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Ann. Geophys., 25, 1745-1757, 2007
www.ann-geophys.net/25/1745/2007/
© European Geosciences Union 2007
Lightning-driven inner radiation belt energy deposition into the atmosphere: implications for ionisation-levels and neutral chemistry
C. J. Rodger1, C.-F. Enell2, E. Turunen2, M. A. Clilverd3, N. R. Thomson1, and P. T. Verronen4
1Department of Physics, University of Otago, Dunedin, New Zealand
2Sodankylä Geophysical Observatory, Sodankylä, Finland
3Physical Sciences Division, British Antarctic Survey, Cambridge, UK
4Earth Observation, Finnish Meteorological Institute, Helsinki, Finland
Abstract. Lightning-generated whistlers lead to coupling between
the troposphere, the Van Allen radiation belts and the lower-ionosphere
through Whistler-induced electron precipitation (WEP). Lightning produced
whistlers interact with cyclotron resonant radiation belt electrons, leading
to pitch-angle scattering into the bounce loss cone and precipitation into
the atmosphere. Here we consider the relative significance of WEP to the
lower ionosphere and atmosphere by contrasting WEP produced ionisation rate
changes with those from Galactic Cosmic Radiation (GCR) and solar
photoionisation. During the day, WEP is never a significant source of
ionisation in the lower ionosphere for any location or altitude. At
nighttime, GCR is more significant than WEP at altitudes <68 km for all
locations, above which WEP starts to dominate in North America and Central
Europe. Between 75 and 80 km altitude WEP becomes more significant than GCR
for the majority of spatial locations at which WEP deposits energy. The size
of the regions in which WEP is the most important nighttime ionisation
source peaks at ~80 km, depending on the relative contributions of WEP
and nighttime solar Lyman-α. We also used the Sodankylä Ion
Chemistry (SIC) model to consider the atmospheric consequences of WEP,
focusing on a case-study period. Previous studies have also shown that
energetic particle precipitation can lead to large-scale changes in the
chemical makeup of the neutral atmosphere by enhancing minor chemical
species that play a key role in the ozone balance of the middle atmosphere.
However, SIC modelling indicates that the neutral atmospheric changes driven
by WEP are insignificant due to the short timescale of the WEP bursts.
Overall we find that WEP is a significant energy input into some parts of
the lower ionosphere, depending on the latitude/longitude and altitude, but
does not play a significant role in the neutral chemistry of the mesosphere.
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