Timing method for determining the parameters of a 2-D, non-planar discontinuity

A. Blagau (1, 2), B. Klecker (2), G. Paschmann (2), S. Haaland (3, 4), 
O. Marghitu (1), and M. Scholer (2)

(1) Institute for Space Sciences, Bucharest, Romania.  
(2) MPE, Garching, Germany.  
(3) MPS, Katlenburg-Lindau, Germany  
(4) Department of Physics, University of Bergen, Norway.


When Cluster crosses a plasma discontinuity, the differences
in satellites' position and time of encounter can be used to
obtain the discontinuity local orientation, thickness and
motion. This timing technique, commonly assuming a planar
geometry, offers an independent check for various single-spacecraft 
techniques.

We present an extension of the standard timing method, capable 
of determining in a self-consistent way the macroscopic 
parameters of a two-dimensional, non-planar discontinuity. 
Such a configuration is recognized in Cluster data when the 
single spacecraft techniques provide different individual 
normals contained roughly in the same plane. The model we 
adopted for the discontinuity assumes a layer of constant 
thickness of either cylindrical or parabolic shape, which has 
one or two degrees of freedom for the motion in the plane of 
the individual normals.

We applied the method to a magnetopause (MP) transition for 
which the various planar techniques provided inconsistent 
results. By contrast, the solutions obtained from the 
different implementations of the new 2-D method were 
consistent and stable, indicating a convex shape for the MP. 
These solutions perform better than the planar solutions from 
the normal magnetic field variance perspective. The values 
obtained for the MP parameters, together with the 
corresponding error estimate, the MP dynamics, and the 
presence of a non-zero normal magnetic field component in the 
analyzed event are further discussed.