Long-term Spatial and Temporal Variations of Aurora Borealis Events in the Period 1700--1905

TL;DR

This study analyzes 1700-1905 aurora borealis records to understand long-term spatial and temporal variations, revealing insights into solar activity sources and their different impacts on auroral characteristics.

Contribution

It provides a comprehensive long-term analysis of aurorae across large regions, filling gaps in historical records and distinguishing between solar sources based on auroral data.

Findings

Aurorae vary with latitude and solar activity cycles.

Different aurora characteristics correlate with coronal mass ejections and high-speed streams.

Long-term data enhances understanding of solar-terrestrial interactions.

Abstract

Catalogues and other records of aurora-borealis events were used to study the long-term spatial and temporal variation of these phenomena in the period from 1700 to 1905 in the Northern Hemisphere. For this purpose, geographic and geomagnetic coordinates were assigned to approximately 27 000 auroral events with more than 80 000 observations. They were analysed separately in three large-scale areas: i) Europe and North Africa, ii) North America, and iii) Asia. There was a clear need to fill some gaps existing in the records so as to have a reliable proxy of solar activity, especially during the 18th century. In order to enhance the long-term variability, an 11-year smoothing window was applied to the data. Variations in the cumulative numbers of auroral events with latitude (in both geographic and geomagnetic coordinates) were used to discriminate between the two main solar sources: coronal mass ejections and high-speed streams from coronal holes. The characteristics of the associated aurorae correlate differently with the solar-activity cycle.