Showing papers on "Solar constant published in 2012"

Solar irradiance reduction to counteract radiative forcing from a quadrupling of CO2: climate responses simulated by four earth system models

Abstract: . In this study we compare the response of four state-of-the-art Earth system models to climate engineering under scenario G1 of two model intercomparison projects: GeoMIP (Geoengineering Model Intercomparison Project) and IMPLICC (EU project "Implications and risks of engineering solar radiation to limit climate change"). In G1, the radiative forcing from an instantaneous quadrupling of the CO2 concentration, starting from the preindustrial level, is balanced by a reduction of the solar constant. Model responses to the two counteracting forcings in G1 are compared to the preindustrial climate in terms of global means and regional patterns and their robustness. While the global mean surface air temperature in G1 remains almost unchanged compared to the control simulation, the meridional temperature gradient is reduced in all models. Another robust response is the global reduction of precipitation with strong effects in particular over North and South America and northern Eurasia. In comparison to the climate response to a quadrupling of CO2 alone, the temperature responses are small in experiment G1. Precipitation responses are, however, in many regions of comparable magnitude but globally of opposite sign.

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.

Why is the solar constant not a constant

Abstract: In order to probe the mechanism of variations of the solar constant on the inter-solar-cycle scale, the total solar irradiance (TSI; the so-called solar constant) in the time interval of 1978 November 7 to 2010 September 20 is decomposed into three components through empirical mode decomposition and time-frequency analyses. The first component is the rotation signal, counting up to 42.31% of the total variation of TSI, which is understood to be mainly caused by large magnetic structures, including sunspot groups. The second is an annual-variation signal, counting up to 15.17% of the total variation, the origin of which is not known at this point in time. Finally, the third is the inter-solar-cycle signal, counting up to 42.52%, which is inferred to be caused by the network magnetic elements in quiet regions, whose magnetic flux ranges from (4.27-38.01) × 1019 Mx.

A suite of user-friendly global climate models: Hysteresis experiments

Abstract: A hierarchy of global spectral circulation models is introduced ranging from the shallow-water system via the primitive-equation dynamical core of the atmosphere to the Planet Simulator as a Global Climate Model (GCM) of Intermediate Complexity (MIC) which can be used to run climate and paleo-climate simulations for time scales up to ten thousand years or more in an acceptable real time. The priorities in development are set to speed, easy handling and portability with a modular structure suitable for problem-dependent configuration. Adaptions exist for the planetary atmospheres of Mars and of Saturn’s moon Titan and are being extended. Common coupling interfaces enable the addition of ocean, ice, vegetation models and more. An interactive mode with a Model Starter and a Graphical User Interface (GUI) is available to select a configuration from the available model suite, to set its parameters and inspect atmospheric fields while changing the models’ parameters on the fly. This is especially useful for teaching, debugging and tuning of parameterizations. An updated overview of the model suite’s features is presented based on the Earth-like climate model Planet Simulator with mixed-layer ocean introducing static and memory hysteresis in terms of a parameter sweep of the solar constant and CO2 concentrations. The static hysteresis experiment demonstrates that the solar constant varying by 20% reveals warm and snowball Earth climate regimes depending on the history of the system. This hysteresis subjected to a thermodynamic analysis shows the following features: i) Both climate regimes are characterized by global mean surface temperature and entropy growing with increasing solar constant. ii) The climate system’s efficiency decreases (increases) with increasing solar constant in present-day warm (snowball) climate conditions. iii) Climate transitions near bifurcation points are characterized by high efficiency associated with the system’s large distance from the stable regime. Memory hysteresis evolves when changing the direct atmospheric radiative forcing which, associated with a well-mixed CO2 concentration, modifies the planetary thermodynamic state, and hence the surface temperature. The hysteresis effected by different CO2 change rates is analysed: i) The response is due to infrared cooling (for constant temperature lapse-rate) which, in turn, is related to the surface temperature through the Stefan-Boltzmann law in a ratio proportional to the new infrared opacity. Subsequent indirect effects, that are water-vapour-greenhouse and ice-albedo feedbacks, enhance the response. ii) Different rates of CO2 variation may lead to similar transient climates characterized by the same global mean surface temperature but different values of CO2 concentration. iii) Far from the bifurcation points, the model’s climate depends on the history of the radiative forcing thus displaying a hysteresis cycle that is neither static nor dynamical, but is related to the memory response of the model determined by the mixed-layer depth of the ocean. Results are supported by a zero-dimensional energy balance model.

Why isn't the solar constant a constant?

Abstract: In order to probe the mechanism of variations of the Solar Constant on the inter-solar-cycle scale, total solar irradiance (TSI, the so-called Solar Constant) in the time interval of 7 November 1978 to 20 September 2010 is decomposed into three components through the empirical mode decomposition and time-frequency analyses. The first component is the rotation signal, counting up to 42.31% of the total variation of TSI, which is understood to be mainly caused by large magnetic structures, including sunspot groups. The second is an annual-variation signal, counting up to 15.17% of the total variation, the origin of which is not known at this point in time. Finally, the third is the inter-solar-cycle signal, counting up to 42.52%, which are inferred to be caused by the network magnetic elements in quiet regions, whose magnetic flux ranges from $(4.27-38.01)\times10^{19}$ Mx.

Interannual Variability of the Solar Constant

Abstract: It can be concluded from the calculations performed of interannual variations of the distance between the Sun and the Earth in the moments of the Earth’s position in the equinoctial and solstitial points that the mean amplitude (approximately the same for all the equinoctial and solstitial points) is determined to be equal to 5700 km (at the maximum values being approximately equal to 15000 km). The values of the solar constant have been calculated on the basis of the data of varying distances, and the values of its interannual variability (for the period from 1900 up to 2050) have determined. Based on the analysis of the series, new periodic characteristics of a long-term variation of the solar constant, related to the celestial-mechanical process, namely, to the perturbed orbital motion of the Earth, are obtained. A three-year cycle is distinguished in the interannual variability of the solar constant, which alternates with a two-year cycle every eight and eleven years. The amplitude of the interannual variability in the series of equinoctial and solstitial points is on average about 0.1 W/m2 (about 0.008% of the solar constant value). This is comparable to the interannual variability of the solar constant in the eleven-year cycle of the solar activity. The series obtained can be represented by alternation of eleven-year and eight-year cycles. The eleven-year cycle is composed of three three-year cycles and one two-year cycle, and the eight-year cycle is composed of two three-year cycles and one two-year cycle.

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.

An Optimum Slope Angle for Solar Collector Systems in Kerman Using a New Model for Diffuse Solar Radiation

Abstract: In the present article, the monthly average daily diffuse solar radiation on a horizontal surface is calculated first, using 12 new hybrid models. A standard isotropic model is then used to estimate the global solar radiation on inclined surfaces. Finally, the monthly, seasonal, and yearly optimum slope angles to gain the maximum global solar radiation are suggested. The monthly optimum tilt angle varies from 0° (May, June, and July) to 60° (December). The seasonal optimum tilt angle is between 4° (spring) to 53° (autumn) and the optimum yearly slope angle is 29°, which is close to the latitude of Kerman.

The Optimal Slope Angle for Solar Collectors in Hot and Dry Parts of Iran

Abstract: The performance of a solar collector is highly susceptible by its slope angle with the horizon. This is due to the fact that the solar radiation intensity over the solar collector surface changes with the slope angle. A well known mathematical model was used for estimating the total (global) solar radiation intensity on an inclined surface faced to the south, and to determine the optimum slope angle for the solar collectors in hot and dry parts of Iran based on experimental data for a horizontal surface. The monthly, seasonal, and yearly optimum slope angles were calculated. The slope angle was calculated for different intensities of total radiation on the collector surface and the corresponding values for maximum total radiation were specified as the optimum slope angles. The results showed that the yearly optimum slope angle for each city is close to the local latitude. The results also indicated that changing the monthly, seasonal, and yearly slope angles causes to achieve a significant yearly...

Determination of the chromospheric quiet network element area index and its variation between 2008 and 2011

Abstract: In general, it is believed that plages and sunspots are the main contributors to solar irradiance. There are small-scale structures on the Sun with intermediate magnetic fields that could also contribute to solar irradiance, but it has not yet been quantified how many of these small scale structures contribute and how much this varies over the solar cycle. We used Ca II K images obtained from the telescope at the Kodaikanal observatory. We report a method to separate the network elements from the background structure and plage regions, and compute the changes in the network element area index during the minimum phase of the solar cycle and part of the ascending phase of cycle 24. The measured area occupied by the network elements is about 30% and the plages cover less than 1% of the solar disk during the observation period from February 2008 to 2011. During the extended period of minimum activity, it is observed that the network element area index decreases by about 7% compared to the area occupied by the network elements in 2008. A long term study of the network element area index is required to understand the variations over the solar cycle.

The Solar Resource

Abstract: This chapter deals with the fundamentals of solar radiation and solar energy. It consists of 12 sections and 4 appendices and bibliography. In the introduction section, a brief description of solar radiation as the principal source of energy for the Earth is provided. In the following sections, the necessary relationships of solar geometry, solar constant, and solar spectrum are given. The interference of solar radiation with the constituents of the atmosphere of the Earth is discussed. The most usable broadband solar radiation models and the basics for solar spectral modeling are discussed. The methods for testing the broadband solar models are presented. The basics of net solar radiation is explained. The need for the formation of networks of solar radiation stations and the generation of solar atlases are discussed. Some utility tools for easy solar-radiation calculations are provided. The last section describes the instruments for measuring solar radiation components with associated errors and uncertainties. The appendices provide the solar-constant values from 0.12 to 10 µm, the terms used in solar radiometry, the maximum wavelength of the solar spectrum considering the Sun as a blackbody and by applying Wien’s law, and the most usable physical constants and conversion factors between solar radiation units.

The Disagreement between Anisotropic-Isotropic Diffuse Solar Radiation Models as a Function of Solar Declination: Computing the Optimum Tilt Angle of Solar Panels in the Area of Southern-Italy

Abstract: In this paper a simulation to maximize the global solar radiation on a sloped collecting surface was applied to typical latitudes in the area of southern Italy, to calculate the optimum tilt angle of solar panels on building structures or large photovoltaic power plants located in that geographical area. Indeed, the area of southern Italy and in particular Sicily and Calabria are the top of European locations for acquiring solar energy. Some models of diffuse solar irradiance were taken into account to determine panels inclinations that maximized the impinging solar radiation by means of global horizontal solar radiation data provided from the Italian Institute of ENEA (Italy). An algorithm was used for the simulation providing a set of tilt angles for each latitude. The optimum tilt angle values obtained from the simulation resulted to be strictly related to the model of diffuse solar radiation that was used. Indeed, the disagreement between the values obtained using anisotropic models of diffuse solar radiation and those obtained from the isotropic model resulted to decrease significantly with increasing solar declination, showing that the isotropic model can be reliable only in summer months.

Bicentennial decrease of the solar constant leads to the Earth’s unbalanced heat budget and deep climate cooling

Abstract: Long-wave energy emitted by the Earth-atmosphere into space is characterized by changes in power over time that always lag behind the changes in power of the absorbed solar radiation due to slow variation in enthalpy of the Earth-atmosphere system. Long-term variation of the solar energy radiation absorbed by the Earth remains uncompensated by the energy radiated into space over the interval of time that is determined by the thermal inertia. The basic state of the climate system is when the debit and credit sides in the Earth’s global annual mean energy budget (including the air and water envelopes) are almost always unbalanced. The annual mean balance of the heat budget of the Earth-atmosphere over a long time period will reliably define the behavior and magnitude of the energy excess accumulated by the Earth or energy deficit to allow us to determine adequately and to predict beforehand the trend and amplitude of the forthcoming climate change using the prognosis of variations in the total solar irradiance (solar constant). The decrease in solar constant has been observed since the early 1990s. The Earth as a planet will have a negative balance in the energy budget in the future as well, because the Sun is entering the decline phase of the bicentennial luminosity changes. This will lead to a drop in temperature in approximately 2014. The increase in albedo and decrease in greenhouse gas concentration in the atmosphere will result in the additional decrease in absorbed portion of the solar energy and reduced greenhouse effect. The additional drop in temperature exceeding the effect of decreased solar constant can occur as a result of successive feedback effects. A deep bicentennial minimum in solar constant is to be anticipated in 2042 ± 11 and the 19th Little Ice Age (for the last 7500 years) may occur in 2055 ± 11.

Passive Control Feasibility of Collinear Equilibrium Points with Solar Balloons

Abstract: A = solar balloon’s surface area, m E = Young’s modulus of the skin, Pa h = auxiliary variable, see Eq. (13) i, ĵ, k = unit vectors of rotating frame K = second-order tensor, see Eq. (5) k = gain ‘ = sun–planet distance (with ‘ ≜ 1 AU), astronomical unit m = mass, kg O = center of mass p = internal pressure, Pa R = solar balloon’s radius, m r = absolute position vector, r krk T = spacecraft equilibrium temperature, K T O; x; y; z = rotating reference frame u = vector, see Eq. (6) W = thermal power flux,W=m W = solar constant, 1350 W=m 2 = coefficient of absorptivity = lightness number = variation = coefficient of emissivity = angular coordinate, deg = planet’s dimensionless mass = skin’s Poisson ratio = dimensionless x coordinate = relative position vector, k k = skin’s tensile stress, Pa ~ = Stefan–Boltzmann constant = coefficient of linear expansion, K 1 ! = angular velocity, rad=s

Solar constant temperature system of swimming pool

Abstract: The utility model relates to a solar constant temperature system of a swimming pool. The solar constant temperature system comprises a solar heat collecting plate, an expansion tank, a solar work station, a heat exchange water tank and a gas furnace, wherein the solar heat collecting plate is connected with the heat exchange water tank through a pipeline, the expansion tank and the solar work station are arranged on the pipeline arranged between the solar heat collecting plate and the water exchange water tank, the heat exchange water tank is connected with the swimming pool through a pipeline, and the gas furnace is connected with the heat exchange water tank through a pipeline. The solar constant temperature system has the advantages that solar energy is utilized for heating water, the energy saving and the environment protection are realized, auxiliary heating systems including fuel gas, heat pumps and the like are adopted, the control is convenient, and the water temperature of the swinging pool is kept constant in four seasons of the year.

Estimation the effects of each site factors, time factors, and optical factors on absorbed solar radiation value that incident on a flat- plate solar collector

Abstract: In this paper, an estimated of absorbed solar radia tion was developed to determine the performance of the solar collectors to develop best thermal energy con version system. The aim of this research is to deve lop a tool for predicting the performance of a flat-plate solar collector from knowledge the absorbed solar radiation quantity. Also, the factors that affects on absorbed solar ra diation value have been considered . These factors represented with collector tilt angle , the season changes that represented with month of year that the global solar radiation on horizontal surfa ce has been measured, the location from the world represented with the latitude, time interval repres ented with hours of daylight from sunrise to sunset . Another optical factors affect on intensity of abso rbed solar radiation has been considered. These fac tors correlated with absorptivity and transmissivity of the transparent glass cover which represented with (type, thickness, and number of glass covers). The result of each factor was analyzed for different collector tilt angle, latitude of place, and solar hour angle.

Evaluation of Solar Spectra and Their Effects on Radiative Transfer and Climate Simulation

Abstract: In this chapter we will discuss solar spectral distributions and their corresponding impact on the climate, especially on the Earth’s atmospheric temperature and energy balance at the surface. Solar spectrum is defined as a spectral distribution of the solar radiation at the top of the atmosphere (TOA). It represents the incoming solar energy to the earth system containing the atmosphere and ocean. Solar radiation is the original driving force for the continuous circulations of atmosphere and ocean. It has been recognized that the variation of total solar irradiance (solar constant) at the TOA is one of the important factors impacting climate change, though the variation in total solar irradiance is very small, approximately only about 0.1% of the solar constant or about 1.3Wm−2 (Krivova et al, 2010). Besides the variation of the total solar irradiance the changes in the spectral distribution of the solar radiation can also affect the climate. However much less attention has been focused on this aspect.

The Study on the Optimal Angle of the Solar Panel using by Solar Radiation Model

Abstract: The angle of solar panels is calculated using solar radiation model for the efficient solar power generation. In ideal state, the time of maximum solar radiation is represented from 12:08 to 12:40 during a year at Gangneung and it save rage time is12:23. The maximum solar radiation is 1012 and 708 inc lear sky and cloudy sky, respectively. Solar radiation is more sensitive to North-South (N-S) slope angle than East-West (E-W) azimuth angle. Daily solar radiation on optimum angle of solar panel is higher than that on horizontal surface except for 90 days during summer. In order to apply to the real atmosphere, the TMY (typical meteorological Year) data which obtained from the 22 solar sites operated by KMA(Korea Meteorological Administration) during 11 years(2000 to 2010) is used as the input data of solar radiation model. The distribution of calculated solar radiation is similar to the observation, except in Andong, where it is overestimated, and in Mokpo and Heuksando, where it is underestimated. Statistical analysis is performed on calculated and observed monthly solar radiation on horizontal surface, and the calculation is overestimated from the observation. Correlationis 0.95 and RMSE (Root Mean Square Error) is10.81 MJ. The result shows that optimum N-S slope angles of solar panel are about lower than station latitude, but E-W slope angles are lower than . There are three types of solar panels: horizontal, fixed with optimum slope angle, and panels with tracker system. The energy efficiencies are on average 20% higher on fixed solar panel and 60% higher on tracker solar panel than compared to the horizontal solar panel, respectively.

Technique for solar simulator

Abstract: In order to improve simulation precision of solar simulator, this paper researched general design scheme of optical system. First of all, this paper discussed optimization techniques for focusing system, optical integrator, collimating system, and which aberrations influenced the uniformity of optical integrator; Secondly, analysis of defocus effect for integrator projector lens and put forward optimal defocus distance formula, then using ZEMAX to design collimating optical system, and simulated the system in LightTools; Finally, tested solar simulator, the results show that: it can simulated one solar constant, irradiation range reached Φ200mm, working distance is 1000mm, irradiation non uniformity in 60mm range is less than ±1%, and in (60-200) mm is less than ± 2%, instability is better than ± 1%/h.

Development of two-axis sun tracking system

Abstract: The volatile fossil fuel price currently creates an opportunity for the development of alternative approaches in electricity generation. Comprehensive and concerted efforts are focused at developing solar electricity generating system (SEGS). One of the challenges faced by SEGS is the apparent trajectory of the sun. Often, SEGS designers use standard testing conditions, whereby the level of solar insolation is taken to be a constant value of 1000W/m2. The only value of solar insolation that is taken to be constant is known as solar constant, which is approximately 1353W/m2. Solar constant is the solar insolation received outside the earth's atmosphere. This value drops significantly as the solar radiation passes through the atmosphere, where the typical range is between 150 W/m2 and 1000W/m2. The reducing intensity of solar insolation is also due to the apparent trajectory of the sun. The sun's path changes daily, and in this project, a novel design of the sun tracker has been tested and is able to do two-axis tracking for photovoltaic based SEGS.

Chapter 12, Solar Radiation

Abstract: Publisher Summary The sun radiates in all regions of the spectrum, from radio waves to gamma rays. The power density of solar radiation on the ground is smaller than that in space owing to atmospheric absorption. Radiation of frequencies above 1000 THz (λ < 300 nm) is absorbed by the upper atmosphere, causing photochemical reactions, producing photoionization, and generally heating up the air. However, this part of the spectrum contains only 1.3% of the solar constant. The ozone layer near 25 km altitude absorbs much of it. Although solar radiation is generated by several different mechanisms, the bulk of it is of the black body type. When one tries to match a black body spectrum to that of the sun, one has the choice of picking the black body temperature that best fits the shape of the solar spectrum or the temperature that, at one astronomical unit, would produce a power density of 1360 W m−2.

Solar Irradiance Variability

Abstract: The Sun has long been considered a constant star, to the extent that its total irradiance was termed the solar constant. It required radiometers in space to detect the small variations in solar irradiance on timescales of the solar rotation and the solar cycle. A part of the difficulty is that there are no other constant natural daytime sources to which the Sun's brightness can be compared. The discovery of solar irradiance variability rekindled a long-running discussion on how strongly the Sun affects our climate. A non-negligible influence is suggested by correlation studies between solar variability and climate indicators. The mechanism for solar irradiance variations that fits the observations best is that magnetic features at the solar surface, i.e. sunspots, faculae and the magnetic network, are responsible for almost all variations (although on short timescales convection and p-mode oscillations also contribute). In spite of significant progress important questions are still open. Thus there is a debate on how strongly irradiance varies on timescales of centuries (i.e. how much darker the Sun was during the Maunder minimum than it is today). It is also not clear how the solar spectrum changes over the solar cycle. Both these questions are of fundamental importance for working out just how strongly the Sun influences our climate. Another interesting question is how solar irradiance variability compares with that of other cool dwarfs, particularly now that observations from space are available also for stars.

Surface Radiation Budget in Hinterland of the Taklimakan Desert

Abstract: The surface radiation budget over the mobile dune and effect of cloud and dust on it were calculated and analyzed based on the radiation data observed at Taklimakan Atmosphere and Environment Observation and Experiment Station(Tazhong observation station) in the hinterland of the Taklimakan Desert.The global solar radiation may be close to the solar constant in some specific weather conditions in summer.The characteristics of radiation budget are quite different under different weather conditions in Tazhong.The global solar radiation is affected the most obviously by dust and cloud weather and its changing amplitude is also the most,and the global solar radiation value in sandstorm day is 80% less than that in sunny day.The daily variation trend of reflecting radiation is consistent with the global solar radiation in different weather conditions in four seasons.The dust and cloud weather has less effect on the downward long wave radiation,and make it increased appreciably;the dust and cloud weather has the least effect on the upward long wave radiation,and the resulted decrease is 10% less than that in a clear day.The net radiation decreases appreciably in the cloudy day,and decreases obviously in the dust day and becomes a negative value.The characteristics of the average daily variation during the experiment period are very close to that in a clear day.The ratios of the average values of the global radiation and the net radiation during the experiment period to that on a clear day are all more than 0.7,which shows that the cloud and dust weather has obvious effect on radiation budget in Tazhong.

Sunsets and solar diameter measurement

Abstract: A sunset over the sea surface offers the possibility to chronometrate a solar transit across the horizon. The vertical solar diameter is proportional to the duration of the sunset, the cosine of the azimuth and the cosine of the latitude of the observing site. The same formula applies to every circle of equal height, called in arabic almucantarat, and it is exploited in the measurements of the solar diameter made with the Danjon's solar astrolabes. The analogies between sunsets and astrolabes observations are presented, showing advantages and sources of errors of these methods of solar astrometry.

Spectral brightness distributions in spectrometric monitoring of the earth from space

Abstract: The effect of the atmosphere on the spectral reflection and scattering of visible and near IR solar radiation by different natural surfaces observed from space and the earth is examined. The shift in the spectral brightness maximum of the emerging radiation relative to the maximum of the solar constant is analyzed. The data are compared with theoretical calculations of the brightness of the emerging radiation.