Magnetopause structure and dynamics of the magnetosphere

It is shown how satellite magnetometer data at a magnetopause penetration can be used to determine the vector normal to the magnetopause current layer and the magnetic field component along this normal. Results from 22 Explorer 12 boundary penetrations indicate normal field components of less than 5 gamma in two-thirds of the cases. Measured field variations within the current layer demonstrate the existence of two fundamentally different types of boundary structure, the rotational and the tangential discontinuity. The rotational discontinuity seems to occur predominantly during magnetic storms. Finally, the calculated normal vector is compared with the normal to the surface of the Mead-Beard magnetosphere model

Magnetopause structure during the magnetic storm of 24 September 1961

Explorer 12 observations of magnetopause structure during 1961 magnetic stor

Investigation of turbulent processes in magnetospheric boundary layers

A self-consistent non-evolving two dimensional slab model of a viscous low-latitude boundary layer (LLBL) coupled to the ionosphere was developed by Phan, et al., (1989). Numerical results from the model and possible use of observations to determine the model parameters are discussed. The dynamical model developed by Lotko, et al., (1987) was used by Lotko and Shen (1991) to examine dynamical processes relevant to the LLBL with particular application to post-noon auroral shear layers. Initial results from a magnetohydrodynamic study of flank-side mangetopause boundary configuration are described. Effects of compressibility, scalar viscosity, and electrical resistivity are included in the MHD equations

On the equilibrium of the magnetopause current layer

Magnetopause current layer equilibriu

Magnetopause Transects

A novel method is described for reconstruction of two-dimensional current-layer structures from measurements taken by a single spacecraft traversing the layer. In its present form, the method is applicable only to 2D magnetohydrostatic structures that are passively convected past the observing spacecraft. It is tested on a magnetopause crossing of the tangential-discontinuity type by the spacecraft AMPTE/IRM. The magnetic structures recovered include a magnetic island located between two X-type nulls as well as a magnetic 'worm hole' through which a bundle of weak magnetic flux appears to connect the magnetosphere and the magnetosheath

First results from ideal 2-D MHD reconstruction: magnetopause reconnection event seen by Cluster

We have applied a new reconstruction method (Sonnerup and Teh, 2008), based on the ideal single-fluid MHD equations in a steady-state, two-dimensional geometry, to a reconnection event observed by the Cluster-3 (C3) space- craft on 5 July 2001, 06:23 UT, at the dawn-side Northern- Hemisphere magnetopause. The event has been previously studied by use of Grad-Shafranov (GS) reconstruction, per- formed in the deHoffmann-Teller frame, and using the as- sumption that the flow effects were either negligible or the flow was aligned with the magnetic field. Our new method allows the reconstruction to be performed in the frame of reference moving with the reconnection site (the X-line). In the event studied, this motion is tailward/equatorward at 140 km/s. The principal result of the study is that the new method functions well, generating a magnetic field map that is qualitatively similar to those obtained in the earlier GS- based reconstructions but now includes the reconnection site itself. In comparison with the earlier map by Hasegawa et al. (2004), our new map has a slightly improved ability (cc=0.979 versus cc=0.975) to predict the fields measured by the other three Cluster spacecraft, at distances from C3 rang- ing from 2132 km (C1) to 2646 km (C4). The new field map indicates the presence of a magnetic X-point, located some 5300 km tailward/equatorward of C3 at the time of its traver- sal of the magnetopause. In the immediate vicinity of the X-point, the ideal-MHD assumption breaks down, i.e. resis- tive and/or other effects should be included. We have cir- cumvented this problem by an ad-hoc procedure in which we allow the axial part of convection electric field to be non- constant near the reconnection site. The new reconstruction method also provides a map of the velocity field, in which the inflow into the wedge of reconnected field lines and the plasma jet within it can be seen, and maps of the electric po- tential and of the electric current distribution

Persistence of small-scale anisotropy of magnetic turbulence as observed in the solar wind

The anisotropy of magnetophydrodynamic turbulence is investigated by using solar wind data from the Helios 2 spacecraft. We investigate the behaviour of the complete high-order moment tensors of magnetic field increments and we compare the usual longitudinal structure functions which have both isotropic and anisotropic contributions, to the fully anisotropic contribution. Scaling exponents have been extracted by an interpolation scaling function. Unlike the usual turbulence in fluid flows, small-scale magnetic fluctuations remain anisotropic. We discuss the radial dependence of both anisotropy and intermittency and their relationship.Comment: 7 pages, 2 figures, in press on Europhys. Let

Structure of the low latitude boundary layer

Observations at high temporal resolution of the frontside magnetopause and plasma boundary layer, made with the LASL/MPE fast plasma analyzer onboard the ISEE 1 and 2 spacecraft, revealed a complex quasiperiodic structure of some of the observed boundary layers. A cool tailward streaming boundary layer plasma was seen intermittently, with intervening periods of hot tenuous plasma which has properties similar to the magnetospheric population. While individual encounters with the boundary layer plasma last only a few minutes, the total observation time may extend over one hour or more

Steady Hall Magnetohydrodynamics Near a X-type Magnetic Neutral Line

Hall magnetohydrodynamics (MHD) properties near a two-dimensional (2D) X-type magnetic neutral line in the steady state are considered via heuristic and rigorous developments. Upon considering the steady-state as the asymptotic limit of the corresponding \textit{time-dependent} problem and using a rigorous development, Hall effects are shown to be able to sustain the hyperbolicity of the magnetic field (and hence a more open X-point configuration) near the neutral line in the steady state. The heuristic development misses this subtle connection of the steady state with the corresponding \textit{time-dependent} problem and predicts only an elongated current-sheet configuration (as in resistive MHD). However, the heuristic development turns out to be useful in providing insight into the lack of dependence of the reconnection rate on the mechanism breaking the frozen-in condition of the magnetic field lines. The latter result can be understood in terms of the ability of the ions and electrons to transport equal amounts of magnetic flux per unit time out of the reconnection region.Comment: 1-10 page