Seasonal Variation of Polar Ice: Implications for Ultrahigh Energy Neutrino Detectors

The upper $100\mathrm{m}$ to $150\mathrm{m}$ of the polar ice sheet, called the firn, has a time-dependent density due to seasonal variations in the surface temperature and snow accumulation. We present RF simulations of an in-ice neutrino-induced radio source that show that these density anomalies create variations in the amplitude and propagation times of radio signals propagating through polar firn at an altitude of $\sim 3000\mathrm{m}$ above sea level. The received power from signals generated in the ice that refract within the upper $\sim 15\mathrm{m}$ firn are subject to a seasonal variation on the order of 10%. These variations result in an irreducible background uncertainty on the reconstructed neutrino energy and arrival direction for detectors using ice as a detection medium.