Showing papers on "Solar constant published in 2000"
TL;DR: The Michelson Doppler Imager instrument on board SOHO has operated for most of a solar cycle as mentioned in this paper, and the data obtained with it from above the Earth's turbulent atmosphere yield the most accurate direct constraint on possible solar radius variations on timescales from minutes to years.
Abstract: The Michelson Doppler Imager instrument on board SOHO has operated for most of a solar cycle Here we present a careful analysis of solar astrometric data obtained with it from above the Earth's turbulent atmosphere These data yield the most accurate direct constraint on possible solar radius variations on timescales from minutes to years and the first accurate determination of the solar radius obtained in the absence of atmospheric seeing
106 citations
TL;DR: In this article, an upper limit to the amplitudes of the g-mode signals at 200 μHz was established, which corresponds to a peak-to-peak vertical displacement of δR/R☉ = 2.3 × 10-8 at the solar surface.
Abstract: Observations made by the Michelson Doppler Imager (MDI) and Variability of solar IRradiance and Gravity Oscillations (VIRGO) on the Solar and Heliospheric Observatory (SOHO) and by the ground-based Birmingham Solar Oscillations Network (BiSON) and Global Oscillations Network Group (GONG) have been used in a concerted effort to search for solar gravity oscillations. All spectra are dominated by solar noise in the frequency region from 100 to 1000 μHz, where g-modes are expected to be found. Several methods have been used in an effort to extract any g-mode signal present. These include (1) the correlation of data—both full-disk and imaged (with different spatial-mask properties)—collected over different time intervals from the same instrument, (2) the correlation of near-contemporaneous data from different instruments, and (3) the extraction—through the application of complex filtering techniques—of the coherent part of data collected at different heights in the solar atmosphere. The detection limit is set by the loss of coherence caused by the temporal evolution and the motion (e.g., rotation) of superficial structures. Although we cannot identify any g-mode signature, we have nevertheless set a firm upper limit to the amplitudes of the modes: at 200 μHz, they are below 10 mm s-1 in velocity, and below 0.5 parts per million in intensity. The velocity limit corresponds very approximately to a peak-to-peak vertical displacement of δR/R☉ = 2.3 × 10-8 at the solar surface. These levels which are much lower than prior claims, are consistent with theoretical predictions.
87 citations
TL;DR: In this article, the authors used a hydrostatic regional weather prediction model to simulate the tropospheric response to the total solar eclipse on the 11 August 1999 is simulated over central Europe both with real-time data and for a water vapor and cloud free scenario.
Abstract: Using a hydrostatic regional weather prediction model, the tropospheric response to the total solar eclipse on the 11 August 1999 is simulated over central Europe both with real time data and for a water vapor and cloud free scenario. The solar constant in the model is reduced stepwise along the surface path of the moon's shadow, reaching a value of 0 W/m 2 for a typical time span of 2 minutes during totality. In the presence of a large scale upper tropospheric trough centered over western Europe, the predicted radiative cooling ranging from -2°C over the UK, France and Germany to -5°C along the almost cloudless coast line of Croatia is in good agreement with observations. Over southeastern Europe the maximum cooling reaches -6°C to -7°C and the maximum sea surface pressure rise is enhanced from +0.4 hPa to +1.2 hPa, when the simulation is done without water vapor and clouds. The normally observed wind reduction is simulated as well as the temperature dependent increase of relative humidity near the ground. For some minutes even a slight cyclonic circulation is shown by the model surface winds. The upper air response to the eclipse is clearly correlated with the distribution of water vapor and clouds. The temperature and geopotential signals at the 500 hPa level are in the order of -0.01°C and -1 gpm remaining well below the sensitivity of routine sensors.
19 citations
01 Jan 2000
12 citations
01 Jan 2000
TL;DR: The PICARD microsatellite mission as mentioned in this paper provides 3 to 4 years simultaneous measurements of the solar diameter, differential rotation and solar constant to investigate the nature of their relations and variabilities.
Abstract: The PICARD microsatellite mission will provide 3 to 4 years simultaneous measurements of the solar diameter, differential rotation and solar constant to investigate the nature of their relations and variabilities. The 110 kg satellite has a 42 kg payload consisting of 3 instruments: SODISM, which will deliver an absolute measure (better than 4 milliarcsec) of the solar diameter and solar shape, SOVAP, measuring the total solar irradiance, and PREMOS, dedicated to the UV and visible flux in selected wavelength bands. Now in Phase B, PICARD is expected to be launched by 2005. We review the scientific goals linked to the diameter measurement with interest for Earth Climate, Space Weather and Helioseismology, present the payload and instruments' concepts and design, and give a brief overview of the program aspects.
12 citations
TL;DR: In this paper, a Fourier transform infrared (FTIR) spectrometer was used to check the spectral composition of databases that form the basis for most atmospheric absorption parameterizations used in climate models, remote sensing, and other radiative transfer simulations.
Abstract: A Fourier transform infrared (FTIR) spectrometer, operating at 1 cm−1 resolution between 9000 and 24,669 cm−1 (0.405–1.111 μm) has been used to check the spectral composition of databases that form the basis for most atmospheric absorption parameterizations used in climate models, remote sensing, and other radiative transfer simulations. The spectrometer, operating near sea level under clear skies, obtained relative atmospheric transmission measurements of the direct solar beam by means of a heliostat. The spectroscopic data were compared with a line-by-line radiative transfer model (LBLRTM) calculation of direct solar beam flux, which used a input data a monochromatic model extraterrestrial solar flux spectrum currently in common use. This intercomparison revealed that the extraterrestrial solar flux spectrum contains 266 solar absorption features that do not appear in the data, resulting in an excess of approximately 1.92 W m−2 in the model's solar constant. The intercomparison also revealed 97 absorption features in the data that do not appear in the HITRAN-96 database as used by LBLRTM, resulting in a model underestimate of shortwave absorption of ∼0.23 W m−2 for a solar zenith angle of 42°. These small discrepancies revealed by the intercomparison indicate that current extraterrestrial solar irradiance models and spectroscopic databases used by shortwave atmospheric radiative transfer models are nearly entirely complete for purposes of atmospheric energy budget calculation. Thus clear or cloudy sky ‘excess absorption’ is unlikely to be related to an incomplete identification of atmospheric absorbing gases and their spectroscopic features, at 1 cm−1 resolution, for a clean troposphere of normal composition.
8 citations
TL;DR: In this paper, the ratios of radio to optical diameter of the solar disc at 10.7 and 3 cm wavelengths were examined and it was found that the apparent disc diameter is slightly greater at solar minimum than it is at solar maximum, suggesting that the radio diameter varies over the cycle.
Abstract: The ratios of radio to optical diameter of the solar disc at 10.7 and 3 cm wavelengths are examined. The radio observations are daily east–west scans of the solar disc, made over the period 1975–1992, which includes almost two complete solar cycles. We find that the apparent disc diameter is slightly greater at solar minimum than it is at solar maximum, suggesting that the radio diameter varies over the cycle. Moreover, the ratio is smaller at 3 cm wavelength than it is at 10.7 cm, at both solar maximum and minimum.
5 citations
TL;DR: The PICARD microsatellite mission as mentioned in this paper provides 2 to 6 years simultaneous measurements of the solar diameter, differential rotation and solar constant to investigate the nature of their relations and variabilities.
Abstract: The PICARD microsatellite mission will provide 2 to 6 years simultaneous measurements of the solar diameter, differential rotation and solar constant to investigate the nature of their relations and variabilities. The 100 kg satellite has a 40 kg payload consisting of 3 instruments which will provide an absolute measure (better than 10 milliarcsec) of the diameter and the solar shape, a measure of total solar irradiance, and UV and visible flux in selected wavelength bands. Now in Phase B, PICARD is expected to be launched before mid-2003. The engineering model of the diameter telescope will be used on ground simultaneously with the satellite to investigate the atmospheric bias and state on the possible accuracy of the ground measurements carried up to now. We review the scientific goals linked to the diameter measurement, present the payload, and give a brief overview of the program aspects.
3 citations
Patent•
15 Mar 2000
TL;DR: In this article, the authors proposed a method for measuring solar constant from earth or satellite features that an absolute radiometer is such installed that it faces against sun, that is, the included angle between the optical axis of radiometer and light vector of sun varies, and the measurement of solar constant is conducted in variation procedure.
Abstract: A method for measuring solar constant from earth or satellite features that an absolute radiometer is such installed that it faces against sun. In the measuring procedure, the included angle between the optical axis of absolute radiometer and light vector of sun varies, that is, the measurement of solar constant is conducted in variation procedure. Its advantages are no need of two-axle rotating platform, sun tracker and its drive mechanism, simple structure, light weight, low power consumption, high reliability and simplified measurement.
3 citations
01 Jan 2000
TL;DR: The PICARD microsatellite mission as discussed by the authors provides 2 to 6 years simultaneous measurements of the solar diameter, differential rotation and solar constant to investigate the nature of their relations and variabilities.
Abstract: The PICARD microsatellite mission will provide 2 to 6 years simultaneous measurements of the solar diameter, differential rotation and solar constant to investigate the nature of their relations and variabilities. The 100 kg satellite has a 40 kg payload consisting of 3 instruments which will provide an absolute measure (better than 10 milliarcsec) of the diameter and the solar shape, a measure of total solar irradiance, and UV and visible flux in selected wavelength bands. Now in Phase B, PICARD is expected to be launched before mid-2003. The engineering model of the diameter telescope will be used on ground simultaneously with the satellite to investigate the atmospheric bias and state on the possible accuracy of the ground measurements carried up to now. We review the scientific goals linked to the diameter measurement, present the payload, and give a brief overview of the program aspects.
2 citations
Journal Article•
TL;DR: In this paper, the change of the solar radiation in Qinghai Tibet Plateau was studied using the data of the conventional and automatic observational stations, where the conventional observation data include the maximum daily solar radiation and the time occurred.
Abstract: To study the change of the solar radiation in Qinghai Tibet Plateau the data of the conventional and automatic observational stations are used. The conventional observation data include the maximum daily solar radiation and the time occurred. The Sino Japan Asian Monsoon Project since 1993 has collected these data every 20 minutes. The anomaly of the solar radiation greater than the solar constant in Qinghai Tibet Plateau is discovered based on the study of the above data. The statistics of this phenomenon shows some interesting results. Under the hypothesis of non local thermodynamic equilibrium the possible explanation for this phenomenon is presented.
TL;DR: In this article, preliminary results of processing of radiometer measurements from the Resurs-1 (No. 4) heliosynchronous satellite are given for 48 days of observations, distributed over the course of eight months.
Abstract: Some preliminary results of processing of radiometer measurements from the Resurs-1 (No. 4) heliosynchronous satellite are given. Values of the solar constant, recorded using a second-generation “solar-constant measuring instrument” are presented for 48 days of observations. Measurements of outgoing short-wave radiation and albedo (IKOR measuring instrument) were made on 109 days of observations, distributed over the course of eight months.
TL;DR: In this paper, the solar radiation budget is investigated with seven pyranometers, three of which have horizontally aligned sensors and the remaining four sensors are vertically aligned in such a way that their normals point to the north, south, east, and west.
Abstract: The solar radiation budget is investigated with seven pyranometers. Three of these instruments have horizontally aligned sensors. The sensors of the remaining four instruments are vertically aligned in such a way that their normals point to the north, south, east, and west. With this system, the authors are able to detect all properties of interest for radiation budget considerations. These are the flux densities of direct solar, diffuse-sky, global, and reflected radiation; the vector of the solar net flux density; and the solar radiation supply (for atmospheric absorption and/or photochemical processes). Equations for the vector of the net flux density and the radiation supply in terms of the pyranometer readings are derived and discussed. Whenever the solar radiation supply and the mean solar absorption coefficient of the atmosphere or of specific atmospheric species are known, the relevant solar volume absorption rate and the appertaining solar heating rate of the atmosphere can be calculated...
01 Jan 2000
TL;DR: In this paper, the authors focus on direct measurement of solar output not on traditional indicators of solar activity related to global solar variability in its broadest sense, and distinguish between sunspot numbers, plage indices, magnetic indices, etc., and the direct measurements of the Sun's physical output.
Abstract: Variability of the solar output of radiation and particles is currently recorded in experiments that measure the total radiative output, i. e., the Total Solar Irradiance (TSI) and spectral irradiances, and the particulate output of solar wind plasma and energetic particles. Our emphasis is on direct measurement of solar output not on the traditional indicators of solar activity related to global solar variability in its broadest sense. We then distinguish between sunspot numbers, plage indices, magnetic indices, etc., and the direct measurement of the Sun’s physical output. Because of the paucity of measurements of the solar output before 1980, climatic significance of the solar output is usually established through these indices of solar activity. Of these two outputs, the radiation is the most energetic in terms of possible climatic effect. To establish both the total radiative energy input to the terrestrial atmosphere and that absorbed by particular chemical species in the upper atmosphere, we now have measurements of both the Total Solar Irradiance (TSI) and the spectral irradiance in the near UV from 400 nm to 100 nm. The 10.7 cm radio flux measurement is an absolute spectral irradiance of great value as an indicator of radiative variability because the record is so long, i. e., from 14 February 1947 to date. This radio flux record is the basis for estimating radiative output throughout the solar spectrum at times when no absolute measurements are available. The effects of the Sun’s particulate output tend to be short term: minutes to hours following solar flares and coronal mass ejections. Energetically, their effects appear to be small in the troposphere, but we should consider their aggregate effects of recurrent events such as flares and coronal mass ejections. One such effect discussed at this workshop is modulation of the cosmic ray input to the Earth’s atmosphere where it affects ionization and dissociation of chemical species. This effect is not a direct effect of the solar output but rather an aggregate effect on