The rates of production and loss of electrons in the f region of the ionosphere

Abstract

In the preceding paper by Schmerling & Thomas (1956) it was shown how, from experimental h'{f) records, it is possible to deduce the electron distributions in the F layer appropriate to an average magnetically quiet day in any one month; and some account was given of these distributions at Slough, Huancayo and Watheroo for different times of day, seasons and epochs in the solar cycle. In this paper these distributions are used as experimental facts from which the rates of production and loss of electrons are deduced. Use is also made of electron distributions determined, in rapid succession, near sunrise at Cambridge. It is here recognized that there may be important vertical movements of the electrons in the F region, but no assumptions are made about their magnitudes. Methods of analysis are used which minimize their effects. In part I it is shown that the behaviour of the quiet F layer, above 240 km, at the three places mentioned, at all times of the day, the year, and the solar cycle, is more consistent with the supposition that the rate of loss of electrons is given by — dNjdt = Kl A" rather than by — dNjdt= K2 N 2. Between heights of about 250 and 350 km the loss coefficient t seems to vary with height as given approximately by Kx = 10-4 exp 300—A (km)l —50 ) The significance of this type of loss coefficient is discussed. In part II it is realized that, if the above-mentioned loss coefficient were the correct one, then, because it decreases rapidly upwards, it could give rise to a peak of electron density considerably above the peak of electron production. This leads us to consider in detail the hypothesis of Bradbury (1938) that the Fl and F2 layers are both produced by the same ionizing radiation, acting on the same atmospheric constituent, and that the two peaks of electron density are caused by a suitable height variation of the loss coefficient. This hypothesis is discussed critically, in relation to the experimental results, and is shown to be self-consistent. It is shown that, if Bradbury’s hypothesis is accepted as correct, the scale height of the ionizable constituent between 180 and 350 km is about 45 km. This is in better agreement with the R model of the upper atmosphere deduced by Bates (1954) from the results of rocket experiments, than with the G model deduced from the results of experiments made on the ground. It is also shown how the experimental results lead to the deduction of limits to the movements caused by the diffusion of electrons under gravity. The movements expected on Bates’s R model are greater than those deduced from the experiments. Although the mechanisms of electron loss and production discussed in this paper seem to fit the experimental facts there might be others, of more or less complication, which would also be self-consistent and would satisfy the tests we have used. Much more work is required, on world-wide results, before an explanation can be claimed to be unique.