Contribution of proton precipitation to space-based auroral FUV
observations

Marina Galand, Dirk Lummerzheim, Larry Paxton, Harald Frey


Energetic electrons and protons precipitating from the magnetosphere
are a major energy source in the high latitude regions inducing
significant ionospheric and thermospheric perturbations through
ionization and heating. Aurora is the optical manifestation of the
interaction of these energetic particles with atmospheric
neutrals. Auroral brightness and brightness ratios can be used as
remote sensing of the particle characteristics for estimation of the
subsequent atmospheric response or for tracking magnetospheric
processes.  Imaging from space offers a unique way to access to the
global picture, and its temporal varibility, of the particle energy
input over the auroral ovals. Usually only the electron component of
the precipitation is considered. Electron characteristics are inferred
from the analysis of auroral images taken from space in two different
spectral bands in UV or visible.  In aurora most of the energy is
carried by electrons, but at some locations and certain times protons
are a major energy source, that is, a major ionization source of the
atmosphere. The response of POLAR/UVI, IMAGE/WIC and SI13, and
TIMED/GUVI -used for retrieving the electron components- to proton
precipitation will be estimated. Secondary electrons produced within
the proton beam also contribute to auroral emissions. Since they are
less energetic than the secondary electrons produced in electron
precipitation, they have a different spectral signature. In addition,
for a given energy flux, protons are usually more efficient to ionize
than electrons and yield larger values of the Pedersen ionospheric
conductance.  Therefore, the difference between proton and electron
aurora can lead to misinterpretation when brightness ratios are used
to derive ionospheric conductances with parameterizations that are
based on electron aurora.  The validation and limitations of auroral
analysis will be discussed, especially in the winter cusp region and
at the equatorward edge of the afternoon oval, where protons are
expected to be a significant energy source.

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Fall 2002 Meeting of the American Geophysical Union
San Francisco, CA, USA, 6-10 December 2002