Compatibility of an Observed Geoelectric Jerk With Field Variations Influenced by Highly Electrically Conducting LLSVP

Sudden changes of geomagnetic secular variation (first time derivative of geomagnetic main field) have been observed several times since 1969 and the changes are called geomagnetic jerks. Among the geomagnetic jerks, those occurred at 2003, 2007 and 2011 were identified only regionally in the Atlantic and Indian Ocean. The regional geomagnetic jerks might be caused by fast equatorial magnetohydrodynamic waves propagating near the surface of the Earth's core (Chulliat et al., 2015). On the other hand, geoelectric field observed in the northwestern Pacific using long baseline submarine cables showed a jerk-like sudden change in its secular variation near the end of 2005. Relatively short time-difference in the magnetic and electric field variations, about one year, implies that the two variations have a common origin in the deep interior of the Earth. In a previous study (Shimizu and Utada, AGU fall meeting, 2014), we supposed that the toroidal magnetic field variation at the CMB as the common origin and showed numerically that appearance time and typical amplitude of the jerks in the electromagnetic fields can be explained by a simple electrical conductivity model in the D" layer if a very high electrical conductivity region exists beneath the area where the magnetic jerk was evident. Since the magnetic and electric field variations can be caused by the toroidal magnetic field, which is the electric mode, we call the jerks as geoelectric jerk. In this presentation, we show results of numerical experiment on the geoelectric jerk influenced by a more realistic distribution of the electrical conductivity in the D" layer, with highly conducting LLSVP, based on the SH-wave velocity model obtained by Takeuchi (2012), assuming a simple relation between the properties. Although the electric field variations observed by the submarine cables were compatible with the modeled results, it was found that polarity of magnetic field variations at some of the magnetic observatories could not be reproduced by the assumed electrical conductivity structure. This would imply that a simple conversion from the SH-wave velocity to electrical conductivity does not hold. The results also suggest that the geoelectric jerk has a potential to constrain the electrical conductivity structure at the bottom of the mantle.