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Results for “reconfigurable sheets”

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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

A search for the solar roots of the most disturbed interplanetary field intervals of solar cycle 21

During the course of the Pioneer Venus Orbiter mission, fairly continuous interplanetary plasma and magnetic field data were obtained which span the interval from prior to the last solar maximum to the current solar minimum recovery. Within this nearly complete solar cycle interval, several periods of exceptional disturbance of the interplanetary field stand out. The available solar data have been examined to determine what features, if any, distinguish these periods. Neither flare nor coronal mass ejection reports show particularly unusual behavior. However, these periods appear to occur in conjunction with marked changes in the interplanetary sector structure. This suggests that heliospheric current sheet reconfiguration is an indicator of the level of interplanetary disturbance distinct from the more traditional solar activity data.

Luhmann, J. G.↗
NASA NTRS2000

Plasma Sheet Source and Loss Processes

Data from the TIMAS ion mass spectrometer on the Polar satellite, covering 15 ev/e to 33 keV/e in energy and essentially 4(pi) in view angles, are used to investigate the properties of earthward (sunward) field-aligned flows of ions, especially protons, in the plasma sheet-lobe transition region near local midnight. A total of 142 crossings of this region are analyzed at 12-sec time resolution, all in the northern hemisphere, at R(SM) approx. 4 - 7 R(sub E), and most (106) in the poleward (sunward) direction. Earthward proton flows are prominent in this transition region (greater than 50% of the time), typically appearing as sudden "blasts" with the most energetic protons (approx. 33 keV) arriving first with weak flux, followed by protons of decreasing energy and increasing flux until either: (1) a new "blast" appears, (2) the flux ends at a sharp boundary, or (3) the flux fades away within a few minutes as the mean energy drops to a few keV. Frequent step-like changes (less than 12 sec) of the flux suggest that perpendicular gradients on the scale of proton gyroradii are common. Peak flux is similar to central plasma sheet proton flux (10(exp 5) - 10(exp 6)/[cq cm sr sec keV/e] and usually occurs at E approx. 4 - 12 keV. Only the initial phase of each "blast" (approx. 1 min) displays pronounced field-alignment of the proton velocity distribution, consistent with the time-of-flight separation of a more or less isotropic source distribution with df/d(nu) less than 0. The dispersive signatures are often consistent with a source at R(SM) less than or equal to 30 R(sub E). No systematic latitudinal velocity dispersion is found, implying that the equatorial plasma source is itself convecting. In short, the proton "blasts" appear as sudden local expansions of central plasma sheet particles along reconfigured ("dipolarized") magnetic field lines.

Lennartsson, O. W.↗
NASA NTRS1990

Extreme energetic particle decreases near geostationary orbit - A manifestation of current diversion within the inner plasma sheet

A qualitative model of magnetic field reconfiguration as might result from neutral line formation in the central plasma sheet late in a substorm growth phase is considered. It is suggested that magnetic reconnection probably begins before the substorm expansion phase and that cross-tail current is enhanced across the plasma sheet both earthward and tailward of a limited region near the neutral line. Such an enhanced cross-tail current earthward of the original X line region may contribute to thinning the plasma sheet substantially, and this would in turn affect the drift currents in that location, thus enhancing the current even closer toward the earth. In this way a redistribution and progressive diversion of normal cross-tail current throughout much of the inner portion of the plasma sheet could occur. The resulting intensified current, localized at the inner edge of the plasma sheet, would lead to a very thin plasma confinement region. This would explain the very taillike field and extreme particle dropouts often seen late in substorm growth phases.

Baker, D. N.↗
NASA NTRS1988

Multipoint measurements of magnetotail dynamics

The role of multipoint spacecraft measurements in revealing the morphology of magnetospheric substorm is described. Information has been provided on the storage of energy in the tail during the growth phase, the thinning of the plasma sheet relative to onset, reconfiguration and energy loss after onset, and how these phenomena are controlled by the IMF. Smaller-scale phenomena that need to be observed on finer time scales and detected in more limited spatial regions were studied by ISEE 1 and 2 and a number of spacecraft near geosyncronous orbit.

Fairfield, D. H.↗
NASA NTRS1994

Tearing mode instability in a multiple current sheet system

The tearing mode and magnetic reconnection are studied for multiple current sheet systems by two-dimensional magnetohydrodynamic (MHD) simulations. Both the linear and nonlinear evolution of this process are anaylsed for laminar perturbations. The results illustrate the existence of a linear regime with a symmetric and antisymmetric mode and agree with previous analytic results (Otto and Birk, 1992). The nonlinear evolution shows a number of interesting new features and may explain some properties in corresponding studies of turbulent reconnection. For wavelengths larger than twice the current sheet separation the evolution of antisymmetric modes leads to an entire reconfiguration of the magnetic field and converts a major portion of the magnetic energy into kinetic energy. Antisymmetric modes with smaller wavelengths and symmetric modes are found to saturate. The influence of the value of the resistivity on the reconnection rate decreases in the nonlinear evolution, and the ratio of current sheet separation to wavelength seems to be of major importance. A comparion of the dynamics of periodic current sheets with the evolution of only two current sheets indicates that some of the results for the periodic system also apply to the evolution of only two interacting current sheets. The results are discussed with respect to observations of large-scale plasma and magnetic field reconfigurations in the magnetosheath and near the Earth's bow shock.

Yan, M.↗
NASA NTRS2017

Observations of Deep Ionospheric F-Region Density Depletions with FPMU Instrumentation and Their Relationship with the Global Dynamics of the June 22-23, 2015 Geomagnetic Storm

The magnetic storm that commenced on June 22, 2015 was one of the largest storms in the current solar cycle, resulting from an active region on the Sun that produced numerous coronal mass ejections (CMEs) and associated interplanetary shock waves. On June 22 at 18:36 UT the magnetosphere was impacted by the leading-edge shock wave and a sheath carrying a large and highly variable interplanetary magnetic field (IMF) Bz with values ranging from +25 to -40 nT. During the subsequent interval from 0000 to 0800 UT, there was a second intensification of the geomagnetic storm resulting from the impact of the CME. We present dramatic responses of simultaneous particle measurements from the high-altitude Magnetospheric Multiscale Mission (MMS) at high altitudes in the magnetosphere (approx. 9-12 Re) and from the low-altitude (F-region) Floating Potential Measurement Unit (FPMU) on board the International Space Station (ISS). We analyze potential causes of these dramatic particle flux dropouts by putting them in the context of storm-time electrodynamics, and support our results with numerical simulations of the global magnetosphere and ionosphere. During the sheath phase of the storm, the MMS spacecraft in the near-earth equatorial plane observed a rapid reconfiguration of the magnetic field near 1923 UT. Initially in the warm plasma sheet, particle flux dropouts were observed as they tracked the plasma-sheet to lobe transitions with the stretching and thinning of the plasma sheet. Anti-sunward flowing O+ ions of ionospheric origin were also measured during this period, confirming that the MMS spacecraft temporarily was in a lobe.

Coffey, Victoria↗
NASA NTRS2004

Self-Organized Criticality, Multifractals, and Intermittent Turbulence in Earth's Magnetotail

We have achieved all the goals stated in our grant proposal in collaboration with Dr. C.C. Wu of the University of California at Los Angeles. Specifically, these include: The understanding of the complexity induced nonlinear spatiotemporal structures and the coexisting propagating modes. The development of plasma resonances and coherent structures in space plasmas. The study of fluctuation-induced nonlinear instabilities and their role in the reconfiguration of magnetic topologies in the magnetotail. The development of "anisotropic three-dimensional complexity" in the plasma sheet due to localized merging and interactions of the magnetic coherent structures and associated topological phase transitions. The understanding of the intermittent turbulence and energization process of the observed Bursty Bulk Flows (BBF's) in the Earth s magnetotail. The acceleration of ions due to the intermittent turbulence of propagating arid nonpropagating fluctuations In the following, we include lists of our published papers, invited talks, and professional activities. A detailed description of our accomplished research results is given in Section IV.

Chang, Tom↗
NASA NTRS1995

The solar/interplanetary event of 14 April 1994 observed by Yohkoh/SXT

The polar crown event of April 14 1994 is one of the largest scale eruptive events observed by the Yohkoh/SXT. Associated with the formation of an arcade of soft X-ray loops at the Sun was the detection of an interplanetary forward/reverse shock event by the Ulysses spacecraft some 4-7 days later. The relationship between the coronal and interplanetary signatures of these events is important if we are to address fully the initialization and consequent acceleration of interplanetary phenomena, such as CMEs and counter-streaming electrons, originating at the Sun. From detailed analysis of the energetics of the arcade formed during the eruption of April 14 1994, we find peak temperatures and emission measures of approximately 5MK and approximately 10(exp 48)cm(exp -3) respectively. The total thermal content of the arcade loop structure observed in soft X-rays is calculated to be some 5 x 10(exp 29) ergs. The development of these parameters as the event proceeds and their relationship to the dynamics of the eruption are investigated. Although spanning a longitudinal range of some 150 degrees the April 14 event displayed the typical helmet streamer structure normally associated with coronal mass ejections These helmet streamers are thought to be related to the global solar magnetic field through the heliospheric current sheet (HCS). The arcade formation, together with the eruption of material into interplanetary space, signifies a large-scale reconfiguration of the coronal magnetic field. We examine the effects of the formation of such a coronal arcade structure on the HCS and discuss the dynamics involved with the passage of a large scale disturbance through the interplanetary magnetic field.

Alexander, D.↗
NASA NTRS1996

Estimates of magnetic flux, and energy balance in the plasma sheet during substorm expansion

The energy and magnetic flux budgets of the magnetotail plasma sheet during substorm expansion are investigated. The possible mechanisms that change the energy content of the closed field line region which contains all the major dissipation mechanisms of relevance during substorms, are considered. The compression of the plasma sheet mechanism and the diffusion mechanism are considered and excluded. It is concluded that the magnetic reconnection mechanism can accomplish the required transport. Data-based empirical magnetic field models are used to investigate the magnetic flux transport required to account for the observed magnetic field dipolarizations in the inner magnetosphere. It is found that the magnetic flux permeating the current sheet is typically insufficient to supply the required magnetic flux. It is concluded that no major substorm-type magnetospheric reconfiguration is possible in the absence of magnetic reconnection.

Hesse, Michael↗
NASA NTRS1986

Detailed observations of the plasma sheet during a substorm on April 24, 1979

Plasma, magnetic field, and energetic particle data obtained by ISEE 1 and 2 satellites for the April 24, 1979 substorm are studied in relation to the neutral line model and the boundary layer model. The ISEE 1 and 2 instruments and experiments utilized to collect the data are discussed. The major reconfiguration of the tail plasma and magnetic field plasma region, and the plasma ion flows observed support the neutral line model for interpreting substorms. The plasma ion distribution function and plasma flow are examined. The region of lobe-plasma sheet interface referred to as the separatrix layer is identified. The differences in times of plasma sheet dropout and recovery, and absence or presence of flux anisotropies are investigated. Energetic particle measurements are analyzed to study the relationship between energetic ions and plasma ions, and the velocity distributions. The data support the application of the neutral line model to the evaluation of substorms; however, the data are inconsistent with the boundary layer dynamics model.

Hones, E. W., Jr.↗
NASA NTRS2017

Observations of Deep Ionospheric F-Region Density Depletions with FPMU Instrumentation and their Relationship with the Global Dynamics of the June 22-23, 2015 Geomagnetic Storm

The magnetic storm that commenced on June 22, 2015 was one of the largest storms in the current solar cycle, resulting from an active region on the Sun that produced numerous coronal mass ejections (CMEs) and associated interplanetary shock waves. On June 22 at 18:36 UT the magnetosphere was impacted by the leading-edge shock wave and a sheath carrying a large and highly variable interplanetary magnetic field (IMF) Bz with values ranging from +25 to -40 nT. During the subsequent interval from 0000 to 0800 UT, there was a second intensification of the geomagnetic storm resulting from the impact of the CME. We present dramatic responses of simultaneous particle measurements from the high-altitude Magnetospheric Multiscale Mission (MMS) at high altitudes in the magnetosphere (approx. 9-12 Re) and from the low-altitude (F-region) Floating Potential Measurement Unit (FPMU) on board the International Space Station (ISS). We analyze potential causes of these dramatic particle flux dropouts by putting them in the context of storm-time electrodynamics, and support our results with numerical simulations of the global magnetosphere and ionosphere. During the sheath phase of the storm, the MMS spacecraft in the near-earth equatorial plane observed a rapid reconfiguration of the magnetic field near 1923 UT. Initially in the warm plasmasheet, particle flux dropouts were observed as they tracked the plasma-sheet to lobe transitions with the stretching and thinning of the plasmasheet. Anti-sunward flowing O+ ions of ionospheric origin were also measured during this period, confirming that the MMS spacecraft temporarily was in a lobe.

Coffey, Victoria↗
NASA NTRS2005

Investigation of the Dynamics of Coherent Structure, BBF, and Intermittent Turbulence in Earth's Magnetotail: A Study of Complexity in Nonlinear Space Plasmas

We have achieved all the goals stated in our grant proposal. Specifically, these include: 1. The understanding of the complexity induced nonlinear spatiotemporal coherent structures and the coexisting propagating modes. 2. The understanding of the intermittent turbulence and energization process of the observed Bursty Bulk Flows (BBF's) in the Earth s magnetotail. 3. The development of "anisotropic three-dimensional complexity" in the plasma sheet due to localized merging and interactions of the magnetic coherent structures. 4. The study of fluctuation-induced nonlinear instabilities and their role in the reconfiguration of magnetic topologies in the magnetotail based on the concepts of the dynamic renormalization group. 5. The acceleration of ions due to the intermittent turbulence of propagating and nonpropagating fluctuations. In the following, we include lists of our published papers, invited talks, and professional activities. A detailed description of our accomplished research results is given..

Chang, Tom↗
NASA NTRS1995

Average motion, structure and orientation of the distant magnetotail determined from remote sensing of the edge of the plasma sheet boundary layer with E greater than 35 keV ions

We study gradients of the energetic ion intesity observed at the edge of the plasma sheet boundary layer (PSBL) by the energetic ion anisotropy spectrometer (EPAS) on International Sun Earth Explorer 3 (ISEE 3). In particular, we have determined the velocity of the boundary relative to the spacecraft in the direction perpendicular to the tail axis and the angle which the boundary normal makes to the spacecraft spin axis for 1160 PSBL encounters at X(sub GSM) greater than -240 R(sub E). By asuming that, on average, the edge of the PSBL is parallel to the cross-tail current sheet, we are then able to determine a number of properties of the structure, orientation and motion of the deep geomagnetic tail. We conclude the following: (1) Most crossings of the edge of the PSBL are caused by transverse motuion of the entire tail induced by solar wind direction variations, although some are caused by reconfiguration of the tail due to geomagnetic activity. (2) The typical velocity of the PSBL (and hence of the tail) in the direction perpendicular to the tail axis is 50-85 km/s. (3) The average twist of the tail is near zero, with the edge of the PSBL (and by inference the cross-tail current sheet) lying parallel to the ecliptic plane (however, large twists are found in individual events and the distribution of twists is broad, with one standard deviation of approximately 50 deg. (4) The width of the distribution decreases with downtail distance. (5) The variation of the distributions with cross-tail position reveals that this decreas in width is most likely due to the edge of the PSBL being concave, or significantly flared at the tail flanks, in the near-Earth region. (6) During days on which the Interplanetary Magnetic Field (IMF) has 'away' sector structure, the north lobe of the trail is twisted on average towards dawn by 7.0 +/-2.4 deg. (7) During days on which the IMF has 'toward' sector structure, the north lobe is tilted towards duskby 3.8 +/- 2.3. (8) A subset of events for which IMP 8 solar wind data are available show that, for southward IMF BH(sub z) the tail has a mean twist of -12.3 +/- 5.0 deg for IMF B(sub Y) greater than 0 and 5.5 +/- 3.8 deg for IMF B(sub Y) less than 0 (positive twist angles correspond to a tilt of the northern lobe towards dusk). (9) For northward IMF B(sub z) the tail has a twist of -23.9 +/- 5.0 deg for IMF B(sub Y) greater than 0 and 13.4 +/- 6.0 deg for IMF B(sub y) less than 0. Hence the tail appears more twisted on average for the IMF B(sub Z) northward case. (10) The distribution of tail twist is wider for lower levels of geomagnetic activity, indicating that the tail is able to twist more at lower levels of activity. (11) The data set reveals no evident effect of the earth's dipole wobble; tail orientation appears to be controlled by the solar wind and IMF, such that the GSE coordinate system may be appropriate for the study of field and plasma structures in the distant tail region.

Owen, C. J.↗
NASA NTRS1993

Structured plasma sheet thinning observed by Galileo and 1984-129

On December 8, 1990, the Galileo spacecraft used the Earth for a gravity assist on its way to Jupiter. Its trajectory was such that it crossed geosynchronous orbit at approximately local midnight between 1900 and 2000 UT. At the same time, spacecraft 1984-129 was also located at geosynchronous orbit near local midnight. Several flux dropout events were observed when the two spacecraft were in the near-Earth plasma sheet in the same local time sector. Flux dropout events are associated with plasma sheet thinning in the near-profile of the near-Earth plasma sheet while 1984-129 provided an azimuthal profile. With measurements from these two spacecraft we can distinguish between spatial structures and temporal change. Our observations confirm that the geosynchronous flux dropout events are consistent with plasma sheet thinning which changes the spacecraft's magnetic connection from the trapping region to the more distant plasma sheet. However, for this period, thinning occurred on two spatial and temporal scales. The geosynchronous dropouts were highly localized phenomena of 30 min duration superimposed on a more global reconfiguration of the tail lasting approximately 4 hours.

Reeves, G. D.↗
NASA NTRS1975

Substorm-associated reconfiguration of the dusk side equatorial magnetosphere - A possible source mechanism for isolated plasma regions

A rapid reconfiguration of the dusk side magnetosphere was observed near the magnetic equator by particle and field experiments aboard Explorer 45 at 1715 UT on June 17, 1972. Following the onset of an 800-gamma negative bay in the auroral zone, Explorer 45, inbound at 1700 MLT and L about 5, observed a sharp dropout of outer zone electrons. Simultaneously, the plasma density dropped from a level typical of the plasmasphere to one typical of the ion trough, and plasma sheet proton fluxes increased, producing a 100-gamma depression in B, in a shift to a taillike configuration. Outer zone electrons with pitch angles near 45 deg returned with delay times consistent with injection near midnight at the time of dropout and eastward drift to the dusk meridian. Approximately 45 min after the reconfiguration, the satellite reentered the plasmasphere, and the electron fluxes returned to previous levels. In the next orbit, approximately 6 hours later, a region of isolated plasma was detected near apogee at 1400 MLT. There is therefore circumstantial evidence that the type of magnetospheric reconfiguration observed here is responsible for the detachment of regions of cold plasma from the plasmasphere.

Barfield, J. N.↗
NASA NTRS1990

Cleft contribution to ring current formation

The storm time transport of ionospheric plasma from the 'cleft fountain' to the plasma sheet and ring current is investigated by means of three-dimensional trajectory codes. Using observations to define the source location and flow rate, test particles are traced during a 'taillike' to 'dipolelike' reconfiguration of the geomagnetic field. Emphasis is placed on the behavior of heavy ions of low charge state, O(+). As a result of their long periods of gyration, these ions are highly sensitive to rapid field variations and possibly display transient nonadiabatic motions. It is demonstrated that O(+) which have originated in the high-latitude ionosphere but which find themselves in the vicinity of the equator at substorm onset can experience considerable energization (from several keV up to several hundred keV) and pitch angle increase leading to trapping, as an effect of the induced electric field.

Delcourt, D. C.↗
NASA NTRS1986

Multipurpose Scribing and Drawing Tool

Two-part tool reconfigured for variety of jobs. Tool performs several functions useful in layout. Lines, curves, and angles made visible as either bright scribe marks or as dark pencil (or ink) marks. Multipurpose tool speeds up laying out of patterns on sheet metal, wood, plastic, or paper. Tool is carried in pocket, then quickly assembled for service as height gauge, pair of dividers, protractor, surface gauge, or square.

Ellis, J. M.↗