Radio Observations
of Gyroresonance Emission
from Coronal Magnetic Fields
| Review the mechanism by which we measure coronal magnetic fields with radio techniques | |
| Discuss examples of observations | |
| Discuss problem of 3D analysis | |
| Constraints for FASR |
| Opacity results from electrons gyrating in coronal magnetic fields at fB = 2.8 106 B Hz. | |
| In the non-flare (non-relativistic) corona this produces narrow resonances. | |
| Opacity µ n B/(¶B/¶l) (T/mc2 sin2q)s-1 where s = 1, 2, 3, … is the harmonic | |
| Because T/mc2 is 1/3000, opacity drops by 3 orders of magnitude from one layer to the next | |
Gyroresonance opacity at low harmonics
Model sunspot gyroresonance layers
Model sunspot: positive temperature gradient
Model sunspot: peaked temperature gradient
Spatially varying gyroresonance spectra
Radio profiles of a sunspot vs frequency
Radio sunspot variability: 3 hour maps
Radio sunspot variability: 3 hour maps
| Radio observations still the only means for reliably measuring coronal magnetic field strengths anywhere on the solar disk | |
| Measures temperatures on surface of constant field strength – directly see regions of strong heating | |
| Because emission is optically thick in regions of strong field, we get 3D information on fields | |
| Relatively insensitive to density, therefore complements EUV/soft X-ray observations which are dominated by density contrast | |
| Important role in testing techniques for extrapolating surface fields into corona |
Active regions at different radio frequencies
Active regions at different radio frequencies
Radio emission from complex regions
Tests of magnetic field extrapolations
Coronal magnetic fields: intrinsically 3D
Radio tests of magnetic field extrapolations
The pipe dream:
3D deconvolution of coronal fields
What frequency resolution do we need?
Active regions at different radio frequencies
Sunspot oscillations: where is the corona?
Sunspot oscillations: where is the corona?
Sunspot oscillations: where is the corona?
Sunspot oscillations: where is the corona?
Evolution of photospheric field (MDI)
Polarization at low frequencies: origin?
Polarization at low frequencies: origin?
Gyroresonance measurements: FASR issues
Magnitude of B and line-of-sight direction