Michel Blanc

Magnetic storm modeling in the Earth's electron belt by the Salammbô code

The Salammbo code, which solves the three-dimensional phase-space diffusion equation for the electron radiation belt, was used to explain the dynamic conditions present during a geomagnetic storm. With a simple injection model, we have characterized the dynamic behavior for relativistic electrons in the outer belt. The particles in the range 100 keV – 500 keV are diffused throughout the belt, with a shape essentially dependent on the radial diffusion coefficients. Particles with higher energies are “created” by acceleration of slower particles near the plasmapause location. The calculated shape of the fluxes in an L versus time grid for the 1 MeV electrons looks globally like those measured aboard the CRRES satellite.

Electron and proton radiation belt dynamic simulations during storm periods: A new asymmetric convection‐diffusion model

Using a convection-diffusion theory, we give the first results from a four-dimensional model of electron and proton radiation belts. This work is based on the numerical solution of a convection-diffusion equation taking into account (1) for protons, the deceleration of protons by the free and bounded thermospheric and ionospheric electrons, the charge exchange loss process, radial and azimuthal transports, and (2) for electrons, the deceleration of electrons by the free and bounded electrons of the medium, pitch angle diffusion by Coulomb and wave-particle interactions, radial and azimuthal transport. This model allows for simulation of a magnetic storm effects by increasing convective electric field and injecting particles with keV range energies in the nightside region. Particles in the energy range 50 – 100 keV are “created” by acceleration of slower particles in the L = 4 region. Four hours are needed for ring current formation. The calculated particle distribution at 6.6 Earth radii as well as at low altitude are in good agreement with those deduced from ATS 6 measurements (the drift echo is well reproduced at this altitude) and from statistical studies of the precipitation by the DMSP satellites, respectively.

Modeling the high‐energy proton belt

We use and extend our previously published physical model of low-energy particle fluxes in the Earths radiation belts [Boscher et al., 1998] to study four components of the temporal variations of radiation belt particle fluxes: the secular variation, related to that of the Earths magnetic field; the solar cycle modulation; the magnetic storm effects; and the solar proton events. Our previous proton model, initially developed for equatorially mirroring low-energy particles, has been extended to higher energies in order to reproduce (1) the solar cycle influence on very high energy particles (around 100 MeV) at low altitudes and (2) the effects induced by strong active periods on protons with energies between 1 and 50 MeV. The good agreement found between our model results and observations shows that our physical model can be a safe contribution to the future development of engineering models that will be able to reproduce both the long-term variations of trapped proton fluxes (to define mission specifications) and short-term fluctuations (to understand in-flight satellite anomalies).

Contribution of Incoherent Scatter Radars to the Study of Middle and Low Latitude Ionospheric Electric Fields

Electrodynamics of the earth’s upper atmosphere has been one of the most important fields of interest in the development of space research. Its situation in the body of outer geophysics is quite original because of its first-order importance in coupling mechanisms, making a local understanding of electric currents and fields almost impossible: coupling between neutral atmosphere and ionospheric plasma motions by dynamo action of the neutral winds; coupling between ionospheric and magnetospheric plasma along the same magnetic field line by means of strong field-aligned conductivities, participating in particular to the equilibrium of the F layer; coupling between magnetospheric and solar-wind plasma motions by generation of the so-called convection electric fields at the magnetopause. Because of the long range of electromagnetic interactions, the global atmospheric circuit cannot be closed until all the region of space enclosed between the lower boundary of the ionosphere and the solar wind/ magnetosphere bow shock is considered.

Magnetosphere-ionosphere coupling

Abstract The ionosphere and the magnetosphere are coupled by three basic processes: transmission of electric fields, exchange of electric charges (field-aligned currents), and exchange of particles (by precipitation and/or outflow). All the three processes essentially operate along the same field lines, and are intimately connected in such a complicated way that for many purposes their description and understanding requires numerical simulation. Ionosphere-magnetosphere coupling operates at different temporal and spatial scales, and each different scale domain is part of a different problem and needs to be described by a different approach. At small transverse scales (1 km or less at ionospheric altitudes), when the drift time of magnetospheric current sources across frozen-in field lines is smaller than the Alfven travel time to the ionosphere and back, the main mechanism of ionosphere-magnetosphere coupling is probably transmission of shear Alfven waves. Small-scale auroral structures (simple or multiple narrow discrete arcs) may belong to this domain. For larger scales, a steady-state current circuit can be established. Up to a transverse scale of 100 km (at ionospheric altitudes) approximately, the potential differences generated across field lines in the magnetosphere are transmitted only in part to the ionosphere, and a fraction of the potential is applied along field lines, where it contributes to particle acceleration in both directions. This is the intermediate scale domain , to which inverted-V precipitation regions are most likely to belong. For large spatial scales (above 100 km), and temporal scales larger than a fraction of the drift period of trapped hot ions, the electrostatic field can be assumed to map along equipotential field lines. We review in more detail this large-scale domain of magnetosphere-ionosphere coupling. After a discussion of the sources of large-scale field-aligned currents based on recent results of global MHD simulations of the solar-wind–magnetosphere interaction, we describe a category of models, whose validity is limited to the inner magnetosphere (the region of the magnetosphere, the tail itself being not included, where the plasma return flow from the magnetotail to the dayside magnetopause is strongly controlled by coupling with the ionosphere). These models are essentially 2-D electrostatic, and use either fluid or kinetic descriptions of the plasma.