Solar Electromagnetic Radiation Research Articles

Measurement of insolation using CdS photoresistor

Using cadmium sulphide (CdS) photoresistor, the intensity of solar electromagnetic radiation (insolation) was estimated daily and hourly at Nsukka Campus of the University of Nigeria (latitude 6.8° North and longitude 7.35° East) for a period (October to January) of more than 3 months 1978/79. The mean daily insolation for the period was found to be 17.4 million J/m 2/day. A modification of Rapp and Hoffman's empirical equation for local insolation was also obtained. The influence of rain and harmattan was observed.

Solar constants and radiometric scales

The basic requirement for any type of measurement in which comparisons are made in a scale, relative or absolute. The values used by the Committee on Solar Electromagnetic Radiation to derive the solar constant were in different radiometric scales. Assuming that only difference in radiometric references produced the wide scatter of individual values, an attempt was made to convert all values to one radiometric reference. A radiometric scale based on electrical power equivalence was used as the reference. The resulting value was 137.5 mW cm(-2), as compared to the CSER derived value of 135.3 mW cm(-2) . This revised value lies within the error bounds of all the values used in the analysis. The revised estimate was then compared to values derived from more recent experiments. out of the atmosphere. There appears to be a discrepancy between values derived in and.

Relativistic electron events in interplanetary space

This review is concerned with relativistic electron events observed in interplanetary space. The different types of event are identified and illustrated. The relationships between solar X-ray and radio emissions and relativistic electrons are examined, and the relevance of the observations to solar flare acceleration models is discussed. A statistical analysis of electron spectra, the electron/proton ratio and propagation from the flare site to the Earth is presented. A model is outlined which can account for the release of electrons from the Sun in a manner consistent with observations of energetic solar particles and electromagnetic solar radiation.

The Next Decade in Observational Solar Research

The last two decades have been exceptionally fruitful for astrophysics. Because of very rapid developments, especially in the area of observational astrophysics, our view of the Universe has been substantially completed, challenged and altered. Solar Physics has very much been part of this progress. Developments in space and ground-based technology have virtually completely opened up the entire spectrum of solar electromagnetic and corpuscular radiations. Electromagnetic radiation of the sun can now be studied from gamma ray wavelengths shorter than 10-4 Å to radio wavelengths as long as 1014 Å, a range of approximately 60 octaves. Continuing improvements of spatial resolution of the Sun at all these wavelengths and concommitant development of our theoretical understanding of both the radiative and magneto-hydrodynamic processes on the Sun have made solar physics an exciting field to those interested in the Sun per se, as well as to those who view the Sun as a star whose study aids us in the understanding of astrophysics in a broader sense.A committee of The National Academy of Sciences in the United States under the chairmanship of J. L. Greenstein conducted between 1969 and 1971 a study of the needs of astronomy in the next decade. I took part in this study and it is probably because of this that I was asked to give this review on the next decade in observational solar physics. This review is therefore partly based on the results of the discussions in that committee and in its solar panel. Most of this review will reflect, however, my own opinions.

Solar energy outside the Earth's atmosphere

Extensive measurements have been made in different countries and by many research groups to determine the solar constant and the spectral distribution of solar energy. Earlier determinations were made from ground-based observations. The extrapolation to zero air mass under the highly variable conditions of the atmosphere led to large uncertainties in the proposed values. In recent years renewed interest in this topic has arisen due to the direct effect of solar radiation on thermal balance of spacecraft, electrical output of solar panels, and other satellite-related problems. Measurements of the solar constant have been made by total irradiance detectors from high altitude research aircraft, balloons, and space probes. Their data have produced converging evidence that the value of the solar constant commonly accepted in earlier years, 2·00 cal cm −2 min −1, was too high. Spectral irradiance measurements at high altitude were made using a variety of monochromators and filter radiometers. The results of all recent high altitude measurements have been critically examined by an ad hoc committee on “Solar Electromagnetic Radiation.” The committee has proposed standard values for engineering use for the solar constant and the solar spectrum. These values will be presented and also the reasons for recommending their acceptance. Detailed comparisons have been made between the revised spectral irradiance values and those which had been widely accepted in earlier years. New values have been computed for frequently-cited astrophysical quantities which are derived from the solar constant and the solar spectrum. The spectrum has been extended to 10A in the X-ray range and to 10 m in the microwave range. The revised value of the solar constant is 1·94 cal cm −2 min −1. The proposed standard solar spectrum shows significant differences from other curves throughout the spectral range.

The release of energetic particles from the Sun

A model is developed to account for the release of solar cosmic rays from the Sun. The solar atmosphere out to 3–5 solar radii above the photosphere is permeated with magnetic field lines which trap low rigidity (≲ 50 MV) flare particles. Plasma heated by the flare process disturbs the trapping field, and not until the disturbance reaches 3–5 solar radii can the low rigidity flare particles have access to interplanetary space. If the plasma is not heated sufficiently to overcome the coronal field, flare particles are trapped, efficiently. Subsequent leakage of these particles into interplanetary space forms corotating streams. Reference is made to satellite observations of solar electromagnetic radiation and charged particles.

Theory, Applications, and Results of the Long-Line Correlation Spectrometer

This paper considers the techniques of correlation spectroscopy as applied to the remote sensing of air-polluting gases SO2 and NO2. The occurrence of molecular absorption of solar and artificial electromagnetic radiation is used to determine the quantitative value of the gases over a long-line length. The paper will consider the instrument principles of operation, applications of a portable remote sensing system, and results for the long-line determinations of S02 and NO2 quantities. The system and application techniques presented here are in consideration of inimizing distorting and interfering factors that are inherently present in solar radiation. The remote sensing long-line system that is portable is significant to air-pollution monitoring, because it adds accurate quantitative dimension to the usual point sampling methods of measurement.

Solar extreme ultraviolet emissions in the range 260?1300 � observed from OSO-III

Solar electromagnetic radiation of wavelengths ranging from 260–1300 A was measured by a grazing-incidence grating spectrometer on OSO-III, which operated as a monochromator with a wavelength bandwidth of about 2 A and an acceptance angle covering the whole disk without any instrumental discrimination of source locations. The monochromator was commanded either to scan the whole spectrum or to operate at variously chosen fixed wavelengths. The latter mode of operation afforded a high-time resolution in the observation of temporal variations such as those associated with solar flares, and also allowed accurate determinations of the absorption characteristic of the earth's upper atmosphere (near sunset and sunrise).

The solar electromagnetic radiation environment

Observations of the spectral distribution of solar electromagnetic radiation have been made from wavelengths shorter than 1 Å (10 −8cm) to wavelengths longer than 100 m (10 4cm) by many different techniques, each of which is applicable over only a small part of the total range. Most of the energy emitted by the sun (98 per cent) lies between 3000 and 40,000 Å. A large fraction of the solar radiation falling between these wavelength limits manages to penetrate the Earth's atmosphere, so that it can be studied from ground level. By observing the amount of solar energy reaching the ground at many times during the day, an extrapolation can be made that gives a reasonably accurate value of the energy received at the top of the atmosphere—the solar constant. No radiation from the Sun at wavelengths below approximately 2900 Å has been detected at ground level, and very little radiation in the i.r. at wavelengths greater than 30–40,000 Å can come through the atmosphere. Therefore, observations in these spectral regions must be made from rockets or satellites. Balloons and certain aircraft can also be used to advantage, especially in the i.r. In addition to the usual difficulties involved in the carrying out of space experiments, there are those due to the lack of adequate laboratory standards and the variability of the Sun in the extreme u.v. and X-ray region. Nevertheless, the uncertainties in information about the spectral distribution of solar radiant flux are smaller than the departures from the solar irradiance curve of the flux from the best high energy solar simulators available.

Thermoluminescence of the Moon

Thermoluminescence is investigated as a possible cause of transient lunar events. Energy derived from earthshine, or from solar particle and electromagnetic radiation, could be stored in surface traps and released after sunrise to yield observable thermal glow. Glow curves are computed using the actual lunar heating rates applied to materials whose parameters describe the range of all solids. The glow intensities of some possible materials are found to exceed the scattered solar background up to several days after sunrise. Of ninety-seven recent events, one-third occurred in the first 24 hours after dawn. However, two observational effects increase the apparent frequency of dawn events so that the data neither support nor contradict the hypothesis of thermal glow. Other possible mechanisms for lunar glow, i.e. internal effects, photon-stimulated luminescence, and cryoluminescence, are briefly discussed. It is shown that the Aristarchus events were probably caused by internal effects.

Correlation of meteoroid environments in the solar system.

Meteoroid masses cannot be inferred from the observed decelerations of meteors in the Earth's atmosphere. Moreover, the effects of solar electromagnetic radiation on the smaller meteoroids cannot be related to their alone. The name mass concentration and symbol C* are proposed for the pertinent property, essentially the per unit projected area, g cm~. The radiation pressure limit may be designated as C* = 10~ without reference to density, porosity, or size. The name meteoroid perforation capability and symbol C are proposed for a similar property, directly measureable in space experiments, regardless of statistical variations in density and velocity. Meteor observations, space experiments, and hypervelocity impact data are analyzed in terms of C* and C, and a log-normal form for the mean cumulative flux of meteoroids at 1 a.u. is derived. The influences of heliocentric longitude and of unknown streams in the interplanetary environment are treated statistically for space missions to Venus and Mars.

Reviews

This handbook was written by over 60 scientists of the Air Force Cambridge Research Laboratory. It is intended to serve a broad spectrum of users: “the planner, designer, developer and operator of aerospace systems, scientists and science‐minded people who seek summary of space‐age environmental research.” It supersedes the Handbook of Geophysics (also written by AFCRL scientists and published in 1961) and contains much similar material that has now been considerably amplified. This new handbook contains 22 chapters geodesy and gravity; model atmospheres; atmospheric temperature, density, pressure, and moisture; winds; precipitation, clouds, and terosols; atmospheric composition; atmospheric optics; atmospheric electricity; some aspects of electromagnetic wave propagation; transmission and detection of infrared radiation; the geomagnetic field; ionospheric physics; airglow and aurorae; meteoritic phenomena the Sun; solar electromagnetic radiation; corpuscular radiation; interplanetary space and the solar atmosphere; the lunar environment; planetary environments; astrophysics and astronomy and radio astronomy. Some parts of geophysics, such as nuclear geology, oceanography, and seismology are not included.

Absolute intensity measurements in the extreme ultraviolet spectrum of solar radiation

Experimental results and problems of absolute intensity measurements of solar electromagnetic radiation in the extreme ultraviolet (EUV) and soft X-ray region of the spectrum (designated cumulatively as “XUV” for brevity) are reviewed. The numerous practical problems are divided in two major areas, (a) general problems of heterochromatic absolute XUV spectrophotometry in the laboratory and (b) specific problems characteristic of requirements of solar physics, the physics of planetary atmospheres, and existing restrictions of space technology. Within the first area (a) emphasis is placed on recent progress toward justified reliance on ionization detectors without necessary connection to source standards. For the second area (b), emphasis is placed on the immediate need to have existing exploratory observations followed by a new phase of more systematic experiments of increased accuracy.

Experimental determination of absolute intensities in the solar XUV spectrum

Experimental problems of absolute intensity measurements of solar electromagnetic radiation in the extreme ultra-violet (EUV) and soft X-ray region of the spectrum (designated cumulatively as “XUV” for brevity) are reviewed. From an evaluation of existing rocket and satellite data together with existing projects and goals of future observations from space vehicles, it is suggested that the numerous associated practical problems be devided into two major areas, namely (a) the general experimental art of heterochromatic absolute XUV spectrophotometry in the laboratory and (b) specific problems characteristic of the objectives of solar physics as well as existing restrictions of space technology. Within the first area (a) emphasis is placed on recent progress toward justified reliance on ionization detectors without necessary connection to source standards. For the second area (b), emphasis is placed on the immediate need to have existing exploratory observations followed by a new phase of more systematic experiments of increased accuracy.

Radiation and life in space.

Information and conjectures concerning conditions in space are summarized. The probability of life on other planets is considered, with emphasis on the effects of radiation on biological systems. Based on present knowledge, it is postulated that when man visits other planets of the solar system he may be confronted with primordial conditions on some planets, strange forms of life on others, and evidence of ancient life which has become extinct on others. It is pointed out that much may be learned in earthbound laboratories concerning the role of penetrating and solar electromagnetic radiation in the generation of biological materials, the mutation and evolution of the species, and the relative role of radiation as compared to chemical environment and temperature in evolution. (C.H.)

Solar Radio Emissions and Sunspots

THE ratio of the equivalent source temperatures as deduced from observations of solar electromagnetic radiation for frequencies of 80 Mc./s. and 175 Mc./s. (T80/T175) by Ryle and Vonberg1 would appear to have considerable significance to solar as well as radio physicists.