BEXCO - Room F(201/202/203/204)
[CRD044] Circular polarization of radio emission from extensive air showers probes atmospheric electric fields in thunderclouds.
During thunderstorms, radio emission from extensive air showers are influenced by atmospheric electric fields. These effects are observed at LOw Frequency ARray (LOFAR) radio telescope. We have presented a non-intrusive method to determine the atmospheric electric fields by using the intensity data of the radio signals. We have developed a method by using not only the intensity data but also the polarization signature of the radio signals. We show that the events recorded during thunderstorms have a larger circular polarization component near the shower axis than the events measured during fair weather. We demonstrate quantitatively that this is related to the change in direction of the transverse current which is caused by the variation of the atmospheric electric fields. Therefore, the use of the circular polarization data puts strong additional constrains on the structure of the atmospheric electric fields than what could be achieved by using only the radio intensity.