  Observations of coronal waves (CWs) interacting with coronal holes (CHs) show
the formation of typical wave-like features, such as reflected, refracted and
transmitted waves (collectively, secondary waves). In accordance with these
observations, numerical evidence for the wave characteristics of CWs is given
by simulations which demonstrate effects of deflection and reflection when a CW
interacts with regions exhibiting a sudden density drop, such as CHs. However,
secondary waves are usually weak in their signal and simulations are limited in
the way the according idealisations have to be chosen. Hence, several
properties of the secondary waves during a CW-CH interaction are unclear or
ambiguous and might lead to misinterpretations. In this study we follow a
theoretical approach and focus in particular on the geometrical properties of
secondary waves caused by the interaction between oblique incoming CWs and CHs.
Based on a linear theory, we derive analytical expressions for reflection and
transmission coefficients, which tell us how strongly the amplitudes of the
secondary waves increase and decrease with respect to the incoming wave,
respectively. Additionally, we provide analytical terms for crucial incidence
angles that are capable of giving information about the energy flux, the phase
and the reflection properties of the secondary waves. These novel expressions
provide a supplementary tool for estimating CW properties in a fast and
straightforward way and, therefore, might have relevant consequences for a
possible new interpretation of already studied CW-CH interaction events and the
clarification of ambiguous observational data.
