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  • 1
    Electronic Resource
    Electronic Resource
    Variation of the solar constant during the solar cycle (1986)
    Springer
    Astrophysics and space science 127 (1986), S. 55-71 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Measurements of the Nimbus-7 and Solar Maximum Mission satellites reported temporary large decreases of the solar constant of the order of a few tenths of a percent on a time-scale from days to weeks. Our investigations show that these decreases were caused by ‘active’ sunspot groups with fast development and complex structure. This connection between the solar constant variation and the appearance of the active groups seems to be more clear in the maximum of the solar activity. At the time of the solar minimum, mainly in the second part of 1984, there were not any active sunspot groups practically on the solar disk, the value of the solar constant only fluctuated around its mean without large variation. The results of time series analyses show that the periodicity of the solar constant values, of young and active spot areas was nearly 23.5 days in 1980, which increases to 28 days towards the minimum of the solar cycle till 1983. During this time interval the main periodicity of the old, ‘passive’ spot areas was around 28 days. In 1984, at the time of the solar minimum, there were not any obvious periodicities practically in the projected areas of the different types of the sunspot groups.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00637762
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  • 2
    Electronic Resource
    Electronic Resource
    Variation of the solar constant connected with the coronal activity (1987)
    Springer
    Solar physics 109 (1987), S. 373-386 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A strong correlation was found between the dips in the total solar irradiance and the peaks in the active sunspot areas as well as in the 260 MHz coronal radio flux. This connection might indicate that Alfvén-waves, generated during the interaction of the magnetic fields of the active sunspot groups with the convection, are able to transport away part of the missing energy in the solar constant decreases. These waves can heat the solar corona above the sunspot groups. Another part of the missing energy could be re-radiated later, for example during the decay of the active regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00160660
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  • 3
    Electronic Resource
    Electronic Resource
    Variation of the solar constant during 1983 and 1984 (1987)
    Springer
    Solar physics 112 (1987), S. 181-193 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Measurements of the Nimbus-7/ERB and SMM/ACRIM radiometers indicated several dips in the total solar irradiance in 1983 and in the first part of 1984. The dips in 1983, which should have a real solar origin, were selected according to the peaks of the projected areas of the active sunspot groups above the 2σ error limit of their data set. In the first part of 1984 the sunspot activity was strong and few irradiance dips with relatively large amplitudes were observed. In the second part of 1984 the sunspot activity disappeared and at that time the solar constant only fluctuated around its mean.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00148497
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  • 4
    Electronic Resource
    Electronic Resource
    Periodicities of solar irradiance and solar activity indices, I (1990)
    Springer
    Solar physics 129 (1990), S. 165-189 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using a standard FFT time series analysis, our results show an 8–11 months periodicity in the solar total and UV irradiances, 10.7 cm radio flux, Ca-K plage index, and sunspot blocking function. The physical origin of this period is not known, but the evidence in the results exclude the possibility that the observed period is a harmonic due to the FFT transform or detrending. Periods at 150–157 and 51 days are found in those solar data which are related to strong magnetic fields. The 51-day period is the dominant period in the projected areas of developing complex sunspot groups, but it is missing from the old decaying sunspot areas. This evidence suggests that the 51-day period is related to the emergence of new magnetic fields. A strong 13.5-day period is found in the total irradiance and projected areas of developing complex groups. This confirms those results (e.g., Donnelly et al., 1983, 1984; Bai, 1987, 1989) which show that ‘active centers’ are located 180 deg apart from each other. Our study also shows that the modulation of various solar data due to the 27-day solar rotation is more pronounced during the declining portion of solar cycle than during the rising portion. This arises from that the active regions and their magnetic fields are better organized and more long-lived during the maximum and declining portion of solar cycle than during its rising portion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00154372
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  • 5
    Electronic Resource
    Electronic Resource
    Preface (1994)
    Springer
    Solar physics 152 (1994), S. ix 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01473174
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  • 6
    Electronic Resource
    Electronic Resource
    Estimating Long-Term Solar Irradiance Variability: A New Approach (1997)
    Springer
    Solar physics 176 (1997), S. 1-21 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The detection of solar irradiance variations (both bolometric and at various wavelengths) by satellite-based experiments during the last one-and-a-half decades stimulated modeling efforts to help identify their causes and to provide estimates of irradiance data for those time intervals when no satellite observations exist. In this paper we present estimates of the long-term irradiance changes developed with Fourier and wavelet transforms. The month-to-month irradiance variations, after removing the solar cycle related long-term changes, are studied with the cross-correlation technique. Results of the analysis reveal a significant phase shift at 3 months between the full-disk magnetic field strength and total solar and UV irradiance, with irradiance leading the magnetic field variability. In addition to this time delay between the changes in solar irradiance and the magnetic field, a 10-month phase shift has been found between the UV flux at 280 nm and total solar irradiance corrected for sunspot darkening. The existence of these phase shifts suggests the possibility of a coupling between the physical processes taking place below, in, and above the photosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004951101497
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  • 7
    Electronic Resource
    Electronic Resource
    VIRGO: Experiment for helioseismology and solar irradiance monitoring (1995)
    Springer
    Solar physics 162 (1995), S. 101-128 
    Details
    ISSN: 1573-093X
    Keywords: Helioseismology ; Total Solar Irradiance ; Spectral Solar Irradiance ; Low-Resolution Solar Radiance ; SOHO Mission
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The scientific objective of the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) is to determine the characteristics of pressure and internal gravity oscillations by observing irradiance and radiance variations, to measure the solar total and spectral irradiance and to quantify their variability over periods of days to the duration of the mission. With these data helioseismological methods can be used to probe the solar interior. Certain characteristics of convection and its interaction with magnetic fields, related to, for example, activity, will be studied from the results of the irradiance monitoring and from the comparison of amplitudes and phases of the oscillations as manifest in brightness from VIRGO, in velocity from GOLF, and in both velocity and continuum intensity from SOI/MDI. The VIRGO experiment contains two different active-cavity radiometers for monitoring the solar ‘constant’, two three-channel sunphotometers (SPM) for the measurement of the spectral irradiance at 402, 500 and 862 nm, and a low-resolution imager (LOI) with 12 pixels, for the measurement of the radiance distribution over the solar disk at 500 um. In this paper the scientific objectives of VIRGO are presented, the instruments and the data acquisition and control system are described in detail, and their measured performance is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00733428
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  • 8
    Electronic Resource
    Electronic Resource
    Improvement of the photometric sunspot index and changes of thedisk-integrated sunspot contrast with time (1994)
    Springer
    Solar physics 152 (1994), S. 111-118 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The photometric sunspot index (PSI) was developed to study the effects of sunspots on solar irradiance. It is calculated from the sunspot data published in theSolar-Geophysical Data catalogue. It has been shown that the formerPSI models overestimate the effect of dark sunspots on solar irradiance; furthermore results of direct sunspot photometry indicate that the contrast of spots depends on their area. An improvedPSI calculation is presented; it takes into account the area dependence of the contrast and calculates ’true’ daily means for each observation using the differential rotation of the spots. Moreover, the observations are screened for outliers which improves the homogeneity of the data set substantially, at least for the period after December 1981 when NOAA started to report data from a few instead of one to two stations. A detailed description of the method is provided. The correlation between the newly calculatedPSI and total solar irradiance is studied for different phases of the solar cycles 21 and 22 using bi-variate spectral analysis. The results can be used as a ‘calibration’ ofPSI in terms of gain, the factor by whichPSI has to be multiplied to yield the observed irradiance change. This factor changes with time from about 0.6 in 1980 to 1.1 in 1990. This unexpected result cannot be interpreted by a change of the contrast relative to the quiet Sun (as it is normally defined and determined by direct photometry) but rather as a change of the contrast between the spots and their surrounding as seen in total irradiance (integrated over the solar disk). This may partly be explained by a change in the ratio between the areas of the spots and the surrounding faculae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01473192
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  • 9
    Electronic Resource
    Electronic Resource
    Activity of sunspots and solar constant variations during 1980 (1985)
    Springer
    Solar physics 97 (1985), S. 21-33 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A strong inverse correlation is shown between the irradiance dips observed by the SMM/ACRIM radiometer and the projected areas of the ‘active’ sunspots. This strong correlation and the results of a preliminary time series analysis indicate that the value of the solar constant decreased when quickly developing sunspot groups with complex structure occurred on the solar disk. On the other hand, when the old groups with simple structure were dominant the value of the solar constant increased slightly or these groups could reduce the effects of the ‘active’ spots. On the basis of our investigations it seems that the formation of the sunspots and the new activity of the older ones as well as the decreases of the solar constant may be the common symptoms of such a physical process which takes place in deeper regions of the Sun through the interaction of magnetic fields with the convection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152976
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  • 10
    Electronic Resource
    Electronic Resource
    FIRST RESULTS FROM VIRGO, THE EXPERIMENT FOR HELIOSEISMOLOGY AND SOLAR IRRADIANCE MONITORING ON SOHO (1997)
    Springer
    Solar physics 170 (1997), S. 1-25 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract First results from the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) on the ESA/NASA Mission SOHO (Solar and Heliospheric Observatory) are reported. The observations started mid-January 1996 for the radiometers and sunphotometers and near the end of March for the luminosity oscillation imager. The performance of all the instruments is very good, and the time series of the first 4–6 months are evaluated in terms of solar irradiance variability, solar background noise characteristics and p-mode oscillations. The solar irradiance is modulated by the passage of active regions across the disk, but not all of the modulation is straightforwardly explained in terms of sunspot flux blocking and facular enhancement. Helioseismic inversions of the observed p-mode frequencies are more-or-less in agreement with the latest standard solar models. The comparison of VIRGO results with earlier ones shows evidence that magnetic activity plays a significant role in the dynamics of the oscillations beyond its modulation of the resonant frequencies. Moreover, by comparing the amplitudes of different components ofp -mode multiplets, each of which are influenced differently by spatial inhomogeneity, we have found that activity enhances excitation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004969622753
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