Turbulent Reconnection in the Lower Solar Atmosphere Triggers UV Bursts Connecting with Ellerman Bombs

Ellerman bombs (EBs) and ultraviolet (UV) bursts are two of the smallest observed solar activities triggered by magnetic reconnection in the lower solar atmosphere, typically associated with flux emergence regions. Joint observations from the Interface Region Imaging Spectrograph (IRIS) satellite and ground-based solar telescopes reveal that approximately 20% of hot UV bursts are temporally and spatially connected with the cooler EBs. Using 3D radiation magnetohydrodynamic (RMHD) simulations with the MURaM code, we investigated the spontaneous emergence of a magnetic flux sheet, leading to complex magnetic field structures and diverse high-temperature activities due to magnetic reconnection. The simulations show that opposite-polarity magnetic fields converge in the lower solar atmosphere, forming thin current sheets and triggering plasmoid instability, which results in small twisted magnetic flux ropes and highly nonuniform plasma density and temperature. Hot plasmas (>20,000 K) emitting strong UV radiation coexist with cooler plasmas (<10,000 K) showing Hα wing emissions, with the former located ~700 km above the solar surface and the latter above them. Synthesized images and spectral line profiles exhibit characteristics of both EBs and UV bursts, demonstrating that turbulent reconnection mediated by plasmoid instability can occur in small-scale reconnection events in the partially ionized lower solar atmosphere. This model explains the formation mechanisms of UV bursts connected with EBs and indicates that UV bursts can form in atmospheric layers extending from the lower chromosphere to the transition region.