On the action of ultra-violet sunlight upon the upper atmosphere

The ordinary solar spectrum extends, as is well known, to about λ2913, the more ultra-violet parts being cut off by ozone absorption in the upper atmosphere. We have thus no direct knowledge of the distribution of intensity in the solar spectrum beyond λ2913, as it will appear to an observer situated outside the atmosphere of the earth. But it is now recognized that a number of physical phenomena is directly caused by the photochemical action of this part of sunlight on the constituents of the upper atmosphere. Such phenomena are (1) the luminous spectrum of the night sky and of the sunlit aurora, (2) the ionization in the E, F and other layers which is now being intensely studied by radio-researchers all over the world, (3) the formation and equilibrium of ozone (see Ladenburg 1935), (4) magnetic storms and generally the electrical state of the atmosphere. Formerly it was a debatable point whether some of these phenomena were not to be ascribed to the action of streams of charged particles emanating from the sun. There seems to be no doubt that the polar aurora and certain classes of magnetic storms are to be ascribed to the bombardment of molecules of N 2 and O 2 by such charged particles, for these phenomena show a period which is identical with the eleven year period of the sun, and are found in greater abundance, the nearer we approach the magnetic poles. But there now exists no doubt that the ionization observed by means of radio-methods in the E and F 1 regions, their variation throughout day and night, and at different seasons is due to the action of ultra-violet sunlight. This was decisively proved by observations during several total solar eclipses since 1932 (Appleton and Chapman 1935). The luminous night-sky spectrum, though it has certain points of similarity to the polar aurora, is on the whole widely different, and is found on nights free from electrical disturbances. The prevailing opinion is that it is mainly due to the ultra-violet solar rays, i. e. in the course of the day sunlight is stored up by absorption by the molecules in the upper atmosphere, and again given up during the night, in one or several steps, as a fluorescence spectrum. According to S. Chapman (1930) the formation of the ozone layer and its equilibrium under different seasonal conditions is also to be mainly ascribed to the action of ultra-violet sunlight. In the following paper an attempt will be made to discuss some of these questions in as rigorous a way as is possible with our present knowledge. It is evident that an adequate discussion is possible only if we have a good knowledge of (1) the distribution of intensity in the solar spectrum beyond λ2900, (2) the photochemical action of light of shorter wave-length than λ2900 on the constituent molecules of the upper atmosphere, which are mainly oxygen and nitrogen. We shall first consider (1).

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Measurements of the sun’s ultra-violet radiation and its absorption in the earth’s atmosphere

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character ◽

10.1098/rspa.1923.0107 ◽

1923 ◽

Vol 104 (725) ◽

pp. 252-271 ◽

Cited By ~ 2

Keyword(s):

Wave Length ◽

Solar Spectrum ◽

Ultra Violet ◽

Upper Atmosphere ◽

Stray Light ◽

Solar Constant ◽

Absorption Bands ◽

Ultra Violet Radiation ◽

Short Period ◽

Violet Radiation

1. It is now well known that a connection exists between the variations in solar phenomena and changes in terrestrial weather. Thus the occurrence of an eleven-year cycle in the earth’s temperature, rainfall, etc., which is coincident with the eleven-year period of sunspots has long been recognised. More recently a marked connection has been found between the irregular short -period variations also. In this connection the work of H. H. Clayton, of the Argentine Meteorological Service, may be particularly mentioned. He has found that a very definite connection exists between the variations of the “solar constant,” as measured by the Smithsonian Astrophysical Department, and the temperature and rainfall some few days later in South America. The causes which lead to this connection are at present not known, though various theories have been proposed. For example, it has been suggested that the short wave-length radiation from the sun will produce ozone from oxygen in the upper atmosphere, and owing to the absorption bands of ozone both in the infra-red and ultra-violet, a change in the amount of this gas might change the radiation equilibrium temperature of the upper atmosphere, and so affect the pressure and temperature of the air below. The measurements of ultra-violet radiation made during “solar constant” determinations by the Smithsonian Institute are very uncertain, owing to the relatively small energy in this part of the solar spectrum, and the large errors due to stray light in the spectrometer. Since the measurements here described were started, Fabry and Buisson have published measurements of the amount of ozone in the atmosphere—measured spectroscopically—but only for about a dozen days.

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VI. The ultra-violet band of ammonia, and its occurrence in the solar spectrum

Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a Mathematical or Physical Character ◽

10.1098/rsta.1919.0006 ◽

1919 ◽

Vol 218 (561-569) ◽

pp. 351-372 ◽

Cited By ~ 12

Keyword(s):

Solar Spectrum ◽

Ultra Violet ◽

Maximum Intensity ◽

Resolving Power ◽

The Sun ◽

Sufficient Detail ◽

Other Substances ◽

Violet Band ◽

Band Spectra

A question of great interest in connection with the solar spectrum is that of the origin of the thousands of unidentified faint lines which were catalogued by Rowland in his “Preliminary Table of Solar Spectrum Wave-lengths.” Some of these lines may possibly be identical with faint lines in metallic spectra which have not yet been completely tabulated, but in view of the presence of bands of cyanogen, carbon and hydrocarbon, the possibility of the correspondence of most of them with band spectra of other substances should not be overlooked. As a contribution to this inquiry, the present investigation was undertaken primarily in order to determine whether Group P in the ultra-violet region of the solar spectrum might not be mainly due to the presence of ammonia in the absorbing atmosphere of the sun. Ammonia was already known to give a remarkable band in this region, having its position of maximum intensity near λ 3360, but it had not been investigated in sufficient detail to permit of an adequate comparison with the solar tables. Photographs have accordingly been taken with spectrographs of high resolving power for the purpose of this comparison, and, as will appear from the details which follow, it has been established that the ammonia band is certainly represented in the solar spectrum, and accounts for a considerable number of faint lines for which no other origins have been suggested.

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V. Researches in spectrum-analysis in connexion with the spectrum of the sun

Proceedings of the Royal Society of London ◽

10.1098/rspl.1873.0073 ◽

1874 ◽

Vol 22 (148-155) ◽

pp. 391-391

Keyword(s):

Spectrum Analysis ◽

Wave Length ◽

Solar Spectrum ◽

The Other ◽

Photographic Method ◽

The Sun ◽

The Third

Maps of the spectra of calcium, barium, and strontium have been constructed from photographs taken by the method described in a former communication (the third of this series). The maps comprise the portion of the spectrum extending from wave-length 3900 to wave-length 4500, and are laid before the Society as a specimen of the results obtainable by the photographic method, in the hope of securing the cooperation of other observers. The method of mapping is described in detail, and tables of wave-lengths accompany the maps. The wave-lengths assigned to the new lines must be considered only as approximations to the truth. Many of the coincidences between lines in distinct spectra recorded by former observers bave been shown, by the photographic method, to be caused by the presence of one substance as an impurity in the other; but a certain number of coincidences still remain undetermined. The question of the reversal of the new lines in the solar spectrum is reserved till better photographs can be obtained.

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Kristian Birkeland's pioneering investigations of geomagnetic disturbances

History of Geo- and Space Sciences ◽

10.5194/hgss-1-13-2010 ◽

2010 ◽

Vol 1 (1) ◽

pp. 13-24 ◽

Cited By ~ 4

Author(s):

A. Egeland ◽

W. J. Burke

Keyword(s):

Magnetic Storms ◽

Upper Atmosphere ◽

The Arctic ◽

The Sun ◽

Geomagnetic Disturbances ◽

Cell Pattern ◽

Auroral Phenomena ◽

Lord Kelvin ◽

Kristian Birkeland ◽

Auroral Latitude

Abstract. More than 100 years ago Kristian Birkeland (1967–1917) addressed questions that had vexed scientists for centuries. Why do auroras appear overhead while the Earth's magnetic field is disturbed? Are magnetic storms on Earth related to disturbances on the Sun? To answer these questions Birkeland devised terrella simulations, led coordinated campaigns in the Arctic wilderness, and then interpreted his results in the light of Maxwell's synthesis of laws governing electricity and magnetism. After analyzing thousands of magnetograms, he divided disturbances into 3 categories: 1. Polar elementary storms are auroral-latitude disturbances now called substorms. 2. Equatorial perturbations correspond to initial and main phases of magnetic storms. 3. Cyclo-median perturbations reflect enhanced solar-quiet currents on the dayside. He published the first two-cell pattern of electric currents in Earth's upper atmosphere, nearly 30 years before the ionosphere was identified as a separate entity. Birkeland's most enduring contribution toward understanding geomagnetic disturbances flowed from his recognition that field-aligned currents must connect the upper atmosphere with generators in distant space. The existence of field-aligned currents was vigorously debated among scientists for more than 50 years. Birkeland's conjecture profoundly affects present-day understanding of auroral phenomena and global electrodynamics. In 1896, four years after Lord Kelvin rejected suggestions that matter passes between the Sun and Earth, and two years before the electron was discovered, Birkeland proposed current carriers are "electric corpuscles from the Sun" and "the auroras are formed by corpuscular rays drawn in from space, and coming from the Sun". It can be reasonably argued that the year 1896 marks the founding of space plasma physics. Many of Birkeland's insights were rooted in observations made during his terrella experiments, the first attempts to simulate cosmic phenomena within a laboratory. Birkeland's ideas were often misinterpreted or dismissed, but were verified when technology advances allowed instrumented spacecraft to fly in space above the ionosphere.

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The spectrum of magnesium hydride

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character ◽

10.1098/rspa.1910.0008 ◽

1910 ◽

Vol 83 (561) ◽

pp. 210-210 ◽

Cited By ~ 1

Keyword(s):

Wave Length ◽

Solar Spectrum ◽

Magnesium Hydride ◽

High Dispersion ◽

Calcium Hydride ◽

The Sun ◽

Or Groups ◽

Concave Grating ◽

Limits Of Error ◽

Reduced Temperature

The author has previously discovered that many of the band lines peculiar to the sun-spot spectrum are identical with lines composing the green fluting attributed to magnesium hydride by Liveing and Dewar. The present paper gives the results of a further investigation of this spectrum with high dispersion, together with details of wave-length determinations. The principal results may be briefly summarised as follows: -(1) No sufficient reason has been found for modifying Leveing and Dewar’s conclusion that the spectrum is produced by the combination of magnesium with hydrogen. (2) Lines are shown at short intervals in all parts of the spectrum from the extreme red to λ 2300, and definite groups of flutings begin at 5621.57, 5211.11, 4844.92, 4371.2, and near 2430. (3) From photographs of the magnesium arc in hydrogen at low temperatures, taken with a 10-foot concave grating, the positions of close upon 2000 lines composing the three principal bands have been determined. The wave-lengths were derived from the interference standards of Fabry and Buisson, but have been corrected to Rowland’s scale to facilitate comparsion with solar spectra. (4) Twelve of the series of none of the formulæ which have been proposed are sufficiently general in their application to represent all of these series within the limits of error of measurements. For the longer series the closest approximation is given by Halm’s equation. (5) The identification of magnesium hydride in the sun-spot spectrum has been fully confirmed, and is clearly demonstrated by photographs submitted for reproduction. (6) It is shown that many of the bright lines, but merely clear interspaces between lines or groups of lines in the spectrum of magnesium hydride. (7) The presence of the magnesium hydride flutings, together with flutings of titanium oxide and calcium hydride discovered at Mount Wilson, accords with the view that spots are regions of reduced temperature, and that their darkness is at least partly due to absorption. (8) The investigation of the possible presence of lines of magnesium hydride in the ordinary solar spectrum is for several reasons inconclusive, but there is evidence that very few, if any, of the thousands of faint lines tabluated by Rowland are to be accounted for by this substance.

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Study of solar radiation at high altitudes using rocket-borne instruments

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1956.0130 ◽

1956 ◽

Vol 236 (1205) ◽

pp. 211-216

Keyword(s):

Solar Radiation ◽

Research Program ◽

Solar Spectrum ◽

Ultra Violet ◽

Upper Atmosphere ◽

High Altitudes ◽

Research Instrument ◽

Grating Spectrometer ◽

High Degree ◽

Better Than

After the capture of a number of German V 2’ s in 1946 the study of the solar spectrum beyond 2900 Å first became possible. The V 2 was a ballistic rocket with a range of 180 miles, and when used as a research instrument was capable of carrying a load of 1 ton well into the ionosphere. Although, in this role, it was uneconomic and has now been superseded, it played an important part in demonstrating the value of this means of research. The Aerobee, developed largely because of the success of the V 2 experiments, has replaced it and has attained a high degree of reliability and an altitude performance better than the V 2. Its pay-load of 150 lb. is adequate to enable it to carry a complete 40 cm grating spectrometer mounted on a biaxial sun-seeker. Among the earliest instruments to be carried into the upper atmosphere as part of the American rocket research program were grating spectrographs operating in the ultra-violet region. On 10 October 1946, the first successful flight of this kind was made when a V 2 obtained a, now historic, spectrogram demonstrating the effect of absorption by ozone. Since that time more than forty flights have been made by rockets carrying a wide variety of instruments for the study of the solar spectrum. This paper will describe briefly the types of instrument used and will summarize the principal data obtained.

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An investigation into the Nature and occurrence of the auroral Green line λ 5577 Å

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character ◽

10.1098/rspa.1927.0022 ◽

1927 ◽

Vol 114 (766) ◽

pp. 1-22 ◽

Cited By ~ 7

Keyword(s):

Electrical Discharge ◽

Wave Length ◽

Upper Atmosphere ◽

Characteristic Line ◽

The Past ◽

Pressure Oxygen ◽

Solid Nitrogen ◽

Mode Of Occurrence ◽

The Subject ◽

Night Sky

The wave-length at 5577 Å, which is the most prominent line in the spectrum of the auroral light, and which is the characteristic line of the spectrum of the light from the night sky, has been the subject of extensive research. Its wavelength has been measured very accurately by Babcock* and has been found to be 5577·350 ± 0·005 Å. In 1923 Prof. Vegard,f in Norway, put forward the view that the line had its origin in the luminescence of solid nitrogen suspended in a state of fine division in the upper atmosphere, but that view, in the light of a rigid investigation, has been found to be untenable. In 1925 McLennan and ShrumJ announced that they had been able to obtain a green spectral line at λ 5577 Å from the electrical discharge in a tube containing a mixture of helium and oxygen, and that its wave-length agreed with that found by Babcock for the line in the spectrum of the night sky. Later they obtained it quite strongly in a mixture of neon and oxygen, and in addition they found at a still later time that it could be observed faintly in the spectrum of the electrical discharge in low pressure oxygen presumably pure. During the past year we have been engaged in a research to elucidate further the nature of this elusive radiation at λ 5577 Å, and to locate more definitely its origin and mode of occurrence.

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On the limit of Solar and stellar light in the ultra-violet part of the spectrum

Proceedings of the Royal Society of London ◽

10.1098/rspl.1889.0020 ◽

1890 ◽

Vol 46 (280-285) ◽

pp. 133-135

Keyword(s):

Solar Spectrum ◽

Ultra Violet ◽

The Sun ◽

Earth’S Atmosphere ◽

Rapid Extinction ◽

Earth's Atmosphere

It has been long known that the solar spectrum stops abruptly, but not quite suddenly, at the ultra-violet end, and much sooner than the spectra of many terrestrial sources of light. The observations of Cornu, of Hartley, and, quite recently, of Liveing and Dewar, appear to show that the definite absorption to which the very rapid extinction of the solar spectrum is due, has its seat in the earth’s atmosphere, and not in that of the sun; and that, consequently, all ex-terrestrial light should be cut off at the same place in the spectrum.

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