SEARCH · Search NASA

Results for “magnetosheath”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9

All sources NASA NTRS DOE OSTI

NASA NTRS1978

Electric field measurements in the solar wind, bow shock, magnetosheath, magnetopause, and magnetosphere

Electro-field measurements are reported at 11 magnetopause crossings that occurred during a single in-bound ISEE-1 satellite pass near a local time of 10:30. In combination with magnetic-field data, these measurements show the existence of electro-field components tangential to the actual magnetopause in the frame of rest of the magnetopause on every crossing of the current-carrying layers associated with the 11 magnetopause traversals. These tangential electric-field components were oriented with respect to the magnetopause sheet currents, such that there was an electrical power dissipation of between 30 and 110 W/sq km on 10 of the 11 crossings. These results are in agreement with requirements of reconnection theories. Histograms of the normal electric-field components and of the orientation, velocity, and thickness of the current-carrying layer are presented. The existence of a parallel electric field in the magnetosheath near the magnetopause and of propagation of large-amplitude waves along the magnetopause is suggested.

Mozer, F. S.↗

NASA NTRS1979

Magnetosheath electrostatic turbulence

The spectrum of electrostatic wave turbulence in the terrestrial magnetosheath is investigated. Measurements of electric and magnetic field fluctuations in the range 20 Hz to 200 kHz were made by two 16-channel spectrum analyzers on board the IMP 6 satellite. It is found that the electrostatic wave spectra generally consist of three components, which may occur in any combination: a low frequency component which shows a decrease in spectral density with increasing frequency and which is associated with the bow shock wave, a high frequency component identified with electron plasma oscillations and an intermediate frequency component. The minimum wavelength of electrostatic waves is found to be about 0.1 km, with intensity of from 0.01 to 1.0 mV/m. Electric field polarization has been found to be parallel to the local magnetic field direction, implying the presence of longitudinal electrostatic wave modes, electron plasma oscillations and ion sound waves.

Rodriguez, P.↗

NASA NTRS1979

H/+/ and He/2+/ in the dawnside magnetosheath

Mass and energy analyses of energetic ions in the dawnside magnetosheath have been made by the energetic ion composition experiment on the ISEE-1 spacecraft over the energy range 10 eV/e to 17 keV/e. The significant observations are: the bulk flows of the H(+) and He(2+) components determined from first moments of the distributions averaged over several minutes are equal within the uncertainties of the measurement. The H(+) and He(2+) distributions are similar in that they both show temperature anisotropies with perpendicular temperature not less than parallel temperature; however, the distributions are not well characterized by temperatures derived from second moments. In at least one case high energy tails of both distributions can be characterized by an additional higher temperature component. The major difference between the H(+) and He(2+) distributions is the depletion of the low velocity (in the center of mass frame) part of the He(2+) distributions, relative to the H(+) distributions.

Peterson, W. K.↗

NASA NTRS1980

Sunward flow in Jupiter's magnetosheath

The position of Voyager crossings of Jupiter's bow shock show a dependence on solar wind pressure to the -1/3 power. This dependence is used to calculate typical bow shock speeds of 50 km/s from Voyager solar wind plasma data. Since the bow shock and magnetopause move approximately in unison in response to solar wind pressure changes, the resulting movement of the magnetosheath at a sizeable fraction of the solar wind speed leads to reversed, sunward flow in large portions of the dayside region when the boundaries are expanding. Voyager 1 plasma data show evidence of such reversed flow.

Siscoe, G. L.↗

NASA NTRS1981

Magnetospherically trapped ions as a source of magnetosheath energetic ions

It has been suggested that energetic ions observed in the magnetosheath may be due to the direct leakage of trapped magnetospheric ions. To test this hypothesis, three-dimensional ion spectra from the energetic particle experiment on ISEE 1 for a magnetopause crossing on Nov. 10, 1977 are utilized to construct three-dimensional distribution functions in the magnetosphere and in the sheath. Using the observed magnetic field, a simple one-dimensional model of the magnetopause is developed. Ions are then followed in the model, starting in the magnetosphere, through the magnetopause and ending up in the sheath. Using Liouville's Theorem a model sheath distribution function is then built up by following the magnetospheric distribution function through the model fields. The model distribution is then compared with the observed sheath distribution. For this case it is found that the main features of the observed ions in the sheath are consistent with direct leakage and with no energization or de-energization processes, and an inward-pointing normal component is required. The energetic particles mapped in this case apparently follow a flux tube which does not penetrate the magnetopause where local tangential electric fields have been reported.

Speiser, T. W.↗

NASA NTRS1981

A note on the location of the stagnation point in the magnetosheath flow

While observational and theoretical investigations have clearly indicated that the shape of the magnetosphere is very nearly symmetric about the plane determined by the aberrated solar wind flow direction and the earth's magnetic dipole, many processes such as magnetic pulsations and geomagnetic activity which should be shape dependent do not exhibit symmetry about this plane. The present paper proposes a solution to this apparent paradox in terms of the shifting of the stagnation point in the magnetosheath flow. It is shown that the interplanetary magnetic field can act to shift the stagnation point on the order of 15 deg from the nose towards dawn during periods of low Alfven Mach number without an appreciable aberration of the magnetopause, accounting for the observations of pulsation demarcation and magnetic reconnection.

Russell, C. T.↗

NASA NTRS1983

Magnetic field fluctuations in the Venus magnetosheath

Using a model for the convection pattern of the shocked solar wind flow around the Venus obstacle, Pioneer Venus observations of ultra-low-frequency (about 10-40 s period) magnetic field fluctuations in the magnetosheath have been traced along streamlines to the regions of the quasi-parallel bow shock. The periods and polarizations of the sinusoidal fluctuations are similar to those observed upstream of the quasi-parallel bow shock, where streaming superthermal particles are believed to produce MHD waves by a beam-plasma instability. The results suggest that both disturbances at the ionopause at Venus and the earth's magnetopause may be caused by convection of turbulent magnetic fields from the subsolar bow shock when the interplanetary field direction produces a quasi-parallel shock there.

Luhmann, J. G.↗

NASA NTRS1983

Field-aligned ion beams upstream of the earth's bow shock Evidence for a magnetosheath source

High time resolution ISEE-1 and -2 observations of upstream field-aligned ion beams at several crossings of the earth's bow shock indicate that some beams are due to high energy magnetosheath particles leaking through the shock into the upstream region. The distribution immediately downstream of these oblique shocks consists of a 'core' of directly transmitted, slightly heated ions, plus a crescent-shaped, high-velocity distribution, centered roughly on the magnetic field in the direction toward the upstream region, with a fairly well defined low velocity cutoff.

Thomsen, M. F.↗

NASA NTRS1984

Magnetospheric ions and electrons in the distant magnetosheath at about 50 and 180 earth radii - ISEE-3 observations

Energetic particle data were obtained in the dawn magnetosheath at about 50 earth radii (ER), analyzed, and compared with data taken at 180 ER. Both data sets were acquired during the ISEE-3 geotail mission. The results of analyses of the 16 sec time profiles of 32 and 130 keV protons, 75-115 keV electrons, and some of the 30-36 keV proton angular distributions (PAD) are presented. No temporal dispersions were detected in the particle bursts, implying instead a spatial dispersion. The particles filled flux tubes of 6 ER, with the energetic electrons being beamed along magnetic field lines. PADs displayed anisotropy symmetric relative to the magnetic field. The electrons were not detected at 180 ER. The phenomena are modeled as flux tubes connected to the magnetotail magnetic field in the near-earth magnetopause. The particles leak out along connected field lines. Lion roars scatter the electrons, which escape into interplanetary space. Ions, however, may carry their intensity out to 200 ER, a factor which awaits verification by further data.

Scholer, M.↗

NASA NTRS1984

Large-scale flow in the dayside magnetosheath

The degree of control over plasma flow direction exerted by the compressed magnetic field in the dayside magnetosheath is examined by comparing ISEE 1 LEPEDEA data with hydrodynamic and MHD predictions. In 11 of 20 observed cases, the flow pattern followed the predictions of simple hydrodynamic theory; in the nine other cases, the flow deviated from this pattern. One case with large deflection was persistent over 1.5 hr, and its direction was consistent with a stagnation point displacement resulting from increased, asymmetric magnetic field pressure contributions during periods of low Alfven Mach number. The eight other cases of observed large deflection are consistent with either the subsolar merging line or the antiparallel merging hypothesis, but not exclusively with one or the other.

Crooker, N. U.↗

NASA NTRS1986

Solar wind carbon, nitrogen and oxygen abundances measured in the earth's magnetosheath with AMPTE/CCE

The solar wind number density ratios of C(6+) + C(5+) and N(7+) + N(6+) + N(5+) relative to O(8+) + O(7+) + O(6+) have been measured for the first time using data from the Charge-Energy-Mass Spectrometer on the AMPTE/CCE spacecraft during four solar active periods from Sept. 19 to Nov. 1, 1984 when CCE traversed the subsolar magnetosheath of the compressed magnetosphere. It is found that the average values of the density ratios of C/O and N/O to be 0.43 + or - 0.03 and 0.15 + or - 0.06, respectively. These ratios, as well as the average He(2+)/O ratio of 43 + or - 5 for these same time periods, are in excellent agreement with Solar Energetic Particles (SEP) abundance ratios as well as SEP-derived coronal abundances of these elements. The solar wind C/O ratio is substantially below the generally accepted photospheric value of 0.60.

Gloeckler, G.↗

NASA NTRS1986

Interplanetary magnetic field control of the Venus magnetosheath field and bow shock location

Six Venus years of Pioneer Venus Orbiter (PVO) data are analyzed in a coordinate system which isolates magnetic effects. The field draping pattern features two lobes easily identifiable even in the near planet region. The magnetosheath magnetic magnitude has a hemispherical asymmetry controlled by the IMF orientation in a manner suggesting preferrential ion pickup in one hemisphere. This result complements recent findings that the bow shock position is responsive to IMF direction. Examination of the ionopause position to evaluate ionospheric effects on the overall asymmetry of thfe Venus-solar wind interaction produces negative but not conclusive results.

Phillips, J. L.↗

NASA NTRS1986

Origin of large magnetic fluctuations in the magnetosheath of Venus

The origin of large-amplitude hydromagnetic waves in the Venus magnetosheath downstream of the quasi-parallel bow shock is investigated by means of numerical simulations. It is shown that the most likely source of these waves is the bow shock itself, rather than an instability involving the solar wind and oxygen ions of planetary origin. Pickup of O(+) ions by these waves is also examined and shown to be in agreement with previous test particle calculations. The effect of mass loading on the structure of the shock is also discussed.

Winske, D.↗

NASA NTRS1987

On the generation of magnetosheath lion roars

A theoretical model is proposed to discuss the electron dynamics associated with the mirror waves and their effects on the generation of the observed lion roars in the magnetosheath. It is pointed out that the usual double-adiabatic theory of hydromagnetics is not applicable to the electrons in mirror waves. Although the electron magnetic moment is conserved, the energy of each electron in the mirror waves is expected to be constant. Assuming an initial electron temperature anisotropy, it can be shown that in the low field region the electron temperature and thermal anisotropy are higher than the initial values, whereas in the high field region the electron temperature and anisotropy are lower. This point can lead to a theoretical explanation of the important features of the observed lion roars. Then present discussion complements the existing theories in the literature.

Lee, L. C.↗

NASA NTRS1988

AMPTE/CCE observations of shell-like He(2+) and O(6+) distributions in the magnetosheath

Simultaneous observations of solar wind He(2+) and O(6+) shell-like distributions in the magnetosheath were obtained by the AMPTE CCE on November 1, 1984. It is found that the present distributions are centered on the downstream H(+) bulk velocity and have radii proportional to the mass/charge ratio. The results support an electrostatic cross-shock potential model.

Fuselier, S. A.↗

NASA NTRS1991

Venus ionospheric 'clouds' - Relationship to the magnetosheath field geometry

The magnetic field control of Venus plasma 'clouds' relative to the planet has been analyzed by rotating the observed locations of the clouds into a coordinate system in which all of the transverse upstream magnetic fields were aligned. The results indicate that clouds are scattered around the periphery of the planet in the terminator plane. There is no evidence of a concentration of clouds where the magnetosheath magnetic field is most strongly 'draped'. On the other hand, statistics show that the change in the orientation of the transverse upstream magnetic field between the inbound and outbound bow shock crossings, for the orbits where clouds are seen is about 30 deg greater than the average upstream change at Venus over the same time intervals.

Ong, M.↗

NASA NTRS1992

Origins of Energetic Ions in the Earth's Magnetosheath

The analysis and interpretation of the combined scientific data from the Hot Plasma Composition Experiment (HPCE) and the Charge Energy Mass (CHEM) spectrometer on the Active Mesospheric Particle Tracer Experiment (AMPTE) Charge Composition Explorer (CCE) spacecraft are discussed. These combined data sets have and will be used to survey the energetic ion environment in the Earth's magnetosheath to determine the origins and relative strengths of the energetic ion populations found there. A computer code was developed to analyze and interpret the data sets. The focus of the first year was on the determination of the contribution of leaked magnetospheric protons to the total energetic proton population. Emphasis was placed on intervals when the AMPTE spacecraft was in the plasma depletion layer because it was argued that in this region, only the leaked population contributes to the energetic ion population. Manipulation of the CHEM data and comparison of the CHEM and HPCE data over their common energy range near the magnetopause also contributed directly to a second study of that region.

Fuselter, S. A.↗

NASA NTRS1992

Variable carbon and oxygen abundances in the solar wind as observed in earth's magnetosheath by AMPTE/CCE

A comprehensive list is presented of the solar wind oxygen and carbon charge states and abundances measured in all magnetosheath periods during the lifetime of the AMPTE/CCE satellite, 1984-1988. A surprisingly variable C/O ratio is found. The variations seem to be strongly correlated to the source temperature in the corona where the solar wind responsible for the particular flow originated.

Von Steiger, R.↗