Speaker
Description
Solar active regions are rich in dynamic phenomena driven by wave propagation. Among the most striking are umbral flashes, sudden brightenings observed in the chromospheric core of some spectral lines. Traditionally attributed to upward-propagating shock waves, this interpretation has been recently questioned by observations of downflowing umbral flashes and the identification of resonant cavities above sunspots. In this talk, I will discuss some recent results obtained from observations and modeling of chromospheric waves and umbral flashes. Non-LTE inversions of multi-line SST observations of a sunspot reveal predominantly upflowing plasma during umbral flashes. The fluctuations exhibit signatures of both propagating and standing waves, and evidence of dynamic and spatial changes in the transition region height has been found. In contrast, pore umbral flashes are dominated by downflowing plasma. This finding was explored through numerical simulations incorporating varying radiative cooling times.
