Showing papers on "Solar constant published in 1983"

The solar absolute spectral irradiance 1150-3173 A - May 17, 1982

Abstract: The full-disk solar spectral irradiance in the spectral range 1150-3173 A was obtained from a rocket observation above White Sands Missile Range, NM, on May 17, 1982, half way in time between solar maximum and solar minimum. Comparison with measurements made during solar maximum in 1980 indicate a large decrease in the absolute solar irradiance at wavelengths below 1900 A to approximately solar minimum values. No change above 1900 A from solar maximum to this flight was observed to within the errors of the measurements. Irradiance values lower than the Broadfoot results in the 2100-2500 A spectral range are found, but excellent agreement with Broadfoot between 2500 and 3173 A is found. The absolute calibration of the instruments for this flight was accomplished at the National Bureau of Standards Synchrotron Radiation Facility which significantly improves calibration of solar measurements made in this spectral region.

Solar oscillations observed in the total irradiance

Abstract: The total solar irradiance measurements obtained by the active-cavity radiometer on board the Solar Maximum Mission have been analyzed for evidence of global oscillations. We find that the most energetic low-degree p-mode oscillations in the five-minute band have amplitudes of a few parts per million of the total irradiance, and we positively detect modes with l = 0, 1, and 2. The distribution in l differs from that of the velocity spectrum, with relatively more power at lower l values. The individual modes have narrow line widths, corresponding to values of Q greater than a few thousand, or lifetimes of at least a week. We do not detect the 160-min oscillation in the power spectrum, and place an upper limit of 5 parts per million (99.9% confidence) on its amplitude.

Solar irradiance variations: 2. Analysis of the extreme ultraviolet measurements onboard the Atmosphere Explorer E satellite

Abstract: Five of the extreme ultraviolet channels (L-alpha, L-beta, He I, He II, Fe XV) measuring irradiance fluctuations on board the AE-E satellite between 1977 and 1980 have been studied in detail. It is shown that the daily variations correspond very closely to the daily variations in solar radio emission (F10.7), but that the UV data are afflicted with serious and to date unrecognized calibration changes during the period of operation of the instruments. In order to correct for these changes, a statistical analysis is carried out, and a set of corrections to the raw data is suggested. The resulting, now uniform, data are then compared with rocket measurements (L-alpha) and data acquired onboard the AE-C satellite (L-beta). Finally the remaining discrepancies are discussed. After concluding that they are below the overall level of uncertainties, a first-order 10-year run of EUV irradiances derived from F10.7 data is proposed. This estimate includes the ratio of irradiance levels between the maxima of solar cycles 20 and 21 and the intervening minimum.

Data on total and spectral solar irradiance

Abstract: This paper presents a brief survey of the data available on solar constant and extraterrestrial solar spectral irradiance. The spectral distribution of solar radiation at ground surface, computed from extraterrestrial solar spectral irradiance for several air mass values and for four levels of atmospheric pollution, is also presented. The total irradiance at ground level is obtained by integration of the area under the spectral irradiance curves. It is significant that, as air mass increases or as turbidity increases, the amount of energy in the infrared relative to the total increases and that the energy in the UV and visible decreases.

Solar Luminosity Variations

Abstract: The most interesting result in solar luminosity studies in teh ast decade has been the detection of significant variations in the total irradiance by precision radiometers on teh the NIMBUS-7 and SMM spacecraft. A substantial fraction of the observed variation can be attributed to sunspot blocking. Thermanl storage models indicate that the blocked flux can be stored in a slight increase of the thermal and potential energy of the cinvective zone. The thermal storage time is likely to far exceed one solar activity cycle, implying an a11-year modualtion of the solar constant at a level of about 0.1%. Direct observations of teh 11-year or longer variantions are more difficult but there is some evidence for secular trends below about 0.4% amplitude over the 14-year period of modern sampling. Ongoing photometric programs suggest that luminosity changes exceeding 1% may have been detected in yound, chromospherically active stars.

Upper limits on the total radiant energy of solar flares

Abstract: We establish limits on the total radiant energy of solar flares during the period 1980 February – November, using the solar-constant monitor (ACRIM) on board the Solar Maximum Mission. Typical limits amount to 6 × 1029 erg/s for a 32-second integration time, with 5σ statistical significance, for an impulsive emission; for a gradual component, about 4 × 1032 ergs total radiant energy. The limits lie about an order of magnitude higher than the total radiant energy estimated from the various known emission components, suggesting that no heretofore unknown dominant component of flare radiation exists.

Solar Variability, Weather, and Climate

Abstract: Solar Variability, Weather, and Climate reassesses the question of solar variability and its effects on weather and climate, taking into account new measurements and more recent theories of the earth's atmosphere. The papers, which make up this book, were presented at an American Geophysical Union meeting in December 1978. Besides a review of the current basic knowledge on the topic, fundamental questions requiring additional research form the basis of the conclusions and recommendations. Eight papers, five stating the background and three the possible mechanisms, comprise the book. Solar, weather, and climate variability and evidence of the effect of solar variations on the atmosphere are reviewed. Solar variability is recognized to exist at different time scales (from minutes to decades), and these variations cover a broad range of the spectral irradiance (from X rays and extreme ultraviolet to the centimeter wavelengths). Regarding total luminosity, the parts of the solar constant that are known to vary constitute less than 1% of the total budget of energy that the earth receives from the sun and is far less than the total energy required to force direct changes in atmospheric circulation. Moreover, the variable portions of the solar output are mainly absorbed or dissipated in the upper atmosphere. Thus, for known solar changes to perturb the dynamics of the troposphere they must work through mechanisms that are complex and indirect. A number of such possible dynamic, radiative, chemical, and electrical couplings of solar inputs through various regions of the atmosphere are discussed in chapters 6, 7, and 8.

Data on total and spectral solar irradiance: comments

Abstract: This Letter is in response to a paper by Mecherikunnel et al. In recent years our knowledge of the solar constant has significantly increased, and modern values are, although referenced, completely ignored by the authors of the above article. The best value today is between 1366 and 1368 W m 2 (Refs. 2 and 3) and not 1353 W m 2 . The latter is based on the mean of measurements from airplanes, which we know are not very reliable, mainly due to the uncertainty of the atmospheric and window transmissions. Furthermore, the radiometric scale used is off by more than 1%. As to the spectral irradiance, the ignorance of the authors is even more striking, and it is difficult to understand why this article appeared in a reputable journal such as Applied Optics. Since the data were published by Thekaekara about ten years ago, they are questioned for several reasons: inconsistency of the different data sets used to produce the final results; the correction methods adopted; calibration standards and procedures used. Even at that time it was obvious, by comparison with the Labs and Neckel data, that systematic errors must have influenced the Thekaekara spectrum. Some can be explained by the use of NBS irradiance standards, the calibration of which was at that time off by a few percent. Due to the fact that Labs and Neckel measured the radiance at the center of the solar disk and used published limb darkening data to deduce the irradiance at 1 astronomical unit, the reliability of data could obviously be questioned. However, in the meantime this drawback of the data set has been eliminated (Neckel and Labs), and it is demonstrated that the differences between the old and new spectra are small. Even before the publication of Ref. 8 and after application of the corrections in Ref. 9, independent determinations by Shaw and Fröhlich showed good agreement with the data of Ref. 8. Fröhlich and Wehrli also find evidence that the revised Neckel and Labs spectrum is an improvement over the former version and the absolute uncertainty is now 1-2% (Ref. 2) (Fig. 1). This latter statement is supported further by the most recent limb darkening data gathered by Neckel and Labs at Kitt Peak with the same spectrometer as used at Jungfraujoch in the 1960s for determination of the center radiance. Another indication of the quality of this spectrum is that the integral over the Neckel and Labs spectrum yields a value in very close agreement (within 0.2%) with the most modern determinations of the solar constant.

The nature of the short period fluctuations in solar irradiance received by the earth

Abstract: An analysis of the periodicities found in the Nimbus-7 satellite measurements of solar irradiance (Solar Constant) indicates variations on three scales. Two of these variations are shown to be related to variations in solar activity as given by various indicators of solar photosphere disturbances. The high frequency periodicity is due to the solar rotation period. The second periodicity is based on the integral effect of the high frequency oscillation over an 11 year solar cycle. The third variation (secular trend) is discussed in regard to the high precision cavity data and the recent record of high altitude solar constant measurements.

Solar irradiance modulation by active regions from 1969 through 1981

Abstract: Recent satellite measurements of the solar total irradiance (S) indicate that on time scales of days to months the solar constant varies by a few tenths of a percent. The predominant part of these variations can be explained by blocking of the upward solar flux by sunspots. The observations are consistent with current theoretical models of energy storage in which the energy blocked by the sunspots is temporarily stored in the convective zone. We present modelled solar constant variations on a day by day basis selected from model calculations for the period 1874 through 1981 (Hoyt and Eddy, 1982). Because neither faculae nor bright rings about sunspots balance the net blocking by sunspots, there is a net eleven year modulation in irradiance with a relative depression of as much as 0.07% for the period 1969-1981. The model is compared with satellite observations and to other recently published models that impose immediate reradiation of blocked flux and therefore fail to predict an eleven year modulation of S.

The solar constant and its spectral distribution

Abstract: This chapter discusses the physics of the sun, the nature of the radiant energy emanating from its surface, spectral distribution, and the total quantity of that energy arriving just outside the earth's atmosphere. The sun is the star closest to the earth, and its radiant energy is practically the only source of energy that influences atmospheric motions and our climate. The sun is a completely gaseous body composed mainly of hydrogen. The spectral distribution of radiation arriving on the surface of the earth is indeed a function of its extraterrestrial distribution and the atmospheric constituents. The solar constant is the rate of total solar energy at all wavelengths incident on a unit area, exposed normally to rays of the sun at one astronomical unit. The temperature of the sun is calculated from two types of information: the solar constant and its spectral distribution. The chapter describes more recent values of the solar constant and its spectral distribution.

The nature of the short period fluctuations in solar irradiance received by the earth

Abstract: An analysis of the periodicities found in the Nimbus-7 satellite measurements of solar irradiance (Solar Constant) indicates variations on three scales. Two of these variations are shown to be related to variations in solar activity as given by various indicators of solar photosphere disturbances. The high frequency periodicity is due to the solar rotation period. The second periodicity is based on the integral effect of the high frequency oscillation over an 11 year solar cycle. The third variation (secular trend) is discussed in regard to the high precision cavity data and the recent record of high altitude solar constant measurements.

The solar constant and climate

Abstract: As has been shown by observations from the Nimbus-7 and SMM satellites, the non-periodic, comparatively rapid decreases of the solar constant (to 0.25%) are mainly determined by the size and location of groups of sunspots passing through the Sun's central meridian. Variations of a quarter per cent are a rare enough occasion (occurring approximately once every two years). In the majority of cases, drops to 0.1% are noted. The question of long-period (11-, 22-, and 80–90-year) variations of the astronomical solar constant (ASC) is still open to speculation. The four-year series of observations on Nimbus-7 indicates very definitely the presence of a maximum in smoothed ASC values in January of 1979, and the following permanent decrease in 1980–82 with the varying rate up to 0.05% annual. The compiled by the authors temporal series of the ASC variability for the 1925–1980 period has been confirmed, in our opinion, experimentally. Obviously, the long-period variations must be associated not with the development of active areas, but with temperature changes in the non-perturbed photosphere. It is supposed that the temperature gradient variation in the photosphere in the 11-year cycle leads to the redistribution of radiation from various photospheric levels. As a result, the ASC varies quasi-periodically both within the cycle, and from one cycle to another. Since the phase variation of the ASC has been noted in some cycles (e.g., cycle No. 16), the existence of a component of another periodicity can be supposed. Solar activity variations are relevant to different kinds of solar radiation: from cosmic and X-rays to radiofrequency radiation. The combined influence of these emissions on the atmosphere apparently leads to a several times enhancement of small ASC variations (drops), probably by a factor of ten. The ‘enhancement’ of the solar radiation variation can be detected in the so-called meteorological solar constant (MSC). Analysis of experimental data has shown that at tropospheric levels the cyclic MSC variations can reach 4% (cycle No. 19). It should be noted that in the mid-latitude belt of the northern hemisphere the MSC changes occur in phase with the variation of the intensity of galactic cosmic rays. The 22-year component in the ASC is considerably weaker than the 11-year component.

Climatic response to a time varying solar constant

Abstract: Recent measurements of the solar constant, theoretical arguments, and climatic measurements combined with signal processing suggest the possibility that the solar constant varies significantly on time scales ranging from billions of years to 11-yr (sunspot) cycles, and even to scales of a few weeks Simple climate models with a time varying solar constant are examined here, with emphasis on the heat balance models (North et al, 1981) Linear heat balance model results are presented for high (10 cycles/yr) and low (01 cycle/yr) frequencies, providing a useful guide in estimating the direct heat response to solar variability

Sunspot cycle and associated variation of the solar spectral irradiance

Abstract: Precise monitoring of the solar absorption-line spectrum in the period 1976–80 has revealed systematic changes of the strength of photospheric lines during the ascending part of the current solar cycle1. The most likely cause is a slight cooling of the lower photosphere and a concomitant heating of higher layers. The total energy radiated into space thereby remains unchanged, in accordance with high-precision radiometry2 covering the same period. Nevertheless, a flattening of the photospheric temperature gradient will be accompanied by a redistribution of energy in the solar spectrum. Its magnitude is predicted here using stellar model-atmosphere techniques. This ‘change of colour’ is characterized by a 0.2% decrease of the irradiance in the blue, and an increase of the same order in the red and near IR. In this way solar activity may modulate terrestrial climate even in the absence of perceptible changes of the solar constant.

Chapter 2 – solar radiation

Abstract: Publisher Summary This chapter provides an overview on solar radiation. The availability of solar energy in any location in the world can be studied by two methods. The first involves measurements from a radiation monitoring network and the second is based on the use of physical formulae and constants. Solar constant is a term used to define the rate at which solar radiation is received outside the earth's atmosphere, at the earth's mean distance from the sun, by a unit surface perpendicular to the solar beam. The spectral distribution of direct solar radiation is altered as it passes through the atmosphere by absorption and scattering. The amount of energy absorbed depends on the length of path in which the solar beam traverses. A common method of describing relative energy levels is the air mass, which is the ratio of the actual length the solar beam traverses relative to the depth of the atmosphere with the sun in its zenith position. The chapter also highlights the data from a radiation measurement network. It is difficult to obtain reliable solar radiation data. The most reliable data is associated with the main meteorological stations, but these are often widely dispersed and a considerable distance from the location of any potential application.

Helioseismology in the future

Abstract: We review the observables of helioseismology that can contribute to our knowledge of the physical conditions in the solar interior. We discuss the limitations which presently prevent helioseismology from reaching its ultimate goal. We finally present a list of projects which either are already underway or that are planned for the near future, and we conclude by showing the crucial role that space observations may play in the future.

Radiometry - The data

Abstract: This chapter presents a summary of many of the important advances in the art and science of the use of solar radiation measurements. Emphasis is placed on those advances which will have the most impact in the utilization of solar energy. The work cited is mainly that done since 1977. The literature includes more comprehensive texts on solar radiation measurement,1-3 a bibliography,4 and a previous review of this field.5

A Summary of the Joint Discussion at Patras on Solar Luminosity Variations

Abstract: The most interesting result in solar luminosity studies in the past decade has been the detection of significant variations in the total irradiance by precision radiometers on the NIMBUS-7 and SMM spacecraft. A substantial fraction of the observed variation can be attributed to sunspot blocking. Thermal storage models indicate that the blocked flux can be stored in a slight increase of the thermal and potential energy of the convective zone. The thermal storage time is likely to far exceed one solar activity cycle, implying an 11-year modulation of the solar constant at a level of about 0.1%. Direct observations of the 11-year or longer variations are more difficult but there is some evidence for secular trends below about 0.4% amplitude over the 14-year period of modern sampling. Ongoing stellar photometric programs suggest that luminosity changes exceeding 1% may have been detected in young, chromospherically active stars. H. S. Hudson (University of California, San Diego) reviewed observations of short-term solar irradiance variations from spacecraft, commenting principally on the precision measurements of the solar constant (S) made by the Active Cavity Radiometer (ACRIM) on the Solar Maximum Mission (SMM) spacecraft (Willson et al., 1981).