Mapping the ionospheric electric field together with the magnetic field provides a very complementary set of measurements. Up to date a reliable model of the global electric field distribution is still missing. Previous missions have concentrated their attention either on high or low latitudes. With its newly developed and advanced Digital Ion Drift Meter (DIDM), CHAMP promises to deliver global maps of the electric field covering all latitudes with a sufficient resolution. The long mission life-time together with the precessing orbit allows to study the dependence of the electric field patterns on magnetic activity, on local time, on season and on the solar cycle phase.
From the ionospheric electric field point of view the low and mid latitudes are distinctly different from the polar regions. At the high latitudes, poleward of about 60°, the prevailing electric field is controlled by plasma convection in the magnetosphere. At lower latitudes the much smaller electric field is primarily generated by thermally driven winds which move charged particles across geomagnetic field lines. In reality these two systems are not fully decoupled. Issues that should be addressed are:
Answers to these questions will help to better understand the ionospheric current systems and thus improve the ability to separate the external magnetic field contributions from the internal. As a by-product the measured electric fields and the estimated currents are important input parameters for modeling the "Space Weather", which has been recognised to become a relevant issue in the near future.
The International Geomagnetic Reference Field (IGRF) is a frequently used geophysical model. Its application goes far beyond the navigation of ships and aeroplanes. In satellites it is employed for attitude control. Estimates of hazards from radiation belt particles depend heavily on correct magnetic field models. In exploration techniques the magnetic field is often used as a directional reference.
The CHAMP mission will enable an improvement of the global magnetic field models to an unprecedented accuracy. This will be valid both for the spatial resolution (l ~ 500 km) and the amplitude and direction precision. Particular improvements are expected in the southern hemispheric ocean areas and in both polar regions. a correct description of the magnetic field will be very helpful for the explorations of these remote regions.
Of paramount importance are these models for exploration techniques. For example drilling heads for bore holes are given nowadays directions significantly differing from vertical. The comparison between measured magnetic fields close to the head and the model determines the steering action needed to achieve the desired direction. Similarly, for sea seismic surveys the orientation of the vector geophones is determined with respect to the magnetic reference frame.
In space applications, magnetic field models are needed in satellites using magneto torquers for manoeuvring. Also the prediction of radiation belts and the assessment of cosmic ray particle orbits, hence the safety of spacecraft and crews, rely on the quality of the models. Due to the continuous and unpredictable change of the magnetic field, global mappings have to be repeated at least every decade to assure the necessary quality of the models.
A continuous monitoring of the external electric and magnetic fields will be an important contribution to the presently starting Space Weather Prediction initiative. Suitable activity indices are intended to be generated and made available with short delays.