Solar constant

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

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.

Solar radiation energy (fundamentals).

Abstract: The fundamentals of solar radiation are presented here Irradiance and irradiation are defined; we explain the origin of the energy emitted by the sun and reaching the ground and its amount as a function of the wavelength – the spectral distribution The energy reaching the earth depends on the geometry of the earth relative to the Sun This geometry is described as well as its variation throughout the year The concept of time is very important in solar radiation It is detailed here and the notions of mean solar time and true solar time are dealt with The apparent course of the sun in the sky is described; the zenithal, elevation and azimuth angles are defined We offer a series of equations to compute the radiation at the top of the atmosphere – the extraterrestrial irradiation- for any instant and for any inclined surface During its path downwards to the ground, the constituents of the atmosphere deplete the incident light We introduce the concepts of scattering a! nd absorption We discuss the main processes affecting the incident radiation in clear and cloudy atmospheres, and especially the effects of molecules, aerosols, gases and clouds Several examples are given that illustrate atmospheric effects as a function of the solar zenithal angle and atmospheric optical properties The spectral distribution of the irradiance is discussed for several different conditions The direct, diffuse and reflected components of the irradiance are defined How to compute them on an inclined surface is briefly discussed Many equations are given in this contribution that can be easily introduced in eg, a spreadsheet or a computer routine, to reproduce the figures

On the Determination and Constancy of the Solar Oblateness

Abstract: The equator-to-pole radius difference (Δr=R eq−R pol) is a fundamental property of our star, and understanding it will enrich future solar and stellar dynamical models. The solar oblateness (Δ⊙) corresponds to the excess ratio of the equatorial solar radius (R eq) to the polar radius (R pol), which is of great interest for those working in relativity and different areas of solar physics. Δr is known to be a rather small quantity, where a positive value of about 8 milli-arcseconds (mas) is suggested by previous measurements and predictions. The Picard space mission aimed to measure Δr with a precision better than 0.5 mas. The Solar Diameter Imager and Surface Mapper (SODISM) onboard Picard was a Ritchey–Chretien telescope that took images of the Sun at several wavelengths. The SODISM measurements of the solar shape were obtained during special roll maneuvers of the spacecraft by 30° steps. They have produced precise determinations of the solar oblateness at 782.2 nm. After correcting measurements for optical distortion and for instrument temperature trend, we found a solar equator-to-pole radius difference at 782.2 nm of 7.9±0.3 mas (5.7±0.2 km) at one σ. This measurement has been repeated several times during the first year of the space-borne observations, and we have not observed any correlation between oblateness and total solar irradiance variations.

Solar-cycle variation of sound speed near the solar surface

Abstract: We present evidence that the sound-speed variation with solar activity has a two-layer configuration, similar to the one observed below an active region, which consists of a negative layer near the solar surface and a positive one in the layer immediately below the first one. Frequency differences between the activity minimum and maximum of solar cycle 23, obtained applying global helioseismology to the Michelson Doppler Imager on board the Solar and Heliospheric Observatory, is used to determine the sound-speed variation from below the base of the convection zone to a few Mm below the solar surface. We find that the sound speed at solar maximum is smaller than at solar minimum at the limit of our determination (5.5 Mm). The min-to-max difference decreases in absolute values until ~7 Mm. At larger depths, the sound speed at solar maximum is larger than at solar minimum and the difference increases with depth until ~10 Mm. At this depth, the relative difference (δc 2/c 2) is less than half of the value observed at the lowest depth determination. At deeper layers, it slowly decreases with depth until there is no difference between maximum and minimum activity.

The sensitivity of the modeled energy budget and hydrological cycle to CO 2 and solar forcing

Abstract: . The transient responses of the energy budget and the hydrological cycle to CO2 and solar forcings of the same magnitude in a global climate model are quantified in this study. Idealized simulations are designed to test the assumption that the responses to forcings are linearly additive, i.e. whether the response to individual forcings can be added to estimate the responses to the combined forcing, and to understand the physical processes occurring as a response to a surface warming caused by CO2 or solar forcing increases of the same magnitude. For the global climate model considered, the responses of most variables of the energy budget and hydrological cycle, including surface temperature, do not add linearly. A separation of the response into a forcing and a feedback term shows that for precipitation, this non-linearity arises from the feedback term, i.e. from the non-linearity of the temperature response and the changes in the water cycle resulting from it. Further, changes in the energy budget show that less energy is available at the surface for global annual mean latent heat flux, and hence global annual mean precipitation, in simulations of transient CO2 concentration increase compared to simulations with an equivalent transient increase in the solar constant. On the other hand, lower tropospheric water vapor increase is similar between simulations with CO2 and solar forcing increase of the same magnitude. The response in precipitation is therefore more muted compared to the response in water vapor in CO2 forcing simulations, leading to a larger increase in residence time of water vapor in the atmosphere compared to solar forcing simulations. Finally, energy budget calculations show that poleward atmospheric energy transport increases more in solar forcing compared to equivalent CO2 forcing simulations, which is in line with the identified strong increase in large-scale precipitation in solar forcing scenarios.