HR: 0800h
AN: GP21A-0009    [Abstracts]
TI: Global models CALS3K.1 and CALS7K.2: Which of them is more trustworthy, and why?
AU: * Winkler, U
EM: winklerulf@hotmail.com
AF: School of Earth, Ocean and Environmental Sciences, University of Plymouth, Plymouth, PL1 4NQ United Kingdom
AB: Using archaeo- and paleomagnetic data, Korte and Constable produced two different spherical harmonics models of the global Earth's magnetic field. CALS3K.1, published 2003, reaches from 1000BC until 1800AD, and CALS7K.2, published 2005, stretches from 5000BC until 1990AD. The step from CALS3K.1 to CALS7K.2 consists not only in the extension of the time range further into the past by 4000 years, but also in a fundamental change of approach. In case of CALS3K.1 paleointensity measurements were only used for producing an assumption about the first Gauss coefficient, while all other coefficients were derived solely on the basis of directional measurements. In case of CALS7K.2 both intensity and direction measurements ere used to reconstruct all Gauss coefficients. While for the two millennia AD CALS3K.1 and CALS7K.2 agree fairly well with each other, major differences show up during the first millennium BC in the declination and intensity results. Those differences require clarification because of the significance of this period for geodynamic research (turnaround of the trend of the dipole moment). CALS3K.1 produces strong easterly declinations for Europe, accompanied with high intensities. CALS7K.2 misses out this event, despite of strong evidence within the database used for the making of this model. Moreover CALS7K.2 produces a significantly lower dipole moment than generally assumed. I will show indications that those problems arose because of the spatial inhomogeneous distribution of intensity measurements, and a resulting overweighting of intensity measurements from Greece. Therefore, I suggest that for the first millennium BC preference should be given to the CALS3K.1 results.
DE: 1503 Archeomagnetism
DE: 1510 Dynamo: theories and simulations
DE: 1513 Geomagnetic excursions
DE: 1521 Paleointensity
DE: 1560 Time variations: secular and longer
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005