Occurrence of auroral reports, 1700−1900. The green line is the number of auroral nights at geomagnetic latitudes below 56° from a combination of several catalogues (Nevanlinna 1995; Fritz 1873, 1881; Legrand & Simon 1987). The points show the geomagnetic latitude and time of auroral sightings from the catalogue of Vázquez et al. (2014) (their Fig. 9). Black diamonds, red squares and red triangles are, respectively, for observing sites in Europe and North Africa, North America, and Asia. Blue dashed lines mark the minimum latitude of auroral reports in the last solar cycle of the MM and in the two cycles of the DM.
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