Kinematics of an untwisting solar jet in polar coronal hole observed by SDO/AIA

TL;DR

This study analyzes the kinematics and magnetic field variation of an untwisting solar jet in a polar coronal hole using multi-wavelength SDO/AIA data, revealing detailed plasma motions and magnetic flux conservation.

Contribution

First detailed measurement of plasma velocities and magnetic field variation in an untwisting solar jet using multi-wavelength imaging data.

Findings

Plasma moved at ~114 km/s along the jet axis.

Jet exhibited a circular transverse motion with ~136 km/s.

Magnetic flux density decreased from 15 G to 3 G with height.

Abstract

Using the multi-wavelength data from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) spacecraft, we study a jet occurred in coronal hole near the northern pole of the Sun. The jet presented distinct helical upward motion during ejection. By tracking six identified moving features (MFs) in the jet, we found that the plasma moved at an approximately constant speed along the jet's axis, meanwhile, they made a circular motion in the plane transverse to the axis. Inferred from linear and trigonometric fittings to the axial and transverse heights of the six tracks, the mean values of axial velocities, transverse velocities, angular speeds, rotation periods, and rotation radiuses of the jet are 114 km s$^{-1}$, 136 km s$^{-1}$, 0.81\degr\ s$^{-1}$, 452 s, and 9.8 $\times$ 10$^{3}$ km respectively. As the MFs rose, the jet width at the corresponding height increased. For the first time, we derived the height variation of the longitudinal magnetic field strength in the jet from the assumption of magnetic flux conservation. Our results indicate that, at the heights of 1 $\times$ 10$^{4}$ $\sim$ 7 $\times$ 10$^{4}$ km from jet base, the flux density in the jet decreased from about 15 to 3 G as a function of B=0.5(R/R$_{\sun}$-1)$^{-0.84}$ (G). A comparison was made with the other results in previous studies.