DR. GIRJESH GUPTA

Heating of the solar corona along with acceleration of solar wind remain two of the most puzzling problems in the solar and space physics. There are several theories proposed to explain the phenomena, however, to identify any one dominant process is extremely difficult to do. Magnetohydrodynamics (MHD) waves are believed to play an important role in the heating of solar corona. In this model, convective motions at the footpoints of magnetic flux tubes are assumed to generate wave-like fluctuations that propagate up into the corona, and dissipate gradually. Although waves and oscillations have been studied and observed for decades, we are still far away from understanding the propagation and coupling of different wave phenomena observed in different layers of solar atmosphere, and their damping. In this talk, I will present simultaneous observations of photospheric p-mode waves, chromospheric umbral flash and associated umbral waves, and propagating slow magneto-acoustic coronal waves in a sunspot and associated active region. Our analysis suggest that all these different waves are driven by a common source. Using the non-thermal velocity measurements which are signatures of unresolved wave-motions, we found spectroscopic evidence of damping of Alfven waves in the active region corona with height. Damping lengths obtained from various spectral lines covering temperature range of 1.1-2.8 MK showed some temperature dependence. Results suggest that thermal conduction might play an important role in the damping of Alfven waves in the lower corona.