An observationally constrained model of strong magnetic reconnection in the solar chromosphere

Abstract

Context. The evolution of the photospheric magnetic field plays a key role in the energy transport into the chromosphere and the corona. In active regions, newly emerging magnetic flux interacts with the pre-existent magnetic field, which can lead to reconnection events that convert magnetic energy into thermal energy. Aims. We aim to study the heating caused by a strong reconnection event that was triggered by magnetic flux cancelation. Methods. We use imaging and spectropolarimetric data in the Fe I 6301& 6302 Å, Ca II 8542 Å, and Ca II K spectral lines obtained with the CRISP and CHROMIS instruments at the Swedish 1-m Solar Telescope. These data were inverted with the STiC code by performing multi-atom, multi-line, non-local thermodynamic equilibrium inversions. These inversions yielded a three-dimensional model of the reconnection event and surrounding atmosphere, including temperature, velocity, microturbulence, magnetic field, and radiative loss rate. Results. The model atmosphere shows the emergence of magnetic loops with a size of several arcseconds into a pre-existing predominantly unipolar field. Where the reconnection region is expected to be, we see an increase in the chromospheric temperature of roughly 2000 K as well as bidirectional flows of the order of 10 km s−1 emanating from there. We see bright blobs of roughly 0.2 arcsec in diameter in the Ca II K, moving at a plane-of-the-sky velocity of the order of 100 km s−1 and a blueshift of 100 km s−1, which we interpret as ejected plasmoids from the same region. This scenario is consistent with theoretical reconnection models, and therefore provides evidence of a reconnection event taking place. The chromospheric radiative losses at the reconnection site are as high as 160 kW m−2, providing a quantitative constraint on theoretical models that aim to simulate reconnection caused by flux emergence in the chromosphere.

An ALMA Observation of Time Variations in Chromospheric Temperature of a Solar Plage Region

“…In active regions, newly emerging magnetic flux interacts with the pre-existing magnetic field, leading to magnetic reconnection events. Indeed, this scenario has been reported with high spatial resolution observations of granular-sized emerging fluxes and of their chromospheric response carried out in recent years (e.g., Guglielmino et al, 2008Guglielmino et al, , 2010Vargas Domínguez et al, 2012;Ortiz et al, 2014;de la Cruz Rodríguez et al, 2015;Centeno et al, 2017;Guglielmino et al, 2018;Díaz Baso et al, 2021). A complex fan-spine magnetic topology may be responsible for triggering UV bursts (Chitta et al, 2017;Smitha et al, 2018).…”

Spectropolarimetric inversions: Our key to unlocking the secrets of the solar atmosphere

“…Nevertheless, there have been significant advances in fundamental chromospheric science enabled by state-of-the-art inversions applied to high-resolution observations, for example in evaluating the role of magnetic fields in the heating of the quiet Sun chromosphere through ubiquitous magnetic flux cancellation events (Gošić et al, 2018), in inferring the stratification of the atmosphere undergoing magnetic reconnection (Vissers et al, 2019;Díaz Baso et al, 2021), in constraining heating rates due to emerging magnetic flux in an active region (da Silva Santos et al, 2022), in assessing the role of Alfvén waves and ion-neutral effects in plage heating (Anan et al, 2021), and in constraining temperatures of off-limb solar structures such as prominences (Jejčič et al, 2022) and spicules (Kuridze et al, 2021).…”