Bright Network, UVA, and the Physical Modeling of Solar Spectral and Total Irradiance in Recent Solar Cycles

<jats:title>Abstract</jats:title> <jats:p>In this paper we study the total solar irradiance (TSI) and the spectral solar irradiance (SSI) by applying the solar disk image decomposition algorithm (SDIDA) and solar irradiance synthesis algorithm (SISA) methods. These methods were applied to space-based observations in previous works, but in this work, they are applied to ground-based observations from various observatories, which allows for a long-term determination of TSI and SSI. We discuss the results of the SDIDA and SISA methods for the areas of solar features and the synthesized TSI and SSI. We find that SDIDA decompositions based on Ca <jats:sc>ii</jats:sc> K line images from various sources are all in good agreement between them and with previous space results when cross-calibration is performed, and consequently yield essentially the same TSI and SSI when SISA is applied. This paper shows the synthesized TSI and SSI, as well as the contributions from various feature types, during the recent solar cycles 23 and 24 and suggest further work can provide historical extended coverage using archival ground-based observations. The results demonstrate the presence of a significant variable bright network contribution during the cycle maximum, and of a reduced one at solar minimum, and that such a presence and variability affect both the SSI and TSI. We also find that all activity features are loosely correlated over solar cycle variations, but this correlation is nonlinear, and we show differences between cycles 23 and 24. Furthermore, we find that the SISA method can be successfully applied to determine the TSI and SSI for any particular state of the solar disk, and that the results depend not only on the total areas on the disk for each feature, but also on the relative distances from disk center of the active region features.</jats:p>