Atmospheric oscillations in solar magnetic flux tubes - II. Excitation by transverse tube waves and random pulses

The response of an exponentially diverging magnetic flux tube embedded in an isothermal solar atmosphere to the propagation of transverse tube waves and random transverse pulses generated in the solar convection zone is studied analytically. General solutions are presented and applied to solar flux tubes located in the interior region and at the boundary of supergranulation cells. It is shown that the period of the free oscillations driven by transverse waves and pulses ranges from 7 to 10 min for the considered values of the tube magnetic field, and that these oscillations decay in time as t(-3/2). Since the observational signatures of these transverse oscillations are hard to detect, we also consider the generation of longitudinal tube waves by nonlinear mode coupling and the excitation of free atmospheric oscillations by longitudinal waves. Our results show that the basic properties of oscillations driven by transverse and longitudinal tube waves are different. While transverse waves excite oscillations with 7-10 min periods, oscillations by longitudinal waves have periods near 3 min. This is consistent with the observed 3-min oscillations inside the supergranule cells but inconsistent with the 7-min oscillations observed in the chromospheric network. We suggest that an explanation of the observed 7-min oscillations might be found by taking into account a more realistic structure of flux tubes located in the magnetic network.