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02 August 2009

Does a polar coronal hole’s flux emergence follow a Hale-like law?

Does a polar coronal hole’s flux emergence follow a Hale-like law?
A. Savcheva1, J.W. Cirtain2, E.E. DeLuca1, L. Golub1

Recent increases in spatial and temporal resolution for solar telescopes sen-sitive to EUV and X-ray radiation have revealed the prevalence of transient jetevents in polar coronal holes. Using data collected by the X-Ray Telescope on Hinode, Savcheva et al. (2007) confirmed the observation, made first by the SoftX-ray Telescope on Yohkoh, that some jets exhibit a motion transverse to the jet outflow direction. The velocity of this transverse motion is, on average, 20 kms−1. The direction of the transverse motion, in combination with the stan-dard reconnection model for jet production (e.g. Shibata et al. 1992), reflects the magnetic polarity orientation of the ephemeral active region at the base of the jet. From this signature, we find that during the present minimum phase of the solar cycle the jet-base ephemeral active regions in the polar coronal holes had a preferred east-west direction, and that this direction reversed during the cycle’s progression through minimum. In late 2006 and early 2007, the preferred direction was that of the active regions of the coming sunspot cycle (Cycle 24), but in late 2008 and early 2009 the preferred direction has been that of the ac-tive regions of sunspot cycle 25. These findings are consistent with the results of Wilson et al. (1988) that there is a high latitude expansion of the solar activity cycle.

Subject headings: Sun: corona, Sun: UV radiation, Sun: x-ray jets, Sun: polar coronal hole, Sun: flux emergance

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