Solar constant

The sun radiates approximately as a blackbody, with an effective temperature of about 6000 K. The total solar flux is 3.9 x 10 W. Using Wien s law, it has been found that the frequency of maximum solar radiation intensity is 6.3 x 10 s (X = 0.48 /rm), which is in the visible part of the spectrum 99% of solar radiation occurs between the frequencies of 7.5 X 10 s (X = 4/um) and 2 x 10 s (X = 0.15/um) and about 50% in the visible region between 4.3 x 10 s (X = 0.7 /rm) and 7.5 X 10 s (X = 0.4 /Ltm). The intensity of this energy flux at the distance of the earth is about 1400 W m on an area normal to a beam of solar radiation. This value is called the solar constant. Due to the eccentricity of the earth s orbit as it revolves around the sun once a year, the earth is closer to the sun in January (perihelion) than in July (aphelion). This results in about a 7% difference in radiant flux at the outer limits of the atmosphere between these two times. 

Hence, the radiative equilibrium temperature is sensitive to changes in the solar constant, planetary albedo, and the radiative properties of the earth-atmosphere-ocean system. In addition, changes internal to the earth-atmosphere-ocean system may alter the climate. Table I is an incomplete list of phenomena that individually or in concert could alter climate. 

Solar Constant solar irrad-iance sunspots Milankovitch cycles... 

The simplest forcing to define and describe -although by no means easy to quantify - is the change or variability of the so-called solar constant. The IPCC (1990, 1995, 1996) provides several estimates of this forcing, e.g.,... 

It must, however, be taken into account that the radiation flux has not always been constant during the 4.6 billion years since the formation of the sun. The solar constant is in fact not a constant at all, as it depends on the state of the sun s surface. For prebiotic syntheses, it is important to consider the wavelengths which can be absorbed by small molecules such as CO2, CO, CH4, N2, NH3, H2O, H2S etc. The premise here, of course, is that most of the synthetic reactions occurred in the gas phase. 

Other parameters of the simulation are specified in subroutine SPECS. The quantity solcon is the solar constant, available here for tuning within observational limits of uncertainty. The quantity diffc is the heat transport coefficient, a freely tunable parameter. The quantity odhc is the depth in the ocean to which the seasonal temperature variation penetrates. In this annual average simulation, it simply controls how rapidly the temperature relaxes into a steady-state value. In the seasonal calculations carried out later in this chapter it controls the amplitude of the seasonal oscillation of temperature. The quantity hcrat is the amount by which ocean heat capacity is divided to get the much smaller effective heat capacity of the land. The quantity hcconst converts the heat exchange depth of the ocean into the appropriate units for calculations in terms of watts per square meter. The quantity secpy is the number of seconds in a year. 

I start program DAV07 at 1 year of simulation time and run it to 10 years of simulation time. A time step of less than a day is necessary initially, as the system adjusts rapidly from its starting values. The time step increases as the system approaches steady state. I tune the simulation by adjusting the value of diffc, the transport parameter, and solcon, the solar constant, to... 

Very little is known about fluctuations of the solar constant and even less about fluctuations of the ultraviolet part of the solar constant. Until now, periodicities of the sun have been evaluated solely from the sun spot cycles, observed over some four hundred years (except for a few desultory observations in ancient China), but the sun has many ways to vary besides sunspot variations. 

Solar cells, 22 220, 9 729, 23 32. See also Photovoltaic (PV) cells antimony compounds, 3 53-54 dye-sensitized, 26 878 degradation of, 22 139 economics of, 22 140 efficiency of, 23 15 for electricity generation, 23 26 hydrogenated amorphous silicon in, 22 135, 136, 138-139 materials for, 23 14-15 micromorph, 22 140 polymethine dyes in, 20 516-517 silicon for, 22 507-508 silicon purification for, 22 496 stacking, 23 38-39 vitreous silica in, 22 444 Solar collectors, 23 25 Solar constant, 23 2 Solar control coatings, 23 16 Solar desalination, 26 89-94 Solar electricity, 23 51, 52 Solar energy... 

Since the earth has temperature, it emits radiant energy called thermal radiation or planetary infrared radiation. Measurements by satellites show an average radiant emission from the earth of about 240 watts per square meter. This is equivalent to the radiation that a black body would emit if its temperature is at -19°C (-3°F). This is also the same energy rate as the solar constant averaged over the earth s surface minus the 30% reflected radiation. This shows that the amount of radiation emitted by the earth is closely balanced by the amount of solar energy absorbed and since the earth is in this state of balance, its temperature will change relatively slowly from year to year. 

The total intensity of sunlight outside the earth s atmosphere is characterized by the solar constant, defined as the total amount of light received per unit area normal to the direction of propagation of the light the mean value is 1368 W m-2, although variations from this mean are common (Lean, 1991). 

The solar constant (intensity of solar radiation outside the Earth s atmosphere at die mean distance between die earth and the sun) has been determined by measurements from satellites and high-altitude aircraft and is 1.353 kilowatts per square meter. This extraterrestrial radiation,... 

Fig. 5.46. Typical I/V curves for an as-produced polymer-fullerene solar cell before and after sealing. Measurements were performed with a solar simulator (Steuer-nagel Solar Constant 575) at an irradiance level of 800 W/m2 and a cell temperature of 55°C. Measured data were corrected to the plotted AM 1.5 values using a calculated mismatch factor of 0.76...

Fig. 5.51. Short-circuit current (Isc) vs. irradiance level of solar simulator (Steuer-nagel Solar Constant 575), at various cell temperatures, for a typical cell sample...

Solar radiation is a form of thermal radiation having a particular wavelength distribution. Its intensity is strongly dependent on atmospheric conditions, time of year, and the angle of incidence for the sun s rays on the surface of the earth. At the outer limit of the atmosphere the total solar irradiation when the earth is at its mean distance from the sun is 1395 W/m2. This number is called the solar constant and is subject to modification upon collection of more precise experimental data. 

The insolation at the outer edge of the atmosphere is expressed in terms of the solar constant by... 

Solar constant. This does not change much (less than 2%). Most of the change is due to sunspots, which change on an 11-year cycle. Generally, this factor is ignored by policy wonks, in part, because we cannot do anything about it. 

By how much would the Earth s atmospheric temperature change if the greenhouse effect, the albedo, and the solar constant are all increased by 1.5%, relative Please give your answer to two significant figures. 

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