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.

Motions of the Earth's Core and Mantle, and Variations of the Main Geomagnetic Field

Abstract: Theoretical work on the magnetohydrodynamics of the earth9s liquid core indicates (a) that horizontal variations in the properties of the core-mantle interface that would escape detection by modern seismological methods might nevertheless produce measurable geomagnetic effects; (b) that the rate of drift, relative to the earth9s surface, of nonaxisymmetric features of the main geomagnetic field might be much faster than the average zonal speed of hydrodynamic motion of core material relative to the surrounding mantle; and (c) why magnetic astronomical bodies usually rotate. Among the consequences of (a) and (b) are the possibilities that (i) the shortest interval of time that can be resolved in paleomagnetic studies of the geocentric axial dipole component of the earth9s magnetic field might be very much longer than the value often assumed by many paleomagnetic workers, (ii) reversals in sign of the geomagnetic dipole might be expected to show some degree of correlation with processes due to motions in the mantle (for example, tectonic activity, polar wandering), and (iii) variations in the length of the day that have hitherto been tentatively attributed to core motions may be due to some other cause.

Geomagnetic polarity zones for icelandic lavas

Abstract: Analysis of cores collected from a sequence of lavas in Eastern Iceland has made possible an accurate calculation of the average rate of reversal of the Earth's magnetic field.

Solar illumination as cause of the equinoctial preference for geomagnetic activity

Abstract: Geomagnetic and auroral activity vary seasonally with maxima at equinoxes, as has been known for more than a century. The cause remains under debate. The angle made by the Earth's dipole axis with the typical direction of the interplanetary magnetic field (IMF) can explain a portion (about 17%) of the effect. To explain the majority of the equinoctial effect, we suggest that geomagnetic activity peaks when the nightside auroral zones of both hemispheres are in darkness, as happens at equinox. Under such conditions, no conducting path exists in the ionosphere to complete the currents required by solar wind-magnetosphere-ionosphere coupling, and geomagnetic disturbances maximize. To test this theory, the Universal Time (UT) variation of geomagnetic activity was explored. As our model predicts, geomagnetic activity in December, measured by the Am index, evinces a deep minimum around 0300–0600 UT when the auroral oval of both hemispheres are in darkness and a maximum around 1500–1600 UT when the southern nightside oval is sunlit. In June, complementary effects are predicted and observed. Previous studies using the AE index have shown more ambiguous results. Here we show that if AE is resolved into the AU and AL components, the discrepancy disappears, with the AL component following the same pattern as does Am. We thus conclude that the intensity of global geomagnetic activity is well ordered by whether the nightside auroral oval is sunlit in one hemisphere or neither.

Quantitative parametrization of energetic ionospheric ion outflow

Abstract: Upflowing ionospheric ion (UFI) data from the DE 1 energetic ion composition spectrometer, acquired from near the maximum to the minimum of solar cycle 21, were used to determine the UFI outflow rate as a function of geomagnetic and solar activity conditions. Its solar and magnetic dependences were parameterized empiricaly. It was found that the ion outflow rate increases exponentially with Kp by a factor of 20 for O(+) and 4 for H(+) from Kp = 0 to 6.

Energy and momentum theorems in magnetospheric processes

Abstract: This review deals with the several energy and momentum theorems that relate to magnetospheric processes that have been developed. The region of primary consideration in this paper is the magnetospheric domain that extends between the ionosphere and the interplanetary medium, although, for studying certain phenomena, ionospheric and solar wind properties are of central importance and must be included. Both energy theorems and momentum theorems with their applications are presented. Since energy is an integral property of the system variables, analytical results can be found without knowledge of detailed dynamical processes. Thus, relations are derived between particle and magnetic system energies, and application is made to the shape of the magnetopause and various phases of a magnetic storm. Particular attention is given to symmetric and asymmetric ring currents, including energy and momentum equilibrium conditions; a review of nonlinear self-consistent models and a discussion of how charge exchange and energy diffusion participate in the recovery phase are presented. Comprehensive expressions for the storm time disturbance field are given in terms of both ring current and boundary current energies, and changes that occur during magnetospheric compressions are discussed. The momentum theorems center around the requirement of static force balance during geomagnetically quiet intervals. Whereas the energy theorems give expressions for the average disturbance field over the earth, the momentum theorems give the gradient in the disturbance field across the earth. The forces between earth and the boundary current, the ring current, and the tail current are derived for various models. It is noted that existing vacuum models of the geomagnetic tail are deficient in meeting the combined requirements of energetics and dynamics of the quiet time tail. Introducing the plasma sheet removes the difficulty by allowing an extra degree of freedom in adjusting the force between the earth and the tail. The role of the plasma sheet in making force adjustments is shown to be consistent with the observed thinning of the plasma sheet before sub storms.