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This paper uses linear magnetohydrodynamics to model resonant absorption incoronal plasma with a Cartesian coordinate system. We impose line-tied boundaryconditions and tilt the background magnetic field to be oblique to thetransition region. Halberstadt & Goedbloed (1993, 1995); Goedbloed& Halberstadt(1994); Arregui et al. (2003) show that line-tied boundary conditions causetheir resonant absorption models to produce steep boundary layers/evanescentfast waves. We aim to study the importance of the boundary layers and assesstheir significance in a solar context. We calculate the solutions in a modelwhere we impose line-tied boundary conditions and compare this with a modelwhere we include the chromosphere instead. Results are calculated analyticallyand then verified numerically. We show that line-tied boundary conditions cancause the model to overestimate the boundary layers' amplitude significantly.If the fast waves can propagate in the chromosphere, then the line-tied modelaccurately predicts the boundary layers' amplitude. However, if the fast wavesare evanescent, then the boundary layers' size is reduced significantly, andthe line-tied model overestimates their amplitude. This leads to thecounter-intuitive result that the length scales tangential to the transitionregion can play an essential role in determining line-tied boundary conditions'validity. The results suggest that line-tied boundary conditions can cause themodel to generate unphysically large boundary layers. However, researchers maywish to continue to use them in their models for their simplicity and abilityto significantly reduce computation time if they understand and are aware oftheir flaws.

Line-tied boundary conditions can cause resonant absorption models to generate unphysically large boundary layers