Showing papers on "Solar constant published in 1977"

Climate and the changing sun

Abstract: Long-term changes in the level of solar activity are found in historical records and in fossil radiocarbon in tree-rings. Typical of these changes are the Maunder Minimum (A.D. 1645–1715), the Sporer Minimum (A.D. 1400–1510), and a Medieval Maximum (c. A.D. 1120–1280). Eighteen such features are identified in the tree-ring radiocarbon record of the past 7500 years and compared with a record of world climate. In every case when long-term solar activity falls, mid-latitude glaciers advance and climate cools; at times of high solar activity glaciers recede and climate warms. We propose that changes in the level of solar activity and in climate may have a common cause: slow changes in the solar constant, of about 1% amplitude.

Nimbus-6 earth radiation budget experiment

Abstract: This paper describes the Nimbus-6 earth radiation budget experiment including its prelaunch calibration and in-flight performance. A preliminary assessment of the data shows the ERB measurement of the solar constant to be 1392 W/m2 which is 1.6% higher than the expected value of 1370 W/m2. Both values are traceable to the cavity radiometer scale. There is a disagreement between the fixed wide-angle and scanning narrow-angle measurements of planetary outgoing longwave radiation flux. Since the scanning channels are calibrated in-flight and show good agreement with previous observations of the Nimbus-3 satellite, the discrepancy is believed to be due to erroneous wide-angle flux estimates. The erroneous estimates may be caused by the misinterpretation of the transfer function for the wide-angle-earth-flux sensing thermopile detectors when viewing the earth which, unlike the prelaunch calibration source, does not fill the field of view of the detector and is not an isotropic radiation source. A field of view factor for the wide-angle channels is determined using an in-flight calibration procedure using the night-time scanning channel longwave radiation flux measurements as the absolute standard. The planetary global albedoes, longwave radiation fluxes, and net radiation are about 30%, 240 W/m2, and −4 W/m2 for the months of July and August 1975, which is in good agreement with previous Nimbus-3 estimates.

Frequency of nearby supernovae and climatic and biological catastrophes

Abstract: MCCREA1,2 has proposed that the encounter of the Solar System with a dense cloud of interstellar material during its passage through a spiral arm of the Galaxy may produce such climatic catastrophes on Earth as the ice epochs. His thesis, an extension of several earlier investigations3,4,5, is based on the expected effect on the solar constant of an increased accretion rate. Unfortunately, the cloud density necessary to produce the required variation is 105 to 107 cm−3, and although clouds with such extreme densities are thought to exist6, Begelman and Rees7 point out that they are so compact and unusual as to reduce the likelihood of the Sun ever encountering one. (Dennison and Mansfield's suggestion8 that there is no evidence for the existence of a nearby super-dense cloud which could have caused the most recent ice epoch has been answered by McCrea9.) Begelman and Rees7 in fact showed that a much more modest cloud density (≃102 to 103 cm−3) would prevent the solar wind from reaching the Earth, with resulting modification of the near-Earth environment; however, the climate consequences of such a modification are not well understood. We present here an alternative hypothesis which still retains McCrea's association with the passage of the Solar System through a spiral arm, but which relates the initiation of an ice epoch, plus biological catastrophes, to an encounter of the Solar System with a nearby supernova outburst rather than a super-dense interstellar cloud.

The effect of sunspots and faculae on the solar constant.

Abstract: We study the available measurements of the solar constant made at ground sites and from recent space observations to determine whether sunspots or faculae produce a detectable modulation of either the solar flux or the earth's atmospheric transmission. The data from radiometers on Mariners 6 and 7 rule out any relative change of the solar constant in space due directly to faculae or spots exceeding 0.03%. This limit is two orders of magnitude smaller than previous values obtained from ground measurements. The measurements made at mountain stations of the Smithsonian Astrophysical Observatory between 1923 and 1952 show a marginally significant increase of solar constant at the level of 0.1%, related specifically to high projected facular area. Since this increase is not seen in the space measurements, we suggest that it may reflect a change in the earth's atmospheric transmission, possibly due to a change in ozone concentration induced by variation of facular ultraviolet radiation.

Feedbacks in Vertical-Column Energy Balance Models

Abstract: Order-of-magnitude estimates are made for the feedbacks between the global mean surface temperature and the mean tropospheric lapse rate, the mean surface relative humidity and the mean atmospheric relative humidity profile. It is found that with the possible exception of the surface temperature-surface relative humidity feedback the magnitudes of these feedback are not sufficient to significantly alter the sensitivity of the global mean surface temperature to changes in the solar constant as calculated using a vertical-column energy balance model of the earth's atmosphere.

Rocket calibration of the Nimbus 6 solar constant measurements.

Abstract: Total solar irradiance was observed simultaneously outside the earth's atmosphere by three types of absolute cavity radiometers and duplicates of four of the Nimbus 6 Earth Radiation Budget (ERB) solar channels in a June 1976 sounding rocket experiment. The preliminary average solar constant result from the cavity radiometers is 1367 Wm (-2) with an uncertainty of less than + or - 0.5% in S.I. units. The duplicate ERB channel 3 on the rocket gave a value of 1389 Wm (-2) which agreed exactly with the Nimbus 6 ERB channel 3 measurement made simultaneously with the rocket flight.

Solar constants and radiometric scales

Abstract: The basic requirement for any type of measurement in which comparisons are made in a scale, relative or absolute. The values used by the Committee on Solar Electromagnetic Radiation to derive the solar constant were in different radiometric scales. Assuming that only difference in radiometric references produced the wide scatter of individual values, an attempt was made to convert all values to one radiometric reference. A radiometric scale based on electrical power equivalence was used as the reference. The resulting value was 137.5 mW · cm−2, as compared to the CSER derived value of 135.3 mW · cm−2. This revised value lies within the error bounds of all the values used in the analysis. The revised estimate was then compared to values derived from more recent experiments. There appears to be a discrepancy between values derived in and out of the atmosphere.

Measurement of the earth radiation balance as an instrument design problem.

Abstract: The net radiation balance of the earth is important globally for synoptic scale models and long-term climatic trends. It is important at the mesoscale level because it is a strong driving force on local meteorological phenomena. Both synoptic and mesoscale measurements are possible only from earth orbiting spacecraft, and serious efforts have been made to implement them. They have not achieved sufficient accuracy, precision, and stability to be really meaningful meteorologically. Measuring a small difference between two large numbers—the input to the earth and the earth radiation to space—is quite difficult and compounded by the spectral differences between the two. The instrumental considerations to achieving improvements in net radiation balance are discussed. The ratio of input to outflow, like albedo, is a dimensionless number which is amenable to measurement without recourse to calibrated instruments. If the solar constant is indeed reasonably constant, this ratio, which is more easily measured than an absolute value of either quantity, will be acceptable. Instrument stability, both spectral and absolute, as well as calibration methods and accuracy will be discussed with specific emphasis on estimating how and to what degree they can be improved.

The Effects of Changing Fluxes of Solar UV Radiation and Solar Cosmic Rays on the Middle Atmosphere Temperature and Ozone Concentration

Abstract: The question “How constant is the solar constant ?” has been the subject of much speculation for many years. Heath (1973) made significant progress in placing this curiosity on firmer ground; using Nimbus 3 and 4 data he reported on variations of the solar constant between 120 nm and 340 nm suggesting that the variations were mainly associated with two active regions on the sun. Ruderman and Chamberlain (1975) demonstrated that cosmic rays produce nitric oxide in the atmosphere which in turn catalytically destroys odd oxygen. Since solar cosmic rays are modulated by the interplanetary magnetic field sector structure, which appears to be related to active regions (Heath et al. 1975) it is appropriate to estimate the combined effects of these variations of the solar output on the stratosphere and mesosphere.

The self-calibrating sensor of the Eclectic Satellite Pyrheliometer /ESP/ program

Abstract: A self-calibrating thermopile sensor having a cavity type receiver is described. Its incorporation into pyrheliometric instrumentation, including the electronics and control, is also discussed. Completed devices are capable of solar irradiance measurements with an accuracy to within 0.5% and can detect solar variability to a level approaching 0.001% in space.

Current pyrheliometry for total solar irradiance observations

Abstract: A Type IV active cavity radiometer (ACR IV) was developed at JPL in 1975-76 as part of the NASA Weather and Climate Program. It is capable of defining the absolute radiation scale with an uncertainty near 0.1% and a resolution of 0.02% at the nominal solar 'constant' level. The ACR IV is the first pyrheliometer capable of measurements at the 0.1% level, which is the threshold of solar 'constant' variability of significance for climatological modeling. A prototype has been tested, and a flight instrument was flown in a 1976 sounding rocket experiment which determined a solar 'constant' value of 1368 W/sq m. A three-detector version of the ACR IV is being developed to monitor the solar 'constant' during 1979-80 as part of NASA's Solar Maximum Mission. Another ACR IV will measure the solar 'constant' as part of the Spacelab I mission in 1980.