Laurence Rezeau

Characterization of small-scale structures at the magnetopause from ISEE measurements

High-resolution data (covering up to 8 Hz) from the flux gate magnetometers on the two ISEE spacecraft are used to analyze ultralow-frequency (ULF) fluctuations observed at the magnetopause and in the adjacent layers. Intersatellite correlations are computed to show that the same structure can be identified in the fluctuations observed on both spacecraft when the interspacecraft distance is small. Then the possibility of deducing the velocity of the structure from two-point measurements is discussed; it is shown that it can be estimated only in certain cases.

Resonant amplification of MHD waves in realistic subsolar magnetopause configurations

Broadband ULF fluctuations are routinely observed throughout the magnetosheath; the fluctuation level peaks at the magnetopause and becomes very small in the magnetosphere. The present paper analyzes the propagation of magnetosheath waves and the transport of energy at the subsolar magnetopause by means of a linear perturbation analysis in the limit of the MHD approximation. We examine realistic equilibrium magnetopause configurations with a cold and dense magnetosheath and a hot, tenuous magnetosphere, possibly including a trapped magnetopause population. The effects of magnetic field rotation are examined. Resonant amplification of monochromatic magnetosonic waves at the magnetopause is found to occur under various conditions. For a given frequency, several field lines inside the magnetopause layer can resonate simultaneously.

Whistler mode waves and Hall fields detected by MMS during a dayside magnetopause crossing

We present Magnetospheric Multiscale (MMS) mission measurements during a full magnetopause crossing associated with an enhanced southward ion flow. A quasi-steady magnetospheric whistler mode wave ...

Asymmetric kinetic equilibria: Generalization of the BAS model for rotating magnetic profile and non-zero electric field

Finding kinetic equilibria for non-collisional/collisionless tangential current layers is a key issue as well for their theoretical modeling as for our understanding of the processes that disturb them, such as tearing or Kelvin Helmholtz instabilities. The famous Harris equilibrium [E. Harris, Il Nuovo Cimento Ser. 10 23, 115–121 (1962)] assumes drifting Maxwellian distributions for ions and electrons, with constant temperatures and flow velocities; these assumptions lead to symmetric layers surrounded by vacuum. This strongly particular kind of layer is not suited for the general case: asymmetric boundaries between two media with different plasmas and different magnetic fields. The standard method for constructing more general kinetic equilibria consists in using Jeans theorem, which says that any function depending only on the Hamiltonian constants of motion is a solution to the steady Vlasov equation [P. J. Channell, Phys. Fluids (1958–1988) 19, 1541 (1976); M. Roth et al., Space Sci. Rev. 76, 251–317 ...

BV technique for investigating 1‐D interfaces

To investigate the internal structure of the magnetopause with spacecraft data, it is crucial to be able to determine its normal direction and to convert the measured time series into spatial profiles. We propose here a new single-spacecraft method, called the BV method, to reach these two objectives. Its name indicates that the method uses a combination of the magnetic field (B) and velocity (V) data. The method is tested on simulation and on Cluster data, and a short overview of the possible products is given. We discuss its assumptions and show that it can bring a valuable improvement with respect to previous methods.

Rotational/ Compressional nature of the Magnetopause: application of the BV technique on a magnetopause case study

The magnetopause boundary implies two kinds of variations: a density/ temperature gradient and a magnetic field rotation. These two kinds are always observed in a close vicinity of each other, if not inseparably mixed. We present a case study from the Cluster data where the two are clearly separated and investigate the natures of both layers. We evidence that the first one is a slow shock while the second is a rotational discontinuity. The interaction between these two kinds of discontinuities is then studied with the help of 1,5-D magnetohydrodynamics simulations. The comparison with the data is quite positive and leads to think that most of the generic properties of the magnetopause may be interpreted in this sense.

Magnetopause orientation: Comparison between generic residue analysis and BV method

Determining the direction normal to the magnetopause layer is a key step for any study of this boundary. Various techniques have been developed for this purpose. We focus here on generic residue analysis (GRA) methods, which are based on conservation laws, and the new iterative BV method, where B represents the magnetic field and V refers to the ion velocity. This method relies on a fit of the magnetic field hodogram against a modeled geometrical shape and on the way this hodogram is described in time. These two methods have different underlying model assumptions and validity ranges. We compare here magnetopause normals predicted by BV and GRA methods to better understand the sensitivity of each method on small departures from its own physical hypotheses. This comparison is carried out first on artificial data with magnetopause-like noise. Then a statistical study is carried out using a list of 149 flank and dayside magnetopause crossings from Cluster data where the BV method is applicable, i.e., where the magnetopause involves a single-layer current sheet, with a crudely C-shaped magnetic hodogram. These two comparisons validate the quality of the BV method for all these cases where it is applicable. The method provides quite reliable normal directions in all these cases, even when the boundary is moving with a varying velocity, which distorts noticeably the results of most of the other methods.

A new instrument for space plasma exploration: The current density coil

This paper presents an instrument aimed at measuring current densities in space plasmas: a current density coil. Such an instrument already exists for the estimation of currents in the laboratory. A special design has been developed and tested for use on board spacecraft. The characteristics of the instrument are explained in details and many tests performed on the ground are presented. It is shown that the current density coil is sensitive enough to measure ionospheric currents.