Showing papers on "Solar constant published in 1975"

The Effects of Changing the Solar Constant on the Climate of a General Circulation Model

Abstract: A study is conducted to evaluate the response of a simplified three-dimensional model climate to changes of the solar constant. The model explicitly computes the heat transport by large-scale atmospheric disturbances. It contains the following simplifications: a limited computational domain, an idealized topography, no heat transport by ocean currents, no seasonal variation, and fixed cloudiness. It is found that the temperature of the model troposphere increases with increasing solar radiation. The greatest increase occurs in the surface layer of higher latitudes due to the effects of the snow-cover feedback mechanism as well as the suppression of vertical mixing by a stable lower troposphere. This result is found to be qualitatively similar to that obtained from previous studies with one-dimensional zonal mean models. One of the most interesting features of this investigation is the extreme sensitivity of the intensity of the computed hydrologic cycle to small changes of the solar constant. Cur...

Analytical Analysis of a Budyko-Type Climate Model

Abstract: For a given value of the solar constant we have found that the Budyko-type climate model gives two positions for the edge of the polar ice sheet. The results of the Budyko model suggest that with a decrease in the solar constant of about 1.6%, the ice cap reaches a latitude of about 50°. At this point the model breaks down and the solution for the position of the edge of the polar ice sheet becomes complex. We have based our conclusions on analytic investigations. Numerical calculations were used only to support our analytic results.

Long term variations in the albedo and surface temperature of the Earth

Abstract: THE surface temperature of the Earth depends primarily on the solar constant, the Earth's albedo and the total mass and chemical composition of the terrestrial atmosphere. Studies of climate covering the past few million years have generally allowed for variations in albedo in calculating average values of the surface temperature. But over longer periods of time, however, less allowance has been made for albedo variations; it has, indeed, frequently been assumed that the albedo, when averaged over a long enough time, can be taken to be constant (see ref. 1). We wish to point out that, on the contrary, long term variations in the albedo can be expected to occur, and to produce significant changes in the average surface temperature.

Planetary Brightness Changes: Evidence for Solar Variability

Abstract: Brightness changes of Uranus and Neptune at 440 nanometers were highly correlatedfrom 1956 to 1966. Recent observations ofSaturn's satellite Titan and of Uranus and Neptune show a steady brightening at 551 and 472 nanometers since 1972. Either the solar constant is slightly variable or solar activity causes correlated changes in the albedos ofplanetary bodies. 1972 1973 1974 1975 Year Fig. 1. Variations of the narrow-band blue (b) and yellow (y) magnitudes of Titan, Uranus, and Neptune since 1972, reduced to mean opposition distances of 9.539, 19.191, and 30.071 A.U., respectively, and corrected to a solar phase angle of zero. The zero point of the ordinate is arbitrary, with brightness increasing in the upward direction. Numbers at the left are the magnitudes of the first (leftmost) plotted points and (in parentheses) the subsequent increases. The number of nights on which measurements contributing to each mean were made is indicated below each point. Note that 0.01 mag 1 percent. continuously at Lowell Observatory by various investigators from 1950 to 1966 (6, 7). Possible systematic errors in the data prior to 1956, resulting from changes in the early instrumentation, reduce the weight of these initial magnitudes, but later data show no evidence of such errors. The annual mean magnitudes are summarized in Fig. 2, which also includes the recent b magnitudes; I converted all the magnitudes here to the b scale, using a transformation based on the observations and reductions of Jerzykiewicz (3). A strong variation in Uranus, illustrated in Fig. 2, results from its oblateness and changing aspect. From the observations a \"photometric\" oblateness of 0.045 was derived, in reasonable agreement with observed values of the geometrical oblateness (8). Variations in the brightness of Neptune during the same interval are also shown in Fig. 2. Of considerably greater interest than the individual variations in the brightness of the planets is the fact that fluctuations in the brightness of the two planets, with respect to the oblateness curve for Uranus and the straight line curve for Neptune, are very highly correlated with one another. The correlation coefficient is 0.66, significant at the 97.5 percent level, and it is not sensitive to different adopted values of the oblateness of Uranus in the range 0.03 to 0.06. The initial data (1950-1955), despite 7 NOVEMBER 1975 their low weight, tend to confirm this relationship. Overall, there is a strong suggestion of common causation for the variations as in the data since 1972. No obvious association is seen between the fluctuations and the solar maxima of 1957 and 1968. Systematic errors in the broadband data seem to be ruled out by the fact that the planets were observed at different seasons, with only a few overlapping nights. Magnitudes determined on the same nights, moreover, are totally uncorrelated and simply exhibit normal observational scatter. The conclusion, then, is that the brightening trend of Titan, Uranus, and Neptune has been in progress since at least 1972. Furthermore, there is strong evidence for correlated photometric variations of Uranus and Neptune during the years 1956 through 1966. No reasonable explanation for the cause of the brightness variations is evident that does not involve the sun, directly or indirectly, as the causative factor. Approximately half of the increase in the brightening of Uranus since 1972 may be explained in terms of the oblateness effect. This being the case, the increases in Uranus and Neptune may not be significantly different from one another. If, moreover, we choose to consider the brightening of Titan as anomalous, possibly due to a seasonal effect, then an increase in solar brightness of about 2 percent may have occurred since 1972. (Titan perhaps represents a special case since its orbit is inclined 260 with respect to the ecliptic. Maximum inclination of the orbit as seen from Earth occurred in mid-1973.) Such a large variation in visible output, if real, would be unique for solar-type stars. Jerzykiewicz and Serkowski (7), in a 10-year survey of stars similar in luminosity and temperature to the sun, found no variations in excess of 0.8 percent. Even these may have been the result of normal observational errors. Therefore, it seems that an alternative explanation for the current variations of planetary brightness must be sought. The sun is known to vary both at wavelengths shortward of the visible spectrum and in the solar wind flux, in response to localized activity (for example, flares) and the 11-year cycle. Geophysical effects due to this activity, such as auroras and ionospheric disturbances, are often dramatic, but the effects, if any, on Earth's albedo and radiation balance are not known. It appears reasonable, therefore, to hypothesize that the variations we see in the planets may be due, at least in part, to albedo changes caused by some form of solar variation not necessarily in the visible spectrum. Photochemical effects, for example, are a possibility. .oa 5.76\".

Solar flux and its variations

Abstract: Data are presented on the solar irradiance as derived from a number of sources. An attempt was made to bring these data onto a uniform scale. Summation of fluxes at all wavelengths yields a figure of 1357.826 for the solar constant. Estimates are made of the solar flux variations due to flares, active regions (slowly varying component), 27-day period, and the 11-yr cycle. Solar activity does not produce a significant variation in the value of the solar constant. Variations in the X-ray and EUV portions of the solar flux may be several orders of magnitude during solar activity, especially at times of major flares. It is established that these short wavelength flux enhancements cause significant changes in the terrestrial ionosphere.

The Total and Spectral Solar Irradiance and Its Possible Variations

Abstract: The present status of knowledge of the total and spectral irradiance of the sun is briefly reviewed. Currently accepted values of the solar constant and the extraterrestrial solar spectral irradiance are presented along with a discussion of how they were derived. Data on the variability of the solar constant are shown to be conflicting and inconclusive. Some of the alleged sun-weather relationships are cited in support of the need of knowing more precisely the variations in total and spectral solar irradiance. An overview of a solar monitoring program is discussed, with special emphasis on the Solar Energy Monitor in Space experiment which was proposed for several spacecraft missions. It is a combination of a solar constant detector and a prism monochromator. The determination of absolute values and the possible variations of the total and spectral solar irradiance, from measurements outside of the atmosphere is discussed.

Variation of the solar atmospheric rotation over the 11 year cycle

Abstract: The synodic rotation period and power spectra of solar microwave sources are investigated using accurate data in the interval 1956 to 1970. The variation of the approximate 27 day period is obtained over a complete solar cycle and is thought to be a result of the latitude change over the solar cycle of the origins of the radio emissions. High resolution power spectra have also been obtained and revealed the existence of a double peaked line near 160 day period. This line is attributed to changes in either the Eartn's heliographic latitudes or the Earth's inclination to the Earth-Sun line.

Numerical experiments on short-term meteorological effects of solar variability

Abstract: A set of numerical experiments was conducted to test the short-range sensitivity of a large atmospheric general circulation model to changes in solar constant and ozone amount. On the basis of the results of 12-day sets of integrations with very large variations in these parameters, it is concluded that realistic variations would produce insignificant meteorological effects. Any causal relationships between solar variability and weather, for time scales of two weeks or less, rely upon changes in parameters other than solar constant or ozone amounts, or upon mechanisms not yet incorporated in the model.

The Energy Flux of the Sun

Abstract: About seven years ago Labs and Neckel (1968) prepared a review of the then current status of the solar energy flux. The most reliable solar radiation data were given in an appendix in the form of extensive tables. Some minor corrections (Labs and Neckel, 1970) transform these data into the “International Practical Temperature Scale of 1968” (IPTS 68, see Barber, 1969).