Observations of Solar Irradiance Variability

Willson, R. C.; Gulkis, S.; Janssen, M. A.; Hudson, H. S.; Chapman, G. A.

doi:10.1126/science.211.4483.700

Cited by 386 publications

(149 citation statements)

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“…The most important discovery of the satellitebased irradiance observations is that total solar irradiance varies by about a small fraction of 1% over the solar cycle, being higher during maximum solar activity conditions (e.g. Willson and Hudson, 1988). This solar-cyclerelated variation of total solar irradiance is attributed in a large part to the changing emission of bright magnetic elements and a third component, the so-called "active network", has been introduced to explain the long-term irradiance changes (Foukal and Lean, 1988).…”

Section: Variations Observed In Solar Irradiancementioning

confidence: 99%

“…Various space-borne observations of total solar irradiance over the last two decades established conclusively that total solar irradiance is not constant and the changes on time scales from minutes to the 11-year solar activity cycle are related to changes in the Sun's interior and atmosphere (Willson and Hudson, 1988;Fröhlich et α/., 1991). High precision photometric observations of solar-type stars clearly show that year-to-year variations connected with magnetic activity is a widespread phenomenon among such stars (Radick, 1994).…”

Section: Introductionmentioning

confidence: 99%

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Long-term solar irradiance variability

Pap

1997

Symp. - Int. Astron. Union

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Abstract. Measurements of the solar energy throughout the solar spectrum and understanding its variability provide important information about the physical processes and structural changes in the solar interior and in the solar atmosphere. Solar irradiance measurements (both bolometric and at various wavelengths) over the last two decades have demonstrated that the solar radiative output changes with time as an effect of the waxing and waning solar activity. Although the overall pattern of the long-term variations is similar in the entire spectrum and at various wavelengths, being higher during high solar activity conditions, remarkable differences exist between the magnitude and shape of the observed changes. These differences arise from the different physical conditions in the solar atmosphere where the irradiances are emitted. The aim of this paper is to discuss the solar-cycle-related long-term changes in solar total and UV irradiances. The space-borne irradiance observations are compared to ground-based indices of solar magnetic activity, such as the Photometric Sunspot Index, full disk magnetic flux, and the Mt. Wilson Magnetic Plage Strength Index. Considerable part of the research described in this paper was stimulated by the discussions with the late Philippe Delache, who will always remain in the heart and memory of the author of this paper.

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Section: Variations Observed In Solar Irradiancementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Long-term solar irradiance variability

Pap

1997

Symp. - Int. Astron. Union

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“…It was discovered in the early time that the variation of TSI is related to the disc sunspots and faculae (e.g., Willson et al 1981). Further studies (e.g., Solanki & Krivova 2006) show that faculae and bright network made an increase of TSI, while the sunspots let TSI be decreased.…”

Section: Introductionmentioning

confidence: 99%

“…Although there looks quite a number of periods, the obviously shortest one is the period of 6.7 days. This period seems to be related to the discovery of the cutoff of 7 days, based on the data analysis for the initial 153 days, observed with ACRIM onboard SMM (Willson et al 1981). at https://www.cambridge.org/core/terms.…”

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confidence: 99%

The periodic variation of 6.7 days for total solar radiation

Gan

2009

Proc. IAU

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Abstract. Analyzing the power spectrum of Total Solar Irradiance (TSI) for the period from 2003 February 25 to 2009 July 6, observed with the Total Irradiance Monitor (TIM) onboard SOlar Radiation and Climate Experiment (SORCE), we found that there are quite a number of periodic variations. The outstanding shortest one is the period of 6.7 days, about one fourth of the period of solar rotation. Checking the solar magnetic field for the same period of time observed with MDI onboard SOHO, we found that there is about 90 degree difference in longitude for the distribution of solar magnetic field. We therefore conclude that both the 90 degree difference in longitude for the distribution of solar magnetic field and the solar rotation are the reason resulting in the periodic variation of 6.7 days for the total solar radiation.

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“…An early example is that of Willson et al (1981) in which about half of the variance could be removed from the ACRIM I signal (Hudson 1988, and references therein). The sunspot effect was modeled by a Photometric Sunspot Index (PSI) in which it was assumed that the temperature structure of all sunspots is the same and that their contrast does not depend on position on the disk.…”

Section: The Effect Of Sunspots On Solar Irradiancementioning

confidence: 99%

Photometric Observations of the Sun

Chapman

1994

International Astronomical Union Colloquium

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Ground-based calorimetry and photometry of the Sun have been carried out for many years. Following the early years, ground-based photometry has largely replaced ground-based calorimetry, in part due to the advent of airborne and spaceborne detector systems for the broad-band measurement of the solar irradiance and the realization of the difficulty of correcting calorimetry measurements for the effects of the terrestrial atmosphere. Even from spacecraft, recent measurements of the total solar irradiance range from about 1367 to 1374 W/m 2 . Most of this difference can be ascribed to differences in instrumental scales, while a variation of about 1 to 2 W / m 2 appears to be due to solar variability. The quiet Sun may also change, globally, over longer time scales. Using disparate data to understand solar variability will require cooperation between a number of current groups, supported by various governments, covering several zones of longitude. I n t r o d u c t i o nStudying the Sun's output of energy (luminosity) has been a long-standing endeavor. Within the past decade or so, satellites have measured the solar output and have very clearly revealed variability. However, while the satellite measurements have agreed on the actual solar luminosity, agreeing for the most part on the short-and long-term temporal changes. Ground-based measurements, on the other hand, are hampered by the uncertainties in the opacity of the terrestrial atmosphere and its variations and cannot accurately determine the solar luminosity but might be able to measure relative changes in it. This review will attempt to place ground-based efforts into context with space-based experiments. An interesting, broad review of ground-based photometric measurements is that of LaBonte (1988). A general review of solar luminosity variability can be found in (Hudson 1988), Frohlich et al. (1991) and Frohlich (1992). We will not review nonimaged programs here. For a good review of these see White (1988) and Livingston (1992).One of the reasons for carrying out ground-based programs of relative photometry is to help understand the cause of the solar variations seen by satellites. Most of the satellite data have been obtained without any spatial resolution on the solar disk. By having photometric images obtained at selected wavelengths, the satellite measurements can be modeled using selected contrast features seen in ground-based images. We assume t h a t there is a non-changing quiet Sun output and that photometrically detectable features add to or subtract from this quiet Sun output. For relative ground-based photometry, the (assumed) quiet Sun is our photometric standard. If this assumption is not true, we can only find out by doing our very best in removing the effects of features on the solar output.It has been shown that most of the variations can be attributed to magnetic features Chapman et al. 1992). By modeling their effects on the solar output, we hope to gain a better understanding of the flow of energy in and around a solar active region and...

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Observations of Solar Irradiance Variability

Cited by 386 publications

References 5 publications

Long-term solar irradiance variability

Long-term solar irradiance variability

The periodic variation of 6.7 days for total solar radiation

Photometric Observations of the Sun

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