SPINNING MOTIONS IN CORONAL CAVITIES
- Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352 (United States)
- Also at Interferometrics, Inc., Herndon, VA 20171, USA. (United States)
In movies made from Fe XII 19.5 nm images, coronal cavities that graze or are detached from the solar limb appear as continually spinning structures, with sky-plane projected flow speeds in the range 5-10 km s{sup -1}. These whirling motions often persist in the same sense for up to several days and provide strong evidence that the cavities and the immediately surrounding streamer material have the form of helical flux ropes viewed along their axes. A pronounced bias toward spin in the equatorward direction is observed during 2008. We attribute this bias to the poleward concentration of the photospheric magnetic flux near sunspot minimum, which leads to asymmetric heating along large-scale coronal loops and tends to drive a flow from higher to lower latitudes; this flow is converted into an equatorward spinning motion when the loops pinch off to form a flux rope. As sunspot activity increases and the polar fields weaken, we expect the preferred direction of the spin to reverse.
- OSTI ID:
- 21450955
- Journal Information:
- Astrophysical Journal Letters, Vol. 719, Issue 2; Other Information: DOI: 10.1088/2041-8205/719/2/L181; ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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