HR: 12:05h
AN: GP41D-08    [PDF]
TI: How Long Does it Take for the Earth's Magnetic to Reverse?
AU: * Clement, B M
EM: clementb@fiu.edu
AF: Department of Earth Science, Florida International University SW 8th St & 107th Ave, Miami, FL 33199 United States
AB: One of the most fundamental questions about geomagnetic polarity reversals is that of duration: how long does it take for the field to reverse? Detailed paleomagnetic records across polarity boundaries provide our best source of information about what happens as Earth's magnetic field reverses. An analysis of the duration estimates available from paleomagnetic records of the past four polarity transitions has been presented elsewhere. That analysis, based on thirty transition records, yielded an estimate of 6000 years for the average duration of the directional change during the reversals. The durations do not vary randomly about this mean, but exhibit a pronounced dependence upon the site latitude. The directional change took nearly four times longer to occur at mid- to high-latitude sites that it did at low latitude sites. The analysis has been extended to include the older transition records from the TRANS00 database. As in the previous study two methods are used to define the transition zone thickness, one based on the circular standard deviation (CSD) of the full polarity mean directions, and one based on a VGP latitude cutoff of plus or minus 45 degrees. Unlike the case for the past four reversals, not all of the older reversals have multiple records. Therefore it is more difficult to assess the effect of the geographical distribution of site locations on the dataset. Nevertheless, the average duration of directional change based on the total dataset is statistically indistinguishable from 6000 years. The combined dataset still exhibits a marked overall dependence of transition duration with site latitude. Both the average duration and the variation with latitude provide a useful constraint for numerical simulations of the geodynamo.
DE: 1510 Dynamo theories
DE: 1535 Reversals (process, timescale, magnetostratigraphy)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting