Scientific objectives

 

The objective of the SEAM satellite is to contribute to three scientific areas by providing high resolution measurements of three components of DC and AC magnetic field and one component of AC electric field in the ionosphere for:

  • Characterization of auroral current systems;
  • Monitoring of natural VLF and ELF waves;
  • Observation of antropogenic VLF and ELF waves.
Contributing to geomagnetic field modeling is beyond the scope of the mission, but is considered as a benchmark for DC magnetometer performance.

Aurora is created by precipitation of energetic electrons in the ionosphere. The electrons are accelerated by electric fields associated with auroral current systems. Electric currents along the magnetic field lines associated with the aurora cannot be measured directly from the ground. Knowing the strength of the current systems is important for characterizing the energy transfer between the magnetosphere and the ionosphere. The efficiency of the magnetosphere-ionosphere coupling depends strongly on the filamentation of the currents, as the Ohmic heating is a non-linear phenomenon.
Current filamentation can lead to very high current densities, termed as “current singularities” found on Freja satellite. Relating the current singularities to ground based data has been rather challenging due to the difficulties of precise timing/positioning of the satellite. On SEAM, equipped with a GPS receiver, it will be easier to address this question. We intend to make coordinated in-situ studies and ground based observations with instruments such as ionospheric radars and optical networks.

A number of important emissions are observed in the frequency range below 20 kHz. Whistler waves are an important element in understanding space weather. Wave-particle interactions generate hiss and chorus emissions in aurora, providing information on aurora.
Whistlers are plasma waves with frequencies of hundreds Hz to tens of kHz, generated by lightning discharges. Since the wave propagation velocity depends on plasma density, the waves are dispersed during propagation. Analysis of dispersion allows to derive the plasma density on the propagation path (Lichtenberger, 2009). Whistlers propagating from the opposite hemisphere can be ducted along the field line, in which case the dispersion contains information on the plasma density on the given magnetic shell. Fractional hop whistlers, propagating from the troposphere into the ionosphere provide a measure of columnar electron content in the ionosphere along the propagation path.
The SEAM satellite will contribute both with routine observations of whistlers globally, and detailed observations not available on other missions – full waveform in three components of the magnetic field and one component of the electric field.

Observations of power line harmonics radiation (PLHR) has recently been reported, but are still poorly understood. Very scarce experimental data are available on the PLHR and there is no theoretical explanation.
PLHR is formed by electromagnetic waves radiated by electric power systems on the ground at harmonic frequencies of 50 or 60 Hz, depending on the frequency of the system. When represented in the form of frequency-time spectrograms, they usually have a form of intense parallel lines with mutual distances of 50/100 or 60/120 Hz, because odd/even harmonics can sometimes be strongly suppressed. The role of PLHR in the ionosphere and magnetosphere is still questionable, but it could be quite important, because they can serve as a trigger for generated whistler mode emissions.
SEAM satellite will contribute to monitoring of the PLHR occurrence in the ionosphere. Our specific goal in the project is the study of PLHR which we consider as induction field component that interacts with the ionosphere plasma right above the power supply line and possibly far around.