Stephen H. Brecht
University of California, Berkeley
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Space Science Reviews | 2004
Andrew F. Nagy; D. Winterhalter; K. Sauer; T. E. Cravens; Stephen H. Brecht; C. Mazelle; Dana Hurley Crider; E. Kallio; A Zakharov; E. Dubinin; M. I. Verigin; Galina A. Kotova; W. I. Axford; C. Bertucci; J. G. Trotignon
When the supersonic solar wind reaches the neighborhood of a planetary obstacle it decelerates. The nature of this interaction can be very different, depending upon whether this obstacle has a large-scale planetary magnetic field and/or a well-developed atmosphere/ionosphere. For a number of years significant uncertainties have existed concerning the nature of the solar wind interaction at Mars, because of the lack of relevant plasma and field observations. However, measurements by the Phobos-2 and Mars Global Surveyor (MGS) spacecraft, with different instrument complements and orbital parameters, led to a significant improvement of our knowledge about the regions and boundaries surrounding Mars.
Journal of Geophysical Research | 1991
Stephen H. Brecht; John R. Ferrante
Results from three-dimensional hybrid particle simulations of the solar wind interaction with the planets Mars and Venus are presented. The simulations produce shocks and magnetic barriers which are asymmetric. These results are qualitatively in agreement with data. In the absence of an ionosphere the subsolar shock standoff distance was found to agree with the observations if the Hall current is limited. It was also found that the solar wind interaction with Mars and Venus was substantially different. The interaction with Venus can be generally viewed as a magnetized interaction. The Mars interaction is very kinetic in nature and appears not to have a shock in the classic sense.
Journal of Geophysical Research | 2000
Stephen H. Brecht; J. G. Luhmann; David J. Larson
Flowing plasma interactions with small bodies in the solar system are frequently complicated by the significant size of the ion gyroradii relative to the scale size of the body and the interaction region. This situation often applies to both the flowing ion populations and the atmospheric pickup ions added to the flow in the vicinity of the body. Titan represents an important example of this type of system and is scheduled to be probed in some detail during the Cassini mission tour of Saturn. Initial results from global hybrid (particle ions, fluid electrons) numerical simulations of Saturns magnetospheric plasma encountering Titans ionosphere reveal the complexity of the interaction introduced by the ion kinetics. The scale of the interaction region is dominated by the heavy ion gyroradii of the ambient and pickup ions rather than the size of Titan and is found to depend on the mass loading of the magnetospheric flow encountering Titan. Comparison with data from the Voyager 1 flyby suggests that ion kinetics as well as the relative orientations of external plasma ram and pickup ion production regions affect what was observed.
Journal of Geophysical Research | 1997
Stephen H. Brecht
The structure of the magnetic field surrounding the planet Mars has been investigated using a fully three-dimensional hybrid particle code. The results of these simulations are found to agree well with Phobos 2 data. However, the results also indicate that the solar wind interaction with the planet Mars produces a magnetic environment around the planet that is unique among the planets of the solar system. This paper reports the findings from a series of large-scale, three-dimensional simulations and many two-dimensional simulations used to address numerical issues.
Journal of Geophysical Research | 1993
Stephen H. Brecht; John R. Ferrante; J. G. Luhmann
Three-dimensional hybrid particle simulations of the dayside portion of the Mars/solar wind interaction have been performed. These simulations are compared with the in situ measurements taken during the elliptical orbits of Phobos 2. The comparisons show considerable agreement between the magnetic field data and the simulations results. The results of the simulations bring into question the type of structures created in the subsolar region of Mars. It appears that the large larmor radius of the solar wind ions prevents the formation of a traditional collisionless shock in the subsolar region of the interaction.
Journal of Geophysical Research | 1997
Imke de Pater; Michael Schulz; Stephen H. Brecht
High-resolution radio images of Jupiter at wavelength λ = 20 cm obtained with the Very Large Array (VLA) in June 1994 (a few weeks before comet Shoemaker-Levy 9 collided with the planet) are compared with detailed model calculations. All major features of the radio emission can be explained or simulated through model calculations. In particular, we infer how the pitch angle distribution of high-energy electrons varies with L value. The electron pitch angle distribution seems to undergo a dramatic change at Amaltheas orbit: A fraction of the electron population is redistributed in pitch angle (isotropized) there, so that fewer electrons mirror near the magnetic equator and more electrons mirror off the equator at L ≤ 2.65 than beyond. The isotropic component leads to the high-latitude emission regions, while the decreased number of equatorially mirroring electrons results in a shoulder or flattening in the radio intensity pattern at L∼2.5, as is observed. Perhaps Amaltheas motion through Jupiters magnetic field induces Alfven or whistler wings or electrostatic high-frequency waves which lead to the observed pitch angle scattering. Jupiters ring absorbs 80%-100% of electrons with small pitch angles that diffuse through the region it occupies. The observed effect of this absorption is that the high-latitude emission peaks remain distinct from the equatorial maximum. Ring absorption causes nearly all electrons at L ≤ 2 to be narrowly confined to the magnetic equator, a distribution which accounts for the east-west asymmetry, which is very prominent at certain central meridian longitudes. The azimuthal variation (east-west asymmetry) over a Jovian rotation is completely determined by the magnetic field configuration, as was suspected by many researchers in the past but never modeled succesfully before. We infer, however, that Connerneys O 6 magnetic field model from 1992-1993 is slightly oversimplified, since the radiation characteristics cannot be completely matched at all Jovian longitudes: Deviations appear in particular at longitudes λ cml ∼ 140°-180° and λ cml ∼ 300°-340° (corresponding to λ III ∼ 30°-90° and λ III ∼ 210°-270° in Jovicentric coordinates).
Journal of Geophysical Research | 1997
Stephen H. Brecht
The direct impact of solar wind H+ with the planet Mars is calculated using a three-dimensional hybrid particle code. The simulation results show a strong dependence on solar wind velocity and interplanetary magnetic field angle with the solar wind velocity vector. The energy fluxes calculated approach the solar EUV heating rates from photoelectrons and are found to be asymmetric. The heating is also found on the nightside of the planet due to the large ion gyroradii of the incoming solar wind protons. The percentage of solar wind protons lost to the surface of simulation ranged from 3% to 28% depending on the ram presssure of the solar wind. Finally, these results support earlier suggestions that the solar wind may be a significant source of He in the atmosphere of Mars.
Computer Physics Communications | 1988
Stephen H. Brecht; V. A. Thomas
Abstract In this paper the advantages and disadvantages of using a hybrid particle code approach to simulate highly nonlinear plasma phenomena on scale lengths beyond the Debye length are discussed. The formalism for building hybrid codes is discussed. It is shown that many features not attainable with traditional MHD formalisms can be simulated on scale sizes that can approach planetary scales. Results of 2 1 2 and 3-D simulations will be discussed to demonstrate the strengths and weakness of this approach.
Physics of Fluids | 1986
V. A. Thomas; Stephen H. Brecht
In this paper a hybrid particle–fluid simulation code is used to examine the large‐scale (λ∼c/ωpi) low‐frequency (ω∼ωci) formation and evolution of a collisonless shock in two dimensions where the shock is caused by a plasma slug of finite thickness traveling perpendicular to the ambient magnetic field in the presence of a uniform background plasma. During the evolution of the shock structure, background ions are energized in the perpendicular direction and then isotropized. The isotropization process is associated with the presence of large‐amplitude, primarily electromagnetic, waves propagating parallel to the ambient magnetic field that are created by the self‐consistent plasma interaction. High Mach number shocks are found to be inherently two‐dimensional objects.
Geophysical Research Letters | 2014
Stephen H. Brecht; Stephen A. Ledvina
A hybrid particle code has been used to examine the interaction of the solar wind with Mars. It is found that the presence of the crustal magnetic fields modifies the heavy ion (O+ and O2+) loss rates. In the case of the solar minimum situation the modification was found to be significant and reported in Brecht and Ledvina (2012). In this paper both solar minimum and solar maximum results are reported and compared with data. The crustal magnetic fields reduce the ionospheric loss rate; and when the energy limits imposed on the data fits are considered, the results of the simulations are in reasonable agreement with data. The agreement with the data provides a strong argument for the physical control demonstrated by the simulations being realistic.