European Research Council Starting Grant

MILESTONE | Software/hardware | Papers | ESTIMATED % OF TOTAL REQUESTED GRANT | |
---|---|---|---|---|

#1 Compute cluster | operational since 01.06.2009 |
30.00% | ||

#2 Computation of traveltime sensitivity to pressure, density, and magnetic perturbations | 2a. Writing the expressions for the travel-time sensitivity kernels for all types of physical perturbations | Burston et al 2013 in prep | 15.00% | |

2b. Extending the kernel code of A. Birch to include all travel-time sensitivity kernels | Kernel code Download |
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#3 Parametric sunspot models | Cameron et al, Constructing semi-empirical sunspot models for helioseismology, Sol. Phys. 2010 | 10.00% | ||

#4 Full-waveform modelling of sunspots (basic parameters) | 4a. Analyzing observations of waves interacting with sunspots, e.g. using a cross-correlation technique | Helioseismology of sunspots: defocusing, folding, and healing of transmitted wavefronts by Liang, Z. -C., Gizon, L., Schunker, H. and Phillipe, T. submitted to Astronomy and Astrophysics arXiv : http://arxiv.org/abs/1010.0216 | 25.00% | |

4b. Further developing the SLiM code to include, for example, the excitation of waves by random sources | Schunker et al. Constructing and Characterising Solar Structure Models for Computational Helioseismology, 2011, Sol Phys, 271, 1 | |||

4c. Defining and implementing a procedure to minimize the discrepancy between the simulated and observed seismic signatures of sunspots. | Adjoint method code Download |
Hanasoge et al, The Adjoint Method Applied to time distance helioseismology, 2011, ApJ, 738, 100 | ||

#5 Linear inversion of traveltimes for all physical quantities | 5a. Developing an efficient algorithm for solving the linear inverse problem. | Inversion code Download |
Svanda et al, Validated helioseismic inversions for 3D vector flows, 2011,A&A, 530, A148 | 20.00% |

5b. Inverting for all physical quantities in the solar interior |

(Jan. 2013) **Milestone #4a**:
A paper on the Helioseismology of sunspots: defocusing, folding, and healing of transmitted wavefronts by Liang, Gizon, Schunker and Phillipe was submitted to the journal Astronomy & Astrophysics.

**Abstract**: We observe and characterize the scattering of acoustic wave packets by a sunspot, in a regime where the wavelength is comparable to the size of the sunspot. Spatial maps of wave travel times and amplitudes are measured from the cross-covariance function of the random wave field observed by SOHO/MDI around the sunspot in Active Region NOAO~9787. We consider separately incoming plane wave packets consisting of f modes and p modes with radial orders up to four. Observations show that the travel-time perturbations diminish with distance far away from the sunspot -- a finite-wavelength phenomenon known as wavefront healing in scattering theory. Observations also show a reduction of the amplitude of the waves after their passage through the sunspot. We suggest that a significant fraction of this amplitude reduction is due to the defocusing of wave energy by the fast wave-speed perturbation introduced by the sunspot. This ``geometrical attenuation'' will contribute to the wave amplitude reduction in addition to the physical absorption of waves by sunspots. We also observe an enhancement of wave amplitude away from the central path: diffracted rays intersect with unperturbed rays (caustics) and wavefronts fold and triplicate. Wave amplitude measurements in time-distance helioseismology provide independent information that can be used in concert with travel-time measurements.

(Nov. 2012) Dr. Hannah Schunker gives an invited talk presenting results that explore the sensitivity of travel times to sound speed and magnetic perturbations using the SISI sunspot model and waveform analysis at the GONG 2012 / LWS/SDO-5 / SOHO 27 conference in Palm Cove, Australia.

(Jul. 2012) A major paper by Drs. Laurent Gizon and Aaron Birch, Helioseismology challenges models of solar convection, was published in the Proceedings of the National Academy of Science, **109**, 30.

(Feb. 2012) A paper on a new method for helioseismic inversions Multichannel Three-Dimensional SOLA Inversion for Local Helioseismology by Jackiewicz et al. was published in the journal Solar Physics, 276, 19.

(20.05.2012) Drs. Hamed Moradi, Michal Svanda, Raymond Burston and Prof. L. Gizon present results from the SISI project at the ESF conference The Modern Era of Helio- and Asteroseismology

(31.10.2011) Dr. Hannah Schunker presents results using the SISI sunspot at the LWS-SDO3 Workshop: Solar Dynamics and Magnetism from the Interior to the Atmosphere at Stanford University, U.S.A.

(11.07.2011) Thorsten Stahn attends the 4th KASC workshop: From unprecedented data to revolutionary science in Boulder, Colorado to discuss inversion techniques.

(04.05.2011) SISI results were presented by H. Moradi, R. Burston and L. Gizon at the PCTS workshop "Seismology of the Earth and stars" and conference "Differential rotation in stars" held in Princeton, U.S.A.

(Sept. 2011) **Milestone #4c**:
The paper
The Adjoint Method Applied to Time-distance Helioseismology by Hanasoge et al. 2011 was published in The Astrophysical Journal, 738, 21.

**Abstract**:For a given misfit function, a specified optimality measure of a model, its gradient describes the manner in which one may alter properties of the system to march toward a stationary point. The adjoint method, arising from partial-differential-equation-constrained optimization, describes a means of extracting derivatives of a misfit function with respect to model parameters through finite computation. It relies on the accurate calculation of wavefields that are driven by two types of sources, namely, the average wave-excitation spectrum, resulting in the forward wavefield, and differences between predictions and observations, resulting in an adjoint wavefield. All sensitivity kernels relevant to a given measurement emerge directly from the evaluation of an interaction integral involving these wavefields. The technique facilitates computation of sensitivity kernels (FrNichet derivatives) relative to three-dimensional heterogeneous background models, thereby paving the way for nonlinear iterative inversions. An algorithm to perform such inversions using as many observations as desired is discussed.

(June 2011) **Milestone #5**:
Validated helioseismic inversions for 3D vector flows by Svanda et al. published in Astronomy & Astrophysics, 530, 23

**Abstract**:
Context. According to time-distance helioseismology, information about internal fluid motions is encoded in the travel times of solar waves. The inverse problem consists of inferring three-dimensional vector flows from a set of travel-time measurements. While only few tests of the inversions have been done, it is known that the retrieval of the small-amplitude vertical flow velocities is problematic. A thorough study of biases and noise has not been carried out in realistic conditions.
Aims: Here we investigate the potential of time-distance helioseismology to infer three-dimensional convective velocities in the near-surface layers of the Sun. We developed a new subtractive optimally localised averaging (SOLA) code suitable for pipeline pseudo-automatic processing. Compared to its predecessor, the code was improved by accounting for additional constraints in order to get the right answer within a given noise level. The main aim of this study is to validate results obtained by our inversion code.
Methods: We simulate travel-time maps using a snapshot from a numerical simulation of solar convective flows, realistic Born travel-time sensitivity kernels, and a realistic model of travel-time noise. These synthetic travel times are inverted for flows and the results compared with the known input flow field. Additional constraints are implemented in the inversion: cross-talk minimization between flow components and spatial localization of inversion coefficients.
Results: Using modes f, p1 through p4, we show that horizontal convective flow velocities can be inferred without bias, at a signal-to-noise ratio greater than one in the top 3.5 Mm, provided that observations span at least four days. The vertical component of velocity (vz), if it were to be weak, is more difficult to infer and is seriously affected by cross-talk from horizontal velocity components. We emphasise that this cross-talk must be explicitly minimised in order to retrieve vz in the top 1 Mm. We also show that statistical averaging over many different areas of the Sun allows for reliably measuring of average properties of all three flow components in the top 5.5 Mm of the convection zone.

(01.10.2011) Michael Sobol joins the SISI project to work on IT.

(Jul. 2011) **Milestone #4b**:
A paper using random sources in the SLiM code Constructing and Characterising Solar Structure Models for Computational Helioseismology by Schunker et al. published in Solar Physics, 271, 26

**Abstract**:
One goal of helioseismology is to determine the subsurface structure of sunspots. In order to do so, it is important to understand first the near-surface effects of sunspots on solar waves, which are dominant. Here we construct simplified, cylindrically-symmetric sunspot models that are designed to capture the magnetic and thermodynamics effects coming from about 500 km below the quiet-Sun Nt 5000=1 level to the lower chromosphere. We use a combination of existing semi-empirical models of sunspot thermodynamic structure (density, temperature, pressure): the umbral model of Maltby et al. (1986, Astrophys. J. 306, 284) and the penumbral model of Ding and Fang (1989, Astron. Astrophys. 225, 204). The OPAL equation-of-state tables are used to derive the sound-speed profile. We smoothly merge the near-surface properties to the quiet-Sun values about 1 Mm below the surface. The umbral and penumbral radii are free parameters. The magnetic field is added to the thermodynamic structure, without requiring magnetostatic equilibrium. The vertical component of the magnetic field is assumed to have a Gaussian horizontal profile, with a maximum surface field strength fixed by surface observations. The full magnetic-field vector is solenoidal and determined by the on-axis vertical field, which, at the surface, is chosen such that the field inclination is 45N0 at the umbral - penumbral boundary. We construct a particular sunspot model based on SOHO/MDI observations of the sunspot in active region NOAA 9787. The helioseismic signature of the model sunspot is studied using numerical simulations of the propagation of f, p 1, and p 2 wave packets. These simulations are compared against cross-covariances of the observed wave field. We find that the sunspot model gives a helioseismic signature that is similar to the observations.

(Feb. 2011) **Milestone #3**: The SISI sunspot model was published in the paper Constructing semi-empirical sunspot models for helioseismology , by Cameron et al. in the journal Solar Physics, 268, 293. The model is available on request.

**Abstract**:
One goal of helioseismology is to determine the subsurface structure of sunspots. In order to do so, it is important to understand first the near-surface effects of sunspots on solar waves, which are dominant. Here we construct simplified, cylindrically-symmetric sunspot models that are designed to capture the magnetic and thermodynamics effects coming from about 500 km below the quiet-Sun Nt 5000=1 level to the lower chromosphere. We use a combination of existing semi-empirical models of sunspot thermodynamic structure (density, temperature, pressure): the umbral model of Maltby et al. (1986, Astrophys. J. 306, 284) and the penumbral model of Ding and Fang (1989, Astron. Astrophys. 225, 204). The OPAL equation-of-state tables are used to derive the sound-speed profile. We smoothly merge the near-surface properties to the quiet-Sun values about 1 Mm below the surface. The umbral and penumbral radii are free parameters. The magnetic field is added to the thermodynamic structure, without requiring magnetostatic equilibrium. The vertical component of the magnetic field is assumed to have a Gaussian horizontal profile, with a maximum surface field strength fixed by surface observations. The full magnetic-field vector is solenoidal and determined by the on-axis vertical field, which, at the surface, is chosen such that the field inclination is 45N0 at the umbral - penumbral boundary. We construct a particular sunspot model based on SOHO/MDI observations of the sunspot in active region NOAA 9787. The helioseismic signature of the model sunspot is studied using numerical simulations of the propagation of f, p 1, and p 2 wave packets. These simulations are compared against cross-covariances of the observed wave field. We find that the sunspot model gives a helioseismic signature that is similar to the observations.

(01.02.2011) Student Pauline Martin joins the SISI project to work on kernels until July 2011.

(01.09.2010) Dr. Michal Svanda joins the SISI project to work on helioseismic inversions.

(Sept. 2010) The paper Local Helioseismology: Three-Dimensional Imaging of the Solar Interior by L. Gizon, A. Birch and H. Spruit was published in the Annual Review of Astronomy and Astrophysics, 48, 289.

(Oct. 2010) The paper Scattering of helioseismic waves by a sunspot: wavefront healing and folding by Liang, Z. -C., Gizon, L and Schunker, H. was published on the arXiv.

(19.07.2010) Ankit Bhagatwala visits MPS to work on setting up computational code for sunspot seismology for the SISI project until August.

(June 2010) The SISI sunspot model and helioseismic analysis of AR9787 were presented by Dr. Hannah Schunker and Z.-C. Liang at the GONG2010-SOHO24 conference in Aix-en-Provence, France.

(23.04.2010) Raphael Attie joins the SISI project to work on IT and data management.

(Feb. 2010) Details of the system architecture were presented (via a poster contribution) and preliminary results regarding density and pressure kernels were presented by R. Burston (via an oral presentation) at the 4th HELAS International Conference in Lanzarote, Spain.

(15.02.2010) Student Thorsten Stahn joins the SISI project to work on IT and software implementation.

(2010) **Milestone #2**:
"Modeling the subsurface structure of sunspots"
by H. Moradi et al. published in the journal *Solar Physics*, 267, 1

**Abstract**: While sunspots are easily observed at the solar surface, determining their subsurface structure is not trivial. There are two main hypotheses for the subsurface structure of sunspots: the monolithic model and the cluster model. Local helioseismology is the only means by which we can investigate subphotospheric structure. However, as current linear inversion techniques do not yet allow helioseismology to probe the internal structure with sufficient confidence to distinguish between the monolith and cluster models, the development of physically realistic sunspot models are a priority for helioseismologists. This is because they are not only important indicators of the variety of physical effects that may influence helioseismic inferences in active regions, but they also enable detailed assessments of the validity of helioseismic interpretations through numerical forward modeling. In this paper, we provide a critical review of the existing sunspot models and an overview of numerical methods employed to model wave propagation through model sunspots. We then carry out an helioseismic analysis of the sunspot in Active Region 9787 and address the serious inconsistencies uncovered by Gizon et al. (2009). We find that this sunspot is most probably associated with a shallow, positive wave-speed perturbation (unlike the traditional two-layer model) and that travel-time measurements are consistent with a horizontal outflow in the surrounding moat.

(11.02.2010) Launch of SDO (see also NASA). The Helioseismic and Magnetic Imager (HMI) is designed to deliver ideal data for local helioseis- mology. HMI is one of several instruments onboard NASAN"s Solar Dynamics Observatory (SDO), which was successfully launched on 11 February 2010 in a geosynchronous orbit. HMI will trans- mit 4, 096 NW 4, 096-pixel Doppler images of the Sun at the cadence of one image every 45 s. It will combine high spatial resolution (1 arcsec) and full spatial coverage, with a very high duty cycle over a nominal mission duration of five years. This combination will make possible the local helioseismic analysis of regions closer to the limb (less foreshortening), in order to study higher solar latitudes and the evolution of magnetic active regions as they rotate from limb to limb across the solar disk. In addition to Dopplergrams, HMI will provide images of the three components of the vector magnetic field, providing important information for the interpretation of helioseismic data. A stated goal of SDO/HMI is the subsurface detection of the magnetic field before it emerges at the surface, leading to reliable predictive capability (Kosovichev & HMI Science Team 2007). In combination with observations from the Atmospheric Imaging Assembly (AIA), a set of four SDO telescopes designed to provide an unprecedented view of the lower corona, HMI and local helioseismology will help establish relationships between the internal structure and dynamics of the Sun and the various components of magnetic activity in the solar atmosphere. SDO instru- ments will generate a total data flow of about 1.5 TB day$(B!](B1, which represents a real challenge for the ground segment in terms of data storage, processing, and analysis.The Helioseismic and Magnetic Imager (HMI) is designed to deliver ideal data for local helioseis- mology. HMI is one of several instruments onboard NASAN"s Solar Dynamics Observatory (SDO), which was successfully launched on 11 February 2010 in a geosynchronous orbit. HMI will trans- mit 4, 096 NW 4, 096-pixel Doppler images of the Sun at the cadence of one image every 45 s. It will combine high spatial resolution (1 arcsec) and full spatial coverage, with a very high duty cycle over a nominal mission duration of five years. This combination will make possible the local helioseismic analysis of regions closer to the limb (less foreshortening), in order to study higher solar latitudes and the evolution of magnetic active regions as they rotate from limb to limb across the solar disk. In addition to Dopplergrams, HMI will provide images of the three components of the vector magnetic field, providing important information for the interpretation of helioseismic data. A stated goal of SDO/HMI is the subsurface detection of the magnetic field before it emerges at the surface, leading to reliable predictive capability (Kosovichev & HMI Science Team 2007). In combination with observations from the Atmospheric Imaging Assembly (AIA), a set of four SDO telescopes designed to provide an unprecedented view of the lower corona, HMI and local helioseismology will help establish relationships between the internal structure and dynamics of the Sun and the various components of magnetic activity in the solar atmosphere. SDO instru- ments will generate a total data flow of about 1.5 TB day$(B!](B1, which represents a real challenge for the ground segment in terms of data storage, processing, and analysis.

(01.06.2009) **Milestone #1**: Compute cluster operational. See the Compute cluster webpage.

(2009) The paper Helioseismology of Sunspots: A Case Study of NOAA Region 9787, Gizon, L. et al published in Space Science Reviews 144, 249-273

(12.05.2009) SISI results presented at the Third HELAS Local Helioseismology Workshop in Berlin, Germany

(01.09.2009) Dr. Raymond Burston joins SISI to work on travel-time sensitivity kernels.

(01.03.2009) Dr. Hamed Moradi joins SISI to work on parametric sunspot models.

(Dec. 2008) Dr. Raymond Burston attends meeting in Nice France to discuss SDO data access with Dr. R. Bogart.

(Oct. 2008) Y. Saidi participated in preparations for SDO data processing at Marina del Ray and Stanford, U.S.A.

(07.10.2008) Conference "Le Conseil européen pour la recherche pour une politique d'excellence: les premiers jeunes lauréats ouvrent la voie", Collège de France, Paris. [Read SISI project summary]

(01.08.2008) SISI project officially starts.

(11.07.2008) Grant agreement signed.

(05.06.2008) Postdoctoral Fellowships: Positions have been filled!

(13.02.2008) Prime Minister Francois Fillon receives ERC StG finalists.

(05.02.2008) Minister of Higher Education Valerie Pecresse congratulates ERC StG finalists.

(24.01.2007) ERC publishes the results of the first ERC Starting Grant competition. Project "Seismic Imaging of the Solar Interior using space-based data" ranked 243 out of over 9000 applications.