|10:00 - 10:30||Coffee & Registration|
|10:30 - 12:35||Morning Session
Chair: Lyndsay Fletcher (University of Glasgow)
|10:30 - 11:05||Invited Talk: Solar flares: old problems - new answers?
Astrid Veronig (University of Graz, Austria)
In this talk, we will review observational aspects of solar flares. We focus on (long-lasting) problems in our understanding of the flare physics and on possible new insights by recent satellite missions, such as RHESSI, STEREO, and Hinode. Among the issues discussed are: the flare standard model, energy release and transport, particle acceleration, relation to coronal mass ejections (dynamics and energetics) and global shock waves.
|11:05 - 11:20||Do all Flares have White Light Emission?|
David Jess (Queen's University Belfast)
High-cadence, multi-wavelength optical observations of a solar active region (NOAA 10969), obtained with the Swedish Solar Telescope, are presented. Difference imaging of white light continuum data reveals a white light brightening, 2 min in duration, linked to a co-temporal and co-spatial C2.0 flare event. The flare kernel observed in the white light images has a diameter of 300 km, thus rendering it below the resolution limit of most space-based telescopes. Continuum emission is present only during the impulsive stage of the flare, with the effects of chromospheric emission subsequently delayed by 2 min. The localized flare emission peaks at 300% above the quiescent flux. This large, yet tightly confined, increase in emission is only resolvable due to the high spatial resolution of the Swedish Solar Telescope. We suggest that the creation of white-light emission is a common feature of all solar flares.
|11:20 - 11:35||Coronal response to emerging flux|
Alison Wallace (MSSL-UCL)
Alison Wallace, Louise Harra, Lidia van Driel-Gesztelyi, Lucie Green, Sarah Matthews, Alphonse Sterling & Suguru Kamio
Using observations from Hinode, TRACE, SOHO and STEREO, we follow the evolution of emerging flux into an existing active region and study the coronal response over a period of an hour during which we observe siphon flows and flaring. We discuss the possible driver of the siphon flows and the role of magnetic reconnection.
|11:35 - 11:50||Hinode/EIS observations of small flares|
Urmila Mitra-Kraev (DAMTP, University of Cambridge)
Urmila Mitra-Kraev, Giulio Del Zanna and Helen Mason
We present Hinode/EIS spectral observations of small flares, complemented by imaging at different temperatures (TRACE, Hinode/XRT). Firstly, we discuss the diagnostic possibilities of EIS to observe flares. We show that some of the strongest flare lines are blended and careful analysis is needed to interpret the observations. Then, we present measurements of flows and non-thermal broadenings and discuss their interpretation within the standard flare models.
|11:50 - 12:05||Hydrodynamics and kinematics of flares|
Claire Raftery (Trinity College Dublin)
The hydrodynamic evolution of solar flare is analysed from both an observational and theoretical point of view. Combining the observations with hydrodynamic simulations allows the heating and cooling mechanisms, along with dynamic phenomena such as chromospheric evaporation to be fully investigated.
Following the analysis of flare hydrodynamics, loop top and CME kinematics are investigated. Evidence of X to Y type reconnection is presented using observations from STEREO, RHESSI and Mercury Messenger.
|12:05 - 12:20||Inertial Alfvén wave acceleration of solar flare electrons|
Ken McClements (Culham - EURATOM/UKAEA)
The possibility that electrons could be accelerated by inertial Alfvén waves to hard X-ray-emitting energies in the low solar corona during flares is investigated theoretically. This investigation is prompted in part by recent microwave observations indicating that the Alfvén speed above active regions could be of the order of a tenth of the speed of light or more; electrons can be accelerated to velocities in excess of the Alfvén speed on collisionless timescales via reflection by a single inertial Alfvén wave pulse. It is shown that the fraction of particles accelerated is a sensitive function of the initial electron temperature and the transverse length scale of the shear Alfvén wave pulse; under typical pre-flare coronal conditions, a significant fraction of the electron population can be accelerated if the transverse length scale is of the order of a few metres or less. The energy distribution of electrons accelerated by a single wave pulse is also determined.
|12:20 - 12:35||Collisionless phase mixing as solar flare electron acceleration mechanism - a parametric study|
David Tsiklauri (University of Salford)
Previous studies of phase mixing of ion cyclotron (IC), Alfvénic, waves in the collisionless regime have established the generation of parallel electric field and hence acceleration of electrons in the regions of transverse density inhomogeneity. However, outstanding issues were left open. Here we use the 2.5 D, relativistic, fully electromagnetic particle-in-cell code and an analytic magnetohydrodynamic (MHD) formulation, to establish the following points: (i) Using the generalized Ohm's law we find that the parallel electric field is supported mostly by the electron pressure tensor, with a smaller contribution from the electron inertia term. (ii) The generated parallel electric field and the fraction of accelerated electrons are independent of the IC wave frequency remaining at a level of six orders of magnitude larger than the Dreicer value and approximately 20%, respectively. The generated parallel electric field and the fraction of accelerated electrons increase with the increase of IC wave amplitude. The generated parallel electric field seems to be independent of plasma beta, while the fraction of accelerated electrons strongly increases with the decrease of plasma beta (for plasma beta of 0.0001 the fraction of accelerated electrons can be as large as 47%). (iii) In the collisionless regime IC wave dissipation length (that is defined as the distance over which the wave damps) variation with the driving frequency shows a deviation from the analytical MHD result, which we attribute to a possible frequency dependence of the effective resistivity. (iv) Effective anomalous resistivity, inferred from our numerical simulations, is at least four orders of magnitude larger than the classical Spitzer value.
|12:35 - 14:00||Lunch (available for purchase) & Poster Session|
|14:00 - 15:30||Afternoon Session
Chair: Iain Hannah (University of Glasgow)
|14:00 - 14:15||Stationary and impulsive injection of electron beams in presence of converging magnetic field|
Taras Siversky (University of Bradford)
Taras Siversky, Valentina Zharkova
Precipitation of a fast electron beam with power-law energy spectrum in the solar atmosphere is studied by numerical simulation of the Fokker-Planck equation, in order to investigate the influence of a converging magnetic field in comparison with collisional and Ohmic losses. Three models of the converging magnetic field are considered: exponential, parabolic and exponential-constant. The exponential and parabolic magnetic field profiles are shown to only affect high energy electrons (> 100 keV). The exponential-constant model, where the magnetic field exponentially increases with depth in the corona and is constant in the chromosphere, is found to be most effective for the whole spectrum of precipitated electrons. A comparison of stationary versus short impulsive injection allows to establish further dynamics of electron beams in time and depth.
|14:15 - 14:30||Direct Observations of the Coronal Acceleration Region of a Solar Flare|
Säm Krucker (UC Berkeley, USA)
Säm Krucker, H.S. Hudson, R.P. Lin, SSL, UC Berkeley, USA
S.M. White, University of Maryland, USA
Solar flares essentially convert the intrinsic energy of coronal magnetic field into the kinetic energy of accelerated particles. Hard X-ray emission from flare-accelerated electrons produced by the bremsstrahlung mechanism provides the most direct diagnostics of electron acceleration. The most discussed coronal hard X-ray source has been the above-the-loop-top source observed in the Masuda flare. The poor spectral resolution of these observations, however, made an interpretation ambiguous, and the exact location of the acceleration remained elusive. We present high spatial and spectral resolution RHESSI hard X-ray observations of an above-the-loop-top source with simultaneous microwave observations from NoRH. These observations provide a unambiguous interpretation of above-the-loop-top sources: The above-the-loop-top source itself is the acceleration region, where all electrons within an extended volume (1e27 cm3) are accelerated. The distribution of the accelerated electrons is definitely non-thermal, with a power law distribution extending from ~10 keV up to the relativistic range (few MeV). The plasma beta in the acceleration region changes from the pre-flare value of ~0.01 to ~1, indicating that roughly half of the magnetic energy has been transformed into kinetic energy.
|14:30 - 14:45||The Propagation of Impulsive Solar Energetic Electrons through the Heliosphere|
Hamish Reid (University of Glasgow)
Electron beams propagating from the Sun to the Earth can generate Langmuir waves in the ambient solar corona plasma which in turn generate radio emission otherwise known as type III solar radio bursts. Some solar impulsive events show good agreement with time of flight dispersion and it is often believed that electrons propagate scatter-free. We model the propagation of an electron beam in the solar corona plasma taking into account the generation and absorption of Langmuir waves. The results show electrons transferring energy to created Langmuir waves, causing the electron distribution function to be smeared down in velocity space. This deceleration of electrons in transit could account for the observed early injection of low energy electrons.
|14:45 - 15:00||Scientific Understanding and the Risk from Extreme Space Weather|
Mike Hapgood (STFC RAL)
The Carrington event is increasingly recognised as the canonical example of extreme space weather. It provides credible evidence that the Sun can produce an event that would severely challenge many of the technologies critical to our twenty-first century society, notably the ubiquitous use of electrical power and huge range of public and commercial services that depend on space-based systems. It shows that there is a clear need to express space weather risks in similar form to other natural hazards, e.g. to develop scientific methodologies that can estimate the likelihood of future Carrington-class events at Earth. This presentation will outline some key issues that need to be addressed in developing such methodologies, e.g. the severe limitations imposed on statistical techniques by the global nature of space weather and the need to develop physics-based methods that can realistically handle major departures from average conditions.
|15:00 - 15:15||A Survey of Stellar X-ray Flares from the 2XMM Catalogue|
John Pye (University of Leicester)
John Pye, Duncan Fyfe, Simon Rosen, Anja Schroeder Department of Physics and Astronomy, University of Leicester
The XMM-Newton 2XMM Serendipitous Source Catalogue (Watson et al, 2008, A&A, in press) is being used as the basis for a survey of stellar X-ray flares. As 2XMM is the largest X-ray-source catalogue to date, and as X-ray lightcurves are produced as a standard data product, the catalogue provides an excellent basis for a comprehensive and sensitive survey of stellar flares - both from targeted active stars and from those observed serendipitously in the ~half-degree diameter field-of-view of each observation. We present results for a subset corresponding to those sources which have 2XMM lightcurves and have late-type stellar counterparts in the Hipparcos Tycho catalogue: ~700 stars, with a total of ~150 X-ray flares. Whilst the target stars are mainly well-known coronally-active objects, most of the serendipitously-detected flaring stars have little previously published information, the X-ray flares thus providing the first indication of their highly active nature. The observed flares range in duration from ~1000 s to ~10,000 s, have peak X-ray luminosities log(Lx, erg/s) from ~29 to ~32, and X-ray energy output log(Ex, erg) from ~32 to ~35. We present simultaneous UV/optical lightcurves for those flares also observed with the XMM-Newton Optical Monitor.
|15:15 - 15:30||The Solar-C space mission - a follow-on to the Hinode mission|
Louise Harra (UCL-MSSL)
The Japanese Hinode space mission was launched in September 2006, and has made many new scientific discoveries. These include the ubiquitous behaviour of waves, the kG magnetic field at the poles, source of solar wind and pre-flare behaviour. In this talk I will describe the plans for the next japanese mission - Solar-C - and the science goals that will be addressed.
|15:30 - 16:00||Tea prior to RAS Ordinary Meeting|
|16:00 - 18:00||RAS Ordinary Meeting
features a talk by Stuart Clark, author "The Sun Kings", about Carrington and the 1859 event.