Title of article :
Geomagnetic field evolution during the Laschamp excursion
Author/Authors :
Leonhardt، نويسنده , , Roman and Fabian، نويسنده , , Karl and Winklhofer، نويسنده , , Michael and Ferk، نويسنده , , Annika and Laj، نويسنده , , Carlo and Kissel، نويسنده , , Catherine، نويسنده ,
Issue Information :
روزنامه با شماره پیاپی سال 2009
Pages :
9
From page :
87
To page :
95
Abstract :
Since the last geomagnetic reversal, 780,000 years ago, the Earthʹs magnetic field repeatedly dropped dramatically in intensity. This has often been associated with large variations in local field direction, but without a persistent global polarity flip. The structure and dynamics of geomagnetic excursions, and especially the difference between excursions and polarity reversals, have remained elusive so far. For the best documented excursion, the Laschamp event at 41,000 years BP, we have reconstructed the evolution of the global field morphology by using a Bayesian inversion of several high-resolution palaeomagnetic records. We have obtained an excursion scenario in which inverse magnetic flux patches at the core-mantle boundary emerge near the equator and then move poleward. Contrary to the situation during the last reversal (Leonhardt, R., Fabian, K., 2007. Paleomagnetic reconstruction of the global geomagnetic field evolution during the Matuyama/Brunhes transition: Iterative Bayesian inversion and independent verification. Earth Planet. Sci. Lett. 253, 172–195), these flux patches do not cross the hydrodynamic boundary of the inner-core tangent cylinder. While the last geomagnetic reversal began with a substantial increase in the strength of the non-dipolar field components, prior to the Laschamp excursion, both dipolar and non-dipolar field decay at the same rate. This result suggests that the nature of an upcoming geomagnetic field instability can be predicted several hundred years in advance. Even though during the Laschamp excursion the dipolar field at the Earthʹs surface was dominant, the reconstructed dynamic non-dipolar components lead to considerable deviations among predicted records at different locations. The inverse model also explains why at some locations no directional change during the Laschamp excursion is observed.
Keywords :
geomagnetism , Excursion , palaeomagnetism , Laschamp
Journal title :
Earth and Planetary Science Letters
Serial Year :
2009
Journal title :
Earth and Planetary Science Letters
Record number :
2327410
Link To Document :
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