EXPERIMENTAL PROOF OF THE EXISTENCE OF ELECTRIC CURRENTS IN THE IONOSPHERE

As is known, the numerous anomalies and variations of the Earth’s magnetic field have still not received an exhaustive explanation. The theories proposed up to now have inevitably included an element of conjecture connected with the lack of sufficient information about the electric currents occurring in the solid, liquid, and gaseous envelopes of our planet. A significant step forward was made recently by V. V. Shuleikin1, who showed that electric currents in the oceans play an important role in the formation of a number of especially significant anomalies of the Earth’s magnetic field (the displacement of the poles, the connection with the coastline). At the same time, harmonic analysis of the diurnal variations observed at the Earth’s surface had long since shown that the principal source of the variable field responsible for these variations is located above the Earth’s surface.

Fig. 1.

In the literature, various possibilities have been considered for the occurrence of a variable magnetic field of nonterrestrial origin, but the most probable source of diurnal variations appeared to be various kinds of electric currents which, generally speaking, may occur in the upper layers of the atmosphere. Although the hypothesis of the existence of ionospheric currents seemed plausible, and various mechanisms capable of producing them were discussed in detail, the very fact of their existence remained hypothetical and had not found any convincing experimental confirmation. Such confirmation of the existence of ionospheric currents and of their influence on the Earth’s magnetic field was obtained by the authors of the work under review2.

In the experiments described, the intensity of the magnetic field was measured directly at various altitudes up to 105 km above sea level. The measurements were made with magnetometers raised to the appropriate altitude by a rocket. The launches were carried out on the coast of Peru near 89° west longitude and 11° south latitude, which corresponds to 341° geomagnetic longitude and −1° geomagnetic latitude. The choice of a point located near the geomagnetic equator was especially favorable for detecting ionospheric currents, since the magnetometer used

...the meter made it possible to determine only the absolute magnitude of the field strength, without regard to its direction, and the field of the assumed ionospheric currents should, under these conditions, be parallel to the main terrestrial field. Moreover, the chosen region is distinguished by anomalously large diurnal variations.

In all, two ascents were made: on March 17, 1949, at 17 h 20 m, and on March 22 of the same year at 11 h 20 m (90th-meridian time). The results obtained are shown in Figs. 1 and 2, which depict the decrease in field strength (in milligausses) as a function of the height of ascent of the magnetometer. Circles indicate the data obtained during ascent, and crosses those obtained during the rocket’s descent. The solid line corresponds to the decrease

Fig. 2.

of the field according to the inverse-cube law of distance (the field of a dipole). Both ascents revealed distinct deviations from this law at low altitudes. These deviations can, tentatively, be attributed to the presence of a local anomaly near the Earth’s surface. There are no other data on the existence of such an anomaly in the indicated region; however, similar anomalies have been observed in a number of other regions of the Pacific Ocean. The dotted curves in Figs. 1 and 2 indicate the decrease in field strength that should be expected if the influence of this surface anomaly is taken into account.

The measurements in Fig. 1 were carried out under conditions when the diurnal variations at the surface of the Earth were very weak. The experimental points lie well on the curve corresponding to the field of a dipole (with correction for the surface anomaly), and, consequently, in the region investigated there are no areas with appreciable electric currents.

An estimate of the accuracy of the measurements shows that the error does not exceed ±1 milligauss.

In contrast to the first ascent, during the ascent on March 22 (Fig. 2) the diurnal variations at the surface of the Earth were close to a maximum. In this case, in the altitude interval from 93 to 105 km, a sharp decrease in the field strength is observed, amounting (after subtraction of the regular decrease corresponding to the field of a dipole, with allowance for the surface anomaly) to \(4 \pm 0.5\) milligausses. This decrease cannot be attributed to a current located within the Earth, and must be ascribed to the rocket’s penetration deep into the layer in which electric currents occur.

If the magnetometer had penetrated the entire region filled with currents, then the change in the strength of the magnetic field would have had to be approximately twice as large as the diurnal variations observed at the Earth’s surface.

A comparison of the results of the ascent on March 22 with the magnetogram of the Tihany observatory (Peru) showed that there is known agreement here, although an accurate comparison was made difficult by the magnetic storm that developed during the week when the ascents were carried out. Since the rocket evidently did not pass completely through the current layer, the observed change in the magnetic field (4 milligauss) in the interval 93–105 km is a surplus. The authors believe that this may have been due to the strongly disturbed magnetic conditions on the day of the ascent. In any case, the experiments described prove the existence of a system of currents in the region of the ionospheric \(E\) layer, as well as the connection of these currents with the diurnal variations observed at the Earth’s surface. Thus, theories of terrestrial magnetism based on the assumption of the existence of such currents receive serious substantiation. The authors rightly note that further rocket ascents for the purpose of investigating ionospheric currents may bring substantial clarity to the question of the Earth’s magnetic field.

G. Rosenberg

References Cited

1. V. V. Shuleikin, DAN 76, 57 (1950). See also UFN 44, issue 4, 616 (1951).
2. E. Marple, W. A. Bowen, Jr. and S. F. Singer, Phys. Rev. 82, 957 (1951).