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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Energetic and magnetosheath energy particle signatures of the low-latitude boundary layer at low altitudes near noon

The energetic and magnetosheath energy particle signature of the low-latitude boundary layer (LBL) and its separation from the cusp are investigated using particle data from the polar-orbiting S3-3 satellite. The LBL and its boundaries, as determined from the energetic particles are compared with the LBL and boundaries determined from a modified set of low-energy plasma criteria based on Newell and Meng (NM, 1988, 1989). Excellent agreement was found in 68 percent of the 19 orbits where the LBL was identified by the energetic electron data. In 10 percent of the remaining orbits, the modified NM criteria did not provide numerical LBL identification, though a clear boundary region was visually identifiable in the data. For the remaining orbits, the modified NM criteria identified the LBL, but not its full latitudinal extent.

Roeder, J. L.↗
NASA NTRS1992

Waves in the inner magnetosheath - A case study

We study the waves within, and upstream of, the density enhancements in front of the magnetopause using magnetic field and plasma measurements from ISEE 1 and 2. The waves upstream of the density enhancements are most likely to be mirror modes and are convected with the magnetosheath flow. Within the density enhancements there is additional wave power at lower frequencies. These low frequency waves appear to be slow modes propagating sunward and quasi-standing in the flow. These observations lend support to the contention that the outer edge of the density enhancement is a slow mode wave front which marks the greatest distance that slow modes can propagate upstream into the solar wind.

Song, P.↗
NASA NTRS1993

Magnetic pulsations from 0.1 to 4.0 Hz and associated plasma properties in the earth's subsolar magnetosheath and plasma depletion layer

AMPTE CCE magnetic field data acquired during periods of magnetospheric compressions when the spacecraft sampled the magnetosheath are analyzed on the basis of a dynamic spectral analysis covering frequencies 0.1 to 4.0 Hz. Ion and electron data are used to identify regions, to monitor the upstream shock geometry, and to evaluate moments of the proton distribution. Fourteen encounters representing 46 hr of observations are analyzed. A compilation of the temporal sequence of spectral structures shows that electromagnetic ion cyclotron (EMIC) waves occur next to the magnetopause, while mirror waves occur outside the region of EMIC waves. It is concluded that there is a close relationship between EMIC waves in the sheath and the plasma depletion layer. For quasi-parallel upstream conditions, the magnetic field power spectra often exhibit no band limited structures but only broadband noise.

Anderson, B. J.↗
NASA NTRS1993

Ion cyclotron anisotropy instabilities in the magnetosheath - Theory and simulations

Second-order theory and 1D hybrid computer simulations are used to examine the nonlinear properties of proton and helium cyclotron anisotropy instabilities in the terrestrial magnetosheath at relatively weak fluctuations levels and at propagation parallel to the background magnetic field. The simulations confirm the second-order predictions that both instabilities yield efficient wave-particle interactions; the rate at which the driving species anisotropy is reduced is much greater than the rate at which that species loses kinetic energy. It is suggested that these instabilities should saturate at relatively low levels. An approximate expression is derived for the fluctuating field energy at saturation of the fastest growing modes, and it is found that it is in fair agreement with three computer simulations.

Gary, S. P.↗
NASA NTRS1993

Simulations of ion cyclotron anisotropy instabilities in the terrestrial magnetosheath

Enhanced transverse magnetic fluctuations observed below the proton cyclotron frequency in the terrestrial magnetosheath have been identified as due to the proton cyclotron and helium cyclotron instabilities driven by the T-perpendicular greater than T-parallel condition of the sheath ions. One-dimensional hybrid computer simulations are used here to examine the nonlinear properties of these two growing modes at relatively weak fluctuation energies and for wave vectors parallel to the background magnetic field. Second-order theory predicts fluctuating magnetic field energies at saturation of the proton cyclotron anisotropy instability in semiquantitative agreement with the simulation results. Introduction of the helium component enhances the wave-particle exchange rate for proton anisotropy reduction by that instability, thereby reducing the saturation energy of that mode. The simulations demonstrate that wave-particle interactions by the proton cyclotron and helium cyclotron instabilities lead to the anticorrelation observed by Anderson and Fuselier (1993).

Gary, S. P.↗
NASA NTRS1994

Origins of energetic ions in the Earth's magnetosheath

This final report describes activities under NASA contract NAS5-31213 to Lockheed Missiles and Space Company. The report covers the entire contract period from 8 May 1991 to 7 Jun. 1994. This is a contract under the NASA Guest Investigator Program for 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 AMPTE/Charge Composition Explorer (CCE) spacecraft. These combined data sets have been 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.

Source record↗
NASA NTRS1994

Observations in the sheath region ahead of a magnetic cloud and in the dayside magnetosheath during magnetic cloud passage

We present magnetic field and particle (protons and electrons) observations in the sheath region behind an interplanetary shock driven by a magnetic cloud, and in the magnetic cloud itself. We also discuss observations in the dayside terrestrial magnetosheath during cloud passage. We find that the region ahead of the cloud is in pressure balance. Further, throughout its extent (greater than 0.06 AU), the magnetic field strength is anticorrelated with the plasma density, with the latter decreasing steadily as the cloud is approached. This behavior is indicative of magnetic forces influencing the flow topology and highlights a large-scale breakdown of predictions based solely on gas dynamical considerations. We also study density structures inside the cloud which result in an undulating dynamic pressure being applied to the magnetopause causing it to oscillate with amplitudes of approximately 1-3 Re and period approximately 2h.

Farrugia, C. J.↗
NASA NTRS1995

Penetration of the interplanetary magnetic field B(sub y) magnetosheath plasma into the magnetosphere: Implications for the predominant magnetopause merging site

Magnetosheath plasma peertated into the magnetospere creating the particle cusp, and similarly the interplanetary magnetic field (IMF) B(sub y) component penetrates the magnetopause. We reexamine the phenomenology of such penetration to investigate implications for the magnetopause merging site. Three models are popular: (1) the 'antiparallel' model, in which merging occurs where the local magnetic shear is largest (usually high magnetic latitude); (2) a tilted merging line passing through the subsolar point but extending to very high latitudes; or (3) a tilted merging line passing through the subsolar point in which most merging occurs within a few Earth radii of the equatorial plane and local noon (subsolar merging). It is difficult to distinguish between the first two models, but the third implies some very different predictions. We show that properties of the particle cusp imply that plasma injection into the magnetosphere occurs most often at high magnetic latitudes. In particular, we note the following: (1) The altitude of the merging site inferred from midaltitude cusp ion pitch angle dispersion is typically 8-12 R(sub E). (2) The highest ion energy observable when moving poleward through the cusp drops long before the bulk of the cusp plasma is reached, implying that ions are swimming upstream against the sheath flow shortly after merging. (3) Low-energy ions are less able to enter the winter cusp than the summer cusp. (4) The local time behavior of the cusp as a function of B(sub y) and B(sub z) corroborates predictions of the high-latitude merging models. We also reconsider the penetration of the IMF B(sub y) component onto closed dayside field lines. Our approach, in which closed field lines ove to fill in flux voids created by asymmetric magnetopause flux erosion, shows that strich subsolar merging cannot account for the observations.

Newell, Patrick T.↗
NASA NTRS1995

Low-frequency fluctuations in the magnetosheath near the magnetopause

There are four low-frequency modes which may propagate in a high-beta nearly bi-Maxwellian plasma. These are the magnetosonic, Alfven, ion acoustic, and mirror modes. This manuscript defines a procedure based on linear Vlasov theory for the unique identification of these modes by use of transport ratios, dimensionless ratios of the fluctuating field and plasma quantities. A single parameter, the mode deviation is calculated using the plasma and magnetic field data gathered by the Active Magnetospheric Particle Tracer Explorers/Ion Release Module (AMPTE/IRM) spacecraft to identify the modes observed in the terrestial magnetosheath near the magnetopause. As well as determining the mode which best describes the observed fluctuations, it gives us a measure of whether or not the resulting identification is unique. Using 17 time periods temporally close to a magnetopause crossing, and confining our study to the frequency range from 0.01 to 0.04 Hz, we find that the only clearly identified mode in this frequency range is the mirror mode. Most commonly, the quasi-perpendicular mirror mode (with wave vector k roughly perpendicular to the background magnetic field B(sub zero) is observed. In two events the quasi-parallel mirror mode k parallel B(sub zero) was identified.

Denton, Richard E.↗
NASA NTRS2001

Stochastic Growth of Ion Cyclotron And Mirror Waves In Earth's Magnetosheath

Electromagnetic ion cyclotron and mirror waves in Earth's magnetosheath are bursty, have widely variable fields, and are unexpectedly persistent, properties difficult to reconcile with uniform secular growth. Here it is shown for specific periods that stochastic growth theory (SGT) quantitatively accounts for the functional form of the wave statistics and qualitatively explains the wave properties. The wave statistics are inconsistent with uniform secular growth or self-organized criticality, but nonlinear processes sometimes play a role at high fields. The results show SGT's relevance near marginal stability and suggest that it is widely relevant to space and astrophysical plasmas.

Cairns, Iver H.↗
NASA NTRS2011

Examination of Bursty Electromagnetic Waves Observed During Intervals of Turbulent Magnetosheath Reconnection

We investigate observations of intense bursts of electromagnetic waves in association with magnetic reconnection in the turbulent magnetosheath. These structured, broadband bursts occur above 80-Hz, often displaying features reminiscent of absorption bands and are observed at local minima in the magnetic field. We present detailed analyses of these intense bursts of electromagnetic waves and quantify their proximity to X- and O-nulls.

Adrian, Mark L.↗
NASA NTRS2011

Bursty, Broadband Electromagnetic Waves Associated with Thin Current Layers and Turbulent Magnetosheath Reconnection

We investigate observations of intense bursts of electromagnetic wave energy in association with the thin current layers of turbulent magnetosheath reconnection. These observed emissions form two distinct types: (i) broadband emissions that extend continuously to lOs of Hertz; and (ii) structured bursts of emitted energy that occur above 80-Hz, often displaying features reminiscent of absorption bands and are observed at local minima in the magnetic field. We present detailed analyses of these intense bursts of electromagnetic energy and quantify their proximity to X- and O-nulls, as well as their correlation to the amount of magnetic energy converted by the process of magnetic reconnection.

Adrian, M. L.↗
NASA NTRS2012

Bursty, Broadband Electromagnetic Waves Associated with Three-Dimensional Nulls Observed in Turbulent Magnetosheath Reconnection

We investigate observations of intense bursts of electromagnetic wave energy in association with the thin current layers of turbulent magnetosheath reconnection. These observed emissions - typically detected in the layers immediately outside of the current layer proper - form two distinct types: (i) broadband emissions that extend continuously to lOs of Hertz; and (ii) structured bursts of emitted energy that occur above 80-Hz, often displaying features reminiscent of absorption bands and are observed near the local minima in the magnetic field. We present detailed analyses of these intense bursts of electromagnetic energy and quantify their proximity to X-IO-nulls and magnetic spine connected null pairs, as well as their correlation - if any - to the amount of magnetic energy converted by the process of magnetic reconnection.

Adrian, Mark L.↗
NASA NTRS2012

AXIOM: Advanced X-Ray Imaging Of the Magnetosheath

AXIOM (Advanced X-ray Imaging Of the Magnetosphere) is a concept mission which aims to explain how the Earth's magnetosphere responds to the changing impact of the solar wind using a unique method never attempted before; performing wide-field soft X-ray imaging and spectroscopy of the magnetosheath. magnetopause and bow shock at high spatial and temporal resolution. Global imaging of these regions is possible because of the solar wind charge exchange (SWCX) process which produces elevated soft X-ray emission from the interaction of high charge-state solar wind ions with primarily neutral hydrogen in the Earth's exosphere and near-interplanetary space.

Sembay, S.↗
NASA NTRS2013

Current Structure and Nonideal Behavior at Magnetic Null Points in the Turbulent Magnetosheath

The Poincaré index indicates that the Cluster spacecraft tetrahedron entraps a number of 3-D magnetic nulls during an encounter with the turbulent magnetosheath. Previous researchers have found evidence for reconnection at one of the many filamentary current layers observed by Cluster in this region. We find that many of the entrained nulls are also associated with strong currents. We dissect the current structure of a pair of spiral nulls that may be topologically connected. At both nulls, we find a strong current along the spine, accompanied by a somewhat more modest current perpendicular to the spine that tilts the fan toward the axis of the spine. The current along the fan is comparable to the that along the spine. At least one of the nulls manifests a rotational flow pattern in the fan plane that is consistent with torsional spine reconnection as predicted by theory. These results emphasize the importance of examining the magnetic topology in interpreting the nature of currents and reconnection in 3-D turbulence.

cluster↗
NASA NTRS2016

Electron Scale Structures and Magnetic Reconnection Signatures in the Turbulent Magnetosheath

Collisionless space plasma turbulence can generate reconnecting thin current sheets as suggested by recent results of numerical magnetohydrodynamic simulations. The Magnetospheric Multiscale (MMS) mission provides the first serious opportunity to verify whether small ion-electron-scale reconnection, generated by turbulence, resembles the reconnection events frequently observed in the magnetotail or at the magnetopause. Here we investigate field and particle observations obtained by the MMS fleet in the turbulent terrestrial magnetosheath behind quasi-parallel bow shock geometry. We observe multiple small-scale current sheets during the event and present a detailed look of one of the detected structures. The emergence of thin current sheets can lead to electron scale structures. Within these structures, we see signatures of ion demagnetization, electron jets, electron heating, and agyrotropy suggesting that MMS spacecraft observe reconnection at these scales.

Yordanova, E.↗
NASA NTRS2017

Electron Heating at Kinetic Scales in Magnetosheath Turbulence

We present a statistical study of coherent structures at kinetic scales, using data from the Magnetospheric Multiscale mission in the Earths magnetosheath. We implemented the multi-spacecraft partial variance of increments (PVI) technique to detect these structures, which are associated with intermittency at kinetic scales. We examine the properties of the electron heating occurring within such structures. We find that, statistically, structures with a high PVI index are regions of significant electron heating. We also focus on one such structure, a current sheet, which shows some signatures consistent with magnetic reconnection. Strong parallel electron heating coincides with whistler emissions at the edges of the current sheet.

Chasapis, Alexandros↗