Magnetic Dipole Axis Research Articles

Solar proton impact zones

The trajectories of charged particles moving in a magnetic dipole field were calculated by numerical integration for application to data on the intensity variation of cosmic rays during recent solar events. All seasons and times of day were covered by assuming a range of orientations of the incident particle beam with respect to the magnetic dipole axis. The points of impact with the earth were determined for protons with energies from 0.05 to 50 Bev. The computation includes 4000 trajectories and fills gaps in previous investigations. In agreement with earlier calculations the results indicate that the protons strike in well-defined areas between 0 and 1200 hours local time, and are focused into small areas of impact at low energies. The investigation revealed two points that are not new but received relatively little attention in earlier work. First, the relative number of impacts in the northern and southern geomagnetic hemispheres is strongly dependent on season. Second, under certain conditions of season there is a class of trajectories, which may be called quasi-trapped, constituting a set of paths resembling the trapped trajectories first discovered by Stormer but connected to infinity. It is suggested that injection into trapped orbits from these quasi-trapped trajectoriesmore » may raake a contribution to the population of the Van Allen belts. (auth)« less

Some remarks on the interaction of solar plasma and the geomagnetic field

A brief review of the magnetohydrodynamic and ion-cloud theories of magnetic storms and auroras suggests some difficulties, principally connected with the small scale of magnetic disturbances from point to point on the earth's surface. Currents flowing in ion clouds closer than one earth's radius from the surface of the earth appear to be necessary to explain the difficulties. The principal conclusion of this paper is that such currents will flow in plasma sheets moving along the curved magnetic lines of force as a condition of dynamic balance of centripetal forces. Furthermore, these currents produce perturbation fields of the size and direction required to explain storm-time geomagnetic variations. The plasma involved is assumed to enter the region near the earth through ‘horns’ in incident ion clouds. The material flowing into the horns follows the lines of force to the auroral zone. Finally, these horns are supposed to develop into sheets, mathematically generated by the rotation of a line of force to the auroral zone about the earth's magnetic dipole axis. Plasma flowing along such sheets performs trajectories that concentrate in the midnight hemisphere. The high energies of auroral particles follows from the headlong collisions of such clouds in the night sky.

Palaeomagnetic Researches for the Pliocene Volcanic Rocks in Central Japan (1)

All the rock specimens collected from middle Pliocene Komoro group and Shigarami group, have shown the marked magnetic polarisations in the direction of highly westward trend ranging roughly from N 60°W to N 110°W. The pole positions indicated by these specimens are calculated to be situated within a range from Lat. 32°N to Lat. 35°S.A series of volcanic rocks including the middle Pliocene rock specimens above-mentioned and ranging from early Pliocene to late Pliocene, seems to indicate that the pole position would have shifted continuously from Lat. 75°N to Lat. 70°S during Pliocene times.As far as the writer's examination goes, it should be stressed that the direction of the earth's magnetic dipole axis in Pliocene age would have shifted from the North polar region, continuously southward to the South polar region.

Rock Magnetism and Polar Wandering

Lava flows and other igneous rocks become magnetized in the direction of the local geomagnetic field when they cool down after their formation. Similarly, sediments acquire a weak magnetic polarization on deposition. The mean direction of magnetization of series of recent lava flows and sediments has been determined; it is found that these mean directions agree closely with the theoretical dipole field. This field is the field due to a geocentric axial magnetic dipole. The conclusion is therefore drawn that the mean position of the magnetic poles (taken over a period of several thousand years) coincides with the geographic poles. Assuming that the same is true for the geological past, the position of the geographic poles can be defined within fairly narrow limits by using the mean direction of magnetization of older rocks. Measurements on igneous rocks, of Tertiary and Quaternary age and from Europe only, are available. It is concluded that the large amount of polar wandering suggested by Kreichgauer, Köppen and Wegener, and Milankovitch cannot be reconciled with the new data. If polar wandering has taken place at all, it has not exceeded 5°-10° since Eocene times.