Solar Dynamics Observatory

Launch scheduled in February 2010

The 3.3-ton satellite will blast off from Cape Canaveral on February 9. SDO is the first mission of NASA's Living With a Star program, which seeks to reveal how solar activity is generated and to understand the causes of solar variability and its impact on Earth. SDO will peer into the Sun's atmosphere and probe the Sun's inner workings using helioseismology.

To accomplish some of the helioseismology goals of the mission, a dedicated data and computing center has been set up at the Max Planck Institute. Public outreach material is available from the HELAS Local Helioseismology web site.

"SDO will take full-disk, high-definition images of the Sun all of the time," says project manager Liz Citrin at NASA's Goddard Space Flight Center, Greenbelt, Maryland. Previous missions could not capture images at as rapid a cadence as SDO will, nor did they have the bandwidth to transmit all of the data back to Earth for processing. "These advances will provide the data to better understand how the Sun works and will allow us to develop the tools to predict its behavior."

Research Highlight

Helioseismology probes sunspots

Sunspots have been seen on the surface of the Sun for thousands of years, and have been the subject of almost constant attention since the invention of the telescope. Despite this, much remains unknown because telescopes alone cannot see below the Sun's surface. Helioseismology, like terrestrial seismology, offers us a way to pierce the veil and "see" what lies hidden below. On the Earth, for example, we can look for oil deposits or cracks in the tectonic plates.

Below sunspots we are interested in magnetic fields, flows and temperature changes. Sunquake observations have been collected by the SOHO/MDI space experiment since 1996, while the soon to be launched SDO satellite will provide even higher quality data. In order to understand the observations scientists at the MPS have started performing numerical simulations of wave propagation through magnetic, fully nonlinear sunspots and have began comparing these with the data. The comparison allows us to learn about the structure of the sunspot.

A relevant paper is available with "open access" from the journal Solar Physics and can be downloaded here. The image shows a comparison of the processed helioseismic observations (top half) and the numerical simulations (bottom half):

2009 Karen Harvey Prize

Awarded to Laurent Gizon

The 2009 Karen Harvey Prize of the American Astronomical Society is awarded to Laurent Gizon "for his significant contributions and leadership in the development of local helioseismology techniques for the study of the Sun's internal dynamics." The 2009 Harvey Prize lecture, delivered at the 2009 SPD meeting, is available here.

Helioseismology, Asteroseismology, and MHD Connections

Inspired by the HELAS II and SOHO19/GONG 2007 conferences

Hardcover: 638 pages/ Publisher: Springer (January 6, 2009)/ ISBN-13: 978-0387894812/ amazon.com

This volume presents a timely snapshot of the state of helio- and asteroseismology in the era when SOHO/MDI is about to be replaced by SDO/HMI and CoRoT is yielding its first long-duration light curves of thousands of stars. This Topical Issue of Solar Physics is inspired by two seminal conferences, HELAS II and SOHO19/GONG 2007, and was open for general submission on the core topics of these conferences. Three papers describing the current status of asteroseismology, global helioseismology, and local helioseismology were specially commissioned for the volume, and these set the context for the other contributions.

Research Highlight

Banana-doughnut tomography of the Sun

Finite-wavelength tomography of the Earth or the Sun critically relies on models of the sensitivity of seismic travel times to localized heterogeneities (as evidenced by the controversial discovery of plumes in the Earth's mantle). On the Sun, the magnetic field is dragged by convective motions into concentrations that form the quiet-Sun magnetic network. Because these magnetic features are smaller than the wavelengths of solar oscillations, they are ideal to study the response of finite-wavelength seismic travel times to point-like perturbations.

An international team of scientists, including helioseismologists from the MPS, have used time-distance helioseismology to directly measure the spatial sensitivity of surface-gravity wave travel times to magnetic perturbations (ApJ article). The data strongly speak in favour of 'banana-doughnut' theory according to which body-wave travel times are sensitive to the wave speed in a broad region surrounding the geometrical ray path. As can be seen in the Figure, the spatial sensitivity is not restricted to the geometrical ray path, is spread on an ellipse, and oscillatory.

This study provides an observational confirmation of the basic banana-doughnut theory originally developed for finite-wavelength tomography of the Earth. This is the first test outside the laboratory showing the relevance of scattering theory to cross-correlation travel times (laboratory tests exist for ultrasonic waves). As in Earth seismology, finite-wavelength modelling will be essential in revealing deep structures in the solar interior, including those related to the solar dynamo.

Figure: Sensitivity of solar surface-wave travel times to small magnetic features. (a) Observations based on data from the high-resolution field of view of the MDI-SOHO space telescope. A magnetic feature at position (x,y) causes a shift in the travel time measured between the two observation points (crosses). The grey scale gives the shift in travel time due to a one kilogauss magnetic field covering one square megameter. (b) Phenomenological model for a point magnetic scatterer based on banana-doughnut theory. A scatterer located anywhere along an ellipse (with focii at the observation points) causes travel-time shifts of the same sign, giving rise to Fresnel zones. The hyperbolic features are due to the scattering of waves generated by distant sources.