qs090.canfield06 Posted: 10-Jun-95 Updated: 03-Feb-96, 20-Sep-96 Events specified: N/A
R. Canfield, A. Pevtsov, S. Tsuneta, L. Acton We propose to use Mees vector magnetograms and Yohkoh SXT images to study the variation of the sign of the magnetic helicity density of _interacting_ active regions_ and _large-scale_ structures in the solar atmosphere, as opposed to that of active regions alone, as proposed in TeamBB topic ar080.
Most existing dynamo theories predict a strong hemisphere vs sign-of-helicity rule. Our (Pevtsov, Canfield, Metcalf, ApJ, 440, L109) previous study of the latitudinal variation of the magnetic helicity density of photospheric magnetic fields shows that this is a weak rule; the data show numerous examples of both signs of helicity density in both hemispheres. We also find (Pevtsov, Canfield, Metcalf, 1995, Eos Trans. AGU, 76(17), Spring Meet. Suppl., S228) that active regions in given _ranges_ of latitude and longitude tend to keep the same sign of helicity for several succesive rotations, even if the sign does not agree with the hemispheric rule. Our preliminary comparison of the magnetic helicity density computed using Mees vector magnetograms and Yohkoh SXT images shows that, in several cases, active regions that are interacting (even across equator) show same sign of magnetic helicity, which might be an indirect argument for the reality of the large-scale helicity areas.
Interpreting the observations described above, we speculate that there are large-scale areas (much larger and more long-lived than single active regions) of uniform sign of helicity (or clusters of active regions), which can be tracked in both the photosphere and the corona. We plan to investigate the occurrence and evolution of such helicity structures in both the photosphere and the corona by analyzing both photospheric vector magnetic fields observed at Mees Solar Observatory and the twist and connections shown by the coronal structures in SXT observations. We plan to use the routine SXT full disk images taken throughout the mission for this purpose.
ar068: Soft X-Ray Coronal Structures and Magnetic and Chromospheric Patterns (Harvey_J)
At the present time a manuscript is in preparation on this topic: The draft title and authorship of this manuscript is: "Signature of Convection in the Helicity of Solar Photospheric Magnetic Fields" Authors are Richard C. Canfield, Alexei A. Pevtsov, and Gary A. Glatzmaier The paper presents observations of the distribution of helicity with time and solar longitude and interprets the observations in terms of long-lived coherent flows in the convection zone.
Update 03-Feb-96
The following abstract has been submitted for the Bath meeting. Please use it to update our proposal qs090: Large-Scale Structures of Helicity in the Photosphere and Corona (Canfield).
Magnetic Chirality and Coronal Reconnection R.C. Canfield and A.A. Pevtsov Institute for Astronomy, University of Hawaii
We have used Mees Solar Observatory vector magnetograms and Yohkoh SXT images to study the role of magnetic chirality (magnetic field handedness) in the trans-equatorial reconnection of active regions.
Most dynamo theories predict a strong hemispheric chirality rule. Our previous study of the latitudinal variation of the magnetic helicity density of photospheric magnetic fields (Pevtsov, Canfield, Metcalf, ApJ, 440, L109) shows that this is a weak rule; the data show numerous examples of both signs of helicity density in both hemispheres. Our comparison of the magnetic chirality determined from Mees vector magnetograms and Yohkoh SXT images of seven pairs of trans-equatorial interacting active regions shows that the chirality of the two regions is the same in all cases.
We interpret this result in terms of active region current systems.