Modeling Extreme Compression of the Magnetosphere: Results from a Global MHD Simulation of the May 4, 1998 Event

Berchem, J.; El‐Alaoui, M.; Ashour‐Abdalla, M.

doi:10.1029/gm125p0241

Cited by 6 publications

References 21 publications

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Dayside Proton Aurora: Comparisons Between Global MHD Simulations and IMAGE Observations

Berchem

Fuselier

Petrinec

et al. 2003

Magnetospheric Imaging — The Image Prime Mission

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Abstract.The IMAGE mission provides a unique opportunity to evaluate the accuracy of current global models of the solar wind interaction with the Earth's magnetosphere. In particular, images of proton auroras from the Far Ultraviolet Instrument (FUV) onboard the IMAGE spacecraft are well suited to support investigations of the response of the Earth's magnetosphere to interplanetary disturbances. Accordingly, we have modeled two events that occurred on June 8 and July 28, 2000, using plasma and magnetic field parameters measured upstream of the bow shock as input to threedimensional magnetohydrodynamic (MHD) simulations. This paper begins with a discussion of images of proton auroras from the FUV SI-12 instrument in comparison with the simulation results. The comparison showed a very good agreement between intensifications in the auroral emissions measured by FUV SI-12 and the enhancement of plasma flows into the dayside ionosphere predicted by the global simulations. Subsequently, the IMAGE observations are analyzed in the context of the dayside magnetosphere's topological changes in magnetic field and plasma flows inferred from the simulation results. Finding include that the global dynamics of the auroral proton precipitation patterns observed by IMAGE are consistent with magnetic field reconnection occurring as a continuous process while the iMF changes in direction and the solar wind dynamic pressure varies. The global simulations also indicate that some of the transient patterns observed by IMAGE are consistent with sporadic reconnection processes. Global merging patterns found in the simulations agree with the antiparallel merging model. though locally component merging might broaden the merging region, especially in the region where shocked solar wind discontinuities first reach the magnetopause. Finally, the simulations predict the accretion of plasma near the bow shock in the regions threaded by newly open field lines on which plasma flows into the dayside ionosphere are enhanced. Overall the results of these initial comparisons between global MHD simulation results and IMAGE observations emphasize the interplay between reconnection and dynamic pressure processes at the dayside magnetopause. as well as the intricate connection between the bow shock and the auroral region.

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Dayside Proton Aurora: Comparisons Between Global MHD Simulations and IMAGE Observations

Berchem

Fuselier

Petrinec

et al. 2003

Magnetospheric Imaging — The Image Prime Mission

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A stochastic sea: The source of plasma sheet boundary layer ion structures observed by Cluster

Ashour‐Abdalla¹,

Bosqued²,

El‐Alaoui³

et al. 2005

J. Geophys. Res.

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the Cluster Ion Spectrometry (CIS) experiment onboard three of the Cluster spacecraft observed velocity-dispersed ion structures (VDIS) as the spacecraft passed from the tail lobes into the plasma sheet boundary layer. These are the first multiple spacecraft observations of the VDIS phenomenon. The Cluster 1 spacecraft (SC1) observed a dispersed ion signature with beamlets and a second structure like that expected to be produced by an echo, while Cluster 3 (SC3) observed much less pronounced structuring a few minutes later. During this same event and over an extended interval the ACE spacecraft observed an interplanetary magnetic field that was directed southward. We have inferred the sources and acceleration mechanisms of the ions in these VDIS observations by following millions of ion trajectories backward and forward in time through time-dependent electric and magnetic fields obtained from a global MHD simulation. ACE data were used as input for the MHD model. We found that almost all of the particles comprising the first (A1) and second (A2) beamlets observed by SC1 had been nonadiabatic earlier in their history, while particles in the A3 beamlet exhibited a combination of adiabatic and nonadiabatic behavior. Beamlet A4 particles were always adiabatic. Moreover, for all of the beamlets the current sheet crossing that took place prior to their detection occurred between x = À13 R E and x = À16 R E in the tail, well earthward of the permanent stochastic ''sea'' from which all of the beamlets originated. Our model does not favor the multiple source scenario suggested by A. Keiling et al. Instead, it indicates that the source regions of the structures are spatially correlated. We have carried out a similar analysis of the SC3 observations. In general, SC3 beamlets have higher k values, partly because of the depolarization of the field lines during these observations. In time forward calculations only a small fraction of ions from SC1 A structures returned to the spacecraft location. ''Echoes'' were more pronounced on SC3. In addition, in our calculations, some particles from SC1 A structures interacted with the current sheet and returned to the SC3 location, at the time when SC3 observed the A structures. When Cluster observations were organized by latitude instead of time, we found that all three Cluster spacecraft seemed to observe the same primary structure that persisted throughout the interval of observation.

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Magnetospheric convection during prolonged intervals with southward interplanetary magnetic field

et al. 2006

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[1] We have used a global magnetohydrodynamic simulation to investigate magnetospheric convection during a prolonged interval with modest southward driving. The interval simulated occurred on 13 and 14 February 2001 during a period when the interplanetary magnetic field (IMF) remained weakly southward for over 12 hours. Early in the simulation a near-Earth neutral line located between 20 R E and 40 R E in the tail drove flows earthward and then around the near-Earth obstacle to return magnetic flux to the dayside. The earthward flow led to increased ionospheric conductance and developed a modest earthward pressure gradient in the inner plasma sheet. Ionospheric line tying slowed the earthward flow. The pressure gradient caused the inner tail to become interchange unstable and lead to the tailward flow. When the tailward moving flux tube reached the near-Earth neutral line additional reconnection occurred between the tailward moving flux tube and IMF field lines created by lobe reconnection thereby returning flux to the nightside tail lobes. Late in the event the new lobe field lines reconnected at the duskside magnetopause creating additional rapid tailward motion. The tailward flow led to a reduction in both the ionospheric conductance and near-Earth tail pressure gradient and earthward flow was again established. This sequence repeated at least three times during the interval simulated.

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Modeling Extreme Compression of the Magnetosphere: Results from a Global MHD Simulation of the May 4, 1998 Event

Cited by 6 publications

References 21 publications

Dayside Proton Aurora: Comparisons Between Global MHD Simulations and IMAGE Observations

Dayside Proton Aurora: Comparisons Between Global MHD Simulations and IMAGE Observations

A stochastic sea: The source of plasma sheet boundary layer ion structures observed by Cluster

Magnetospheric convection during prolonged intervals with southward interplanetary magnetic field

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