Direct Evidence of the Cosmic Origin of Hydrogen in the Upper Layers of the Atmosphere

As early as 1933, Vegard¹ put forward the hypothesis that hydrogen, whose lines are occasionally observed in the spectra of auroras, enters the upper layers of the atmosphere not from near-Earth layers, but intrudes into the Earth’s atmosphere in the form of protons as part of the corpuscular streams ejected by the Sun. Strong confirmation of this hypothesis has been found, in particular, in the broadening—recently detected by Vegard²—and displacement toward the short-wavelength end of the spectrum of the $H_\alpha$ line in the spectrum of an aurora observed in Oslo on the night of February 23–24, 1950.

The determination of the velocity of hydrogen atoms from the spectra of an aurora that occurred on September 30, 1950, near Arnprior (USA, Ontario), carried out by the author of the note under review³˒⁵, leaves no doubt as to the validity of this hypothesis.

Spectrography was carried out simultaneously from two points: from Arnprior—approximately along the lines of force of the magnetic field—and from Ithaca (located 330 km south of Arnprior)—perpendicular to the lines of force. In both cases, one and the same region of the aurora was spectrographed. The position and character of the hydrogen line $H_\alpha$ ($\lambda = 6563$ Å) proved different in the two spectra. In the spectrogram obtained at Ithaca, this line was located at $\lambda = 6563$ Å and was broadened both into the short-wavelength and into the long-wavelength part of the spectrum by approximately 10 Å. In the spectrogram obtained at Arnprior, the broadening of the line into the red part of the spectrum amounted to about 10 Å, while in the violet part of the spectrum the line extended approximately to 6530 Å.

Thus, the mean displacement of the line toward shorter waves amounted to approximately 15 Å, and the maximum displacement in the same direction was more than 30 Å.

From this it could be concluded that the hydrogen atoms in the auroral zone were moving toward the Earth with an average velocity of 675 km/sec, while the maximum velocity of their motion toward the Earth reached 1350 km/sec. Such values of the velocities and their direction (along the lines of force toward the Earth) are unquestionable evidence that the hydrogen atoms penetrated into the Earth’s atmosphere from outside in the form of charged particles—protons—and had managed, before becoming neutralized, to use up the reserve of energy they possessed. As for the broadening of the hydrogen line in the spectrum obtained from Ithaca, it is evidently due both to scattering of the atoms as a result of collisions and to the spiral character of their motion around the lines of force of the magnetic field. The component of the velocity perpendicular to the lines of force was approximately 450 km/sec.

A similar result was obtained by Meinel⁴ in observing an aurora that occurred on the nights of August 18–19 and 19–20, 1950, in the Ithaca region. On the night of August 19–20 the auroral arc was located at the magnetic zenith of the observing point, and the spectrography, as at Arnprior, was carried out along the direction of the lines of force of the magnetic field. The contour of the hydrogen line $H_\alpha$ obtained in this case was asymmetric, the maximum being shifted into the short-wavelength part of the spectrum by 60 Å, which corresponded to an average velocity of the hydrogen atoms in the direction toward the Earth of 2800 km/sec. The maximum velocity of motion of the hydrogen atoms in the direction toward the Earth reached in this case 3200 km/sec⁶. Thus, the velocity of the protons before their penetration into the Earth’s atmosphere must have exceeded 3300 km/sec,

which is considerably greater than is given by determinations by other methods: 800–1600 km/sec).

When spectrographing in a direction perpendicular to the magnetic lines of force, the maximum of the \(H_\alpha\) line remained undisplaced, but the line itself was symmetrically broadened in both directions by \(6\) Å.

Since the aurora investigated by Meinel was very powerful (magnetic-disturbance index \(K=9\)), whereas the intensity of the aurora to which Gartlein’s measurements pertain was small (\(K=5\)), it may be supposed that there is a connection between the intensity of the aurora and the energy of the proton fluxes penetrating into the atmosphere.

The great geophysical interest of the results obtained is beyond doubt.

G. Rozenberg

CITED LITERATURE

1. See, for example, I. A. Khvostikov, The Luminescence of the Night Sky. Publishing House of the Academy of Sciences of the USSR, 1948.
2. L. Vegard, Nature 165, 1012 (1950).
3. C. W. Gartlein, Nature 167, 277 (1951).
4. A. B. Meinel, Science 112, 590 (1950).
5. C. W. Gartlein, Phys. Rev. 81, 463 (1951).
6. A. B. Meinel, Astrophys. J. 113, 50 (1950).