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

TL;DR

Seasonal density changes in polar ice's upper layers affect radio signal propagation, causing a 10% variation in received power and introducing background uncertainties for ultrahigh energy neutrino detection.

Contribution

This study models how seasonal firn density variations impact radio signal propagation, highlighting their effect on neutrino detector measurements.

Findings

Radio signal amplitude varies seasonally by about 10%.

Density anomalies cause uncertainties in neutrino energy reconstruction.

Propagation times are affected by seasonal firn density changes.

Abstract

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.