Dn. Stewart et Ka. Whaler, OPTIMAL PIECEWISE REGRESSION-ANALYSIS AND ITS APPLICATION TO GEOMAGNETIC TIME-SERIES, Geophysical journal international, 121(3), 1995, pp. 710-724
The geomagnetic secular variation of declination at many observatories
in Europe is approximately two straight lines, with a sudden and mark
ed change in slope at around 1969, Different components of the field a
t other observatories show a similar change at around the same time, a
nd there are suggestions of the same phenomenon, commonly referred to
as a geomagnetic impulse, having occurred at other epochs. Modelling o
f geomagnetic observatory records has usually assumed that an impulse
occurred, and specified its date, making the analysis somewhat subject
ive. Here we present a new algorithm, using regression, which tests th
e hypothesis of quadratic time dependence of the field over all possib
le time intervals, ranking them such that the data series are modelled
by the fewest such quadratics (i.e. the smallest number of parameters
) that provide an adequate fit to the data. In this way, the dates of
any impulses are determined objectively, rather than imposed a priori,
and the adequacy of quadratic time dependence is assessed, The method
is tested on synthetic data, and then applied to a total of 5766 vect
or annual means of geomagnetic data from 119 observatories.