HR: 0800h
AN: GP31A-0068    [Abstracts]
TI: Combining Satellite and Ground Magnetic Measurements to Improve Estimates of Electromagnetic Induction Transfer Functions
AU: * Balasis, G
EM: gbalasis@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AU: Egbert, G D
EM: (541) - 737 - 2064
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, Oceanography Admin Bldg 104, Corvallis, OR 97331-5503 United States
AB: Electromagnetic (EM) induction studies using satellite and ground-based magnetic data may ultimately provide critical new constraints on the electrical conductivity of Earth's mantle. Unlike ground-based observatories, which leave large areas of the Earth (especially the ocean basins) unsampled, satellites have the potential for nearly complete global coverage. However, because the number of operating satellites is limited, spatially complex (especially non-zonal) external current sources are sampled relatively poorly by satellites at any fixed time. The comparatively much larger number of ground-based observatories provides more complete synoptic sampling of external source structure. By combining data from both satellites and observatories models of external sources can be improved, leading to more reliable global mapping of Earth conductivity. For example, estimates of EM induction transfer functions estimated from night-side CHAMP data have been previously shown to have biases which depend systematically on local time (LT). This pattern of biases suggests that a purely zonal model does not adequately describe magnetospheric sources. As a first step toward improved modeling of spatial complexity in sources, we have applied empirical orthogonal function (EOF) methods to exploratory analysis of night-side observatory data. After subtraction of the predictions of the CM4 comprehensive model, which includes a zonally symmetric storm-time correction based on D_st, we find significant non-axisymmetric, but large scale coherent variability in the mid-latitude night-side observatory residuals. Over the restricted range of local times (18:00-6:00) and latitudes (50°S to 50°N) considered, the dominant spatial mode of variability is reasonably approximated by a q₂₁ quadrupole spherical harmonic. Temporal variability of this leading EOF mode is well correlated with D_st. Strategies for moving beyond this initial exploratory EOF analysis to combine observatory data with satellite data, and to develop improved models of night-side current systems will be discussed.
DE: 1515 Geomagnetic induction
DE: 1541 Satellite magnetics: main field, crustal field, external field
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005