation for starting the Max Millennium program and Major Flare Watch (MFW) alerts, aimed at coordinating observations of all flares ≥ X1 GOES X-ray classification (including those partially occulted by the limb). We present a review of the performance of MFWs from 1 February 2001 to 31 May 2010, inclusive, which finds that (1) 220 MFWs were issued in 3407 days considered (6.5 % duty cycle), with these occurring in 32 uninterrupted periods that typically last 2 - 8 days; (2) 56% of flares ≥ X1 were caught, occurring in 19 % of MFW days; (3) MFW periods ended at suitable times, but substantial gain could have been achieved in percentage of flares caught if periods had started 24 h earlier; (4) MFWs successfully forecast X-class flares with a true skill statistic (TSS) verification metric score of 0.500, that is comparable to a categorical flare/no-flare interpretation of the NOAA Space Weather Prediction Centre probabilistic forecasts (TSS = 0.488). Title: CorPITA: An Automated Algorithm for the Identification and Analysis of Coronal "EIT Waves" Authors: Long, D. M.; Bloomfield, D. S.; Gallagher, P. T.; Pérez-Suárez, D. Bibcode: 2014SoPh..289.3279L Altcode: 2014arXiv1403.6722L; 2014SoPh..tmp...66L The continuous stream of data available from the Atmospheric Imaging Assembly (AIA) telescopes onboard the Solar Dynamics Observatory (SDO) spacecraft has allowed a deeper understanding of the Sun. However, the sheer volume of data has necessitated the development of automated techniques to identify and analyse various phenomena. In this article, we describe the Coronal Pulse Identification and Tracking Algorithm (CorPITA) for the identification and analysis of coronal "EIT waves". CorPITA uses an intensity-profile technique to identify the propagating pulse, tracking it throughout its evolution before returning estimates of its kinematics. The algorithm is applied here to a data set from February 2011, allowing its capabilities to be examined and critiqued. This algorithm forms part of the SDO Feature Finding Team initiative and will be implemented as part of the Heliophysics Event Knowledgebase (HEK). This is the first fully automated algorithm to identify and track the propagating "EIT wave" rather than any associated phenomenon and will allow a deeper understanding of this controversial phenomenon. Title: A study of sympathetic eruptions using the Heliophysics Events Knowledgebase Authors: Higgins, Paul A.; Schrijver, Carolus J.; Title, Alan M.; Bloomfield, D. Shaun; Gallagher, Peter T Bibcode: 2014AAS...22412316H Altcode: Over the past few decades there have been a number of papers investigating the connection between flares occurring in succession. Statistically, any connection that affects the timing of successive flares that exists is found to be weak. However, the majority of previous investigations has been limited by only considering the causal connection between soft X-ray flares. More recent case studies have shown convincing evidence that large eruptions cause a global reorganization of overlying magnetic fields that can result in the eruption of both flares and filaments at large distances from the original event. In this work, the connection between GOES X-ray flares (C-, M-, and X-class) and filament eruptions occurring in succession in two different active regions is considered statistically. The filament eruptions are recorded in the Heliophysics Events Knowledgebase by observers using SDO/AIA data. A significant causal connection is found between the two event types, such that large flares are followed by filament eruptions within 24 hours much more often than they are preceded by filament eruptions. This stipulates that the flares either cause the filaments to erupt or affect the eruption timing such that the filament eruptions follow the flares more closely in time. Title: The formation heights of coronal shocks from 2D density and Alfvén speed maps Authors: Zucca, Pietro; Carley, Eoin P.; Bloomfield, D. Shaun; Gallagher, Peter T. Bibcode: 2014A&A...564A..47Z Altcode: 2014arXiv1402.4051Z Context. Super-Alfvénic shocks associated with coronal mass ejections (CMEs) can produce radio emission known as Type II bursts. In the absence of direct imaging, accurate estimates of coronal electron densities, magnetic field strengths, and Alfvén speeds are required to calculate the kinematics of shocks. To date, 1D radial models have been used, but these are not appropriate for shocks propagating in non-radial directions.
Aims: Here, we study a coronal shock wave associated with a CME and Type II radio burst using 2D electron density and Alfvén speed maps to determine the locations that shocks are excited as the CME expands through the corona.
Methods: Coronal density maps were obtained from emission measures derived from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) and polarized brightness measurements from the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO). Alfvén speed maps were calculated using these density maps and magnetic field extrapolations from the Helioseismic and Magnetic Imager (SDO/HMI). The computed density and Alfvén speed maps were then used to calculate the shock kinematics in non-radial directions.
Results: Using the kinematics of the Type II burst and associated shock, we find our observations to be consistent with the formation of a shock located at the CME flanks where the Alfvén speed has a local minimum.
Conclusions: The 1D density models are not appropriate for shocks that propagate non-radially along the flanks of a CME. Rather, the 2D density, magnetic field and Alfvén speed maps described here give a more accurate method for determining the fundamental properties of shocks and their relation to CMEs. Title: Quasiperiodic acceleration of electrons by a plasmoid-driven shock in the solar atmosphere Authors: Carley, Eoin P.; Long, David M.; Byrne, Jason P.; Zucca, Pietro; Bloomfield, D. Shaun; McCauley, Joseph; Gallagher, Peter T. Bibcode: 2013NatPh...9..811C Altcode: 2014arXiv1406.0743C Cosmic rays and solar energetic particles may be accelerated to relativistic energies by shock waves in astrophysical plasmas. On the Sun, shocks and particle acceleration are often associated with the eruption of magnetized plasmoids, called coronal mass ejections (CMEs). However, the physical relationship between CMEs and shock particle acceleration is not well understood. Here, we use extreme ultraviolet, radio and white-light imaging of a solar eruptive event on 22 September 2011 to show that a CME-induced shock (Alfvén Mach number ) was coincident with a coronal wave and an intense metric radio burst generated by intermittent acceleration of electrons to kinetic energies of 2-46keV (0.1-0.4c). Our observations show that plasmoid-driven quasiperpendicular shocks are capable of producing quasiperiodic acceleration of electrons, an effect consistent with a turbulent or rippled plasma shock surface. Title: The Bursty Nature of Solar Flare X-Ray Emission. II. The Neupert Effect Authors: McAteer, R. T. James; Bloomfield, D. Shaun Bibcode: 2013ApJ...776...66M Altcode: We carry out a novel statistical test of the Neupert effect based on multifractal spectra. The multifractal spectrum is the number distribution of the strengths (i.e., the Hölder exponents) of bursts in a signal. This is tested on simulations and carried out on RHESSI X-ray data from a well observed GOES X4.8 magnitude flare. The multifractal spectra is ideally suited to quantifying the relative smooth and bursty signals typically found in (thermal) soft X-ray and (non-thermal) hard X-ray data of solar flares. We show that light curves from all energies between 3 keV and 25 keV are statistically similar, suggesting that all these signals are dominated by the same (presumably thermal) emission. Emission lying between 25 keV and 100 keV probably contains some contribution from both thermal and non-thermal sources. The multifractal spectrum of a signal and that of its (cumulative) temporal integration are statistically similar (i.e., low residuals upon subtraction), but shifted by one in the peak Hölder exponent. We find the pairs of 3-6 keV and 100-300 keV emissions, the 6-12 keV and 100-300 keV emissions and the 12-25 keV and 100-300 keV emissions are all consistent with the Neupert effect. The best agreement with the Neupert effect is between the 12-25 keV and 100-300 keV pair, although possibly with some secondary source of thermal emission present. Title: Oscillatory Behavior in the Corona Authors: Calabro, B.; McAteer, R. T. J.; Bloomfield, D. S. Bibcode: 2013SoPh..286..405C Altcode: We detect and analyze the oscillatory behavior of waves using a coronal seismology tool on sequences of coronal images. We study extreme-ultraviolet image sequences of active and quiet Sun regions and of coronal holes we identify 3- and 5-minute periodicities. In each studied region the 3- and 5-minute periodicities are similarly frequent. The number of pixels exhibiting a 3-minute periodicity is between 6 % - 8 % and those pixels exhibiting a 5-minute periodicity is between 5 % - 9 % of the total number of observed pixels. Our results show 3-minute oscillations along coronal loop structures but do not show 5-minute oscillations along these same loop structures. The number of pixels exhibiting 3- and 5-minute periodicities in one type of region (active Sun, quiet Sun, and coronal holes) is roughly the same for all observed regions, leading us to infer that the 3- and 5-minute oscillations are the result of a global mechanism. Title: Improved methods for determining the kinematics of coronal mass ejections and coronal waves Authors: Byrne, J. P.; Long, D. M.; Gallagher, P. T.; Bloomfield, D. S.; Maloney, S. A.; McAteer, R. T. J.; Morgan, H.; Habbal, S. R. Bibcode: 2013A&A...557A..96B Altcode: 2013arXiv1307.8155B Context. The study of solar eruptive events and associated phenomena is of great importance in the context of solar and heliophysics. Coronal mass ejections (CMEs) and coronal waves are energetic manifestations of the restructuring of the solar magnetic field and mass motion of the plasma. Characterising this motion is vital for deriving the dynamics of these events and thus understanding the physics driving their initiation and propagation. The development and use of appropriate methods for measuring event kinematics is therefore imperative.
Aims: Traditional approaches to the study of CME and coronal wave kinematics do not return wholly accurate nor robust estimates of the true event kinematics and associated uncertainties. We highlight the drawbacks of these approaches, and demonstrate improved methods for accurate and reliable determination of the kinematics.
Methods: The Savitzky-Golay filter is demonstrated as a more appropriate fitting technique for CME and coronal wave studies, and a residual resampling bootstrap technique is demonstrated as a statistically rigorous method for the determination of kinematic error estimates and goodness-of-fit tests.
Results: It is shown that the scatter on distance-time measurements of small sample size can significantly limit the ability to derive accurate and reliable kinematics. This may be overcome by (i) increasing measurement precision and sampling cadence; and (ii) applying robust methods for deriving the kinematics and reliably determining their associated uncertainties. If a priori knowledge exists and a pre-determined model form for the kinematics is available (or indeed any justified fitting-form to be tested against the data), then its precision can be examined using a bootstrapping technique to determine the confidence interval associated with the model/fitting parameters.
Conclusions: Improved methods for determining the kinematics of CMEs and coronal waves are demonstrated to great effect, overcoming many issues highlighted in traditional numerical differencing and error propagation techniques. Title: The SWAP EUV Imaging Telescope Part I: Instrument Overview and Pre-Flight Testing Authors: Seaton, D. B.; Berghmans, D.; Nicula, B.; Halain, J. -P.; De Groof, A.; Thibert, T.; Bloomfield, D. S.; Raftery, C. L.; Gallagher, P. T.; Auchère, F.; Defise, J. -M.; D'Huys, E.; Lecat, J. -H.; Mazy, E.; Rochus, P.; Rossi, L.; Schühle, U.; Slemzin, V.; Yalim, M. S.; Zender, J. Bibcode: 2013SoPh..286...43S Altcode: 2012SoPh..tmp..217S; 2012arXiv1208.4631S The Sun Watcher with Active Pixels and Image Processing (SWAP) is an EUV solar telescope onboard ESA's Project for Onboard Autonomy 2 (PROBA2) mission launched on 2 November 2009. SWAP has a spectral bandpass centered on 17.4 nm and provides images of the low solar corona over a 54×54 arcmin field-of-view with 3.2 arcsec pixels and an imaging cadence of about two minutes. SWAP is designed to monitor all space-weather-relevant events and features in the low solar corona. Given the limited resources of the PROBA2 microsatellite, the SWAP telescope is designed with various innovative technologies, including an off-axis optical design and a CMOS-APS detector. This article provides reference documentation for users of the SWAP image data. Title: The Projects for Onboard Autonomy (PROBA2) Science Centre: Sun Watcher Using APS Detectors and Image Processing (SWAP) and Large-Yield Radiometer (LYRA) Science Operations and Data Products Authors: Zender, J.; Berghmans, D.; Bloomfield, D. S.; Cabanas Parada, C.; Dammasch, I.; De Groof, A.; D'Huys, E.; Dominique, M.; Gallagher, P.; Giordanengo, B.; Higgins, P. A.; Hochedez, J. -F.; Yalim, M. S.; Nicula, B.; Pylyser, E.; Sanchez-Duarte, L.; Schwehm, G.; Seaton, D. B.; Stanger, A.; Stegen, K.; Willems, S. Bibcode: 2013SoPh..286...93Z Altcode: 2012SoPh..tmp..142Z The PROBA2 Science Centre (P2SC) is a small-scale science operations centre supporting the Sun observation instruments onboard PROBA2: the EUV imager Sun Watcher using APS detectors and image Processing (SWAP) and Large-Yield Radiometer (LYRA). PROBA2 is one of ESA's small, low-cost Projects for Onboard Autonomy (PROBA) and part of ESA's In-Orbit Technology Demonstration Programme. The P2SC is hosted at the Royal Observatory of Belgium, co-located with both Principal Investigator teams. The P2SC tasks cover science planning, instrument commanding, instrument monitoring, data processing, support of outreach activities, and distribution of science data products. PROBA missions aim for a high degree of autonomy at mission and system level, including the science operations centre. The autonomy and flexibility of the P2SC is reached by a set of web-based interfaces allowing the operators as well as the instrument teams to monitor quasi-continuously the status of the operations, allowing a quick reaction to solar events. In addition, several new concepts are implemented at instrument, spacecraft, and ground-segment levels allowing a high degree of flexibility in the operations of the instruments. This article explains the key concepts of the P2SC, emphasising the automation and the flexibility achieved in the commanding as well as the data-processing chain. Title: Temperature Response of the 171 Å Passband of the SWAP Imager on PROBA2, with a Comparison to TRACE, SOHO, STEREO, and SDO Authors: Raftery, Claire L.; Bloomfield, D. Shaun; Gallagher, Peter T.; Seaton, Daniel B.; Berghmans, David; De Groof, Anik Bibcode: 2013SoPh..286..111R Altcode: We calculated the temperature response of the 171 Å passbands of the Sun Watcher using APS detectors and image Processing (SWAP) instrument onboard the PRoject for OnBoard Autonomy 2 (PROBA2) satellite. These results were compared to the temperature responses of the Extreme Ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO), the Transition Region and Coronal Explorer (TRACE), the twin Extreme Ultraviolet Imagers (EUVI) onboard the Solar TErrestrial RElations Observatory (STEREO) A and B spacecraft, and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). Multiplying the wavelength-response functions for each instrument by a series of isothermal synthetic spectra and integrating over the range 165 - 195 Å produced temperature-response functions for the six instruments. Each temperature response was then multiplied by sample differential emission-measure functions for four different solar conditions. For any given plasma condition (e.g. quiet Sun, active region), it was found that the overall variation with temperature agreed remarkably well across the six instruments, although the wavelength responses for each instrument have some distinctly different features. Deviations were observed, however, when we compared the response of any one instrument to different solar conditions, particularly for the case of solar flares. Title: Measuring the Diffusion of Solar Magnetic Flux on Large Spatio-Temporal Scales Authors: Higgins, Paul Anthony; Bloomfield, D. Shaun; Gallagher, Peter T. Bibcode: 2013shin.confE..91H Altcode: We present an investigation of the large-scale flows that influence magnetic fields at the solar surface. The aim of this work is to accurately characterise the supergranular diffusion coefficient, D, that governs the dispersal rate of magnetic features in the photosphere. There is a disconnect between the measured rate of magnetic field dispersal ( 50 - 300 km2/s) and the value of D used in global simulations of solar magnetic field evolution ( 500 - 600 km2/s). We track the poleward motion of magnetic features in a latitude-time map and compare the poleward progression to a data-driven simulation that includes differential rotation, the meridional flow, and supergranular diffusion. We find that over a time scale of months, setting D = 100 km2/s matches observations, but over a time scale of years, setting D = 500 km2/s is a better match. This supports the idea that observational time scale causes the disconnect in D values, which leads us to the conclusion that the present magnetic surface flux transport model is not adequate to explain the observed evolution of the solar surface magnetic field. Title: Solar Flare Prediction Using Advanced Feature Extraction, Machine Learning, and Feature Selection Authors: Ahmed, Omar W.; Qahwaji, Rami; Colak, Tufan; Higgins, Paul A.; Gallagher, Peter T.; Bloomfield, D. Shaun Bibcode: 2013SoPh..283..157A Altcode: 2011SoPh..tmp..404A Novel machine-learning and feature-selection algorithms have been developed to study: i) the flare-prediction-capability of magnetic feature (MF) properties generated by the recently developed Solar Monitor Active Region Tracker (SMART); ii) SMART's MF properties that are most significantly related to flare occurrence. Spatiotemporal association algorithms are developed to associate MFs with flares from April 1996 to December 2010 in order to differentiate flaring and non-flaring MFs and enable the application of machine-learning and feature-selection algorithms. A machine-learning algorithm is applied to the associated datasets to determine the flare-prediction-capability of all 21 SMART MF properties. The prediction performance is assessed using standard forecast-verification measures and compared with the prediction measures of one of the standard technologies for flare-prediction that is also based on machine-learning: Automated Solar Activity Prediction (ASAP). The comparison shows that the combination of SMART MFs with machine-learning has the potential to achieve more accurate flare-prediction than ASAP. Feature-selection algorithms are then applied to determine the MF properties that are most related to flare occurrence. It is found that a reduced set of six MF properties can achieve a similar degree of prediction accuracy as the full set of 21 SMART MF properties. Title: The Coronal Pulse Identification and Tracking Algorithm (CorPITA) Authors: Long, David M.; Bloomfield, D. Shaun; Feeney-Barry, R.; Gallagher, Peter T.; Pérez-Suárez, David Bibcode: 2013enss.confE..68L Altcode: The Coronal Pulse Identification and Tracking Algorithm (CorPITA) is an automated technique for detecting and analysing "EIT Waves" in data from the Solar Dynamics Observatory (SDO) spacecraft. CorPITA will operate as part of the Heliophysics Event Knowledgebase (HEK), providing unbiased, near-real-time identification of coronal pulses. When triggered by the start of a solar flare, the algorithm uses an intensity profile technique radiating from the source of the flare to examine the entire solar disk. If a pulse is identified, the kinematics and morphological variation of the pulse are determined for all directions along the solar surface. Here, CorPITA is applied to a test data-set encompassing a series of solar flares of different classes from 13-20 February 2011. This allows the effectiveness of the algorithm in dealing with the varied morphology of different eruptions to be characterised. The automated nature of this approach will enable an unbiased examination of "EIT Waves" and their relationship to coronal mass ejections. Title: Evidence for partial Taylor relaxation from changes in magnetic geometry and energy during a solar flare Authors: Murray, S. A.; Bloomfield, D. S.; Gallagher, P. T. Bibcode: 2013A&A...550A.119M Altcode: 2012arXiv1212.5906M Context. Solar flares are powered by energy stored in the coronal magnetic field, a portion of which is released when the field reconfigures into a lower energy state. Investigation of sunspot magnetic field topology during flare activity is useful to improve our understanding of flaring processes.
Aims: Here we investigate the deviation of the non-linear field configuration from that of the linear and potential configurations, and study the free energy available leading up to and after a flare.
Methods: The evolution of the magnetic field in NOAA region 10953 was examined using data from Hinode/SOT-SP, over a period of 12 h leading up to and after a GOES B1.0 flare. Previous work on this region found pre- and post-flare changes in photospheric vector magnetic field parameters of flux elements outside the primary sunspot. 3D geometry was thus investigated using potential, linear force-free, and non-linear force-free field extrapolations in order to fully understand the evolution of the field lines.
Results: Traced field line geometrical and footpoint orientation differences show that the field does not completely relax to a fully potential or linear force-free state after the flare. Magnetic and free magnetic energies increase significantly ~6.5-2.5 h before the flare by ~1031 erg. After the flare, the non-linear force-free magnetic energy and free magnetic energies decrease but do not return to pre-flare "quiet" values.
Conclusions: The post-flare non-linear force-free field configuration is closer (but not equal) to that of the linear force-free field configuration than a potential one. However, the small degree of similarity suggests that partial Taylor relaxation has occurred over a time scale of ~3-4 h. Title: Studying Sun-Planet Connections Using the Heliophysics Integrated Observatory (HELIO) Authors: Pérez-Suárez, D.; Maloney, S. A.; Higgins, P. A.; Bloomfield, D. S.; Gallagher, P. T.; Pierantoni, G.; Bonnin, X.; Cecconi, B.; Alberti, V.; Bocchialini, K.; Dierckxsens, M.; Opitz, A.; Le Blanc, A.; Aboudarham, J.; Bentley, R. B.; Brooke, J.; Coghlan, B.; Csillaghy, A.; Jacquey, C.; Lavraud, B.; Messerotti, M. Bibcode: 2012SoPh..280..603P Altcode: 2012SoPh..tmp..215P The Heliophysics Integrated Observatory (HELIO) is a software infrastructure involving a collection of web services, heliospheric data sources (e.g., solar, planetary, etc.), and event catalogues - all of which are accessible through a unified front end. In this paper we use the HELIO infrastructure to perform three case studies based on solar events that propagate through the heliosphere. These include a coronal mass ejection that intersects both Earth and Mars, a solar energetic particle event that crosses the orbit of Earth, and a high-speed solar wind stream, produced by a coronal hole, that is observed in situ at Earth (L1). A ballistic propagation model is run as one of the HELIO services and used to model these events, predicting if they will interact with a spacecraft or planet and determining the associated time of arrival. The HELIO infrastructure streamlines the method used to perform these kinds of case study by centralising the process of searching for and visualising data, indicating interesting features on the solar disk, and finally connecting remotely observed solar features with those detected by in situ solar wind and energetic particle instruments. HELIO represents an important leap forward in European heliophysics infrastructure by bridging the boundaries of traditional scientific domains. Title: The spectrometer telescope for imaging x-rays on board the Solar Orbiter mission Authors: Benz, A. O.; Krucker, S.; Hurford, G. J.; Arnold, N. G.; Orleanski, P.; Gröbelbauer, H. -P.; Klober, S.; Iseli, L.; Wiehl, H. J.; Csillaghy, A.; Etesi, L.; Hochmuth, N.; Battaglia, M.; Bednarzik, M.; Resanovic, R.; Grimm, O.; Viertel, G.; Commichau, V.; Meuris, A.; Limousin, O.; Brun, S.; Vilmer, N.; Skup, K. R.; Graczyk, R.; Stolarski, M.; Michalska, M.; Nowosielski, W.; Cichocki, A.; Mosdorf, M.; Seweryn, K.; Przepiórka, A.; Sylwester, J.; Kowalinski, M.; Mrozek, T.; Podgorski, P.; Mann, G.; Aurass, H.; Popow, E.; Onel, H.; Dionies, F.; Bauer, S.; Rendtel, J.; Warmuth, A.; Woche, M.; Plüschke, D.; Bittner, W.; Paschke, J.; Wolker, D.; Van Beek, H. F.; Farnik, F.; Kasparova, J.; Veronig, A. M.; Kienreich, I. W.; Gallagher, P. T.; Bloomfield, D. S.; Piana, M.; Massone, A. M.; Dennis, B. R.; Schwarz, R. A.; Lin, R. P. Bibcode: 2012SPIE.8443E..3LB Altcode: The Spectrometer Telescope for Imaging X-rays (STIX) is one of 10 instruments on board Solar Orbiter, a confirmed Mclass mission of the European Space Agency (ESA) within the Cosmic Vision program scheduled to be launched in 2017. STIX applies a Fourier-imaging technique using a set of tungsten grids (at pitches from 0.038 to 1 mm) in front of 32 pixelized CdTe detectors to provide imaging spectroscopy of solar thermal and non-thermal hard X-ray emissions from 4 to 150 keV. The status of the instrument reviewed in this paper is based on the design that passed the Preliminary Design Review (PDR) in early 2012. Particular emphasis is given to the first light of the detector system called Caliste-SO. Title: Toward Reliable Benchmarking of Solar Flare Forecasting Methods Authors: Bloomfield, D. Shaun; Higgins, Paul A.; McAteer, R. T. James; Gallagher, Peter T. Bibcode: 2012ApJ...747L..41B Altcode: 2012arXiv1202.5995B Solar flares occur in complex sunspot groups, but it remains unclear how the probability of producing a flare of a given magnitude relates to the characteristics of the sunspot group. Here, we use Geostationary Operational Environmental Satellite X-ray flares and McIntosh group classifications from solar cycles 21 and 22 to calculate average flare rates for each McIntosh class and use these to determine Poisson probabilities for different flare magnitudes. Forecast verification measures are studied to find optimum thresholds to convert Poisson flare probabilities into yes/no predictions of cycle 23 flares. A case is presented to adopt the true skill statistic (TSS) as a standard for forecast comparison over the commonly used Heidke skill score (HSS). In predicting flares over 24 hr, the maximum values of TSS achieved are 0.44 (C-class), 0.53 (M-class), 0.74 (X-class), 0.54 (>=M1.0), and 0.46 (>=C1.0). The maximum values of HSS are 0.38 (C-class), 0.27 (M-class), 0.14 (X-class), 0.28 (>=M1.0), and 0.41 (>=C1.0). These show that Poisson probabilities perform comparably to some more complex prediction systems, but the overall inaccuracy highlights the problem with using average values to represent flaring rate distributions. Title: The Evolution of Sunspot Magnetic Fields Associated with a Solar Flare Authors: Murray, Sophie A.; Bloomfield, D. Shaun; Gallagher, Peter T. Bibcode: 2012SoPh..277...45M Altcode: 2011arXiv1105.1978M; 2011SoPh..tmp..129M; 2011SoPh..tmp..185M; 2011SoPh..tmp..254M Solar flares occur due to the sudden release of energy stored in active-region magnetic fields. To date, the precursors to flaring are still not fully understood, although there is evidence that flaring is related to changes in the topology or complexity of an active-region's magnetic field. Here, the evolution of the magnetic field in active region NOAA 10953 was examined using Hinode/SOT-SP data over a period of 12 hours leading up to and after a GOES B1.0 flare. A number of magnetic-field properties and low-order aspects of magnetic-field topology were extracted from two flux regions that exhibited increased Ca II H emission during the flare. Pre-flare increases in vertical field strength, vertical current density, and inclination angle of ≈ 8° toward the vertical were observed in flux elements surrounding the primary sunspot. The vertical field strength and current density subsequently decreased in the post-flare state, with the inclination becoming more horizontal by ≈ 7°. This behavior of the field vector may provide a physical basis for future flare-forecasting efforts. Title: Active Regions and the Global Magnetic Field of the Sun Authors: Higgins, P. A.; Bloomfield, D. S.; Gallagher, P. T. Bibcode: 2011AGUFMSH43B1940H Altcode: The Sun follows an 11 year activity cycle, over which the global magnetic field begins highly dipolar, and becomes more complex at cycle maximum, until reverting back to a dipole state, but with reversed polarity. Many magnetic structures of varying complexity (active regions) are observed to emerge, evolve, and decay over the cycle. Beyond location and orientation, the dependence of active region magnetic properties on the phase of the solar cycle is not well known. Here, we use automated feature detection methods to detect and characterize thousands of active region detections and statistically investigate their physical properties. We find that the mean size and flux of magnetic features on the solar disk is dependent on the phase of the cycle. We establish a direct connection between the spatial distribution of active regions on the solar disk and the configuration of the global solar magnetic field by investigating the polarity imbalance of feature magnetic flux. Using a global potential field source surface model, we find that the shape of the global field is strongly dependent on the large scale distribution of imbalanced flux. Title: Deceleration and dispersion of large-scale coronal bright fronts Authors: Long, D. M.; Gallagher, P. T.; McAteer, R. T. J.; Bloomfield, D. S. Bibcode: 2011A&A...531A..42L Altcode: 2011arXiv1104.4334L Context. One of the most dramatic manifestations of solar activity are large-scale coronal bright fronts (CBFs) observed in extreme ultraviolet (EUV) images of the solar atmosphere. To date, the energetics and kinematics of CBFs remain poorly understood, due to the low image cadence and sensitivity of previous EUV imagers and the limited methods used to extract the features.
Aims: In this paper, the trajectory and morphology of CBFs was determined in order to investigate the varying properties of a sample of CBFs, including their kinematics and pulse shape, dispersion, and dissipation.
Methods: We have developed a semi-automatic intensity profiling technique to extract the morphology and accurate positions of CBFs in 2.5-10 min cadence images from STEREO/EUVI. The technique was applied to sequences of 171 Å and 195 Å images from STEREO/EUVI in order to measure the wave properties of four separate CBF events.
Results: Following launch at velocities of ~240-450 km s-1 each of the four events studied showed significant negative acceleration ranging from ~-290 to -60 m s-2. The CBF spatial and temporal widths were found to increase from ~50 Mm to ~200 Mm and ~100 s to ~1500 s respectively, suggesting that they are dispersive in nature. The variation in position-angle averaged pulse-integrated intensity with propagation shows no clear trend across the four events studied. These results are most consistent with CBFs being dispersive magnetoacoustic waves.

Figures 3-8, 10, 11, 13-15, 17, 18 and the movie are available in electronic form at http://www.aanda.org Title: Solar magnetic feature detection and tracking for space weather monitoring Authors: Higgins, P. A.; Gallagher, P. T.; McAteer, R. T. J.; Bloomfield, D. S. Bibcode: 2011AdSpR..47.2105H Altcode: 2010arXiv1006.5898H We present an automated system for detecting, tracking, and cataloging emerging active regions throughout their evolution and decay using SOHO Michelson Doppler Interferometer (MDI) magnetograms. The SolarMonitor Active Region Tracking (SMART) algorithm relies on consecutive image differencing to remove both quiet-Sun and transient magnetic features, and region-growing techniques to group flux concentrations into classifiable features. We determine magnetic properties such as region size, total flux, flux imbalance, flux emergence rate, Schrijver’s R-value, R∗ (a modified version of R), and Falconer’s measurement of non-potentiality. A persistence algorithm is used to associate developed active regions with emerging flux regions in previous measurements, and to track regions beyond the limb through multiple solar rotations. We find that the total number and area of magnetic regions on disk vary with the sunspot cycle. While sunspot numbers are a proxy to the solar magnetic field, SMART offers a direct diagnostic of the surface magnetic field and its variation over timescale of hours to years. SMART will form the basis of the active region extraction and tracking algorithm for the Heliophysics Integrated Observatory (HELIO). Title: Short-term Evolution of Coronal Hole Boundaries Authors: Krista, Larisza D.; Gallagher, Peter T.; Bloomfield, D. Shaun Bibcode: 2011ApJ...731L..26K Altcode: 2011arXiv1103.2660K The interaction of open and closed field lines at coronal hole (CH) boundaries is widely accepted to be due to interchange magnetic reconnection. To date, it is unclear how the boundaries vary on short timescales and at what velocity this occurs. Here, we describe an automated boundary tracking method used to determine CH boundary displacements on short timescales. The boundary displacements were found to be isotropic and to have typical expansion/contraction speeds of <=2 km s-1, which indicate magnetic reconnection rates of <=3 × 10-3. The observed displacements were used in conjunction with the interchange reconnection model to derive typical diffusion coefficients of <=3 × 1013 cm2 s-1. These results are consistent with an interchange reconnection process in the low corona driven by the random granular motions of open and closed fields in the photosphere. Title: Automated Solar Feature Detection for Space Weather Applications Authors: Pérez-Suárez, David; Higgins, Paul A.; Bloomfield, D. Shaun; McAteer, R. T. James; Krista, Larisza D.; Byrne, Jason P.; Gallagher, Peter. T. Bibcode: 2011asip.book..207P Altcode: 2011arXiv1109.6922P The solar surface and atmosphere are highly dynamic plasma environments, which evolve over a wide range of temporal and spatial scales. Large-scale eruptions, such as coronal mass ejections, can be accelerated to millions of kilometres per hour in a matter of minutes, making their automated detection and characterisation challenging. Additionally, there are numerous faint solar features, such as coronal holes and coronal dimmings, which are important for space weather monitoring and forecasting, but their low intensity and sometimes transient nature makes them problematic to detect using traditional image processing techniques. These difficulties are compounded by advances in ground- and space- based instrumentation, which have increased the volume of data that solar physicists are confronted with on a minute-by-minute basis; NASA's Solar Dynamics Observatory for example is returning many thousands of images per hour (~1.5 TB/day). This chapter reviews recent advances in the application of images processing techniques to the automated detection of active regions, coronal holes, filaments, CMEs, and coronal dimmings for the purposes of space weather monitoring and prediction. Title: The Solar Cycle Dependence of Active Region Properties Authors: Higgins, P.; Gallagher, P. T.; Bloomfield, D. Bibcode: 2010AGUFMSH53B..01H Altcode: The solar cycle dependence of global active region (AR) emergence and dynamics is analysed using the SolarMonitor Active Region Tracker (SMART), which automatically detects and characterises magnetic flux concentrations using full-disk magnetograms. SMART is run on a magnetogram data set ranging from 1997 to 2009, resulting in measurements of each AR on disk each day. AR properties such as heliographic location, orientation, magnetic flux, flux imbalance, Schrijver's R value, Falconer's WLSG proxy for non-potentiality, and flare productivity are compared over cycle 23. We find several solar cycle modulations in the globally summed AR flux which may help to characterize the subsurface solar dynamo as well as global magnetic flux transport. The global flare index is better correlated to the global R value than WLSG or magnetic flux. Also, the emergence of highly non-potential, flare-productive ARs is found to be more confined in latitude than ARs in general, with little dependence on the phase of the solar cycle. Title: Solar flares: Multiscale detection and analysis Authors: Bloomfield, D. Shaun Bibcode: 2010ada..confE...6B Altcode: No abstract at ADS Title: The SolarMonitor Active Region Tracking (SMART) Algorithm: Variation of magnetic feature properties through solar cycle 23 Authors: Higgins, P.; Gallagher, P.; McAteer, R.; Bloomfield, D. Bibcode: 2009AGUFMSH51B1278H Altcode: The SolarMonitor Active Region Tracking (SMART) algorithm is an automated system for detecting, tracking, and cataloging magnetic features throughout their evolution and decay. The SMART method will form the basis of active region extraction and tracking within the Heliophysics Integrated Observatory (HELIO). Magnetic properties such as total flux, flux imbalance, flux emergence rate, Schrijver's R-value, R* (a modified version of R), and Falconer's measurement of non-potentiality are determined for individual features throughout solar cycle 23. The variation of these feature property distributions with progression through the solar cycle is presented. Feature detections using the SMART algorithm for line-of-sight level 1.8 SOHO/MDI magnetogram taken 22 October 2003 at 12:47. Active region candidates are denoted "AR", emerging flux concentrations are denoted "EF", plage regions are denoted "PL" and other flux concentrations are labeled "NF". Title: The Temperature Response of EUV Imagers Authors: Raftery, Claire; Bloomfield, D. Shaun; Gallagher, P. Bibcode: 2009SPD....40.1213R Altcode: The temperature response of an EUV imager provides the user with the temperature range over which the instrument or passband is sensitive. These response curves appear to be highly peaked, implying a narrow range of temperature sensitivity. However, in the past, these response functions have been calculated using quiet sun spectra or constant density, assumptions which are relevant only in specific circumstances. The multithermal response of the EUV imagers - TRACE, SOHO/EIT, STEREO/EUVI, PROBA2/SWAP and SDO/AIA were investigated. It was found that a highly peaked response curve is only appropriate when looking at cooler material. However, studying higher temperature emission from e.g. active regions and flares produces a very broad, almost flat response between 105 and 107 K for all instruments. CLR is supported by an SPD studentship and the ESA/Prodex grant administered by Enterprise Ireland. Title: Possible Connection Between Umbral and Bright Point Oscillations Authors: Andic, Aleksandra; Jess, D. B.; Mathioudakis, M.; Keenan, F. P.; Bloomfield, D. S. Bibcode: 2009SPD....40.0909A Altcode: Active region NOAA 10794 was observed using the Rapid Dual Imager (RDI) instrument on the Dunn Solar Telescope at the National Solar Observatory, Sacramento Peak. G-band and H-alpha filters were employed for the observations, and the resulting data were subjected to both speckle reconstruction and wavelet analyses.

Intensity oscillations in the period range 8--584 s were detected. Those with frequencies near the Nyquist value of 125 mHz had a similar behavior to other oscillations detected in the period range of 8 - 60 s.

However, oscillations in the range around 180s observed above bright points show a temporal coincidence in the light curve shape and the number of the emitted frequencies in an umbral flash, indicating a possible connection. Title: The Kinematics of a Globally Propagating Disturbance in the Solar Corona Authors: Long, David M.; Gallagher, Peter T.; McAteer, R. T. James; Bloomfield, D. Shaun Bibcode: 2008ApJ...680L..81L Altcode: 2008arXiv0805.2023L The kinematics of a globally propagating disturbance (also known as an "EIT wave") is discussed using Extreme UltraViolet Imager (EUVI) data from the Solar Terrestrial Relations Observatory (STEREO). We show for the first time that an impulsively generated propagating disturbance has similar kinematics in all four EUVI passbands (304, 171, 195, and 284 Å). In the 304 Å passband the disturbance shows a velocity peak of 238 ± 20 km s-1 within ~28 minutes of its launch, varying in acceleration from 76 to -102 m s-2. This passband contains a strong contribution from a Si XI line (303.32 Å) with a peak formation temperature of ~1.6 MK. The 304 Å emission may therefore be coronal rather than chromospheric in origin. Comparable velocities and accelerations are found in the coronal 195 Å passband, while lower values are found in the lower cadence 284 Å passband. In the higher cadence 171 Å passband the velocity varies significantly, peaking at 475 ± 47 km s-1 within ~20 minutes of launch, with a variation in acceleration from 816 to -413 m s-2. The high image cadence of the 171 Å passband (2.5 minutes compared to 10 minutes for the similar temperature response 195 Å passband) is found to have a major effect on the measured velocity and acceleration of the pulse, which increase by factors of ~2 and ~10, respectively. This implies that previously measured values (e.g., using EIT) may have been underestimated. We also note that the disturbance shows strong reflection from a coronal hole in both the 171 and 195 Å passbands. The observations are consistent with an impulsively generated fast-mode magnetoacoustic wave. Title: High frequency oscillations in the solar chromosphere and their connection with heating Authors: Andic, Aleksandra; Mathioudakis, M.; Keenan, F. P.; Jess, D. B.; Bloomfield, D. S. Bibcode: 2008IAUS..247..312A Altcode: 2007IAUS..247..312A High frequency acoustic waves have been suggested as a source of mechanical heating in the quiet solar chromosphere. To investigate this, we have observed intensity oscillations of several lines in the frequency interval 1.64-70mHz using data from the VTT Tenerife and the Dunn Solar Telescope at the National Solar Observatory. Our analysis of Fe i 543.45 nm, Fe i 543.29 nm and the G-band, indicate that the majority of oscillations are connected with the magnetic fields and do not provide sufficient mechanical flux for the heating of the chromosphere. This correlation is also observed in quiet Sun areas. Title: The nature of running penumbral waves revealed Authors: Bloomfield, D. S.; Lagg, A.; Solanki, S. K. Bibcode: 2008IAUS..247...55B Altcode: 2007IAUS..247...55B We seek to clarify the nature of running penumbral (RP) waves: are they chromospheric trans-sunspot waves or a visual pattern of upward-propagating waves? Full Stokes spectropolarimetric time series of the photospheric Sii10827 Å line and the chromospheric Hei10830 Å multiplet were inverted using a Milne-Eddington code. Spatial pixels were paired between the outer umbral/inner penumbral photosphere and the penumbral chromosphere using inclinations retrieved by the inversion and the dual-height pairings of line-of-sight velocity time series were studied for signatures of wave propagation using a Fourier phase difference analysis. The dispersion relation for radiatively cooling acoustic waves, modified to incorporate an inclined propagation direction, fits well the observed phase differences between the pairs of photospheric and chromospheric pixels. We have thus demonstrated that RP waves are in effect low-β slow-mode waves propagating along the magnetic field. Title: Twisting flux tubes as a cause of micro-flaring activity Authors: Jess, D. B.; McAteer, R. T. J.; Mathioudakis, M.; Keenan, F. P.; Andic, A.; Bloomfield, D. S. Bibcode: 2008IAUS..247..360J Altcode: 2007IAUS..247..360J High-cadence optical observations of an H-α blue-wing bright point near solar AR NOAA 10794 are presented. The data were obtained with the Dunn Solar Telescope at the National Solar Observatory/Sacramento Peak using a newly developed camera system, the rapid dual imager. Wavelet analysis is undertaken to search for intensity-related oscillatory signatures, and periodicities ranging from 15 to 370 s are found with significance levels exceeding 95%. During two separate microflaring events, oscillation sites surrounding the bright point are observed to twist. We relate the twisting of the oscillation sites to the twisting of physical flux tubes, thus giving rise to reconnection phenomena. We derive an average twist velocity of 8.1 km/s and detect a peak in the emitted flux between twist angles of 180° and 230°. Title: The Nature of Running Penumbral Waves Revealed Authors: Bloomfield, D. Shaun; Lagg, Andreas; Solanki, Sami K. Bibcode: 2007ApJ...671.1005B Altcode: 2007arXiv0709.3731B We seek to clarify the nature of running penumbral (RP) waves: are they chromospheric trans-sunspot waves or a visual pattern of upward-propagating waves? Full Stokes spectropolarimetric time series of the photospheric Si I λ10827 line and the chromospheric He I λ10830 multiplet were inverted using a Milne-Eddington atmosphere. Spatial pixels were paired between the outer umbral/inner penumbral photosphere and the penumbral chromosphere using inclinations retrieved by the inversion and the dual-height pairings of line-of-sight velocity time series were studied for signatures of wave propagation using a Fourier phase difference analysis. The dispersion relation for radiatively cooling acoustic waves, modified to incorporate an inclined propagation direction, fits well the observed phase differences between the pairs of photospheric and chromospheric pixels. We have thus demonstrated that RP waves are in effect low-β slow-mode waves propagating along the magnetic field. Title: Twisting flux tubes as a cause of micro-flaring activity Authors: Jess, D. B.; McAteer, R. T. J.; Mathioudakis, M.; Keenan, F. P.; Andic, A.; Bloomfield, D. S. Bibcode: 2007A&A...476..971J Altcode: 2007arXiv0709.2268J High-cadence optical observations of an H-α blue-wing bright point near solar AR NOAA 10794 are presented. The data were obtained with the Dunn Solar Telescope at the National Solar Observatory/Sacramento Peak using a newly developed camera system, the rapid dual imager. Wavelet analysis is undertaken to search for intensity-related oscillatory signatures, and periodicities ranging from 15 to 370 s are found with significance levels exceeding 95%. During two separate microflaring events, oscillation sites surrounding the bright point are observed to twist. We relate the twisting of the oscillation sites to the twisting of physical flux tubes, thus giving rise to reconnection phenomena. We derive an average twist velocity of 8.1 km s-1 and detect a peak in the emitted flux between twist angles of 180° and 230°.

Figure 4 is available as a movie at http://www.aanda.org Title: High-frequency oscillations in a solar active region observed with the RAPID DUAL IMAGER Authors: Jess, D. B.; Andić, A.; Mathioudakis, M.; Bloomfield, D. S.; Keenan, F. P. Bibcode: 2007A&A...473..943J Altcode: 2007arXiv0707.2716J High-cadence, synchronized, multiwavelength optical observations of a solar active region (NOAA 10794) are presented. The data were obtained with the Dunn Solar Telescope at the National Solar Observatory/Sacramento Peak using a newly developed camera system: the rapid dual imager. Wavelet analysis is undertaken to search for intensity related oscillatory signatures, and periodicities ranging from 20 to 370 s are found with significance levels exceeding 95%. Observations in the H-α blue wing show more penumbral oscillatory phenomena when compared to simultaneous G-band observations. The H-α oscillations are interpreted as the signatures of plasma motions with a mean velocity of 20 km s-1. The strong oscillatory power over H-α blue-wing and G-band penumbral bright grains is an indication of the Evershed flow with frequencies higher than previously reported. Title: Modified p-modes in penumbral filaments? Authors: Bloomfield, D. S.; Solanki, S. K.; Lagg, A.; Borrero, J. M.; Cally, P. S. Bibcode: 2007A&A...469.1155B Altcode: 2007arXiv0705.0481B Aims:The primary objective of this study is to search for and identify wave modes within a sunspot penumbra.
Methods: Infrared spectropolarimetric time series data are inverted using a model comprising two atmospheric components in each spatial pixel. Fourier phase difference analysis is performed on the line-of-sight velocities retrieved from both components to determine time delays between the velocity signals. In addition, the vertical separation between the signals in the two components is calculated from the Stokes velocity response functions.
Results: The inversion yields two atmospheric components, one permeated by a nearly horizontal magnetic field, the other with a less-inclined magnetic field. Time delays between the oscillations in the two components in the frequency range 2.5-4.5 mHz are combined with speeds of atmospheric wave modes to determine wave travel distances. These are compared to expected path lengths obtained from response functions of the observed spectral lines in the different atmospheric components. Fast-mode (i.e., modified p-mode) waves exhibit the best agreement with the observations when propagating toward the sunspot at an angle ~50° to the vertical. Title: Observations of Running Waves in a Sunspot Chromosphere Authors: Bloomfield, D. S.; Lagg, A.; Solanki, S. K. Bibcode: 2007ASPC..368..239B Altcode: 2007astro.ph..2056B Spectropolarimetric time series data of the primary spot of active region NOAA 9448 were obtained in the Si I 10827 Å line and the He I 10830 Å multiplet with the Tenerife Infrared Polarimeter. Throughout the time series the spectrograph slit was fixed over a region covering umbra, a light bridge, penumbra, and quiet sun. We present speeds of running penumbral waves in the chromosphere, their relation to both photospheric and chromospheric umbral oscillations, and their dependence on the magnetic field topology. Title: Detection of MHD waves in the solar chromosphere Authors: Kontogiannis, Giannis; Bloomfield, D. Shaun; McAteer, James R. T.; Mathioudakis, Mihalis; Antonopoulou, E. Bibcode: 2007AIPC..895...80K Altcode: One of the main features of the quiet solar chromosphere is the Network Bright Points (NBP), formed by emerging magnetic flux at the boundaries of supergranular cells. Using SSW IDL routines and wavelet analysis of series of images in four bandpasses (CaIIK3, Mgb1, Mgb2 and Hα core) we have detected MHD wave modes in the Network Bright Points of the solar chromosphere. The observations have been analyzed using cross-correlation techniques and we have drawn conclusions on wave propagation and mode-coupling. Title: Modified p-modes in penumbral filaments Authors: Bloomfield, D. S.; Lagg, A.; Solanki, S. K.; Borrero, J. M. Bibcode: 2007msfa.conf..241B Altcode: A time series analysis was performed on velocity signals in a sunspot penumbra to search for possible wave modes. The spectropolarimetric photospheric data obtained by the Tenerife Infrared Polarimeter were inverted using the SPINOR code. An atmospheric model comprising two magnetic components and one stray-light component gave an optimal fit to the data. Fourier phase difference analysis between line-of-sight velocities of both magnetic components provided time delays between the two atmospheres. These delays were combined with the speeds of atmospheric wave modes and compared to height separations derived from velocity response functions to determine the wave mode. Title: The Influence of Magnetic Field on Oscillations in the Solar Chromosphere Authors: Bloomfield, D. Shaun; McAteer, R. T. James; Mathioudakis, Mihalis; Keenan, Francis P. Bibcode: 2006ApJ...652..812B Altcode: 2006astro.ph..8314B Two sequences of solar images obtained by the Transition Region and Coronal Explorer in three UV passbands are studied using wavelet and Fourier analysis and compared to the photospheric magnetic flux measured by the Michelson Doppler Interferometer on the Solar Heliospheric Observatory to study wave behavior in differing magnetic environments. Wavelet periods show deviations from the theoretical cutoff value and are interpreted in terms of inclined fields. The variation of wave speeds indicates that a transition from dominant fast-magnetoacoustic waves to slow modes is observed when moving from network into plages and umbrae. This implies preferential transmission of slow modes into the upper atmosphere, where they may lead to heating or be detected in coronal loops and plumes. Title: The periodic variations of a white-light flare observed with ULTRACAM Authors: Mathioudakis, M.; Bloomfield, D. S.; Jess, D. B.; Dhillon, V. S.; Marsh, T. R. Bibcode: 2006A&A...456..323M Altcode: 2006astro.ph..5196M High time resolution observations of a white-light flare on the active star EQ PegB show evidence of intensity variations with a period of ≈10 s. The period drifts to longer values during the decay phase of the flare. If the oscillation is interpreted as an impulsively-excited, standing-acoustic wave in a flare loop, the period implies a loop length of ≈3.4 Mm and ≈6.8 Mm for the case of the fundamental mode and the second harmonic, respectively. However, the small loop lengths imply a very high modulation depth making the acoustic interpretation unlikely. A more realistic interpretation may be that of a fast-MHD wave, with the modulation of the emission being due to the magnetic field. Alternatively, the variations could be due to a series of reconnection events. The periodic signature may then arise as a result of the lateral separation of individual flare loops or current sheets with oscillatory dynamics (i.e., periodic reconnection). Title: Opacity in the upper atmospheres of active stars. II. AD Leonis Authors: Christian, D. J.; Mathioudakis, M.; Bloomfield, D. S.; Dupuis, J.; Keenan, F. P.; Pollacco, D. L.; Malina, R. F. Bibcode: 2006A&A...454..889C Altcode: 2006astro.ph..2447C We present FUV and UV spectroscopic observations of AD Leonis, with the aim of investigating opacity effects in the transition regions of late-type stars. The C III lines in FUSE spectra show significant opacity during both the quiescent and flaring states of AD Leonis, with up to 30% of the expected flux being lost during the latter. Other FUSE emission lines tested for opacity include those of O VI, while C IV, Si IV and N V transitions observed with stis are also investigated. These lines only reveal modest amounts of opacity with losses during flaring of up to 20%. Optical depths have been calculated for homogeneous and inhomogeneous geometries, giving path lengths of ≈20-60 km and ≈10-30 km, respectively, under quiescent conditions. However path lengths derived during flaring are ≈2-3 times larger. These values are in excellent agreement with both estimates of the small-scale structure observed in the solar transition region, and path lengths derived previously for several other active late-type stars. Title: Traveling Waves In Network Bright Points Authors: Kontogiannis, G.; Bloomfield, D. Shaun; McAteer, J. R. T.; Mathioudakis, M.; Antonopoulou, E. Bibcode: 2006AIPC..848..229K Altcode: One of the main features of the quiet solar chromosphere is the Network Bright Points (NBP), formed by the emerging magnetic flux, at the boundaries of supergranular cells. Triggered by the motions of magnetic loop foot-points, at the top of the convection zone, MHD waves propagate inside the NBP's. Using SSW IDL routines and wavelet analysis of series of images in four bandpasses (CaII K3, Mgb1-0.4, Mgb2 and Ha core) we detected these MHD wave modes. The observations have been analyzed using cross-correlation techniques and we have drawn conclusions on wave propagation and mode coupling. Title: Soft X-Ray Emission Lines of Fe XV in Solar Flare Observations and the Chandra Spectrum of Capella Authors: Keenan, F. P.; Drake, J. J.; Chung, S.; Brickhouse, N. S.; Aggarwal, K. M.; Msezane, A. Z.; Ryans, R. S. I.; Bloomfield, D. S. Bibcode: 2006ApJ...645..597K Altcode: 2006astro.ph..1591K Recent calculations of atomic data for Fe XV have been used to generate theoretical line ratios involving n=3-4 transitions in the soft X-ray spectral region (~52-83 Å), for a wide range of electron temperatures and densities applicable to solar and stellar coronal plasmas. A comparison of these with solar flare observations from a rocket-borne spectrograph (X-Ray Spectrometer/Spectrograph Telescope [XSST]) reveals generally good agreement between theory and experiment. In particular, the 82.76 Å emission line in the XSST spectrum is identified, for the first time to our knowledge in an astrophysical source, as the 3s3d3D3-3s4p3P2 transition of Fe XV. Most of the Fe XV transitions that are blended have had the species responsible clearly identified, although there remain a few instances in which this has not been possible. The line ratio calculations are also compared with a co-added spectrum of Capella obtained with the Chandra satellite, which is probably the highest signal-to-noise ratio observation achieved for a stellar source in the ~25-175 Å soft X-ray region. Good agreement is found between theory and experiment, indicating that the Fe XV lines are reliably detected in Chandra spectra and hence may be employed as diagnostics to determine the temperature and/or density of the emitting plasma. However, the line blending in the Chandra data is such that individual emission lines are difficult to measure accurately, and fluxes may only be reliably determined via detailed profile fitting of the observations. The co-added Capella spectrum is made available to hopefully encourage further exploration of the soft X-ray region in astronomical sources. Title: Opacity in the transition region of cool dwarfs: A powerful diagnostic Authors: Mathioudakis, M.; Christian, D. J.; Bloomfield, D. S.; Keenan, F. P.; Linsky, J. L.; Dupuis, J. Bibcode: 2006ASPC..348..159M Altcode: A detailed study of the C III 1176Å multiplet in active cool stars has shown significant deviations of the line flux from the optically thin approximation. These deviations become more pronounced during flares. Opacity can be used as a powerful diagnostic to estimate path lengths in the transition region. Our analysis reveals that stellar transition regions have very small spatial characteristics typically in the range of 10 - 100 km. These path lengths are in agreement with the small scale structure seen in the solar transition region. Title: A Comparative Study of Flaring Loops in Active Stars Authors: Mullan, D. J.; Mathioudakis, M.; Bloomfield, D. S.; Christian, D. J. Bibcode: 2006ApJS..164..173M Altcode: Dynamo activity in stars of different types is expected to generate magnetic fields with different characteristics. As a result, a differential study of the characteristics of magnetic loops in a broad sample of stars may yield information about dynamo systematics. In the absence of direct imaging, certain physical parameters of a stellar magnetic loop can be extracted if a flare occurs in that loop. In this paper we employ a simple nonhydrodynamic approach introduced by Haisch, to analyze a homogeneous sample of all of the flares we could identify in the EUVE DS database: a total of 134 flares that occurred on 44 stars ranging in spectral type from F to M and in luminosity class from V to III. All of the flare light curves that have been used in the present study were obtained by a single instrument (EUVE DS). For each flare, we have applied Haisch's simplified approach (HSA) in order to determine loop length, temperature, electron density, and magnetic field. For each of our target stars, a literature survey has been performed to determine quantitatively the extent to which our results are consistent with independent studies. The results obtained by HSA are found to be well supported by results obtained by other methods. Our survey suggests that, on the main sequence, short loops (with lengths <=0.5R*) may be found in stars of all classes, while the largest loops (with lengths up to 2R*) appear to be confined to M dwarfs. Based on EUVE data, the transition from small to large loops on the main sequence appears to occur between spectral types K2 and M0. We discuss the implications of this result for dynamo theories. Title: An investigation of Fe XV emission lines in solar flare spectra Authors: Keenan, F. P.; Aggarwal, K. M.; Bloomfield, D. S.; Msezane, A. Z.; Widing, K. G. Bibcode: 2006A&A...449.1203K Altcode: 2005astro.ph.12571K Previously, large discrepancies have been found between theory and observation for Fe XV emission line ratios in solar flare spectra covering the 224-327 Å wavelength range, obtained by the Naval Research Laboratory's S082A instrument on board Skylab. These discrepancies have been attributed to either errors in the adopted atomic data or the presence of additional atomic processes not included in the modelling, such as fluorescence. However our analysis of these plus other S082A flare observations (the latter containing Fe XV transitions between 321-482 Å), performed using the most recent Fe XV atomic physics calculations in conjunction with a chianti synthetic flare spectrum, indicate that blending of the lines is primarily responsible for the discrepancies. As a result, most Fe XV lines cannot be employed as electron density diagnostics for solar flares, at least at the spectral resolution of S082A and similar instruments (i.e. 0.1 Å). An exception is the intensity ratio I(3s3p 3P{2}-3p2 3P{1})/I(3s3p 3P{2}-3p2 1D{2}) = I(321.8 Å)/I(327.0 Å), which appears to provide good estimates of the electron density at this spectral resolution. Title: RHESSI and SOHO CDS Observations of Explosive Chromospheric Evaporation Authors: Milligan, Ryan O.; Gallagher, Peter T.; Mathioudakis, Mihalis; Bloomfield, D. Shaun; Keenan, Francis P.; Schwartz, Richard A. Bibcode: 2006ApJ...638L.117M Altcode: 2005astro.ph..9664M Simultaneous observations of explosive chromospheric evaporation are presented using data from the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) and the Coronal Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric Observatory. For the first time, cospatial imaging and spectroscopy have been used to observe explosive evaporation within a hard X-ray emitting region. RHESSI X-ray images and spectra were used to determine the flux of nonthermal electrons accelerated during the impulsive phase of an M2.2 flare. When we assumed a thick-target model, the injected electron spectrum was found to have a spectral index of ~7.3, a low-energy cutoff of ~20 keV, and a resulting flux of >=4×1010 ergs cm-2 s-1. The dynamic response of the atmosphere was determined using CDS spectra; we found a mean upflow velocity of 230+/-38 km s-1 in Fe XIX (592.23 Å) and associated downflows of 36+/-16 and 43+/-22 km s-1 at chromospheric and transition region temperatures, respectively, relative to an averaged quiet-Sun spectra. The errors represent a 1 σ dispersion. The properties of the accelerated electron spectrum and the corresponding evaporative velocities were found to be consistent with the predictions of theory. Title: Plasma diagnostics of active-region evolution and implications for coronal heating Authors: Milligan, R. O.; Gallagher, P. T.; Mathioudakis, M.; Keenan, F. P.; Bloomfield, D. S. Bibcode: 2005MNRAS.363..259M Altcode: 2005MNRAS.tmp..764M; 2005astro.ph..9219M A detailed study is presented of the decaying solar-active region NOAA 10103 observed with the Coronal Diagnostic Spectrometer (CDS), the Michelson Doppler Imager (MDI) and the Extreme-ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). Electron-density maps formed using SiX (356.03 Å/347.41 Å) show that the density varies from ~1010cm-3 in the active-region core to ~7 × 108cm-3 at the region boundaries. Over the 5d of observations, the average electron density fell by ~30 per cent. Temperature maps formed using FeXVI (335.41 Å)/FeXIV (334.18 Å) show electron temperatures of ~2.34 × 106 K in the active-region core and ~2.10 × 106 K at the region boundaries. Similarly to the electron density, there was a small decrease in the average electron temperature over the 5-d period. The radiative, conductive and mass-flow losses were calculated and used to determine the resultant heating rate (PH). Radiative losses were found to dominate the active-region cooling process. As the region decayed, the heating rate decreased by almost a factor of 5 between the first and last day of observations. The heating rate was then compared to the total unsigned magnetic flux , yielding a power law of the form PH~Φ0.81+/-0.32tot. This result suggests that waves rather than nanoflares may be the dominant heating mechanism in this active region. Title: Soft X-ray emission lines of Fe XV in spectra of the Sun and Capella Authors: Drake, J. J.; Keenan, F. P.; Chung, S.; Brickhouse, N. S.; Aggarwal, K. M.; Msezane, A. Z.; Ryans, R. S. I.; Bloomfield, D. S. Bibcode: 2005AIPC..774..349D Altcode: Recent calculations of atomic data for Fe XV have been used to generate theoretical line ratios involving n = 3-4 transitions in the soft X-ray spectral region (~52-83 Å) for a wide range of electron temperatures and densities applicable to solar and stellar coronal plasmas. The line ratio calculations are compared with solar flare observations from a rocket-borne spectrograph (XSST) and with a co-added spectra of Capella obtained with the Chandra LETGS, representing the highest signal-to-noise observation achieved for a stellar source in the 30-80 Å soft X-ray region. Results are promising for use of Fe XV as astrophysical plasma diagnostics: Agreement between theory and observation is generally good, after particular account is taken of line blending. The 82.76 Å emission line in the XSST spectrum is identified, for the first time to our knowledge in an astrophysical source, as the 3s3d 3D3-3s4p 3P2 transition of Fe XV. Title: Fe XI Emission Lines in a High-Resolution Extreme-Ultraviolet Active Region Spectrum Obtained by the Solar Extreme Ultraviolet Research Telescope and Spectrograph Authors: Keenan, F. P.; Aggarwal, K. M.; Ryans, R. S. I.; Milligan, R. O.; Bloomfield, D. S.; Brosius, J. W.; Davila, J. M.; Thomas, R. J. Bibcode: 2005ApJ...624..428K Altcode: 2005astro.ph..4106K New calculations of radiative rates and electron impact excitation cross sections for Fe XI are used to derive emission-line intensity ratios involving 3s23p4-3s23p33d transitions in the 180-223 Å wavelength range. These ratios are subsequently compared with observations of a solar active region obtained during the 1995 flight of the Solar Extreme Ultraviolet Research Telescope and Spectrograph (SERTS). The version of SERTS flown in 1995 incorporated a multilayer grating that enhanced the instrumental sensitivity for features in the ~170-225 Å wavelength range, observed in second order between 340 and 450 Å. This enhancement led to the detection of many emission lines not seen on previous SERTS flights, which were measured with the highest spectral resolution (0.03 Å) ever achieved for spatially resolved active region spectra in this wavelength range. However, even at this high spectral resolution, several of the Fe XI lines are found to be blended, although the sources of the blends are identified in the majority of cases. The most useful Fe XI electron density diagnostic line intensity ratio is I(184.80 Å)/I(188.21 Å). This ratio involves lines close in wavelength and free from blends, and it varies by a factor of 11.7 between Ne=109 and 1011 cm-3 yet shows little temperature sensitivity. An unknown line in the SERTS spectrum at 189.00 Å is found to be due to Fe XI, the first time (to our knowledge) this feature has been identified in the solar spectrum. Similarly, there are new identifications of the Fe XI 192.88, 198.56, and 202.42 Å features, although the latter two are blended with S VIII/Fe XII and Fe XIII, respectively. Title: Wavelet Analysis Methods of Oscillatory Power in Chromospheric Lightcurves Authors: McAteer, R. T.; Bloomfield, D. S. Bibcode: 2005AGUSMSH13C..07M Altcode: The symbiotic relationship between time-series oscillatory power and waves in the chromosphere is studied using several novel wavelet techniques. Theses include automated wave-packet searching routines for large datasets, correlation of wave-packets at multiple heights in the atmosphere, and a full multi-wavelength wavelet-phase analysis (including the cross transform, phase difference and phase coherence). In each study we interpret oscillatory power as a signature of waves in the quiet-Sun chromosphere and relate these wave modes to the underlying photospheric magnetic field. Title: Intensity oscillations during a flare on EQ Peg Authors: Mathioudakis, M.; Bloomfield, D. S.; Dhillon, V. S.; Marsh, T. R. Bibcode: 2005ESASP.560..803M Altcode: 2005csss...13..803M No abstract at ADS Title: Magnetohydrodynamic mode coupling in the quiet-Sun network Authors: Bloomfield, D. S.; McAteer, R. T. J.; Mathioudakis, M.; Williams, D. R.; Keenan, F. P. Bibcode: 2005ESASP.560..449B Altcode: 2005csss...13..449B No abstract at ADS Title: Observations of Hα Intensity Oscillations in a Flare Ribbon Authors: McAteer, R. T. James; Gallagher, Peter T.; Brown, Daniel S.; Bloomfield, D. Shaun; Moore, Ruth; Williams, David R.; Mathioudakis, Mihalis; Katsiyannis, A.; Keenan, Francis P. Bibcode: 2005ApJ...620.1101M Altcode: High-cadence Hα blue wing observations of a C9.6 solar flare obtained at Big Bear Solar Observatory using the Rapid Dual Imager are presented. Wavelet and time-distance methods were used to study oscillatory power along the ribbon, finding periods of 40-80 s during the impulsive phase of the flare. A parametric study found statistically significant intensity oscillations with amplitudes of 3% of the peak flare amplitude, periods of 69 s (14.5 mHz) and oscillation decay times of 500 s. These measured properties are consistent with the existence of flare-induced acoustic waves within the overlying loops. Title: Emission lines of FeXV in spectra obtained with the Solar Extreme-Ultraviolet Research Telescope and Spectrograph Authors: Keenan, F. P.; Aggarwal, K. M.; Milligan, R. O.; Ryans, R. S. I.; Bloomfield, D. S.; Srigengan, V.; O'Mullane, M. G.; Lawson, K. D.; Msezane, A. Z.; Brosius, J. W.; Davila, J. M.; Thomas, R. J. Bibcode: 2005MNRAS.356.1592K Altcode: 2004MNRAS.tmp..752K Recent R-matrix calculations of electron impact excitation rates in Mg-like FeXV are used to derive theoretical emission-line ratios involving transitions in the 243-418 Åwavelength range. A comparison of these with a data set of solar active region, subflare and off-limb spectra, obtained during rocket flights by the Solar Extreme-Ultraviolet Research Telescope and Spectrograph (SERTS), reveals generally very good agreement between theory and observation, indicating that most of the FeXV emission lines may be employed with confidence as electron density diagnostics. In particular, the 312.55-Åline of FeXV is not significantly blended with a CoXVII transition in active region spectra, as suggested previously, although the latter does make a major contribution in the subflare observations. Most of the FeXV transitions which are blended have had the species responsible clearly identified, although there remain a few instances where this has not been possible. We briefly address the long-standing discrepancy between theory and experiment for the intensity ratio of the 3s21S-3s3p 3P1 intercombination line at 417.25 Åto the 3s21S-3s3p 1P resonance transition at 284.16 Å. Title: Oscillatory phenomena in solar and stellar atmospheres Authors: Bloomfield, David Shaun Bibcode: 2005PhDT........17B Altcode: This thesis presents varying studies into the nature of intensity oscillations observed both on the Sun and two active cool stars. The first part concentrates on the detection of correlated oscillations occuring between differing heights in the solar atmosphere above quiet-Sun magnetic network bright points (NBPs), interpreted as signatures of energy propagation. This is achieved through correlating in time the wavelet power spectra of lightcurves from images obtained in several optical wavelengths. In four of the eleven NBPs studied, evidence is found for upwardly-propagating, low-frequency waves (1.4 mHz, 2.1 mHz) in the lower chromosphere, decreasing in oscillatory power with the onset, or increase in power, of higher-frequency waves (2.9 mHz, 4.0 mHz) within the upper chromosphere. Moving higher into the atmosphere two of the four cases of higher frequency waves also show a decrease in power. These observational detections are interpreted as transverse-mode magnetohydrodynamic (MHD) waves undergoing non-linear mode coupling to longitudinal-modes at double the frequency, which shock or otherwise dissipate in the high chromosphere. Evidence is also found for additional upward- and downward- directed waves within all the NBPs studied.

The extension of wavelet power techniques into the analysis of phase difference and phase coherence is also presented, utilising UV intensities obtained from above a weak solar network element. The problems associated with the quantification of phase coherence values are outlined and a comparison of two differing methods is carried out. Changes observed in the evolution of phase difference between oscillations detected in the UV emission of the temperature minimum and low transition region are shown to be due to the alteration of the underlying magnetic topology, occuring when same polarity flux emerges nearby.

The final part of this thesis concerns the differing situation of intensity variations during energetic flare phenomena on two active cool stars. Repeated fluctuations are analysed in broad-band optical flare emission from the RS CVn binary II Peg and the B component of binary star EQ Peg, yielding medium- (220 s) and short- (10 s) oscillation periods, respectively. These periods are discussed in terms of a simplified model of standing waves within a closed coronal loop. In both cases the observed decrease of oscillation period up to flare peak and subsequent increase during initial flare decay follows the inverse proportionality to loop temperature expected by the simple model. Title: GRB 050724: WHT optical observations. Authors: Wiersema, K.; Rol, E.; Starling, R.; Tanvir, N.; Bloomfield, D. S.; Thompson, H. Bibcode: 2005GCN..3699....1W Altcode: No abstract at ADS Title: Wavelet Phase Coherence Analysis: Application to a Quiet-Sun Magnetic Element Authors: Bloomfield, D. Shaun; McAteer, R. T. James; Lites, Bruce W.; Judge, Philip G.; Mathioudakis, Mihalis; Keenan, Francis P. Bibcode: 2004ApJ...617..623B Altcode: A new application of wavelet analysis is presented that utilizes the inherent phase information residing within the complex Morlet transform. The technique is applied to a weak solar magnetic network region, and the temporal variation of phase difference between TRACE 1700 Å and SOHO/SUMER C II 1037 Å intensities is shown. We present, for the first time in an astrophysical setting, the application of wavelet phase coherence, including a comparison between two methods of testing real wavelet phase coherence against that of noise. The example highlights the advantage of wavelet analysis over more classical techniques, such as Fourier analysis, and the effectiveness of the former to identify wave packets of similar frequencies but with differing phase relations is emphasized. Using cotemporal, ground-based Advanced Stokes Polarimeter measurements, changes in the observed phase differences are shown to result from alterations in the magnetic topology. Title: A Detailed Study of Opacity in the Upper Atmosphere of Proxima Centauri Authors: Christian, D. J.; Mathioudakis, M.; Bloomfield, D. S.; Dupuis, J.; Keenan, F. P. Bibcode: 2004ApJ...612.1140C Altcode: We present far-UV and UV spectroscopic observations of Proxima Centauri obtained as part of our continued investigation into the optically thin approximation assumed for the transition regions of late-type stars. Significant opacity is found in the C III lines during both the quiescent and flaring states of Proxima Cen, with up to 70% of the expected flux being lost in the latter. Our findings cast some doubt on the suitability of the C III λ977 line for estimating the electron density in stellar atmospheres. However, the opacity has no significant effect on the observed line widths. We calculate optical depths for homogeneous and inhomogeneous geometries and estimate an electron density of 6×1010 cm-3 for the transition region using the O IV line ratios at 1400 Å. The combination of electron density and optical depth indicates path lengths as low as ~10 km, which are in excellent agreement with estimates of the small-scale structure seen in the solar transition region. Title: Erratum: ``Propagating Waves and Magnetohydrodynamic Mode Coupling in the Quiet-Sun Network'' (ApJ, 604, 936 [2004]) Authors: Bloomfield, D. Shaun; McAteer, R. T. James; Mathioudakis, Mihalis; Williams, David R.; Keenan, Francis P. Bibcode: 2004ApJ...609..465B Altcode: Proof corrections were not carried correctly to the final printed version of this paper, which resulted in an extra set of overbars appearing in both terms of the denominator of equation (3). The correct form of this equation is:C(Δt,ν)=(Σ[Pλ1(t,ν)-Pλ1(t,ν)][Pλ2(t+Δt,ν)-Pλ2(t+Δt,ν)])/(sqrt(Σ[Pλ1(t,ν)-Pλ1(t,ν)]2Σ[Pλ2(t,ν)-Pλ2(t,ν)]2)). (3)As noted in footnote 3, this correlation equation was stated incorrectly in our previous paper (eq. [4] in R. T. J. McAteer et al., ApJ, 604, 936 [2004]). However, the correct form of equation (3), now given here, was used for the analysis in both papers.

The press sincerely regrets this error. Title: Plasma Diagnostics of Active Region Evolution and Implications for Coronal Heating Authors: Milligan, R. O.; Gallagher, P. T.; Mathioudakis, M.; Bloomfield, D. S.; Keenan, F. P. Bibcode: 2004AAS...204.9803M Altcode: 2004BAAS...36..984M The decaying solar active region NOAA 10103 was observed during 2002 September 10--14 using the Coronal Diagnostic Spectrometer (CDS) onboard the Solar and Heliospheric Observatory (SOHO). Electron density maps were created using the Si X (356Å/347Å) ratio, which show densities of ∼1010cm-3 in the active region core, and ∼7x108cm-3 in the region boundaries. Over the five days of observations, the average electron density fell by approximately a factor of two. Temperature maps were created using the Fe XVI (335.4Å)/Fe XIV (334.2Å) ratio, which show electron temperatures of ∼2.2x106K in the active region core, and ∼2.0x106K in the region boundaries. Similarly to the electron density, the average electron temperature decreased over the five days, but by only ∼3%. The radiative and conductive losses, and resultant heating rate, were then calculated and compared to the total unsigned magnetic flux (Φ tot = ∫ dA |Bz|) from Michelson Doppler Interferometer (MDI) magnetograms. Losses due to radiation were found to exceed conductive losses by a factor of ten. As the region decayed, the heating rate decreased by close to an order of magnitiude between the first and last day of observations. In line with several coronal heating theories, a power-law relationship of the form Ptot} ∼Φ {tot0.95±0.07 was found between the heating rate and the unsigned magnetic flux. This result provides further observational evidence for wave rather than nanoflare heating of solar active regions.

Ryan Milligan would like to thank the Solar Physics Division for being awarded an SPD Studentship. Title: Propagating Waves and Magnetohydrodynamic Mode Coupling in the Quiet-Sun Network Authors: Bloomfield, D. Shaun; McAteer, R. T. James; Mathioudakis, Mihalis; Williams, David R.; Keenan, Francis P. Bibcode: 2004ApJ...604..936B Altcode: High-cadence multiwavelength optical observations were taken with the Dunn Solar Telescope at the National Solar Observatory, Sacramento Peak, accompanied by Advanced Stokes Polarimeter vector magnetograms. A total of 11 network bright points (NBPs) have been studied at different atmospheric heights using images taken in wave bands centered on Mg I b1 - 0.4 Å, Hα, and Ca II K3. Wavelet analysis was used to study wave packets and identify traveling magnetohydrodynamic waves. Wave speeds were estimated through the temporal cross-correlation of signals, in selected frequency bands of wavelet power, in each wavelength. Four mode-coupling cases were identified, one in each of four of the NBPs, and the variation of the associated Fourier power with height was studied. Three of the detected mode-coupling, transverse-mode frequencies were observed in the 1.2-1.6 mHz range (mean NBP apparent flux density magnitudes over 99-111 Mx cm-2), with the final case showing 2.0-2.2 mHz (with 142 Mx cm-2). Following this, longitudinal-mode frequencies were detected in the range 2.6-3.2 mHz for three of our cases, with 3.9-4.1 mHz for the remaining case. After mode coupling, two cases displayed a decrease in longitudinal-mode Fourier power in the higher chromosphere. Title: Ultraviolet Oscillations in the Chromosphere of the Quiet Sun Authors: McAteer, R. T. James; Gallagher, Peter T.; Bloomfield, D. Shaun; Williams, David R.; Mathioudakis, Mihalis; Keenan, Francis P. Bibcode: 2004ApJ...602..436M Altcode: Quiet-Sun oscillations in the four Transition Region and Coronal Explorer (TRACE) ultraviolet passbands centered on 1700, 1600, 1216, and 1550 Å are studied using a wavelet-based technique. Both network and internetwork regions show oscillations with a variety of periods and lifetimes in all passbands. The most frequent network oscillation has a period of 283 s, with a lifetime of 2-3 cycles in all passbands. These oscillations are discussed in terms of upwardly propagating magnetohydrodynamic wave models. The most frequent internetwork oscillation has a period of 252 s, again with a lifetime of 2-3 cycles, in all passbands. The tendency for these oscillations to recur in the same position is discussed in terms of ``persistent flashers.'' The network contains greater oscillatory power than the internetwork at periods longer than 300 s in the low chromosphere. This value is shown to decrease to 250 s in the high chromosphere. The internetwork also displays a larger number of short-lifetime, long-period oscillations than the network, especially in the low chromosphere. Both network and internetwork regions contain a small number of nonrecurring long-lifetime oscillations. Title: Intensity Oscillations During a flare on II Peg Authors: Avgoloupis, S.; Seiradakis, J. H.; Mathioudakis, M.; Bloomfield, D. Shaun; McAteer, J. Bibcode: 2004hell.conf..120A Altcode: No abstract at ADS Title: Oscillatory Signatures above Quiet Sun Magnetic Elements Authors: Bloomfield, D. S.; McAteer, R. T. J.; Lites, B. W.; Judge, P. G.; Mathioudakis, M.; Keenan, F. P. Bibcode: 2004ESASP.547...51B Altcode: 2004soho...13...51B A new application of wavelet analysis is presented. The data used are part of Joint Observing Proposal 72 between SoHO and TRACE, obtained on 1998 May 16 with accompanying groundbased data taken with the Dunn Solar Telescope at Sacramento Peak, New Mexico. A weak magnetic network region is studied and the temporal variation of phase difference between TRACE 1700 Å and SoHO/SUMER C II intensities is shown. The example clearly highlights the advantages of wavelet analysis over more classical techniques such as Fourier analysis, where the effectiveness of the technique to identify wavepackets with differing phase difference relations is emphasised. Title: An Automated Wavelet Analysis Approach to TRACE Quiet Sun Oscillations Authors: McAteer, R. T. J.; Gallagher, P. T.; Williams, D. R. Williams D. R.; Bloomfield, D. S.; Mathioudakis, M.; Keenan, F. P. Bibcode: 2004ESASP.547..139M Altcode: 2004soho...13..139M An automated wavelet analysis approach to TRACE UV quiet Sun datasets is discussed. Periodicity and lifetime of oscillations present in the network and internetwork are compared and contrasted. This provides a means of extending previous Fourier results into the time-localised domain. The longest lifetime oscillations occur around the acoustic band and the network tends to dominate over the internetwork at periods 4 mins. However, it is shown that the internetwork can dominate over the network at long periods (7 - 20 mins), but only for short lifetimes ( 3 complete oscillations). These results are discussed in terms of chromospheric heating theories. Title: White-light oscillations during a flare on II Peg. Authors: Mathioudakis, M.; Seiradakis, J. H.; Williams, D. R.; Avgoloupis, S.; Bloomfield, D. S.; McAteer, R. T. J. Bibcode: 2003A&A...403.1101M Altcode: We analyse the intensity oscillations observed in the gradual phase of a white-light flare on the RS CVn binary II Peg. Fast Fourier Transform power spectra and Wavelet analysis reveal a period of 220 s. The reliability of the oscillation is tested using several criteria. Oscillating coronal loop models are used to derive physical parameters such as temperature, electron density and magnetic field strength associated with the coronal loop. The derived parameters are consistent with the near-simultaneous X-ray observations of the flare. There is no evidence for oscillations in the quiescent state of the binary. Title: Observational Evidence for Mode Coupling in the Chromospheric Network Authors: McAteer, R. T. James; Gallagher, Peter T.; Williams, David R.; Mathioudakis, Mihalis; Bloomfield, D. Shaun; Phillips, Kenneth J. H.; Keenan, Francis P. Bibcode: 2003ApJ...587..806M Altcode: Oscillations in network bright points (NBPs) are studied at a variety of chromospheric heights. In particular, the three-dimensional variation of NBP oscillations is studied using image segmentation and cross-correlation analysis between images taken in light of Ca II K3, Hα core, Mg I b2, and Mg I b1-0.4 Å. Wavelet analysis is used to isolate wave packets in time and to search for height-dependent time delays that result from upward- or downward-directed traveling waves. In each NBP studied, we find evidence for kink-mode waves (1.3, 1.9 mHz), traveling up through the chromosphere and coupling with sausage-mode waves (2.6, 3.8 mHz). This provides a means for depositing energy in the upper chromosphere. We also find evidence for other upward- and downward-propagating waves in the 1.3-4.6 mHz range. Some oscillations do not correspond to traveling waves, and we attribute these to waves generated in neighboring regions. Title: A Study Of Extreme Ultraviolet Flare Activity On Late-Type Stars Authors: Bloomfield, D. S.; Mathioudakis, M. Bibcode: 2002ASPC..277..425B Altcode: 2002sccx.conf..425B No abstract at ADS Title: Opacity in the upper atmosphere of AU Mic Authors: Bloomfield, D. S.; Mathioudakis, M.; Christian, D. J.; Keenan, F. P.; Linsky, J. L. Bibcode: 2002A&A...390..219B Altcode: In this paper we investigate the validity of the optically thin assumption in the transition region of the late-type star AU Mic. We use Far-Ultraviolet Spectroscopic Explorer (FUSE) observations of the C Iii multiplet and O Vi resonance lines, hence yielding information at two different levels within the atmosphere. Significant deviations from the optically thin fluxes are found for C Iii in both quiescent and flare spectra, where only 60% of the flux is actually observed. This could explain the apparent deviation of C Iii observed in emission measure distributions. We utilize escape probabilities for both homogeneous and inhomogeneous geometries and calculate optical depths as high as 10 for the C Iii 1175.71 Åcomponent of the multiplet. Using a lower limit to the electron density (1011 cm-3) we derive an effective thickness of <100 km for the scattering layer. The emission originates from very small and compact regions, consistent with a filling factor of 10-5 derived for the flare plasma.