Image: Slightly better magnetic change maps to go with the last post
To be viewed with the previous post in the Climate Change Group on ABC Pool.
The top map shows the vertical magnetic field as of 1890. The bottom one shows 1990.
Here are the title of the paper and their abstract:
Geomagnetic polarity reversals and long-term secular variation. Papers of a Discussion Meeting held at The Royal Society.. Roy Soc of London Phil Tr A, vol. 358, Issue 1768, p.957
We present a new model of the magnetic field at the core{mantle boundary for the interval 1590{1990. The model, called gufm1, is based on a massive new compilation of historical observations of the magnetic field. The greater part of the new dataset originates from unpublished observations taken by mariners engaged in merchant and naval shipping. Considerable attention is given to both correction of data for possible mislocation (originating from poor knowledge of longitude) and to proper allocation of error in the data. We adopt a stochastic model for uncorrected positional
errors that properly accounts for the nature of the noise process based on a Brownian motion model. The variability of navigational errors as a function of the duration of the voyages that we have analysed is consistent with this model. For the period before
1800, more than 83 000 individual observations of magnetic declination were recorded at more than 64 000 locations; more than 8000 new observations are for the 17th century alone. The time-dependent field model that we construct from the dataset is
parametrized spatially in terms of spherical harmonics and temporally in B-splines, using a total of 36 512 parameters. The model has improved the resolution of the core field, and represents the longest continuous model of the field available. However, full exploitation of the database may demand a new modelling methodology.
Keywords: Earth’s core; geomagnetic secular variation;
magnetic field; maritime history.
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Four centuries of geomagnetic secular variation from historical records
Jackson, Andrew; Jonkers, Art R. T.; Walker, Matthew R.
Geomagnetic polarity reversals and long-term secular variation. Papers of a Discussion Meeting held at The Royal Society.. Roy Soc of London Phil Tr A, vol. 358, Issue 1768, p.957
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