H.-P. Doerr, T. Hartlep

{Measuring the Sun's internal meridional flow is one of the key issues of helioseismology. Using the Fourier-Legendre analysis is a technique for addressing this problem.} {We validate this technique with the help of artificial helioseismic data.} {The analysed data set was obtained by numerically simulating the effect of the meridional flow on the seismic wave field in the full volume of the Sun. In this way, a 51.2-hour long time series was generated. The resulting surface velocity field is then analyzed in various settings: Two $360^\circ \times 90^\circ$ halfspheres, two $120^\circ \times 60^\circ$ patches on the front and farside of the Sun (North and South, respectively) and two $120^\circ \times 60^\circ$ patches on the northern and southern frontside only. We compare two possible measurement setups: observations from Earth and from an additional spacecraft on the solar farside, and observations from Earth only, in which case the full information of the global solar oscillation wave field was available. } {We find that, with decreasing observing area, the accessible depth range decreases: the $360^\circ \times 90^\circ$ view allows us to probe the meridional flow almost to the bottom of the convection zone, while the $120^\circ \times 60^\circ$ view means only the outer layers can be probed.} {These results confirm the validity of the Fourier-Legendre analysis technique for helioseismology of the meridional flow. Furthermore these flows are of special interest for missions like Solar Orbiter that promises to complement standard helioseismic measurements from the solar nearside with farside observations.}

M. Franz, N. Bello González, V. Martínez Pillet, J.A.Bonet, A. Gandorfer, P. Barthol, S. K. Solanki, T. Berkefeld, W. Schmidt, J. C. del Toro Iniesta, V. Domingo, M. Knölker

Solar oscillations are expected to be excited by turbulent flows in the intergranular lanes near the solar surface. Time series recorded by the IMaX instrument aboard the {\sc Sunrise} observatory reveal solar oscillations at high resolution, which allow studying the properties of oscillations with short wavelengths. We analyze two times series with synchronous recordings of Doppler velocity and continuum intensity images with durations of 32\thinspace min and 23\thinspace min, resp., recorded close to the disk center of the Sun to study the propagation and excitation of solar acoustic oscillations. In the Doppler velocity data, both the standing acoustic waves and the short-lived, high-degree running waves are visible. The standing waves are visible as temporary enhancements of the amplitudes of the large-scale velocity field due to the stochastic superposition of the acoustic waves. We focus on the high-degree small-scale waves by suitable filtering in the Fourier domain. Investigating the propagation and excitation of $f$- and $p_1$-modes with { wave numbers $k > 1.4$\thinspace 1/Mm} we find that also exploding granules contribute to the excitation of solar $p$-modes in addition to the contribution of intergranular lanes.

Frank Hill, Sanjay Gosain, Alexei Pevtsov, Rekha Jain, Michal Sobotka, Illaria Ermolli

This document is deliverable D80.1 of the Solarnet Work Package 80. It is the Science Requirement Document for SPRING - a new network of ground-based observatories for synoptic observations of the sun. This document condesates the ideas of the four SPRING working groups: 1. Synoptic Magnetic Fields 2. Solar Seismology 3. Transient Events 4. Solar Awareness

Community paper as part of the Denkschrift 2017 - Perspektiven der Astrophysik in Deutschland 2017 - 2030