Abstract
We employ ring-diagram analysis to study the sub-surface thermal structure of active regions. We present results using a large number of active regions over the course of Solar Cycle 23. We present both traditional inversions of ring-diagram frequency differences, with a total sample size of 264, and a statistical study using Principal Component Analysis. We confirm earlier results on smaller samples that sound speed and adiabatic index are changed below regions of strong magnetic field. We find that sound speed is decreased in the region between approximately r=0.99 R ⊙ and r=0.995 R ⊙ (depths of 3 Mm to 7 Mm) and increased in the region between r=0.97 R ⊙ and r=0.985 R ⊙ (depths of 11 Mm to 21 Mm). The adiabatic index [Γ1] is enhanced in the same deeper layers where sound-speed enhancement is seen. A weak decrease in adiabatic index is seen in the shallower layers in many active regions. We find that the magnitudes of these perturbations depend on the strength of the surface magnetic field, but we find a great deal of scatter in this relation, implying that other factors may be relevant.
Solar Dynamics and Magnetism from the Interior to the Atmosphere
Guest Editors: R. Komm, A. Kosovichev, D. Longcope, and N. Mansour
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Baldner, C.S., Bogart, R.S., Basu, S. (2012). The Sub-surface Structure of a Large Sample of Active Regions. In: Mansour, N.N., Kosovichev, A.G., Komm, R., Longcope, D. (eds) Solar Dynamics and Magnetism from the Interior to the Atmosphere. Springer, New York, NY. https://doi.org/10.1007/978-1-4899-8005-2_17
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