IAGA School 2025 Presentation Materials

IAGA School Materials International Association of Geomagnetism and Aeronomy 7th IAGA School •2025 ISEL, Lisbon, Portugal Author Ciaran Beggan - https://orcid.org/0000-0002-2298-0578 Resources School Information https://iaga-aiga.org/iagaschool/ Lecture Recordings https://www.youtube.com/@iaga-aiga IAGA Organization https://ror.org/013ym9476 License Creative Commons CC BY-NC-SA (Attribution–NonCommercial–ShareAlike) International 1 Analogue magnetic records CIARAN BEGGAN 27-AUG-2025 Surveying and navigation 2 Jackson, A., Jonkers, A. R., & Walker, M. R. (2000) Jonkers, A.R.T., A. Jackson, and A. Murray. (2003) Halley (1701) 3 https://geomag.bgs.ac.uk/data_service/data/yearbooks/YBpdf/YB_GRW_1869.pdf Magnetic ‘Crusade’ (1832-1840) •Gauss’ invention of absolute measurements •Van Humboldt’s ‘Gottingen Magnetic Union’ •'Magnetic Crusade’ – to survey the global magnetic field –Edward Sabine –Carl Friedrich Gauss and Wilhelm Weber •Establishment of global observatories –Made manually every 5-60 minutes –Automatic photographic system invented in 1847 in Greenwich •Digital measurements began in late 1970s 4 Cawood, J. (1979) doi:10.1086/352338 Technology evolution •Abinger observatory –equipment moved from Greenwich in 1890s due to railway electrification •‘Light lever’ effect –Required a large dark room to enhance small changes –Rotating drum recorded trace of reflected beam –Dwell time fade as activity increases –Trace goes off page –Prisms and mirrors added later 5 Later technology examples 6 Historic measurements across the UK •8 observatories in the UK over the past 180 years •3 operational geomagnetic observatories at present •>250,000 highquality/resolution digital images of the daily paper magnetograms •Freely available to search online in the BGS archives 7 Active recording geomagnetic observatories in the UK from 1840 to 1983. Digitising 4-6 August 1972 Knipp et al (2018), https://doi.org/10.1029/2018S W002024 •“The event [04-Aug-1972] was associated with a nearly instantaneous, unintended detonation of dozens of sea mines near Hai Phong, North Vietnam” 8