| Popis: |
Candidate models were submitted to IAGA Working group V-8 for DGRF 1985 and IGRF 1990. Main field candidates were of degree 10 for each epoch and the 1990 models included secular variation models of degree 8. Two main field candidates for each epoch were submitted by NASA's Goddard Space Flight Center (GSFC), one with and one without DE-2 satellite data. One candidate model for each epoch was submitted by the U. S. Geological Survey (USGS), one by the Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Moscow (IZMIRAN), and one jointly by the British Geological Survey (BGS) and the U. S. Naval Oceanographic Office (NOO). All 1990 models except those from GSFC included a secular variation model for 1990-1995.All models used data from Magsat and from the magnetic observatories. These were the only data used in the IZMIRAN model. All other models used Project Magnet data, but only the GSFC and USGS models incorporated it into their secular variation models. Only the GSFC models made use of the ground survey and marine survey data sets. The GSFC models also incorporated a small amount of Project Magnet data from 1988-89 which was not used in the other models.Each candidate was compared against available data from magnetic observatories, repeat, and the various surveys. The results are comparable for all the models, no model is dramatically better or worse in its, representation of the data.When comparing the models to one another, the two GSFC models are very similar. Of the others, the USGS and GSFC models are more “alike” than other pairs of models and the IZMIRAN models are the most “different”. For any pair of models the largest differences are located where the data are most sparse, i. e. the southern hemisphere and the oceanic regions. The trends of the coefficients and the implied secular variation are nearly identical between the models and the secular variation is consistent with the secular variation trend of the past 15 years. |
