Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsa22b..03m&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #SA22B-03
Physics
1555 Time Variations: Diurnal To Secular, 2409 Current Systems (2708), 2415 Equatorial Ionosphere, 2427 Ionosphere/Atmosphere Interactions (0335), 2447 Modeling And Forecasting
Scientific paper
We use the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General-Circulation Model (TIEGCM) to calculate the electric currents and their associated geomagnetic perturbations generated by the ionospheric wind dynamo, including the effects of magnetospheric field-aligned currents. Calculating the geomagnetic perturbations predicted by the numerical model enables us to compare with world-wide geomagnetic data sets that are available both at ground level and at low-Earth orbit, from satellites like Magsat, Oersted and CHAMP. Comparison between model predictions and observations of magnetic perturbations can help not only to get a better understanding of the physical processes that generate the geomagnetic perturbations but also to improve the numerical models. We will present a method to determine the magnetic perturbations at the ground by spherical-harmonic analysis of the three-dimensional current system. Using spherical harmonics of higher degree and order improves the latitudinal and longitudinal representation which might be necessary in regions with highly variable magnetic perturbations. We consider not only the interhemispheric field-aligned current at middle and low latitudes but also a high-latitude contribution representing the magnetospheric source. In the calculation of the magnetic perturbation we include the diamagnetic effect of the local ionospheric plasma pressure, which can make a difference of a few nanoteslas at low latitudes, and we examine the influence of gravity-driven currents. We will show examples from TIEGCM model runs to illustrate the importance of the different contributions to the calculation of the magnetic perturbations and show how the geomagnetic perturbations can be used to help analyze model results.
Maute A. I.
Richmond Arthur D.
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