Recombination and electron attachment in the F layers of the ionosphere

Abstract

Observational data for the ionosphere at Washington have been used as a basis for computations. The rate of recombination at night is roughly proportional to the square of the electron concentration, but the apparent recombination coefficient , a', tends to increase with decreasing electron concentration over the " half period of a sunspot cycle. This fact and the observed variation of a' with height indicate that electrons disappear both by recombination and by negative-ion formation. The daily variation of electron concentration indicates that the F2 level is far above the level where the rate of production of electrons is a maximum in midsummer and that the FI layer is near the level where the rate is a maximum. It is assumed that both layers corne from the ionization of atomic oxygen. If a' is a function of the pressure, there will be a maximum electron concentration at a pressure, p, given by the relation l E. =~f(X) Po a' , where po is the pressure at the FI level, a is the electronic-recombination coefficient , and X is the ratio of negative ions to electrons. f(X) is 1, if X is small, or a linear function of p. In midsummer, p is 4X 10-8 mm of mercury. p/Po=0.027 and a=2 X 10-12, in good agreement with the theory of recombination. A seasonal variation of p/Po can be explained, if f(X) is not always unity, as X is very sensitive to temperature. The seasonal variation in electron concentration can be accounted for by the change in pressure. The pressure variation also accounts for the fact that F2 changes much more than FJ over a sunspot cycle. The effective collision area for electron attachment to oxygen atoms is 6.5 X 10-21 cm 2 • CONTENTS Page I. Introduction _________________________ _______________ ___ _______ 507 II. Observational data _____________________________________________ 508 III. Elementary theory _____________________________________________ 509 IV. Recombination and electron attachment ____ ____ ____ _____ ______ ___ 512 V. Daytime variation of electron concentration _____________________ __ 514 VI. Pressure at the F 2 IeveL ______________ __________________________ 515 VII. Numerical results _____________________________________ ____ _____ 516 VIII. Conclu~on ________________________ _________________________ ___ 517