When and How Does a Prominence-Like Jet Gain Kinetic Energy?

Abstract

Jet, a considerable amount of plasma being ejected from chromosphere or lower corona into higher corona, is a common phenomenon. Usually a jet is triggered by a brightening or a flare, which provides the first driving force to push plasma upward. In this process, magnetic reconnection is thought to be the mechanism to convert magnetic energy into thermal, non-thermal and kinetic energies. However, most jets could reach an unusual high altitude and end much later than the end of its associated flare. This fact implies that there is another way to continuously transfer magnetic energy into kinetic energy even after the reconnection. The whole picture described above is well known in the community, but how and how much magnetic energy is released through the way other than the reconnection is still unclear. Here, through studying a prominence-like jet observed by SDO/AIA and STEREO-A/EUVI, we find that the continuous relaxation of the post-reconnection magnetic field structure is an important process for a jet to climb up higher than it could through only reconnection. The kinetic energy of the jet gained through the relaxation is 1.6 times of that gained from the reconnection. The resultant energy flux is hundreds of times larger than the flux required for the local coronal heating, suggesting that such jets are a possible source to keep corona hot. Furthermore, rotational motions appear all the time during the jet. Our analysis suggests that torsional Alfvén waves induced during reconnection could not be the only mechanism to release magnetic energy and drive jets.

Spectroscopic and Stereoscopic Observations of the Solar Jets

“…Considering the IRIS slit was oriented nearly perpendicular to the jet axis ( Fig. 1), these sine-like tracks might represent the rotating motions of the jets around their axes (Liu et al 2014). The rotation periods are estimated to be around 20 minutes, which is very close to that reported by Liu et al (2014).…”

“…These observational results indicate the multi-temperature structures and high dynamics in solar jets. The solar jets often rotate or swirl along their axes, which can be clearly seen in the Doppler shifts of spectral lines (Kamio et al 2010;Cheung et al 2015;Kayshap et al 2018) or the time-distance plot along a slit perpendicular to the jet axis (Shen et al 2011a;Zhang & Ji 2014a;Liu et al 2014). The helical structures and untwisting motions of solar jets are also reported, indicating the magnetic-untwisting waves in solar jets (Hong et al 2013;Moore et al 2015).…”

How Many Twists Do Solar Coronal Jets Release?

“…Via a careful examination on these sub-jets, we have found a trend that: 1) when the maximum projected distance is above about 100 Mm, a sub-jet with a larger maximum projected distance reached its maximum projected distance slightly earlier; and 2) when the maximum projected distance is below about 100 Mm, a sub-jet with a smaller maximum projected distance reached its maximum projected distance earlier. A similar behavior of subjets in a rotating coronal jet was also be found in our earlier study [Liu et al, 2014]. We conjecture that the above behavior was caused by the following reason: 1) at the beginning of the eruption, a sub-jet erupted earlier only had a slightly higher initial speed than its successive sub-jet and thus reached its maximum projected distance somewhat earlier; and 2) towards the end of the magnetic reconnection, a sub-jet erupted later had a significantly lower initial speed than its previous sub-jet, and thus reached its maximum projected distance earlier.…”

“…We conjecture that the above behavior was caused by the following reason: 1) at the beginning of the eruption, a sub-jet erupted earlier only had a slightly higher initial speed than its successive sub-jet and thus reached its maximum projected distance somewhat earlier; and 2) towards the end of the magnetic reconnection, a sub-jet erupted later had a significantly lower initial speed than its previous sub-jet, and thus reached its maximum projected distance earlier. A similar relationship between the initial speeds of sub-jets can be found from column 1 of Table 1 in Liu et al [2014].…”

A Complex Solar Coronal Jet with Two Phases

“…They are ubiquitous in the solar atmosphere and occur in active regions, the quiet Sun, and polar regions (Cirtain et al 2007;Shen et al 2012;Liu et al 2014;Zhang & Ji 2014;Hong et al 2016;Raouafi et al 2016;Zhang et al 2016). The typical length of jets is 10-400 Mm, the width is 5-100 Mm, and the apparent velocity is 10-1000 km s −1 with an average value of 200 km s −1 (Shimojo et al 1996(Shimojo et al , 1998.…”