Could you tell us a little bit about yourself?
I am currently Associate Professor at the Indian Institute of Astrophysics, Bangalore, India. I do research in the area of solar physics focussing on helioseismology of magnetic fields and large-scale flows in the solar interior. I also have interests in stellar magnetism and asteroseismology. And, I teach doctoral students (in their first year of course-work) covering subjects like fluid dynamics, plasma physics, solar and stellar physics.
What are the most important recent developments in the field of research discussed in your chapter?
Application of inversion methods and their refinements, as briefly discussed in my Chapter (Modeling Approaches in Helioseismology), for local 3D tomography of magnetic fields and flows constitute some important recent developments. These developments have also led to the realization (as discussed in the last two Sections of my Chapter) that the strong magnetic fields at the solar surface render the conventional seismic inversion modeling inadequate. These ‘surface effects’ require explicit modeling of magnetohydrodynamic (MHD) waves driven by p modes (or seismic waves) within the framework of seismology, and at the same time a clear identification of wave motions (or observables) from the Doppler shifts of a spectral line formed in intense magnetized atmosphere. These latter aspects are just beginning to be addressed in this field, using realistic 3D numerical MHD simulations of near-surface layers of the Sun.
How can other seismologists, planetary scientists and astrophysicists learn from this area of research?
There is huge potential for exchange of ideas between helio- and geo-seismologists for developing new techniques to exploit the very sophisticated and high quality observational data on the Sun. Turbulent convection being the source of seismic waves on the Sun, modeling of noise-dominated wave-field that has been the frontier in geo-seismology could have fruitful applications in helioseismology. Modeling involving 3D numerical simulations and full wave-field tomography, briefly touched on in my Chapter but discussed in detail by Cobden, Fichtner and Tong in their chapter, is an area where geo- and helio-seismologists can find common ground for learning from each other.
Could you recommend one or two of your key research papers related to your book chapter? Could you tell us a bit more about the research?
The modeling approaches discussed in my book chapter face formidable challenges when applied to study localized strong magnetic field structures such as sunspots. As referred to in my answer to question above, major difficulties are to do with the so called ‘surface effects’ that require modeling MHD waves driven by p modes as well as radiative transfer effects that complicate extraction of seismic quantities from the observables (Doppler shifts due to surface motions). I have addressed both these aspects in my research paper, Rajaguru et al. 2010, ApJLetters, 721, L86.
How important is it for you to be involved in international, collaborative, interdisciplinary research linked to seismology?
Helioseismology is largely a data-driven science, and currently it involves exploiting observational data covering more than two solar-cycles (more than two decades), and much of the data come from large international facilities, e.g. GONG (NSO, USA), MDI/SOHO. Progress in helioseismology, especially 3D wavefield tomography to image the sub-surface magnetic and flow fields, requires interdisciplinary research involving geo- and helioseismology as well as the subjects of magnetohydrodynamics, radiative transfer and spectropolarimetry (for accurate measurements and modeling of magnetic fields on the solar surface).
Do you have any other messages to our readers?
I am currently pursuing collaborative research with colleagues in Germany, Australia and the USA to perform 3D numerical MHD computations to address helioseismology of magnetic fields. High quality asteroseismic data from space missions (e.g. Kepler, COROT) are revolutionizing stellar physics, and what we learn from asteroseismology on fundamental processes controlling magnetic activity in stars would have interesting implications for understanding the interior dynamics of the Sun and vice versa.