Electron densities below 100 kilometers at midlatitudes (L = 2.5 to 4.0) during solar minimum and maximum years: preliminary model calculations

Electron production rates due to photoionization, q s (χ, h ), and particle precipitation, q p ( h ), have been calculated for the midlatitude ionosphere from 70 to 140 km for conditions typical of solar minimum and maximum years. A simple model in which E and D regions are defined by Lyman β, EUV (30–120 A), Lyman α, and X rays (2–10 A) is used. An atmospheric model having annual variations for the major constituents and a seasonally constant profile of nitric oxide is also incorporated in the calculations. Electron density profiles have been derived using recent estimates of α eff . Results of calculations are shown for solar zenith angles χ = 37° and 72°, typical of noon values for summer and winter seasons. Fluxes of precipitated electrons typical of geomagnetic midlatitudes (L = 2.5–3.5) are used. For both solar minimum and maximum years, the seasonal variations in q t (h) and N t (h) differ significantly from those of a Chapman layer, partly because production rates from 80 to 100 km due to particle precipitation are from 25 to 90% of the total. One aspect of the 'heavily ionized' winter lower ionosphere is discussed. Calculated diurnal variations in ionization for conditions typical of solar maximum years at higher latitudes ( L = 3.5–4.0) also reveal irregular variations with χ due to the particle precipitation contribution.