Abstract
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.
Highlights
Whistler-induced electron precipitation from the Van Allen radiation belts occurs as a result of coupling between the troposphere and the magnetosphere
As previous studies have described how the Whistler-induced Electron Precipitation (WEP) energy spectra varies with geomagnetic latitude, and the WEP flux magnitude varies with latitude and longitude, we are in a position to describe the variation in WEPdriven ionisation rates with altitude over the entire Earth
Previous studies have identified Whistler-induced Electron Precipitation (WEP) as a significant inner radiation belt loss process, and have described the how the WEP energy spectra varies with geomagnetic latitude, and the WEP flux magnitude varies with latitude and longitude
Summary
Whistler-induced electron precipitation from the Van Allen radiation belts occurs as a result of coupling between the troposphere and the magnetosphere. We considered the lifetimes of radiation belt electrons due to WEP losses, based on Trimpi measurements and an estimate of the a typical WEP burst mean precipitation energy flux (e.g. Rodger and Clilverd, 2002). The reliability of those rates and the validity of the conclusions drawn from those studies was tested by examining a new set of Trimpi observations from New Zealand (Rodger et al, 2005). We investigate the significance of WEP to the chemical makeup of the mesosphere
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