An energy principle for high‐latitude electrodynamics

Barbosa, D. D.

doi:10.1029/ja089ia05p02881

Cited by 13 publications

(12 citation statements)

References 43 publications

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“…6), showed that the Birkeland peak current densities in the simulation are located on average ∼5 • poleward of their observed location. We suggest that the magnetosphereionosphere system in the simulation reacts to the significant under-representation of the Region-2 currents by displacing the Region-1 current system poleward in an attempt to minimize the energy dissipation in the ionosphere (Barbosa, 1984).…”

Section: Birkeland Current Distributionsmentioning

confidence: 99%

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Comparison of Birkeland current observations during two magnetic cloud events with MHD simulations

et al. 2008

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Abstract. Low altitude field-aligned current densities obtained from global magnetospheric simulations are compared with two-dimensional distributions of Birkeland currents at the topside ionosphere derived from magnetic field observations by the constellation of Iridium satellites. We present the analysis of two magnetic cloud events, 17-19 August 2003 and 19-21 March 2001, where the interplanetary magnetic field (IMF) rotates slowly (∼10 • /h) to avoid time-aliasing in the magnetic perturbations used to calculate the Birkeland currents. In the August 2003 event the IMF rotates from southward to northward while maintaining a negative IMF B y during much of the interval. During the March 2001 event the IMF direction varies from dawnward to southward to duskward. We find that the distributions of the Birkeland current densities in the simulations agree qualitatively with the observations for northward IMF. For southward IMF, the dayside Region-1 currents are reproduced in the simulation, but appear on average 5 • further poleward of their observed location, while the nightside Region-1 currents and the Region-2 currents are largely under-represented. Comparison of the observed and simulated Birkeland current distributions, which are intimately related to the plasma drifts at the ionosphere, shows that the ionospheric convection pattern in the MHD model and its dependence on the IMF orientation is essentially correct. The Birkeland total currents in the simulations are about a factor of 2 larger than observed during southward IMF. For B z >0 the disparity in the total current is reduced and the simulations for purely northward IMF agree with the observations to within 10%. The disparities in the magnitudes of the Birkeland currents between the observations and the simulation results are a combined effect of the simulation overestimating the ionospheric electric field and of the Iridium fits underestimating the magnetic perturbations. The marginal difference in the latitude resolution of Correspondence to: H. Korth (haje.korth@jhuapl.edu) the ionospheric grids in the simulations and the observations is shown to have only secondary effect on the magnitudes of the Birkeland currents. The electric potentials in the simulation for southward IMF periods are twice as large as those obtained from measurements of the plasma drift velocities by DMSP, implying that the reconnection rates in the simulation are too large.

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Section: Birkeland Current Distributionsmentioning

confidence: 99%

“…where B is the magnetic field vector (Baumjohann and Treumann, 1997). By examining the current flowing through circles of constant latitude one can determine the partitioning of the Region-1 current closure in the simulation domain.…”

Section: Simulation Current Closurementioning

confidence: 99%

Comparison of Birkeland current observations during two magnetic cloud events with MHD simulations

et al. 2008

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“…The ionospheric conductivity models for the following calculations of the convection electric field are given in Table 1 The first model produces a pattern (Figure 2a) that is similar to those described by Barbosa [1984b]. The electric field distribution is very distorted over the polar cap, and the symmetry axis is skewed away from the dawn-dusk meridian toward noon so that the loci of the two major cells occur just after noon and midnight.…”

Section: Introductionmentioning

confidence: 79%

“…In a previous work it was shown that if the region 1 current is treated as a driving source for the coupled magnetosphereionosphere convection system, then the perfect shielding configuration is the state of minimal Joule dissipation when region 2 currents are allowed to close through the magnetosphere via the ring current [Barbosa, 1984b]. Two major requirements for this result to hold are (1) that the ionospheric gradient in the height-integrated Hall conductivity across auroral oval boundaries (referred to as the Hall discontinuity) is zero and (2) that the current flow through the ring current circuit is dissipationless, thereby providing a loss-free shunt of the region 2 current from the dawnside to the duskside.…”

Section: Introductionmentioning

confidence: 99%

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Polar convection patterns under quiet conditions

Barbosa

1985

J. Geophys. Res.

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Convection electric field patterns at high latitudes appropriate to periods of low geomagnetic activity are presented. The postulate that the global Joule dissipation rate is a minimum is employed to derive characteristic field distributions for the situation when ring current ohmic losses are negligible and the auroral oval enhancement of height‐integrated Hall conductivity is small. The fast Fourier transform is introduced to compute Fourier coefficients of discrete field‐aligned current data, and the method is shown to be quite useful in this context as a least squares fitting routine. The model calculations demonstrate the approach of the high‐latitude ionosphere toward the perfect shielding configuration predicted by the theory for quiet times.

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Minimal Joule Dissipation Models of Magnetospheric Convection

Barbosa

1988

Ionospheric Modelling

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An energy principle for high‐latitude electrodynamics

Cited by 13 publications

References 43 publications

Comparison of Birkeland current observations during two magnetic cloud events with MHD simulations

Comparison of Birkeland current observations during two magnetic cloud events with MHD simulations

Polar convection patterns under quiet conditions

Minimal Joule Dissipation Models of Magnetospheric Convection

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