Using active contours for automated tracking of UV and EUV solar flare ribbons

Solar flare UV and EUV images show elongated bright ``ribbons'' that move over time. If these ribbons are assumed to locate the footpoints of magnetic field lines reconnecting in the corona then it is clear that studying their evolution can provide an important insight into the reconnection process. We propose an image processing method based on active contours (commonly referred to as ``snakes''), for tracking UV and EUV flare ribbons in images from the transition region and coronal explorer (TRACE). Our method aims to provide an efficient, accurate and automatic tool to aid in the study of flare ribbon evolution in large datasets. Chapter 1 provides an introduction to the Sun and solar activity, with a more focussed section on solar flares where the mechanism for the creation of flare ribbons is discussed. We also outline the motivation for solar physics research as a whole and more specifically the motivations behind this project. In this chapter we introduce the TRACE satellite as the source the images used in this project, with a summary of its hardware and the UV and EUV channels which the images used in this project are captured in. Chapter 2 introduces some basics of image processing, such as applying spatial filters. We also look at the different approaches to image segmentation including a more in depth study of active contours. The role of image processing in solar physics and the driving forces for image processing development in solar physics are summarised. The final section of this chapter presents a review of previous methods used for the tracking of solar flare ribbons, including manual, semi-automatic and fully automatic methods. The first part of Chapter 3 details the pre-processing steps applied to the TRACE data before its use by our algorithm. The second part of this chapter introduces our algorithm, with a general overview and detailed discussion of the constituent parts. We also show results from initial tests carried out using a simulated test image, and demonstrate how different parameters of the algorithm can affect its result. Chapter 4 shows results obtained from using our algorithm on TRACE flare images. Some modifications to the algorithm were deemed necessary after applying it to only a small number of flare images, the initial part of this chapter covers the reasons for the modifications and the modifications themselves. The remainder of the chapter presents results of the algorithm applied to a number image sequences from different flares. The results are presented and discussed for each flare separately, with one flare being used as an example of how the parameters of the algorithm can be adapted to suit different flares and images. Chapter 5 discusses to what extent the aim of the project has been achieved and presents a summary of the problems encountered in applying our algorithm to flare images. This chapter finishes with a look at some ideas for future work, both for our algorithm specifically, and for general efforts at flare ribbon tracking

Mercury 2000: Stereoscopic Observations of Gamma Ray Flares

Stereoscopic observations of gamma ray radiation from solar flares would provide further scientific impetus to recent proposals for a planetary observer mission to Mercury in the late 1990's. The solar monitoring phase of this mission could continue through the period of maximum flare activity in the years 2002-2006 with a dawn-dusk polar orbit which would allow continuous solar visibility and minimize solar tracking requirements. Simultaneous measurements of flare radiation from gamma ray instruments with comparable solar flux sensitivity in orbits around Mercury and Earth would provide stereoscopic information on directivity and altitude location in the solar atmosphere of the flare radiation sources and might significantly advance understanding of energy release and particle acceleration processes in solar flares. The closer proximity of Mercury to the Sun would allow use of a much smaller gamma ray spectrometer system than required at 1 A.U. and would also provide the first opportunity for direct detection of solar neutrons at energies of 1-10 MeV. The Mercury orbiter would also be capable of monitoring 1-500 MeV solar protons to search for decay protons from solar neutron flares and to provide automatic early warning of large proton flares which would be a hazard to manned space operations near Earth and beyond

Solar Magnetic Feature Detection and Tracking for Space Weather Monitoring

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)

Coronal mass ejections from the same active region cluster: Two different perspectives

The cluster formed by active regions (ARs) NOAA 11121 and 11123, approximately located on the solar central meridian on 11 November 2010, is of great scientific interest. This complex was the site of violent flux emergence and the source of a series of Earth-directed events on the same day. The onset of the events was nearly simultaneously observed by the Atmospheric Imaging Assembly (AIA) telescope aboard the Solar Dynamics Observatory (SDO) and the Extreme-Ultraviolet Imagers (EUVI) on the Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) suite of telescopes onboard the Solar-Terrestrial Relations Observatory (STEREO) twin spacecraft. The progression of these events in the low corona was tracked by the Large Angle Spectroscopic Coronagraphs (LASCO) onboard the Solar and Heliospheric Observatory (SOHO) and the SECCHI/COR coronagraphs on STEREO. SDO and SOHO imagers provided data from the Earth's perspective, whilst the STEREO twin instruments procured images from the orthogonal directions. This spatial configuration of spacecraft allowed optimum simultaneous observations of the AR cluster and the coronal mass ejections that originated in it. Quadrature coronal observations provided by STEREO revealed a notably large amount of ejective events compared to those detected from Earth's perspective. Furthermore, joint observations by SDO/AIA and STEREO/SECCHI EUVI of the source region indicate that all events classified by GOES as X-ray flares had an ejective coronal counterpart in quadrature observations. These results have direct impact on current space weather forecasting because of the probable missing alarms when there is a lack of solar observations in a view direction perpendicular to the Sun-Earth line.Comment: Solar Physics - Accepted for publication 2015-Apr-25 v2: Corrected metadat