On the possible toroidal field window at the CMB
|対象||教職員向け 大学院生向け 学部生向け|
High electrical conductivity anomaly in the D” layer can cause opposite effects on the poloidal and toroidal magnetic fields. It has been suggested that the secular variations of the non-dipole field in the Pacific area is lower than the other area, and the Pacific area is sometimes called “dipole window”. The screening effect due to the electromagnetic induction on the non-dipole field in the high-conductivity region at the bottom of the mantle is one of the possible causes of the dipole window. On the other hand, the electric current that causes toroidal field in the core may make a circuit including a path in the high conductivity anomaly in the D” layer. The toroidal field is converted to the poloidal field by interaction with the conductivity anomaly, and a signature of the toroidal field may be observed outside of the core. This suggests that the high conductivity anomaly facilitates the escape of the toroidal field from the core. The high conductivity anomaly may be called as “toroidal field window” at the CMB.
We found that a jerk-like magnetic and electric field variations observed at the surface of Earth can be explained by an input of a sudden variation of the toroidal field at the top of the core. The observed geomagnetic and geoelectric jerks around 2006-2007 can be explained if a toroidal field window, i.e. a large-scale high conductivity heterogeneity, exists in the D” layer beneath western Africa. The favored electrical conductivity of the heterogeneity is of order 10^4 S/m.