Disconnecting open solar magnetic flux

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 "U-"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 320kms^-1, thereafter expanding self-similarly until it exited our field of view 1.2AU from the Sun. From acceleration and photometric mass estimates we derive the coronal magnetic field strength to be 8 μT, 6 R _⊙ above the photosphere, and the entrained flux to be 1.6 × 10¹¹ Wb (1.6 × 10¹⁹ Mx). We model the feature's propagation by balancing inferred magnetic tension force against accretion drag. This model is consistent with the feature'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 × 10¹³ Wb yr^-1 (6 × 10²¹ Mx yr^-1) by this mechanism. That rate corresponds to - 0.2 nT yr^-1 change in the radial heliospheric field at 1AU, indicating that the mechanism is important to the heliospheric flux balance.