Abstract
Magnetograms in lines originating high in the solar atmosphere show, away from disk center, diffuse fringes of reverse polarity on the limbward side and diffuse centerwards extensions of normal polarity wherever the field is strong. Analysis of a Mg b2 magnetogram reveals that, in active regions (and, hence, wherever the magnetic network is well developed) fields cover associated supergranules completely at heights mostly below 500–600 km (zero height is at τ 5000 = 1) but possibly up to 700–800 km at great distances (e.g. >104km) from the network. These lie much lower than previously believed, mostly around the solar average temperature minimum. Near plagettes, the low-lying field has been measured out to ∼6000–7000 km. One consequence is that in active regions and plagettes, the chromosphere-corona transition region probably penetrates below 600 km; another is that potential theory is inapplicable at coronal heights below about 15 000 km.
A more accurate analysis requires a specific atmospheric model for magnetic regions. Attention is drawn to the need for studying the consequences for acoustic wave propagation, reflection and dissipation in regions of strong network fields.
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Visiting Astronomer, Kitt Peak National Observatory.
Operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation.
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Giovanelli, R.G. An exploratory two-dimensional study of the coarse structure of network magnetic fields. Sol Phys 68, 49–69 (1980). https://doi.org/10.1007/BF00153266
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DOI: https://doi.org/10.1007/BF00153266