Height Dependence of Gas Flows in an Ellerman Bomb

Abstract

Abstract We performed spectroscopic observations of Ellerman bombs (EBs) in an active region of NOAA 10705 at Hida Observatory on 2004 November 24. The photospheric velocity fields of EBs have for the first time been investigated spectroscopically. From the Doppler shifts of a Ti II absorption line (6559.576 Å) and a broad H$\alpha$ emission line, we derived the photospheric velocity and the lower chromospheric velocity, respectively. The photospheric velocity of EBs was $\sim 0.2$kms$^{-1}$, indicating downward flow, on average. We found that the photospheric velocity variation of EBs has a good temporal correlation with the H$\alpha$ wing emission variation. On the other hand, the chromospheric velocity showed an upward flow of $\sim$1–3 kms$^{-1}$ on the average. From the characteristics of the flow field, we conclude that the observed EB occurred at the upper photospheric level. We suggest that it is important to know the motions of EBs in the photosphere because a plausible triggering mechanism of EBs is magnetic reconnection in the low-lying atmosphere.