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.

Large-scale structure of the interplanetary medium. II - Evolving magnetic configurations deduced from multi-spacecraft observations

Abstract: We introduce a method for constructing large-scale (∼0.25 AU) interplanetary magnetic field lines using only solar wind velocity from well-separated appropriately located spacecraft. The technique is based on ‘labeling’ the field lines at each spacecraft with their coronal connection longitudes calculated in the EQRH (extrapolated quasi-radial hypervelocity) approximation (Nolte and Roelof, 1973). Even though the EQRH approximation is most applicable to quasi-steady solar wind, we propose that it should also be satisfactorily accurate for moderately evolving conditions. For strongly evolving conditions (e.g., flare-associated plasma) we propose a straightforward correction based on the inferred coronal longitudinal velocity profile. To illustrate the multispacecraft EQRH technique, we perform a calculation in which the interplanetary field lines in a model evolving solar wind disturbance are deduced from model observations at separated spacecraft. Since the expected agreement is found, we use data from Pioneers 8 and 9 and Vela to construct field lines for an unusually quiet period (April 26–30, 1969) and for a flare-associated disturbance accompanied by a Forbush decrease (March 23–25, 1969). The deduced field lines (even though strongly distorted by the disturbance), order the onsets of the Forbush decrease at the separated spacecraft, and the interplanetary plasma and field structures correspond to equatorial structures apparent in Hα synoptic charts of chromospheric magnetic features.

Multiple magnetic clouds in interplanetary space

Abstract: An interplanetary magnetic cloud (MC) is usually considered the byproduct of a coronal mass ejection (CME). Due to the frequent occurrence of CMEs, multiple magnetic clouds (multi-MCs), in which one MC catches up with another, should be a relatively common phenomenon. A simple flux rope model is used to get the primary magnetic field features of multi-MCs. Results indicate that the magnetic field configuration of multi-MCs mainly depends on the magnetic field characteristics of each member of multi-MCs. It may be entirely different in another situation. Moreover, we fit the data from the Wind spacecraft by using this model. Comparing the model with the observations, we verify the existence of multi-MCs, and propose some suggestions for further work.

Time scales for the decay of induced large‐scale magnetic fields in the Venus ionosphere

Abstract: Observations made with the aid of a magnetometer on the Pioneer Venus Orbiter have shown large-scale horizontal magnetic fields in the dayside ionosphere of Venus. According to Cloutier and Daniell (1981), the observed magnetic structures may be quasi-steady features produced by an ionospheric current system driven by solar wind interaction. Russell et al. (1983) have suggested that the altitude profiles of the horizontal field on different orbits exhibit a pattern which can be interpreted as phases in the temporal evolution of an initial state in which the ionosphere was permeated with magnetosheath-like fields. The present investigation is concerned with the argument in favor of a temporal versus spatial explanation for some of the observed field structure. A calculation indicates that the diffusion time for ionospheric fields is long enough to justify attributing the observed fields to the 'memory' of the Venus ionosphere in certain regions.

Polar magnetic disturbances and field-aligned currents

Abstract: The results of research of the morphology and physics of polar magnetic disturbances and their connection with three-dimensional magnetospheric currents are reviewed. Magnetic disturbance current systems are examined, also their relation to solar wind parameters and magnetic activity level and their seasonal dependence. On the basis of numerical model calculations it is shown that magnetospheric field-aligned currents observed by the TRIAD and ISIS-2 satellites are the main generation mechanism of high-latitude magnetic disturbances. Plasma pressure gradients are examined as a source of energy for driving field-aligned currents in the closed magnetosphere.

A statistical model of the geomagnetic field

Abstract: A statistical model of the geomagnetic field is derived, based on the assumption of an axial geocentric dipole field of strengthHe at the equator perturbed by randomly directed components of constant magnitudeh. The model fits the dispersions found from an analysis of the 1945 field, and the ratioh/He obtained for this field and from the palaeomagnetic data both average to about 0.4. The model predicts that during reversal of the dipole field, the field intensity falls to between 0.2 and 0.4 of the steady field intensity, and this agrees with estimates made from the palaeomagnetic observations.