Absorption of High-frequency Oscillations and Its Relation to Emissivity Reduction

Sunspots are known to be strong absorbers of solar oscillation modal power. The most convincing way demonstrate this is done via Fourier-Hankel decomposition (FHD), where the local field separated into in- and outgoing waves, showing reduction in Due Helioseismic Magnetic Imager's high-cadence Doppler measurements, power absorption can investigated at frequencies beyond acoustic cutoff frequency. We perform an FHD on five sunspot regions two quiet-Sun control study resulting spectra $\alpha_\ell(\nu)$, specifically $\nu$ > 5.3 mHz. observe unreported high-frequency feature, which only appears presence a sunspot. This feature confined phase speeds one-skip waves whose origins coincide with sunspot's center, $v_{ph}$ = 85.7 km/s case. By employing fit constant speed, we find that peak strength $\alpha_{max}$ lies between 0.166 0.222 noise level about 0.009 (5%). well-known along ridges lower reach up $\alpha_{max}\approx$ 0.5. Thus our finding spectrum weaker, but nevertheless significant. From first considerations regarding energy budget observation likely explained by emissivity within derive simple relation absorption. conclude sunspots yield wave signature (for certain only), may help understanding effect magnetic fields convection source excitation potentially general subsurface structure.