|Paper title||Coupling of electromagnetic waves between the magnetosphere and the topside ionosphere: new proposed science targets for the NanoMagSat mission|
|Form of presentation||Poster|
The NanoMagSat mission, currently under development in the context of the ESA Scout missions, will consist of a constellation of three nanosatellites combining two 60° inclined and one polar orbits, all at initial altitude of about 570 km. The mission will target investigations of the Earth’s magnetic field and ionospheric environment. Each satellite will carry identical payloads and include a miniaturized High Frequency Magnetometer (HFM) providing three component measurements of the magnetic field at a cadence of 2,000 samples per second. Here, we investigate the possibility of taking advantage of these future measurements, also using modern analysis techniques, to investigate polarization and propagation properties of two important classes of electromagnetic waves.
Equatorial noise is a natural electromagnetic emission generated by instability of ion distributions in the magnetosphere. These waves, which can also interact with energetic electrons in the Van Allen radiation belts, have been shown to propagate radially downward to the low-Earth orbit, thanks to previous measurements from the DEMETER spacecraft. Such waves have been observed at frequencies both below and above the local proton cyclotron frequency as a superposition of spectral lines from different distant sources. Changes in the local ion composition encountered by the waves during their inward propagation cause well identifiable cutoffs in the wave spectra, which can provide valuable information on the ionospheric plasma.
A second class of electromagnetic waves, also worthy of investigations, are nonlinear whistler mode chorus and chorus-like emissions known for their ability to locally accelerate electron in the outer radiation belt to relativistic energies and to cause losses of electrons from the radiation belts by their precipitation in the atmosphere. A divergent propagation pattern of waves at chorus frequencies has previously been reported at subauroral latitudes. The waves propagated with downward directed wave vectors, which were slightly equatorward inclined at lower magnetic latitudes and slightly poleward inclined at higher latitudes. Reverse ray tracing indicated a possible source region near the geomagnetic equator at a radial distance between 5 and 7 Earth radii. Detailed measurements of the Cluster spacecraft have already shown chorus propagating outward from this source region. The time-frequency structure and frequencies of chorus observed by Cluster along the reverse ray paths suggests that low altitude observations could indeed possibly be made by NanoMagSat, which would correspond to a manifestation of natural magnetospheric emissions of whistler mode chorus.