C.J. Nelson, E.M. Scullion, J.G. Doyle, N. Freij, R. Erdélyi

Small-scale Structuring of Ellerman Bombs at Solar Limb

Figure 7. The evolution of the EB analysed in Case Study II at +0.8 Å. In the top row, four frames from this wavelength are plotted starting at 7:40:49 UT and separated by 146.3 seconds. The initial EB event is easily observed in the left-hand frame. The most dynamic horizontal motion of the event is shown in the second frame before the generation of the apparent loop is depicted in the third and fourth frames. The bottom row shows the time-distance analysis of the black slit overlaid on the top row with intensity normalised through time to remove the influence of changes in seeing. The black line indicates the speed of the event through time, highlighting the evident deceleration. The speeds of the event at the times marked by 1 and 2 are 6.2 km s−1 and 0.6 km s−1, respectively. White vertical lines depict the temporal position of each of the four top row plots.

Abstract

Ellerman bombs (EBs) have been widely studied in recent years due to their dynamic, explosive nature and apparent links to the underlying photospheric magnetic field implying that they may be formed by magnetic reconnection in the photosphere. Despite a plethora of researches discussing the morphologies of EBs, there has been a limited investigation of how these events appear at the limb, specifically, whether they manifest as vertical extensions away from the disc. In this article, we make use of high-resolution, high-cadence observations of an Active Region (AR) at the solar limb, collected by the CRisp Imaging SpectroPolarimeter (CRISP) instrument, to identify EBs and infer their physical properties. The upper atmosphere is also probed using the Solar Dynamic Observatory’s Atmospheric Imaging Assembly (SDO/AIA). We analyse 22 EB events evident within these data, finding that 20 appear to follow a parabolic path away from the solar surface at an average speed of 9 km s−1, extending away from their source by 580 km, before retreating back at a similar speed. These results show strong evidence of vertical motions associated with EBs, possibly explaining the dynamical 'flaring' (changing in area and intensity) observed in on-disc events. Two in-depth case studies are also presented which highlight the unique dynamical nature of EBs within the lower solar atmosphere. The viewing angle of these observations allows for a direct linkage between these EBs and other small-scale events in the Hα line wings, including a potential flux emergence scenario. The findings presented here suggest that EBs could have a wider-reaching influence on the solar atmosphere than previously thought, as we reveal a direct linkage between EBs and an emerging small-scale loop, and other near-by small-scale explosive events. However, as previous research found, these extensions do not appear to impact upon the Hα line core, and are not observed by the SDO/AIA EUV filters.

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Last Revised: 2014 October 22nd