How elevated sources can cause local increases of sound pressure levels in the upwind domain

While increased sound levels near the ground in downwind conditions are a well-studied topic, comparatively little attention has been given in the literature to increased sound pressure levels in upwind propagation. This increase, however, typically occurs only under specific conditions, including an elevated source location, a non-linear (e.g., logarithmic) wind or temperature profile, and a focus on particular distances within the upwind domain. These conditions are known to be responsible for the formation of caustics. Simultaneously, the sound level enhancement may be disturbed by diffraction, ground reflection, and its characteristics depend on the source structure, being most readily derivable for point sources. Consequently, investigations using models and comparisons with observations are challenging. This work uses two fundamentally different modelling approaches in their ability to capture such phenomena. The goal is to provide an intuitive understanding of the complex interactions involved in sound propagation under real atmospheric conditions, thereby supporting the interpretation of acoustic simulation and measurements in applied contexts.