Oscillations in chromospheric network bright points

Intensity oscillations observed in the H and K lines of Ca II in network bright points in the quiet Sun are interpreted in terms of transverse and longitudinal magnetoacoustic waves propagating upward inside magnetic flux tubes. It is supposed that the waves are generated impulsively in the photosphere as transverse waves. As they propagate upward, their velocity amplitude increases exponentially until they become nonlinear in the chromosphere, where they transfer power to longitudinal waves. The impulsive generation produces waves at the cutoff frequency of transverse waves. On the assumption that this frequency signature is transferred to the longitudinal waves, the magnetic field strength implied by the period observed in the chromosphere is consistent with the Zeeman effect observed in the photosphere.