Ions and Electrical Currents in the Upper Atmosphere of the Earth

Abstract

It is assumed that the ionization in the upper atmosphere is caused by the ultra-violet light of the sun and that the ion and electron densities at noon at the equator are in keeping with the facts of wireless waves. From the laws of recombination of the ions and of diffusion and drift of the ions in the earth's magnetic, gravitational and electric fields the distribution of the ions over the earth is worked out. The distribution is found to agree with wireless data over the earth, and with Gunn's diamagnetic theory of the solar diurnal variation of the earth's magnetism, (Phys. Rev. 32, 133 (1928). The gravitational drift currents are found to flow mainly along the parallels of latitude in the following way: (1) a current sheet in the daylight hemisphere flowing eastward in the levels above 150 kn which at the sunrise and sunset longitudes divides into two sheets; (2) one of these flows westward on the day side of the earth underneath (1) in the levels below 150 km, and (3) the other sheet continues eastward around on the night side of the earth. The current is mainly ($\frac{4}{5}$) between the 40'th parallels of latitude north and south, and falls to lower values at the higher latitudes. The total currents in the three sheets are about 1.16\ifmmode\times\else\texttimes\fi{}${10}^{7}$, 8.7\ifmmode\times\else\texttimes\fi{}${10}^{6}$ and 2.9\ifmmode\times\else\texttimes\fi{}${10}^{6}$ amperes, respectively. The east and west daytime current sheets subtract from each other leaving in effect an eastward current of about 2.9\ifmmode\times\else\texttimes\fi{}${10}^{6}$ amperes flowing around the earth all the time. This causes a magnetic field agreeing in magnitude and type with that obtained by Bauer in his 1922 analysis of the magnetic field of the earth of external origin, (Terr. Mag. 28, 1 (1923)). The current sheets are not of the type required by Chapman's drift current theory of the diurnal magnetic variation, (Proc. Roy. Soc. A122, 369 (1929)). As a result of the drift currents, the sunset longitude of the earth is at a potential around 2000 volts above that of the sunrise longitude. This electric field combined with the earth's magnetic field causes the ions and electrons on the night side of the earth to drift upward with velocities between 100 and 200 cm ${\mathrm{sec}}^{\ensuremath{-}1}$. The ions and electrons move into regions of lower pressure and therefore do not recombine as fast as they otherwise would. This removes a difficulty from an earlier calculation which yielded a slightly too great rate of disappearance of the free charges at night. The upward drift of the ionization causes a rise of the Kennelly-Heaviside layer which is, partially at least, compensated for by the fall due to the cooling and contraction of the atmosphere at night, and is complicated by the diffusion of the ions. It is difficult to say how much of the nighttime rise of the layer observed in experiments with wireless rays may be a genuine rise and how much may be an apparent rise due to delayed group velocities, or to other causes.