Historical Reconstruction of Solar Surface Magnetism from Cycle 1-24 Using the Synthetic Active Region Generator (SARG) and the Advective Flux Transport (AFT) Model

TL;DR

This study reconstructs the Sun's historical surface magnetic field over 265 years using a synthetic active region generator and an advective flux transport model, enabling long-term solar magnetic studies.

Contribution

It introduces a novel combination of SARG and AFT models to generate a comprehensive historical magnetic field catalog from 1755 to 2020.

Findings

Polar fields correlate strongly with observational proxies (r > 0.8).

Synthetic maps are publicly available for diverse solar research.

Cycle-dependent active region tilt improves polar field accuracy.

Abstract

The historical reconstruction of the Sun's surface magnetic field remains a persistent challenge, limiting our ability to investigate the long-term global properties of the Sun, including the evolution of the large-scale magnetic field, solar cycle prediction, reconstruction of total solar irradiance (TSI), and secular solar variability. In this study, we employ the Advective Flux Transport (AFT) model in conjunction with our newly developed Synthetic Active Region Generator (SARG) to construct a catalog of synthetic active regions (ARs) spanning Solar Cycles 1-24 (1755-2020). We use the SIDC/SILSO sunspot number version 2.0 as the sole input governing the properties of the synthetic ARs in this catalog. This SARG catalog is then incorporated into the AFT model, which simulates the emergence of new ARs on the Sun, which are then transported under the influence of surface flows to produce maps of the full-Sun radial photospheric magnetic field over the entire 265-year period. We modulate the active region tilt for each cycle in order to ensure that the polar fields are consistent with the solar cycle amplitudes. We find that the polar fields derived from these simulations exhibit excellent correlation (r > 0.8) with observational proxies, including polar faculae counts and Ca ii K polar network indices. Daily synchronic maps from these simulations for the entire 265-year period are made publicly available to support a wide range of applications beyond those presented in this work.