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\begin{document}

\title{Short-periodic VLF emissions observed simultaneously by Van Allen Probes
and on the ground}



\author[1]{Andrei G. Demekhov}%
\author[2]{Elena E Titova}%
\author[3]{Manninen Jyrki}%
\author[2]{Alexander Nikitenko}%
\author[2]{Sergey Vasilyevich Pilgaev}%
\affil[1]{Institute of Applied Physics, Russian Academy of Sciences}%
\affil[2]{Polar Geophysical Institute}%
\affil[3]{Sodankyla Geophysical Observatory}%


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  \date{June 14, 2024}


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\begin{abstract}
We present simultaneous observations of VLF emissions with periodic (2
or 4 s) bursts by Van Allen Probe near geomagnetic equator and
Kannuslehto and Lovozero ground-based sites. The repetition period and
ground--spacecraft delay are consistent with guided whistler wave
propagation between conjugate ionospheres. In contrast to lightning
whistlers, the group velocity dispersion is not accumulated from one
burst to another, thus implying a nonlinear mechanism of its
compensation. Two regimes are observed. In one regime, Poynting flux
direction alternates in the magnetosphere, and the burst period is twice
lower than on the ground, that corresponds to single wave packet
bouncing along the field line. This regime is switched to the other one,
with burst period unchanged in the magnetosphere but halved on the
ground. In the second regime, no alternating Poynting flux direction is
observed. This second regime corresponds to two symmetrically
propagating wave packets synchronously meeting at the equator.%
\end{abstract}%



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