  Solar proton events (SPEs) cause large-scale ionization in the middle
atmosphere leading to ozone loss and changes in the energy budget of the middle
atmosphere. The accurate implementation of SPEs and other particle ionization
sources in climate models is necessary to understand the role of energetic
particle precipitation (EPP) in climate variability. We use riometer
observations from 16 riometer stations and the Whole Atmosphere Community
Climate Model with added D region ion chemistry (WACCM-D) to study the spatial
and temporal extent of cosmic noise absorption (CNA) during 62 solar proton
events from 2000 to 2005. We also present a correction method for the
non-linear response of observed CNA during intense absorption events. We find
that WACCM-D can reproduce the observed CNA well with some need for future
improvement and testing of the used EPP forcing. The average absolute
difference between the model and the observations is found to be less than 0.5
dB poleward of about $66^\circ$ geomagnetic latitude, and increasing with
decreasing latitude to about 1 dB equatorward of about $66^\circ$ geomagnetic
latitude. The differences are largest during twilight conditions where the
modeled changes in CNA are more abrupt compared to observations. An
overestimation of about $1^\circ$ to $3^\circ$ geomagnetic latitude in the
extent of the CNA is observed due to the fixed proton cutoff latitude in the
model. An unexplained underestimation of CNA by the model during sunlit
conditions is observed at stations within the polar cap during 18 of the
studied events.
