CHAMP Satellite Measurements Research Articles

Correlation between lithospheric magnetic anomalies and tectonic structures in the Norwegian-Greenland region of the Arctic

The studies of the deep structure and tectonics of the Arctic are important for solving the fundamental problems of modern geodynamics and developing its natural resources. This region is also of interest from the geopolitical point of view, in particular, considering the boundaries of the marginal seas. Our study aims to investigate the lithospheric (anomalous) geomagnetic field in the Norwegian-Greenland region of the Arctic and to correlate the identified anomalies with tectonic structures located in the region under study. The database includes the CHAMP satellite measurements of the modulus of the total geomagnetic field vector (the satellite operated at the altitude of ~280 km). This article describes the satellite data processing method applied to distinguish between the lithospheric part and other components of the geomagnetic field. Map showing the total vector modulus of the lithospheric field has been constructed for the studied area. The article discusses the possible nature of the lithospheric magnetic anomalies and their relation to the processes that occur under the territory of Greenland. According to our interpretation of the maps, the geomagnetic field anomalies are related to the modern large-scale geological and tectonic structures located in the studied area. The obtained results can facilitate further comprehensive geological and geophysical studies and contribute to modeling of the evolution of the lithosphere.

A southern Africa harmonic spline core field model derived from CHAMP satellite data

The monitoring of the Earth's magnetic field time variation requires a continuous recording of geomagnetic data with a good spatial coverage over the area of study. In southern Africa, ground recording stations are limited and the use of satellite data is needed for the studies where high spatial resolution data is required. We show the fast time variation of the geomagnetic field in the southern Africa region by deriving an harmonic spline model from CHAMP satellite measurements recorded between 2001 and 2010. The derived core field model, the Southern Africa Regional Model (SARM), is compared with the global model GRIMM-2 and the ground based data recorded at Hermanus magnetic observatory (HER) in South Africa and Tsumeb magnetic observatory (TSU) in Namibia where the focus is mainly on the long term variation of the geomagnetic field. The results of this study suggest that the regional model derived from the satellite data alone can be used to study the small scale features of the time variation of the geomagnetic field where ground data is not available. In addition, these results also support the earlier findings of the occurrence of a 2007 magnetic jerk and rapid secular variation fluctuations of 2003 and 2004 in the region.

Features of the Night-Time F-Region Currents Over Equatorial Africa (August, 2001)

In this paper, we present the features of the equatorial F-region current systems over equatorial Africa during nighttime on 05 th August, 2001 observed at midnight. The observations have inferred from in situ CHAMP satellite measurements of the vector magnetic field. The magnitudes of the current along all the three magnetic field components of the Earth’s magnetic field varied considerably. The Bx-component recorded a diamagnetic effect of about 8nT, By-component recorded a current density of 5mA/m, and Bz-component reached a value of 3mA/m. The F-region dynamo, gravity dynamo and plasmapressure gradients are the possible mechanisms for the occurrence of these currents. The signatures confined to the equatorial region bounded by the Appleton anomaly.

Using MFACE as input in the UAM to specify the MIT dynamics

AbstractThe magnetosphere‐ionosphere‐thermosphere (MIT) dynamic system significantly depends on the highly variable solar wind conditions, in particular, on changes of the strength and orientation of the interplanetary magnetic field (IMF). The solar wind and IMF interactions with the magnetosphere drive the MIT system via the magnetospheric field‐aligned currents (FACs). The global modeling helps us to understand the physical background of this complex system. With the present study, we test the recently developed high‐resolution empirical model of field‐aligned currents MFACE (a high‐resolution Model of Field‐Aligned Currents through Empirical orthogonal functions analysis). These FAC distributions were used as input of the time‐dependent, fully self‐consistent global Upper Atmosphere Model (UAM) for different seasons and various solar wind and IMF conditions. The modeling results for neutral mass density and thermospheric wind are directly compared with the CHAMP satellite measurements. In addition, we perform comparisons with the global empirical models: the thermospheric wind model (HWM07) and the atmosphere density model (Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Extended 2000). The theoretical model shows a good agreement with the satellite observations and an improved behavior compared with the empirical models at high latitudes. Using the MFACE model as input parameter of the UAM model, we obtain a realistic distribution of the upper atmosphere parameters for the Northern and Southern Hemispheres during stable IMF orientation as well as during dynamic situations. This variant of the UAM can therefore be used for modeling the MIT system and space weather predictions.

Enhancement of thermospheric mass density by soft electron precipitation

Enhancements in F‐region electron density and temperature and bottomside Pedersen conductivity caused by soft electron precipitation are shown to enhance the Joule heating per unit mass and the mass density of the thermosphere atF‐region altitudes. The results are derived from the coupled magnetosphere‐ionosphere‐thermosphere model (CMIT) including two types of causally specified soft electron precipitation—direct‐entry cusp precipitation and Alfvén‐wave induced, broadband electron precipitation—the effects of which are self‐consistently included for the first time in a coupled global simulation model. The simulation results provide a causal explanation of CHAMP satellite measurements of statistical enhancements in thermospheric mass density at 400 km altitudes in the cusp and premidnight auroral region.

NOAA/NGDC candidate models for the 11th generation International Geomagnetic Reference Field and the concurrent release of the 6th generation Pomme magnetic model

The International Geomagnetic Reference Field (IGRF) is updated every five years based on candidate model submissions by research institutions worldwide. In the call for the 11th generation of IGRF, candidates were requested for the definitive main field in 2005, the predicted main field in 2010, and the predicted secular variation from 2010 to 2015. The NOAA/NGDC candidate models for IGRF-11 were produced from parent models parameterized in the same way as the 6th generation of our Pomme magnetic model. All models were based on CHAMP satellite measurements, while Orsted satellite measurements were used for model validation. The internal field in Pomme-6 is described by a 2nd degree Taylor time series of spherical harmonic expansion coefficients of a scalar magnetic potential. Magnetic fields of ionospheric origin are avoided by careful data selection. Instead of co-estimating magnetospheric fields, we subtract a magnetospheric field model estimated previously from a more extensive data set covering all local times. From comparison with Orsted measurements and general considerations of magnetic field predictability, we attribute a root mean square (RMS) uncertainty of 1.3 nT to our candidate model for the main field in 2005, 2.5 nT to the predicted main field in 2010 and 26 nT/a to the predicted secular variation from 2010 to 2015.

Fifth‐generation lithospheric magnetic field model from CHAMP satellite measurements

Six years of low‐orbit CHAMP satellite magnetic measurements have provided an exceptionally high‐quality data resource for lithospheric magnetic field modeling and interpretation. Here we describe the fifth‐generation satellite‐only magnetic field model MF5. The model extends to spherical harmonic degree 100. As a result of careful data selection, extensive corrections, filtering, and line leveling, the model has low noise levels, even if evaluated at the Earth's surface. The model is particularly suited for inferring large‐scale structure and composition of the lithosphere. It is also meant to serve as the long‐wavelength part of continental‐ and global‐scale marine and aeromagnetic anomaly maps.

Separating inner and outer Earth's magnetic field from CHAMP satellite measurements by means of vector scaling functions and wavelets

SUMMARY This article is concerned with an approach of modelling the Earth's magnetic field, as measured by satellites, in terms of vector kernel functions, which we will call vector scaling functions and wavelets. The major ingredient is the presentation of a system of vector spherical harmonics which separates a given spherical vector field with respect to its sources, that is, the spherical vector field is separated into a part which is generated by sources inside the sphere, a part which is generated by sources outside the sphere and a part which is generated by sources on the sphere, which are, for example, currents crossing the sphere. Using this special system of vector spherical harmonics vector scaling functions and wavelets are constructed which keep the advantageous property of separating with respect to source but which also allow a locally adapted modelling of the respective vector field. At the end of the article, the method is tested on magnetic field data measured by the German geoscientific research satellite CHAMP.

Earth's lithospheric magnetic field determined to spherical harmonic degree 90 from CHAMP satellite measurements

SUMMARY The CHAMP magnetic field mission is providing highly reliable measurements from which the global lithospheric magnetic field can be determined in unprecedented resolution and accuracy. Using almost 5 yr of data, we derive our fourth generation lithospheric field model termed MF4, which is expanded to spherical harmonic degree and order 90. After subtracting from the full magnetic field observations predicted fields from an internal field model up to degree 15, an external field model up to degree two, and the predicted magnetic field signatures for the eight dominant ocean tidal constituents, we fit and remove remaining external fields and polar electrojet signatures in a track-by-track scheme. From a subset of least disturbed tracks, we estimate the MF4 model by least squares, damping ill-determined coefficients by regularization. The resulting MF4 model provides a good representation of the lithospheric field down to an altitude of about 50 km at lower latitudes, with reduced accuracy in the polar regions. Crustal features come out significantly sharper than in previous models. In particular, bands of magnetic anomalies along subduction zones become visible by satellite for the first time.