 |
| Titel |
Plasma pressure and anisotropy inferred from the Tsyganenkomagnetic field model |
| VerfasserIn |
F. Cao, L. C. Lee |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 12, no. 4 ; Nr. 12, no. 4, S.286-295 |
| Datensatznummer |
250010681
|
| Publikation (Nr.) |
 copernicus.org/angeo-12-286-1994.pdf |
|
|
|
|
|
| Zusammenfassung |
| A numerical procedure has been developed to
deduce the plasma pressure and anisotropy from the Tsyganenko magnetic field
model. The Tsyganenko empirical field model, which is based on vast satellite
field data, provides a realistic description of magnetic field configuration in
the magnetosphere. When the force balance under the static condition is assumed,
the electromagnetic J×B force from the
Tsyganenko field model can be used to infer the plasma pressure and anisotropy
distributions consistent with the field model. It is found that the J×B
force obtained from the Tsyganenko field model is not curl-free. The curl-free
part of the J×B force in an empirical field
model can be balanced by the gradient of the isotropic pressure, while the
nonzero curl of the J×B force can only be
associated with the pressure anisotropy. The plasma pressure and anisotropy in
the near-Earth plasma sheet are numerically calculated to obtain a static
equilibrium consistent with the Tsyganenko field model both in the noon-midnight
meridian and in the equatorial plane. The plasma pressure distribution deduced
from the Tsyganenko 1989 field model is highly anisotropic and shows this
feature early in the substorm growth phase. The pressure anisotropy parameter
αP, defined as αP=1-P\VertP⊥,
is typically ~0.3 at x ≈ -4.5RE and gradually
decreases to a small negative value with an increasing tailward distance. The
pressure anisotropy from the Tsyganenko 1989 model accounts for 50% of the
cross-tail current at maximum and only in a highly localized region near x\sim-10RE.
In comparison, the plasma pressure anisotropy inferred from the Tsyganenko 1987
model is much smaller. We also find that the boundary conditions have
significant effects on the plasma pressure distributions and have to be
considered carefully. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|