Michael Leguèbe, Damien Fournier, Aaron C. Birch, Laurent Gizon in Collaboration with Inria team Magique3D

We compute acoustic Green’s functions in an axisymmetric solar background model, which may include a meridional flow and differential rotation. The wave equation is solved in the frequency domain using a finite element solver. A transparent boundary condition for the waves is implemented in the chromosphere, which represents a great improvement in computational efficiency compared to implementations based on ’sponge layers’. We perform various convergence studies that demonstrate that wave travel times can be computed with an accuracy of 0.001 s. This high level of numerical accuracy is required to interpret travel times in the deep interior, and is achieved thanks to a refined mesh in the near surface layers and around the source of excitation. The wave solver presented here lays the ground for future iterative inversion methods for flows in the deep solar interior.

Wolfgang Schmidt

LARS is an Absolute Reference Spectrograph. It performs fiber-coupled solar observations with the high-resolution Echelle Spectrograph of the Vacuum Tower Telescope (VTT) at the Observatorio del Teide on Tenerife. The scientific instrument is operated by the Kiepenheuer Institute for Solar Physics, Freiburg. The spectral observation is supported by a Laser Frequency Comb which serves as an absolute ruler for the wavelength calibration of the solar spectrum. This novel technique of spectroscopic observations allows the determination of absolute velocities in the solar atmosphere with the best accuracy (m s-1).

B. Lemmerer, A. Hanslmeier, T. Zaqarashvili, A. Veronig, H. Muthsam

Small granules that do not originate from the fragmentation process of regular sized granular cells and evolve on a considerably shorter timescale populate the intergranular lanes. They are found in high-resolution observational and hydrodynamic simulation data of the quiet sun's photosphere. We study their topology and dynamics based on a segmentation algorithm. The flow field suggests that they represent high-vortical jet-like structures that are found to differentially rotate about their center axis. Their associated high horizontal kinetic energy flux exceeds that of regular granules and may excite significant Poynting flux through MHD kink waves and torsional Alfven waves that would be high enough to effectively heat the chromosphere and corona if only 10% of the wave energy is assumed to be dissipated into heat.

The SpaceInn Board

The European Helio- and Asteroseismology Network (HELAS) has initiated the follow-up project "SpaceInn - Exploitation of Space Data for Innovative Helio- and Asteroseismolgoy" with the mission to build on the existing European strength in the field of time-domain stellar physics. SpaceInn activities, which are organized around the themes of data access, scientific expertise and existing coordination, aim to secure optimal use of the existing and planned data, from space and from the ground, in helio- and asteroseismology. Starting in January 1, 2013, the SpaceInn project is funded for four years by the European Union.

There are many parameters representing the conditions of space environments. Those are modulated in general by Solar Cycle (SC) defined by sunspot number temporal variation. However, all parameters do not have same cyclic features. Thus, we compare the temporal variations of solar, interplanetary, geomagnetic (SIG) parameters with that of open solar magnetic flux from 1976 to 2014 (from Solar Cycle 21 to the increasing phase of Cycle 24) in order to identify the possible relationships. We investigate which component of solar magnetic multipoles best correlates with the SIG parameters. As results, the dynamic pressure of the solar wind is strongly correlated with the solar magnetic dipole flux, which varies in anti-phase with SC. Other solar activity indices such as the sunspot number, total solar irradiance, 10.7cm radio flux, and solar flare occurrence and highly correlated with quadrupole component. The geomagnetic activity represented by Ap index is correlated with higher order multipole components, which show relatively a lagged time variation with SC. Given these results, we suggest that the continuous observation of solar photospheric field and calculating the multipole components of the open solar magnetic field at the source surface may complement forecasting the geomagnetic activity intensity long term trend

Michael Leguèbe, Damien Fournier, Aaron C. Birch, Laurent Gizon in Collaboration with Inria team Magique3D

Forward problems in local helioseismology have thus far been addressed in a semi-analytical fashion using the Born approximation and normal-mode expansions or direct simulations. However, it has proven difficult to take into account geometrical and instrumental effects. To avoid these difficulties we employ a numerical method to determine the impulse response of a solar model in a 2.5D geometry. Solving the wave equation in the frequency domain avoids the difficulties (instabilities) faced in the time domain. This framework is flexible, computationally efficient, and produces solar-like power spectrum and cross-covariance that agree reasonably with observations, including the high-frequency continuous spectrum. Additionally, we present accurate travel-time sensitivity kernels for perturbations to the solar medium which hint at the promising potential of this framework in future forward and inversion problems.

Markus Roth, Frank Hill, Michael Thompson

SPRING is an evolving concept for next generation solar synoptic observations network. It is envisaged that the new network will cater to the needs of (i) Helioseismology community, by providing improved resolution Doppler observations at multiple heights in solar atmosphere, (ii) Space weather research community, by providing full disk vector magnetograms at a cadence of few minutes and in multiple heights in the solar atmosphere, and (iii) Large solar telescopes, such as DKIST and EAST, by providing high resolution fulldisk context imaging in multiple wavelengths. We will present the conceptual designs currently being explored for SPRING.

O. Steiner, M. Roth

The contribution of acoustic waves to the chromospheric heating is still an open question. To discuss this Issue, it is crucial to understand the propagation of waves from the convection zone, where the waves are excited, into the higher layers of the solar atmosphere. Traveling upwards through the atmosphere the waves interact with the magnetic field that is present in the photosphere and the chromosphere. This specific interaction takes place in the mode conversion zone, where the sound speed equals the Alfvén speed. Using numerical simulations of wave propagation in a realistic solar model atmosphere, we show how dramatically this interaction influences the propagation of magneto-acoustic waves in the solar atmosphere. Our results demonstrate that due to mode conversion the waves are partially refracted back towards the convection zone and are partially transmitted into the chromosphere. Furthermore, we investigate our simulations for observational quantities to infer properties of the photospheric and chromospheric magnetic field.

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.

Emmanuel Hecht, Markus Roth

In current approaches to time-distance helioseismology, the line-of-sight projection effect on the traveltimes is not fully taken into account. Furthermore, filtering of full-disc data induces leakage due to the projection onto the CCD, which has so far not been accounted for. We develop a theoretical approach to consider these effects when computing sensitivity functions. As the formulas obtained do not seem to give results for spherical Born approximation sensitivity functions in a reasonable computation time, we develop tests to estimate the strength of the effects.

Abalde, J. R., Tardelli, A., de Abreu, A. J.

Studies presented on the relation Sun-Earth system are of great importance currently. Ionospheric irregularities in the F-region, caused by geomagnetic storms have meanings and adverse effects on the Earth. The recent advancement in technology techniques for monitoring space weather has allowed major contributions to this aspect. The main research of this study was to determine whether there was some geomagnetic storm that interfere with the generation, propagation and durability of plasma bubbles that occurred over a period of solar minimum in two cities in the Brazilian sector, São José dos Campos - SP (23.21°S, 45.86°W; dip latitude 17.6°S), designated SJC, low-latitude region and near to south crest ionospheric equatorial anomaly and Palmas - TO, called PAL (10.28°S, 48.33°W; dip latitude 6.7°S), near to the magnetic equator, located in the geographical South, tropical region and the hemisphere opposite to the magnetic equator. This study was conducted with data analysis of five years (2006-2010) of SJC and four years (2007-2010) of PAL, considering the 24th solar cycle, using all-sky imaging photometer operating with interference filters in OI 630.0 nm emission resulting from dissociative recombination process that occurs at an altitude of ~ 250-300 km (F-region).

Markus Roth, Wolfgang Zima, Aaron C. Birch, Laurent Gizon

We extend an existing Born approximation model for calculating the linear sensitivity of helioseismic travel-times to flows from Cartesian to spherical geometry. This development is necessary to use the Born approximation for inferring large-scale flows in the deep solar interior. Two consistency tests show that results for our sensitivity kernels agree with reference values to within a few percent. Consequently, we evaluate the impact of different data analysis filters on the kernels for a meridional travel-distance of 42 degrees. When mainly low-degree modes are used (roughly l < 70), the sensitivity is concentrated in deeper regions and it visually best resembles a ray-path like structure, otherwise the sensitivity is concentrated near the surface. Among the different low-degree filters used, we find the phase-speed filtered kernel to be best localized at depth.