|12:35 - 14:00||Lunch (available for purchase) & Poster Session|
|The effects of magnetic resistivity on a magnetic fly-by model|
Andrew Hayes (University of St. Andrews)
A. L. Haynes ; C. E. Parnell ; K. Galsgaard   University of St Andrews  Niels Bohr Institute, Copenhagen
The solar corona of the quiet-Sun is threaded by a complex magnetic field structure that evolves as it is dragged around by strong photospheric flows. These motions inject energy into the atmosphere where it is stored as currents in the magnetic field. Subsequently it is released into the corona as heat by magnetic reconnection. Here, using a 3D resistive MHD code, we consider the magnetic interaction of two opposite polarity sources driven by an anti-parallel flow on the photosphere within a uniform overlying field (Galsgaard et al, 2000; Haynes et al, 2007) and investigate how the magnetic resistivity affects the magnetic field structure and energy transported, stored and released by these motions. To fully understand the structure of the magnetic field we determine its magnetic skeleton, which contains the most important components of the magnetic field. The evolution of the magnetic skeleton is then analysed and compared to the reconnection and energetics within the model. In these models, we discover that the choice of resistivity is important: as the resistivity decreases the complexity and duration of the interaction increase, leading to more reconnection and a greater amount of energy released. Our results suggest that with a magnetic resistivity of a realistic value for the Sun, our magnetic interaction could lead to chaotic behaviour.
|A Solar Flare in Ly-alpha |
Fatima Rubio de Costa (University of Catania, Sicily)
F. Rubio da Costa, L. Fletcher, N. Labrosse, F. Zuccarello.
The TRACE satellite observed a small number of solar flares in the Lyman alpha channel, which have until now not been analyzed. We look at a two well-observed flares (in 28th February 1999 and in 8th September 1999) to investigate different topics. 1.-We studied spatial and temporal evolution of the flare and associated filament eruption in Lyman alpha. 2.-Hard X-ray and soft X-ray emission has been analyzed for the 8th September 1999 event, using some HXT/Yohkoh and SXT/Yohkoh data. 3.-We have examined the flare energetics using the hard X-rays (in the collisional thick target approximation) to estimate the energy flux carried by electrons at the 8th September 1999 event. 4.-Using TRACE 1216A/1600A channels it is possible to estimate the radiative power in UV assuming different models (black-body, Balmer-Parschen model or Allred model). 5.-Running a code that solves iteratively the statistical equilibrium and radiative transfer equations, taking into account the temperature at each layer, the height of the layer (in terms of mass) and the microturbulent velocity, we are studying the variation of the intensity and the shape of different Hydrogen emission lines (in particular the Lyman alpha line emission) in different layers of the Sun, with the aim of estimate the observational integrated intensity of the flare footpoints at different wavelengths and compare it with the theoretical value obtained.
We will use these observations to anticipate what can be observed in the future by the proposed SMESE satellite mission, and to compare with predictions of semi-empirical and theoretical models of the flare chromosphere.
|Particle Acceleration in Solar Flares by Collapsing Magnetic Traps |
Keith Grady (University of St. Andrews)
A possible particle acceleration mechanism suggested to be operating in solar flares is acceleration by collapsing magnetic traps. We consider 2D collapsing trap models using ideal kinematic MHD. The theory of the models and possible energy gains in example fields are discussed. The effect of the initial conditions on the trapping times and energy gains of particles are examined.
|Quasi-periodic pulsations in solar flares|
Valery Nakariakov (Univerisity of Warwick)
Valery Nakariakov and Andy Inglis
Quasi-periodic pulsations (QPP) is a common feature of flaring energy releases in the solar atmosphere, observed in all bands, from radio and microwave to hard X-ray. Physical mechanisms responsible for the generation of QPP split into two groups: "load/unload" mechanisms (e.g. repetitive regimes of magnetic reconnection) and MHD oscillations. MHD oscillations can affect all elements of the flaring emission generation: triggering of reconnection and modulation of its rate, acceleration and dynamics of non-thermal electrons, and physical conditions in the emitting plasmas. Periods and other parameters of QPP are linked with properties of flaring plasmas and their morphology. Observational investigation of the QPP generation mechanisms based upon the use of spatial information, broadband spectral coverage and multi-periodicity is discussed.
|Particles acceleration in a reconnecting current sheet: PIC simulation|
Taras Siversky (University of Bradford)
Taras Siversky, Valentina Zharkova
The acceleration of protons and electrons in a reconnecting current sheet (RCS) is simulated with a particle-in-cell (PIC) 2D3V code. The electro-magnetic configuration forming the RCS incorporates all three components of the magnetic field (including the guiding field) and a drifted electric field. We also consider the additional electric and magnetic fields induced by plasma particles. The simulations reveal that there is a polarisation electric field that appears during acceleration owing to a separation of electrons from protons towards the midplane of the RCS. The polarisation electric field is shown to generate plasma turbulence that essentially affects the trajectories of the accelerated electrons as well as their energy gains.
|Automated computer-based Prediction of Significant Solar Flares in near real-time|
Rami S Qahwaji (Bradford University)
The importance of real-time processing of solar data especially for space weather applications is increasing continuously. We present our work on the automated short-term prediction of significant flares using SOHO/MDI images. We have designed a machine-learning system to analyse years of sunspots and flares data to create associations that can be represented using computer-based learning rules. The prediction depends mainly on the McIntosh properties of the sunspot region, which are extracted automatically from real-life images and integrated with the machine learning system to deliver the solar flare predictions. Our solar flare prediction tool is available publicly at http://spaceweather.inf.brad.ac.uk/. In this presentation, we will discuss the evaluation of the solar flare prediction system. Also we will introduce some of the future research directions in terms of studying the magnetic properties and the flaring history of active regions to deliver enhanced predictions.
|Hard X-ray emission from a flare-related jet |
Hazel Bain and Lyndsay Fletcher (University of Glasgow)
We report the first observation of hard X-ray emission formed in a coronal jet. The event occurred on the 22nd of August 2002 and its evolution was observed by a number of instruments. In particular we study the pre-impulsive and impulsive phase of the flare using data from RHESSI, TRACE and the Nobeyama Radioheliograph. During this period RHESSI observed significant hard X-ray emission to energies as high as 50 keV in the jet. RHESSI spectroscopy suggests a temperature of the order ~20 MK for the jet material. Radio observations from the Nobeyama Radioheliograph show a positive spectral index for the ejected material, which may be explained by optically-thick gyrosynchrotron emission from non-thermal electrons in the jet.