arXiv subjects

Mats Ola Sand

Publications and source records attributed to Mats Ola Sand.

3 recordsLinked to original sources

arXiv2026

Evidence for plasmoid formation related to a hot UV burst in the solar atmosphere

Magnetic reconnection in the solar atmosphere drives energetic phenomena such as Ellerman bombs, UV bursts, and surges. We used coordinated observations from the Swedish 1-m Solar Telescope (SST), IRIS, SDO, and the Hinode/X-ray Telescope (XRT) to analyze an active region with strong magnetic flux emergence. This region displayed long duration UV burst activity, occurrence of multiple Ellerman bombs, and recurrent ejection of surges. Chromospheric imaging show sthe presence of a dome-like structure that overarched the region where magnetic flux was emerging. The curved chromospheric fibrils were closely associated with bright and similarly curved extensions from a UV burst in the IRIS 1400 A channel. We observed an episode of formation of a bright sheet along the curved fibrils in H-beta that subsequently fragmented into plasmoid-like blobs with peak emission at a Doppler offset of +43 km/s. IRIS Si IV lines in the same region show complex and non-Gaussian line profiles that display asymmetric extensions to high Doppler offsets. Some profiles have clear components with Doppler offsets in excess of 150 km/s on both sides of the nominal line center. The optically thin SDO/AIA channels, including 94 A, show intermittent and repeated occurrences of the burst. Emission measure and filter ratio analysis indicate that the burst is multi-thermal and can attain temperatures beyond 1 MK. AIA and Hinode/XRT observations reveal a localized EUV and soft-X-ray counterpart of the burst/dome system, supporting the presence of intrinsically multithermal plasma that reaches coronal, and likely multi-MK, temperatures.

astro-ph.SR↗

arXiv2025

Shock-induced magnetic reconnection driving Ellerman bomb emission and a spicule

The mechanism that forms dynamic type II spicules has remained elusive for many years. Their dynamical behaviour has long been linked to magnetic reconnection, yet no conclusive evidence has been provided. However, one recent observational study found signs of reconnection, as traced by Ellerman bombs (EBs), at the footpoints of many spicules. The triggering of EBs is generally linked to reconnection due to flux emergence and convective motions in the photosphere. We aim to explore whether we can connect EBs to type II spicules, and to what extent we can use EBs as an observational proxy to probe reconnection in this dynamic. We also aim to provide further insight into the mechanisms that trigger EBs. We used a simulation run with the radiative magnetohydrodynamics code Bifrost to track spicules and study the physical processes behind their formation. To detect EBs and classify the spicules, we synthesised the H-alpha line using the multilevel radiative transfer code RH1.5D. We also traced shocks and current sheets to decipher the origin of EBs and spicules. We selected one type II spicule with a strong EB near its footpoint and studied their formation in detail. A magnetoacoustic shock advects the magnetic field lines towards an oppositely directed ambient field, creating a current sheet. The current sheet accelerates dense plasma via a whiplash effect generated by reconnection into the inclined ambient field, launching the spicule. Several EB profiles trace shock- and magnetic-reconnection-induced dynamics during this process at the spicule footpoint. We present a new EB triggering mechanism in which a shock-induced current sheet reconnects, triggering an EB in the lower solar atmosphere. The shock-induced current sheet generates the launch of a type II spicule via reconnection outflows. These results provide a physical origin for the observed connection between EBs and spicules.

astro-ph.SR↗

arXiv2025

Quiet Sun Ellerman bombs as a possible proxy for reconnection-driven spicules

Spicules are elongated, jet-like structures that populate the solar chromosphere and are rooted in the photosphere. In recent years, high-resolution observations and advanced numerical simulations have provided insights into their properties, structures, and dynamics. However, the formation mechanism of spicules, particularly the more dynamic type II spicules, which are primarily found in the quiet Sun and coronal holes, remains elusive. This study explores whether quiet Sun Ellerman bombs (QSEBs), which are ubiquitous small-scale magnetic reconnection events in the lower atmosphere, are linked to the formation of type II spicules. We analysed a high-quality 40-minute time sequence acquired with the Swedish 1-m Solar Telescope. H-beta data were used to observe QSEBs and spicules, while spectropolarimetric measurements in the photospheric Fe i 6173 A line provided line-of-sight magnetic field information. We employed k-means clustering to automatically detect QSEBs and explored their potential association with spicules. We identified 80 clear cases where spicules occurred soon after the QSEB and not later than 30 s after the ending of the QSEBs. All events involved type II spicules, rapidly fading from the images. The footpoints of the spicules seemed to be rooted in QSEBs, where the onset of QSEBs often preceded the formation of the associated spicules. Additionally, we found around 500 other events that hinted at a connection but with some ambiguities. The combined clear and ambiguous cases constitute 34% of the total detected QSEBs and a smaller percentage of the spicules in our dataset. Our findings suggest that a fraction of type II spicules originate from QSEBs, supporting magnetic reconnection as a potential driving mechanism. In this context, QSEBs and spicules represent the conversion of magnetic energy into thermal and kinetic energy, respectively.

astro-ph.SR↗