ENERGY RECEIVED BY THE EARTH FROM EXTRATERRESTRIAL AND ATMOSPHERIC SOURCES

The question of the amount of energy received by the Earth from extraterrestrial sources is of substantial importance in solving a whole range of both practical and purely scientific problems. Since the energy balance of the Earth is, on average, equal to zero, all the energy received by the Earth is ultimately radiated again into outer space. However, before this energy is radiated, it has time to undergo a number of transformations connected with a multitude of highly diverse phenomena both in the atmosphere and on the Earth’s surface. The study of these processes, which exert the most direct influence on the conditions of human life and activity, constitutes one of the most important tasks of science. It is not surprising that for many years the energy balance of the Earth has attracted, and continues to attract, the close attention of scientists working in the most varied fields of geophysics, astronomy, physics, biology, and so forth. Therefore the brief survey published by Gerzon* and reflecting the present state of knowledge about the integral effectiveness of various extraterrestrial sources of energy is of undoubted interest. This survey does not claim to be complete. It lacks, for example, estimates of such important sources of energy as radioactivity, the action of tide-generating forces, corpuscular radiation from the Sun, and also estimates of the radio emission of the Sun and the Galaxy. At the same time, it also includes some information on the amount of energy reaching the Earth’s surface in the form of various kinds of radiation arising in the Earth’s own atmosphere. The latter is quite justified, since the atmosphere plays a major role in the processes of energy exchange between the Earth and the external world, and some extraterrestrial sources of energy can be judged only by the glow of atmospheric gases they cause. However, here too the survey is very far from complete.

Naturally, the principal source of energy is the Sun. The energy of solar radiation falling on the Earth is distributed as follows. According to modern estimates relating to the Northern Hemisphere, the planetary albedo of the terrestrial globe is approximately 35.5%. Of the remaining 64.5% of the Sun’s radiation energy, 50% is absorbed by the Earth’s surface and 14.5% by the atmosphere. Atmospheric absorption is due mainly to water vapor—10.5%; ozone—2.5%; and water present in the droplet-liquid state (chiefly clouds)—1.5%. The other components of the atmosphere account for a comparatively insignificant amount of energy (in particular, the absorption of the Sun’s ultraviolet radiation in the upper layers of the atmosphere).

It should be assumed that in the Southern Hemisphere conditions are practically the same, or else that the increase in albedo due to the larger area of water surfaces is to a considerable extent compensated by increased cloudiness.

Measurements of the solar constant carried out over a long series of years have led to a value of 1.98 cal/cm² per minute. (Recent rocket measurements indicate that, perhaps, this value should be increased to 2.04 cal/cm² per minute.) Thus the Earth’s solid shell receives from the Sun \(1.76 \cdot 10^{24}\) erg/sec, and if absorption in the atmosphere is taken into account for rays that bypass the planet’s solid shell, it turns out that this quantity is equal to \(2.35 \cdot 10^{24}\) erg/sec.

* J. Atmosph. and Terrestr. Phys. 5, No. 1, 67 (1954).

Solar radiation reaches the Earth not only directly, but also as a result of reflection from the Moon and of the latter’s radiation (the absorption of solar energy by the Moon is much less than 1%). The Moon receives from the Sun \(1.12 \cdot 10^{23}\) erg/sec, of which \(3.09 \cdot 10^{19}\) erg/sec is transmitted to the terrestrial globe, and if the Earth’s atmosphere is taken into account, \(4.15 \cdot 10^{19}\) erg/sec, which amounts to \(1.76 \cdot 10^{-5}\) of the energy received by the Earth directly from the Sun (the ratio of the brightness of the Moon to the brightness of the Sun is \(2.47 \cdot 10^{-6}\)). These data refer to the full moon. Let us note that the Moon’s albedo is only 7%, and the brightness of the Moon in the first and third quarters is equal to \(1/9\) of the brightness of the full Moon.

A noticeable quantity of energy is brought to the Earth by meteors falling upon it. On average, about \(1.16 \cdot 10^4\) g/sec of meteoric matter enters the Earth’s atmosphere. Taking into account that the mean velocity of meteors is \(5.0 \cdot 10^5\) cm/sec, we find that the kinetic energy of meteors entering the terrestrial atmosphere is \(1.44 \cdot 10^{17}\) erg/sec. This energy is distributed among three processes: heating, luminescence, and ionization, in the ratio \(10^4 : 10^2 : 1\).

The extraterrestrial component of the glow of the night sky (including the light of stars, zodiacal light, galactic light, extragalactic light, etc.), according to the most recent estimates, produces an energy flux (both on the illuminated and on the darkened hemispheres) of \(2.61 \cdot 10^{17}\) erg/sec. Finally, the total energy of cosmic rays is estimated at \(1.63 \cdot 10^{17}\) erg/sec.

Table I

Input of energy from various extraterrestrial and atmospheric sources

Table I compares the estimates given above, as well as energy estimates for certain types of radiation generated in the atmosphere.

Table II gives estimates of the relative role of the various components of the night-sky glow. As for the atmospheric component of the night-sky glow, according to preliminary estimates by a number of authors,

Table II

Relative role of the various components of the night-sky glow (in %), according to Meinel, Oliver, and Chamberlain (1953)

on average it is equal to \(1.12 \cdot 10^{17}\) erg/sec and is distributed over the spectrum approximately as follows:

\[ \begin{aligned} \text{line}\quad &\lambda = 5577\ \text{\AA} &&—\ 3\% \\ \text{line}\quad &\lambda = 6300\ \text{\AA} &&—\ 0.2\% \\ D\text{-line of sodium} &&&—\ 0.8\% \\ \text{OH bands}\quad &(4600—11600\ \text{\AA}) &&—\ 96\% \end{aligned} \]

The energy associated with thunderstorm discharges is comparatively large. Taking into account that, on the Earth, on average 100 discharges occur per second and that each lightning flash requires on average approximately \(1.60 \cdot 10^{17}\) erg/sec, the total expenditure of energy on the formation of lightning amounts to about \(1.60 \cdot 10^{19}\) erg/sec.

The value given in Table I for the energy of polar auroras is a rough estimate. It is possible that it should be increased by a factor reaching 100.

P.