Sergiy Shelyag and Paul Cally

Measurements made around active regions are complicated by magneto-acoustic mode-conversion and changes in the radiative properties of magnetic field concentrations. Forward modelling has been performed using the SPARC numerical code in a semi-empirical magneto-hydrostatic model of a large-scale solar magnetic field mimicking a sunspot. The 6173 A absorption line used by the HMI instrument has been synthesized at various positions on the solar disk. Using the response of this spectrum at different observational inclinations slow modes are seen in the sunspot umbra.

François Lignières (IRAP), Jérôme Ballot (IRAP)

Seismology of intermediate-mass and massive stars is limited by our lack of understanding of the effect of fast rotation on gravity modes. In particular, in this regime perturbative methods are unable to identify observed modes. We therefore develop an asymptotic theory for adiabatic gravito-inertial modes in uniformly rotating stars. We first derived a generalized dispersion equation taking the Coriolis force and the centrifugal deformation into account. The corresponding ray dynamics allowed us to explore the structure of the phase space thanks to a ray-tracing code. We observed three coexisting types of structures: (i) nearly integrable structures similar to non- rotating structures, (ii) island chains around stable periodic orbits, (iii) large chaotic zones. These three different types of structures are expected to give three different families of modes.

Stéphane Mathis, François Lignières, Jérôme Ballot, Pierre-Marie Culpin

Most of the information we have about the internal rotation of stars comes from modes that are weakly affected by rotation, for instance thanks to rotational splittings. In contrast, we present here a method (based on the asymptotic theory of Prat et al. 2016, A&A, 587, A110) which allows us to analyze the signature of rotation where its effect is the most important, that is in low-frequency modes that are strongly affected by rotation.

Shukur Kholikov, Jason Jackiewicz, Markus Roth

In this study, we present first inversion results for deep meridional flow using spherical Born approximation kernels and time-distance helioseismology. The computation of Born approximation kernels for flows has only recently become available in spherical geometry. Compared to the ray approximation, the Born approximation is considered to provide a more realistic model of the advection and scattering processes in the solar interior, which are captured in travel time measurements. We first validate this method using artificial data from a linear 3D simulation of solar interior wave propagation. We find that the prediction of the Born approximation model coincides well with the simulated data. We then perform standard SOLA inversions of the solar meridional flow. First, inversion results of the simulated data are discussed and compared to the original flow profile included in the simulation. Finally, we apply the validated method to GONG data spanning periods of low, medium and high solar activity (2001-2003, 2004-2006, and 2007-2009). The results are discussed and compared to literature.

GONG (Global Oscillation Network Group) is now 20 years old and continues to reliably provide data for the international helioseismology community. In addition the role of GONG has expanded to provide data as input to a number of space weather forecasting systems. This talk will give a summary of the status of GONG, its future plans, and a brief review of some recent science results.

Mitchell Berger

It is known that the poloidal field is at its maximum during solar minima, and that its behaviour during this time acts as a strong predictor of the strength of the following solar cycle. This relationship relies on the action of differential rotation (the Omega effect) on the poloidal field, which generates the toroidal flux observed in sunspots and active regions. We measure the helicity flux into both the northern and southern hemispheres using a model that takes account of the Omega effect, which we apply to data sets covering a total of sixty years. We find that the helicity flux offers a strong prediction of solar activity up to 5 years in advance of the next solar cycle.

Markus Roth, Jason Jackiewicz

We present the current status of an undergoing validation of a recently developed model for computing spherical Born approximation sensitivity functions for flows. In a first step, power spectra and reference cross-correlations from the model and a simulation of Hartlep et al. (2013) are matched. Some difficulties in obtaining such a match are discussed. In a second step, travel times from the forward model and from the simulation, which includes a standard meridional flow profile, are to be compared. The analysis procedure including the use of phase-speed filters is identical to the one employed in Jackiewicz et al. (2015). Furthermore, we present a novel approach for a fast computation of integrated sensitivity functions which can be used for interpreting rotationally symmetric flows such as differential rotation and meridional flow.

Markus Roth, Wolfgang Zima

We extend an existing Born approximation model for calculating the linear sensitivity of helioseismic travel-times to flows from plane-parallel to spherical geometry. This extension is necessary especially for dealing with deep flows. Furthermore, we present first results for the sensitivity kernels and validate our model with the help of artificial helioseismic data for a standard meridional flow pattern from Hartlep et al. (2013, ApJ).

By using the photospheric vector magnetogram and subsurface vector velocity field, we studied the systematic behavior of current helicity and relevant quantities of subsurface flow. Mainly it contains three aspects: 1) The spatial distribution and temporal evolution of current helicity. 2) The connection between the current helicity and subsurface kinetic helicity. 3) The spatial distribution ant temporal evolution of subsurface vorticity and divergence.

David Pontin, Gunnar Hornig, Christopher Berg-Smiet, Dirk Bouwmeester

Magnetic helicity is a conserved quantity under an ideal evolution. Here we present methods for simulating such topology conserving systems. We make use of Lagrangian grids and mimetic differential operators. It is shown that the magnetic field topology is exactly conserved. This method is then used to study equilibria of configurations like the Hopf fibration.

Wolfgang Schmidt, Rolf Schlichenmaier, Nazaret Bello González, Franziska Stief

The Laser Absolute Reference Spectrograph (LARS) is a novel scientific instrument for solar observations with the Vacuum Tower Telescope (VTT) on Tenerife. It works as a combination of the high-resolution Echelle Spectrograph of the VTT with an state-of-the-art, ultra-precise Laser Frequency Comb. The solar spectrum is then calibrated by the Frequency Comb spectrum on an absolute scale. Resulting Doppler shifts of spectral lines reach an accuracy of m/s. In this talk, I will present systematic observations of the convective blue-shift in the solar photosphere. The recent data reveal the absolute velocities and the center-to-limb variation for several spectral lines in the visible spectral range. I will present the bisectorial C-shape profiles and systematical variations for Fe I 630.15nm. On behalf of the SOLARNET project, I want to encourage the audience to perform Service-Mode operations with LARS. Co-observations with other telescopes and instruments would provide e.g. spectro-polarimetric solar observations on an absolute wavelength scale.

Discussion about possiblity of using FP Etalon for SPRING project