DISCONNECTING OPEN SOLAR MAGNETIC FLUX

作者：DeForest C E^*; Howard T A; McComas D J

来源：Astrophysical Journal, 2012, 745(1): 36.

DOI：10.1088/0004-637X/745/1/36

• magnetic reconnection
• Sun: corona
• Sun: heliosphere
• techniques: image processing
• techniques: photometric

Disconnection of open magnetic flux by reconnection is required to balance the injection of open flux by coronal mass ejections and other eruptive events. Making use of recent advances in heliospheric background subtraction, we have imaged many abrupt disconnection events. These events produce dense plasma clouds whose distinctive shape can now be traced from the corona across the inner solar system via heliospheric imaging. The morphology of each initial event is characteristic of magnetic reconnection across a current sheet, and the newly disconnected flux takes the form of a %26quot;U-%26quot; shaped loop that moves outward, accreting coronal and solar wind material. We analyzed one such event on 2008 December 18 as it formed and accelerated at 20 m s(-2) to 320 km s(-1), thereafter expanding self-similarly until it exited our field of view 1.2 AU from the Sun. From acceleration and photometric mass estimates we derive the coronal magnetic field strength to be 8 mu T, 6 R-circle dot above the photosphere, and the entrained flux to be 1.6 x 10(11) Wb (1.6 x 10(19) Mx). We model the feature%26apos;s propagation by balancing inferred magnetic tension force against accretion drag. This model is consistent with the feature%26apos;s behavior and accepted solar wind parameters. By counting events over a 36 day window, we estimate a global event rate of 1 day(-1) and a global solar minimum unsigned flux disconnection rate of 6 x 10(13) Wb yr(-1) (6 x 10(21) Mx yr(-1)) by this mechanism. That rate corresponds to similar to-0.2 nT yr(-1) change in the radial heliospheric field at 1 AU, indicating that the mechanism is important to the heliospheric flux balance.

• 出版日期2012-1-20