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\begin{document}

\title{Observations of elves and radio wave perturbations by lightning}



\author[1]{Maja Tomicic}%
\author[2]{Olivier Chanrion}%
\author[3]{Thomas Farges}%
\author[4]{Janusz Mlynarczyk}%
\author[5]{Ivana Kolmasová}%
\author[6]{Serge Soula}%
\author[7]{Christoph Köhn}%
\author[8]{Torsten Neubert}%
\affil[1]{DTU Space, Technical University of Denmark}%
\affil[2]{National Space Institute (DTU Space)}%
\affil[3]{CEA}%
\affil[4]{AGH University of Science and Technology}%
\affil[5]{Department of Space Physics, Institute of Atmospheric Physics, Czech Academy of Sciences}%
\affil[6]{Laboratoire d'Aerologie}%
\affil[7]{Technical University of Denmark}%
\affil[8]{Department of Solar System Physics, Denmark}%


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  \date{May 17, 2024}


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\begin{abstract}
The electromagnetic and electrostatic fields from powerful lightning
heat and ionize the lower ionosphere. The disturbances appear as halos,
sprites and elves, and are also observed as perturbations in crossing
radio signals. The characteristic of the lightning discharges leading to
the various types of perturbations is not fully understood. Here we
present an analysis of 63 elves and corresponding VLF and MF signal
perturbations from an almost stationary thunderstorm that allows us to
untangle some of the dependencies of perturbations on the lightning
characteristics. We characterize the perturbations to a VLF-transmitter
signal as ``long-recovery-early-events'' (LOREs), ``early'' events, or
``rapid-onset-rapid-decay'' (RORD) events. We find that LOREs are
related to high lightning current and bright elves, and their amplitude
and sign depend on their location along the signal path. With
observations in the ELF and MF band, we find that lightning with elves
has three times the impulse charge moment change (iCMC) and ten times
the power than lightning of similar peak current without elves.
Attenuation in MF links appear in a higher proportion and longer
duration observed with elves than with high peak current lightning
without elves. The remaining types of VLF perturbations occur without
TLEs but with sequences of lightning that produce slowly rising CMCs
reaching high values (up to \textasciitilde{}3500 C km within
\textasciitilde{}500 ms). Slower rise times lead to lower fields in the
mesosphere that may not create significant ionization but instead drive
dissociative attachment of free electrons. The depletions can result in
perturbations to crossing VLF signals.%
\end{abstract}%



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