Motion of Photospheric Matter within the Active Region Site with Two Ellerman Bombs

Abstract

Examination results for specific features of variation of line-of-sight plasma velocities in different photosphere layers of the NOAA 11024 active region (AR) under the influence of two evolving Ellerman bombs (EB-1 and EB-2) are presented. Spectroscopic data with high spatial and temporal resolution were obtained with the French–Italian THEMIS solar telescope on July 4, 2009. The observation time was 20 min. The AR was undergoing a sharp increase in activity on the day of observations, and the EBs evolved in the region of one of the three magnetic fluxes that were emerging at the time. The brightness of EB-1 decreased during observations, while EB-2 got brighter. The λ ≈ 630 nm spectral region, which includes Fraunhofer lines forming within a wide range of photospheric heights (neutral iron lines Fe I λ 630.15, 630.25, and 630.35 nm and titanium line Ti I λ 630.38 nm), was used. Changes in the velocity and direction of motion of matter in the region of Ellerman bombs and in their immediate vicinity at different photosphere levels and at different stages of EB evolution were determined and analyzed. It was found that upflows were predominant at all levels of the AR photosphere. At the same time, line-of-sight velocities Vlos and the amplitude of their oscillations decreased considerably in the region of EBs. Apparently, downward matter flows reduced the velocity of upward plasma motion. This suggests that small-scale downward flows induced by magnetic reconnections were superimposed onto the large-scale upward motion of plasma of the new magnetic flux. The profile shape of photospheric lines reinforces this conclusion. The profiles of strong lines had a red asymmetry. The matter velocity determined based on the shift of a prominent component in the red wing of the Fe I λ 630.35 nm line profiles was as high as 2 km/s. Such a Vlos distribution in the EB regions indicates that they consisted of several jets moving with different velocities in different directions. The line-of-sight velocity in the central part of EB-1 and EB-2 varied from –1 to 0 km/s and from –1 to 0.2 km/s in the upper photospheric layer and from –1.6 to –0.2 km/s and from –1.1 to 0.25 km/s in the lower layer of the photosphere, respectively. Vlos variations in the vicinity of these Ellerman bombs were oscillatory, and the interval between oscillations was ~5 min. The pattern of quasiperiodic Vlos oscillations was disturbed in the EB regions: they often occurred in antiphase. It may be concluded that the excitation caused by a pulsed energy release as a result of successive magnetic reconnections associated with the emergence of the new magnetic flux propagated from the EB-1 site along a magnetic loop and triggered the formation of EB-2, and the Ellerman bombs then evolved as a physically connected pair. The studied features of the line-of-sight velocity variation of chromospheric and photospheric matter indicate that during the evolved of EBs differently directed motions of matter there was: it moved upward in the lower chromospheric layer, while downward flows reduced the velocity of ascending plasma at the photospheric level. Magnetic reconnections occurring in the layer between the upper photosphere and the lower chromosphere, where the core of the Hα line was formed, could induce such a velocity distribution.