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Using STEREO/EUVI to Study Active Region Magnetic Fields

This study utilizes STEREO/EUVI data to examine the magnetic fields in active regions through loop tracing, potential field computations, and angle recalculations. Findings suggest variations in agreement with models and the potential benefits of radial stretching. Future work includes exploring more versatile transformations and utilizing better magnetic field observations to enhance model accuracy.

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Using STEREO/EUVI to Study Active Region Magnetic Fields

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  1. Using STEREO/EUVI to Study Active Region Magnetic Fields Anne Sandman (Rice/LMSAL) Markus Aschwanden, Jean-Pierre Wuelser, Marc DeRosa (LMSAL), David Alexander (Rice) STEREO SWG #19 Pasadena, CA, 4 February 2009

  2. Overview • Objective • Data set • Procedure • Findings and future work

  3. Red: linear force-free field lines (MDI). Yellow: STEREO loops. Feng et al. (2007, ApJ 671, L205)

  4. Gary (2007)

  5. Data Set • Three active regions: • AR 10953: 23:00 UT April 30 2007. • AR 10955: 20:30 UT May 9 2007. • AR 10956: 12:40 UT May 19, 2007. • EUVI images in 171, 195, and 284Å. • High-pass filter and boxcar smoothing.

  6. Procedure • Trace loops in EUVI images. • Compute 3D potential magnetic field. • Calculate discrepancy between data and model. • Transform model magnetic field. • Recalculate misalignment angles.

  7. Loop stereoscopy B A

  8. Procedure • Trace loops in EUVI images. • Compute 3D potential magnetic field. • Calculate discrepancy between data and model. • Transform model magnetic field. • Recalculate misalignment angles.

  9. Potential Field Source Surface Longcope (2005)

  10. Procedure • Trace loops in EUVI images. • Compute 3D potential magnetic field. • Calculate discrepancy between data and model. • Transform model magnetic field. • Recalculate misalignment angles.

  11. Local magnetic field vector Vector tangent to observed loop Magnetic field lines Angle calculation points

  12. Visualizations

  13. EUVI loops (yellow) and MDI/PFSS field lines (pink) reveal significantly different magnetic connectivities (courtesy of J.P.Wuelser)

  14. Findings: AR 10955 (9 May): best agreement with potential field. AR 10956 (19 May): worst agreement. NB: AR 10956 produced an eruption within 30 minutes of images.

  15. Procedure • Trace loops in EUVI images. • Compute 3D potential magnetic field. • Calculate discrepancy between data and model. • Transform model magnetic field. • Recalculate misalignment angles.

  16. Radial Stretching • Gary & Alexander (1999): • Simple radial stretching improved model’s agreement with observed loop structures.

  17. Radial Stretching • Preserves divergence-free condition. • Injects currents.

  18. Procedure • Trace loops in EUVI images. • Compute 3D potential magnetic field. • Calculate discrepancy between data and model. • Transform model magnetic field. • Recalculate misalignment angles.

  19. Conclusions and Future Work • Wide variation in loop-model agreement. • No significant change with radial stretching. • More versatile transformations? • Need more appropriate magnetic field observations. • Use EUVI data to “bootstrap” a better boundary condition.

  20. Conclusions and Future Work • Wide variation in loop-model agreement. • No significant change with radial stretching. • More versatile transformations? • Need more appropriate magnetic field observations. • Use EUVI data to “bootstrap” a better model.

  21. Results of Radial Stretching

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