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Session 2 - Everything Else.
Display session, Friday, June 27
Ballroom C, Chair: Richard Canfield

[2.55] The Skew of Polar Crown X-ray Arcades

A. H. McAllister (Helio Reasearch/HAO), D. MacKay (U. St. Andrews), A. J. Hundhausen (HAO), E. Priest (U. St. Andrews)

A one-to-one relationship between the chirality of filament channels and the skew (relative orientation) of the overlyingcoronal arcades, as seen with the Yohkoh Soft X-ray Telescope (SXT) was found by Martin and McAllister [1997]. The basis of the relationship is a sample of over 30 mid-and low-latitide filaments during a 6 month period in early 1992. This relationship can be coupled with the predictions for the axial component of polar crown filaments based on the work of Leroy et al. [1983] to predicit the skew of polar crown arcades in the recent cycle 22. Thus the axial component of the filament fields along the southern polar crown is predicted to point to the west and a similar component in the corona will lead to right skewed arcades. As has been pointed out in the past, this orientation is inconsistent with the action of photospheric differential rotation on an east-west arcade [Ballegooijen and Martens, 1990]. In this poster we report on the results of a recent survey of the SXT images over the whole declining phase of cycle 22 (Oct. 1991 to June 1995). These results are not in general agreement with those expected based on the past filament observations. They show highly left skewed polar arcades rather than the predicted right skew. The observations are, however, in general agreement with the effects of differential rotation and with recent numerical simulations of polar crown structures, which we will also briefly present. This posses an unexpected and challenging problem and we will discuss some possible ways of reconciling the different observational results.

Leroy, Bommier, and Sahal-Brechot, The Magnetic Field in Prominences of the Polar Crown, Solar Physics, 83, 135-142, 1983. Martin and McAllister, The Chirality of X-ray Coronal Arcades Overlying Quiescent Filaments, Astrophys. Journ., submitted, 1997. Ballegooijen and Martens, Magnetic Fields in Quiescent Prominences, ApJ, 361, 283-289, 1990.

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