Theoretical Estimate of the Effective Recombination Coefficient in the D Region

Abstract

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, a' = + lambda ( alpha /sub ion/), as is customarily used in the uppe r regions. Here, ( alpha /sub e/) is the electronic recombination coefficient averaged with weights proportional to the abundance of various kinds of positive ions, and ( alpha /sub ion/) 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 is given as (1 + lambda )a' in which the negative ion-electron ratio, lambda , changes in a wide range as a function of altitude. Under the assumption of a model atmosphere containing eight minor constituents, the density distributions of thirteen species of positive ions and seven species of negative ions as well as of electrons are calculated. Based on the result, the effective recombination coefficient is estimated to be 4.2 x 10/ sup -7/ cm/sup 3/ sec/sup -1/ a t the 80 km-level, 1.5 x 10/sup -6/ cm/sup 3/ sec/ sup -1/more » at 70 km, and 1 9 x 10/s up -5/ cma sec/sup -1/ at 60 km, while lambda increases rapidly with decreasing height, being about 5.3 x 10/sup -3/ at 80 km, 7.9 x 10/sup -1/ at 70 km, and 1.0 x 10/sup -1/ at 60 km in a daytime condition. The effective loss rate estimated is shown to be consistent with the results derived from observations of solar eclipse, SID, and PCA events. (auth)« less