KINEMATICS AND FINE STRUCTURE OF AN UNWINDING POLAR JET OBSERVED BY THE <i>SOLAR DYNAMIC OBSERVATORY</i> /ATMOSPHERIC IMAGING ASSEMBLY

Abstract

We present an observational study of the kinematics and fine structure of an\nunwinding polar jet, with high temporal and spatial observations taken by the\nAtmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO)\nand the Solar Magnetic Activity Research Telescope (SMART). During the rising\nperiod, the shape of the jet resembled a cylinder with helical structures on\nthe surface, while the mass of the jet was mainly distributed on the cylinder's\nshell. In the radial direction, the jet expanded successively at its western\nside. The radial expansion presented three distinct phases: the gradually\nexpanding phase, the fast expanding phase, and the steady phase. Each phase\nlasted for about 12 minutes. The angular speed of the unwinding jet and the\ntwist transferred into the outer corona during the eruption are estimated to be\n11.1 \\times 10{-3} rad/s (period = 564 s) and 1.17 to 2.55 turns (or 2.34 to\n5.1{\\pi}) respectively. On the other hand, by calculating the azimuthal\ncomponent of the magnetic field in the jet and comparing the free energy stored\nin the non-potential magnetic field with the jet's total energy, we find that\nthe non-potential magnetic field in the jet is enough to supply the energy for\nthe ejection. These new observational results strongly support the scenario\nthat the jets are driven by the magnetic twist, which is stored in the twisted\nclosed field of a bipole, and released through magnetic reconnection between\nthe bipole and its ambient open field.\n