Solar Feature Catalogues In Egso

The Solar Feature Catalogues (SFCs) are created from digitized solar images using automated pattern recognition techniques developed in the European Grid of Solar Observation (EGSO) project. The techniques were applied for detection of sunspots, active regions and filaments in the automatically standardized full-disk solar images in Caii K1, Caii K3 and Hα taken at the Meudon Observatory and white-light images and magnetograms from SOHO/MDI. The results of automated recognition are verified with the manual synoptic maps and available statistical data from other observatories that revealed high detection accuracy. A structured database of the Solar Feature Catalogues is built on the MySQL server for every feature from their recognized parameters and cross-referenced to the original observations. The SFCs are published on the Bradford University web site http://www.cyber.brad.ac.uk/egso/SFC/ with the pre-designed web pages for a search by time, size and location. The SFCs with 9 year coverage (1996–2004) provide any possible information that can be extracted from full disk digital solar images. Thus information can be used for deeper investigation of the feature origin and association with other features for their automated classification and solar activity forecast.     

Electron beam as origin of white-light solar flares

We study the effect of chromospheric bombardment by an electron beam during solar flares. Using a semi-empirical flare model, we investigate energy balance at temperature minimum level and in the upper photosphere. We show that non-thermal hydrogen ionization (i.e., due to the electrons of the beam) leads to an increase of chromospheric hydrogen continuum emission, H^– population, and absorption of photospheric and chromospheric continuum radiation. So, the upper photosphere is radiatively heated by chromospheric continuum radiation produced by the beam. The effect of hydrogen ionization is an enhanced white-light emission both at chromospheric and photospheric level, due to Paschen and H^– continua emission, respectively. We then obtain white-light contrasts compatible with observations, obviously showing the link between white-light flares and atmospheric bombardment by electron beams.     

Automation of the Filament Tracking in the Framework of the HELIO Project

We present a new method to automatically track filaments over the solar disk. The filaments are first detected on Meudon Spectroheliograph Hα images of the Sun, applying the technique developed by Fuller, Aboudarham, and Bentley (Solar Phys. 227, 61, 2005). This technique combines cleaning processes, image segmentation based on region growing, and morphological parameter extraction, including the determination of filament skeletons. The coordinates of the skeleton pixels, given in a heliocentric system, are then converted to a more appropriate reference frame that follows the rotation of the Sun surface. In such a frame, a co-rotating filament is always located around the same position, and its skeletons (extracted from each image) are thus spatially close, forming a group of adjacent features. In a third step, the shape of each skeleton is compared with its neighbours using a curve-matching algorithm. This step will permit us to define the probability [P] that two close filaments in the co-rotating frame are actually the same one observed on two different images. At the end, the pairs of features, for which the corresponding probability is greater than a threshold value, are associated using tracking identification indices. On a representative sample of filaments, the good agreement between automated and manual tracking confirms the reliability of the technique to be applied on large data sets. This code is already used in the framework of the Heliophysics Integrated Observatory (HELIO) to populate a catalogue dedicated to solar and heliospheric features (HFC). An extension of this method to other filament observations, and possibly sunspots, faculae, and coronal-holes tracking, can also be envisaged.     

Fluctuations in the Intensity of Radiation Emerging from a Multicomponent Stochastic Atmosphere. II

This part of a series of papers examines the more general problem in which it is assumed that the fluctuations in the intensity of radiation emerging from a medium are caused by random variations in both the optical thickness of the structural elements and the power of the energy sources contained in them. The frequency dependence of the relative mean square deviation (RelMSD) is investigated for different possible relationships among the parameters of the fine structure components. It is shown that the level of fluctuations at the central frequencies of a line can be greater than or smaller than in the far wings. The dependence of the RelMSD on the number of components and the number of possible realizations of their optical properties is discussed. The influence of random variations in the scattering coefficient on the observed integral intensity of a spectrum line is also examined. Observations of several relatively strong EUV lines from the SOHO/ SUMER space program are presented for comparison. These data indicate that there is a correlation between the frequency dependence of the RelMSD and the characteristic temperature for formation of these lines.__________Translated from Astrofizika, Vol. 48, No. 2, pp. 303–313 (May 2005).     

A full-disk image standardisation of the synoptic solar observations at the Meudon Observatory

Robust techniques are developed to put the H and Ca K line full-disk images taken at the Meudon Observatory into a standardised form of a `virtual solar image'. The techniques include limb fitting, removal of geometrical distortion, centre position and size standardisation and intensity normalisation. The limb fitting starts with an initial estimate of the solar centre using raw 12-bit image data and then applies a Canny edge-detection routine. Candidate edge points for the limb are selected using a histogram based method and the chosen points fitted to a quadratic function by minimising the algebraic distance using SVD. The five parameters of the ellipse fitting the limb are extracted from the quadratic function. These parameters are used to define an affine transformation that transforms the image shape into a circle. Transformed images are generated using the nearest neighbour, bilinear or bicubic interpolation. Intensity renormalisation is also required because of a limb darkening and other non-radial intensity variations. It is achieved by fitting a background function in polar coordinates to a set of sample points having the median intensities and by standardising the average brightness. Representative examples of intermediate and final processed results are presented in addition to the algorithms developed. The research was done for the European Grid of Solar Observations (EGSO) project.     

Solar EUV/FUV irradiance variations: analysis and observational strategy

The knowledge of solar extreme and far ultraviolet (EUV) irradiance variations is essential for the characterization of the Earth’s upper atmosphere. For a long time, this knowledge has been based on empirical models, which are themselves based on proxies of the solar activity. However, the accurate modeling and prediction of the Earth’s upper atmosphere necessitate to improve the precision on the irradiance and its variations below about 200 nm. Here, we present a review of recent works made by the authors that aim at quantifying the irradiance variability at these wavelengths, and that lead to new way of monitoring the solar EUV/FUV irradiance spectrum. In more details, it is shown that the quantification of the high level of redundancy in the solar spectrum variability allows to envisage measuring only a small portion of the spectrum without losing essential knowledge. Finally, we discuss what should and could be measured in order to retrieve the solar extreme and far ultraviolet spectrum.     

Studying Sun–Planet Connections Using the Heliophysics Integrated Observatory (HELIO)

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.     

Automated Technique For Comparison Of Magnetic Field Inversion Lines With Filament Skeletons From The Solar Feature Catalogue

We present an automated technique for comparison of magnetic field inversion-line maps from SOHO/MDI magnetograms with solar filament data from the Solar Feature Catalogue created as part of the European Grid of Solar Observations project. The Euclidean distance transform and connected component labelling are used to identify nearest inversion lines to filament skeletons. Several filament inversion-line characteristics are defined and used to automate the decision whether a particular filament/inversion-line pair is suitable for quantitative comparison of orientation and separation. The technique is tested on 551 filaments from 14 Hα images at various dates, and the distributions of angles and distances between filament skeletons and line-of-sight (LOS) magnetic inversion lines are presented for six levels of magnetic field smoothing. The results showed the robustness of the developed technique which can be applied for a statistical analysis of magnetic field in the vicinity of filaments. The method accuracy is limited by the static filament detection which does not distinguish between filaments, fibrils, pre-condensations and filament barbs and this may increase the asymmetries in magnetic distributions and broadening in angular distributions that requires the incorporation of a feature tracking technique.     

Effect of electron beams during solar flares

Electron bombardment of the solar atmosphere has two effects: one is to enhance hydrogen recombination emission, the other is to increase the opacity via an increase of H^– population. The first effect is the most important in the upper part of the atmosphere and the second in the lower part. We predict that, when enhanced absorption dominates in the part of the atmosphere where radiation originates, there will be a decrease in the white-light emission, leading to a negative flare, or what we call a Black-Light Flare. This phenomenon occurs only for a short duration, not more than 20 s. Black-Light Flares have already been observed in the case of flare stars and we suggest here that they could also be present on the Sun, just prior to a White-Light Flare.Also Dept. of Physics and Astronomy, University of Glasgow, Scotland.Also Sterrekundig Instituut, Rijksuniversiteit te Utrecht, The Netherlands.Also Heliophysical Observatory of the Hungarian Academy of Sciences, Debrecen, Hungary.     

Filament Recognition and Image Cleaning on Meudon Hα Spectroheliograms

This paper presents the techniques developed for the automated detection of filaments on Meudon H spectroheliograms, and, by extension, on any full-disk H Sun observations. Some cleaning processes are first applied to the images to correct them from defects characteristic of the instrument. Indeed, these defects may lead to spurious detections. From the cleaned images, filament areas are then segmented using a region growing method which efficiently returns the full extent of these dark areas. The filaments are finally described by means of their pruned skeleton. This representation allows one to compare the automatically segmented filaments with those manually recorded for Meudon Synoptic Maps. The very good agreement observed on a representative set of images confirms that this method can effectively be used in the frame of the EGSO (European Grid of Solar Observations) project in order to produce a reliable catalog dedicated to solar features.