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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
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NASA NTRS1992

Bow shocks and magnetotails of Venus and Mars - A comparison

Observations of the bow shock location and the structure of the magnetotail of Mars by the Phobos spacecraft and of Venus by the Pioneer Venus Orbiter reveal the solar wind interactions with these two planets to be quite similar. The subsolar bow shocks of both Venus and Mars lie at 1.47 planetary radii while at the terminator they are at 2.40 and 2.65 planetary radii, respectively. Both bow shocks have oval cross sections when viewed from the sun whose major axes are controlled by the orientation of the interplanetary magnetic field. The tail lobes of both planets are similarly controlled by the IMF orientation. The strength of the solar/antisolar component of the magnetic field is 17 nT at Venus and 14 nT at Mars. The component perpendicular to the tail axis is about 1/2 the corresponding IMF component at Venus and 2 times this component at Mars. However, when these measurements are compared in terms of the distance down the tail at which each were taken, the data from the two planets are quite consistent. Hence both Venus and Mars have principally induced magnetospheres and magnetotails which stand off the solar wind flow.

Russell, C. T.↗
NASA NTRS1993

Shaping of the magnetotail from the mantle - Global and local structuring

Kinetic modeling of the properties of magnetotail formation from a plasma mantle source are discussed, and a unified view of the structure of the central part of the magnetotail plasma sheet as well as the structure of its boundary layer is developed. The Tsyganenko magnetic field model for quiet periods of magnetospheric activity is used to trace trajectories of mantle protons in the presence of a uniform dawn-dusk electric field. The present model shows the evolution of the global structure of the tail with a clearly defined central plasma sheet and plasma sheet boundary layer developing from its beginnings as a plasma 'nucleus' in the distant tail current sheet. This large-scale restructuring is accompanied by the creation of small-scale features in the particle distribution functions. It is also shown that complementary ring distribution structures should also exist in the central plasma sheet. The ion distribution functions in the central plasma sheet should take a rather specific form in velocity space with loss regions oriented predominantly orthogonal to the magnetic field.

Ashour-Abdalla, Maha↗
NASA NTRS1992

Geotail mission to explore earth's magnetotail

The Geotail satellite mission is a cooperative venture of NASA and ISAS of Japan for exploration of the magnetotail region of the earth's magnetosphere. Geotail will deepen understanding into fundamental processes, such as those of energy transfer from the solar wind to the magnetosphere, magnetotail particle acceleration, tail energy release onset, the transport of particles between the tail and the inner magnetosphere, the bow shock, and wave-particle interactions. Attention is given to both Geotail spacecraft and mission design.

Nishida, A.↗
NASA NTRS1993

Simultaneous observation of the poleward expansion of substorm electrojet activity and the tailward expansion of current sheet disruption in the near-earth magnetotail

A substorm that occurred on 7 June 1985 at 2209 UT for which simultaneous measurements from ground stations and CCE are available is considered. The event occurred during a close conjunction between CCE, the EISCAT magnetometer cross, and the STARE radar, allowing a detailed comparison of satellite and ground-based data. Two discrete activations took place during the first few minutes of this substorm: the expansion phase onset at 2209 UT and an intensification at 2212 UT, corresponding to a poleward expansion of activity. The energetic particle data indicate that the active region of the magnetotail during the 2212 UT intensification was located tailward of the active region at 2209 UT. This is direct evidence for a correspondence between tailward expansion of localized activity in the near-earth magnetotail (current disruption and particle energization) and poleward expansion of activity (electrojet formation) in the ionosphere.

Lopez, R. E.↗
NASA NTRS1993

Physics of the magnetotail current sheet

The Earth's magnetotail plays an important role in the solar-wind-magnetosphere coupling. At the midplane of the magnetotail is a current sheet where the dominant magnetic field component reverses sign. The charged particle motion in and near the current sheet is collisionless and nonintegrable, exhibiting chaotic scattering. The current understanding of the dynamical properties of the charged particle motion is discussed. In particular, the relationships between particle dynamics and global attributes of the system are elucidated. Geometrical properties of the phase space determine important physical observables on both micro- and macroscales.

Chen, James↗
NASA NTRS1993

ISEE 3 observations of traveling compression regions in the earth's magnetotail

A comprehensive study is conducted of traveling compression regions (TCRs) in the distant magnetotail; a total of 116 TCRs were studied from ISEE 3 observations. Strong support is obtained for the interpretation of TCRs as large-scale compressions of the lobes that are caused by the rapid downtail motion of plasmoids. TCRs furnish information on the 3D shape and volume of the plasmoid bulge. The close association noted between the substorm expansion phase onset and the TCRs provides strong support for the plasmoid model of magnetotail dynamics.

Slavin, J. A.↗
NASA NTRS1993

On the cause of thin current sheets in the near-Earth magnetotail and their possible significance for magnetospheric substorms

The formation of thin current sheets in the near-Earth magnetotail during substorm growth phases is addressed in terms of a simple model. An appropriate part of the unperturbed magnetotail is represented by a plane sheet model. Perturbations are applied to the upper and to the left boundaries, representing the magnetopause and the near-Earth tail boundary, where the perturbation at the latter models the interaction between the tail and the inner magnetosphere. Treating the perturbation as ideal (dissipation-free), we found that singular current sheets develop in the midplane of the tail. The analytical results are explored numerically. Using realistic dimensions of the domain considered, the influence of the earthward boundary on current sheet formation dominates. It is argued that current sheet formation of this type plays an important role in the processes associated with the onset of magnetospheric substorms.

Schindler, K.↗
NASA NTRS1993

Contributions of the low-latitude boundary layer to the finite width magnetotail convection model

The finite tail width model of magnetotail plasma sheet convection has been extended in order to characterize the steady-state convection process. The model assumes uniform plasma sources and accounts for both the duskward gradient/curvature drift and the earthward E x B drift of ions in a 2D magnetic geometry. A secondary source of plasma originating in the dawnside low-latitude boundary layer (LLBL) is added. Model results show that the LLBL may be a significant source of near-tail central plasma sheet plasma during periods of weak convection; a cross-tail pressure gradient from dawn to dusk is predicted in the near magnetotail.

Spence, Harlan E.↗
NASA NTRS1993

Galileo observations of the motions of ion and electron plasmas in the magnetotail

A series of simultaneous determinations is presented of the 3D bulk flows of ion and electron plasmas in the magnetotail at radial distances near the lunar orbit. In the plasma mantle the ion and electron bulk velocities are identical within measurement accuracy. In the plasma sheet the electron bulk flows, densities, and temperatures are consistent with the results of the previous ISEE-3 survey at these radial distances as given by Zwickl et al. (1984). The present observations show that the electron bulk flows are often dominantly field-aligned and attributable to field-aligned currents, not convective motions within the magnetotail. The E x B convection of the plasmas as determined directly from the ion observation is often significantly slower and/or in a different direction than the bulk motions of either the ion or the electron plasmas. Thus, the ISEE-3 observations of electron bulk flows cannot be reliably used as measures of the E x B convection of plasmas or ion bulk motions at these distances in the plasma sheet.

Frank, L. A.↗
NASA NTRS1994

MHD modeling of magnetotail instability for localized resistivity

We present results of a three-dimensional magnetohydrodynamic (MHD) simulation of magnetotail evolution initiated by a sudden occurrence or increase of spatially localized resistivity as the major expected concequence of some localized microinstability. Because of the absence of a quantitative model, possible variations of resistivity levels with current density, or the reduction thereof, are not incorporated in the present investigation. The emphasis of the study is on an investigation of the changes to the overall evolution brought about by this localization, in particular, on the disruption and diversion of the cross-tail current and the nonlinear evolution of the magnetotail instability. The immediate consequences of the occurrence of the localized resistance and the resulting electric field are a reduction and diversion of the electric current around the region of high resistivity, associated with an increase of B(sub z) ('dipolarization') at the earthward edge and a decrease of B(sub z) at the tailward edge of this region. These effects, however, are localized and do not involve a reduction of the total cross-tail current and hence do not lead to the global development of a 'substorm current wedge,' which includes not only the reduction of the cross-tail current but also the buildup of a global field-aligned current system of 'regional 1' type (toward the Earth on the dawnside and away on the duskside of the tail). Such signatures develop at a later time, as consequences of a three-dimensional tearing instability, which is triggered by the occurrence of the resistivity. These features are found in combination with plasmoid formation and ejection, quite similar to results of earlier simulations with uniform resistivity. Differences are found in the timescale of the evolution, which tends to be shorter for localized resistivity, and in the propagation of the dipolarization effects in the equatorial plane. Whereas for uniform resistivity the temporal increase in B(sub z) tends to propagate tailward, apparently due to a pileup effect in the near-Earth region, an earthward propagation is found for the localized resistivity. This propagation results from an earthward convection of the gradient in B(sub z), which is set up by the reconnection process further tailward.

Hesse, Michael↗
NASA NTRS1994

Magnitude of B(sub Z) in the neutral sheet of the magnetotail

Statistical estimates of the average value of B(sub Z) in the magnetotail neutral sheet between 10 and 22 R(sub E) in X, and -10 to 10 R(sub E) in Y (GSM coordinates) are given for different phases of geomagnetic activity. With few exceptions the average value of B(sub Z) is found to be between 5 and 8 nT, but generally near 7 nT, irrespective of the type or phase of activity. This is considerably higher than is predicted in current magnetic field models of the magnetotail. The magnetic field within 2 R(sub E) of the neutral sheet is examined to determine whether B(sub Z) remains approximately constant. We do not find this to be true, B(sub Z) decreasing significantly over this distance from Delta-Z = 0. The structure of the cross-tail current and variations in current density with substorm phase appear to be more complicated than is commonly accepted.

Huang, C. Y.↗
NASA NTRS1994

Survey of electron and ion bulk flows in the distant magnetotail with the Geotail spacecraft

A histogramic survey is reported for the electron and ion bulk flows in Earth's magnetotail at geocentric radial distances in the range of about 10 to 210 R(sub E) from the Comprehensive Plasma Instrumentation on board the Geotail spacecraft. Specifically the X-components of the bulk flows are examined for high ion temperatures, greater than 5 x 10(exp 6) K, and for the lower ion temperatures. This separation of plasmas provides a reasonably effective criterion for identifying the hot plasmas associated with the plasma sheet and its boundary layers and the colder plasmas found in the magnetotail lobes and magnetopause boundary layer. The survey shows that the distributions of earthward bulk flows of ions and electrons are similar for each of the two temperature regimes, respectively. However, average speeds for the ions and electrons as a function of radial distance are dissimilar in that the electron bulk speeds are greater than those for the ions. All average electron and ion bulk flows are directed tailward at geocentric radial distances greater than 30 R(sub E). The most striking dissimilarity in the occurrence frequencies of the bulk flows is the large number with high tailward speeds for the electrons, greater than 500 km/s, relative to those for the ions. It is found that the disparity in bulk flows is due to the presence of two ion velocity distributions, one with high temperatures and a bulk speed similar to that of the electrons and the second, colder distribution with higher number density and considerably lesser bulk flow speed.

Frank, L. A.↗
NASA NTRS1993

Solar wind control of the distant magnetotail: ISEE 3

During a 40-day period in 1983, International Sun Earth Explorer 3 (ISEE 3) was located about 225 R(sub E) behind the Earth and remained within 12 R(sub E) of the nominal tail axis. During this time the spacecraft spent at least 70% of its time in the magnetotail with occasional excursions into the magnetosheath. However, during five geomagnetically distrubed intervals of 1 - 3 days duration during this period, ISEE 3 remained within the magnetosheath for extended intervals, even when it was very near the center of an average tail. Simultaneous observations of the solar wind direction and thermal pressure suggest that nonradial solar wind flow associated with interacting solar wind streams moves a compressed tail away from the nominal position at these times and explains most of these observations. However, during several few-hour intervals of strongly northward interplanetary magnetic field (IMF) within these periods, the solar wind is more radial and cannot explain the residence of the spacecraft in the magnetosheath. At these times ISEE 3 seems to be moving back and forth between two regions, one a higher-density, lower-temperature magnetosheathlike region but with density somewhat lower than the normal magnetosheath, the other a lower-density, higher-temperature taillike region but with density higher than the normal tail. Both regions have larger B(sub z) components and B(sub x) components that tend to vary as if the spacecraft were moving from one hemisphere of the tail to the other. It is suggested that the magnetotail at these times of northward IMF consists mostly of field lines that close Earthward of the spacecraft with a narrow remaining tail at 225 R(sub E) waving back and forth across the spacecraft. If relatively rare intervals of long-duration, very northward IMF can eliminate the extended tail, it seems likely that more common, less northward IMF might well have very important, though less drastic, effects on the tail configurations.

Fairfield, D. H.↗
NASA NTRS1995

The double oval UV auroral distribution. 2: The most poleward arc system and the dynamics of the magnetotail

The poleward arc system of a double oval distribution is shown to activate at the end of the optical expansion phase signifying the beginning of substorm recovery. The velocity dispersed ion signature (VDIS) can exist coincident with this discrete aurora developing on the most poleward oval. Although the VDIS is usually associated with ion beams in the plasma sheet boundary layer, it is demonstrated that the ionospheric signature is not beamlike but distributed in pitch angle. At the time when the double oval begins to form, the magnetic field in the magnetotail lobe becomes less flared and can show Pc 5 period oscillations. Similar pulsations also exist in the ionosphere associated with the most poleward oval and with stationary surge formation. Theoretical considerations link this phenomenon with a wave source tailward of x(sub GSE) = -30R(sub E) and fast mode evanescent waves propagating earthward in the tail lobe region. In this case the magnetotail appears to act like a waveguide and the plasma sheet boundary layer as a resonance region. This implies that the coupling of this fast mode waves is with the plasma sheet boundary layer and not with dipolar like field lines. The implications of this for the reconnection model of substorms are discussed.

Elphinstone, R. D.↗
NASA NTRS1996

Structure of the Magnetotail Current Sheet

An orbit tracing technique was used to generate current sheets for three magnetotail models. Groups of ions were followed to calculate the resulting cross-tail current. Several groups then were combined to produce a current sheet. The goal is a model in which the ions and associated electrons carry the electric current distribution needed to generate the magnetic field B in which ion orbits were traced. The region -20 R(E) less than x less than -14 R(E) in geocentric solar magnetospheric coordinates was studied. Emphasis was placed on identifying the categories of ion orbits which contribute most to the cross-tail current and on gaining physical insight into the manner by which the ions carry the observed current distribution. Ions that were trapped near z = 0, ions that magnetically mirrored throughout the current sheet, and ions that mirrored near the Earth all were needed. The current sheet structure was determined primarily by ion magnetization currents. Electrons of the observed energies carried relatively little cross-tail current in these quiet time current sheets. Distribution functions were generated and integrated to evaluate fluid parameters. An earlier model in which B depended only on z produced a consistent current sheet, but it did not provide a realistic representation of the Earth's middle magnetotail. In the present study, B changed substantially in the x and z directions but only weakly in the y direction within our region of interest. Plasmas with three characteristic particle energies were used with each of the magnetic field models. A plasma was found for each model in which the density, average energy, cross-tail current, and bulk flow velocity agreed well with satellite observations.

Larson, Douglas J.↗
NASA NTRS1996

Structure of the Magnetotail Current Sheet

An orbit tracing technique was used to generate current sheets for three magnetotail models. Groups of ions were followed to calculate the resulting cross-tail current. Several groups then were combined to produce a current sheet. The goal is a model in which the ions and associated electrons carry the electric current distribution needed to generate the magnetic field B in which ion orbits were traced. The region -20 R(sub E) less than x less than - 14 R(sub E) in geocentric solar magnetospheric coordinates was studied. Emphasis was placed on identifying the categories of ion orbits which contribute most to the cross-tail current and on gaining physical insight into the manner by which the ions carry the observed current distribution. Ions that were trapped near z = 0, ions that magnetically mirrored throughout the current sheet, and ions that mirrored near the Earth all were needed. The current sheet structure was determined primarily by ion magnetization currents. Electrons of the observed energies carried relatively little cross-tail current in these quiet time current sheets. Distribution functions were generated and integrated to evaluate fluid parameters. An earlier model in which B depended only on z produced a consistent current sheet, but it did not provide a realistic representation of the Earth's middle magnetotail. In the present study, B changed substantially in the x and z directions but only weakly in the y direction within our region of interest. Plasmas with three characteristic particle energies were used with each of the magnetic field models. A plasma was found for each model in which the density, average energy, cross-tail current, and bulk flow velocity agreed well with satellite observations.

Larson, Douglas J.↗
NASA NTRS2001

The Magnetospheric Constellation Mission. Dynamic Response and Coupling Observatory (DRACO): Understanding the Global Dynamics of the Structured Magnetotail

Magnetospheric Constellation Dynamic Response and Coupling Observatory (DRACO) is the Solar Terrestrial Probe (STP) designed to understand the nonlinear dynamics, responses, and connections within the Earth's structured magnetotail, using a constellation of approximately 50 to 100 distributed vector measurement spacecraft. DRACO will reveal magnetotail processes operating within a domain extending 20 Earth radii (R(sub E)) across the tail and 40 R(sub E)down the tail, on spatial and time scales accessible to global circulation models, i.e., approximately 2 R(sub E) and 10 seconds.

Source record↗
NASA NTRS2001

Electron Dynamics in the Magnetotail

The goal of this research has been to study the effects of electrons on magnetotail dynamics and current sheet structure. The approach is to follow ion trajectories in a global model of the magnetotail, use a Boltzmann approximation to include electrons, and then to update the field model according to the currents that are generated by the cross-tail electric field and/or induced fields. Parallel (and perpendicular) electric fields that form are included through the Boltzmann relation. Transverse electron currents are to be included through adiabatic drift equations.

Schriver, David↗