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.

Ionospheric annual asymmetry observed by the COSMIC radio occultation measurements and simulated by the TIEGCM

Abstract: [1] Average F2-layer electron densities at December solstice are higher than those at June solstice. This phenomenon, which is often called the F2-layer annual asymmetry, has been observed for several decades, but its causes are still not fully understood. This study investigates global variations of this annual asymmetry observed from one year of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) ionospheric radio occultation (IRO) measurements. The IRO observations show that there is a strong NmF2 annual asymmetry that has significant longitudinal and local time variations. A strong peak of the asymmetry occurs at about noon and another one at midnight, both located at around 25° geomagnetic latitude. Numerical simulations using the Thermosphere-Ionosphere Electrodynamics Global Circulation Model (TIEGCM) are in very good agreement with these observations. The modeled NmF2 annual asymmetry has a similar magnitude, and similar semidiurnal and longitudinal variations as those in the observations. TIEGCM simulations show that changes in solar extreme ultraviolet (EUV) radiation between the December and June solstices and the displacement of the geomagnetic axis from the geographic axis are the two primary processes that cause the annual asymmetry and its associated longitudinal and local time variations. The tides propagating from lower altitudes also contribute to this asymmetry, but to a smaller extent.

An ellipsoidal harmonic representation of Earth's lithospheric magnetic field to degree and order 720

Abstract: [1] While high-degree models of the Earth's gravity potential have been inferred from measurements for more than a decade, corresponding geomagnetic models are difficult to produce. The primary challenge lies in the estimation of the magnetic potential, which is not completely determined by available field intensity measurements and cannot be computed by direct integration. Described here is the methodology behind the third generation of the National Geophysical Data Center's degree 720 magnetic model. Key issues are (1) the ellipsoidal harmonic representation of the magnetic potential, (2) the reduction of ambiguities by a suitable penalty function, and (3) the use of an iterative method to estimate the model coefficients. The NGDC-720 model provides the lithospheric magnetic field vector at any desired location and altitude close to and above the Earth's surface. Anticipated uses are in geological and tectonic studies of the lithosphere, as a local correction for magnetic navigation and heading systems, and the calibration of ground, marine, airborne, and spaceborne magnetometers. The NGDC-720 model is available at http://geomag.org/models/ngdc720.html and for long-term archive at http://earthref.org/cgi-bin/er.cgi?s=erda.cgi?n=989.

Geomagnetically induced currents in the New Zealand power network

Abstract: [1] Adverse space weather conditions have been shown to be directly responsible for faults within power networks at high latitudes. A number of studies have also shown space weather to impact power networks at lower latitudes, although most of these studies show increases in GIC activity within networks not directly related to hardware faults. This study examines a GIC event that occurred in New Zealand's South Island power network on 6th November 2001. A transformer failure that occurred during this day is shown to be associated with a change in the solar wind dynamic pressure of nearly 20 nPa. Measurements of GICs recorded on the neutral lines of transformers across the Transpower network during this event show good correlation with a GIC-index, a proxy for the geoelectric field that drives GIC. Comparison of this event with GIC activity observed in the Transpower network during large space weather storms such as the “2003 Halloween storm,” suggests that solar wind shocks and associated geomagnetic sudden impulse (SI) events may be as hazardous to middle latitude power networks as GIC activity occurring during the main phase of large storms. Further, this study suggests that the latitudinal dependence of the impacts of SI events on power systems differs from that observed during large main phase storms. This study also highlights the importance of operating procedures for large space weather events, even at middle latitude locations.

Simulations of a QuasiTaylor State Geomagnetic Field Including Polarity Reversals on the Earth Simulator

Abstract: High-resolution, low-viscosity geodynamo simulations have been carried out on the Earth Simulator, one of the fastest supercomputers, in a dynamic regime similar to that of Earth's core, that is, in a quasi-Taylor state. Our dynamo models exhibit features of the geodynamo not only in spatial and temporal characteristics but also in dynamics. Polarity reversals occurred when magnetic flux patches at high latitudes moved poleward and disappeared; patches with reversed field at low and mid-latitudes then moved poleward.