HR: 14:00h
AN: U42A-02    [PDF]
TI: Trends of the Geomagnetic Dipole from Observations Over the Last Three Centuries
AU: Mozzoni, D T
EM: cyric@geomag.gfdi.fsu.edu
AF: GFDI and CSIT Florida State University, 18 Keene Bldg, Tallahassee, FL 32306-4360 United States
AU: * Cain, J C
EM: cain@geomag.gfdi.fsu.edu
AF: GFDI and CSIT Florida State University, 18 Keene Bldg, Tallahassee, FL 32306-4360 United States
AB: A review is made of published geomagnetic models utilizing data from the 18th century when absolute measurements were first introduced and those created with angular data back to the 15th century, through those using spacecraft surveys such as POGO, Magsat, \O rsted and CHAMP. The more detailed variations since 1900 of the strength of the centered dipole are viewed to evaluate whether the apparent $\sim 60$ year periodicity in the average 5% decay per century is a valid feature of the observed poloidal field or a result of the irregular distribution of data used prior to full global coverage by spacecraft. Simulated data using distributions for past epochs computed with recent global models were analyzed. The results indicate that whereas the higher components are suspect for early and mid 20th century, the variations seen in the dipole itself are likely valid. No acceleration of dipole decay over the average century--long rate is indicated from these studies provided this periodicity is taken into account. The energy being lost by the dipole continues to be fed into that of the $n=2$ and $n=3$ terms as originally noted by Verosub and Cox, though there is excess loss presumably being converted to heat. The direction of the dipole axis has continued to slowly drift on a clockwise path (westward) as represented by $G-H(1,1)$ dialgrams since 1690, with the absolute value of that non--axial contribution decreasing at least since the middle of the 19th century.
DE: 1532 Reference fields (regional, global)
DE: 1545 Spatial variations (all harmonics and anomalies)
DE: 1560 Time variations--secular and long term
SC: U
MN: 2003 Fall Meeting