What mechanisms allow 5-minute oscillations in active regions of the solar surface to penetrate from the photosphere into the chromosphere?

Abstract

Some properties of the propagation of 5-minute oscillations from the bottom of the photosphere (h = 0 km) to the bottom of the chromosphere (h = 1600 km) are investigated based on the results of filter (at the center of the line Ca II λ 396.8 nm), spectral (in the line Ba IIλ 455.4 nm), and spectropolarimetric (in the lines Fe I λλ 1564.3–1565.8 nm) observations of the active region (isolated faculae at the center of the solar disk) on the German vacuum tower telescope (VTT) of the Institute of Astrophysics of the Canary Islands. Oscillations in the lower photosphere, in the transition region, and in the middle chromosphere reach their maximum during the period close to P ≈ 5 min. At the height h = 1600 km, another period of oscillations P ≈ 700 s can be seen well. Two factors facilitate the penetration of 5-minute oscillations from the photosphere into the chromosphere: the inclination of magnetic field lines and the deviation of the wave propagation process from the adiabatic one. The maximum power of 5-minute oscillations at the height h = 1600 km falls on inclination angles of the magnetic field in the range of 11°–13° and on the phase shift between oscillations of temperature and velocity of 40°–50°.