Solar constant

About: Solar constant is a research topic. Over the lifetime, 967 publications have been published within this topic receiving 29647 citations.

The Solar Wind Energy Flux

Abstract: The solar-wind energy flux measured near the Ecliptic is known to be independent of the solar-wind speed. Using plasma data from Helios, Ulysses, and Wind covering a large range of latitudes and time, we show that the solar-wind energy flux is independent of the solar-wind speed and latitude within 10 %, and that this quantity varies weakly over the solar cycle. In other words the energy flux appears as a global solar constant. We also show that the very high-speed solar wind (VSW>700 km s−1) has the same mean energy flux as the slower wind (VSW<700 km s−1), but with a different histogram. We use this result to deduce a relation between the solar-wind speed and density, which formalizes the anti-correlation between these quantities.

Total solar irradiance measurements with PREMOS/PICARD

Abstract: PREMOS on the French satellite PICARD is the first spaceborne absolute radiometer measuring Total Solar Irradiance that has been irradiance-calibrated in vacuum with SI-traceability. The measurements of PREMOS at first light on July 27, 2010, yield a TSI value of 1360.9±0.4 W/m2 (k=1). This value agrees with the absolute TSI value measured by TIM/SORCE for this date within their combined uncertainties, and it differs by more than ten sigma from the absolute value of other space experiments, e.g. VIRGO/SOHO. The PREMOS measurements thus establish SI-traceability to a solar constant value of 1361 W/m2.

Differences in water vapor radiative transfer among 1d models can significantly affect the inner edge of the habitable zone

Abstract: An accurate estimate of the inner edge of the habitable zone is critical for determining which exoplanets are potentially habitable and for designing future telescopes to observe them. Here, we explore differences in estimating the inner edge among seven one-dimensional radiative transfer models: two line-by-line codes (SMART and LBLRTM) as well as five band codes (CAM3, CAM4_Wolf, LMDG, SBDART, and AM2) that are currently being used in global climate models. We compare radiative fluxes and spectra in clear-sky conditions around G and M stars, with fixed moist adiabatic profiles for surface temperatures from 250 to 360 K. We find that divergences among the models arise mainly from large uncertainties in water vapor absorption in the window region (10 μm) and in the region between 0.2 and 1.5 μm. Differences in outgoing longwave radiation increase with surface temperature and reach 10–20 W m^(−2); differences in shortwave reach up to 60 W m^(−2), especially at the surface and in the troposphere, and are larger for an M-dwarf spectrum than a solar spectrum. Differences between the two line-by-line models are significant, although smaller than among the band models. Our results imply that the uncertainty in estimating the insolation threshold of the inner edge (the runaway greenhouse limit) due only to clear-sky radiative transfer is ≈10% of modern Earth's solar constant (i.e., ≈34 W m^(−2) in global mean) among band models and ≈3% between the two line-by-line models. These comparisons show that future work is needed that focuses on improving water vapor absorption coefficients in both shortwave and longwave, as well as on increasing the resolution of stellar spectra in broadband models.

The effect of magnetic fields on solar luminosity

Abstract: The paper presents an investigation into the influence of magnetic fields in sunspots and faculae on solar luminosity, using measurements of the solar constant from ground level and from space. Attention is given to an analysis that shows that it is difficult to devise an atmospheric mechanism that would rapidly lower visible and infrared transmission in response to sunspots, increase it in response to faculae, and anticipate the magnetic development of these features by about one day. It is shown that the phase shift of the luminosity variation provides a promising new technique to determine the depth at which the magnetic fields of sunspots and faculae redistribute the flow of convective energy.

Radiation in the Solar System: its effect on temperature and its pressure on small bodies

Abstract: When a surface is a full radiator and absorber its temperature can be determined at once by the fourth-power law if we know the rate at which it is radiating energy. If it is radiating what it receives from the sun, then a knowledge of the solar constant enables us to find the temperature. We can thus make estimates of the highest temperature which a surface can reach when it is only receiving heat from the sun. We can also make more or less approximate estimates of the temperatures of the planetary surfaces by assuming conditions under which the radiation takes place, and we can determine, fairly exactly, the temperatures of very small bodies in interplanetary space. These determinations require a knowledge of the constant of radiation and of either the solar constant or the effective temperature of the sun, either of which, as is well known, can be found from the other by means of the radiation constant. It will be convenient to give here the values of these quantities before proceeding to apply them to our special problems.