An Analytical Representation of the Estimated Geomagnetic Field and its Secular Change for the Epoch 1965.0

All available surface and airborne observations of magnetic declination from 1955.0 and of vector force components from 1945.0 up to mid-June 1964 have been brought up to the epoch 1965.0. The reduced data have been subjected to a series of four spherical harmonic analyses in such a way that the apparent external part has been reduced whilst retaining a reasonable fit to the observations. Three similar analyses have been performed on the extrapolated time derivatives of X, Y and Z at 113 magnetic observatories. Results are given in terms of Schmidt quasi-normal coefficients up to the 8th order and degree for the main field and up to the 6th order and degree for its rate of change.