MHD modeling of magnetotail instability for anisotropic pressure

Hesse, Michael; Birn, J.

doi:10.1029/92ja00793

Cited by 30 publications

(18 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Recently, Samsonov et al [2007]validated their 3‐D anisotropic MHD model of the magnetosheath by comparing the model results to Cluster data. The magnetotail has also been simulated with a 3‐D anisotropic MHD model by Hesse and Birn [1992]. These regional models significantly contribute to the numerical modeling of space plasmas with anisotropic pressure, however they cannot reveal the global impacts of pressure anisotropy.…”

Section: Introductionmentioning

confidence: 99%

Pressure anisotropy in global magnetospheric simulations: A magnetohydrodynamics model

et al. 2012

View full text Add to dashboard Cite

[1] In order to better describe the space plasmas where pressure anisotropy has prominent effects, we extend the BATS-R-US magnetohydrodynamics (MHD) model to include anisotropic pressure. We implement the anisotropic MHD equations under the double adiabatic approximation with an additional pressure relaxation term into BATS-R-US and perform global magnetospheric simulations. The results from idealized magnetospheric simulations confirm previous studies: pressure anisotropy widens the magnetosheath, increases the density depletion in the vicinity of the magnetopause, enhances the nightside plasma pressure, and introduces an eastward ring current. In addition, we find that the flow speed in the magnetotail is significantly reduced by including pressure anisotropy in MHD simulations. Our model is validated through comparing the simulations to the THEMIS data on both the dayside and nightside of the magnetosphere during quiet times. The comparison to the results from isotropic MHD simulations implies that although anisotropic MHD is comparable to isotropic MHD in matching the measurement, it improves the simulated plasma velocity in some cases.

show abstract

Section: Introductionmentioning

confidence: 99%

Pressure anisotropy in global magnetospheric simulations: A magnetohydrodynamics model

et al. 2012

View full text Add to dashboard Cite

show abstract

“…In the absence of heat conduction, and not regarding the coupling of the pressure components by microinstabilities, the equations for the parallel and perpendicular components of the pressure tensor can then be written as (Hesse and Birn, 1992)…”

Section: Anisotropymentioning

confidence: 99%

On the propagation of bubbles in the geomagnetic tail

et al. 2004

View full text Add to dashboard Cite

Abstract. Using three-dimensional magnetohydrodynamic simulations, we investigate the propagation of low-entropy magnetic flux tubes ("bubbles") in the magnetotail. Our simulations address fundamental properties of the propagation and dynamics of such flux tubes rather than the actual formation process. We find that the early evolution, after a sudden reduction of pressure and entropy on a localized flux tube, is governed by re-establishing the balance of the total pressure in the dawn-dusk and north-south directions through compression on a time scale less than about 20 s for the typical magnetotail. The compression returns the equatorial pressure to its original unperturbed value, due to the fact that the magnetic field contributes only little to the total pressure, while farther away from the equatorial plane the magnetic field compression dominates. As a consequence the pressure is no longer constant along a flux tube. The subsequent evolution is characterized by earthward propagation at speeds of the order of 200-400 km/s, depending on the initial amount of depletion and the cross-tail extent of a bubble. Simple acceleration without depletion does not lead to significant earthward propagation. It hence seems that both the entropy reduction and the plasma acceleration play an important role in the generation of fast plasma flows and their propagation into the near tail. Earthward moving bubbles are found to be associated with field-aligned current systems, directed earthward on the dawnward edge and tailward on the duskward edge. This is consistent with current systems attributed to observed bursty bulk flows and their auroral effects.

show abstract

“…The momentum is replaced by and the energy is also modified as in the approach of Hesse and Birn [1992], using the double adiabatic approximation [ Chew et al , 1956] …”

Section: Approachmentioning

confidence: 99%

Computing magnetospheric equilibria with anisotropic pressures

Toffoletto

Wolf

et al. 2009

J. Geophys. Res.

View full text Add to dashboard Cite

[1] We present initial results from an equilibrium code that has been modified to include the effect of anisotropic pressures. This equilibrium code uses a frictional technique to iterate a set of modified MHD equations to equilibrium. We describe the modifications made to the original isotropic equilibrium code, including changes to the initial conditions that include a procedure to enforce the specified anisotropy with the restriction that the total energy on a flux tube be conserved. This allows ready comparisons with an isotropic version of the code. The initial pressure distribution is obtained from a one-dimensional curve fit and the empirical model of that specifies the pressure anisotropy as a function of position down the tail. The initial magnetic field is a magnetic field model. As a preliminary exercise with the code, we examined the differences in the equilibrium magnetic field between an anisotropic and an isotropic equilibrium pressure distribution for the same total energy per flux tube under various initial magnetic field configurations. Using anisotropy-driven instabilities and chaos effects as a guide, we made a further modification by choosing the boundary where the anisotropy transitions to zero in the tail. When the modified boundary was used, this initial investigation found that differences on the magnetic field between the anisotropic and isotropic case can be very sensitive to where we set the isotropy boundary.

show abstract

MHD modeling of magnetotail instability for anisotropic pressure

Cited by 30 publications

References 27 publications

Pressure anisotropy in global magnetospheric simulations: A magnetohydrodynamics model

Pressure anisotropy in global magnetospheric simulations: A magnetohydrodynamics model

On the propagation of bubbles in the geomagnetic tail

Computing magnetospheric equilibria with anisotropic pressures

Contact Info

Product

Resources

About