The interpretation of oscillations in sunspot umbrae

Abstract

AbstractWe review possibilities for an interpretation of oscillations observed in several period bands (3 min., 5 min., 20 min.) and at different heights in sunspot umbrae. At subphotospheric depths two independent resonators are acting: A resonator for slow, quasi‐transverse waves can explain the lifetimes of bright umbral dots (≥20 sec.), while a resonator for fast (acoustic), quasi‐longitudinal waves could result in the 5‐min. oscillations. The acoustic resonator strongly couples with the slow‐mode longitudinal resonator at photospheric and chromospheric heights, the latter produces the resonance peaks in the 3‐min. period band. The whole scheme of resonance levels generalizes and corroborates a chromospheric resonator model earlier proposed by the present authors. Comparisons with alternative models and recent measurements show that the present model most naturally explains the majority of observed data.