Prof aa aa (ss)

Double layers and the intensities of dielectronic satellite lines in solar flares

Dr Jaroslav Dudik (DAMTP, CMS, University of Cambridge)
Departures from the Maxwellian distribution are known to occur during solar flares, with the high-energy tails being the most routinely observed example. However, changes in the bulk of the distribution at energies of only several keV occur as well. These are manifested by increase of dielectronic satellite lines with respect to the allowed lines. This increase occur during impulsive phase and are correlated to the radio bursts. Here we discuss the influence of various energy distributions proposed to model the intensities of the dielectronic satellite line and conclude that the intensities can be explained by particle acceleration in plasma double layers.

The effect of guide field on collisionless magnetic reconnection in a stressed X-point collapse

Mr Jan Graf von der Pahlen (Queen Mary University, London)
Works of Tsiklauri D., T. Haruki, Phys. of Plasmas, 15, 102902 (2008) and Tsiklauri D. and T. Haruki, Phys. of Plasmas, 14, 112905, (2007) are extended by inclusion of the out-of-plane magnetic (guide) field. In particular, magnetic reconnection during collisionless, stressed X-point collapse for varying out-of-plane guide-fields was studied using a kinetic, 2.5D, fully electromagnetic, relativistic particle-in-cell numerical code. We find that an increase of guide field generally yields later onset in the reconnection peak rates. The normalized reconnection rate is fast 0.15-0.25. It is found that the existence of the guide field stimulates the generation of electron vortices. Possible causes of the vortex generation are explored based on strong, localized plasma heating and vortex-induced tearing mode models. Before peak reconnection onset, oscillations in the out-of-plane electric field are found which may have observational implications for the solar radio burst fine structure spikes.

The location of non-thermal velocity in the early phases of large flares

Prof Louise Harra (UCL - MSSL)
Non-thermal velocity measurements of the solar atmosphere, particularly from UV and X-ray emission lines have demonstrated over the decades that this parameter is important in understanding the triggering of solar flares. Enhancements have often been observed before intensity enhancements are seen. However, until the launch of Hinode, it has been difficult to determine the spatial location of the enhancements to understand the location. The Hinode EUV Imaging Spectrometer (EIS) has the spectral and spatial resolution to allow us to probe the early stages of flares in detail. We analyse four events, all of which are M or X-classification flares, and all are located towards the limb for ease of determining the existence of any above the loop-top sources.

SDO AIA and EVE Observations and Modelling of Solar Flare Loops

Dr Helen Mason (University of Cambridge)
Petkaki, P.; Del Zanna, G.; Mason, H. E.; Bradshaw, S. J.
We present imaging and spectroscopic observations of small solar flare, obtained with the Atmospheric Imaging Assembly (AIA) and Extreme ultraviolet Variability Experiment (EVE) on the Solar Dynamics Observatory (SDO). We obtain excellent agreement between the peak flare temperatures estimated using the EVE spectra with those obtained from the ratio of the 94 Å and 131 Å AIA channels, which are found to be dominated by Fe XVIII and Fe XXI. The flare loops are close to isothermal during the gradual phase. We have run several hydrodynamic simulations (using HYDRAD) to study the cooling of the flare loops. We find good agreement between observed and predicted temperatures and densities when a gradual increase and decrease of the heating is assumed. We plan to extend these studies to include observations with Hinode/EIS and RHESSI.

Distinct wave trains in propagating fast wave associated with flaring energy releases

Mr Ding Yuan (Department of Physics, University of Warwick)
Large-scale fast magneto-acoustic waves are well resolved both in temporal and spatial scale by SDO/AIA. The waves may carry sufficient energy for coronal heating. It is also a potential tool for MHD seismology.
We aim to probe the link between the propagating fast wave trains and quasi-periodic pulsations in flaring energy releases. By measuring the wave parameters, we investigate the potential of propagating fast wave trains in the diagnostics of their energy source and wave guides.
The wave amplitude and propagating speed are measured to probe the characteristics of its energy source and coronal condition. The correlation of fast wave trains with flare-generated radio bursts is tested.
The wavelet spectrum of the difference intensity variation shows a typical tadpole structure. It implies that the fast magneto-acoustic waves were generated impulsively. The wave train releases are found to be highly correlated in start time with the radio bursts (non-thermal electrons), it indicates that during the flare several energy pulses were released. The wave amplitude reaches maximum in the midway of its course. This can be an combined effects of wave energy diffusing across the coronal loops and density stratification. Besides, it may have an associated energy source propagating at the same speed, i.e. Alfven wave. The cross-sectional amplitude distribution perpendicular to the wave vector follows well a Gaussian profile, it implies that the wave energy is more close to a point source. This feature is more close to a kink wave. The propagating speed displays significant deceleration, from ~735-845 km/s to ~600 km/s. This can be caused by the decrease of \alfven speed, however the projection effect cannot be excluded.