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Everyone wants to measure coronal magnetic fields: flares, coronal
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heating,
CMEs, ….
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Most of us come from Flatland: we are
accustomed to 2D photospheric
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field
measurements.
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The corona is different: intrinsically 3D. Have to think
differently. Can’t
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measure
3D fields with an optically thin diagnostic; here radio has an
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advantage
because it is optically thick: get different layers of the corona at
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different
frequencies.
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Extrapolations of surface fields will be
just as crucial because we don’t
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measure
the height of the gyroresonance layers.
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But extrapolations need radio
measurements of coronal field strengths
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because
the photospheric and chromospheric measurements are
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incomplete.
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