Gerrard Brown (University of Glasgow)
The influence of coronal emission lines on prominence plasma
Prominences are cool, high-density structures located in the corona; the surrounding corona can influence the processes, which go on inside the prominence via the effect of coronal radiation illuminating the prominence. This can affect the ionisation degree of the plasma inside the prominence. Several strong emission lines are found in the coronal spectrum, and the impact that these lines in the coronal spectrum has on the radiative transfer processes of the prominence is examined. A one-dimensional model is used to model the radiative transfer processes of the prominence. Previous modeling did not include the coronal lines. In this study a coronal line is added to the code's incident radiation; we present the influence of this additional coronal radiation on the state of the prominence plasma. The additional line affects the ionisation degree and level populations of the prominence plasma and so the intensity of the prominence plasma's emissions. The scale of this effect varies with the wavelength of the coronal line, as would be expected from consideration of photoionisation cross section.
Sandra Milena Conde Cuellar (Instituto Nacional de Pesquisas Espaciais, Brasil), M.H. Ibanez (Centro de Fysica Fundamental Universidad de Los Andes, Venezuela) Heating of non-adiabatic ows by hydrodynamic waves in the solar atmosphere
Dissipation of sound waves are assumed to be an important source of heat input in several astrophysical plasmas. Most of the works consider linear disturbances, however in physical situations occurring in the solar atmosphere, one must expect that waves with arbitrary amplitude occur. The present work generalizes the sound wave propagation up to a second order as well as considers the propagation of disturbances with arbitrary amplitude in the traveling wave approximation. The thermal equilibrium resulting in a general plasma heated by waves and cooling by optically thin radiation with a rate per unit mass and time (L(ρ,T)) characteristic of plasmas with solar abundances is also analyzed. Finally, we apply this to the solar atmosphere case.
Thomas Conlon (University of Leicester)
A survey of corotating interaction regions as seen by the STEREO HI 2007 – 2010
We present observations of corotating interaction regions (CIRs) by the heliospheric imagers (HI) aboard NASA’s Solar Terrestrial Relations Observatory (STEREO). CIRs are formed by the interaction between fast and slow solar wind streams ejected from source regions on the solar surface that rotate with the Sun. High density blobs formed at the interface between fast and slow solar wind appear in HI as families of features that propagate outwards from the Sun, which can be used to estimate the location of the source region and outward speed. We identify the corresponding features in situ at L1 using the Advanced Composition Explorer, and validate the fitted characteristics. We undertake a survey of all CIR features observed by HI and ACE for the period 2007 – 2010 and show that not all CIRs are detected by HI. Possible causes of the incomplete identification are discussed.
Márcia Guedes (INPE, Brasil)
The CME occurrence in the descending phase of solar cycle 23
Coronal Mass Ejections (CME) are energetic phenomena (up to 10^(33-34) erg), whose occurrence predominates during the maximum period in a solar cycle. Presenting a varied morphology,typical CMEs are formed by large (up to 10^17 g) magnetized (few to hundreds of G) arc-like gas clouds. In general, CMEs either accelerate or decelerate as move from the solar atmosphere towards outer space. Their velocity of propagation is between tens to thousands of km/s, with an average of 470 km/s. The distribution of events, recorded by the LASCO experiment during the solar cycle 23 (1996-2008), showed unexpected increase in the number of events during the descending phase of the cycle (2005-2008). This effect is only observed for those events with velocities in the range 100-300 km/s. Taking the number of CMEs within the two (100-200 km/s, 200-300 km/s) ranges recorded during 2007, the increase is about a factor two in comparison to the absolute number recorded on other velocity ranges for the year 2001, which coincides with the maximum of the 23rd cycle. An analysis of this anomaly in terms of CME parameters observed and phase of the cycle is presented.
Chris Hornsey (University of Warwick)
Sausage Oscillations of Coronal Plasma Structures
We performed a parametric study of linear axisymmetric fast magneto-acoutsic (sausage) oscillations of coronal loops modelled as a field-aligned low-beta plasma cylinder with a smooth inhomogeneity of the plasma density in the radial direction. Numerical simulations of an initial value problem covered both trapped and leaky regimes. The period of the sausage oscillations was found to always grow with the increase in the longitudinal wavelength, with the saturation of this dependence in the long-wavelength limit. Deeper and steeper profiles of the Alfven speed across the cylinder correspond to more efficient trapping of sausage modes: the cutoff value of the wavelength increases with the steepness and the density (or Alfven speed) contrast ratio. In the leaky regime, the period is always longer than the period of a trapped mode of a shorter wavelength, and also is longer than the ratio of the wavelength and alfven speed far from the cylinder. For shallow profiles of the density and shorter wavelengths, the period grows with the wavelength. In the long wavelength limit, the period becomes independent of the wavelength and increases with the depth and steepness of the radial profile of the Alfven speed.
Lauren Jeska (Aberystwyth University)
Analysis of SDO Data for propagation of waves and other features using a graphical user interface based IDL package.
Data from the Solar Dynamics Observatory have the potential to reveal new information on wave propagation in the solar corona. Working at the limits of optical resolution, and looking for tiny fluctuations compared to the signal size, means that the choice between different image re-normalization tactics, or the use of various image difference techniques, is critical to enhance the desired features. I will demonstrate a GUI-based IDL package that facilitates the trial use of many different techniques, and at many different image locations. The package will be used to show the analysis of a large eruption event on 7th March 2011, in which waves can be seen propagating around the solar limb and across the solar disc. The subroutines developed also have the potential to allow a larger-scale automated approach to data analysis.
Drew Leonard (Aberystwyth University)
Temperature analysis of the solar corona
Many studies which look at the temperature of the solar corona fail to account for the various multi-thermal structures along the line of sight (LOS). The high-quality multi-channel observations of AIA/SDO are used to estimate temperature across large regions of the corona. Preliminary results are shown which are broadly consistent with other published results. This preliminary work lays the foundation for a more comprehensive tomographical approach which will accurately resolve the LOS in the next few years.
Julie McCormick (University of St Andrews)
The Strucutre and Collapse of Magnetic Separators
Magnetic reconnection plays a key role in many plasma processes on the Sun and in the magnetosphere. Reconnection in three dimensions is known to be profoundly different from that in two dimensions. One of the main places where 3D reconnection can occur is in the vicinity of separators, special field lines that link pairs of null points and lie along the intersection of four topologically distinct domains. Although separators are key locations for reconnection, little is know about their local magnetic field structure, but such knowledge is essential to understand fully the nature of separator reconnection. This poster will highlight the main characteristics of magnetic reconnection in 2D and in 3D. A brief overview of 3D null point magnetic structures will be given in order to help explain the general expression for the local magnetic field about a potential separator.
Sarah Platten (University of St Andrews)
The Global 3D Magnetic Skeleton of the Solar Corona over a Solar Cycle
The magnetic field observed at the photosphere changes constantly and varies significantly over the course of a solar cycle. Naturally the magnetic structure of the solar corona follows suit with striking differences visible between solar maximum and solar minimum. Specific field structures are closely associated with, and may play a key role in, various solar phenomena such as CMEs and the acceleration of the solar wind. The magnetic skeleton highlights the key topological structures of the magnetic field and is a clear/robust way of analysing a magnetic field's structure. Using a potential magnetic field reconstruction of the global solar corona, from Kitt-Peak Magnetogram data (van Ballegooijen et al, 1998), we look at the changes in the magnetic field structure of the corona over 25 years through a study of their magnetic skeletons. This poster will give a brief introduction to the magnetic skeleton before moving on to an analysis of the data from our potential field models. In particular, we focus on differences in the characteristics of field structures present at solar minimum and solar maximum and the possible influence of different field structures on the solar wind.
Owen Wyn Roberts (University of Aberystwyth)
Solar wind turbulence measured by Cluster and the k-filtering method
The k-filtering method has long been used for analysing magnetic field data from the Cluster mission in the magnetosheath and in the foreshock, but it is only recently that attempts have been made to apply this technique to the solar wind plasma. The method itself has many caveats and great care is needed when interpreting results. We found that velocity differences between protons and minor ions cause small change to the bulk velocity used in the Doppler shifting from the spacecraft frame to the plasma frame. The change is small but can be significant to influence the interpretation of the character of plasma fluctuations present in the solar wind, especially those at high wavenumbers where direct wave/particle interaction may be readily possible. The difference in the velocities of the different species is investigated through the analysis of the ion velocity distribution function also from the CIS instrument on Cluster. Using this method in conjunction with the k-filtering method several time intervals from 2004 and 2005 are analysed. These intervals consist of slow and fast wind, and also plasma that could have been disturbed by a coronal mass ejection. The turbulence that is discovered by the method for all plasmas is found to be propagating at highly oblique angles with respect to the background magnetic field. The frequencies of the turbulence of several datasets are found to be much lower than the proton ion-cyclotron frequency. These are consistent with the frequencies and propagation angles expected for obliquely propagating kinetic Alfvén waves.
Luke Selzer (University of Warwick)
Wave Processes in the Terrestrial Foreshock
The purpose of current research is to inspect waves modes in the Foreshock, focusing primarily on their contribution to the solar wind’s heating mechanism. The dominant aim is to understand how the waves are generated in-situ and the importance of their compressible effects. Using the Cluster Satellite group observations of plasma instabilities have been observed in high resolution and com- parisons to theory have been carried out. Multiple data analysis techniques were deployed to test well known observations. The waves were then assessed and sorted into the already pre-established categories for the foreshock.
Flow Ionization in a gas-plasma MHD code
The study of partially ionized plasmas is highly important in a large number of astrophysical situations. The interactions between the plasma and neutral gas can lead to changes in the ionization fraction. We present a technique for incorporating this ionization in the context of MHD. We show that it is possible to allow the momentum of the plasma to ionize the gas within MHD while still remaining energy conserving by using additional terms in the momentum equations for each species. This has a variety of effects on the propagation of waves in the plasma as well as allowing changes in the ionization fraction as a result of perturbations in either species.