Identification of possible intense historical solar storms during the years 1781-1788 inferred from auroras and geomagnetic observations in Rio de Janeiro

Vaquero J.M., Trigo R.M.
Solar Physics, 235; 419-432, DOI: 10.1007/s11207-006-0024-6

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The reconstruction of solar activity during the late 18th century is a puzzle for researchers due to the scarcity of sunspot observations in that epoch. In this work, we analyse some details of the solar activity during the years 1781-1788, inferred from geomagnetic measurements and visual observations of aurorae performed by the Portuguese scientist Bento Sanches Dorta from Rio de Janeiro. We describe in greater detail four large solar storms that induced large changes in daily values of geomagnetic declination and, simultaneously, correspond to visual observations of aurorae described by Sanches Dorta.