The acoustic cutoff frequency of the Sun and the solar cycle

Abstract

The acoustic cutoff frequency - highest frequency for acoustic solar eigenmodes-is an important parameter of the solar atmosphere because it determines the upper boundary of the p mode cavities. At frequencies beyond this value, acoustic disturbances are no longer trapped waves but traveling waves. Interferences amongst them, originate higher frequency peaks -the pseudomodes- in the solar acoustic spectrum. Using data from GOLF and VIRGO instruments aboard SoHO spacecraft, we determine the acoustic cutoff frequency using the coherence function between both sets of data, velocity and intensity. By using data gathered by these instruments during the whole lifetime of the mission (1996 till present), it is found a variation of this parameter with the solar magnetic activity cycle. © Published under licence by IOP Publishing Ltd.