Studies of the Deep Solar Meridonal Flow Free Conference is closed
Conference is closed
Hosted by Markus Roth
Affiliation Kiepenheuer-Institut fuer Sonnenphysik
Berne, Switzerland
28.11.2016 - 02.12.2016

Organizing institutions
International Space Science Institue (ISSI)
Main category Natural Sciences (Astrophysics and Astrononmy)
Conference/Workshop objectives

The meridional flow inside the Sun is a large-scale flow that is observed on both hemispheres of the Sun. Its structure and variation inside the Sun is of major interest as it transports mass, angular momentum and magnetic flux. Therefore, a detailed knowledge is required to understand the magneto-hydrodynamics of the Sun's convection zone and consequently the Sun's magnetic variability.

Recently, the helioseismic measurement of this flow throughout the whole convection zone of the Sun has made significant progress by the development of improved methods in form of time-distance helioseismology (Zhao et al., 2013, ApJ Lett, 774, L29) and new approaches in global helioseismology (Schad et al., (2013, ApJ Lett, 778, L38). Techniques developed earlier based on tracking supergranulation provide a complementary view on the meridional flow (Hathaway, 2012, ApJ 760, 84). These and further studies (e.g. Jackiewicz et al., 2015, ApJ, 805, 133) reveal that the meridional flow has a possible multi-cellular structure in latitude and depth. Furthermore, there are indications that this flow varies during the solar activity cycle. However, a final consensus on the structure and temporal evolution of the flow has not been achieved, especially as the signal is weak and affected by noise and systematic effects. Estimating the latter properly and deciding on the physical constraints on the inversions is important as those can alter the result significantly (Rajaguru and Antia, 2015, ApJ, 813, 114).

During the past years where the groups involved have worked independently on analysing various available data sets, it has become evident that it requires the inspiring atmosphere of ISSI to make progress on this important topic of solar physics. With this in mind, we have created a team consisting of all scientists active in this field who have indicated their great interest in such an international collaborative effort. These researchers bring in their expertise on methods of time series analysis, helioseismic inversion methods as well as theoretical and numerical modelling of the interaction of the acoustic wave field with the meridional flow. This team would focus on coordinated studies on validating helioseismic methods, joint analysis of existing data sets, and further development of techniques in order to understand the origin of possible discrepancies between the methods. It is the ultimate goal to provide the best possible estimate on the structure and temporal variability of the Sun's meridional flow and its role in the solar dynamo process. Consequently, the results of this international effort will find direct application in the modelling of the solar dynamo, resulting in a better understanding of the Sun's magnetic activity.

The team consisting of 12 renowned experts and 2 young scientists would meet twice in 2015 and 2016. The team leaders are Markus Roth (Kiepenheuer-Institut für Sonnenphysik, Freiburg) and Junwei Zhao (co-leader, University Stanford).

Local organizing committee
Scientific organizing committee (SOC)

Markus Roth, Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany
Junwei Zhao, University of Stanford, USA

  • Main session
Invited speakers

Team Members:
H.M. Antia, Tata Institute of Fundamental Research, Mumbai, India
Doug Braun, NorthWest Research Associates, CoRA Office, USA
Dean-Yi Chou, National Tsing Hua University, Taiwan
Tom Duvall, Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany
David Hathaway, NASA Ames Research Center, Moffet Field, USA
Jason Jackiewicz, New Mexico State University, Las Cruces, USA
Shukur Kholikov, National Solar Observatory, Tucson, USA
Paul S. Rajaguru, Indian Institute of Astrophysics, Bangalore, India
Markus Roth (Team Leader), Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany
Ariane Schad, Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany
Jesper Schou, Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany
Junwei Zhao (Team Co-Leader), University of Stanford, USA

Young Scientists:
Vincent Böning, Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany
Ruizhu Chen, University of Stanford, USA
Zhi-Chao Liang, Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany

Important dates Team members, please register until November 28, 2016.
Registration and payment information Registration is only possible for invited participants.
Conference venue Berne, Switzerland
Hotel information

A block reservation of rooms in nearby hotels will be done by ISSI

Travel information
There are no uploaded videos yet.
Thomas Duvall

Session: Main session

Date of upload:
1) By measuring the travel times for multiple skips, it should be possible to remove center-to-limb effects in place rather than referencing north-south times to east-west times. 2) Instead of using quadrants (4 sectors), it may be advantageous to use more, like 12 or 16. 3) To learn more about center-to-limb effects, it is useful to measure the temporal frequency dependence. Tests of 1)-3) have been done using 1-year of HMI data and Thomas Hartlep's simulations including a center-to-limb effect.
Markus Roth

Session: Main session

Date of upload:
This presentation was given at the 1st ISSI International Team Meeting on "Studies of the Deep Solar Meridional Flow" (CID: iss2016). It deals with validating the Fourier-Legendre Analysis technique by using artifical data.
There are no uploaded posters yet.
Markus Roth

Session: Main session

Date of upload:
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.}
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