Issue |
J. Space Weather Space Clim.
Volume 14, 2024
|
|
---|---|---|
Article Number | 34 | |
Number of page(s) | 11 | |
DOI | https://doi.org/10.1051/swsc/2024035 | |
Published online | 15 November 2024 |
Research Article
TSI modeling: A comparison of ground-based Ca II K-line data with space-based UV images from the SDO/AIA instrument
California State University Northridge, San Fernando Observatory, Department of Physics and Astronomy, 18111 Nordhoff St., Northridge, CA 91330, USA
* Corresponding author: gary.chapman@csun.edu
Received:
29
February
2024
Accepted:
26
September
2024
The Total Solar Irradiance (TSI) is an important input for the Earth’s climate. To describe the competing contributions of sunspots and faculae on irradiance variability, the San Fernando Observatory (SFO) irradiance model has two components: One component is an index derived from a continuum image that provides a sunspot signal. The other component is an index determined from a Ca II K-line image that provides a facular signal. These components are determined using two different methods, one based on feature identification and one based on photometric sum. Feature identification determines whether an active region feature is darker or brighter than the surrounding quiet Sun and by how much. Photometric sum simply adds up all the image pixels to determine a single value for that image. In this paper, we investigate the use of space-based UV images from the Solar Dynamics Observatory (SDO) as a substitute for ground-based Ca II K-line images from the San Fernando Observatory in modeling TSI variability. SDO indices are obtained by processing SDO/Atmospheric Imaging Assembly (AIA) 160 nm and 170 nm images with SFO algorithms, then SFO models are modified by substituting either a 160 nm or a 170 nm UV index from SDO in place of the Ca II K image. The different models are regressed against TSI measurements from the Total Irradiance Monitor (TIM) on the Solar Radiation and Climate Experiment (SORCE) spacecraft. The sunspot signal for all models used here is determined from SFO red continuum images at 672.3 nm. The facular signal is determined from either Ca II K-line images at 393.4 nm or space-based UV images from the SDO/AIA experiment. Images at both AIA wavelengths are processed with the standard San Fernando Observatory (SFO) algorithms. The SFO data is obtained from two photometric telescopes, which differ in spatial resolution by a factor of 2. The results of the linear regressions show good agreement between the fits that use SFO Ca II K-line data and the fits that use SDO UV data. However, facular indices obtained from SDO/AIA 170 nm images give significantly better fits than SDO/AIA 160 nm. We compare the goodness of the correlation using R2, that is, the multiple regression coefficient R, squared. The best two-component fit using ground-based Ca II K-line data was R2 = 0.873; using AIA 170 nm produced R2 = 0.896. Correlations using the AIA 160 nm data were consistently lower with values of R2 as low as 0.793, where R2 is the coefficient of multiple correlation.
Key words: Total irradiance / Sun / Variability / Photometry / Solar indices
© G.A. Chapman et al., Published by EDP Sciences 2024
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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