Atmospheric electric fields during thunderstorm conditions measured by LOFAR
Strong atmospheric electric fields, even if they are not strong enough to initiate lightning activity, significantly affect radio emission from extensive air showers. Measurements of radio emission from extensive air showers at LOFAR show that intensity and polarization signatures of the showers measured under “thunderstorm” conditions are very different from those measured during fair weather. For this reason, the “thunderstorm” events can be used to determine atmospheric electric fields. The physics understanding of this effect as well as the technique to extract the atmospheric electric fields are presented in this thesis. It is shown that in order to reconstruct these events it is generally sufficient to model the atmospheric electric fields in clouds as composed of three layers. The electric fields extracted from these events have large horizontal components of the electric fields in the middle and the top layers. The height of the bottom layer depends on the season.