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Figure II.4.22
Possible relationship between the total brightness variability of the Sun and solar-typestars as measured by DR'HK, which depends on chromospheric emission of Ca II H and Kspectroscopic lines. Chromospheric emission is sensitive to magnetic activity, whereas the totalbrightness variation includes sunspot blocking, chromospheric brightening, and other less wellunderstood effects. Quantities shown are root-mean-square variations; peak-to-peak variationsare roughly three times larger. Position of the Sun as indicated by image is taken from SSMmeasurements and the solar DR'HK. Dashed line defines the solar brightnesschromospheric activity change ratio based on yearly averaged data of SSM and NSOfrom 1980 to 1988. Inverted triangle (image) is longer-term upper bound of thesolar total irradiance variation from 1967 to 1984 taken from rocket and balloon measurements;corresponding value of DR'HK is estimated from combined solar measurements of MWO (1967-1978)and NSO (1976-1984). Solid line is linear regression using all data except the upper limit for the Sun.Most noteworthy in this figure is the fact that the variability of solar total output seems to be less than that for other solar-type stars with similar chromospheric activity. Source: Soon et al., 1994.Reprinted with permission of Springer-Verlag New York.

Contributions to the Solution of Societal Problems

The program of research described above will lead to greater understanding of the nature of solar variability, and will improve our ability to predict future states of the Sun. Understanding of the way in which solar variability affects the Earth and its climate will be enhanced, and we will have more confidence in our ability to distinguish anthropogenic effects from effects caused by solar influences.

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