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Register a new userEllerman Bombs - Evidence for Magnetic Reconnection in the Lower Solar Atmosphere
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The presence of photospheric magnetic reconnection has long been thought to give rise to short and impulsive events, such as Ellerman bombs (EBs) and Type II spicules. In this article, we combine high-resolution, high-cadence observations from the Interferometric BIdimensional Spectrometer (IBIS) and Rapid Oscillations in the Solar Atmosphere (ROSA) instruments at the Dunn Solar Telescope, National Solar Observatory, New Mexico with co-aligned Atmospheric Imaging Assembly (SDO/AIA) and Solar Optical Telescope (Hinode/SOT) data to observe small-scale events situated within an active region. These data are then compared with state-of-the-art numerical simulations of the lower atmosphere made using the MURaM code. It is found that brightenings, in both the observations and the simulations, of the wings of the H alpha line profile, interpreted as EBs, are often spatially correlated with increases in the intensity of the FeI 6302.5A line core. Bi-polar regions inferred from Hinode/SOT magnetic field data show evidence of flux cancellation associated, co-spatially, with these EBs, suggesting magnetic reconnection could be a driver of these high-energy events. Through the analysis of similar events in the simulated lower atmosphere, we are able to infer that line profiles analogous to the observations occur co-spatially with regions of strong opposite polarity magnetic flux. These observed events and their simulated counterparts are interpreted as evidence of photospheric magnetic reconnection at scales observable using current observational instrumentation.
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High-resolution imaging-spectroscopy movies of solar active region NOAA 10998 obtained with the CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish 1-m Solar Telescope show very bright, rapidly flickering, flame-like features that appear intermittently in the wings of the Balmer H-alpha line in a region with moat flows and likely some flux emergence. They show up at regular H-alpha blue-wing bright points that outline magnetic network, but flare upward with much larger brightness and distinct jet morphology seen from aside in the limbward view of these movies. We classify these features as Ellerman bombs and present a morphological study of their appearance at the unprecedented spatial, temporal, and spectral resolution of these observations. The bombs appear along magnetic network with footpoint extents up to 900km. They show apparent travel away from the spot along the pre-existing network at speeds of about 1 km/s. The bombs flare repetitively with much rapid variation at time scales of seconds only, in the form of upward jet-shaped brightness features. These reach heights of 600-1200km and tend to show blueshifts; some show bi-directional Doppler signature, and some seem accompanied with an H-alpha surge. They are not seen in the core of H-alpha due to shielding by overlying chromospheric fibrils. The network where they originate has normal properties. The morphology of these jets strongly supports deep-seated photospheric reconnection of emergent or moat-driven magnetic flux with pre-existing strong vertical network fields as the mechanism underlying the Ellerman bomb phenomenon.
Ellerman Bombs (EBs) are often found co-spatial with bipolar photospheric magnetic fields. We use H$alpha$ imaging spectroscopy along with Fe I 6302.5 AA spectro-polarimetry from the Swedish 1-m Solar Telescope (SST), combined with data from the Solar Dynamic Observatory (SDO) to study EBs and the evolution of the local magnetic fields at EB locations. The EBs are found via an EB detection and tracking algorithm. We find, using NICOLE
Recent observations from the Interface Region Imaging Spectrograph (IRIS) appear to show impulsive brightenings in high temperature lines, which when combined with simultaneous ground based observations in H$alpha$, appear co-spatial to Ellerman Bombs (EBs). We use the RADYN 1-dimensional radiative transfer code in an attempt to try and reproduce the observed line profiles and simulate the atmospheric conditions of these events. Combined with the MULTI/RH line synthesis codes, we compute the H$alpha$, Ca II 8542~AA, and Mg II h & k lines for these simulated events and compare them to previous observations. Our findings hint that the presence of superheated regions in the photosphere ($>$10,000 K) is not a plausible explanation for the production of EB signatures. While we are able to recreate EB-like line profiles in H$alpha$, Ca II 8542~AA, and Mg II h & k, we cannot achieve agreement with all of these simultaneously.
White-light flares (WLFs), first observed in 1859, refer to a type of solar flares showing an obvious enhancement of the visible continuum emission. This type of enhancement often occurs in most energetic flares, and is usually interpreted as a consequence of efficient heating in the lower solar atmosphere through non-thermal electrons propagating downward from the energy release site in the corona. However, this coronal-reconnection model has difficulty in explaining the recently discovered small WLFs. Here we report a C2.3 white-light flare, which are associated with several observational phenomena: fast decrease in opposite-polarity photospheric magnetic fluxes, disappearance of two adjacent pores, significant heating of the lower chromosphere, negligible increase of hard X-ray flux, and an associated U-shaped magnetic field configuration. All these suggest that this white-light flare is powered by magnetic reconnection in the lower part of the solar atmosphere rather than by reconnection higher up in the corona.
Ellerman bombs (EBs) are small-scale intense brightenings in H$alpha$ wing images, which are generally believed to be signatures of magnetic reconnection events around the temperature minimum region of the solar atmosphere. They have a flame-like morphology when observed near the solar limb. Recent observations from the Interface Region Imaging Spectrograph (IRIS) reveal another type of small-scale reconnection events, termed UV bursts, in the lower atmosphere. Though previous observations have shown a clear coincidence of some UV bursts and EBs, the exact relationship between these two phenomena is still under debate. We investigate the spatial and temporal relationship between flame-like EBs and UV bursts using joint near-limb observations between the 1.6--meter Goode Solar Telescope (GST) and IRIS. In total 161 EBs have been identified from the GST observations, and 20 of them reveal signatures of UV bursts in the IRIS images. Interestingly, we find that these UV bursts have a tendency to appear at the upper parts of their associated flame-like EBs. The intensity variations of most EB-related UV bursts and their corresponding EBs match well. Our results suggest that these UV bursts and EBs are likely formed at different heights during a common reconnection process.
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