Showing papers on "Solar constant published in 1986"

The Mg 280‐nm doublet as a monitor of changes in solar ultraviolet irradiance

Abstract: Solar irradiance data gathered with the Nimbus 7 spacecraft from 1978-1985 are compared with atmospheric MG 289-nm doublet emission line data to evaluate the possibility of using the rotational line data to calculate the total solar UV input. The satellite instrumentation is described, including the calibration equipment and procedures. The spacecraft records solar irradiance once per day and the remainder of the time records irradiance scattered by the atmosphere. The measured irradiances are converted to equivalent brightness temperatures, which can be interpolated for specific layers of the atmosphere. Sample daily data are provided to illustrate the correlation between variations in the Mg-II core radiation and the soalr UV irradiance. Techniques are defined for correcting for periodic variations in instrument performance to quantify long-term solar UV radiance variations. Using the atmospheric Mg-II doublet radiation for measuring soalr UV irradiance is concluded of value for characterizing the effects of solar radiation on the atmosphere.

The influence of faculae on total solar irradiance and luminosity

Abstract: The reported investigation of the facular contribution to the total solar irradiance is based on the data provided by the Active Cavity Radiometer Irradiance Monitor (ACRIM) for 1980-1982, and on the Earth Radiation Budget (ERB) radiometry for 1978-1982. It is found that the solar irradiance records from the ACRIM and the ERB radiometers, after subtraction of the calculated sunspot-blocking contribution, exhibit a short-term modulation which is better explained by faculae than be errors in the sunspot-blocking function. The evidence indicates that faculae produce an important contribution to short-term modulation of the total solar irradiance.

Assessment of Atmospheric Limitations on the Determination of the Solar Spectral Constant from Ground-Based Spectroradiometer Measurements

Abstract: Ground-based solar radiometer measurements have long been used to investigate various properties of both the Earth's atmosphere and the sun. This paper addresses the problem of attempting to measure the solar spectral irradiance with heretofore unachieved levels of accuracy and precision (~0.5 and ~0.1 percent, respectively) via spectroradiometer measurements made at high-altitude ground stations. Instrumentation and calibration approaches are discussed, but attention is primarily directed toward assessing limitations imposed by the atmosphere. Assessments of factors such as diffuse light contributions, uncertainty in airmass determination, variability in atmospheric optical depth, spectroradiometer bandwidth, and data analysis methods are included in the paper.

General circulation model CO2 sensitivity experiments: Snow-sea ice albedo parameterizations and globally averaged surface air temperature

Abstract: Two experiments are performed with the NCAR Community Climate Model (CCM) coupled to a swamp ocean with annually averaged solar forcing. A swamp ocean model is one in which the ocean temperature is computed from a surface energy balance. Both experiments are run with present (1 × CO2) and doubled (2 × CO2) amounts of atmospheric carbon dioxide (CO2). The first tests the sensitivity of the model to a snow and sea-ice-albedo formulation which facilitates relatively greater ice melt. The second assesses the model response when the basic state of the model in the control run is colder due to a 2% decrease in solar constant. Both are compared to a previous experiment with the same model using a different snow and sea-ice-albedo formulation and the present value of the solar constant. It is found that the globally averaged surface air temperature increase due to a doubling of CO2 is highly dependent on (1) the type of snow-sea-ice-albedo formulation used such that the parameterization which better facilitates relatively greater ice melt exhibits a greater sensitivity to increased CO2, and (2) the basic state of the control run such that the colder the basic state, the greater the warming due to increased CO2.

Absolute solar flux measurement shortward of 575 Å

Abstract: A rare-gas ionization chamber was used to obtain an accurate measurement of the absolute solar EUV flux in the 50- to 575-A region. The instrument, operating in total and near-total absorption, was flown on a solar-pointing sounding rocket on August 16, 1983. For the day of the flight, the solar activity indices were F sub 10.7 = 132.1 and R sub I = 80, and the integrated solar irradiance at the earth, corrected for atmospheric absorption, was found to be 4.31 + or - 0.31 x 10 to the 10th photons sq cm s. Almost exactly a year earlier (August 10, 1982) the same instrument measured an integrated solar flux of 5.71 + or - 0.42 x 10 to the 10th photons/sq cm s during a time of enhanced solar activity (F sub 10.7 = 209.5 and R sub I = 155).

Bias in a solar constant determination by the Langley method due to structured atmospheric aerosol.

Abstract: The vertical distribution of the atmospheric aerosol 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. This bias error was calculated for three characteristic aerosol height distributions, and it was found that this error becomes more significant when solar observations taken at large zenith angles are included in the Langley analysis. The bias error is not a sensitive function of wavelength or of the seasonal variation of the molecular atmosphere. Volcanic aerosol injected into the lower stratosphere can lead to large bias errors. These can be reduced significantly by using lidar to provide relatively crude measurements of the vertical distribution of the aerosol extinction coefficient.

First data from the earth radiation budget experiment (ERBE)

Abstract: The first data obtained from the Earth Radiation Budget Experiment (ERBE) are presented. These data include emitted infrared radiation, albedo, and estimated scene types for Nov. 15, 1984, as well as measurements of the 'solar constant'. Images from the GOES on the same day are included for comparison with the ERBE scene identification. On an instantaneous basis, clouds appear colder and more reflective than seems to have been noted before. The experiment data will be applied to several key studies of cloud-radiation-climate interactions.

Low threshold solar-pumped iodine laser

Abstract: Solar-pumped lasing of i-C 3 F 7 I and n-C 4 F 9 I has been achieved at very low threshold pumping powers (170 solar constants) using a long (60 cm) gain length box laser configuration. Two xenon arc solar simulators were used to provide an AMO spectrum over the 60 cm gain length. Maximum pulse energy of 73 mJ and average power of 525 mW were achieved at 7.3 kW optical input. A slope efficiency of 0.074 percent was measured, the maximum theoretical efficiency being 0.2 percent. Longer gain lengths allow reduced optical input concentration, thus making the solar trough collector feasible for space applications, n-C 4 F 9 I was found to have less quenching of I*, making it a superior lasant to i-C 3 F 7 I.

Results of the solar constant experiment onboard Spacelab 1

Abstract: A cavity type absolute radiometer was flown on Spacelab 1 in December 1983. We obtain a value of the solar constant of 1361.5 W m−2 with an estimated accuracy of ±2.3 W m−2 or 0.17%. When comparing this with other recent determinations, we find discrepancies which we consider indicative of metrological problems in present day absolute radiometry.

Calculation of solar irradiances for inclined surfaces: Validation of selected hourly and daily models

Abstract: Irradiance data obtained over a long period at Vancouver and Toronto, Canada, and covering a range of slope orientations are used to validate four models that estimate either the direct or diffuse solar irradiances for inclined surfaces. Evaluations are initially performed for daily and hourly time integrals. A simple parametrization of the diffuse sky radiance dramatically improves estimates of the diffuse irradiance. Both of the direct irradiance models have difficulty accommodating the diurnal characteristics of the irradiance, and consequently modelling errors are substantial for slopes not directly facing the equator. For equator‐facing slopes a saving in data requirements and computational effort through the use of daily integrals can be achieved with little additional error. A substantial portion of the differences between the measured and estimated irradiances is non‐systematic in nature and is therefore reduced through temporal averaging.

The Earth Radiation Budget Experiment - Early validation results

Abstract: The primary techniques used to obtain and validate the data of the Earth Radiation Budget Experiment (ERBE) are described, together with preliminary results of the validation. The ERBE consists of radiometers aboard the ERB Satellite, dedicated to a 57-deg orbit, and each of the two NOAA meteorological spacecraft (NOAA 9 and NOAA G) in near polar orbits. The radiometers include scanning narrow field-of-view (FOV) and nadir-looking wide and medium FOV radiometers, and a solar monitoring channel. Measurements of the solar constant by the solar monitors, and the wide and medium FOV radiometers of the ERB and the NOAA 9 spacecraft agree within a fraction of a percent. Comparison of the wide and medium FOV radiometers with the scanning radiometers showed an agreement of 1 to 4 percent. The multiple ERBE satellites are acquiring the first global measurements of regional scale-diurnal variations in the earth's radiation budget. These were verified by comparison with the high-temporal-resolution geostationary satellite data.

ERB Nimbus 7 solar measurements - 7 years

Abstract: A discussion is presented of features of the nearly 7 yr of solar radiation data available from Nimbus-7 Earth Radiation Budget (ERB) experiments as of early 1986. Summaries are provided of the irradiance data collected by each of the 10 solar sensors, with account taken of the degradation of sensor sensitivity over the active life of the sensors. In contrast, however, has been the performance of the cavity pyrheliometer, channel 10C, which has maintained an accuracy of 0.05 percent after over 6 yr on-orbit. As has been observed in SMM data, the total daily solar irradiance has exhibited a downward trend over the lifetimes of both instruments.

Variations in quiet sun radiation at centimetre wavelengths during solar maximum period

Abstract: Observations of solar radio emission at 3 cm wavelength have been made at Japal-Rangapur Observatory for 1980–1981, the solar maximum year using the 3 m radio telescope. The correlation between microwave solar emissions and the sunspot activity on monthly basis has been found to be high during the maximum phase and in the high cm wavelength band. The basic component has been estimated statistically for successive solar rotations using the data obtained at Japal-Rangapur Observatory. Further, this was compared with the data obtained at other cm wavelengths during 1980–1981 and the solar minimum period 1975–1976 of the 21st cycle. The comparison showed pronounced dips in flux levels at different wavelengths during the summer months of the solar maximum year which may be attributed to the presence of coronal holes in the various levels of the solar atmosphere. The computed basic component values showed pronounced variation at high cm wavelengths for the solar maximum period with dissimilar variations at different wavelengths. During the solar minimum period the variations were negligibly small and showed more or less constant level of activity.