14 results on '"Farrugia, Charles J."'
Search Results
2. Coherence Lengths of the Interplanetary Electric Field: Solar Cycle Maximum Conditions.
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Farrugia, Charles J., Matsui, Hiroshi, and Torbert, Roy B.
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INTERPLANETARY magnetic fields , *MAGNETOSPHERE , *MAGNETIC separation - Abstract
It is increasingly being realized that by affecting geoeffective scale lengths the interplanetary electric field (IEF) is a key quantity in space weather discussions. In this work we derive and analyze statistically IEF coherence lengths in year 2000, i.e., near maximum of solar cycle 23, working in a much used formulation for the IEF. We focus on the frequency domain. We use magnetic field and plasma data sets acquired by Wind and ACE. During year 2000, ACE-Wind separations were very variable and, in particular, Wind’s first dayside distant prograde orbit resulted in a Y-separation comparable to the X-separation (∼220 RE). We find IEF coherence lengths of 200–250 RE (X) and 50–100 RE (Y). The coherence is mainly carried by the low frequency components (f < 0.01 min-1). © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2003
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3. Energy Conversion Within Current Sheets in the Earth's Quasi‐Parallel Magnetosheath.
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Schwartz, Steven J., Kucharek, Harald, Farrugia, Charles J., Trattner, Karlheinz, Gingell, Imogen, Ergun, Robert E., Strangeway, Robert, and Gershman, Daniel
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ENERGY conversion , *CURRENT sheets , *EARTH currents , *INTERPLANETARY magnetic fields , *SOLAR wind , *ENERGY dissipation , *COLLISIONLESS plasmas - Abstract
Shock waves in collisionless plasmas rely on kinetic processes to convert the primary incident bulk flow energy into thermal energy. That conversion is initiated within a thin transition layer but may continue well into the downstream region. At the Earth's bow shock, the region downstream of shock locations where the interplanetary magnetic field is nearly parallel to the shock normal is highly turbulent. We study the distribution of thin current events in this magnetosheath. Quantification of the energy dissipation rate made by the Magnetospheric Multiscale spacecraft shows that these isolated intense currents are distributed uniformly throughout the magnetosheath and convert a significant fraction (5%–11%) of the energy flux incident at the bow shock. Plain Language Summary: Shock waves form when a supersonic flow encounters an immovable object. Thus, ahead of the magnetic bubble formed by the Earth's extended magnetic field, the flow of charged particles emanating from the Sun known as the solar wind is shocked, slowed, and deflected around the Earth. In dense fluids, the conversion of the incident bulk flow energy into heat is accomplished by collisions between particles or molecules. However, the solar wind is so rarefied that such collisions are negligible, and the energy conversion involves more than one kinetic process that couples the different particles to the electromagnetic fields. Under some orientations of the interplanetary magnetic field carried by the wind, the shocked medium is highly turbulent. Within that turbulence are isolated thin regions carrying large electric currents. We have studied those currents, and found that they are converting energy from one form to another at a rate that is a significant fraction of the incident energy flux. Thus, these currents contribute significantly to the overall shock energetics. Key Points: Intense current events are distributed uniformly downstream of a quasi‐parallel bow shockThe events are associated primarily with a conversion of field energy into particle energyThe energy processed by these events is a non‐negligible fraction of the energy incident at the bow shock [ABSTRACT FROM AUTHOR]
- Published
- 2021
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4. Properties of the Sheath Regions of Coronal Mass Ejections with or without Shocks from STEREO in situ Observations near 1 au.
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Salman, Tarik M., Lugaz, Noé, Farrugia, Charles J., Winslow, Reka M., Jian, Lan K., and Galvin, Antoinette B.
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CORONAL mass ejections , *SOLAR-terrestrial physics , *SOLAR wind , *MACH number , *INSPECTION & review , *ALGORITHMS - Abstract
We examine 188 coronal mass ejections (CMEs) measured by the twin Solar Terrestrial Relations Observatory spacecraft during 2007–2016 to investigate the generic features of the CME sheath and the magnetic ejecta (ME) and dependencies of average physical parameters of the sheath on the ME. We classify the CMEs into three categories, focusing on whether the ME drives both a shock and sheath, or only a sheath, or neither, near 1 au. We also re-evaluate our initial classification through an automated algorithm and visual inspection. We observe that even for leading-edge speeds greater than 500 km s−1, 1 out of 4 MEs do not drive shocks near 1 au. MEs driving both shocks and sheaths are the fastest and propagate in high magnetosonic solar wind, whereas MEs driving only sheaths are the slowest and propagate in low magnetosonic solar wind. Our statistical and superposed epoch analyses indicate that all parameters are more enhanced in the sheath regions following shocks than in sheaths without shocks. However, differences within sheaths become statistically less significant for similar driving MEs. We also find that the radial thickness of ME-driven sheaths apparently has no clear linear correlation with the speed profile and associated Mach numbers of the driver. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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5. Evolution of the Radial Size and Expansion of Coronal Mass Ejections Investigated by Combining Remote and In Situ Observations.
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Zhuang, Bin, Lugaz, Noé, Al-Haddad, Nada, Winslow, Réka M., Scolini, Camilla, Farrugia, Charles J., and Galvin, Antoinette B.
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CORONAL mass ejections , *SPACE environment , *MAGNETIC flux density , *CYLINDRICAL shells , *WEATHER forecasting , *HELIOSPHERE - Abstract
A fundamental property of coronal mass ejections (CMEs) is their radial expansion, which determines the increase in the CME radial size and the decrease in the CME magnetic field strength as the CME propagates. CME radial expansion can be investigated either by using remote observations or by in situ measurements based on multiple spacecraft in radial conjunction. However, there have been only few case studies combining both remote and in situ observations. It is therefore unknown if the radial expansion in the corona estimated remotely is consistent with that estimated locally in the heliosphere. To address this question, we first select 22 CME events between the years 2010 and 2013, which were well observed by coronagraphs and by two or three spacecraft in radial conjunction. We use the graduated cylindrical shell model to estimate the radial size, radial expansion speed, and a measure of the dimensionless expansion parameter of CMEs in the corona. The same parameters and two additional measures of the radial-size increase and magnetic-field-strength decrease with heliocentric distance of CMEs based on in situ measurements are also calculated. For most of the events, the CME radial size estimated by remote observations is inconsistent with the in situ estimates. We further statistically analyze the correlations of these expansion parameters estimated using remote and in situ observations, and discuss the potential reasons for the inconsistencies and their implications for the CME space weather forecasting. [ABSTRACT FROM AUTHOR]
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- 2023
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6. Investigating the Cross Sections of Coronal Mass Ejections through the Study of Nonradial Flows with STEREO/PLASTIC.
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Al-Haddad, Nada, Galvin, Antoinette B., Lugaz, Noé, Farrugia, Charles J., and Yu, Wenyuan
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CORONAL mass ejections , *SOLAR wind , *SOLAR oscillations , *SOLAR cycle , *PLASTICS - Abstract
The solar wind, when measured close to 1 au, is found to flow mostly radially outward. There are, however, periods when the flow makes angles up to 15° away from the radial direction, both in the eastâ€"west and northâ€"south directions. Stream interaction regions (SIRs) are a common cause of eastâ€"west flow deflections. Coronal mass ejections (CMEs) may be associated with nonradial flows in at least two different ways: (1) the deflection of the solar wind in the sheath region, especially close to the magnetic ejecta front boundary, may result in large nonradial flows; and (2) the expansion of the magnetic ejecta may include a nonradial component, which should be easily measured when the ejecta is crossed away from its central axis. In this work, we first present general statistics of nonradial solar wind flows as measured by STEREO/PLASTIC throughout the first 13 yr of the mission, focusing on solar cycle variation. We then focus on the larger deflection flow angles and determine that most of these are associated with SIRs near solar minimum and with CMEs near solar maximum. However, we find no clear evidence of strongly deflected flows, as would be expected if large deflections around the magnetic ejecta or ejecta with elliptical cross sections with large eccentricities were common. We use these results to develop a better understanding of CME expansion and the nature of magnetic ejecta, and point to shortcomings in our understanding of CMEs. [ABSTRACT FROM AUTHOR]
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- 2022
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7. The stability of the pristine magnetopause
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Gratton, Fausto T., Gnavi, Graciela, Farrugia, Charles J., and Bender, Laurence
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MAGNETIC fields , *MAGNETOPAUSE , *MAGNETOSPHERE - Abstract
A MHD theory of combined Kelvin–Helmholtz (KH) and Rayleigh–Taylor (RT) instabilities for a transition layer with two different scale lengths (
Δ andδ for the variation of velocity/magnetic fields and density, respectively) is presented. The study is motivated by reports of magnetopauses with no low latitude boundary layer, in which a sharp density drop over a distanceδ≪Δ is observed (“pristine” magnetopauses (J. Geophys. Res. 101 (1996) 49). The theory ignores compressibility effects and applies to subsonic regions of the dayside magnetopause. The RT effect is included to account for temporary periods of acceleration of the magnetopause, caused by sudden changes of the solar wind dynamic pressure. For small wavelengthsλ , such thatδ≪λ≪Δ , a WKB solution shows that the velocity gradient operates, together with magnetic tensions, to attenuate or even stabilize the Rayleigh–Taylor instability within a certain wavelength range. An exact dispersion relation for flute modes, valid for allλ , in the form of a fourth order polynomial for the complex frequencyω , is obtained from a model with a constant velocity gradient,dV/dy withinΔ , and withδ→0 . Flute modes are possible because of the existence of bands of very small magnetic shear on the dayside magnetopause (J. Geophys. Res. 103 (1998) 6703). The exact solution allows for a study of the change of the action of the velocity gradient withλ from the long-λ range wheredV/dy is KH destabilizing to the short-λ range wheredV/dy produces a stabilizing effect. Both, the WKB approximation and the well known tangential discontinuity model(Δ→0) are recovered as limiting cases of the exact solution. Properties of the KH and RT instabilities, for different density ratios on either side of the magnetopause, are described. For flute modes, at very smallλ the RT instability grows faster and becomes the dominant effect. However, it is shown that the growth rate remains bounded at a finite value asλ→0 , when a theory with a finiteδ model is considered. To study configurations with finite, arbitrary,δ/Δ ratios, the MHD perturbation equations are solved numerically, using hyperbolic tangent functions for both the density and velocity transitions across the magnetopause. To examine the influence of differentδ/Δ ratios on the growth rates of KH and RT, calculations are performed for differentδ/Δ , with and without acceleration, and for two different density ratios. It is found that the general features exhibited by the constantdV/dy model, are confirmed by these numerical solutions. The stability of pristine magnetopauses, and the possibility of observing some theoretical predictions during magnetopause crossings in ongoing missions, are discussed. [Copyright &y& Elsevier]- Published
- 2003
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8. Inconsistencies Between Local and Global Measures of CME Radial Expansion as Revealed by Spacecraft Conjunctions.
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Lugaz, Noé, Salman, Tarik M., Winslow, Réka M., Al-Haddad, Nada, Farrugia, Charles J., Zhuang, Bin, and Galvin, Antoinette B.
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PLASMA sheaths , *CORONAL mass ejections , *DYNAMIC pressure , *SPACE vehicles - Abstract
The radial expansion of coronal mass ejections (CMEs) is known to occur from remote observations, from the variation of their properties with radial distance, and from local in situ plasma measurements showing a decreasing speed profile throughout the magnetic ejecta (ME). However, little is known on how local measurements compare to global measurements of expansion. Here, we present results from the analysis of 42 CMEs measured in the inner heliosphere by two spacecraft in radial conjunction. The magnetic-field decrease with distance provides a measure of their global expansion. Near 1 au, the decrease in their bulk speed provides a measure of their local expansion. We find that these two measures have little relation with each other. We also investigate the relation between characteristics of CME expansion and CME properties. We find that the expansion depends on the initial magnetic-field strength inside the ME, but not significantly on the magnetic field inside the ME measured near 1 au. This is indirect evidence that CME expansion in the innermost heliosphere is driven by the high magnetic pressure inside the ME, while by the time the MEs reach 1 au, they are expanding due to the decrease in the solar-wind dynamic pressure with distance. We also determine the evolution of the ME tangential and normal magnetic-field components with distance, revealing significant deviations as compared to the expectations from force-free field configurations as well as some evidence that the front half of MEs expand at a faster rate than the back half. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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9. CME–HSS Interaction and Characteristics Tracked from Sun to Earth.
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Heinemann, Stephan G., Temmer, Manuela, Farrugia, Charles J., Dissauer, Karin, Kay, Christina, Wiegelmann, Thomas, Dumbović, Mateja, Veronig, Astrid M., Podladchikova, Tatiana, Hofmeister, Stefan J., Lugaz, Noé, and Carcaboso, Fernando
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CORONAL mass ejections , *SOLAR corona , *SOLAR wind , *PROGRAMMED cell death 1 receptors , *HELIOSEISMOLOGY , *MAGNETIC fields , *CYLINDRICAL shells - Abstract
In a thorough study, we investigate the origin of a remarkable plasma and magnetic field configuration observed in situ on June 22, 2011, near L1, which appears to be a magnetic ejecta (ME) and a shock signature engulfed by a solar wind high-speed stream (HSS). We identify the signatures as an Earth-directed coronal mass ejection (CME), associated with a C7.7 flare on June 21, 2011, and its interaction with a HSS, which emanates from a coronal hole (CH) close to the launch site of the CME. The results indicate that the major interaction between the CME and the HSS starts at a height of 1.3 R ⊙ up to 3 R ⊙ . Over that distance range, the CME undergoes a strong north-eastward deflection of at least 30 ∘ due to the open magnetic field configuration of the CH. We perform a comprehensive analysis for the CME–HSS event using multi-viewpoint data (from the Solar TErrestrial RElations Observatories, the Solar and Heliospheric Observatory and the Solar Dynamics Observatory), and combined modeling efforts (nonlinear force-free field modeling, Graduated Cylindrical Shell CME modeling, and the Forecasting a CME's Altered Trajectory – ForeCAT model). We aim at better understanding its early evolution and interaction process as well as its interplanetary propagation and related in situ signatures, and finally the resulting impact on the Earth's magnetosphere. [ABSTRACT FROM AUTHOR]
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- 2019
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10. A Survey of Interplanetary Small Flux Ropes at Mercury.
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Murphy, Amy K., Winslow, Reka M., Schwadron, Nathan A., Lugaz, Noé, Yu, Wenyuan, Farrugia, Charles J., and Niehof, Jonathan T.
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MAGNETIC flux density , *SOLAR wind , *MERCURY , *FLUX (Energy) , *WIND measurement , *MAGNETIC flux - Abstract
Interplanetary magnetic flux ropes with durations from a few minutes to a few hours have been termed small flux ropes (SFRs). We have built a comprehensive catalog of SFRs at Mercury using magnetometer data from the orbital phase of the MESSENGER mission (2011–2015). In the absence of solar wind plasma measurements, we developed strict identification criteria for SFRs in the magnetometer observations, including force-free field fits for each flux rope. We identified a total of 48 events that met our strict criteria, with events ranging in duration from 2.5 minutes to 4 hr. Using superposed epoch analysis, we obtained the generic SFR magnetic field profile at Mercury. Due to its eccentric orbit, Mercury's heliospheric distance varies between 0.31 and 0.47 au, a range of ∼0.16 au. This distance is potentially large enough for the SFRs to undergo measurable changes due to distance. Thus, we split the data into two distance bins to look for such changes. We found that the average SFR profile is more symmetric farther from the Sun, in line with the idea that SFRs form closer to the Sun and undergo a relaxation process in the solar wind. Based on this result, as well as the SFR durations and the magnetic field strength fall-off with heliocentric distance, we infer that the SFRs observed at Mercury are expanding as they propagate with the solar wind. We also determined that the SFR occurrence frequency is nearly four times as high at Mercury as for similarly detected events at 1 au. Most interestingly, we found two SFR populations in our data set, one likely generated in a quasi-periodic formation process near the heliospheric current sheet, and the other formed away from the current sheet in isolated events. [ABSTRACT FROM AUTHOR]
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- 2020
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11. Unusually low density regions in the compressed slow wind: Solar wind transients of small coronal hole origin.
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Liu, Yong C.-M., Zhaohui Qi, Jia Huang, Chi Wang, Hui Fu, Klecker, Berndt, Linghua Wang, and Farrugia, Charles J.
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SOLAR wind , *STELLAR winds , *MAGNETIC fields , *MAGNETIC reconnection , *SOLAR oscillations , *SOLAR surface , *DENSITY - Abstract
We report on two small solar wind transients embedded in the corotating interaction region, characterized by surprisingly lower proton density compared with their surrounding regions. In addition to lower density, these two small solar wind transients showed other interesting features like higher proton temperature, higher alpha-proton ratios, and lower charge states (C+6/C+5 and O+7/O+6). A synthesized picture for event One combining the observations by STEREO B, ACE, andWind showed that this small solar transient has an independent magnetic field. Back-mapping links the origin of the small solar transient to a small coronal hole on the surface of the Sun. Considering these special features and the back-mapping, we conclude that such small solar wind transients may have originated from a small coronal hole at low latitudes. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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12. The Interaction of Successive Coronal Mass Ejections: A Review.
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Lugaz, Noé, Temmer, Manuela, Yuming Wang, and Farrugia, Charles J.
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CORONAL mass ejections , *SOLAR energetic particles , *MAGNETIC reconnection , *SOLAR-terrestrial physics , *MAGNETIC storms , *PARTICLE acceleration , *MASS spectrometry - Abstract
We present a review of the different aspects associated with the interaction of successive coronal mass ejections (CMEs) in the corona and inner heliosphere, focusing on the initiation of series of CMEs, their interaction in the heliosphere, the particle acceleration associated with successive CMEs, and the effect of compound events on Earth’s magnetosphere. The two main mechanisms resulting in the eruption of series of CMEs are sympathetic eruptions, when one eruption triggers another, and homologous eruptions, when a series of similar eruptions originates from one active region. CME – CME interaction may also be associated with two unrelated eruptions. The interaction of successive CMEs has been observed remotely in coronagraphs (with the Large Angle and Spectrometric Coronagraph Experiment – LASCO – since the early 2000s) and heliospheric imagers (since the late 2000s), and inferred from in situ measurements, starting with early measurements in the 1970s. The interaction of two or more CMEs is associated with complex phenomena, including magnetic reconnection, momentum exchange, the propagation of a fast magnetosonic shock through a magnetic ejecta, and changes in the CME expansion. The presence of a preceding CME a few hours before a fast eruption has been found to be connected with higher fluxes of solar energetic particles (SEPs), while CME – CME interaction occurring in the corona is often associated with unusual radio bursts, indicating electron acceleration. Higher suprathermal population, enhanced turbulence and wave activity, stronger shocks, and shock – shock or shock – CME interaction have been proposed as potential physical mechanisms to explain the observed associated SEP events. When measured in situ, CME – CME interaction may be associated with relatively well organized multiple-magnetic cloud events, instances of shocks propagating through a previous magnetic ejecta or more complex ejecta, when the characteristics of the individual eruptions cannot be easily distinguished. CME – CME interaction is associated with some of the most intense recorded geomagnetic storms. The compression of a CME by another and the propagation of a shock inside a magnetic ejecta can lead to extreme values of the southward magnetic field component, sometimes associated with high values of the dynamic pressure. This can result in intense geomagnetic storms, but can also trigger substorms and large earthward motions of the magnetopause, potentially associated with changes in the outer radiation belts. Future in situ measurements in the inner heliosphere by Solar Probe+ and Solar Orbiter may shed light on the evolution of CMEs as they interact, by providing opportunities for conjunction and evolutionary studies. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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13. Kinetic temperatures of iron ions in the solar wind observed with STEREO/PLASTIC.
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Bochsler, Peter, Lee, Martin A., Karrer, Reto, Popecki, Mark A., Galvin, Antoinette B., Kistler, Lynn M., Möbius, Eberhard, Farrugia, Charles J., Kucharek, Harald, Simunac, Kristin D. C., Blush, Lisa M., Daoudi, Hagar, Wurz, Peter, Klecker, Berndt, Wimmer-Schweingruber, Robert F., Thompson, Barbara, Luhmann, Janet G., Jian, Lan K., Russell, Christopher T., and Opitz, Andrea
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SOLAR wind , *SOLAR activity , *STELLAR winds , *SOLAR corona , *IONS - Abstract
STEREO/PLASTIC provides detailed information on the three-dimensional velocity distributions of solar wind iron ions with a time resolution of 5 minutes. In general the distributions at 1 AU contain complicated structures showing persistence over several records, i.e., over intervals of up to 30 minutes, but no clear correlation of the properties of these distributions with the direction of the ambient magnetic field is evident. We have performed a statistical analysis using nearly 9000 observations. Iron ions follow the same trends as protons, alpha particles, and electrons: The ratio T⊥/T| seems to be limited by the ion cyclotron instability, whereas T|/T⊥ is bounded by the firehose instability. [ABSTRACT FROM AUTHOR]
- Published
- 2010
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14. Ideal magnetohydrodynamic flow around a blunt body under anisotropic pressure.
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Erkaev, Nikolai V., Biernat, Helfried K., and Farrugia, Charles J.
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MAGNETOHYDRODYNAMICS , *PLASMA conductivity - Abstract
The plasma flow past a blunt obstacle in an ideal magnetohydrodynamic (MHD) model is studied, taking into account the tensorial nature of the plasma pressure. Three different closure relations are explored and compared with one another. The first one is the adiabatic model proposed by Chew, Goldberger, and Low. The second closure is based on the mirror instability criterion, while the third depends on an empirical closure equation obtained from observations of solar wind flow past the Earth's magnetosphere. The latter is related with the criterion of the anisotropic ion cyclotron instability. In the presented model, the total pressure, defined as the sum of magnetic pressure and perpendicular plasma pressure, is assumed to be a known function of Cartesian coordinates. The calculation is based on the Newtonian approximation for the total pressure along the obstacle and on a quadratic behavior with distance from the obstacle along the normal direction. Profiles of magnetic field strength and plasma parameters are presented along the stagnation stream line between the shock and obstacle of an ideal plasma flow with anisotropy in thermal pressure and temperature. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]
- Published
- 2000
- Full Text
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