Coupling between the solar interior and atmosphere

Global helioseismic oscillation modes are a window to the solar interior. They are acoustic waves trapped in the interior of the Sun and can give valuable information about the directly unobservable inner layers. The information can be properly decoded only if theoretical models explain how properties of the observed oscillations are influenced by their environment. Recent observations provide evidence that helioseismic modes are affected not only by the sub-photospheric layers but also by the lower atmosphere. Realistic numerical codes and simplified analytical models try to discover the complex nature of the interaction between helioseismic oscillations and the atmosphere. The complexity of the coupling is mainly due to the presence of an atmospheric magnetic field. Characteristic properties of oscillations, such as frequency, lifetime and penetration depth, can be derived from magnetohydrodynamic (MHD) equations, which govern the processes. Those properties are functions of the temperature profile of the coupled interior and atmospheric environment and the magnetic structure of the atmosphere. The derived equations provide valuable information about the ways oscillation modes are affected by the different properties of their medium. The models take into account realistic vertical profiles of temperature, plasma flows and magnetic field structures. In narrow layers, where the characteristic frequency of local magnetohydrodynamic (MHD) slow and/or Alfvén waves are equal to the global frequency of an acoustic wave, the latter will be resonantly coupled to the atmospheric magnetic field. The consequences of this resonant coupling are also studied by using dissipative MHD equations.