Properties of sound wave propagation in the solar faculae

Abstract

The results of observations of the faculae region near the center of the solar disk, which were obtained on the German Vacuum Tower Telescope VTT (Tenerife, Spain) are discussed. It is shown that the contrast (brightness) of the facula increases non-monotonouslywith an increase of the magnetic field strength, and, starting from the strength 140 mTl, it decreases.This is contrary to the currently accepted explanation of the increased brightness of facular regions as a result of the Wilson effect. The facular brightness in the upper chromosphere strongly depends on the propagation direction of sound waves. The regions of the facula, where the upward propagating waves are observed, look brighter than the regions in which the waves propagate in the opposite direction from the photosphere to the chromosphere. Dependence of the facular brightness on the wave propagation direction is caused by the fact that upward sound waves, for some reason, prefer to propagate in those regions of the solar facula where the magnetic field strength is above the average value. On the contrary, downward waves are observed in areas where the magnetic field is below average.