Spatial-temporal modeling of the geomagnetic field for 1980–2000 period and a candidate IGRF secular-variation model for 2000–2005

Abstract

A new generation of the IZMST series (STM—space-time models based on data from observatories, POGS and Ørsted) was developed as a model of the main geomagnetic field from 1980.0 up to 2000.0. A set of the natural orthogonal components (NOCs) was used as the basic time functions. The NOCs were derived from data series from 23 observatories widely distributed on the globe. These series were extrapolated by hand from epochs 1997.0 or 1998.0 to 2000.0. The data set for the spherical harmonic analyse included observed vector values from the worldwide network of observatories, synthesized F values at 700 km, computed from WMM92.5, and X, Y, Z values computed from IGRF 2000. Depending on the data used, this gave a series of models called STM-XXX. These models were then compared with WMM92.5 (based partly on POGS data) and with IGRF 2000.0 (based entirely on Ørsted data). This comparison shows a rather good agreement over the globe except for the vector components of the field in the Southeast Pacific and Indian Oceans. Adding the Ørsted data to the database decreased this disagreement. The observatory biases, derived from STM OPE (Observatories, POGS, Ørsted) are stable over the whole time interval. Also reported in this paper is the derivation of a candidate IGRF secular-variation model for the 2000.0–2005.0 period.