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\begin{document}
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\title{11pt, fleqn, a4paper, {]}LegrandOrangeBook Nightside Ionospheric Oxygen
Outflows during Geomagnetic Storms: Van Allen Probes Statistics}



\author[1]{Changning Chen}%
\author[2]{Qiu-Gang Zong}%
\author[3]{Zhi-Yang Liu}%
\affil[1]{Institute of Space Physics and Applied Technology}%
\affil[2]{Peking University}%
\affil[3]{Institut de Recherche en Astrophysique et Planetologie}%


\vspace{-1em}



  
  \date{April 17, 2026}


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\selectlanguage{english}
\begin{abstract}
Oxygen ions (O+) contribute dominantly to the energy density of the ring
current during geomagnetic storms, thereby driving the evolution of
storms. The majority of magnetospheric oxygen ions originate from the
high latitude ionosphere in the form of ionospheric outflows. In this
work, we employ Van Allen Probes data from January 2013 to December 2018
to analyze ionospheric oxygen outflows during storms. A superposed epoch
analysis discovers that the statistical outflow rate enhances more than
twice during storms, with the total outflow rate reaching 4.36\selectlanguage{ngerman}×1024 s-1
in the main phase and 2.34×1024 s-1 in the recovery phase compared to
0.46×1024 s-1 in quiet times. An examination of the magnetic
latitude-local time distributions of these outflows indicates that this
enhancement stems from both increase in outflow flux at specific
locations and increase in the area of outflow. Statistical analysis
shows that the ionospheric footprints of these outflows migrate
equatorward with increasing geomagnetic activity. However, the
equatorward expansion of the auroral oval occurs more pronounced,
resulting in a growing proportion of outflows originating from within
the auroral oval as geomagnetic activity develops. A further
investigation of the geomagnetic indices combining local magnetic and
electric fields relates this enhancement to: (1) the increased
geomagnetic disturbance during storms; (2) enhanced plasma waves in the
ultra-low-frequency range and near oxygen ion gyrofrequency, whose power
shows a positive correlation with oxygen outflow rates. Besides, the
distributions by season shows the total outflow rate more than doubles
in local summer compared to other seasons.%
\end{abstract}\selectlanguage{ngerman}%



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\begin{figure}[H]
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\includegraphics[width=0.70\columnwidth]{figures/Figure2-SuperposedEpochAnalysis/Figure2-SuperposedEpochAnalysis}

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\includegraphics[width=0.70\columnwidth]{figures/Figure3-MLT-Mlat-Distribution/Figure3-MLT-Mlat-Distribution}

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\includegraphics[width=0.70\columnwidth]{figures/Figure4-Season-Distribution/Figure4-Season-Distribution}

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\includegraphics[width=0.70\columnwidth]{figures/Figure5-Distribution-Fluence-Parameters/Figure5-Distribution-Fluence-Parameters}

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\includegraphics[width=0.70\columnwidth]{figures/Figure6-Storm-time-Parameter-Distribution/Figure6-Storm-time-Parameter-Distribution}

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\includegraphics[width=0.70\columnwidth]{figures/Figure7-Distribution-Flow-WavePower-Combined/Figure7-Distribution-Flow-WavePower-Combined}

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\includegraphics[width=0.70\columnwidth]{figures/Figure10-convective-electric-fields/Figure10-convective-electric-fields}

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