Simulation of radio emission from air showers in atmospheric electric fields

TL;DR

This study investigates how atmospheric electric fields, especially during thunderstorms, influence the radio signals emitted by cosmic ray air showers, affecting their reliability for energy measurement.

Contribution

The paper introduces a Monte Carlo simulation incorporating electric field effects into air shower radio emission modeling, highlighting the impact of thunderstorms.

Findings

Electric fields of ~100 V/cm significantly alter radio pulses.

Radio signals during thunderstorms are unreliable for energy estimation.

Polarization differences can help identify electric field-affected signals.

Abstract

We study the effect of atmospheric electric fields on the radio pulse emitted by cosmic ray air showers. Under fair weather conditions the dominant part of the radio emission is driven by the geomagnetic field. When the shower charges are accelerated and deflected in an electric field additional radiation is emitted. We simulate this effect with the Monte Carlo code REAS2, using CORSIKA-simulated showers as input. In both codes a routine has been implemented that treats the effect of the electric field on the shower particles. We find that the radio pulse is significantly altered in background fields of the order of ~100 V/cm and higher. Practically, this means that air showers passing through thunderstorms emit radio pulses that are not a reliable measure for the shower energy. Under other weather circumstances significant electric field effects are expected to occur rarely, but nimbostratus clouds can harbor fields that are large enough. In general, the contribution of the electric field to the radio pulse has polarization properties that are different from the geomagnetic pulse. In order to filter out radio pulses that have been affected by electric field effects, radio air shower experiments should keep weather information and perform full polarization measurements of the radio signal.