Determining Electric Fields in Thunderclouds With the Radiotelescope LOFAR.

T N G Trinh,S Ter Veen,H Leijnse,G K Krampah,S Buitink,A Bonardi,J R Hörandel,J P Rachen,B M Hare,A Corstanje,K Mulrey,P R Krehbiel,T Huege,P Mitra,A Nelles,T Winchen,L Rossetto,H Falcke,Ute Ebert ,Olaf Scholten ,Casper Rutjes ,Hershal Pandya

doi:10.1029/2019jd031433

Abstract

An analysis is presented of electric fields in thunderclouds using a recently proposed method based on measuring radio emission from extensive air shower events during thunderstorm conditions. This method can be regarded as a tomography of thunderclouds using cosmic rays as probes. The data cover the period from December 2011 till August 2014. We have developed an improved fitting procedure to be able to analyze the data. Our measurements show evidence for the main negative‐charge layer near the −10° isotherm. This we have seen for a winter as well as for a summer cloud where multiple events pass through the same cloud and also the vertical component of the electric field could be reconstructed. On the day of measurement of some cosmic‐ray events showing evidence for strong fields, no lightning activity was detected within 100 km distance. For the winter events, the top heights were between 5 and 6 km, while in the summer, typical top heights of 9 km were seen. Large horizontal components in excess of 70 kV/m of the electric fields are observed in the middle and top layers.

Highlights

Lightning is a very interesting phenomenon, but a detailed understanding of the process is still missing (Dwyer & Uman, 2014)
In the Low-Frequency Array (LOFAR) measurements, we are primarily sensitive to the component of the atmospheric electric field that is perpendicular to the shower axis due to the dynamics in a cosmic ray-induced air shower (Trinh et al, 2016)
We have used the radio footprint of cosmic ray-induced air showers as measured at the LOFAR core to analyze 10 “thunderstorm” events measured from December 2011 to August 2014

Summary

Introduction

Lightning is a very interesting phenomenon, but a detailed understanding of the process is still missing (Dwyer & Uman, 2014). This offers a unique opportunity to perform these measurements, which are made automatically (unavoidably) whenever LOFAR measures cosmic rays This opens the possibility for random testing of cloud electric fields in thunderclouds of the temperate zone. In the LOFAR measurements, we are primarily sensitive to the component of the atmospheric electric field that is perpendicular to the shower axis due to the dynamics in a cosmic ray-induced air shower (Trinh et al, 2016). It is tempting to interpret our measurements of the electric field in terms of horizontal charge layers at certain heights These clouds will contribute to the Global Electric Circuit (Bering-III et al, 1998; Williams & Heckman, 1993) since the lower charge layers will discharge through rain to the surface of Earth

Cosmic-Ray Tomography of Cloud Electric Fields

Findings

Discussion

Conclusion