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.

Plasma regimes in the deep geomagnetic tail: ISEE 3

Abstract: The spacecraft remained close to or within a previously unexplored part of the distant (60-220 earth radii) geomagnetic tail nearly continuously from January 1 to March 30, 1983. Analysis of the data reveals that all of the plasma regimes identified previously with near-earth measurements (plasma sheet, low-latitude boundary layer, plasma mantle, lobe, and magnetosheath) remain recognizable in the distant tail. These regimes, however, are found to be intermingled in a more chaotic fashion than near the earth. Within the plasma sheet at approximately 200 earth radii, typical flow velocities are about 500 km/s tailward, considerably higher than in the near-earth plasma sheet. Earthward flow within the plasma sheet is observed occasionally, indicating the temporary presence of a neutral line beyond 220 earth radii. Also found are strong bidirectional electron anisotropies throughout much of the distant plasma sheet, boundary layer, and magnetosheath.

Geomagnetic Deep Sounding and Upper Mantle Structure in the Western United States

Abstract: Summary Magnetic field time variations were observed in September 1967, with a two-dimensional array of 42 three-component variometers between latitudes 36" and 43" N and longitudes 101" W and 116" W. Fourier analysis of a polar substorm and of a storm shows that the former has a smooth spectrum and the latter a complex spectrum with many maxima. Upper mantle conductivity structure can be seen qualitatively in the original variograms, but is far more sharply defined in maps of Fourier spectral component amplitudes and phases. A ridge of high conductivity runs at a depth no greater than 200 km under the Southern Rocky Mountains between the Great Plains and the Colorado Plateau, which marks a low-conductivity region within the Cordillera. A strong conductivity anomaly runs north-south along the Wasatch Front through central Utah, and indicates the presence of an upwelling of highly conductive material at depth no greater than 120 km along the edge of a step structure which brings the conductive mantle to shallower depth under the Basin and Range Province than under the Colorado Plateau. Long-period maps from the storm suggest a rise in the conductive mantle between the northsouth structures, from the Colorado Plateau southward to the Basin and Range. The daily variation shows the conductivity structures and indicates their great extent in depth. The geomagnetic deep sounding anomalies are found to be in excellent agreement with existing heat flow data, and this supports correlation of electrical conductivity with temperature. There is also good correlation with the available seismic velocity information for the upper mantle. 1. Introdaction Geophysical observations of several kinds indicate that the upper mantle of the Earth under North America is laterally inhomogeneous. Upper mantle seismic velocities of 8.0 km s-' or larger are characteristic of the eastern United States and the Great Plains Province, while velocities decrease to values of 7.9 km s-' or lower west of the Rocky Mountains (Herrin & Taggart 1962). A similar pattern is shown by travel-time anomalies of seismic waves at vertical incidence. P and S waves arrive early at stations in the eastern United States; late arrivals are predominant in the western United States (Cleary & Hales 1966; Doyle & Hales 1967; Hemn & Taggart 1968). As the differences between the P travel-time residuals and the gravity anomalies in the central and western U.S. cannot be explained by the Birch (1961) relation between velocity and density, Hales & Doyle (1967) suggested that tempera

Asymptotic cones of acceptance and their use in the study of the daily variation of cosmic radiation

Abstract: The dependence of the counting rate of a cosmic ray detector on the asymptotic directions of approach of the primary cosmic radiation is discussed. By means of a simulation of the geomagnetic field that uses spherical harmonics up to the sixth degree, and an arbitrary anisotropy in the primary cosmic radiation a method for calculating the time variations in the counting rate of a cosmic ray detector is developed. Resolving the arbitrary anisotropy as a Fourier series in longitude, the amplitude and phases of the diurnal (24-hourly) and semi-diurnal (12hourly) components of the daily variation are calculated for a number of stations. No simple relationship is observed between the phases and the latitudes and longitudes, geographic or geomagnetic. Moreover, the theoretical calculations point out that a difference of more than five hours between the diurnal phases at two different places could arise purely from the known geomagnetic configuration. A study of the time-averaged diurnal component of the daily variation experimentally observed by 22 neutron monitors during the International Geophysical Year (1957-1958) reveals good agreement with the theoretical calculations and leads to the following conclusions: (1) The results are consistent with an anisotropy that is independent of rigidity in the rangemore » 1-- 200 bv, the exponent of the power law which fits the data being 0.0 plus or minus 0.05. (2) The anisotropy varies as the cosine of the asymptotic latitude and has a maximum in the direction 85 deg to the east of the earth-sun line. (3) The maximum amplitude of the average anisotropy is 4 x 10-3 times the average cosmic ray flux. (auth)« less