Programme

This is the programme for the first meeting. Some of the talks are now available as a PDF or ppt.

Monday 27th March
09:00 Introduction from ISSI
09:30 A history of solar atmospheric magnetoseismology –  Gary Verth

A brief overview of the history of atmospheric seismology, looking at key observations and theoretical models that have helped to develop the field.

10:30 Break
11:00 Dynamic magnetoseismology: Pathways & road blocks –  Richard Morton

A look towards the future. Over the last few years, insights from SDO, CoMP and chromospheric observatories clearly show that the atmospheric plasma is highly dynamic. Such behaviour is typically neglected in magneto-seismological models and should be a future direction for theory. I discuss recent observations of waves in these highly dynamic plasma environments, highlighting areas with potential for future focus.

13:00 Lunch

14:00 Seismology of propagating kink MHD waves in the presence of flow –  Marcel Goossens

A recent evolution in research on MHD waves of the solar atmosphere is the detection of MHD waves in the presence of flows, see e.g. Morton (2014) and Morton et al.(2015). The present talk discusses ways to include background flows along the magnetic field in a seismological analysis for propagating kink MHD waves.

Seismology of propagating MHD waves in the presence of flows is more complicated than that for propagating MHD waves on a static background. For the latter case there are two observable quantities, i.e. the phase velocity and the damping length of the propagating wave. There are three quantities that we would like to determine by seismology, i.e. the Alfv ́en velocity, the density contrast and the quantity that determines the damping. In case of resonant absorption this quantity is the thickness of the non-uniform layer. For MHD waves in the presence of an equilibrium flow there is a forward and a backward propagating wave both with a phase velocity and a damping length. The quantities related to the background that appear in the seismological analysis are the Alfv ́en velocity, the density contrast, the velocity of flow, the velocity contrast, and the thickness of the nonuniform layers for density and velocity. In practice there are no accurate observations of all of these quantities.

This talk presents an analytical theory for propagating MHD waves in cylindrical waveg- uides with a flow along the waveguide based on the thin tube (TT) and the thin bound- ary (TB) approximations. The damping is assumed to be due to resonant absorption. The focus is on kink waves that contain transverse motions. Seismological applica- tions of this theory to observations as well as the limitations of the adopted TTTB approximations are discussed.

16:00 Force-free magnetic fields in coronal seismology –  Markus Aschwanden

One of the promises of coronal seismology is the measurement of the 3D magnetic field in the solar corona, most prominently accomplished with the observations of kink-mode oscillations and the relationship between the oscillation periods and the Alfvenic travel time in coronal loops that exhibit standing eigen-modes. However, the magnetic field is varying along each field line, which needs to be accounted for in a 3D magnetic field model. On the other hand, coronal 3D magnetic field models have been developed for potential fields (PF), linear (LFFF), and nonlinear force-free fields (NLFFF), which can be constrained by automated tracing of coronal loops in EUV and soft X-ray wavelengths. The NLFFF methods are particularly important because they quantify the free energy that can be released in solar flares and CMEs. We discuss recent progress with the VCA-NLFFF code,
the Vertical Current Approximation Nonlinear Force-Free Field Code, including performance tests, measurements of the dissipated free energy during flares, and tests
of the resulting 3D magnetic fields with the magnetic field strengths inferred from observed loop oscillations.

Tuesday 28th March
09:00 Phase mixing of kink waves in solar flux tubes –  Roberto Soler

Magnetohydrodynamic kink waves are routinely observed in the solar atmosphere and may play relevant roles in the transport and dissipation of energy. The theoretical study of kink wave dynamics has received much attention in the recent years. In this talk, I will discuss and compare two different approaches that have been used to theoretically understand the behavior of kink waves in the linear regime: the so-called quasi-mode and an alternative method based on a spatial Fourier expansion.
     On the one hand, the quasi-mode approach is based on two main assumptions: (1) the kink mode is a global mode of the flux tube and (2) the global mode is damped because it is resonant in the Alfven continuum. When compared with full numerical simulations, the quasi-mode correctly describes the damping of the transverse motion of the flux tube. However, numerical simulations also show the generation of small-scale rotational motions around the nonuniform boundary of the tube, which dominate dynamics and contain all the wave energy after the kink oscillation is damped. This important ingredient of the temporal evolution is not captured by the quasi-mode.
On the other hand, there is an alternative method to compute the temporal evolution of kink waves in which there are no hypothetical global modes and no resonances. In this other scenario, a spatial Fourier expansion is used to express the kink wave as a superposition of Alfven continuum modes, which undergo phase mixing as time evolves. The damping of the large-scale transverse motion and the building up of small-scale rotational motions can both be explained by the process of phase mixing alone. This alternative approach is able to consistently reproduce the temporal evolution seen in full numerical simulations.
    In view of these results, resonant absorption and phase mixing are shown to represent two aspects of the same underlying physical mechanism: a process that causes the cascade of energy from large scales to small scales due to plasma and/or magnetic field inhomogeneities. This process naturally provides the required scenario for efficient dissipation of transverse wave energy in the atmospheric plasma

10:30 Break
11:00 Effect of magnetic twist on nonlinear transverse kink oscillations of line-tied magnetic tubes –  Jaume Terradas

Magnetic twist is thought to play an important role in for example, coronal loops. One of the effects of twist is to modify the properties of the eigenmodes of magnetic tubes. In the linear regime and under the presence of twist, standing kink solutions are characterized by a change in polarisation of the transverse displacement along the tube. Here we investigate the effect of twist on the development of shear instabilities that appear, in the nonlinear regime, at the tube boundary. The shear instabilities are produced either by the jump in the azimuthal component of the velocity at the edge of the sharp boundary between the internal and external part of the tube, or either by the phase-mixing process taking place when there is a smooth inhomogeneous layer. It is found that twist always delays the appearance of the shear instability. This can have some important implications regarding observations of transverse kink modes and the instability itself.

13:00 Lunch
14:00 Spicule Dynamics with a 3D Touch –  Rahul Sharma
16:00 How do transverse MHD waves shape the coronal plasma –  Norbert Magyar

We present and discuss the results of recent numerical simulations of coronal plasma disturbed by standing and propagating transverse waves. We will show how the presence of these waves has a great influence on the appearance of the coronal plasma in the cross-section (perpendicular to the main magnetic field). We will talk about the Kelvin-Helmholtz instability, turbulence, and other phenomena induced by the presence of transverse MHD waves in the solar corona.

Wednesday 29th March
09:00 Upgraded Coronal Multi-channel Polarimeter (UCoMP) –  Steve Tomczyk

I will discuss the ongoing effort to upgrade the CoMP instrument led by PI Enrico Landi (U Michigan). Upgrades include increased field-of-view, spatial resolution and wavelength range. My talk will focus on increased capabilities in coronal wave observations. The UCoMP will be deployed in the late summer 2017.

10:30 Break
11:00 Analysis, Modelling and Seismological Application of Wave Dynamics in Coronal Rain –  Erwin Verwichte
13:00 Lunch
14:00 Open discussion

Thursday 30th March
09:00 Alfvén Wave Dissipation in the Chromosphere –  David Jess

The magnetic nature of the Sun’s tenuous atmosphere naturally supports the plethora of magnetohydrodynamic (MHD) wave activity that has been brought to our attention in recent years. Sunspots, with their powerful magnetic fields, naturally provide energy conduits for upwardly propagating MHD wave activity. Previous work has focused on magneto-acoustic waves in the lower atmosphere of sunspots, including the manifestation of wave steepening in the form of umbral flashes (UFs). Here, high-resolution spectral imaging observations, inversion routines and MHD wave theory will be discussed to reveal how the signatures of Alfvén wave dissipation is also prevalent within the confines of sunspot atmospheres. Improvements that will be brought about by the next generation of solar telescopes will also be described.

10:30 Break
11:00 Transverse wave induced Kelvin-Helmholtz (TWIKH) rolls in coronal loops and their observability –  Tom Van Doorsselaere

As was previously found, transverse kink waves are Kelvin-Helmholtz unstable, forming so-called TWIKH rolls. In this talk, I will perform forward modelling of 3D simulations of coronal loops with TWIKH rolls. These forward models show how TWIKH rolls can be observed in the corona. It is clear that these coronal loop models are compatible with current observations of coronal loops, such as appearing multi-stranded, having broad DEMs and peculiar Doppler shifts.

13:00 Lunch
14:00 Kink oscillations of non-stationary expanding magnetic flux tubes in the presence of flow –  Misha Ruderman

16:00 Study of waves from Aditya mission and NLST –  Dipankar Banerjee

Aditya-L1 is India’s first dedicated scientific mission to study the sun. Aditya-L1 will provide observations of Sun’s Photosphere, Chromosphere (NUV) and corona (Visible and NIR). I will give an overview of the capabilities of the NUV full disk imager and also the coronagraph. The instrument specifications will provide new windows to the observation of waves. For wave diagnostic the current status with the existing instruments, its limitations will be addressed.    How these new instruments can enhance our understanding will be the point of discussion. I will also discuss on the current status of the National Large Solar Telescope project (NLST) and its high resolution capabilities which will enhance our understanding on the wave properties.

Friday 31st March
09:00 Open discussion