CoREAS simulations of inclined air showers predict refractive displacement of the radio-emission footprint

Simulating the radio emission of inclined extensive air showers for a ground-based radio-antenna array we find a systematic displacement of the radio emission with respect to the Monte-Carlo shower impact point. We correct the radio-emission footprint for the asymmetries due to the superposition of geomagnetic and charge-excess radiation as well as for the early-late effect. The remaining displacement is found to be ∼1500 m along the ground plane for showers with a zenith angle of 85°, which is relevant for air shower detectors. A model describing this displacement by refraction in the atmosphere based on Snell’s law yields good agreement with our observations from CoREAS simulations. We thus conclude that the displacement is caused by refraction in the atmosphere.