25 research outputs found
Validation of the stream function method used for reconstruction of experimental ionospheric convection patterns
No full textIn this study we test a stream function method suggested by Israelevich and Ershkovich for instantaneous reconstruction of global, high-latitude ionospheric convection patterns from a limited set of experimental observations, namely, from the electric field or ion drift velocity vector measurements taken along two polar satellite orbits only. These two satellite passes subdivide the polar cap into several adjacent areas. Measured electric fields or ion drifts can be considered as boundary conditions (together with the zero electric potential condition at the low-latitude boundary) for those areas, and the entire ionospheric convection pattern can be reconstructed as a solution of the boundary value problem for the stream function without any preliminary information on ionospheric conductivities. In order to validate the stream function method, we utilized the IZMIRAN electrodynamic model (IZMEM) recently calibrated by the DMSP ionospheric electrostatic potential observations. For the sake of simplicity, we took the modeled electric fields along the noon-midnight and dawn-dusk meridians as the boundary conditions. Then, the solution(s) of the boundary value problem (i.e., a reconstructed potential distribution over the entire polar region) is compared with the original IZMEM/DMSP electric potential distribution(s), as well as with the various cross cuts of the polar cap. It is found that reconstructed convection patterns are in good agreement with the original modeled patterns in both the northern and southern polar caps. The analysis is carried out for the winter and summer conditions, as well as for a number of configurations of the interplanetary magnetic field.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47864/1/585_2000_Article_180454.pd
Validation of the stream function method used for reconstruction of experimental ionospheric convection patterns
No full textIn this study we test a stream function
method suggested by Israelevich and Ershkovich for instantaneous reconstruction
of global, high-latitude ionospheric convection patterns from a limited set of
experimental observations, namely, from the electric field or ion drift velocity
vector measurements taken along two polar satellite orbits only. These two
satellite passes subdivide the polar cap into several adjacent areas. Measured
electric fields or ion drifts can be considered as boundary conditions (together
with the zero electric potential condition at the low-latitude boundary) for
those areas, and the entire ionospheric convection pattern can be reconstructed
as a solution of the boundary value problem for the stream function without any
preliminary information on ionospheric conductivities. In order to validate the
stream function method, we utilized the IZMIRAN electrodynamic model (IZMEM)
recently calibrated by the DMSP ionospheric electrostatic potential
observations. For the sake of simplicity, we took the modeled electric fields
along the noon-midnight and dawn-dusk meridians as the boundary conditions.
Then, the solution(s) of the boundary value problem (i.e., a reconstructed
potential distribution over the entire polar region) is compared with the
original IZMEM/DMSP electric potential distribution(s), as well as with the
various cross cuts of the polar cap. It is found that reconstructed convection
patterns are in good agreement with the original modelled patterns in both the
northern and southern polar caps. The analysis is carried out for the winter and
summer conditions, as well as for a number of configurations of the
interplanetary magnetic field.Key words: Ionosphere (electric fields and currents;
plasma convection; modelling and forecasting
Parallel electric field in the auroral ionosphere: excitation of acoustic waves by Alfvén waves
No full textInternational audienceWe investigate a new mechanism for the formation of a parallel electric field observed in the auroral ionosphere. For this purpose, the excitation of acoustic waves by propagating Alfvén waves was studied numerically. We find that the magnetic pressure perturbation due to finite amplitude Alfvén waves causes the perturbation of the plasma pressure that propagates in the form of acoustic waves, and gives rise to a parallel electric field. This mechanism explains the observations of the strong parallel electric field in the small-scale electromagnetic perturbations of the auroral ionosphere. For the cases when the parallel electric current in the small-scale auroral perturbations is so strong that the velocity of current carriers exceeds the threshold of the ion sound instability, the excited ion acoustic waves may account for the parallel electric fields as strong as tens of mV/m
Bifurcation of Jovian magnetotail current sheet
No full textInternational audienceMultiple crossings of the magnetotail current sheet by a single spacecraft give the possibility to distinguish between two types of electric current density distribution: single-peaked (Harris type current layer) and double-peaked (bifurcated current sheet). Magnetic field measurements in the Jovian magnetic tail by Voyager-2 reveal bifurcation of the tail current sheet. The electric current density possesses a minimum at the point of the Bx-component reversal and two maxima at the distance where the magnetic field strength reaches 50% of its value in the tail lobe
Bifurcation of the tail current sheet and ion temperature anisotropy
No full textAbstract. We investigated the relation between the geotail current sheet structure and the anisotropy of the ion temperature in the plasma sheet. Current density distribution in the geomagnetic tail is shown not to depend on the ratio between the parallel and perpendicular ion temperature. The tail current sheet bifurcation is controlled by non-gyrotropicity of plasma pressure: double peaked current density distribution is observed when the ion perpendicular temperature exhibits anisotropy, and the electric current density is stronger for larger ratio · (T⊥max−T⊥min)/T⊥. The current sheet thinning is accompanied by the perpendicular temperature anisotropy, and, generally, double-peaked current sheets are thinner than single-peaked sheets.
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Bifurcation of the tail current sheet and ion temperature anisotropy
No full textWe investigated the relation between the geotail current sheet structure and
the anisotropy of the ion temperature in the plasma sheet. Current density
distribution in the geomagnetic tail is shown not to depend on the ratio
between the parallel and perpendicular ion temperature. The tail current
sheet bifurcation is controlled by non-gyrotropicity of plasma pressure:
double peaked current density distribution is observed when the ion
perpendicular temperature exhibits anisotropy, and the electric current
density is stronger for larger ratio · (T⊥max−T⊥min)/T⊥. The current sheet thinning is accompanied by the
perpendicular temperature anisotropy, and, generally, double-peaked current
sheets are thinner than single-peaked sheets
A new method to reconstruct the ionospheric convection patterns in the polar cap
No full textInternational audienceA new method to reconstruct the instantaneous convection pattern in the Earth's polar ionosphere is suggested. Plasma convection in the polar cap ionosphere is described as a hydrodynamic incompressible flow. This description is valid in the region where the electric currents are field aligned (and hence, the Lorentz body force vanishes). The problem becomes two-dimensional, and may be described by means of stream function. The flow pattern may be found as a solution of the boundary value problem for stream function. Boundary conditions should be provided by measurements of the electric field or plasma velocity vectors along the satellite orbits. It is shown that the convection pattern may be reconstructed with a reasonable accuracy by means of this method, by using only the minimum number of satellite crossings of the polar cap. The method enables us to obtain a reasonable estimate of the convection pattern without knowledge of the ionospheric conductivity
A new method to reconstruct the ionospheric convection patterns in the polar cap
No full textA new method to reconstruct the instantaneous
convection pattern in the Earth's polar ionosphere is suggested. Plasma
convection in the polar cap ionosphere is described as a hydrodynamic
incompressible flow. This description is valid in the region where the electric
currents are field aligned (and hence, the Lorentz body force vanishes). The
problem becomes two-dimensional, and may be described by means of stream
function. The flow pattern may be found as a solution of the boundary value
problem for stream function. Boundary conditions should be provided by
measurements of the electric field or plasma velocity vectors along the
satellite orbits. It is shown that the convection pattern may be reconstructed
with a reasonable accuracy by means of this method, by using only the minimum
number of satellite crossings of the polar cap. The method enables us to obtain
a reasonable estimate of the convection pattern without knowledge of the
ionospheric conductivity.Key words. Ionosphere (modelling and forecasting;
plasma convection; polar ionosphere
