抄録
In the presence of a large number of positive and negative ionic species, an analytical expression for the effective recombination coefficient of electrons in the D region is derived in the same from, α′=‹αe›+λ‹αion›, as is customarily used in the upper regions. Here, ‹αe› is the electronic recombination coefficient averaged with weights proportional to the abundance of various kinds of positive ions, and ‹αion› is the weighted mean of the various ionic recombination coefficients according to the composition of positive and negative ions. The effective loss rate of electrons are given as (1+λ)α′ in which the negative ion-electron ratio λ changes in a wide range as a function of altitude. Under the assumption of a model atmosphere containing eight minor constituents, this paper calculates the density distributions of thirteen species of positive ions and seven species of negative ions as well as of electrons. Based on the result, the effective recombination coefficient is estimated to be 4.2×10-7cm3sec-1 at the 80km-level, 1.5×10-6cm3sec-1 at 70km, and 1.9×10-5cm3sec-1 at 60km, while λ increases rapidly with decreasing height, being about 5.3×10-3 at 80km, 7.9×10-1 at 70km, and 1.0×10-1 at 60km in a daytime condition. The effective loss rate estimated in this paper is shown to be consistent with the results derived from observations of solar eclipse, SID, and PCA events.
