Showing papers on "Solar constant published in 2010"

Measuring solar reflectance Part I: Defining a metric that accurately predicts solar heat gain

Abstract: R. Levinson, H. Akbari and P. Berdahl Measuring solar reflectance—Part I Measuring solar reflectance—Part I: defining a metric that accurately predicts solar heat gain Ronnen Levinson Hashem Akbari ∗ Paul Berdahl Heat Island Group Lawrence Berkeley National Laboratory April 28, 2010 Abstract Solar reflectance can vary with the spectral and angular distributions of incident sunlight, which in turn depend on surface orientation, solar position and atmospheric conditions. A widely used solar reflectance metric based on the ASTM Standard E891 beam-normal solar spectral irradiance underestimates the solar heat gain of a spectrally selective “cool colored” surface because this irradiance contains a greater fraction of near-infrared light than typically found in ordinary (unconcentrated) global sunlight. At mainland U.S. latitudes, this metric R E891BN can underestimate the annual peak solar heat gain of a typical roof or pavement (slope ≤ 5:12 [23 ◦ ]) by as much as 89 W m −2 , and underestimate its peak surface temperature by up to 5 K. Using R E891BN to characterize roofs in a building energy simulation can exaggerate the economic value N of annual cool-roof net energy savings by as much as 23%. We define clear-sky air mass one global horizontal (“AM1GH”) solar reflectance R g,0 , a simple and easily measured property that more accurately predicts solar heat gain. R g,0 predicts the annual peak solar heat gain of a roof or pavement to within 2 W m −2 , and overestimates N by no more than 3%. R g,0 is well suited to rating the solar reflectances of roofs, pavements and walls. We show in Part II that R g,0 can be easily and accurately measured with a pyranometer, a solar spectrophotometer or version 6 of the Solar Spectrum Reflectometer. Akbari’s current address: Department of Building, Civil and Environmental Engineering, Concordia University, Montreal, Quebec, Canada. In press at Progress in Solar Energy April 28, 2010

Reconstruction of solar spectral irradiance since the Maunder minimum

Abstract: [1] Solar irradiance is the main external driver of the Earth's climate. Whereas the total solar irradiance is the main source of energy input into the climate system, solar UV irradiance exerts control over chemical and physical processes in the Earth's upper atmosphere. The time series of accurate irradiance measurements are, however, relatively short and limit the assessment of the solar contribution to the climate change. Here we reconstruct solar total and spectral irradiance in the range 115–160,000 nm since 1610. The evolution of the solar photospheric magnetic flux, which is a central input to the model, is appraised from the historical record of the sunspot number using a simple but consistent physical model. The model predicts an increase of 1.25 W/m2, or about 0.09%, in the 11-year averaged solar total irradiance since the Maunder minimum. Also, irradiance in individual spectral intervals has generally increased during the past four centuries, the magnitude of the trend being higher toward shorter wavelengths. In particular, the 11-year averaged Ly-α irradiance has increased by almost 50%. An exception is the spectral interval between about 1500 and 2500 nm, where irradiance has slightly decreased (by about 0.02%).

Thermodynamic analysis of snowball Earth hysteresis experiment: Efficiency, entropy production and irreversibility

Abstract: We present an extensive thermodynamic analysis of a hysteresis experiment performed on a simplified yet Earth-like climate model. We slowly vary the solar constant by 20% around the present value and detect that for a large range of values of the solar constant the realization of snowball or of regular climate conditions depends on the history of the system. Using recent results on the global climate thermodynamics, we show that the two regimes feature radically different properties. The efficiency of the climate machine monotonically increases with decreasing solar constant in present climate conditions, whereas the opposite takes place in snowball conditions. Instead, entropy production is monotonically increasing with the solar constant in both branches of climate conditions, and its value is about four times larger in the warm branch than in the corresponding cold state. Finally, the degree of irreversibility of the system, measured as the fraction of excess entropy production due to irreversible heat transport processes, is much higher in the warm climate conditions, with an explosive growth in the upper range of the considered values of solar constants. Whereas in the cold climate regime a dominating role is played by changes in the meridional albedo contrast, in the warm climate regime changes in the intensity of latent heat fluxes are crucial for determining the observed properties. This substantiates the importance of addressing correctly the variations of the hydrological cycle in a changing climate. An interpretation of the climate transitions at the tipping points based upon macro-scale thermodynamic properties is also proposed. Our results support the adoption of a new generation of diagnostic tools based on the second law of thermodynamics for auditing climate models and outline a set of parametrizations to be used in conceptual and intermediate-complexity models or for the reconstruction of the past climate conditions. Copyright © 2010 Royal Meteorological Society

Solar Cycles in 150 Years of Global Sea Surface Temperature Data

Abstract: The purpose of the present work is to demonstrate that a solar cycle response exists in surface temperature using the longest global dataset available, which is in the form of 1854‐2007 sea surface temperature (SST), with an emphasis on methods and procedures, data quality, and statistical tests and the removal of deterministic signals, such as volcano aerosol forcing and greenhouse gas warming. Using the method of compositemean difference (CMD) projection, signals of warming during solar maximum and cooling during solar minimum years are found in the global SST over the 14 cycles, dispelling previous claims that the solar cycle response before 1920 is opposite to that of the modern era. The magnitude of the solar cycle response averaged over the oceans between 608S and 608N is about 0.18C of warming for each W m 22 variation of the solar constant (but is slightly lower, at ;0.0858C, when periods of suspected bad data are averaged in, which is consistent with previous work). The signal is robust provided that the years near the Second World War are excluded, during which transitions from British ships to U.S. ships introduced warm bias in the SST, as recently pointed out by D. Thompson and his colleagues. Monte Carlo tests show that the extracted signal has less than 0.02% chance of being a random occurrence. This establishes the existence of a solar cycle response at the earth’s surface at high statistical confidence. Contamination of the signal by volcano aerosols is estimated using the multiple CMD inversion method and found to be small over this long record, although ENSO contamination varies depending on the period chosen but is also small. The multidecadal trend of response to solar forcing is found to account for no more than a quarter of the observed warming in SST during the past 150 yr, under a reasonable but unproven assumption that the climate response to secular solar forcing and to solar cycle forcing has the same spatial pattern.

On the constancy of the solar radius. iii.

Abstract: The Michelson Doppler Imager on board the Solar and Heliospheric Observatory satellite has operated for over a sunspot cycle. This instrument is now relatively well understood and provides a nearly continuous record of the solar radius in combination with previously developed algorithms. Because these data are obtained from above Earth's atmosphere, they are uniquely sensitive to possible long-term changes of the Sun's size. We report here on the first homogeneous, highly precise, and complete solar-cycle measurement of the Sun's radius variability. Our results show that any intrinsic changes in the solar radius that are synchronous with the sunspot cycle must be smaller than 23 mas peak to peak. In addition, we find that the average solar radius must not be changing (on average) by more than 1.2 mas yr{sup -1}. If ground- and space-based measurements are both correct, the pervasive difference between the constancy of the solar radius seen from space and the apparent ground-based solar astrometric variability can only be accounted for by long-term changes in the terrestrial atmosphere.

Solar Thermal and Biomass Energy

Abstract: Part I: Sun Energy Chapter 1: The solar radiation The solar physics The solar constant The extraterrestrial radiation The position of the Sun in the celestial vault The solar radiation on the Earth's soil during clear sky days Instantaneous direct radiation received on a surface Instantaneous global radiation received on a surface Calculation of direct energy received on a surface The true solar time The diagram of solar trajectories The monthly average solar radiation on inclined surfaces Daily radiation on an inclined surface Hourly solar radiation on inclined surfaces The local radiation data retrieval Variation in the energy which can be intercepted by the position of the surfaces Chapter 2: Solar energy utilization Introduction Low-temperature solar thermal technology Medium-temperature solar thermal technology High-temperature solar thermal technology General bibliography and consulted websites - Part I Part II: Biomasses Energy Chapter 3: Biomasses identities Introduction Definition and classification Origin and nature Commercial forms Chapter 4: Energy from biomasses Biomass energy conversion Biochemical conversion Thermochemical conversion Chapter 5: Environmental aspects Reduction of emissions into the atmosphere

Solar luminous constant versus lunar luminous constant

Abstract: The Sun illuminates the earth directly during the day while it provides a dim light indirectly via moon during night. The measure of this light is illuminance and it is defined in photometry as the total luminous flux or apparent intensity of light hitting or passing through a surface. Both these constants are equivalent to solar constant but with the power at each wavelength being weighted according to the spectral luminous efficiency of the human eye. Theoretical expressions and numerical estimates for these are presented and compared with the reported values satisfactorily.

Fast changes of the solar irradiance

Abstract: The results of special measurements of solar irradiance with high resolution in time domain are compared with results of traditional measurements. Three possible characteristic parameters are studied to describe the dynamic quality of the recorded dataset: standard deviation, frequency density distribution law of increments and the number of fronts of the solar radiation per time unit. Recording traditionally one-minute average values of the solar irradiance, most of the changes cannot be registered in the condition of clouds cumulus humilis.

A Null Hypothesis for CO2

Abstract: Energy transfer at the Earth's surface is examined from first principles. The effects on surface temperature of small changes in the solar constant caused by the sunspot cycle and small increases in downward long wave infrared (LWIR) flux due to a 100 ppm increase in atmospheric CO2 concentration are considered in detail. The changes in the solar constant are sufficient to change ocean temperatures and alter the Earth's climate. The surface temperature changes produced by an increase in downward LWIR flux are too small to be measured and cannot cause climate change. The assumptions underlying the use of radiative forcing in climate models are shown to be invalid. A null hypothesis for CO2 is proposed that it is impossible to show that changes in CO2 concentration have caused any climate change, at least since the current composition of the atmosphere was set by ocean photosynthesis about one billion years ago.

Photosynthetic Solar constant

Abstract: An important concept of photosynthetic solar constant is proposed. This signifies the value of power produced in the form of biomass through the photosynthetic engine by making use of the visible band present in the standard solar constant under ideal conditions. Its value is estimated as 70 W/m 2 which corresponds to an equivalent biomass of 4.5x10 -6 Kg/m 2 /s.

Solar Radiation at Total Solar Eclipse, 29-March 2006, at Tobruq

Abstract: Problem statement: Measurement of the different components of solar radiation and fractions of these components for the global (horizontal and tracker), direct (white and three colors, yellow, red and infrared) and diffuse solar radiation during the solar eclipse, 29 March 2006 at Tobruq, Libya (Lat. 32.08°N and Long. 23.98°E). The time interval of solar eclipse was 2 h: 40 m and the maximum magnitude of eclipse at this region was 0.995. Conclusion: The results showed that the maximum percent of color in the total direct solar radiation during the true eclipse from the first contact to the end contact was in the infrared, where the percent were in the green (11.74%), yellow (15.69%), red (14.88%) and infrared (57.68%).

Mini solar constant heat cup

Abstract: The utility model discloses a mini solar constant heat cup, which mainly solves the problem that people cannot timely drink hot water when being on a business trip or going out to travel. The mini solar constant heat cup consists of a cup body and a cup cover, and is characterized in that the shell of the cup body is provided with a solar cell panel, the bottom part of the cup body is provided with a solar battery which is connected with an electric heater, the shell of the cup body is provided with a switch, a hand-operated charger is arranged between the shell of the cup body and a liner, and both the hand-operated charger and the solar cell panel can charge the solar battery. When being placing on the place with sunlight, the solar cell panel can convert the sunlight into energy to be stored in the battery; when a user needs to drink hot water, the switch can be opened, and cold water can be heated by the battery; and when sunlight is not available, the handle of the hand-operated charger can quickly charge the solar battery, and thereby the user can drink hot water at any time and at any place.

Concerning the photosynthetic solar constant

Abstract: The photosynthetic solar constant is revised by considering experimental determinations of the wavelengthdependence of photosynthetic quantum efficiency and absorbance. Using the efficiency of the light-independent metabolic phase of photosynthesis, a new estimate of 17.5 W m -2 is obtained for the photosynthetic solar constant.