Abstract
In a recent paper, Leka et al. (Solar Phys. 260, 83, 2009) constructed a synthetic vector magnetogram representing a three-dimensional magnetic structure defined only within a fraction of an arcsec in height. They rebinned the magnetogram to simulate conditions of limited spatial resolution and then compared the results of various azimuth disambiguation methods on the resampled data. Methods relying on the physical calculation of potential and/or non-potential magnetic fields failed in nearly the same, extended parts of the field of view and Leka et al. (Solar Phys. 260, 83, 2009) attributed these failures to the limited spatial resolution. This study shows that the failure of these methods is not due to the limited spatial resolution but due to the narrowly defined test data. Such narrow magnetic structures are not realistic in the real Sun. Physics-based disambiguation methods, adapted for solar magnetic fields extending to infinity, are not designed to handle such data; hence, they could only fail this test. I demonstrate how an appropriate limited-resolution disambiguation test can be performed by constructing a synthetic vector magnetogram very similar to that of Leka et al. (Solar Phys. 260, 83, 2009) but representing a structure defined in the semi-infinite space above the solar photosphere. For this magnetogram I find that even a simple potential-field disambiguation method manages to resolve the ambiguity very successfully, regardless of limited spatial resolution. Therefore, despite the conclusions of Leka et al. (Solar Phys. 260, 83, 2009), a proper limited-spatial-resolution test of azimuth disambiguation methods is yet to be performed in order to identify the best ideas and algorithms.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Alissandrakis, C.E.: 1981, On the computation of constant alpha force-free magnetic field. Astron. Astrophys. 100, 197 – 200.
Aly, J.J.: 1987, On the uniqueness of the determination of the coronal potential magnetic field from line-of-sight boundary conditions. Solar Phys. 111, 287 – 296. doi: 10.1007/BF00148521 .
Chiu, Y.T., Hilton, H.H.: 1977, Exact Green’s function method of solar force-free magnetic-field computations with constant alpha. I – Theory and basic test cases. Astrophys. J. 212, 873 – 885. doi: 10.1086/155111 .
Crouch, A.D., Barnes, G., Leka, K.D.: 2009, Resolving the azimuthal ambiguity in vector magnetogram data with the divergence-free condition: application to discrete data. Solar Phys. 260, 271 – 287. doi: 10.1007/s11207-009-9454-2 .
Gary, G.A.: 1989, Linear force-free magnetic fields for solar extrapolation and interpretation. Astrophys. J. Suppl. 69, 323 – 348. doi: 10.1086/191316 .
Georgoulis, M.K.: 2005, A new technique for a routine azimuth disambiguation of solar vector magnetograms. Astrophys. J. Lett. 629, 69 – 72. doi: 10.1086/444376 .
Georgoulis, M.K., LaBonte, B.J.: 2007, Magnetic energy and helicity budgets in the active region solar corona. I. Linear force-free approximation. Astrophys. J. 671, 1034 – 1050. doi: 10.1086/521417 .
Georgoulis, M.K., Raouafi, N., Henney, C.J.: 2008, Automatic active-region identification and azimuth disambiguation of the SOLIS/VSM full-disk vector magnetograms. In: Howe, R., Komm, R.W., Balasubramaniam, K.S., Petrie, J.G.D. (eds.) Subsurface and Atmospheric Influences on Solar Activity, ASP Conf. Ser. 383, 107 – 114.
Harvey, J.W.: 1969, Magnetic Fields Associated with Solar Active-Region Prominences, PhD thesis, University of Colorado.
Henney, C.J., Keller, C.U., Harvey, J.W., Georgoulis, M.K., Hadder, N.L., Norton, A.A., Raouafi, N., Toussaint, R.M.: 2009, SOLIS Vector Spectromagnetograph: status and science. ASP Conf. Ser. 405, 47 – 50.
Keller, C.U., Harvey, J.W., Giampapa, M.S.: 2003, SOLIS: an innovative suite of synoptic instruments. In: Keil, S.L., Avakyan, S.V. (eds.) Innovative Telescopes and Instrumentation for Solar Astrophysics, Proc. SPIE 4853, 194 – 204.
Leka, K.D., Metcalf, T.R.: 2003, Active-region magnetic structure observed in the photosphere and chromosphere. Solar Phys. 212, 361 – 378. doi: 10.1023/A:1022996404064 .
Leka, K.D., Barnes, G., Crouch, A.D., Metcalf, T.R., Gary, G.A., Jing, J., Liu, Y.: 2009, Resolving the 180-degree ambiguity in solar vector magnetic field data: evaluating the effects of noise, spatial resolution, and method assumptions. Solar Phys. 260, 83 – 108. doi: 10.1007/s11207-009-9440-8 .
Li, J., Amari, T., Fan, Y.: 2007, Resolution of the 180-deg ambiguity for inverse horizontal magnetic field configurations. Astrophys. J. 654, 675 – 686. doi: 10.1086/509062 .
Lites, B.W., Elmore, D.F., Streander, K.V.: 2001, The solar-B spectro-polarimeter. In: Sigwarth, M. (ed.) Advanced Solar Polarimetry – Theory, Observation, and Instrumentation, ASP Conf. Ser. 236, 33 – 40.
Longcope, D.W., Welsch, B.T.: 2000, A model for the emergence of a twisted magnetic flux tube. Astrophys. J. 545, 1089 – 1100. doi: 10.1086/317846 .
Metcalf, T.R.: 1994, Resolving the 180-degree ambiguity in vector magnetic field measurements: The ‘minimum’ energy solution. Solar Phys. 155, 235 – 242. doi: 10.1007/BF00680593 .
Metcalf, T.R., Leka, K.D., Barnes, G., Lites, B.W., Georgoulis, M.K., Pevtsov, A.A., Balasubramaniam, K.S., Gary, G.A., Jing, J., Li, J., Liu, Y., Wang, H.N., Abramenko, V., Yurchyshyn, V., Moon, Y.: 2006, An overview of existing algorithms for resolving the 180-degree ambiguity in vector magnetic fields: quantitative tests with synthetic data. Solar Phys. 237, 267 – 296. doi: 10.1007/s11207-006-0170-x .
Metropolis, N., Rosenbluth, A.W., Rosenbluth, M.N., Teller, A.H., Teller, E.: 1953, Equation of state calculations by fast computing machines. J. Chem. Phys. 21, 1087 – 1092. doi: 10.1063/1.1699114 .
Parker, E.N.: 1996, Inferring mean electric currents in unresolved fibril magnetic fields. Astrophys. J. 471, 485 – 488. doi: 10.1086/177983 .
Press, W.H., Teukolsky, S.A., Vetterling, W.T., Flannery, B.P.: 1992, Numerical Recipes in FORTRAN77. The Art of Scientific Computing, 326 – 334.
Sakurai, T.: 1982, Green’s function methods for potential magnetic fields. Solar Phys. 76, 301 – 321. doi: 10.1007/BF00170988 .
Sakurai, T.: 1989, Computational modeling of magnetic fields in solar active regions. Space Sci. Rev. 51, 11 – 48. doi: 10.1007/BF00226267 .
Scherrer, P.H., SDO/HMI Team: 2002, The helioseismic and magnetic imager for the Solar Dynamics Observatory. Bull. Am. Astron. Soc. 34, 735.
Schmidt, H.U.: 1964, On the observable effects of magnetic energy storage and release connected with solar flares. In: Hess, W.N. (ed.) The Physics of Solar Flares, NASA SP-50, 107 – 114.
Tsuneta, S., Ichimoto, K., Katsukawa, Y., Nagata, S., Otsubo, M., Shimizu, T., Suematsu, Y., Nakagiri, M., Noguchi, M., Tarbell, T., Title, A., Shine, R., Rosenberg, W., Hoffmann, C., Jurcevich, B., Kushner, G., Levay, M., Lites, B., Elmore, D., Matsushita, T., Kawaguchi, N., Saito, H., Mikami, I., Hill, L.D., Owens, J.K.: 2008, The Solar Optical Telescope for the Hinode mission: an overview. Solar Phys. 249, 167 – 196. doi: 10.1007/s11207-008-9174-z .
Author information
Authors and Affiliations
Corresponding author
Additional information
M.K. Georgoulis is also a Marie Curie Fellow.
Rights and permissions
About this article
Cite this article
Georgoulis, M.K. Comment on “Resolving the 180° Ambiguity in Solar Vector Magnetic Field Data: Evaluating the Effects of Noise, Spatial Resolution, and Method Assumptions”. Sol Phys 276, 423–440 (2012). https://doi.org/10.1007/s11207-011-9819-1
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11207-011-9819-1