Spectral Study of the Active Region with the Ellerman Bomb and Hα Surges. Chromosphere. Ellerman Bomb

Abstract

The results from the analysis of spectral observations in the Hα line of the active region (AR) NOAA 11024, in which the Ellerman bomb (EB) and various chromospheric surges developed, are presented. Spectral data with high spatial and temporal resolution were obtained using the THEMIS French–Italian solar telescope (Tenerife, Spain) on July 4, 2009. The observation time was 20 min. On the day of the observations, the AR was at the stage of a sharp increase in activity. The Hα line profiles obtained for different periods of the Ellerman bomb development were very diverse, mainly consisted of several components, and were asymmetrical with excess emission in the short-wavelength wing. The maximum increase in the intensity of the emission component, compared with the profile for the AR segment without active formations, in the short-wavelength wing by 73% and in the long-wavelength wing by 35% occurred at a distance of ±0.16 nm from the core of the Hα line. The temporal variations of intensity in the wings of the Hα line indicate that there was a gradual energy release for the first 8 min of the Ellerman bomb development and then there was a pulse energy release for 6 min. The EB brightness increase period consisted of five peaks with an interval of approximately 1 min. The obtained temporal changes in the line-of-sight velocity (Vlos) of the chromospheric matter over the EB development region at the level of the Hα line core formation indicate that the velocity distribution in this region was mainly due to the development of chromospheric surges. In the segment without active formations, values of Vlos experienced small fluctuations within ±2 km/s. Two periods of increase in Vlos are distinguished. They consisted of several individual peaks: in the first half of the observations, the chromospheric matter mainly moved upward, while it mainly moved downward in the second half of the observations. Above the EB development region, different kinds of Hα-surges were observed. The maximum upward velocity in the return surges reached –12 to –16 km/s and the chromospheric matter descended along the same trajectories of magnetic loops with two times higher velocity, up to 22–30 km/s. In the loop surge, the maximum upward velocity on one side of the loop was –7 km/s and the downward velocity on the other side reached 18 km/s. One of the surges showed signs of plasma vortex motions, as evidenced by the inclined dark streaks in the spectra. Features of intensity variation in the wings of the Hα line and in the line-of-sight velocity of the chromospheric matter indicate that the Ellerman bomb and the accompanying Hα-surges, which appeared and developed in the AR under study, resulted from the magnetic reconnection caused by the emergence of the new serpentine magnetic flux and its interaction with the pre-existing magnetic field or between the magnetic loops of the flux itself.