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.

A Proposed Model for the International Geomagnetic Reference Field-1965

Abstract: A best current model of the main geomagnetic field is presented as a response to a need for an “International Geomagnetic Reference Field”. This model is described by a series of 120 spherical harmonic coefficients and their first and second time derivatives from an epoch 1960.0. It was derived from a sample of all magnetic survey data available from the interval 1900-1964 plus a recent global distribution of preliminary total field observations from the OGO-2 (1965-81A) spacecraft for epoch 1965.8. A duplicate data selection was made and the resulting field model compared with the first to help evaluate the minimum error. It was noted that the root —mean—square difference between the two models was about 30γ in the force components, 0.04 degrees in dip and 0.3 degrees in declination at the earth's surface for 1965.0.

A new predictive model for determining solar wind-terrestrial planet interactions

Abstract: A computational model has been developed for the determination of the gasdynamic and magnetic field properties of the solar wind flow around a magnetic planet, such as the earth, or a nonmagnetic planet, such as Venus. The procedures are based on an established single-fluid, steady, dissipationless, magnetogasdynamic model and are appropriate for the calculation of axisymmetric, supersonic, super-Alfvenic solar wind flow past a planetary magneto/ionosphere. Sample results are reported for a variety of solar wind and planetary conditions. Some of these are new applications; others are included to show that the new procedures produce the same results as previous procedures when applied to the same conditions. The new methods are completely automated and much more efficient and versatile than those employed heretofore.

Alfven wave resonances in a realistic magnetospheric magnetic field geometry

Abstract: The notion of magnetic field line resonance has been very effective in explaining many features of long-period geomagnetic pulsations. To date the decoupled transverse wave equations have been solved in a magnetic dipole field, whereas only WKB approximate solutions have been used in more general geometries. We have developed a solution of the decoupled equations that includes both a general magnetic field geometry and the effects of density and mass composition. The aim of this paper is to isolate and examine the effect on eigenfrequencies of only the field geometry by keeping density constant along all field lines. We review the diurnal variations in wave period predicted on the ground and in space by using the recent Olson-Pfitzer magnetospheric magnetic field model in our solution. For example, on the ground at 67° magnetic latitude the diurnal variation in period caused by field geometry is larger than a factor of 2. At 6.6 RE, where the dipole field line from 67° crosses the magnetospheric equator, there is negligible diurnal variation in period. Significant diurnal variations in period (≳10%) at fixed radial distance in the equatorial plane in space occur only at distances ≳10 RE. Knowledge of the field geometry is shown to be important for the determination of mass density in space from ground pulsation observations. We discuss the impact of our results in interpretation of experimental data.

The heliospheric magnetic field over the South polar region of the sun.

Abstract: Magnetic field measurements from the Ulysses space mission overthe south polar regions of the sun showed that the structure and properties of the three-dimensional heliosphere were determined by the fast solar wind flow and magnetic fields from the large coronal holes in the polar regions of the sun. This conclusion applies at the current, minimum phase of the 11-year solar activity cycle. Unexpectedly, the radial component of the magnetic field was independent of latitude. The high-latitude magnetic field deviated significantly from the expected Parker geometry, probably because of large amplitude transverse fluctuations. Low-frequency fluctuations had a high level of variance. The rate of occurrence of discontinuities also increased significantly at high latitudes.

Hill model of transpolar potential saturation: Comparisons with MHD simulations

Abstract: [1] We present a comparison between a simple but general model of solar wind-magnetosphere-ionosphere coupling (the Hill model) and the output of a global magnetospheric MHD code, the Integrated Space Weather Prediction Model (ISM). The Hill model predicts transpolar potential and region 1 currents from environmental conditions specified at both boundaries of the magnetosphere: at the solar wind boundary, electric field strength, ram pressure, and interplanetary magnetic field direction; at the ionospheric boundary, conductance and dipole strength. As its defining feature, the Hill model predicts saturation of the transpolar potential for high electric field intensities in the solar wind, which accords with observations. The model predicts how saturation depends on boundary conditions. We compare the output from ISM runs against these predictions. The agreement is quite good for non-storm conditions (differences less than 10%) and still good for storm conditions (differences up to 20%). The comparison demonstrates that global MHD codes (like ISM) can also exhibit saturation of transpolar potential for high electric field intensities in the solar wind. We use both models to explore how the strength of solar wind-magnetosphere-ionosphere coupling depends on the strength of Earth's magnetic dipole, which varies on short geological timescales. As measured by power into the ionosphere, these models suggest that magnetic storms might be considerably more active for high dipole strengths.