Sunspot oscillations: where is the corona?

• 3 minute oscillations are a chromospheric phenomenon: should not occur in the corona • At high frequencies (> 15 GHz), surfaces never get very high, so not unexpected •At lower frequencies where gyroresonance surfaces are higher in the corona, expect to see effects at edges where surfaces drop into chromosphere, or in o mode which is 2nd harmonic, hence lower • Observations at 5 GHz show oscillations at edges (Nindos et al. 2002) • Observations that 8 GHz V oscillations are anticorrelated with I oscillations consistent: 2nd harmonic o mode TB varies, 3rd harmonic x mode does not, so V decreases as o mode TB and hence I increases