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.

Some global features of palaeointensity in geological time

Abstract: SUMMARY A global palaeointensity data base was constructed from all published data from volcanic rocks in geological time older than 0.03 Ma. The data base contains a total of 1123 flow mean data retrieved from 83 original papers. Various features of the Earth's dipole moment were examined from the data which are based on Thellier and Shaw methods. Long-term variation of the Earth's dipole moment seems to have existed in the past 300 Ma with a broad minimum at 120–180 Ma as suggested by Prevot et al. (1990). However, due to limited site distribution we cannot regard this Mesozoic dipole low as being completely established. Precambrian palaeointensity data are still insufficient to conclude any long-term variation in this time range, although the geodynamo processes of moderate magnitude definitely existed in the early time of the Earth's history. The χ2 test was applied to the distribution of the virtual dipole moment for the past 5 Ma in which the transitional data were excluded; the results indicate that the distribution of virtual dipole moment is better represented by a log-normal distribution rather than a normal distribution, and this tendency seems to be true for the past 20 Ma. The relation of mean palaeointensity versus palaeomagnetic colatitude was examined for the past 10 Ma for the data excluding transitions. The relation is concordant with a theoretical curve from a geocentric axial dipole. This reconfirms that the dipole field was dominant in the past geomagnetic field, which is the dipole hypothesis in palaeomagnetism. On the other hand, the virtual dipole moment is much smaller for transitional palaeomagnetic fields, and a virtual geomagnetic pole lower than 45° seems to be a reasonable criterion to be categorized as a transition. The mean dipole moment for the pole latitude of 30°N-50°N band is larger than that for 30°S-50°S, indicating that there might have been a persistent asymmetry of palaeointensity between normal and reversed states, or some kind of geometrical asymmetry between the Northern and Southern Hemispheres.

Thermal interaction of the core and the mantle and long‐term behavior of the geomagnetic field

Abstract: The effects of temperature changes at the earth's core-mantle boundary on the velocity field of the core are analyzed It is assumed that the geomagnetic field is maintained by thermal convection in the outer core A model for the thermal interaction of the core and the mantle is presented which is consistent with current views on the presence of heat sources in the core and the properties of the lower mantle Significant long-term variations in the frequency of geomagnetic reversals may be the result of fluctuating temperatures at the core-mantle boundary, caused by intermittent convection in the lower mantle The thermal structure of the lower mantle region D double prime, extending from 2700 to 2900 km in depth, constitutes an important test of this hypothesis and offers a means of deciding whether the geomagnetic dynamo is thermally driven

Plate motions and the geomagnetic field. II. Jurassic to Tertiary.

Abstract: Summary. The analysis of the time-averaged geomagnetic field is extended back to 200Ma. Palaeomagnetic poles from the major plates have been carefully selected from recent compilations of reliable results for each region. These were returned, with their corresponding sampling sites, to their locations at the estimated dates of magnetization, in a fixed-hotspots framework. The corrected results were then grouped into 20Ma windows at intervals of 10Ma representing the past 100Ma, and 40Ma windows at 30Ma intervals for the more sparse 100–200Ma data. Global means and Fisher statistics were calculated for each window having included the axial quadrupole in the calculation. The value of this coefficient which gave the maximum value for the Fisher precision parameter (tightest grouping of poles) was taken as representative of each interval. The results indicate that a small axial quadrupole of the same sign as the axial dipole may have persisted throughout the Cenozoic. This is equivalent to a northward offset axial dipole field (far-sided effect). During the late Cretaceous, this component appears to have changed sign with respect to the dipole. Negative values seem to have obtained throughout the Cretaceous long normal polarity interval, corresponding to a southward offset dipole (near-sided effect). The data distribution is inadequate for the resolution of the quadrupole at earlier times, and zero values cannot be discounted. Little relative motion is implied between the hotspots and the geomagnetic axis for the past 90 Ma, the global mean polar path curving around the predicted fixed-hotspots pole at a distance of typically 5° latitude with little sign of rapid Tertiary polar wander as implied by studies of Pacific data alone. Between 100 and 200 Ma, however, there is a clear difference between the two reference frames, amounting to 17–19° in the Jurassic. This may reflect motion of the mantle relative to the geomagnetic axis, but may also include errors due to inaccurate determination of hotspot tracks and inter-hotspot motion.

Monitoring spatial and temporal variations in the dayside plasmasphere using geomagnetic field line resonances

Abstract: It is well known that the resonant frequency of geomagnetic field lines is determined by the magnetic field and plasma density. We used cross-phase and related methods to determine the field line resonance frequency across 2.4≤

Geomagnetic activity forecasting: The state of the art

Abstract: Short-term (days to weeks) geomagnetic forecasts are valuable for a variety of public and private sector endeavors. However, forecast skill, as measured by the success of predicting geomagnetic indices, is disappointing, especially for disturbed conditions. Possible reasons for this lack of proficiency include an incomplete understanding of the solar origins of interplanetary disturbances, insufficient observations of solar phenomena and interplanetary disturbances, and an underestimation of magnetospheric-ionospheric control of observed geomagnetic activity. Until more progress can be made on each of these problems, desirable forecasting precision is likely to remain elusive. The best opportunity for improved service to those agencies requiring advance notice of geomagnetic disturbances is “nowcasting” using real-time, near-Earth observations of the approaching solar wind.