Chromospheric Waves and Oscillations in Sunspots

Abstract:

Chromospheric wave phenomenon has been research focus for several years, and could provide indirect measurement of local conditions that are not otherwise accessible. Our interesting phenomenon are chromospheric oscillations including umbral flashes and running penumbral waves in a sunspot using scanning spectroscopy in H-alpha and Ca II 8542A, with the Fast Imaging Solar Spectrograph (FISS) at the 1.6 meter New Solar Telescope at Big Bear Solar Observatory. A bisector method is applied to spectral observations to construct chromospheric Doppler velocity maps. Temporal sequence analysis of these shows enhanced high-frequency oscillations inside the sunspot umbra in both lines. Their peak frequency gradually decreases outward from the umbra. The oscillation power is found to be associated with magnetic-field strength and inclination, with different relationships in different frequency bands. In this presentation, I will provide possible explanation of the observed properties of the waves and oscillations in sunspot.