Earth's magnetic field

About: Earth's magnetic field is a research topic. Over the lifetime, 20360 publications have been published within this topic receiving 446747 citations. The topic is also known as: magnetic field of Earth & geomagnetic field.

A Review of Higher Order Ionospheric Refraction Effects on Dual Frequency GPS

Abstract: Higher order ionospheric effects are increasingly relevant as precision requirements on GPS data and products increase. The refractive index of the ionosphere is affected by its electron content and the magnetic field of the Earth, so the carrier phase of the GPS L1 and L2 signals is advanced and the modulated code delayed. Due to system design the polarisation is unaffected. Most of the effect is removed by expanding the refractive index as a series and eliminating the first term with a linear combination of the two signals. However, the higher order terms remain. Furthermore, transiting gradients in refractive index at a non-perpendicular angle causes signal bending. In addition to the initial geometric bending term, another term allows for the difference that the curvature makes in electron content along each signal. Varying approximations have been made for practical implementation, mainly to avoid the need for a vertical profile of electron density. The magnetic field may be modelled as a tilted co-centric dipole, or using more realistic models such as the International Geomagnetic Reference Field. The largest effect is from the second term in the expansion of the refractive index. Up to several cm on L2, it particularly affects z-translation, and satellite orbits and clocks in a global network of GPS stations. The third term is at the level of the errors in modelling the second order term, while the bending terms appear to be absorbed by tropospheric parameters. Modelling improvements are possible, and three frequency transmissions will allow new possibilities.

Theory of the geomagnetic daily disturbance variations

Abstract: The worldwide ionospheric current system predicted by a previously described theory of the auroral electrojets is computed. Tidal air motions are neglected at first, and the high-latitude current system is assumed to be due entirely to the interaction of magnetospheric rotation with the belt of energetic protons trapped in the distorted geomagnetic field. For a given geomagnetic distortion and trapped proton distribution, the computed current system strongly resembles Chapman's idealized Ds, current system, if sufficiently high E-region electron concentrations independent of geographical position are assumed. As the assumed electron concentrations are decreased, however, the intensity of the computed current system is reduced, first in the auroral zone and then at all latitudes; at the same time the phase of the current system is advanced in the polar cap and is retarded at low latitudes. In view of this limitation of the current system by the available electron concentrations, the large disturbance variations observed during an intense geomagnetic storm can be explained by the present theory only if, in addition to an enhancement in the trapped proton density, greatly enhanced E-region electron concentrations are assumed, particularly in the auroral zone. Such enhanced electron concentrations are known to occur when blanketing sporadic E is observed. The observed correlation between blanketing sporadic E and the strength of the electrojet current is thus predicted by the present theory. The interaction of the tidal wind system with the belt of trapped protons is also considered. The resulting auroral electrojet currents oppose the Ds a current system if the usually accepted pattern of upper atmospheric tidal winds is assumed; the existence of a different wind pattern at high latitudes, at least during geomagnetic storms, is a possibility that cannot altogether be excluded, although it appears unlikely. If the majority of energetic particles in the radiation belt were electrons, their interaction with the usually accepted tidal wind pattern would result in the correct phase for the Ds current system; satellite observations indicate, however, that the majority of the energetic particles are protons. The present theory can also account for the generation of meridional static electric fields of the type that, according to a theory of Megill and Carleton, cause midlatitude red arcs.

Measurements of ionospheric currents off the coast of Peru

Abstract: Ionospheric electric current measurement, determining vertical current density distribution and electron number density for geomagnetic field study

A Dynamic, Rotating Ring Current Around Saturn

Abstract: The idea that there is a ring current of trapped particles encircling the Earth at high altitudes first emerged in the early part of the twentieth century. The idea proved right, and measurements of the current's extent and composition were made in 1957. Ring currents of a different nature were later observed at Jupiter and inferred at Saturn. The magnetospheric imaging instrument on the Cassini probe has now obtained images of the ring current at Saturn. The current is highly variable, with strong longitudinal asymmetries that corotate nearly rigidly with the planet. This contrasts with Earth's ring current, where there is no rotational modulation and initial asymmetries depend on local effects. The concept of an electrical current encircling the Earth at high altitudes was first proposed in 1917 to explain the depression of the horizontal component of the Earth’s magnetic field during geomagnetic storms1,2,3,4. In situ measurements of the extent and composition of this current were made some 50 years later5 and an image was obtained in 2001 (ref. 6). Ring currents of a different nature were observed at Jupiter7,8 and their presence inferred at Saturn9,10. Here we report images of the ring current at Saturn, together with a day–night pressure asymmetry and tilt of the planet’s plasma sheet, based on measurements using the magnetospheric imaging instrument (MIMI) on board Cassini. The ring current can be highly variable with strong longitudinal asymmetries that corotate nearly rigidly with the planet. This contrasts with the Earth’s ring current, where there is no rotational modulation and initial asymmetries are organized by local time effects.