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.

Cosmological magnetic fields from primordial helicity

Abstract: Primordial magnetic fields may account for all or part of the fields observed in galaxies. We consider the evolution of the magnetic fields created by pseudoscalar effects in the early universe. Such processes can create force-free fields of maximal helicity; we show that for such a field magnetic energy inverse cascades to larger scales than it would have solely by flux freezing and cosmic expansion. For fields generated at the electroweak phase transition, we find that the predicted wavelength today can in principle be as large as 10 kpc, and the field strength can be as large as 10^{-10} G.

Systematic bias in interstellar magnetic field estimates

Abstract: Faraday rotation of the polarization plane in magnetized thermal plasma provides one of the most efficient methods to deduce regular magnetic fields from radio astronomical observations. Since the Faraday rotation measure RM is proportional to an integral, along the line of sight, of magnetic field weighted with thermal electron density, RM is believed to yield the regular magnetic field averaged over large volume. Here we show that this is not the case in a turbulent medium where fluctuations in magnetic field and electron density are not statistically independent, and so contribute to RM. For example, in the case of pressure equilibrium, magnetic field can be anticorrelated with plasma density to produce a negative contribution. As a result, the strength of the regular magnetic field obtained from RM can be underestimated if the fluctuations in electron density and magnetic field are neglected. The anticorrelation also reduces the standard deviation of RM. We further discuss the effect of the positive correlations where the standard treatment of RM leads to an overestimated magnetic field. Because of the anisotropy of the turbulent magnetic field, the regular magnetic fields strength, obtained from synchrotron emission using standard formulae, can be overestimated. A positive correlation between cosmic-ray number density and magnetic field leads to an overestimate of the strengths of the regular and total fields. These effects can explain the difference between the strengths of the regular Galactic magnetic field as indicated by RM and synchrotron emissivity data and reconcile the magnetic field strength in the Solar vicinity with typical strength of regular magnetic fields in external galaxies.

Interplanetary Magnetic Flux Ropes and Solar Filaments

Abstract: This paper aims at clarifying the physical relationship between interplanetary magnetic clouds and solar magnetic fields. For this purpose, we analyzed twelve magnetic clouds whose magnetic field variations are well explained by a flux rope model. Attempts were made to determine the geometry of flux ropes that fit the observed magnetic field variations and to identify disappearances of solar filaments that can be associated with the generation of those magnetic structures. A comparison of the magnetic field structures of flux ropes fitted to the interplanetary observations and the structures of solar magnetic fields suggests a model for the generation of magnetic clouds, or interplanetary magnetic flux ropes. We propose that the solar magnetic field surrounding a disappearing filament already has a flux rope structure at the time of eruption and that the structure extends through interplanetary space to be observed as an interplanetary flux rope. In addition, a model is proposed for a possible three-dimensional structure of an interplanetary magnetic flux rope, and observational support is presented.

Dust Detection by the Wave Instrument on STEREO: Nanoparticles Picked up by the Solar Wind?

Abstract: The STEREO wave instrument (S/WAVES) has detected a very large number of intense voltage pulses. We suggest that these events are produced by impact ionisation of nanoparticles striking the spacecraft at a velocity of the order of magnitude of the solar wind speed. Nanoparticles, which are half-way between micron-sized dust and atomic ions, have such a large charge-to-mass ratio that the electric field induced by the solar wind magnetic field accelerates them very efficiently. Since the voltage produced by dust impacts increases very fast with speed, such nanoparticles produce signals as high as do much larger grains of smaller speeds. The flux of 10-nm radius grains inferred in this way is compatible with the interplanetary dust flux model. The present results may represent the first detection of fast nanoparticles in interplanetary space near Earth orbit.

Cosmic ray cut‐off rigidities and the earth's magnetic field

Abstract: Approximate values of the vertical cut-off rigidities for cosmic ray particles in the earth's magnetic field have been deduced taking into account both the dipole and the non-dipole parts of the internal field. The accuracy of these calculated values is discussed and it is shown that they fit the experimental data rather well.