Showing papers on "Solar constant published in 1987"

A study of the radiative effects of enhanced atmospheric CO2 and CH4 on early Earth surface temperatures

Abstract: Large concentrations of atmospheric CO2 in the atmosphere of the early earth have been proposed as a possible explanation of the apparent absence of frozen earth in spite of a faint early sun. However, the most thorough treatments of this question, by Owen et al. (1979) and Kasting et al. (1984), apparently disagree as to the warming effects of large amounts of CO2. We recalculate the evolution of surface temperature over the last 4.25 billion year time period, using the same scenario for CO2 partial pressures and solar constant as employed by the previous authors. We find good agreement with Kasting et al. (1984) and also explain why the results of Owen et al. are at variance with our findings and those of Kasting et al. Using the concept of direct radiative forcing, we present analytic relations between the solar luminosity and CO2 mixing ratio required to maintain the troposphere close to its present thermal structure. As a by-product, we present new broadband parameterizations for the 961 and 1064 cm−1 CO2 bands that can be used in climate models. We also consider the direct radiative forcing of large amounts of CH4, or changes in model clouds, and discuss how these might reduce the CO2 mixing ratio required to balance the faint early sun.

Ultraviolet solar irradiance measurement from 200 to 358 NM during Spacelab 1 mission

Abstract: The paper presents the results obtained from the UV-spectrometer of the ‘Solar Spectrum Experiment’ during the Spacelab 1 mission in December 1983. The irradiance data concern 492 passbands, which are located between 200 and 358 nm at almost equidistant wavelengths separated by about 0.3 nm. The passbands have a well-defined, bell-shaped profile with a full width at half maximum of about 1.3 nm. The data, which have an error budget between 4 and 5%, agree closely with the spectral distributions observed by Heath (1980) and Mentall et al. (1981) and confirm that the solar irradiance and the fluxes of Sun-like stars show about the same spectral distribution down to at least 240 nm.

Variability of the solar “constant” on time scales of minutes to years

Abstract: Solar irradiance variability has been studied from measurements of total solar irradiance at 1 AU, the solar ''constant'' S/sub 0/, since the late 1960s. Power spectra of time series from satellite and balloon experiments show that the irradiance varies, with periods of minutes to several hours and with amplitudes of parts per million to a few hundreths of a percent. Part of this variance is due to coherent pressure and, possibly, gravity oscillations as spherical harmonics of the sun. On time scales of days to months most of the variance is a modulation of the solar irradiance by photospheric features related to solar activity and reaches amplitudes of a few tenths of a pecent. Because of its origin the variance in this range changes by up to 1 order of magnitude with the solar cycle, as shown by comparison of the power spectra from 1980 and 1984/1985, respectively. The first evidence of a persistent long-term change comes from satellite data, which show a downward trend of S/sub 0/ since 1980 by about 0.02% per year. The S/sub 0/ determinations between 1967 and 1970, compared with the modern ones show a statistically significant increase during that period of similar magnitude. Bothmore » trends together could be part of a 22-year cycle related to the magnetic cycle of the sun. copyright American Geophysical Union 1987« less

Variations of solar irradiance due to magnetic activity.

Abstract: Variations in the Sun's luminosity have become, almost overnight, an active and productive field of astrophysics. There is now a nearly unbroken time series of precise data, from two separate satellites, beginning in late 1978 and running to the time of this writing. The study of these solar variations has jumped to a level of activity that might be expected in any field suddenly presented with a three-decade improvement in data quality. This improvement has been created largely by Willson's (90-93) Active Cavity Irradiance Monitor (ACRIM) on the Solar Maximum Mission (SMM). This was the first satellite to have been repaired in space by a manned mission; the repair was tremendously important for the study of solar variability. The variations so far seen have been as large as approximately 0.4% over a time scale of a week. The irradiance has also exhibited a steady decline since 1980 of the order of 0.02% per year. A review of temporal variations is given by Frohlich (3 1 a). In this review, we concentrate on solar luminosity variability due to magnetic activity. The precision of the ACRIM while operating in its normal mode approached 1 0 ppm of the mean solar irradiance, when averaged over a day. At this level of precision, the Sun's output is almost always changing. Another experiment, the Earth Radiation Budget (ERB) on the Nimbus-7 satellite, has produced an even longer record of solar variability measurements, though with less precision (35). The data from the two spacecraft have revolutionized the field within the past six or seven years.

Multiperiodic Irradiance Changes Caused by R-Modes and G-Modes

Abstract: More than 20 real periodicities ranging from 20 days to 2 years modulate the solar irradiance data accumulated since November 1978 by Nimbus 7. Many are quite strong during the first three years (solar maximum) and weak after that. There is a high correspondence between periods in irradiance and 28 periods predicted from the rotation and beating of global solar oscillations (r-modes and g-modes). Angular states l = 1, 2, and 3 are detected as well as some unresolved r-mode power at higher l. The prominence of beat periods implies a nonlinear system whose effective nonlinear power was measured to be about 2. This analysis constitutes a detection of r-modes in the sun, and determines from them a mean sidereal rotation rate for the convective envelope of 459 + or - 4 nHz which converts to a period of 25.2 days (27.1d, synodic).

Physical interpretation of variations in total solar irradiance

Abstract: Radiometry from the Solar Maximum Mission and Nimbus 7 satellites has demonstrated that the solar constant varies at a peak-to-peak level of up to 0.2 percent on time scales of weeks. The rotation and evolution of dark spots and bright faculae across the sun's disk accounts for most of that variation. Reasonable explanations have been put forward to explain how the spot-blocked heat flow might be stored, and to explain the source of the intense radiation that gives rise to the increased irradiance produced by the bright magnetic faculae. Time-dependent models of the response of the solar convection zone to small perturbations also indicate that slower variations in total solar irradiance of comparable magnitude are likely. More precise observations of the total solar irradiance and radius over long time scales are required to demonstrate the existence of such climatologically relevant changes, and to test models that would enable the interpretation and prediction of these changes.

On radiative effects of anthropogenic aerosol components in Arctic haze and snow

Abstract: The Arctic aerosol is strongly enriched by anthropogenic pollution which may cause significant modifications of the Arctic climate. A radiation model with an optically interactive snow surface layer is developed to investigate the effect of anthropogenic elemental carbon (EC) and sulphuric acid in the Arctic atmosphere. The model, based on the delta-Eddington method, has 490 wavelength intervals covering solar and terrestrial radiation domains. Computations were made for aerosols-containing natural components and cases contaminated by anthropogenic EC and sulphuric acid, both categories with dry and moist conditions. Comparisons of model results with measurements in the Arctic of direct and total irradiance agree well. During mid-spring averaged conditions, the increase in the daily mean solar warming is found to be 2 or 3 times lower than earlier estimates. The previously expected surface cooling can be offset by direct to diffuse conversion in the haze and by snow contamination. In the infrared, the haze located in a temperature inversion can increase the upwelling irradiance by about 1%. This earth-atmosphere column cooling is caused by deliquescent aerosol material. In contrast, hygroscopic but non-deliquescent compounds like sulphuric acid result in internal exchange of radiative energy. In haze layers, the local cooling rate nearly offsets the daily averaged mid-spring local solar heating rate. More significant net warming due to EC particles takes place in dry and optically thin aerosol layers typically found above the Arctic boundary layer during pollution episodes. DOI: 10.1111/j.1600-0889.1987.tb00101.x

Active region influences upon the solar constant.

Abstract: The influence that active regions have upon the solar constant is discussed. Sunspots appear to lower the solar constant for the few days in which they are located near central meridian. This raises the possibility that an 11-year, solar-cycle-related depression in the solar constant may occur. Recent findings concerning the physics of active regions suggest that sunspots and faculae are largely surface features. Within that surface faculae reradiate, within a few weeks, the 'missing energy' associated with sunspots. This is consistent with the observations showing that the solar constant does not have an 11-year cycle-related depression that some authors predicted. However, there is a secular variation in the solar constant, whose explanation is not completely understood.

Variation of the solar constant during 1983 and 1984

Abstract: Measurements of the Nimbus-7/ERB and SMM/ACRIM radiometers indicated several dips in the total solar irradiance in 1983 and in the first part of 1984. The dips in 1983, which should have a real solar origin, were selected according to the peaks of the projected areas of the active sunspot groups above the 2σ error limit of their data set. In the first part of 1984 the sunspot activity was strong and few irradiance dips with relatively large amplitudes were observed. In the second part of 1984 the sunspot activity disappeared and at that time the solar constant only fluctuated around its mean.

Absorption of short-wave radiation in the atmosphere over India in winter

Abstract: Considering the importance of radiation studies for the World Climate Programme (WCP) of WMO, a climatic study of warming/cooling of the atmospheric column by solar and terrestrial radiations over India in different seasons has been undertaken. In this paper the absorption in the atmosphere of direct short-wave radiation from the sun and diffuse short-wave radiation from the earth in the month of January (over India) is presented. It shows that only about 25 percent of the incident direct solar radiation, viz., solar constant (Approx. 1360 W/ m2), is absorbed in the atmosphere (345 W/m2) and up to 500mb absorption is just about 1 percent of the amount at the top of the atmosphere. Between 500 and 850mb the absorption is about 26 per cent of it, but between 850mb and the surface it is 34 per cent. Thus, the lowest - half of the atmosphere (below 500mb) absorbs almost 60 per cent of the absorbed part of total short-wave radiation in the atmosphere and of this the major portion is absorbed in the lowest 1500 metres.

Wave motions in the middle atmosphere and relation to the solar activity

Abstract: Periodograms of time series of the 30 mb geopotential heights at 60°N and sunspot numbers for different winter seasons were analysed Amplitudes and the phase differences of the solar and atmospheric oscillations with the 27-28 day period testify in favour of the solar nature of the source of these waves in the atmosphere Significant results subject to clear interpretation have been obtained only for a limited number of winters, and there are periods when the 27 day oscillations are absent both in the sunspot members and in the atmospheric parameters

Effects of Temporal Variations in Optical Depth on the Determination of the Optical Depth and Solar Constant from Solar Photometry

Abstract: The Langley plot technique is a useful and well-known method for estimating atmospheric spectral extinction and/or the exoatmospheric solar spectral irradiance from ground-based spectroradiometer observations This paper addresses the problem of detecting and assessing the bias of temporal optical depth variations with regard to retrieving the spectral solar constant (zero-airmass spectral solar irradiance) and instantaneous optical depth via the Langley method The results of data simulations reveal that a number of possible forms of temporal optical depth variations can severely bias Langley plot estimates of optical depth and zero-airmass solar irradiance while yielding nearly straight Langley plots Analyses of many spectroradiometer data sets reveal that the error in the determination of the zero-airmass solar irradiance is almost always significantly greater than the statistical uncertainty obtained from the Langley plot fit This error can be estimated if the magnitude of the optical depth variation over the observation period is known

Variation of the solar constant connected with the coronal activity

Abstract: A strong correlation was found between the dips in the total solar irradiance and the peaks in the active sunspot areas as well as in the 260 MHz coronal radio flux. This connection might indicate that Alfven-waves, generated during the interaction of the magnetic fields of the active sunspot groups with the convection, are able to transport away part of the missing energy in the solar constant decreases. These waves can heat the solar corona above the sunspot groups. Another part of the missing energy could be re-radiated later, for example during the decay of the active regions.

Half-year variations in the solar neutrino flux given by the Davis data of 1979--1982

Abstract: If the neutrino has a magnetic moment --10/sup -10/..mu../sub B/, then at the maximum of the solar activity the neutrino flux detected in the Davis experiment must be decreased. The configuration of the magnetic fields inside the Sun is such that when the Earth intersects the solar equatorial plane (at the beginning of June and December) the flux of boron neutrinos must be equal to the flux during the quiet Sun years, decreasing as the Earth moves away from the solar equatorial plane. By analyzing the Davis data collected during the last solar activity maximum (1979--1982), we find half-year variations of the neutrino flux which are of this form.

Solar Radiation, its Measurement and Application in Solar Energy Utilization Programme

Abstract: The electromagnetic radiation emitted by the sun, covers a very large range of wavelengths, from radiowaves through the visible to X-rays and gamma rays. But 99 percent of this energy is contained in the region 0.2 to 4μ, in the near ultraviolet, visible and near infra red regions of the solar spectrum, with a maximum about 0.5μ. Roughly one half of this radiation lies in the visible region between 0.38 and 0.77μ and the remainder in the ultraviolet and infrared regions. The radiation received from the sun, on an average, on a surface of unit area exposed normal to the sun’s rays outside the atmosphere, at the mean distance of the earth from the sun, is called the solar constant. It has a value of roughly 2cal/cm/min or 1.36 KW/m2. In its passage through the atmosphere, solar radiation is attenuated by scattering and absorption by air molecules, watervapour, dust and aerosols and clouds, and reduced by geometric factors, so that the maximum intensity received at the earth’s surface’ is only about 1.0 KW/m2, even with very clear, dry air and a cloudless sky.

The Solar Constant (S)

Abstract: We intend to measure the flux of energy, emitted by the sun, and reaching a brass disc, painted dead black. The radiation is absorbed; a thermometer indicates the rise of temperature of the brass (Figure 37). Our instrument is a simplification of Abbot’s ‘silver disc pyrheliometer’. The measurement is admittedly rough but it gives the order of magnitude.

Bias in a Solar Constant Determination by the Langley Method Due to Aerosols

Abstract: The vertical distribution of atmospheric aerosols generally differs from the vertical distribution of the molecular atmosphere. The resulting differences in the optical air masses of the aerosol and molecular constituents lead to a bias error in the solar constant inferred by the Langley method. Volcanic aerosols injected into the lower stratosphere can lead to large bias errors. These can be reduced significantly by using a lidar to provide relatively crude measurements of the vertical distribution of the aerosol extinction coefficient.