GP53A-0769
ESA's Magnetic Field Mission Swarm
Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme. The objective of the Swarm
mission is to provide the best ever survey of the geomagnetic field and its temporal evolution. The Mission
shall deliver data that allow access to new insights into the Earth system by improving our understanding of
the Earth's interior and climate. The mission is nominally scheduled for launch in 2010. After release from a
single launcher, a side-by-side flying slowly decaying lower pair of satellites will be released at an initial
altitude of about 490 km together with a third satellite that will be lifted to 530 km to complete the Swarm
constellation. High-precision and high-resolution measurements of the strength, direction and variation of the
magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will
provide the observations that are required to separate and model various sources of the geomagnetic field.
At present the project is in the development phase. The current project status, planned products and
performances, and on-going scientific studies will be given special attention during the presentation. There
will also be outlook to the next planned Swarm workshop.
http://www.esa.int/esaLP/LPswarm.html
GP53A-0770
Towards diagnostic tools for analysing Swarm data through model retrievals
The objective of the Swarm mission is to provide the best ever survey of the geomagnetic field and its temporal dependency, and to gain new insights into improving our knowledge of the Earth's interior and climate. The Swarm concept consists of a constellation of three satellites in three different polar orbits between 300 and 550 km altitude. Goal of the current study is to build tools and to analyze datasets, in order to allow a fast diagnosis of the Swarm system performance in orbit during the commission phase and operations of the spacecraft. The effects on the reconstruction of the magnetic field resulting from various error sources are investigated. By using a specially developed software package closed loop simulations are performed aiming at different scenarios. We start from the simple noise-free case and move on to more complex and realistic situations which include attitude errors, position errors and data gaps. The magnitude of the different error sources is kept variable so that we not only compare the impact of different error sources, but investigate also the effects on the magnetic field reconstruction for different noise levels. Further extension of this approach will allow testing the influence of for example ionospheric residual signal or the impact of data selection on the lithospheric retrieval. Initially, the study considers one satellite and emphasises on the lithospheric field reconstruction, but in a second step it is extended to a realistic Swarm constellation of three satellites. Thus it gives us the possibility to compare the single- and the multi-satellite gradient approach showing the various advantages of the multi-satellite setup. Once the study is carried out conclusions about how the errors interfere and propagate into the models can be drawn.
GP53A-0771
Error Distribution in Regional Inversion of Potential Fields From Satellite Data
Modeling of potential fields is a major task in geophysics. When the interest is focused on a certain region or the available data are not globally distributed there is a need for regional inversion. In these cases it is necessary to have a clear knowledge of the errors resulting from the incomplete data base and their distribution in space in order to estimate the reliability of the inverted features. This work pursues the question how inversion errors in regional inversion of satellite potential field data are distributed depending on the size of the data region, the satellite altitude, the noise level and the bandwidth of the data. We show the limitations of regional inversion and give estimations of the boundary width needed in order to achieve a certain accuracy in the model region. We also show how our error predictions can be used to decide about the significance of inverted features.
GP53A-0772
Rapid changes in the geomagnetic field: from global to regional scales
A large part of the Earth's magnetic field is generated by fluid motion in the molten outer core. Its temporal change, called secular variation, is characterized by occasional rapid changes known as geomagnetic jerks, sudden change in the second time derivative of the magnetic field. For a while, detailed studies of these phenomena suffered from the sparse distribution of geomagnetic observatories over many parts of the Earth. Recent studies on magnetic data provided by magnetic satellites, with a good global coverage, suggest that more rapid and smaller scale features than previously thought occur in the field change. Indeed, using nine years of magnetic field data obtained from CHAMP, Orsted and SAC-C satellites as well as Earth-based observatories, the temporal changes in the core magnetic field and flow at the top of the core have been determined. Another approach has taken advantage of the high density of geomagnetic observatories in Europe to derive a regional model for detailed study of secular variation and acceleration over the past four decades. All known geomagnetic jerks are detected by this model; however, the time instant of a given jerk does not occur simultaneously in all magnetic field components. Both the regional and the global models indicate that secular variation and acceleration are very dynamic patterns suggesting short-term fluctuations and complex causal processes in the Earth's fluid core.
GP53A-0773
Looking for Geomagnetic Jerks in the Polar Regions
We study the geomagnetic jerks over the Artic and Antarctic regions using an approach based on the comprehensive geomagnetic field model CM4 and derived secular acceleration maps. We are interested to improve our knowledge on spatial distribution and the time occurrence of geomagnetic jerks over the polar areas where, until now, mainly the lack of a sufficient number of permanent geomagnetic observatories and the strong influence of external origin magnetic fields, have limited conclusive results. To do this, secular acceleration maps of the geomagnetic field, were obtained using synthetic data generated by the comprehensive geomagnetic field model CM4, and jerks were detected as jumps in the secular acceleration values. Our analysis confirms that the occurrence of geomagnetic jerks in the Antarctic continent follows, with an average time lag of about two years, the occurrence of geomagnetic jerks in the Artic region and reveals that the local jerk of 1986 could have a larger spatial extension than so far known. Indeed, evidences of abrupt changes in the secular acceleration maps around this date have been found now both in the Artic region and on the Antarctic continent.
GP53A-0774
Time resolution of core flow models
We estimate the robust component of quasi-geostrophic surface core flow models from two secular variation models spanning respectively the periods 1960-2002 (CM4) and 1997-2008 (xCHAOS). We rely on stochastic models to account for the contributions of the hidden small-scale magnetic field at the core-mantle boundary (CMB) interacting with core surface flows to the observed magnetic field changes. These contributions amount to errors of representativeness in the inversion of the radial induction equation at the CMB, which dominate the error budget. Taking into account the finite correlation time of the small scale magnetic field, we find that these errors of representativeness also have finite correlation time, of the order of 10 years. Our conclusion that the advection of the small scale magnetic field does not strongly contribute to the changes of the magnetic field occuring in less than 10 years -such as the geomagnetic jerks- implies that these changes should be well accounted for by core flow models. Our core flow models show, at all epochs, a grand westward current circling around the cylindrical surface tangent to the inner core, at approximately 30° and 60° latitude under the Indian and Pacific oceans, respectively. They account well for the changes in core angular momentum for the most recent epochs. We show that the interaction between the hidden magnetic field and core motions also cause apparent changes of the magnetic flux at the core-mantle boundary, which may be misunderstood as evidence for magnetic diffusion.
GP53A-0775
Principal component analysis of numerical geodynamo models
Principal component analysis (PCA) is used in meteorology and oceanography, in order to detect dynamical patterns responsible for the variability of the atmosphere and the ocean. Through the use of PCA, the dynamical state of a system can be described on a reduced basis, thereby greatly decreasing the computational cost of data assimilation algorithms. Here we investigate the potential of this kind of analysis for geomagnetic data assimilation. We consider different declinations of PCA applied to the output of three-dimensional numerical geodynamo models of increasing spatial and temporal complexity. Our direct knowledge of the core magnetic field stops at its surface, and it is limited in resolution; consequently, we study the relationship between features obtained by restricting the analysis to the core surface and features obtained by considering the variability of the whole core state, and also discuss the impact of spatial truncation on the results of the analysis.
GP53A-0776
EMAG2: A 2-arc-minute resolution global magnetic anomaly grid compiled from satellite, airborne and marine magnetic data
NOAA's National Geophysical Data Center (NGDC) has extensive holdings of airborne and marine magnetic
data. Such data have been collected for more than half a century, providing global coverage of the Earth.
Due to the changing main field from the Earth's core, and due to differences in quality and coverage,
combining these data to a consistent global magnetic anomaly grid is challenging. A key ingredient is the
long wavelength magnetic field observed by the low-orbiting CHAMP satellite. To produce a homogeneous
grid, the marine and aeromagnetic trackline data are first line-leveled and then merged with the existing grids
of continental-scale compilations by Least Squares Collocation. In the final processing step the short-to-
intermediate wavelengths of the near-surface grid are merged with the latest CHAMP satellite magnetic
anomaly model MF6 (http://geomag.org/models/MF6.html). In analogy to NGDC's 2-arc-minute resolution
ETOPO2 grid, we call our magnetic anomaly grid EMAG2. The grid will be updated regularly. It is available in
digital form and as plug-ins for NASA World Wind and Google Earth.
http://geomag.org
GP53A-0777
Aeromagnetic Study of the Amealco Caldera, Central Mexican Volcanic Belt
Analysis of the aeromagnetic anomalies over the central sector of the Mexican Volcanic Belt sheds new light on the structure of Amealco Caldera. This volcanic center located NW of Mexico City is approximately 10 km in diameter,is partially cut by a regional fault (Epitafio Huerta fault). Aguirre-Diaz (1993, 1996) has mapping the Amealco area and described the geology and petrology of the erupted products. This Caldera was formed by a large eruption which produced an ignimbrite which covers the area. The Amealco tuff is the most important volcanic unit because of its volume and distribution. After the emplacement of the central lava dome, volcanism persisted for more than a million years in the periphery and in the Caldera rim. This activity forms the Garabato dome and the Comal Scoria cone. The analyzed region is a rectangular area, approximately from 20o N to 20o 15´ N and between 100o W and 100o 20' W. The total field aeromagnetic data was obtained with a Geometrics G-803 proton magnetometer at a flight altitude of 300 m above ground level. For the analysis of the anomalies, the data was further smoothed to construct a 2 km regularly spaced grid. The anomaly map was compared with the surface geology and larger anomalies were correlated with major volcanic features. Since our main interest was in mapping the subsurface intrusive and volcanic bodies, the total field magnetic anomalies were reduced to the pole by using the double integral Fourier method. The reduced to the pole anomaly map results in a simplified pattern of isolated positive and negative anomalies, which show an improved correlation with all major volcanic structures. For the analysis and interpretation of the anomalies, the reduced to the pole anomalies were continued upward at various reference levels. These operations result in smoothing of the anomaly field by the filtering of high frequency anomalies that may be related to shallow sources. Two profiles were selected that cross the major anomalies on the Amealco Caldera. The Talwani algorithm for 2-D polygonal bodies has been used for calculating the theoretical anomalies. The proposed models reproduce adequately the main observed geological features.
GP53A-0778
Seismic Moho, Curie Isotherm Depth and Proxy Heat Flow Map of Indian Subcontinent
The depth to the bottom of the magnetic crust estimated from the MF5 Lithospheric model of CHAMP satellite, is compared with the Moho depth derived from the available DSS profiles over India. Data from over 15 DSS profiles covering different tectonic blocks like Southern Granulite terrain, Dharwar, Central Indian Shield, Bengal, Cambay, Mahanadi and Godavary basins, Narmada Son, Aravalli, Deccan trap covered region and Saurashtra were used. We find that more than 80 percent of the Moho depths estimated at the DSS shot points are deeper than the calculated bottom of the magnetic crust derived from the MF5. Further, we find that only in a few tectonic blocks this does not hold. An attempt is made to explain these results by incorporating the local geology, seismology, Magnetotelluric and other geophysical data. In a fairly large number of cases, we find that the bottom of the magnetic crust represents a temperature boundary, the Curie isotherm, rather than a compositional change. We further utilize the 1D heat conduction, steady state thermal model for the continental crust to derive the geothermal heat flux from these Curie isotherm depths. In these calculations we utilize the published thermal conductivity and surface heat production values of the different tectonic blocks, where available. We make a comparison of the derived heat flux with available surface heat flow measurements. From the present analysis it is found that for the stable continental regions like Dharwar, Bastar, Singhbhum etc., the match between the measured heat flow and the calculated is reasonably good. This is due to the fact that in stable areas conduction is the major mechanism by which the heat produced by the radioactive isotopes in the crust and heat from the mantle is transferred. However, in regions with large advective heat transfer or where the compositional changes in the crust result in elevation of the Curie isotherm depth, there could be errors in these surface heat flow estimates. An attempt is made to identify blocks where the surface heat production plays a significant role. Results of the comparison between heat flow calculated including the crustal heat sources in the 1D heat equation and excluding the crustal heat production ie., heat flow from the mantle alone, will be presented.
GP53A-0779
Structure of Charnockitic basement in a part of the Krishna–Godavari basin, Andhra Pradesh, India
A regional magnetic survey was carried out over an area of 8000 km2 in Godavari districts of Andhra Pradesh, India, which is covered by the rocks of Eastern Ghat Mobile Belt (EGMB). viz., the Khondalitic series and Charnockites in the northern half and Permian to Mesozoic and Cenozoic sediments in the southern half, and forms a part of the Krishna–Godavari (K–G) basin. The survey brought out a strong NE–SW trending anomaly in the area covered by the rocks of Eastern Ghat Mobile Belt (EGMB), and a mild ENE–WSW trending anomaly in the area covered by the sediments of the Krishna–Godavari (K–G) basin. The NE–SW trending anomaly in the northern half could be attributed to the exposed/near surface Charnockite basement that has come closer to the surface as a result of Eastern Ghat Mobile Belt (EGMB) tectonics. Explanation of the mild ENE–WSW trending anomaly over the sediments of the Krishna–Godavari (K–G) basin required a faulted magnetic basement at depth downthrown towards the south. It is therefore concluded that the Charnockitic basement together with the Khondalite group of rocks which are folded and faulted during the different phases of tectonics of Eastern Ghat Mobile Belt (EGMB) extend into the Krishna–Godavari (K–G) basin and further, were involved in faulting during the phases of formation and sedimentation in the Krishna–Godavari (K–G) basin.
GP53A-0780
KML generator to visualize geomagnetic field models on Google Earth
Google Earth is a widely accepted tool in our geoscience community, which enables us to visualize various
kinds of geoscience data simultaneously on a virtual 3-D globe. This simultaneous visualization has a
potential to bring a new discovery in the structure and/or activities of the Earth's interior. We adopt Google
Earth as a common browser for data related to the solid earth science, and have been promoting a project to
develop KML generators that enable us to obtain KML files easily and quickly applying to various kinds of
geoscience data (Yamagishi et al. in IN02). Some KML generators applicable to seismic tomography data and
geochemical data of rocks are already available via the website of our data center called "Pacific 21".
As a part of this project, we have been developing a KML generator that outputs a KML file from a
geomagnetic field model given as a set of spherical harmonic coefficients. Some parameters used in the
conversion can be controlled through a user interface such as a range of the degrees of coefficients, a grid
interval, an area of interest, and a scale of the color bar. Two types of the KML generators are developed;
one is a Java-based software executable on a stand-alone PC, and another one is a web application software
available via the website of Pacific 21.
We show some examples of KML files obtained from the main field model (e.g., IGRF/DGRF) and the
magnetic anomaly field model (e.g., NGDC-720), and compare these KML files with those obtained from other
geoscience data. It is for the first time in the community of the geomagnetism that such KML generators
applicable to geomagnetic field models are open to public. We believe that these KML generators will play an
important role in the cross-disciplinary researches of the Earth's interior.
http://www.jamstec.go.jp/pacific21/