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Solar constant
About: Solar constant is a research topic. Over the lifetime, 967 publications have been published within this topic receiving 29647 citations.
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TL;DR: In this article, the authors derived the solar diameter from the total solar eclipse observation in Turkey and Egypt on 29 March 2006 and found that the solar radius carried back to 1 AU was 959.22±0.04 arcsec at the time of the observations.
Abstract: Solar diameter measurements have been made nearly continuously through different techniques for more than three centuries. They were obtained mainly with ground-based instruments except for some recent estimates deduced from space observations. One of the main problems in such space data analysis is that, up to now, it has been difficult to obtain an absolute value owing to the absence of an internally calibrated system. Eclipse observations provide a unique opportunity to give an absolute angular scale to the measurements, leading to an absolute value of the solar diameter. However, the problem is complicated by the Moon limb, which presents asphericity because of the mountains. We present a determination of the solar diameter derived from the total solar eclipse observation in Turkey and Egypt on 29 March 2006. We found that the solar radius carried back to 1 AU was 959.22±0.04 arcsec at the time of the observations. The inspection of the compiled 19 modern eclipses data, with solar activity, shows that the radius changes are nonhomologous, an effect that may explain the discrepancies found in ground-based measurements and implies the role of the shallow subsurface layers (leptocline) of the Sun.
14 citations
01 Jul 2013
TL;DR: In this paper, a new model was developed based on Angstrom-Prescott Model to estimate the monthly average daily global solar radiation only using sunshine duration data in hilly areas of North India for the determination of constants "a" and "b" by taking only latitude and altitude of the place into consideration.
Abstract: The main objective of the present study was to develop a new model for the solar radiation estimation in hilly areas of North India for the determination of constants ‘a’ and ‘b’ by taking only latitude and altitude of the place into consideration. In this study, new model was developed based on Angstrom-Prescott Model to estimate the monthly average daily global solar radiation only using sunshine duration data. The monthly average global solar radiation data of four different locations in North India was analyzed with the neural fitting tool (nftool) of neural network of MATLAB Version 7.11.0.584 (R2010b) with 32-bit (win 32). The neural network model was used with 10 hidden neurons. Eight months data was used to train the neural network. Two months data was used for the validation purpose and the remaining two months for the testing purpose. The new developed model estimated the values of ‘a’ which range from 0.209 to 0.222 and values of ‘b’ ranging from 0.253 to 0.407. The values of maximum percentage error (MPE) and mean bias error (MBE) were in good agreement with the actual values. Artificial neural network application showed that data was best fitted for the regression coefficient of 0.99558 with best validation performance of 0.85906 for Solan. This will help to advance the state of knowledge of global solar radiation to the point where it has applications in the estimation of monthly average daily global solar radiation.
14 citations
TL;DR: A cavity type absolute radiometer was flown on Spacelab 1 in December 1983 as mentioned in this paper, where the authors obtained a value of the solar constant of 1361.5 W m−2 with an estimated accuracy of ± 2.17%.
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.
14 citations
TL;DR: In this article, the authors used a simple parametrization of the diffuse sky radiance to improve the estimates of the direct irradiance for slopes not directly facing the equator and found that the difference between measured and estimated irradiances is non-systematic in nature and is therefore reduced through temporal averaging.
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.
14 citations
01 Jan 1991
TL;DR: The most important influences are related to solar activity: during the passage of active regions on the solar disk (sunspots and faculae) changes of a few 0.1 percent lasting for several days are observed as mentioned in this paper.
Abstract: Direct measurements from satellites of the solar 'constant' (the total irradiance at mean sun-earth distance) during more than ten years show variations over time scales from minutes to years and decades. At high frequencies, solar oscillations contribute to the variance. The most important influences are related to solar activity: during the passage of active regions on the solar disk (sunspots and faculae) changes of a few 0.1 percent lasting for several days are observed. The effects of spots can be well reproduced by the projected sunspot index, whereas the influence of faculae have to be modeled from proxy data like the Ca-K plage index or the He I index. Long-term trends are detected which are connected to the 11-yr solar activity cycle.
14 citations