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Brain D.,University of California at Berkeley | Barabash S.,Swedish Institute of Space Physics | Boesswetter A.,TU Braunschweig | Bougher S.,University of Michigan | And 25 more authors.
Icarus | Year: 2010

We present initial results from the first community-wide effort to compare global plasma interaction model results for Mars. Seven modeling groups participated in this activity, using MHD, multi-fluid, and hybrid assumptions in their simulations. Moderate solar wind and solar EUV conditions were chosen, and the conditions were implemented in the models and run to steady state. Model output was compared in three ways to determine how pressure was partitioned and conserved in each model, the location and asymmetry of plasma boundaries and pathways for planetary ion escape, and the total escape flux of planetary oxygen ions. The two participating MHD models provided similar results, while the five sets of multi-fluid and hybrid results were different in many ways. All hybrid results, however, showed two main channels for oxygen ion escape (a pickup ion 'plume' in the hemisphere toward which the solar wind convection electric field is directed, and a channel in the opposite hemisphere of the central magnetotail), while the MHD models showed one (a roughly symmetric channel in the central magnetotail). Most models showed a transition from an upstream region dominated by plasma dynamic pressure to a magnetosheath region dominated by thermal pressure to a low altitude region dominated by magnetic pressure. However, calculated escape rates for a single ion species varied by roughly an order of magnitude for similar input conditions, suggesting that the uncertainties in both the current and integrated escape over martian history as determined by models are large. These uncertainties are in addition to those associated with the evolution of the Sun, the martian dynamo, and the early atmosphere, highlighting the challenges we face in constructing Mars' past using models. © 2009 Elsevier Inc. All rights reserved.


Hewett D.W.,Lawrence Livermore National Laboratory | Brecht S.H.,Lawrence Livermore National Laboratory | Brecht S.H.,Bay Area Research Corporation | Larson D.J.,Lawrence Livermore National Laboratory
Journal of Geophysical Research: Space Physics | Year: 2011

The coupling of a super-Alfvénic plasma expansion in a magnetized background plasma is examined. Such coupling plays an important role in several high-energy, quasi-neutral, plasma configurations; the focus here is on High Altitude Nuclear Explosions (HANEs). Fully 3-D Kinetic Ion Simulation Modeling (KISM) reveals, for some initial conditions, strong coupling of the debris to the magnetized background ionosphere even though all collision processes between the ions have been neglected. The interaction dynamics are found to be altered dramatically for small changes in initial conditions. A slight increase in the ion charge density of the background plasma allows the debris ions to decouple and slip through the magnetized background. These decoupled ions in the expanding plasma then follow trajectories typical of single particle motion. The salient features of this process, guided by 1-D simulations, lead to two thresholds for the onset of decoupling. The first threshold depends on the ratio of the charge density of the expanding plasma to that of the background plasma. The second threshold is evident when the expanding plasma has a finite pulse length comparable to the gyroradius of the energized background ions. Copyright 2011 by the American Geophysical Union.


Ledvina S.A.,University of California at Berkeley | Brecht S.H.,Bay Area Research Corporation | Cravens T.E.,University of Kansas
Earth, Planets and Space | Year: 2012

A hybrid particle code has been used to examine how Titan's interaction with Saturn's magnetosphere is effected by the orientation of the dayside ionosphere with respect to the incident magnetospheric flow. The hybrid code self-consistently includes a version of Titan's ionosphere represented by 7 generic ion species, over 40 ion-neutral chemical reactions, ion-neutral collisions and Hall and Pederson conductivities. Emphasis is placed on what effects the orientation angle has on the ion loss rates, ion densities, and the electric and magnetic fields. The results are analyzed and regardless of the orientation angle the ionosphere is found to be within photochemical equilibrium below 1200 km altitude. The ion loss rates and field structures also show little dependence on the orientation of the dayside ionosphere. It is found to first order illumination angle does not have a significant effect on these features of the Titan interaction. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS).


Brecht S.H.,Bay Area Research Corporation | Ledvina S.A.,University of California at Berkeley
Earth, Planets and Space | Year: 2012

A hybrid particle code has been used to examine the interaction of the solar wind with Mars during solar minimum. The results were surprising as they produced ion loss rates from Mars far in excess of what is estimated from MEX. The results are analyzed and found to be consistent with the competition between photochemical rates and advection of the ionosphere. The simulations showed significant erosion of the ionosphere at altitudes between 200 km and 250 km altitudes. Addition of the crustal magnetic fields reduced the erosion and reduced the ion loss rates to a level consistent with the data. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS).


Ledvina S.A.,University of California at Berkeley | Brecht S.H.,Bay Area Research Corporation
Geophysical Research Letters | Year: 2012

Ahybrid particle code has been used to examine how Titan's interaction with Saturn's magnetosphere is affected by the presence of negative ions in Titan's ionosphere. The simulations self-consistently include a version of Titan's ionosphere represented by 8 generic positive ion species, over 40 ion-neutral chemical reactions, ion-neutral collisions and Hall and Pederson conductivities. A model consisting of 6 generic negative ion species is also included. The presence of negative ions is found to alter the conductivity of Titan's ionosphere, changing the loss rates of the ionospheric species and modifying the topology of Titan's ion tail. © 2012. American Geophysical Union. All Rights Reserved.


Brecht S.H.,Bay Area Research Corporation | Ledvina S.A.,University of California at Berkeley
Icarus | Year: 2010

The simulation of Mars is a very challenging effort. However, simulations are a major method of addressing the issues of the solar wind interaction with Mars. Further, it is via simulations that issues such as water loss from Mars via solar wind pick up of ionospheric ions will be addressed. This paper discusses some of the issues raised during the Chapman Conference on Solar Wind Interactions with Mars, SWIM. It also addresses numerical issues and the authors attempts to address them, coupled with results of preliminary simulations of Mars. © 2009 Elsevier Inc.

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