STEREO/SECCHI Stereoscopic Observations Constraining the Initiation of Polar Coronal Jets

TL;DR

This study presents the first stereoscopic 3D observations of polar coronal jets, revealing their helical structure, dynamics, and untwisting behavior, supporting magnetic untwisting as a key jet initiation mechanism.

Contribution

It provides the first 3D analysis of polar coronal jets using stereoscopic data, confirming the helical structure and magnetic untwisting as the jet driving process.

Findings

Jets accelerate impulsively to over 300 km/s

Helical structures are confirmed as real, not projection effects

Magnetic untwisting is a viable jet initiation mechanism

Abstract

We report on the first stereoscopic observations of polar coronal jets made by the EUVI/SECCHI imagers on board the twin STEREO spacecraft. The significantly separated viewpoints ($\sim$ 11$^\circ$) allowed us to infer the 3D dynamics and morphology of a well-defined EUV coronal jet for the first time. Triangulations of the jet's location in simultaneous image pairs led to the true 3D position and thereby its kinematics. Initially the jet ascends slowly at $\approx$10-20 $\mathrm{{km} {s}^{-1}}$ and then, after an apparent 'jump' takes place, it accelerates impulsively to velocities exceeding 300 $\mathrm{{km} {s}^{-1}}$ with accelerations exceeding the solar gravity. Helical structure is the most important geometrical feature of the jet which shows evidence of untwisting. The jet structure appears strikingly different from each of the two STEREO viewpoints: face-on in the one viewpoint and edge-on in the other. This provides conclusive evidence that the observed helical structure is real and is not resulting from possible projection effects of single viewpoint observations. The clear demonstration of twisted structure in polar jets compares favorably with synthetic images from a recent MHD simulation of jets invoking magnetic untwisting as their driving mechanism. Therefore, the latter can be considered as a viable mechanism for the initiation of polar jets.