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 .