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\begin{document}

\title{Electron density and conductance in the auroral ionosphere during
substorms. Influence of solar wind and plasma sheet state.}



\author[1]{Nikita Stepanov}%
\author[2]{Victor Sergeev}%
\author[2]{Maria Shukhtina}%
\author[3]{Yasunobu Ogawa}%
\author[4]{Xiangning Chu}%
\affil[1]{Arctic and Antarctic Research Institute,Saint Petersburg State University}%
\affil[2]{Saint Petersburg State University}%
\affil[3]{NIPR National Institute of Polar Research}%
\affil[4]{University of Colorado Boulder,University of California Los Angeles}%


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  \date{May 20, 2024}


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\begin{abstract}
Enhanced precipitation of magnetospheric energetic particles during
substorms increases ionospheric electron density and conductance. Such
enhancements, which have timescales of a few hours, are not reproduced
by the current ionospheric models. Using EISCAT (Tromso) measurements we
reconstruct the substorm related response of electron densities and
conductances in the ionosphere with respect to the intensity of substorm
injections. We also investigate how the intensity of the response is
influenced by the variations of the plasma sheet high energy (tens keV)
fluxes and solar wind state. To characterise the intensity of substorm
injection at a 5min time step we use the midlatitude positive bay (MPB)
index which basically responds to the substorm current wedge variations.
We build response functions (LPF filters) between T0-1h and T0+4hrs (T0
is a substorm onset time) in different MLT sectors to estimate the
magnitude and delays of the ionospheric density response at different
altitudes. The systematic and largest relative substorm related changes
are mostly observed in the lowest part of E and in D regions. It starts
and reaches maximum magnitude near midnight, from which it mainly
propagates toward east, where it decays when passing into the
noon-evening sector. Such MLT structure corresponds to the drift motion
of the injected high energy electron cloud in the magnetosphere. Besides
the injection intensity, we look at how the magnitude of the response
depends on the energetic (tens keV) fluxes level in the plasma sheet
before the substorm onset. We use a previously developed empirical model
of the plasma sheet fluxes with solar wind parameters as inputs to count
the plasma sheet fluxes with energy 10, 31 and 93 keV in the reference
point of transition region (6 Re, 270o SM Long). We found that during
enhanced high energy fluxes in the plasma sheet before the substorm
(fast solar wind, high solar wind reconnection electric field) the
background ionisation in the ionosphere, as well as the peak ionisation
value during the substorm, are higher. This implies that together with
substorm intensity the prehistory of the plasma sheet/solar wind state
forms the magnitude development of substorm related ionospheric
response. Research was supported by Russian Ministry of Science and
Higher Education grant  075-15-2021-583%
\end{abstract}%



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