When and How Does A Prominence-like Jet Gain Kinetic Energy?

Usually a jet is triggered by a brightening or flare, which provides the first driving force. In this process, magnetic reconnection is thought to be the mechanism to convert magnetic energy into jet's kinetic energy. However, most jets could reach an unusual height and end far after the end of its associated flare. This fact implies another way continuously transferring magnetic energy into kinetic energy after the reconnection. This picture is well known, 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 AIA and EUVI, we reveal the continuously relaxation of post-reconnection magnetic field structure is an important process to support a jet. The kinetic energy of the jet gained through this way is 1.6 times of that from the reconnection. The resultant energy flux is hundreds of the required for local coronal heating, suggesting such jets are a possible source to keep corona hot. Rotational motion appearing all the time during the jet implies the torsional Alfven wave induced during reconnection is not the only mechanism to release magnetic energy and drive jets. Left column: Difference images taken by SDO/AIA at 304A passband. The FOV of the images is 430"x430". Right column: Difference images from STEREO-A/EUVI at the same passband. The FOV is 450"x450". Since STEREO-A was 120 degree apart away from SDO on 2012 July 8, the SDO limb event right happened ondisk in the view of STEREO-A.

Black and red solid curve: integrated intensity over the cross-section of the jet at different height at 19:11 UT and 19:47 UT, respectively. The two horizontal dashed lines are their average values. Black and red dashed curve with asterisks: axial speed with errors of the eight sub-jets shown in Figure 3 at 19:11 UT and 19:47 UT , respectively. Blue dashed curve with diamonds: angular speed with errors of the jet at different height.