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\begin{document}

\title{Evolution of pitch angle distributions of relativistic electrons during
geomagnetic storms: Van Allen Probes Observations}



\author[1]{Ashley D Greeley}%
\author[2]{Shrikanth G Kanekal}%
\author[3]{David Gary Sibeck}%
\author[4]{Quintin Schiller}%
\author[5]{Daniel N. Baker}%
\affil[1]{NASA Goddard Space Flight Center}%
\affil[2]{National Aeronautics and Space Administration (NASA)}%
\affil[3]{GSFC}%
\affil[4]{NASA, Goddard Space Flight Center}%
\affil[5]{University of Colorado Boulder}%


\vspace{-1em}



  
  \date{May 24, 2024}


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\begin{abstract}
We present a study analyzing relativistic and ultra relativistic
electron energization and the evolution of pitch angle distributions
using data from the Van Allen Probes. We study the connection between
energization and isotropization to determine if there is a coherence
across storms and across energies. Pitch angle distributions are fit
with a Jsin\selectlanguage{greek}θ \selectlanguage{english}function, and the variable `n' is characterized as the
pitch angle index and tracked over time. Our results show that,
consistently across all storms with ultra relativistic electron
energization, electrons become most anisotropic within around a day of
Dst and relax down to prestorm isotropization levels in the following
week. In addition, each consecutively higher energy channel is
associated with higher anisotropy after storm main phase. Changes in the
pitch angle index are reflected in each energy channel; when 1.8 MeV
electrons increase (or decrease) in pitch angle index, so do all the
other energy channels. In a superposed epoch study, we show that the
peak anisotropies differ between CME- and CIR- driven storms and measure
the relaxation rate as the anisotropy falls after the storm. The
relaxation rate in pitch angle index for CME-driven storms is
-0.14+/-0.023 at 1.8 MeV, -0.28+/-0.01 at 3.4 MeV, and -0.36\selectlanguage{ngerman}±0.02 at 5.2
MeV. For CIR-driven storms, the relaxation rates are -0.09±0.01 for 1.8
MeV, -0.12±0.02 for 3.4 MeV, and -0.11±0.02 for 5.2 MeV. This study
shows that there is a global coherence across energies and that storm
type may play a role in the evolution of electron pitch angle
distributions.%
\end{abstract}\selectlanguage{ngerman}%



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\textbf{Hosted file}

\verb`supportinginformation-greeley.docx`  available at \url{https://authorea.com/users/527324/articles/596612-evolution-of-pitch-angle-distributions-of-relativistic-electrons-during-geomagnetic-storms-van-allen-probes-observations}

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