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Abstract:
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The Earth has a time-varying (geo)magnetic field that is tied to changes in the Sun-Earth system. Thus, geomagnetic measurements contain important information about the Sun and its influence on Earth. Both the geomagnetic field and solar activity vary on timescales ranging from seconds to centuries or longer. However, modern digital measurements of the geomagnetic field are limited to 40-50 years, or about four solar activity cycles. We are working with Natural Resources Canada to digitize a much longer geomagnetic record that began in the 1840s at the Toronto magnetic observatory. The magnetograms, originally recorded on photographic paper, were transferred to 35mm film in the 1980s. We are converting these film copies to digital images and using specialized methods for unsupervised extraction of the time series data contained therein. Unsupervised extraction is important not only for reproducibility, but also because there are over 32,000 images totaling about 500Gb of computer storage. A challenge is to scale the time series appropriately in amplitude (magnetic field strength) and time. The extracted data contain periodic components which can be used to infer the unknown scales.
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