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.

Centered and eccentric geomagnetic dipoles and their poles, 1600–1985

Abstract: Using a unified approach, expressions are derived for the various pole positions and other dipole parameters for the centered and eccentric dipole models of the earth's magnetic field. The pole positions and other parameters are then calculated using the 1945–1985 International Geomagnetic Reference Field Gauss coefficients and coefficients from models of the earth's field for earlier epochs. Comparison is made between (1) the recent pole positions and those pertaining since 1600 and (2) the various theoretical pole positions and the observed dip pole positions.

The time‐averaged geomagnetic field: global and regional biases for 0–5 Ma

Abstract: SUMMARY Palaeodirectional data from lava flows and marine sediments provide information about the long-term structure and variability in the geomagnetic field. We present a detailed analysis of the internal consistency and reliability of global compilations of sediment and lava-flow data. Time-averaged field models are constructed for normal and reverse polarity periods for the past 5 Ma, using the combined data sets. Nonzonal models are required to satisfy the lava-flow data, but not those from sediments alone. This is in part because the sediment data are much noisier than those from lavas, but is also a consequence of the site distributions and the way that inclination data sample the geomagnetic field generated in the Earth’s core. Different average field configurations for normal and reverse polarity periods are consistent with the palaeomagnetic directions; however, the differences are insignificant relative to the uncertainty in the average field models. Thus previous inferences of non-antipodal normal and reverse polarity field geometries will need to be re-examined using recently collected high-quality palaeomagnetic data. Our new models indicate that current global sediment and lava-flow data sets combined do not permit the unambiguous detection of northern hemisphere flux lobes in the 0-5 Ma time-averaged field, highlighting the need for the collection of additional high-latitude palaeomagnetic data. Anomalous time-averaged field structure is seen in the Pacific hemisphere centred just south of Hawaii. The location of the anomaly coincides with heterogeneities in the lower mantle inferred from seismological data. The seismic observations can be partly explained by lateral temperature variations; however, they also suggest the presence of lateral compositional variations and/or the presence of partial melt. The role of such heterogeneities in influencing the geomagnetic field observed at the Earth’s surface remains an unresolved issue, requiring higher-resolution time-averaged geomagnetic field models, along with the integration of future results from seismology, mineral physics and numerical simulations.

A model of the geomagnetic field and its secular variation for epoch 2000 estimated from Ørsted data

Abstract: Summary The availability of high-precision geomagnetic measurements from satellites such as Orsted and CHAMP opens a new era in geomagnetic field research. However, in order to take full advantage of the improved data accuracy it is necessary to refine the usual way of deriving field models from satellite data. This paper describes the derivation of a spherical harmonic model of the main field (up to degree/order 29) and of the secular variation (up to degree/order 13) using Orsted data spanning more than 2 yr (1999 March–2001 September) and applying new modelling approaches for a correct statistical treatment of the data errors and for considering external field contributions. Magnetospheric contributions are modelled up to degree/order two; the zonal terms vary with annual and semi-annual periodicity, and terms with degree n= 1 are modulated with the strength of the magnetospheric ring current as measured simultaneously by globally distributed geomagnetic observatories. In addition, the observatory data are used to constrain secular variation. The model is estimated using an iteratively reweighted least-squares method with Huber weights to account for the non-Gaussian data error distribution. The rms misfit achieved at non-polar latitudes is 3 nT for the scalar intensity and for one of the vector components perpendicular to the magnetic field; the third vector component (rms misfit of 6.4 nT owing to attitude noise) is downweighted when estimating the model. Comparing model predictions with actual scalar magnetic field observations from the CHAMP satellite yields an rms misfit of 3.4 nT at non-polar latitudes and 5.4 nT at polar latitudes.

Fluctuating magnetic fields in the magnetosphere. II - ULF waves.

Abstract: At the present time the existing satellite observations of ULF waves suggest that the level of geomagnetic activity controls the types of waves which occur within the magnetosphere. Consequently, we consider separately quiet times, times of magnetospheric substorms, and times of magnetic storms. Within each of these categories, there are distinctly different wave modes distinguished by their polarization: either transverse or parallel to the ambient field. In addition, these wave phenomena occur in distinct frequency bands. In terms of the standard nomenclature of ground micropulsation studies ULF wave types observed in the magnetosphere include quiet time transverse - Pc 1, Pc 3, Pc 4, Pc 5; quiet time compressional - Pc 1 and Pi 1; substorm compressional Pi 1 and Pi 2; storm transverse - Pc 1; storm compressional Pc 4, 5.

Geomagnetic storms caused by coronal mass ejections (CMEs): March 1996 through June 1997

Abstract: (1) All but two geomagnetic storms with Kp ≥ 6 during the operating period (March 1996 through June 1997) of the Large Angle Spectroscopic Coronagraph (LASCO) experiment on the Solar and Heliospheric Observatory (SOHO) spacecraft can be traced to Coronal Mass Ejections (CMEs). (2) These geomagnetic storms are not related to high speed solar wind streams. (3) The CMEs which cause geomagnetic effects, can be classified into two categories: Halo events and toroidal CMEs. (4) The CMEs are accompanied by Coronal Shock Waves as seen in the Extreme Ultraviolet Imaging Telescope (EIT) Fe XII images. (5) Some CMEs are related to flares, others are not. (6) In many cases, the travel time between the explosion on the Sun and the maximum geomagnetic activity is about 80 hours.