Contribution of proton and electron precipitation to the observed electron concentration in October–November 2003 and September 2005
Article, Other literature type
Verronen, P. T.
Andersson, M. E.
Wissing, J. M.
Talaat, E. R.
Sarris, T. E.
- Publisher: Copernicus Publications
(issn: 1432-0576, eissn: 1432-0576)
Geophysics. Cosmic physics | Q | Science | Physics | QC1-999 | QC801-809
Understanding the altitude distribution of particle precipitation forcing
is vital for the assessment of its atmospheric and climate impacts. However,
the proportion of electron and proton forcing around the mesopause region
during solar proton events is not always clear due to uncertainties in
satellite-based flux observations.
Here we use electron concentration observations of the European Incoherent
Scatter Scientific Association (EISCAT) incoherent scatter radars
located at Tromsø (69.58° N, 19.23° E) to
investigate the contribution of proton and electron precipitation to the
changes taking place during two solar proton events. The EISCAT measurements
are compared to the results from the Sodankylä Ion and Neutral Chemistry
Model (SIC). The proton ionization rates are calculated by two different
methods – a simple energy deposition calculation and the Atmospheric
Ionization Model Osnabrück (AIMOS v1.2), the latter providing also the
electron ionization rates.
Our results show that in general the combination of AIMOS and SIC is able to reproduce the observed
electron concentration within ± 50% when both electron and proton forcing is
included. Electron contribution is dominant above 90 km, and can contribute
significantly also in the upper mesosphere especially during low or moderate
proton forcing. In the case of strong proton forcing, the AIMOS electron
ionization rates seem to suffer from proton contamination of satellite-based
flux data. This leads to overestimation of modelled electron concentrations
by up to 90% between 75–90 km and up to 100–150% at 70–75 km.
Above 90 km, the model bias varies significantly between
the events. Although we cannot completely rule out EISCAT data issues, the
difference is most likely a result of the spatio-temporal fine structure of
electron precipitation during individual events that cannot be fully captured
by sparse in situ flux (point) measurements, nor by the statistical AIMOS
model which is based upon these observations.