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.

Inference of Solar Magnetic Field Parameters from Data with Limited Wavelength Sampling

Abstract: We investigate the diagnostic potential of polarimetric measurements with filtergraph instruments. Numerical simulations are used to explore the possibility of inferring the magnetic field vector, its filling factor, and the thermodynamics of model atmospheres when only a few wavelength measurements are available. These simulations assume the magnetic Sun to be represented by Milne–Eddington atmospheres. The results indicate that two wavelength measurements are insufficient to reliably determine the magnetic parameters, regardless of whether magnetograph techniques or least-squares fitting inversions are used. However, as few as four measurements analyzed with the inversion technique provide enough information to retrieve the intrinsic magnetic field with an accuracy better than 10% in most cases.

The Harmonic Analysis of the Earth's Magnetic Field, for Epoch 1942

Abstract: Summary The results are given of the harmonic analysis of the Admiralty magnetic charts of declination, horizontal intensity and inclination for the epoch 1942.5. Within the limits of observational error, the Earth's magnetic field appears to be entirely of internal origin. There is no evidence of a dipole field of external origin greater than 0-1 per cent of the field of internal origin. The intensity of the dipole field is at present decreasing at a rate of about 5 per cent per century. The geomagnetic poles have a westerly drift at a rate of 4°-5 per century; the north magnetic dip pole is moving in a direction a little to the west of north, but the south magnetic dip pole appears to be practically stationary. In consequence of the dearth of magnetic data over the oceans since 1929, magnetic charts are becoming less accurate and there is a great need for airborne magnetic surveys of ocean areas.

Possible displacement of mercury's dipole

Abstract: Earlier attempts to model the Hermean magnetospheric field based on a planet-centered magnetic multipole field have required the addition of a quadrupole moment to obtain a good fit to space vehicle observations. In this work we obtain an equally satisfactory fit by assuming a null quadrupole moment and least squares fitting of the displacement of the planetary dipole from the center of the planet. We find a best fit for a dipole displacement from the planet center of 0.033 RM away from the solar direction, 0.025 RM toward dawn in the magnetic equatorial plane, and 0.189 RM northward along the magnetic dipole axis, where RM is the planet radius. Therefore the presence of a magnetic quadrupole moment is not ruled out. The compressed dipole field more completely represents the field in the present work than in previous work where the intrinsic quadrupole field was not included in the magnetopause surface and field calculations. Moreover, we have corrected a programing error in previous work in the computation of dipole tilt λ away from the sun. We find a slight increase for the planet dipole moment of 190 γ RM³ and a dipole tilt angle λ of only 1.2° away from the sun. All other parameters are essentially unchanged.

The intense magnetic storm of December 19, 1980: Observations at L = 4

Abstract: The intense magnetic storm of December 19, 1980 occurred during a major rocket and balloon geophysical research campaign at Siple Station, Antarctica. A balloon flight measuring the electric field and bremsstrahlung X ray flux was conducted during the main phase of the storm. The balloon data and associated ground-based data from around the world contain several lines of evidence which indicate that the dayside auroral oval expanded to an invariant latitude {le} 59{degree} during the storm. Evidence for this conclusion includes (1) the pattern of ground-based magnetic field and ionospheric electric field perturbations; (2) a substantial departure from the normal diurnal curve of the vertical component of the electric field in the stratosphere; and, (3) identical, relatively rapid equatorward motion of regions of electron precipitation, observed or inferred to occur, simultaneously at three L{approximately}4 stations: Siple, Halley Bay and SANAE, separated by several hours in local time across the dayside. The absence of electron precipitation at Siple after this equatorward motion is an indication that the polar cap had expanded to include Siple during this interval. The power spectra of the magnetic field fluctuations at ULF observed at Siple and in a conjugate latitude chain of magnetometers were consistent withmore » the presence of the dayside auroral oval in the near vicinity of Siple and with the presence of a major magnetospheric boundary slightly equatorward of {approximately} 59 {degree}. The stratospheric electric field measured during the recovery phase was very large for this latitude for a period of several hours. This observation suggests that a subauroral latitude ion drift event of unusual intensity and duration accompanied this storm.« less

A Dynamic Model of Mercury's Magnetospheric Magnetic Field.

Abstract: Mercury's solar wind and interplanetary magnetic field environment is highly dynamic, and variations in these external conditions directly control the current systems and magnetic fields inside the planetary magnetosphere. We update our previous static model of Mercury's magnetic field by incorporating variations in the magnetospheric current systems, parameterized as functions of Mercury's heliocentric distance and magnetic activity. The new, dynamic model reproduces the location of the magnetopause current system as a function of systematic pressure variations encountered during Mercury's eccentric orbit, as well as the increase in the cross-tail current intensity with increasing magnetic activity. Despite the enhancements in the external field parameterization, the residuals between the observed and modeled magnetic field inside the magnetosphere indicate that the dynamic model achieves only a modest overall improvement over the previous static model. The spatial distribution of the residuals in the magnetic field components shows substantial improvement of the model accuracy near the dayside magnetopause. Elsewhere, the large-scale distribution of the residuals is similar to those of the static model. This result implies either that magnetic activity varies much faster than can be determined from the spacecraft's passage through the magnetosphere or that the residual fields are due to additional external current systems not represented in the model or both. Birkeland currents flowing along magnetic field lines between the magnetosphere and planetary high-latitude regions have been identified as one such contribution.