HIGH RESOLUTION OBSERVATIONS OF CHROMOSPHERIC JETS IN SUNSPOT UMBRA

Recent observations of a sunspot's umbra have suggested that it may be finely structured on a subarcsecond scale representing a mix of hot and cool plasma elements. In this study, we report the first detailed observations of umbral spikes, which are cool jet-like structures seen in the chromosphere of an umbra. The spikes are cone-shaped features with a typical height of 0.5-1.0 Mm and a width of about 0.1 Mm. Their lifetime ranges from 2 to 3 minutes and they tend to re-appear at the same location. The spikes are not associated with photospheric umbral dots and they instead tend to occur above the darkest parts of the umbra where magnetic fields are strongest. The spikes exhibit up and down oscillatory motions and their spectral evolution suggests that they might be driven by upward propagating shocks generated by photospheric oscillations. It is worth noting that triggering of the running penumbral waves seems to occur during the interval when the spikes reach their maximum height.