Using the multi-wavelength data from the Atmospheric Imaging Assembly (AIA)onboard the Solar Dynamics Observatory(SDO)spacecraft,we study a jet occurring in a coronal hole near the northern pole of the Sun.The jet presented distinct upward helical 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,the MFs 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 the axial velocities,transverse velocities,angular speeds,rotation periods,and rotation radii of the jet are 114 km s-1, 136 km s-1,0.81-s-1,452 s and 9.8×103 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 heights of 1×104～7× 104 km from the base of the jet,the flux density in the jet decreases from about 15 to 3 G as a function of B=0.5(R/R⊙-1)-0.84(G).A comparison was made with other results in previous studies.
At present it remains to address why the fast solar wind is fast and the slow wind is slow.Recently we have shown that the field line curvature may substantially influence the wind speed v,thereby offering an explanation for the Arge et al.finding that v depends on more than just the flow tube expansion factor.Here we show by extensive numerical examples that the correlation between v and field line curvature is valid for rather general base boundary conditions and for rather general heating functions.Furthermore,the effect of field line curvature is even more pronounced when the proton-alpha particle speed difference is examined.We suggest that any solar wind model has to take into account the field line shape for any quantitative analysis to be made.
In this article I present a review of recent studies on coronal dynamics, including research progresses on the physics of coronal streamers that are the largest structure in the corona, physics of coronal mass ejections (CMEs) that may cause a global disturbance to the corona, as well as physics of CME-streamer interactions. The following topics will be discussed in depth: (1) acceleration of the slow wind flowing around the streamer considering the effect of magnetic flux tube curvature; (2) physical mechanism accounting for persistent releases of streamer blobs and diagnostic results on the temporal variability of the slow wind speed with such events; (3) force balance analysis and energy release mechanism of CMEs with a flux rope magnetohydrodynamic model; (4) statistical studies on magnetic islands along the coronal-ray structure behind a CME and the first observation of magnetic island coalescence with associated electron acceleration; and (5) white light and radio manifestations of CME-streamer interactions. These studies shed new light on the physics of coronal streamers, the acceleration of the slow wind, the physics of solar eruptions, the physics of magnetic reconnection and associated electron acceleration, the large-scale coronal wave phenomenon, as well as the physics accounting for CME shock-induced type II radio bursts.
