Showing papers on "Solar constant published in 2018"

Changes in clouds and thermodynamics under solar geoengineering and implications for required solar reduction

Abstract: . The amount of solar constant reduction required to offset the global warming from an increase in atmospheric CO2 concentration is an interesting question with implications for assessing the feasibility of solar geoengineering scenarios and for improving our theoretical understanding of Earth's climate response to greenhouse gas and solar forcings. This study investigates this question by analyzing the results of 11 coupled atmosphere–ocean global climate models running experiment G1 of the Geoengineering Model Intercomparison Project, in which CO2 concentrations are abruptly quadrupled and the solar constant is simultaneously reduced by an amount tuned to maintain the top-of-atmosphere energy balance and pre-industrial global mean temperature. The required solar constant reduction in G1 is between 3.2 % and 5.0 %, depending on the model, and is uncorrelated with the models' equilibrium climate sensitivity, while a formula from the experiment specifications based on the models' effective CO2 forcing and planetary albedo is well correlated with but consistently underpredicts the required solar reduction. We propose an explanation for the required solar reduction based on CO2 instantaneous forcing and the sum of radiative adjustments to the combined CO2 and solar forcings. We quantify these radiative adjustments in G1 using established methods and explore changes in atmospheric temperature, humidity, and cloud fraction in order to understand the causes of these radiative adjustments. The zonal mean temperature response in G1 exhibits cooling in the tropics and warming in high latitudes at the surface; greater cooling in the upper troposphere at all latitudes; and stratospheric cooling which is mainly due to the CO2 increase. Tropospheric specific humidity decreases due to the temperature decrease, while stratospheric humidity may increase or decrease depending on the model's temperature change in the tropical tropopause layer. Low cloud fraction decreases in all models in G1, an effect that is robust and widespread across ocean and vegetated land areas. We attribute this to a reduction in boundary layer inversion strength over the ocean, and a reduction in the release of water from plants due to the increased CO2 . High cloud fraction increases in the global mean in most models. The low cloud fraction reduction and atmospheric temperature decrease have strong warming effects on the planet, due to reduced reflection of shortwave radiation and reduced emission of longwave radiation, respectively. About 50 % to 75 % of the temperature effect is caused by the stratospheric cooling, while the reduction in atmospheric humidity results in increased outgoing longwave radiation that roughly offsets the tropospheric temperature effect. The longwave (LW) effect of the cloud changes is small in the global mean, despite the increase in high cloud fraction. Taken together, the sum of the diagnosed radiative adjustments and the CO2 instantaneous forcing explains the required solar forcing in G1 to within about 6 %. The cloud fraction response to the G1 experiment raises interesting questions about cloud rapid adjustments and feedbacks under solar versus greenhouse forcings, which would be best explored in a model intercomparison framework with a solar-forcing-only experiment.

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 (1D) 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 um) and in the region between 0.2 and 1.5 um. Differences in outgoing longwave radiation increase with surface temperature and reach 10-20 Wm^-2; differences in shortwave reach up to 60 Wm^-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 Wm^-2 in global mean) among band models and ~3% between the two line-by-line models. These comparisons show that future work is needed focusing on improving water vapor absorption coefficients in both shortwave and longwave, as well as on increasing the resolution of stellar spectra in broadband models.

Earth’s Incoming Energy: The Total Solar Irradiance

Abstract: The Sun provides nearly all the energy powering the Earth climate system, far exceeding all other energy sources combined. The incident net radiant energy, the “total solar irradiance,” varies on timescales from minutes to centuries and can cause commensurate changes in Earth’s climate and can affect global and regional temperatures in different ways. Typical solar variations are 0.1% on timescales from days to the 11-year solar cycle and are well measured by precision space-based radiometric instruments. Variations on longer timescales rely on solar models providing historical reconstructions. These estimate similar magnitude changes over centuries, albeit with uncertainties that increase with historical time. Because of the importance of tracking solar irradiance variability to better understand solar influences on climate, space-borne measurements have been continual since 1978 via a series of temporally overlapping instruments. Improved accuracies and stabilities in the most modern instruments are approaching the needed climate-driven measurement requirements for detection of potential long-term solar trends.

Cyclic Variations in the Solar Radiation Fluxes at the Beginning of the 21st Century

Abstract: The solar activity in the current, that is, the 24th, sunspot cycle is analyzed. Cyclic variations in the sunspot number (SSN) and radiation fluxes in various spectral ranges have been estimated in comparison with the general level of the solar radiation, which is traditionally determined by the radio emission flux F10.7 at a wavelength of 10.7 cm (2.8 GHz). The comparative analysis of the variations in the solar constant and solar indices in the UV range, which are important for modeling the state of the Earth’s atmosphere, in the weak 24th cycle and strong 22nd and 23rd cycles has shown relative differences in the amplitudes of variations from the minimum to the maximum of the cycle. The influence of the hysteresis effect between the activity indices and F10.7 in the 24th cycle, which is taken into account here, makes it possible to refine the forecast of the UV indices and solar constant depending on the quadratic regression coefficients that associate the solar indices with F10.7 depending on the phase of the cycle.

Cyclic Variations in the Solar Radiation Fluxes at the Beginning of the 21st Century

Abstract: The solar activity in the current, that is, the 24-th, sunspot cycle is analyzed. Cyclic variations in the sunspot number (SSN) and radiation fluxes in various spectral ranges have been estimated in comparison with the general level of the solar radiation, which is traditionally determined by the radio emission flux $F_ {10.7} $ at a wavelength of 10.7 cm (2.8 GHz). The comparative analysis of the variations in the solar constant and solar indices in the UV range, which are important for modeling the state of the Earth's atmosphere, in the weak 24th cycle and strong 22nd and 23rd cycles showed relative differences in the amplitudes of variations from the minimum to the maximum of the cycle. The influence of the hysteresis effect between the activity indices and $F_ {10.7} $ in the 24-th cycle, which is considered here, makes it possible to refine the forecast of the UV indices and solar constant depending on the quadratic regression coefficients that associate the solar indices with $F_ {10.7} $ depending on the phase of the cycle.

Spatio-temporal mapping of solar energy potential of Dutse, Jigawa State Nigeria using arcgis solar radiation spatial analyst tool

Abstract: Efficient solar energy harnessing technology is required for sustainability and effective utilization of the resource. In this work, a survey of solar energy potential of Dutse, Jigawa state Nigeria was carried out with the aim of identifying the best location for optimal performance of solar energy power plant. Elevation information of the study area was obtained from Google Earth’s Digital Elevation Model (DEM) data collected by NASA’s Shuttle Radar Topography Mission (SRTM). With the DEM and the solar constant as inputs, ArcGIS’s solar radiation analyst tool was used to estimate the effect of topography and its related parameters (slope, aspect, hillshed, viewshed) on both direct and diffuse solar radiation leading to an area solar insolation map for both the direct and diffuse components. Total insolation map was computed for the 12 months of the year 2017. The insolation map for the whole year varies significantly from 0.080 kWHm -2 to about 2,684.358 kWHm -2 . Two regions receiving maximum insolation were identified: mountainous region 1 km east of Mopol Barrack and the western end of the town, about 7.5 km east of Jidawa Lake. The temporal analysis of the monthly isolation showed that peak value was recorded in the month of April while minimum values were recorded in the months of December and January. The two regions are therefore recommended as the best location for optimal performance of solar power generating plant. Keywords: Solar Energy; Solar Insolation; Solar Radiation; Spatial Analyst; Dutse