Probing atmospheric electric fields in thunderstorms through radio emission from cosmic-ray induced air showers

We present measurements of radio emission from cosmic ray air showersthat took place during thunderstorms. The intensity and polarization patterns of these air showersare radically different from those measured during fair-weather conditions. With the use of a simple two-layer model for the atmospheric electricfield, these patterns can be well reproduced by state-of-the-art simulation codes. This in turn provides a novel way to study atmospheric electricfields.