Abstract
The study of solar irradiance variability is of great importance in heliophysics, Earth’s climate, and space weather applications. These studies require careful identifying, tracking and monitoring of features in the solar photosphere, chromosphere, and corona. Do coronal bright points contribute to the solar irradiance or its variability as input to the Earth atmosphere? We studied the variability of solar irradiance for a period of 10 years (May 2010 – June 2020) using the Large Yield Radiometer (LYRA), the Sun Watcher using APS and image Processing (SWAP) on board PROBA2, and the Atmospheric Imaging Assembly (AIA), and applied a linear model between the segmented features identified in the EUV images and the solar irradiance measured by LYRA. Based on EUV images from AIA, a spatial possibilistic clustering algorithm (SPoCA) is applied to identify coronal holes (CHs), and a morphological feature detection algorithm is applied to identify active regions (ARs), coronal bright points (BPs), and the quiet Sun (QS). The resulting segmentation maps were then applied on SWAP images, images of all AIA wavelengths, and parameters such as the intensity, fractional area, and contribution of ARs/CHs/BPs/QS features were computed and compared with LYRA irradiance measurements as a proxy for ultraviolet irradiation incident to the Earth atmosphere. We modeled the relation between the solar disk features (ARs, CHs, BPs, and QS) applied to EUV images against the solar irradiance as measured by LYRA and the F10.7 radio flux. A straightforward linear model was used and corresponding coefficients computed using a Bayesian method, indicating a strong influence of active regions to the EUV irradiance as measured at Earth’s atmosphere. It is concluded that the long- and short-term fluctuations of the active regions drive the EUV signal as measured at Earth’s atmosphere. A significant contribution from the bright points to the LYRA irradiance could not be found.
Highlights
For more than three decades, the total solar irradiance (TSI) and the solar spectral irradiance (SSI) have been monitored from several radiometers from space (e.g. Foukal and Lean, 1988; Fröhlich et al, 1995; Kariyappa and Pap, 1996; Rottman, Woods, and McClintock, 2006), and their impact on the Earth climate been discussed (e.g. Haigh, 1994; Ermolli et al, 2014; Ball et al, 2016)
All models are based on the assumption that the TSI variations can be reproduced by the evolution of the magnetic field at the solar surface, which is strongly supported by Ball et al (2012) showing a 92% reproducibility of the TSI
As the algorithm implemented by Spatial Possibilistic Clustering Algorithm (SPoCA) does not identify bright points (BP), we present in this paper a morphological algorithm based on 193 Å images from Atmospheric Imaging Assembly (AIA) to compute these, which will be explained in Section 2.2, and the algorithm is described step-by-step in Appendix C
Summary
For more than three decades, the total solar irradiance (TSI) and the solar spectral irradiance (SSI) have been monitored from several radiometers from space (e.g. Foukal and Lean, 1988; Fröhlich et al, 1995; Kariyappa and Pap, 1996; Rottman, Woods, and McClintock, 2006), and their impact on the Earth climate been discussed (e.g. Haigh, 1994; Ermolli et al, 2014; Ball et al, 2016). Several modeling efforts exist to improve the TSI and SSI time series to overcome the instrument and measurement deficiencies These models are either based on the regression of indices of solar activity and their comparison to the solar irradiance (e.g. Lean, 2000; Chapman, Cookson, and Preminger, 2013), or a more physics-based approach using different brightness structures and their corresponding irradiance over time. Ermolli et al (2013) discussed the differences in the relative change in irradiance at various wavelengths and stated that the very short- (EUV) and long- (radio) wavelength radiation is originating from the upper transition region and corona, where the commonly found brightest sources are the complete loop systems rather than the loop foot points as seen in the photosphere These are very short and long wavelengths typically not considered in the TSI analysis, as they are hardly contributing to the TSI, and interact mainly with the uppermost region of the Earth’s atmosphere (mesosphere and above)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
