Magnetic reconnection in the low solar chromosphere with a more realistic radiative cooling model

Abstract

Magnetic reconnection is the most likely mechanism responsible for the high temperature events that are observed in strongly magnetized locations around the temperature minimum in the low solar chromosphere. This work improves upon our previous work ["Magnetic Reconnection in Strongly Magnetized Regions of the Low Solar Chromosphere", The Astrophysical Journal 852, 95 (2018) ] by using a more realistic radiative cooling model computed from the OPACITY project and the CHI-ANTI database. We find that the rate of ionization of the neutral component of the plasma is still faster than recombination within the current sheet region. For low β plasmas, the ionized and neutral fluid flows are well-coupled throughout the reconnection region resembling the single-fluid Sweet-Parker model dynamics. Decoupling of the ion and neutral inflows appears in the higher β case with β 0 = 1.46, which leads to a reconnection rate about three times faster than the rate predicted by the Sweet-Parker model. In all cases, the plasma temperature increases with time inside the current sheet, and the maximum value is above 2 × 10 4 K when the reconnection magnetic field strength is greater than 500 G. While the more realistic radiative cooling model does not result in qualitative changes of the characteristics of magnetic reconnection, it is necessary for studying the variations of the plasma temperature and ionization fraction inside current sheets in strongly magnetized regions of the low solar atmosphere. It is also important for studying energy conversion during the magnetic reconnection process when the hydrogen-dominated plasma approaches full ionization.

Observations of small-scale energetic events in the solar transition region: explosive events, UV bursts, and network jets

“…Judge [2015] performed an independent analysis and suggested that these events were formed in the low to middle chromosphere or above. While Ellerman bombs are phenomena that are well known to be signatures of magnetic reconnections in the photosphere [Ellerman, 1917;Vissers et al, 2015;Reid et al, 2016;Fang et al, 2006;Hong et al, 2014;Nelson et al, 2013Nelson et al, , 2015Nelson et al, , 2016Fang et al, 2017;Ni et al, 2016Ni et al, , 2018a, have crosschecked IRIS observations and Hα images of 10 TR UV burst events from the Chinese New Vacuum Solar Telescope [Xu et al, 2014;Liu et al, 2014] and have found that 6 of the 10 events are associated with Ellerman bombs in the photosphere and the rest 4 are not. This indicates that some UV bursts in the TR are signatures of magnetic reconnections in the photosphere that heat plasma up to at least the TR temperature [Kim et al, 2015;.…”

Kinetic Simulations of Magnetic Reconnection in Partially Ionized Plasmas

“…For example, the solar chromosphere is relatively cool, dense, and weakly ionized, but contains many classes of dynamical events thought to be driven by reconnection, such as UV bursts [2,3], jets [4,5], spicules [6,7], or transition region explosive events [8]. The importance of partially ionized reconnection to chromospheric physics has motivated several studies of partially ionized reconnection [9][10][11][12][13][14][15][16][17][18][19][20]. However, a major open question is under what conditions fast (i.e., Alfvénic and resistivity independent) reconnection can occur.…”

Observations of small-scale energetic events in the solar transition region: explosive events, UV bursts, and network jets

“…This indicates that some UV bursts in the TR are signatures of magnetic reconnections in the photosphere that heat plasma up to at least the TR temperature [Kim et al, 2015;. Such a conclusion has also been confirmed by [Nelson et al, 2017], who established that some Ellerman bombs in the quiet Sun also have responses in the IRIS Si IV lines. It is worth mentioning that the blends of the chromospheric absorption lines in the TR emission lines might also be the results of cold plasma (such as filaments, mini-filaments) at the foreground [Vissers et al, 2015;Huang et al, 2017], and thus it is not complete criteria for this species of UV bursts.…”

“…Judge [2015] performed an independent analysis and suggested that these events were formed in the low to middle chromosphere or above. While Ellerman bombs are phenomena that are well known to be signatures of magnetic reconnections in the photosphere [Ellerman, 1917;Vissers et al, 2015;Reid et al, 2016;Fang et al, 2006;Hong et al, 2014;Nelson et al, 2013Nelson et al, , 2015Nelson et al, , 2016Fang et al, 2017;Ni et al, 2016Ni et al, , 2018a, have crosschecked IRIS observations and Hα images of 10 TR UV burst events from the Chinese New Vacuum Solar Telescope [Xu et al, 2014;Liu et al, 2014] and have found that 6 of the 10 events are associated with Ellerman bombs in the photosphere and the rest 4 are not. This indicates that some UV bursts in the TR are signatures of magnetic reconnections in the photosphere that heat plasma up to at least the TR temperature [Kim et al, 2015;.…”

“…With these observations, some simulation experiments have tried to explain whether magnetic reconnection in the photosphere could heat plasma to transition region temperatures. Ni et al [2018a, b] have found that initially weakly ionized plasmas can become fully ionized within the reconnection region and the current sheet can be strongly heated to above 2.5•10 4 K in the cases that the reconnecting magnetic field is in excess of a kilogauss and the plasma β is lower than 0.0145. For more details of UV bursts, we refer to a review paper by Young et al [2018].…”