Reconstructing daily group sunspot numbers since the maunder minimum with objective inter-calibration algorithms

We present a new daily Group Sunspot Numbers (GSN) reconstruction from the Maunder minimum to Solar Cycle 24/25. This new reconstruction was obtained as a result of rectifying the raw and uncalibrated GSN database of Vaquero et al. (2016) and incorporating data from previously unconsidered GSN sources. Notably, a pivotal challenge encountered during the reconstruction of this GSN activity record, lay in the inter -calibration of different databases reported by multiple observers. The challenge is further compounded by data gaps that are particularly prevalent during the Maunder minimum. We have applied a novel methodology to solve these obstacles, entailing the calibration and standardization of all GSN databases relative to a reference observer. Our novel approach employs calibration techniques, ensuring standardized visual acuity between all individual observers. Moreover, our methodology accommodates variations in climatic, geographic, and instrumental conditions encountered by observers during their respective sunspot observations, thus establishing a uniform comparative framework. Furthermore, a comparative analysis was conducted with a total of four other different GSN reconstructions, revealing notable distinctions and resemblances that can be explained by the implementation of diverse methodologies in the respective GSN reconstruction processes and steps. In addition to the temporal differences found, both the wavelet and multi -cross wavelet analyses were carried out, which allowed a quantification of the differences and similarities in the spectral contents of various GSN records. The wavelet analysis results show the similarities and differences of the new GSN reconstruction with the inter calibration algorithm when comparing it both temporally and spectrally with other GSN reconstructions. The periodicities of this analysis are 1.2, 5.5, 10.9, 20.6, 30.9, 58.4, and 119.8 years and 3.47, 5.4, 9.8, 27.8, 66.1, 117.8, and 160.5 days respectively. (c) 2023 COSPAR. Published by Elsevier B.V. All rights reserved.