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Space Plasma Simulations and Models
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  Magnetohydrostatic model of mirror modes
Magnetic Mirrors

Magnetic mirror structures have been observed in the day side of the terrestrial magnetosphere, between bow-shock and magnetopause in the magnetometric data from EQS spacecraft. These structures have also been observed by previous missions both in the day side of the magnetosheath (ISEE 1 and 2, OGO 5) and in the distant magnetotail (ISEE 3).

We present a self-consistent model of the magnetic mirrors using a perturbative magnetohydrostatic approach. With the help of this model a number of features have been revealed like geometry, stability and behavior for different temperature anisotropies (A=T/T||). The basic relations we use in order to derive the model for the mirror structures are the magnetohydrostatic equilibrium condition and an expression for the anisotropy in the case of bi-Maxwellian distribution. Based on these equations, we have found analytical expressions for the magnetic field (δB), pressure (δp) and temperature (δT) perturbations. From the investigation of the dependence of the magnetic mirrors on the unperturbed anisotropy (A0), we have found the well-known behavior (opposite phase variations of the magnetic field intensity and number density) for A0>1. For A0<1, the behavior is different but the mirror structures still exist. However, if the anisotropy is in a range of values depending on the plasma parameter β0⊥, the magnetic mirrors can no longer exist. From the comparison between the current density deduced from the Ampere law, necessary to sustain the magnetic mirror, and the gradient-curvature drift current density actually being inside the magnetic mirror, we have been able to determine instability regions in the (A00⊥)-plane.

We present a method for identification of magnetic mirror structures (MMS) in multi-point spacecraft measurements and for deriving their full 3D geometry. Multiple minima in magnetic field data are no longer regarded as separate MMS but as belonging to the same mirror structure. The approach is based on fitting a model magnetic field to measured data from one or many spacecraft. Because of the complexity of the model magnetic field, fitting the data from only one spacecraft has proved not to be reliable even if data from the others spacecraft can be used for checking the results. The main reason is the instability of the numerical fit and the non-uniqueness of the solution found. However, performing the fit on the data from multiple spacecraft allow the use of information from different regions of the structure eliminating false results and improving the numerical stability of the fit.

Contact: Dragos Constantinescu
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