Showing papers on "Solar constant published in 1981"

Observations of solar irradiance variability.

Abstract: High-precision measurements of total solar irradiance, made by the active cavity radiometer irradiance monitor on the Solar Maximum Mission satellite, show the irradiance to have been variable throughout the first 153 days of observations. The corrected data resolve orbit-to-orbit variations with uncertainties as small as 0.001 percent. Irradiance fluctuations are typical of a band-limited noise spectrum with high-frequency cutoff near 0.15 day(-1) their amplitudes about the mean value of 1368.31 watts per square meter approach +/- 0.05 percent. Two large decreases in irrradiance of up to 0.2 percent lasting about 1 week are highly correlated with the development of sunspot groups. The magnitude and time scale of the irradiance variability suggest that considerable energy storage occurs within the convection zone in solar active regions.

The solar spectral irradiance 1200–3184 Å near solar maximum: July 15, 1980

Abstract: Full-disk solar spectral irradiances near solar maximum were obtained in the spectral range 1200–3184 A at a spectral resolution of approximately 1 A from rocket observations above White Sands Missile Range, New Mexico, on July 15, 1980. Comparison with measurements made in 1979 and during solar minimum confirms a large increase at solar maximum in the solar irradiance near 1200 A with no change within our measurement errors near 2000 A. Irradiances in the range 1900–2100 A are in excellent agreement with previous measurements, and those in the 2100- to 2500-A range are lower than the Broadfoot results. We find agreement with previous values 2600–2900 A and then fall below those values 2900–3184 A.

Solar Radiation and its Variation in Time

Abstract: In order to assess the variability of the solar radiation, the record of determinations of the total and spectral solar irradiance of the last 15 years is analysed. Although the datapoints for the period before 1969 suggest a slight decrease, the uncertainties of these determinations are too large to render this statement significant. Together with the results of the following period (1969–1980) which show that within the uncertainty no change is detectable, it can be concluded, that the solar constant has not changed during the last 15 years. The same result is found from the spectral distribution record, though not as conclusive as for the solar constant, due to the much larger uncertainties of the spectral data.

Solar wind electron densities from Viking dual-frequency radio measurements

Abstract: Simultaneous phase coherent, two-frequency measurements of the time delay between the earth station and the Viking spacecraft have been analyzed in terms of the electron density profiles from 4 solar radii to 200 solar radii. The measurements were made during a period of solar activity minimum (1976-1977) and show a strong solar latitude effect. The data were analyzed with both a model independent, direct numerical inversion technique and with model fitting, yielding essentially the same results. It is shown that the solar wind density can be represented by two power laws near the solar equator proportional to r exp -2.7 and r exp -2.04. However, the more rapidly falling term quickly disappears at moderate latitudes (approximately 20 deg) leaving only the inverse-square behavior.

Alternate approach to the analysis of solar photometer data.

Abstract: The standard technique of analyzing solar photometer data to determine atmospheric optical depth and the spectral solar constant is shown to inadvertently weight the data unequally. A new approach is proposed which equally weights all the data. Assuming that the deviations of the data points result from real random variations of optical depth during the period of the measurements, this latter approach is shown to yield more reliable results.

Variations of the Solar Constant

Abstract: The variations in data received from rocket-borne and balloon-borne instruments are discussed. Indirect techniques to measure and monitor the solar constant are presented. Emphasis is placed on the correlation of data from the Solar Maximum Mission and the Nimbus 7 satellites.

Solar Activity and Climate

Abstract: Solar activity cannot be disregarded as a possible external cause of the Little Ice Age and the 20th century climatic warming. Climatic responses to the 11- and 22-year solar cycles, although relatively weak are in evidence. Further (case-)studies of short-term influences of solar activity on the atmosphere may reveal the physical nature of these statistical sun-climate relationships. Suggested mechanisms have not been tested quantitatively in numerical models of the atmosphere, with the exception of the possible variation of the solar constant.

Evolutionary variations of solar luminosity

Abstract: The Theoretical arguments for a 30% increase in the solar luminosity over the past 4.7 billion years are reviewed. A scaling argument shows that this increase can be predicted without detailed numerical calculations. The magnitude of the increase is independent of nuclear reaction rates, as long as conversion of hydrogen to helium provides the basic energy source of the Sun. The effect of the solar luminosity increase on the terrestrial climate is briefly considered. It appears unlikely that an enhanced greenhouse effect, due to reduced gases (NH3, CH4), can account for the long-term paleoclimatic trends.

Prelude to solar energy: Pouillet, Herschel, Forbes and the solar constant

Abstract: Summary Inspired by early-nineteenth-century discoveries about heat transfer, the French physicist Claude Pouillet measured the influx of solar radiation at the earth and, in 1838, asked what these observations revealed about the temperature of the sun and of space itself. At about the same time, the British natural philosophers John Herschel and J. D. Forbes made similar measurements in order to better understand the sun's influence on climate. This paper tells how and why Pouillet, Herschel and Forbes made the first estimates of the solar constant, estimates which would acquire new importance with the discovery of the laws of thermodynamics by the mid century.

The effects of surface evaporation parameterizations on climate sensitivity to solar constant variations

Abstract: The effects of two different evaporation parameterizations on the sensitivity of simulated climate to solar constant variations are investigated by using a zonally averaged climate model. One parameterization is a nonlinear formulation in which the evaporation is nonlinearly proportional to the sensible heat flux, with the Bowen ratio determined by the predicted vertical temperature and humidity gradients near the earth's surface (model A). The other is the formulation of Saltzman (1968) with the evaporation linearly proportional to the sensible heat flux (model B). The computed climates of models A and B are in good agreement except for the energy partition between sensible and latent heat at the earth's surface. The difference in evaporation parameterizations causes a difference in the response of temperature lapse rate to solar constant variations and a difference in the sensitivity of longwave radiation to surface temperature which leads to a smaller sensitivity of surface temperature to solar constant variations in model A than in model B. The results of model A are qualitatively in agreement with those of the general circulation model calculations of Wetherald and Manabe (1975).

Sunspots and solar variability

Abstract: The analyses of Willson et al. (1981) and Hudson et al. (1981) are extended in correlating the total solar irradiance monitor (ACRIM) data with the routine synoptic sunspot data. At the simplest level, this correlation reveals clearly that the so-called 'missing flux' is truly missing in the sense that large young active regions do produce at net diminution of the irradiance when their spots cross the central meridian. It is pointed out that the irradiance deficit must of course be made up, either promptly or on intermediate time scales; this is because the surface effects cannot perturb the energy generation processes in the interior. In the approach taken here, simple models of the reemission are constructed, the total reemission is scaled to the estimated sunspot deficit, and an attempt is made to measure the parameters of the models by a statistical comparison with ACRIM data.

Solar variability indications from Nimbus 7 satellite data

Abstract: The cavity pyrheliometer sensor of the Nimbus 7 Earth Radiation Experiment indicated low-level variability of the total solar irradiance. The variability appears to be inversely correlated with common solar activity indicators in an event sense. the limitations of the measuring system and available data sets are described.

Finite bandwidth and scattered light effects on the radiometric determination of atmospheric turbidity and the solar constant.

Abstract: Multispectral solar radiometric measurements are routinely performed at a large number of sites, using equipment of varying degrees of sophistication. From the standard Langley plot technique, one may extract the total optical thickness of the atmosphere (and hence the aerosol component) plus the extraterrestrial solar flux. With increasing concern about possible climatic effects of increased turbidity, or changes in the solar constant, it is becoming more important to know the expected accuracy of these results. In this paper, we analytically examine the effects of finite filter bandwidth (in the absence of spectral lines) and find them to be less than one part in a thousand. This is compared with our earlier results on the effects of scattered light, which turns out to be typically an order of magnitude larger.

Thermal perturbation of the Sun

Abstract: An investigation of thermal perturbations of the solar convective zone via changes in the mixing length parameter were carried out, with a view toward understanding the possible solar radius and luminosity changes cited in the literature. The results show that: (a) a single perturbation of alpha is probably not the cause of the solar radius change and (b) the parameter W = d lambda nR./d lambda nL. can not be characterized by a single value, as implied in recent work.

The variability of the solar output

Abstract: A review of solar constant determinations and measurements of its spectral distribution is presented For the period from 1966 to 1980 a mean value of 1367 Wm-2 was determined Within the corresponding uncertainty, no significant change of both the integral value and the spectral distribution can be detected However, short term solar variations and their spectral dependence were deduced from measurements during four hours on June 20, 1980 from 34 km altitude with amplitudes of + or - 500 ppm at 368 nm, of 200 ppm at 500 nm and + or - 150 ppm at 778 nm Comparison with simultaneous total irradiance data of the Solar Maximum Mission (SMM) shows a high correlation which indicates the solar origin The power spectrum shows a weak peak at about 32 mHz, which corresponds to the frequency of the 5 minutes solar oscillation

Review of ground-based measurements

Abstract: Early measurements of the solar constant are described and discussed with particular emphasis on the Smithsonian program A brief description is given of the monitoring program currently operating at San Diego State

A summary of results from solar monitoring rocket flights

Abstract: Three rocket flights to measure the solar constant and provide calibration data for sensors aboard Nimbus 6, 7, and Solar Maximum Mission (SMM) spacecraft were accomplished. The values obtained by the rocket instruments for the solar constant in SI units are: 1367 w/sq m on 29 June 1976; 1372 w/sq m on 16 November 1978; and 1374 w/sq m on 22 May 1980. The uncertainty of the rocket measurements is + or - 0.5%. The values obtained by the Hickey-Frieden sensor on Nimbus 7 during the second and third flights was 1376 w/sq m. The value obtained by the Active Cavity Radiometer Model IV (ACR IV) on SMM during the flight was 1368 w/sq m.

Study of the response of stratospheric ozone to perturbations in the solar constant and solar UV flux

Abstract: A one-dimensional radiative-convective photochemical model has been used to examine the response of stratospheric and total ozone to perturbations in the solar flux. The model considers a detailed chemical reaction mechanism; vertical transport is parameterized through eddy diffusion coefficients. The temperature profile is calculated using a radiative transfer model for both time-dependent and steady-state cases. Results are discussed for the following types of perturbations: a 5% increase in the solar UV flux in the wavelength range 175-300 nm, a 5% increase in the solar constant, and an annual 6.6% variation in the solar constant associated with the variation in the earth-sun distance.

Measurement of the solar constant

Abstract: The absolute value of the solar constant and the long term variations that exist in the absolute value of the solar constant were measured. The solar constant is the total irradiance of the Sun at a distance of one astronomical unit. An absolute radiometer removed from the effects of the atmosphere with its calibration tested in situ was used to measure the solar constant. The importance of an accurate knowledge of the solar constant is emphasized.

Estimating short-term solar variations by a simple envelope matching technique

Abstract: A simple matching technique is explained which allows the computation of the response of the solar surface to perturbations which occur at any depth within the convective envelope of the Sun. This technique was applied to a perturbation of the convective efficiency (alpha-mechanism), and of the non-gas component of the pressure (beta-mechanism) in different regions of the convection zone. The results indicate that either perturbation affects the solar luminosity. However, the alpha-mechanism has little effect in the solar radius, regardless of the location of the perturbed region, whereas the beta-mechanism produces radius changes that become quite large if the location of the perturbed region is deep within the solar convection zone.

Variation of the Solar He I 10830 A Line: 1977 - 1980

Abstract: Daily measurements of the equivalent width of the 10830 A He I line integrated over the visible disk show: (1) an increase from about 32 to about 74 mA in the monthly mean values from the minimum to the maximum of the current solar cycle; (2) the monthly mean values are more smoothly varying than most other indices of solar activity; (3) rotation modulates the daily values in a highly variable manner with amplitudes as large as plus or minus 20%; (4) the apparent synodic rotation period is 29 days rather than the expected 27 days associated with active regions; (5) despite great differences in the appearance of the sun in 3933 A Ca I and 10830 A He I, the central intensity of the former correlates with the equivalent width of the latter with a value r = 0.97.

Change in the solar constant between 1968 and 1978

Abstract: Solar irradiance measurements made from a balloon on January 27, 1978 and February 10, 1980 show a change of 0.4% over similar measurements made in 1968. This change is greater than the uncertainty of the measurement and is felt to be the result of a change in the solar constant.

1 – characteristics of solar radiation

Abstract: Publisher Summary This chapter discusses the characteristics of solar radiation. The earth receives from the sun approximately 5.4 × 1024 J per year. This is equivalent to about 30,000 times the energy used in the world at present. The most important parameter in solar radiation measurement is the energy received outside the earth's atmosphere called the solar constant. It is defined as the energy received from the sun on a unit area exposed normally to the sun's rays at the average sun–earth distance in the absence of the earth's atmosphere. The variability of solar energy incident on a collector surface on the ground is considerably greater than that of the extraterrestrial solar energy. On a clear sunny day, the energy increases from zero at sunrise to a maximum at solar noon and decreases to zero at sunset. At any moment, clouds may cover the sun and decrease the energy because of diffuse radiation.

Radiation balances and the solar constant

Abstract: The radiometric concepts are defined in order to consider various types of radiation balances and relate them to the diabetic form of the energy balance. Variability in space and time of the components of the radiation field are presented. A specific concept for sweeping which is tailored to the requirements is proposed. Finally, after establishing the truncated character of the present knowledge of the radiation balance. The results of the last observations of the solar constant are given. Ground and satellite measurement techniques are discussed.

Indirect methods for measuring variations of the solar constant

Abstract: The difference between the methods that measure delta S, and those that measure variations in the solar luminosity, delta L, is discussed. It is shown that the past practice of simply relating delta S to delta L by geometrical arguments is not valid because of anisotropy of the solar radiation. It is concluded that direct techniques prove the existence of short term variability that is fully explainable in terms of the passage of active regions (spots and faculae) on the face of the Sun. The obervations of changes in the solar diameter support the existence of structurally induced variations of the solar luminosity on timescales of tens of years, which are significant in the understanding of climatic variations.