Dipole model of the Earth's magnetic field

About: Dipole model of the Earth's magnetic field is a research topic. Over the lifetime, 2756 publications have been published within this topic receiving 83021 citations.

Coronal Magnetic Fields Produced by Photospheric Shear

Abstract: The magneto-frictional method is used for computing force free fields to examine the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. It found that the energy of the sheared field can be arbitrarily large compared with the potential field. It is also found that it is possible to fit the magnetic energy, as a function of shear, by a simple functional form.

Magnetic signatures of medium‐scale traveling ionospheric disturbances as observed by CHAMP

Abstract: [1] In this work we analyze the global distribution and physical characteristics of nighttime midlatitude magnetic field fluctuations (MMFs) as observed by the CHAMP satellite from 2001 to 2002 (solar maximum) and from 2006 to 2007 (solar minimum). MMFs are defined as medium-scale magnetic fluctuations perpendicular to the mean field, which are not accompanied by plasma density irregularities at the CHAMP altitude (∼400 km). MMFs occur at 15°-40° invariant latitude in the ionospheric F region. The occurrence is rare above the southern Atlantic ocean, and bears little connection to geomagnetic activity. The global MMF occurrence rate depends on season. The occurrence is generally low in equinox, maximizes around east Asia/Oceania and Europe/ northern Atlantic Ocean in June solstice, and peaks above the American continents in December solstice. As the solar cycle declines, the detected MMF occurrence rate also decreases. The MMF occurrence peaks around 2100 LT and slowly decreases toward midnight. In the postmidnight sector, events are practically absent. The MMF occurrence is generally consistent with known features of nighttime medium-scale traveling ionospheric disturbances (MSTIDs), such as the conjugate climatology, and premidnight occurrence peak in the east Asia/Oceania region. But differences in their distributions also exist, implying that factors other than MSTIDs, e.g., ionospheric conductivity, sporadic E layer or plasma instabilities, may play a nonnegligible role in generating MMFs. MMFs have a preferred direction of polarization, which is consistent with that of MSTIDs and again corroborates the close connection between these two phenomena. We interpret the observed magnetic deflections in terms of field-aligned currents (FACs). The estimated wavelength range (∼200-500 km) of associated FAC pairs also agrees well with the size of MSTID density structures.

Magnetic fields and radio polarization of barred galaxies - 3D dynamo simulations

Abstract: A three-dimensional (3D) MHD model is applied to simulate the evolution of a large-scale magnetic field in a barred galaxy possessing a gaseous halo extending to about 2.8 kpc above the galactic plane. As the model input we use a time-dependent velocity field of molecular gas resulting from self-consistent 3D N -body simulations of a galactic disk. We assume that the gaseous halo rotates differentially co-rotating with the disk or decreasing its velocity in the Z direction. The dynamo process included in the model yields the amplification of the magnetic field as well as the formation of field structures high above the galactic disk. The simulated magnetic fields are used to construct the models of a high-frequency (Faraday rotation-free) polarized radio emission that accounts for effects of projection and limited resolution, and is thus suitable for direct comparison with observations. We found that the resultant magnetic field correctly reproduces the observed structures of polarization B -vectors, forming coherent patterns well aligned with spiral arms and with the bar. The process initializing a wave-like behavior of the magnetic field, which efficiently forms magnetic maxima between the spiral arms, is demonstrated. The inclusion of the galactic halo constitutes a step towards a realistic model of galactic magnetic fields that includes as many dynamical components as needed for a realistic description.

Earth currents of deep internal origin

Abstract: The current system flowing in the earth's core that is responsible for the dipole geomagnetic field is toroidal and does not appreciably extend into the mantle. However, the mechanism supporting these currents almost certainly generates in addition a poloidal current system that does extend into the mantle and that could, in principle, be measured at the earth's surface. In this paper the current distribution in the mantle is examined for several assumed distributions of conductivity in the mantle. The effect of the oceans is also briefly considered. It is found that the potential gradient at the surface of the earth associated with these deep earth currents may be of the order of a millivolt/kilometer if thermoelectric emf's at the core boundary contribute appreciably to the magnetic field, but will be smaller if the primary emf's are inside the core.