Showing papers on "Solar constant published in 1996"

Simulation with an O-AGCM of the influence of variations of the solar constant on the global climate

Abstract: Two simulations have been carried out With a global coupled ocean—atmosphere circulation model to study the potential impact of solar variability on climate. The Hoyt and Schatten estimate of solar variability from 1700 to 1992 has been used to force the model. Results indicate that the near—surface temperature simulated by the model is dominated by the long periodic solar fluctuations (Gleissberg cycle), with global mean temperatures varying by about 0.5 K. Further results indicate that solar vari— ability induces a similar pattern of surface temperature change as the increase of greenhouse gases, i. e. an increase of the land—sea contrast. However, the solar— induced warming pattern over the ocean during Northern Hemispheric summer is more centered over the Northern Hemisphere subtropics, compared to a more uniform warming associated with the increase in greenhouse gases. Finally, the magni— tude of the estimated solar warming during the 20th century is not sufficient to explain the observed warming. The recent observed 30-year trends are inconsistent with the solar forcing simulation at an estimated 90% significance level. Also, the observed trend pattern agrees better with the greenhouse warming pattern.

The Parameterization of Shortwave and Longwave Radiative Fluxes for Use in Zonally Averaged Climate Models

Abstract: The shortwave and longwave fluxes at the top of the atmosphere (TOA) and at the surface are parameterized in term of solar constant, solar zenith angle, cloud parameters (amount, optical depth, height, and emissivity), surface albedo, surface air temperature, surface temperature, and atmospheric CO2 concentration. Detailed radiative models are used to calculate up- and downward radiative fluxes at TOA and at the surface with input from standard vertical atmospheric profiles of temperature, water vapor, and ozone. Expressions for clear-sky and completely overcast conditions are presented. It is shown that there is reasonably good agreement between the radiative fluxes calculated with this parameterization, with the detailed radiation models and with standard radiation codes (ICRCCM). Furthermore, it is shown that the parameterization is able to produce with reasonable accuracy several aspects of the latitudinally and seasonally varying, zonally averaged shortwave and longwave radiative fluxes at T...

SOLCON Solar Constant Observations from the ATLAS Missions

Abstract: The solar constant observations obtained by the SOLCON/ATLAS experiment during the three successive missions are presented based on the Space Absolute Radiometric Reference (SARR) defined during the ATLAS-2 mission. The objectives of SOLCON, namely to obtain accurate measurements of the solar constant and to compare them with the observations obtained from free flyers in the hope of establishing a baseline and strategy for monitoring the solar constant at climate scale, have been achieved successfully with the three ATLAS missions. The long range objective of insuring the solar constant data continuity will, however, require that an alternative approach than that of the ATLAS program be found to fly and retrieve SOLCON.

Solar Rotation Measurements at Mount Wilson over the Period 1990-1995

Abstract: One of the most fundamental properties of the Sun is its rate of rotation Kinetic energy of large-scale circulation might interact with rotation and cause the surface rate to vary throughout the solar cycle The solar wind carries off angular momentum from the Sun, and the coupling between the outer and inner parts of the heliosphere might produce effects that are evident in the photosphere and chromosphere The quadrapole moment of Sun's gravitational potential depends on the rotation rate The interaction between rotation, convection, and solar magnetic fields forms the solar dynamo which governs the solar cycle of activity Although the rate of solar rotation has been measured for decades, several key questions remain: What is the rotation rate, and what is the uncertainty in this value? Does the rotation rate depend on the solar cycle? Can the gradient of rotation rate as a function of distance from the solar center be detected within the solar atmosphere? The synoptic program of solar observations carried out at the 150 foot tower of the Mount Wilson Observatory has long been a source of measurements which address these questions Improvements in the facilities of this program over the past decade have led to a reduction in the errors of measurement which now permit a new examination of these questions Key improvements were: 12/81?installation of a fiber-optic image reformattor to select the spectral sampling of the absorption lines; 2/86?multiple daily observations were begun; 12/87?the Cr II line at ?52373 was added to the regular program of observation; 9/90?the grating mount and alignment system were replaced; 7/91?the polarization analysis optics were placed in a new alignment box and index matching fluid was introduced around the KDP variable retarder; 11/95?antireflection optics were installed for the KDP end windows to reduce interference fringes Each of these changes resulted in a noticeable reduction in the rms error in the measured rotation rate which is now at the level of 7 m s-1 Within this error we find that there is no solar cycle variation in the rotation rate and the rate is the same for both ?5250 and ?5237 We find that the synodic rotation rate is 284 ? 001 ?rad s-1 This value agrees well with most recent determinations

An Alternative Explanation for the Observed Variation of Solar p-Modes with the Solar Cycle

Abstract: By mimicking the effects of a magnetic field on the interior structure of a solar model, observed changes in p-mode frequencies over the course of the solar cycle are explained in terms of a change in the intensity and distribution of a magnetic field near the top of the solar convection zone; previous attempts of explain these observations have concentrated on magnetic fields extending into the solar atmosphere. Specifically, the observed frequency changes for the 5 ≤ l ≤ 60 modes between 1986 and 1989 can be accounted for by a change in magnetic field strength of 400 G approximately 320 km below the solar surface; in a standard solar model, this depth corresponds to a temperature of 10,800 K and a pressure of 3.63 × 105 dyn cm-2. These results are discussed in light of a measured change in the solar radius of 4 km between 1992 and 1994 by the Solar Disk Sextant Experiment.

SOHO(Solar and Heliospheric Observatory) Contribution to the Measurement of the Energy Sources of the Solar-Terrestrial System. An Introduction to SOHO Project.

Abstract: The possible contributions of the SOHO to the Solar Terrestrial Energy Program are discussed. Several SOHO measurements and observations will be of interest for the study of the energy flow in the solar terrestrial system: - the total solar irradiance or solar constant will be monitored with an accuracy of about 0.15% by solar radiometers in one of the helioseismology instruments, - the solar EUV irradiance will be measured directly by an EUV monitor (at 305 A) and obtained at several wavelength bands between 150 and 1600 A by integration of spectroscopic images, - synoptic maps of the sun at different levels of the chromosphere, transition region and lower corona obtained in extreme ultra-violet (EUV) will be produced by the SOHO telescopes and spectrometers, - solar magnetograms with about 4 arc second resolution (2'' pixels) will be produced several times per day, - the evolution of the large coronal structures that shape the solar wind, as well as the coronal mass ejections will be followed by two coronagraphs and by a solar wind anisotropy measuring instrument; the latter generate the solar wind disturbances that are cause of the most energetic magnetic events in the geosphere, - the elemental, isotopic and charge state composition and energy distribution of the ions that form the solar wind, as well as of the energetic particles that will reach the earth magnetosphere, are determined in SOHO by a set of time-of-flight and solid state detectors.

An Atmospheric Radiative-Convective Model: Solar Forcings

Abstract: In this Letter, we provide a brief description of a new one-dimensional planetary atmospheric radiative-convective (PARC) model and its responses to solar forcings. To undertake this calculation, we ignore changing lower atmospheric effects and consider only variations in solar energy inputs. The model incorporates the following energies/transport processes: solar visible, IR, and UV radiations; and energy transports by conduction, eddy viscosity, and convection. We note the following changes over previous one-dimensional atmospheric models. (1) Rather than only a global energy balance, a detailed (local) energy balance is employed; thus, radiative and convective energy transports are both calculated explicitly, the latter with mixing-length theory (MLT). (2) The IR opacity of the atmospheric gases is calculated in a self-consistent fashion with the other energy inputs. The model was run with large solar variations sufficient to examine clearly possible solar forcing: variations of 10% in the "solar constant" and 9% in the solar UV. The model exhibits a 6.4 K and a 3 K increase in the lower atmospheric temperatures, respectively, to these forcings. The solar constant influence is similar to other climate models. The model responds significantly, however, to solar UV variations in a new and interesting fashion deserving of further study. The effect may be understood as a result of an elevation of the τ ~ 1 level in the atmosphere associated with the deposition of the UV energy. We suggest some observational tests: as solar activity increases, one would expect (1) the total optical depth of the model atmosphere in the IR to increase and (2) the altitude of the IR radiating region to increase. The model has numerous simplifications that warrant caution, if one were to assume blindly the results applied directly to the real Earth.

Hourly to decadal time scale variations of the spectral and total “solar constant”

Abstract: The most significant solar spectral radiation bursts that occurred during more than twelve-years observation period at an high altitude station are analyzed. It is shown that the number and amplitudes of solar spectral bursts increase when the solar activity (SA) maximum is approaching. A plausible mechanism of short-term variations of extra-atmospheric solar spectral irradiance (ETSSI) is discussed. It appears that a burst of ETSSI arises when the Earth is sporadically irradiated by a strong flux of induced violet-blue high coming out of magnetic flux tubes in the active region (AR) of the Sun. We confirm earlier conclusions that on the time-scale of decades there is a close relationship between variations in the areas of faculae, the solar constant, and surface air temperature. On the basis of these results we suggest that at the end of the 1930s, when the Sun was very active, its effective output was about 0.4%, and the surface temperature in the Northern hemisphere about 0.4°C, higher than in the first decade of the 20th century.

The Sun-Earth System

Abstract: This module shows how solar energy is produced and how the Earth's atmosphere interacts with solar radiation, thereby helping students understand such physical phenomena as the greenhouse effect and global warming. The module, which is accessible to any student who has studied introductory algebra, includes problems at the end of each section and a hands-on experiment designed to measure the solar constant with easily obtainable items.

Observed intensity of the solar continuum over the range 0.33–2.45 μm

Abstract: The mean absolute intensity of the solar continuum has been found by averaging the most reliable recent observational data from different authors. We used the modern experimental data on the solar constant, the spectral energy distribution, the limb darkening, and the blanketing effect. The continuum intensity is determined for the center disc and the entire disc. The brightness temperatures are compared with similar temperatures in the model of the photosphere.

White Paper on SBUV/2 Solar Irradiance Measurements

Abstract: The importance of solar irradiance measurements by the Solar Backscatter Ultraviolet, Model 2 (SBUV/2) instruments on NOAA's operational satellites is described. These measurements are necessary accurately monitor the long-term changes in the global column ozone amount, the altitude distribution of ozone in the upper stratosphere, and the degree to which ozone changes are caused by anthropogenic sources. Needed to accomplish these goals are weekly solar irradiance measurements at the operational ozone wavelengths, daily measurements of the Mg II proxy index, instrument-specific Mg II scale factors, and daily measurements of the solar spectral irradiance at photochemically important wavelengths. Two solar measurement schedules are provided: (1) a baseline schedule for all instruments except the NOAA-14 instrument and (2) a modified schedule for the NOAA-14 SBUV/2 instrument. This latter schedule is needed due to the NOAA-14 grating drive problems.

Solar radiant flux : Modern data and related problems

Abstract: Results of measurement of the solar constant and spectrum energy distribution are discussed. Urgent theoretical and observational problems are formulated.