Showing papers on "Solar constant published in 2009"

Excess open solar magnetic flux from satellite data: 2. A survey of kinematic effects

Abstract: [1] We investigate the “flux excess” effect, whereby open solar flux estimates from spacecraft increase with increasing heliocentric distance. We analyze the kinematic effect on these open solar flux estimates of large-scale longitudinal structure in the solar wind flow, with particular emphasis on correcting estimates made using data from near-Earth satellites. We show that scatter, but no net bias, is introduced by the kinematic “bunching effect” on sampling and that this is true for both compression and rarefaction regions. The observed flux excesses, as a function of heliocentric distance, are shown to be consistent with open solar flux estimates from solar magnetograms made using the potential field source surface method and are well explained by the kinematic effect of solar wind speed variations on the frozen-in heliospheric field. Applying this kinematic correction to the Omni-2 interplanetary data set shows that the open solar flux at solar minimum fell from an annual mean of 3.82 × 1016 Wb in 1987 to close to half that value (1.98 × 1016 Wb) in 2007, making the fall in the minimum value over the last two solar cycles considerably faster than the rise inferred from geomagnetic activity observations over four solar cycles in the first half of the 20th century.

Reconstruction of solar UV irradiance since 1974

Abstract: [1] Variations of the solar UV irradiance are an important driver of chemical and physical processes in the Earth's upper atmosphere and may also influence global climate. Here we reconstruct solar UV irradiance in the range 115–400 nm over the period 1974–2007 by making use of the recently developed empirical extension of the Spectral And Total Irradiance Reconstruction (SATIRE) models employing Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) data. The evolution of the solar photospheric magnetic flux, which is a central input to the model, is described by the magnetograms and continuum images recorded at the Kitt Peak National Solar Observatory between 1974 and 2003 and by the Michelson Doppler Imager instrument on SOHO since 1996. The reconstruction extends the available observational record by 1.5 solar cycles. The reconstructed Ly-α irradiance agrees well with the composite time series by Woods et al. (2000). The amplitude of the irradiance variations grows with decreasing wavelength and in the wavelength regions of special interest for studies of the Earth's climate (Ly-α and oxygen absorption continuum and bands between 130 and 350 nm) is 1–2 orders of magnitude stronger than in the visible or if integrated over all wavelengths (total solar irradiance).

Game-theory approach for multi-objective optimal design of stationary flat-plate solar collectors

Abstract: A game-theory approach has been used for the multi-objective optimum design of stationary flat-plate solar collectors. The clear-day solar-beam radiation and diffuse radiation at the location of the solar collector (Miami) are estimated. Three objectives are considered in the optimization-problem formulation: maximization of the annual average incident solar energy; maximization of the lowest month incident solar energy; and minimization of costs. The game-theory methodology is used for the solution of the three objective-constrained optimization problems to find a balanced solution. This solution represents the best compromise in terms of the super-criterion selected. Two types of sensitivity analyses are conducted on the optimum solution in this work. The sensitivity analysis with respect to the design variables indicates which design valuables are more important to different objective functions. The sensitivity analysis with respect to the solar constant shows that small fluctuations of solar constant ...

Solar Radius Determination from Total Solar Eclipse Observations on 29 March 2006

Abstract: Solar diameter measurements have been made nearly continuously through different techniques for more than three centuries. They were obtained mainly with ground-based instruments except for some recent estimates deduced from space observations. One of the main problems in such space data analysis is that, up to now, it has been difficult to obtain an absolute value owing to the absence of an internally calibrated system. Eclipse observations provide a unique opportunity to give an absolute angular scale to the measurements, leading to an absolute value of the solar diameter. However, the problem is complicated by the Moon limb, which presents asphericity because of the mountains. We present a determination of the solar diameter derived from the total solar eclipse observation in Turkey and Egypt on 29 March 2006. We found that the solar radius carried back to 1 AU was 959.22±0.04 arcsec at the time of the observations. The inspection of the compiled 19 modern eclipses data, with solar activity, shows that the radius changes are nonhomologous, an effect that may explain the discrepancies found in ground-based measurements and implies the role of the shallow subsurface layers (leptocline) of the Sun.

Environmental Testing of Thermal Control Materials at Elevated Temperature and Intense Ultraviolet Radiation

Abstract: This paper presents two test campaigns in the frame of the ongoing program for the European Space Agency’s mission toMercury. Improvements on the experimental setup are presented that enable ground-based simulation of such a harsh space environment. The thermal endurance of white ceramic paints is investigated at 350 C. The solar absorptance of all paints increased significantly. Two types of ceramic woven fabrics were irradiated by 17 solar constants of ultraviolet light at an elevated temperature. The available data from the solar absorptance as a function of an ultraviolet dose up to 52,000 equivalent sun hours was extrapolated to the mission’s end-of-life dose of 100,000 equivalent sun hours. The custom-baked Astroquartz 2 was the best performing material with an estimated end-of-life solar absorptance of 0.35.

Search for periodicities of the Solar Irradiance Data from Earth Radiation Budget Satellite (ERBS) using Rayleigh Power Spectrum Analysis

Abstract: The solar irradiance data plays a very important role for understanding of Solar internal Structure and the solar terrestrial relationships. The Total Solar Irradiance (TSI) is integrated solar energy flux over the entire spectrum which arrives at the top of the atmosphere at the mean sun earth distance. TSI has been monitored from several satellites, e.g. Nimbus 7, Solar Maximum Mission (SMM), The NASA, Earth Radiation Budget Satellite (ERBS), NOAA9, NOAA10, Eureca and the Upper Atmospheric Research Satellite (UARS) etc. From these observations it reveals that the total solar irradiance varies about a small fraction of 0.1 over solar cycle being higher during maximum solar activity condition. In the present paper we have analysed the solar irradiance data from ERBS during the time period from October 15, 1984 to October 15, 2003. First filtering the data by Simple Exponential Smoothing we have applied the Rayleigh Power Spectrum Analysis on the processed data in order to search for its time variation. Study exhibits multi-periodicities on these data around 7, 11, 42, 80, 104, 130, 160, 254, 536, 752, 1142, 1388, 2474 and 4951 days with very high confidence levels (more than 95%). Apart from these strong periods there are some other weak periods around 22, 47, 53, 67, 69, 149, 167, 365, 489 and 683 days. These periods are significantly similar with the periods of other solar activities which may suggest that solar irradiance may be associated with other solar activities.

Incidental Solar Radiation According to the Solar Collector Slope -Horizontal Measurements Conversion on an Inclined Panel Laws

Abstract: In this article we are interested in the optimal choice of the tilt angle of solar water heaters, in the case of Tunis (lat 36°.85, long 10°.2). We studied several variations of usage months: spread all year round or solely reduced for some months: nine, seven or five months centered on winter - the most difficult period to satisfy in term of solar energy. Results show that a more elevated tilt of the collector for some degrees in relation to the latitude of the place (1) is essential espe- cially if we want to make favorable the conditions of collecting in winter where resources in solar energy are at their minimum, whereas, the needs in hot water are at their maximum. In a second part of this article, means of conversion are given, for a collector plane tilt of an angle "i", of the solar data of the received global and diffuse solar radiation by the horizontal plane. The results are resemble those of to Duffie (2) but the correlation is shorter. Thus, we can help laborato- ries which are not equipped with measure devices of solar energy; an apparent data to determine performances of all solar energy conversion system or using it as primary energy source. We can rely on solar data which will be converted accord- ing to both the tilt angle and the orientation of the solar panels.

Solar constant versus the electromagnetic spectrum

Abstract: The electromagnetic spectrum emitted by the Sun and reaching the earth comprises of long-waves, radio waves, amateur, microwave, infrared, visible, ultraviolet, x-rays and gamma rays. The contributions of these waves in the evaluation of solar flux, solar constant and total solar irradiance are examined and the possible impacts as well as importance are discussed for the benefit of undergraduate students.

Solar irradiance absolute radiometers and solar irradiance measurement on spacecraft

Abstract: The working principle and design structure of the Solar Irradiance Absolute Radiometers(SIARs) developed by our research group is introduced.The radiometer offers its two improvements in burying the electrical heater winding into the wall of the cavity to improve the equivalence of electrical and radiative heating and in using thermo-electrical temperature sensor to replace the usual resistance temperature sensor.The SIARs took part in International Pyrheliometer Comparisons(IPC) twice,and calibrated data are coincident well with World Radiometric Reference(WRR).Two SIARs have been put on Physikalisch-Meteorologisches Observatorium Davos/World Radiometric Center(PMOD/WRC) to observe the sun together with the instruments of World Standard Group(WSG) for six years,and they show stable performance and uncertainty within 0.2%.Moreover,a Solar Constant Monitor(SCM) composed of three wide field of view SIARs mounted on SZ-3 spacecraft has been used to measure solar irradiance for five months,obtained data are coincident with those of ACRIM in 0.2%.From June 2008,a Solar Total Irradiance Monitor(STIM) made up of three SIARs has also begun to measure total solar irradiance on FY-3 satellite for long term.

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 a substantial bistability: for a large range of values the realization of snowball (SB) or of warm (W) climate conditions depend on the history of the system. Using recent results on the global climate thermodynamics, we show that that the two regimes feature radically different properties. The efficiency of the climate machine increases with decreasing solar constant in W climate conditions, whereas the opposite takes place in the SB regime. Instead, entropy production is increasing with the solar constant in both branches of climate conditions, and its value is about 4 times as large in the W branch than in the corresponding C state. Finally, the degree of irreversibility of the system is much higher in the W conditions, with an explosive growth in the upper range of the considered values of solar constants. Whereas in the SB regime a dominating role is played by changes in the meridional albedo contrast, in the W 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 transitions at the boundary of the bistable region based upon macro-scale thermodynamic properties is also proposed. Our results support the adoption of a new generation of diagnostic tools based on the 2nd law of thermodynamics for auditing climate model and outline a set of parameterizations to be used in conceptual and intermediate complexity models or for the reconstruction of the past climate conditions.

An optimal method for determining the time of the minimum of the 23rd solar cycle, July 2008

Abstract: The time of the minimum of the solar cycle is usually determined by the minimum of the average monthly sunspot number smoothed over 13 months, i.e., with a large time delay, not earlier than eight months after the event. A new optimal method which allows one to establish the time of the minimum of the cycle as early as four months after the event is proposed. In the new method, the indicator of the time of a cycle minimum is the time of reaching the minimum level of average monthly values of the solar constant after which four succeeding values of this constant are larger than the pre-ceding minimum level. It is shown that the minimum of the past 23rd solar cycle took place in July, and the new 24th cycle started in August 2008.

Direct Solar Radiation and Atmospheric Turbidity in Mikołajki in the Years 1971–1980 and 1991–2000

Abstract: The present study deals with the changing amount of incoming direct solar radiation and the optical state of the atmosphere in Mikolajki in the years 1971–1980 and 1991–2000. The highest level of solar irradiance in these two decades occurred on 23rd June 1977 and amounted to 1043.9 W·m-2. Compared to the first decade analysed, the percentage of the solar constant reaching the Earth in the second decade was higher. The spectral structure of the radiation also changed – the share of the shortest waves (λ<525 nm) increased, whereas the amount of waves with a wavelength of 710 nm or more decreased. In both study periods the annual course of solar extinction (expressed in terms of Linke’s turbidity factor) turned out to have been typical, with the highest values in summer and the lowest in winter. In the years 1991–2000, in all seasons, a lower atmospheric turbidity was observed in comparison with the years 1971–1980. The atmospheric turbidity was also analysed with relation to the air masses. In both decades in question the lowest turbidity occurred in arctic air masses and the highest in tropical air masses. An improved optical state of the atmosphere was observed in all considered air masses, though the biggest decrease in turbidity was found in polar air masses, particularly in the polar maritime old air ( T LAM2 dropped by 0.75) and polar continental air (by 0.70).

The periodic variation of 6.7 days for total solar radiation

Abstract: Analyzing the power spectrum of Total Solar Irradiance (TSI) for the period from 2003 February 25 to 2009 July 6, observed with the Total Irradiance Monitor (TIM) onboard SOlar Radiation and Climate Experiment (SORCE), we found that there are quite a number of periodic variations. The outstanding shortest one is the period of 6.7 days, about one fourth of the period of solar rotation. Checking the solar magnetic field for the same period of time observed with MDI onboard SOHO, we found that there is about 90 degree difference in longitude for the distribution of solar magnetic field. We therefore conclude that both the 90 degree difference in longitude for the distribution of solar magnetic field and the solar rotation are the reason resulting in the periodic variation of 6.7 days for the total solar radiation.

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.