Determination Of Sub Photosphere Solar Active Region 3d Magnetic Field Structure From Emergence Observations
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Determination of Sub-photosphere Solar Active Region 3D Magnetic Field Structure from Emergence Observations
In this thesis, we study the emergence process of a bipolar solar active region NOAA 11416, a Hale class [beta gamma/gamma] active region, and reconstruct its global 3D magnetic structure through a novel image-stacking technique. The emergence began on 8 February 2012, and data was taken through 11 February 2012. Magnetograms from the Solar Dynamics Obersvatory's (SDO) Helioseismic and Magnetic Imager (HMI) are used in this study, and we take advantage of the unprecedented high imagery cadence offered by the observatory. We describe the selection process of observed candidate active regions covering the full data set since SDO first light. Using this magnetogram imagery, we visualize the detailed 3D magnetic structure by stacking the high-cadence SDO imagery and producing 3D isosurface plots, which yield extraordinary detail of the fine magnetic structure of the AR. The 3D structure shows a distinct asymmetric [lambda] shape to the emerging flux tube with tilt characteristic of Joy's Law. This asymmetric [lambda] shape exhibited a differing slope of the leading and trailing legs, the leading leg being 61° and the trailing leg 52° for an assumed rise velocity of 100 m/s. Close examination of the 3D structure indicates a highly fragmented flux rope whose organization appears to increase as the eruption progresses. We also find that the leading polarity is more fragmented in magnetogram imagery, which appears to support thin flux tube approximations and the results of analastic magneto-hydrodynamic simulations. Continuum imagery, however, shows the opposite situation, with the leading polarity being the more cohesive of the two. Additionally, the extracted AR parameters for center motion, tilt, polarity centroid separation, and flux per polarity are fit to functions, producing mathematical formulations for the 3D shape and magnetic flux of the flux tube. These functions not only accurately describe the shape and strength of the flux tube, but their exponential nature allows predictions of end points in terms of flux (~8x10^21 Mx), centroid separation (59.0 Mm), and centroid tilt angle (18.5°). We find that both tilt angle evolution and movement of the center fit well to underdamped harmonic oscillator equations. The former indicates interplay between the Coriolis force and shear forces resulting from differing Lorentz forces beneath and above the photosphere, producing an initially anti-Joy's-law tilt which rapidly changes to tilt following Joy's law, overshoots, then settles back towards the final value. The center motion's underdamped "overshoot, then settle" behavior, on the other hand, suggests interplay between magnetic tension of the rising flux tube and convective turbulence.
Highlights of Astronomy: Volume 14
Author: Karel van der Hucht
language: en
Publisher: Cambridge University Press
Release Date: 2008-01-21
Recording the proceedings of the IAU XXVI General Assembly, this volume of the IAU Highlights of Astronomy covers virtually all aspects of modern astrophysics as discussed by 2400 participants from 73 countries. Notably, the common aspects of astrophysical phenomena known to exist in widely differing interstellar environments is thoroughly examined, providing fertile cross correlation from one specialisation to another. This text highlights the importance of the triennial IAU General Assemblies in bringing together the work of observers and theoreticians in widely different fields, but working towards a common goal: understanding the physics of the Universe. Together with the Proceedings of the IAU Symposia 235-240, this volume examines all of the astrophysics presented at the General Assembly.
Determination of Sub-photosphere Solar Active Region 3D Magnetic Field Structure from Emergence Observations
Author: Brian S. Briggs (George Mason University graduate)
language: en
Publisher:
Release Date: 2012
In this thesis, we study the emergence process of a bipolar solar active region NOAA 11416, a Hale class [beta gamma/gamma] active region, and reconstruct its global 3D magnetic structure through a novel image-stacking technique. The emergence began on 8 February 2012, and data was taken through 11 February 2012. Magnetograms from the Solar Dynamics Obersvatory's (SDO) Helioseismic and Magnetic Imager (HMI) are used in this study, and we take advantage of the unprecedented high imagery cadence offered by the observatory. We describe the selection process of observed candidate active regions covering the full data set since SDO first light. Using this magnetogram imagery, we visualize the detailed 3D magnetic structure by stacking the high-cadence SDO imagery and producing 3D isosurface plots, which yield extraordinary detail of the fine magnetic structure of the AR. The 3D structure shows a distinct asymmetric [lambda] shape to the emerging flux tube with tilt characteristic of Joy's Law. This asymmetric [lambda] shape exhibited a differing slope of the leading and trailing legs, the leading leg being 61° and the trailing leg 52° for an assumed rise velocity of 100 m/s. Close examination of the 3D structure indicates a highly fragmented flux rope whose organization appears to increase as the eruption progresses. We also find that the leading polarity is more fragmented in magnetogram imagery, which appears to support thin flux tube approximations and the results of analastic magneto-hydrodynamic simulations. Continuum imagery, however, shows the opposite situation, with the leading polarity being the more cohesive of the two. Additionally, the extracted AR parameters for center motion, tilt, polarity centroid separation, and flux per polarity are fit to functions, producing mathematical formulations for the 3D shape and magnetic flux of the flux tube. These functions not only accurately describe the shape and strength of the flux tube, but their exponential nature allows predictions of end points in terms of flux (~8x10^21 Mx), centroid separation (59.0 Mm), and centroid tilt angle (18.5°). We find that both tilt angle evolution and movement of the center fit well to underdamped harmonic oscillator equations. The former indicates interplay between the Coriolis force and shear forces resulting from differing Lorentz forces beneath and above the photosphere, producing an initially anti-Joy's-law tilt which rapidly changes to tilt following Joy's law, overshoots, then settles back towards the final value. The center motion's underdamped "overshoot, then settle" behavior, on the other hand, suggests interplay between magnetic tension of the rising flux tube and convective turbulence.