Solar Irradiance Variations Modelled from Ca II K Excess and Magnetic Field
Abstract
The facular contribution (Δ S(λ)/S(λ))_{f} to the variation of the total solar irradiance Δ S(λ)/S(λ), for two continuum wavelengths and for a period of 60 not consecutive days in 1999, is calculated according to two different methods, namely via RISE/PSPT Ca II K images and via magnetograms of the MDI instrument on board of the SOHO spacecraft. The results are correlated with the values of the total irradiance channel of the VIRGO instrument on board of SOHO. The correlation coefficient for the first method (via Ca II K images) is 0.55, and 0.23 for the second method (via magnetograms). Particularly with regard to faculae, Ca II K irradiance appears to be much more representative than the line-of-sight magnetic field. For use of the magnetograms the relationship between the Ca II K excess E_{k} and the line-of-sight magnetic flux density |B| is analysed. E_{k} is measured in dependence on the two variables μ and |B|. A multivariate fit yields a compact presentation of this function and the exponent β of the power law E_{k}=α\cdot|B|^{β} is determined; the values 0.48≤ β ≤ 0.57 agree with those found by Harvey and White (1999).
- Publication:
-
Hvar Observatory Bulletin
- Pub Date:
- 2005
- Bibcode:
- 2005HvaOB..29...79V
- Keywords:
-
- Solar activity;
- faculae;
- plages;
- magnetic field