Thunderstorm electric fields probed by extensive air showers through their polarized radio emission

T N G Trinh ,P Mitra,H Falcke,K Mulrey,S Ter Veen,T Winchen,L Rossetto,S Buitink,A Corstanje,A Nelles,A Bonardi,P Schellart,J R Hörandel ,J E Enriquez ,J P Rachen ,Satyendra Thoudam ,Casper Rutjes ,Ute Ebert ,Olaf Scholten ,B M Hare

doi:10.1103/physrevd.95.083004

Abstract

We observe a large fraction of circular polarization in radio emission from extensive air showers recorded during thunderstorms, much higher than in the emission from air showers measured during fair-weather circumstances. We show that the circular polarization of the air showers measured during thunderstorms can be explained by the change in the direction of the transverse current as a function of altitude induced by atmospheric electric fields. Thus by using the full set of Stokes parameters for these events, we obtain a good characterization of the electric fields in thunderclouds. We also measure a large horizontal component of the electric fields in the two events that we have analysed.

Highlights

Lightning initiation [1] and propagation [2] are driven by the electric fields in a thunderstorm
We show that the circular polarization of the air showers measured during thunderstorms can be explained by the change in the direction of the transverse current as a function of altitude induced by atmospheric electric fields
We present data on circular polarization seen in the radio emission of a large number of thunderstorm events close to the shower axis as measured with the Low-Frequency Array (LOFAR) radio telescope array; see Sec

Summary

INTRODUCTION

Lightning initiation [1] and propagation [2] are driven by the electric fields in a thunderstorm. This current varies with altitude, thereby producing radio emission This radiation is linearly polarized in the ev×B direction, where v is the velocity of the shower front, B is the geomagnetic field, and edenotes a unit vector. For fair-weather events, we observe a small fraction of circular polarization due to the fact that the time structures of the radio pulses emitted from the charge-excess component and those from the transverse-current component are different [8]. The usage of the circular polarization measurements puts strong additional constraints on the structure of the atmospheric electric fields on top of the information obtained by using only the radio intensity.

LOFAR AND DATA ANALYSIS

MODELING

PROBING THE STRUCTURES OF ATMOSPHERIC ELECTRIC FIELDS

CONCLUSION