Computational Model of D-Region Ion Production Caused by Energetic
Electron Precipitations Based on General Monte Carlo Transport
Calculations
Abstract
During enhanced magnetic activities, large ejections of energetic
electrons from radiation belts are deposited in the upper polar
atmosphere where they play important roles in its physical and chemical
processes, including VLF signals subionospheric propagation. Electron
deposition can affect D-Region ionization, which are estimated based on
ionization rates derived from energy depositions. We present a model of
D-region ion production caused by an arbitrary (in energy and pitch
angle) distribution of fast (10 keV - 1 MeV) electrons. The model relies
on a set of pre-calculated results obtained using a general Monte Carlo
approach with the latest version of the MCNP6 (Monte Carlo N-Particle)
code for the explicit electron tracking in magnetic fields. By
expressing those results using the ionization yield functions, the
pre-calculated results are extended to cover arbitrary magnetic field
inclinations and atmospheric density profiles, allowing ionization rate
altitude profile computations in the range of 20 and 200 km at any
geographic point of interest and date/time by adopting results from an
external atmospheric density model (e.g. NRLMSISE-00). The
pre-calculated MCNP6 results are stored in a CDF (Common Data Format)
file, and IDL routines library is written to provide an end-user
interface to the model.