ELLERMAN BOMBS AT HIGH RESOLUTION. II. TRIGGERING, VISIBILITY, AND EFFECT ON UPPER ATMOSPHERE

We use high-resolution imaging spectroscopy with the Swedish 1-m Solar Telescope (SST) to study the transient brightenings of the wings of the Balmer H alpha line in emerging active regions that are called Ellerman bombs. Simultaneous sampling of Ca II 8542 angstrom with the SST confirms that most Ellerman bombs also occur in the wings of this line, but with markedly different morphology. Simultaneous images from the Solar Dynamics Observatory (SDO) show that Ellerman bombs are also detectable in the photospheric 1700 angstrom continuum, again with differing morphology. They are also observable in 1600 angstrom SDO images, but with much contamination from C IV emission in transition-region features. Simultaneous SST spectropolarimetry in Fe I 6301 angstrom shows that Ellerman bombs occur at sites of strong-field magnetic flux cancellation between small bipolar strong-field patches that rapidly move together over the solar surface. Simultaneous SDO images in He II 304 angstrom, Fe IX 171 angstrom, and Fe XIV 211 angstrom show no clear effect of the Ellerman bombs on the overlying transition region and corona. These results strengthen our earlier suggestion, based on H alpha morphology alone, that the Ellerman bomb phenomenon is a purely photospheric reconnection phenomenon.