Photometric quantities for solar irradiance modeling

Details Photometric quantities for solar irradiance modeling Photometric quantities for solar irradiance modeling

Nov 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002jgra..107.1354p&link_type=abstract

Journal of Geophysical Research (Space Physics), Volume 107, Issue A11, pp. SSH 6-1, CiteID 1354, DOI 10.1029/2001JA009169

Astronomy and Astrophysics

Astrophysics

15

Solar Physics, Astrophysics, And Astronomy: Photosphere, And Astronomy: Solar And Stellar Variability, And Astronomy: Instruments And Techniques, And Astronomy: Solar Irradiance, And Astronomy: Solar Activity Cycle (2162)

Scientific paper

We analyze photometric quantities for the modeling of the total solar irradiance, S. These quantities are derived from full-disk solar images taken at the San Fernando Observatory. We introduce a new quantity, the photometric sum, Σ, which is the sum over an entire image of each pixel's contribution to the irradiance in that image. Σ combines both bright and dark features; and because the sum is over the entire image, it will include low contrast features that cannot be identified directly. Specifically, we examine Σr, Σb, and ΣK, the photometric sums over broadband red, broadband blue, and 1-nm bandpass Ca II K images, respectively. Σr and Σb measure the effects of solar features on the variability in S at two different continuum wavelengths. ΣK measures the variability in spectral lines due to solar features. We find that Σr and Σb have no long-term trend. ΣK, however, varies in phase with the solar cycle. We carry out several multiple linear regressions on the value of S from cycle 22; the best fit uses Σr and ΣK and reproduces the observed composite S with a multiple regression coefficient R = 0.96. We conclude that the long-term change in S over the solar cycle can be accounted for by the variability in the spectral lines as measured by ΣK, assuming no change in the quiet Sun; the contribution of the continuum to the variations in S is only on active region timescales.

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