Effect of Nuclear Explosions Upon the Ionosphere

ABSTRACT

Nuclear explosion tests during September-October 1961 and August-September 1962 carried out by the USSR at Novaya Zemlya (75°N, 60°E) are found to have caused widespread ionospheric disturbance in both upper and lower ionosphere. In this paper an analysis is presented of the observed radio effects of all the 27 nuclear detonations around 5 megatons and above.

An analysis of hourly values of f₀F₂, following a nuclear detonation, given by 40 widely separated ionosonde stations situated on different geomagnetic and geographical co-ordinates has revealed an isotropic spread, up to a distance of 8000 km. from the source, of a disturbance-pattern in the shape of increase in electron density. The speed of the spread in the F₂-layer has been found to lie between 230 and 580 m/s., the most probable speed being 355 m/s.

Analysis of records of long-wave field strength continuously recorded at Delhi of Radio Tashkent on 164 kc/s. has shown that similar disturbance occurs in the D-region and the speed of propagation of this disturbance is found to lie between 390 and 1320 m/s. A plausible explanation of the higher speed of the disturbance observed from the analysis of long-wave record has been indicated in the paper.

It is significant to note that out of 20 events for which long-wave records are available, effects of 13 events could be clearly seen. Further, marked relationship between the intensity of the explosion and the relative increase in long-wave signal in db. appears to exist. Thus, the long-wave experiment appears to offer a reliable technique of obtaining information about nuclear detonations in the atmosphere and their intensities.

In three instances clear effect of the nuclear detonation on Cosmic Noise Absorption (18·9 Mc/s.) was observed.