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.

Standing Alfvén waves in the magnetosphere

Abstract: Transverse LF oscillations in geomagnetic field observed during January 1967, noting possibility of being second harmonic of magnetospheric standing Alfven waves

Penetration of magnetosheath plasma to low altitudes through the dayside magnetospheric cusps

Abstract: Daytime high-latitude fluxes of low-energy ( 107 cm−2 ster−1 sec−1 with typical energy fluxes in the range 0.01 to 0.1 ergs cm−2 ster−1 sec−1. It is concluded that solar wind plasma can penetrate to low altitudes through the high-latitude cusp in the magnetopause, which is often referred to as the neutral point. This flux is related to a number of geophysical phenomena, including magnetospheric surface currents, daytime auroras, VLF and LF emissions, ionospheric irregularities, and geomagnetic fluctuations.

Thermal and electrical conductivity of iron at Earth/'s core conditions

Abstract: First principles calculations of the thermal and electrical conductivities of liquid iron mixtures under Earth's core conditions suggest a relatively high adiabatic heat flux of 15 to16 terawatts at the core–mantle boundary, indicating that the top of the core must be thermally stratified. The thermal and electrical properties of iron are important for understanding the thermal evolution of the deep Earth and the power available to drive the dynamo that generates Earth's magnetic field. These parameters have previously been estimated by extrapolating results from conditions with lower pressure or temperature, but Monica Pozzo and colleagues now present a calculation from first principles of these parameters at the pressure and temperature of Earth's outer core. Both conductivities are found to be two to three times higher than earlier estimates, prompting a re-evaluation of power estimates for the dynamo. The results greatly restrict models for powering the geodynamo, and indicate that the top of the core must be thermally stratified. The Earth acts as a gigantic heat engine driven by the decay of radiogenic isotopes and slow cooling, which gives rise to plate tectonics, volcanoes and mountain building. Another key product is the geomagnetic field, generated in the liquid iron core by a dynamo running on heat released by cooling and freezing (as the solid inner core grows), and on chemical convection (due to light elements expelled from the liquid on freezing). The power supplied to the geodynamo, measured by the heat flux across the core–mantle boundary (CMB), places constraints on Earth’s evolution1. Estimates of CMB heat flux2,3,4,5 depend on properties of iron mixtures under the extreme pressure and temperature conditions in the core, most critically on the thermal and electrical conductivities. These quantities remain poorly known because of inherent experimental and theoretical difficulties. Here we use density functional theory to compute these conductivities in liquid iron mixtures at core conditions from first principles—unlike previous estimates, which relied on extrapolations. The mixtures of iron, oxygen, sulphur and silicon are taken from earlier work6 and fit the seismologically determined core density and inner-core boundary density jump7,8. We find both conductivities to be two to three times higher than estimates in current use. The changes are so large that core thermal histories and power requirements need to be reassessed. New estimates indicate that the adiabatic heat flux is 15 to 16 terawatts at the CMB, higher than present estimates of CMB heat flux based on mantle convection1; the top of the core must be thermally stratified and any convection in the upper core must be driven by chemical convection against the adverse thermal buoyancy or lateral variations in CMB heat flow. Power for the geodynamo is greatly restricted, and future models of mantle evolution will need to incorporate a high CMB heat flux and explain the recent formation of the inner core.