Constraints on mantle electrical conductivity from geomagnetic jerks observation

Geomagnetic jerks involve abrupt temporal changes in the secular variation of Earth's magnetic field and are believed to be due to motions in the fluid core. We detected global jerks occurring at 1969, 1978, and 1991 that show different time arrivals at the surface of the order of 3 years. We consider jerks generated instantaneously in the core and the time delays caused by a conducting mantle. The geomagnetic field observed at the surface will correspond to a filtered version of the original field generated in the core. In order to constrain some information about the electrical conductivity of the mantle we solved the inverse problem using Velímsky & Martinec's (2005) approach. The 1-D mantle conductivity model of Kuvshinov & Olsen (2006) was adopted up to 700 km depth and below that simulations were performed with one to three-layers with electrical conductivities varying from 1000 S/m to 0.4 S/m. The results showed to be consistent with similar patterns of early/late jerks for a lower mantle about 1 S/m and allowing a broad variation for the D''.