SEARCH · Search NASA

Results for “EARTH MAGNETOSPHERE”

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 649 records · Page 36

All sources NASA NTRS DOE OSTI

NASA NTRS1989

Relativistic electrons at geosynchronous orbit, interplanetary electron flux, and the 13-month Jovian synodic year

Results are reported from a search to determine the correlation, if any, between the temporal behaviors of 0.2-7 MeV or higher electrons at GEO (6.6 earth radii) and 6-10 MeV electrons in the interplanetary region near earth at the period of the Jovian synodic year (about 13 months). The 13-month intensity variation results from the synodic interplanetary magnetic field conection of earth to Jupiter. Direct compariosn of intensity-time flux profiles for the years 1976-1984, about 7 synodic Jovian electron seasons, shows that the intensity envelope of peak electron flux at GEO does not appear to be correlated to the observed 13 month intensity envelope of relativistic electron flux in the interplanetary region near earth. A persistent 13-month variation of GEO flux is not obvious, thus indicating that the intensity of electron flux at GEO is not directly and soley related to the intensity of Jovian electron flux near earth. It is concluded that dynamic erergization and redistribution processes in earth's magnetosphere must be invoked to produce the intensity variations of relativistic electron flux at GEO and not interplanetary magnetic field connection to Jupiter.

Christon, S. P.↗

NASA NTRS1990

Observation of the Z mode with DE 1 and its analysis by three-dimensional ray tracing

Certain Z-mode wave emissions in the earth's magnetosphere have been identified using the wave spectra and polarization measurements of the DE 1 satellite. Although such emissions accompany the aurora, and thus presumably originate from the evening-sector auroral zone, they are found to occur over much wider ranges of latitude and longitude. Since the predicted cyclotron maser emission at the cyclotron frequency could not have produced waves which travel such great distances, as shown by three-dimensional ray tracing, it is proposed instead that these emissions must originate from lower altitudes within the auroral zone and probably from near the plasma frequency inside the auroral plasma cavity.

Hashimoto, Kozo↗

NASA NTRS1990

Plasma fluctuations in the magnetosheath downstream from Uranus

The Voyager plasma experiment observed large-amplitude plasma fluctuations in the Uranian magnetosheat downstream from the planet. This is a region that has not been well sampled in the earth's magnetosphere. These waves have periods of tens of minutes, are characterized by an anticorrelation between the plasma density and temperature, and are associated with deflections in the flow angle of the plasma. These fluctuations are observed only in regions where the magnetic field is rapidly varying. These waves have time and distance scales placing them in the MHD regime, but their characteristics are not compatible with any known solution of the MHD equations. It is suggested that these fluctuations are produced by the solar wind interaction with the magnetosphere at the bow shock, but the physics governing the production and propagation of these fluctuations is not understood.

Richardson, John D.↗

NASA NTRS1990

Space sciences - Keynote address

The present status and projected future developments of the NASA Space Science and Applications Program are addressed. Emphasis is given to biochemistry experiments that are planned for the Space Station. Projects for the late 1990s which will study the sun, the earth's magnetosphere, and the geosphere are briefly discussed.

Alexander, Joseph K.↗

NASA NTRS1989

Discrete electromagnetic emissions in planetary magnetospheres

The present state of knowledge and observations of discrete electromagnetic emissions detected in the magnetospheres of earth and the outer planets are reviewed. The history of ground observations and satellite observations is included. Active experiments studying wave propagation, wave-wave and wave-particle interactions, and the generation and triggering of discrete emissions are addressed. The various theories proposed to explain the phenomena are examined, and computer simulations of wave-particle interactions and the generation and triggering of discrete emissions are reviewed. Related phenomena observed at frequencies above both the electron cyclotron frequency and the plasma frequency are considered. Areas of future investigation are discussed.

Anderson, Roger R.↗

NASA NTRS1990

Linear prediction filter analysis of relativistic electron properties at 6.6 R(E)

The relationship between relativistic electron flux variations at 6.6 R(E) and various published indices and solar wind properties is studied. An attempt is made to characterize the temporal and dimensional relationships between solar wind or magnetic indices and electron flux enhancements. It is shown that the solar wind speed upstream of the earth's magnetosphere is correlated with large increases in the flux of highly relativistic electrons at geostationary orbit.

Baker, D. N.↗

NASA NTRS1990

The electron edge of the low latitude boundary layer during accelerated flow events

Magnetosheath plasma entering the earth's magnetosphere to populate the low latitude boundary layer, LLBL, is often accelerated to speeds considerably greater than are observed in the adjacent magnetosheath. Measurements made during such accelerated flow events reveal separate electron and ion edges to the LLBL, with the electron edge being found earthward of the ion edge. Plasma electron velocity distributions observed at the earthward edge of the LLBL are often highly structured, exhibiting large asymmetries parallel and antiparallel, as well as perpendicular, to the local magnetic field. These features can consistently be interpreted as time-of-flight effects on recently reconnected field lines, and thus are strong evidence in support of the reconnection interpretation of accelerated plasma flow events.

Gosling, J. T.↗

NASA NTRS1990

Interaction of space radiation with matter

The physical interactions of high-energy space radiations with bulk matter are described with particular emphasis on the nuclear and electromagnetic interactions of solar and galactic cosmic rays. Methods of incorporating these interactions into radiation transport models which accurately describe the propagation of the incident cosmic rays and their subsequent-generation reaction products are also explained. Representative results for solar and galactic cosmic ray doses and dose equivalents are presented for various aluminum and water absorber depths. For the first time, the main contributions to human exposure in space from galactic cosmic rays will be presented on a component by component basis, including a breakdown of the dose-equivalent contributions into primary ions, heavy fragments, alpha particles, neutrons, and protons. For the galactic cosmic ray environment outside of the earth's magnetosphere, over 70 percent of the total dose equivalent results from only seven nuclear species (hydrogen, helium, carbon, oxygen, silicon, magnesium, and iron ions). Of these, the largest single contributor is cosmic ray iron and its secondaries, which account for nearly one-fourth of the unshielded total dose equivalent during solar minimum.

Townsend, L. W.↗

NASA NTRS1990

The HZE radiation problem

Radiation-exposure limits have yet to be established for missions envisioned in the framework of the Space Exploration Initiative. The radiation threat outside the earth's magnetosphere encompasses protons from solar particle events and the highly charged energetic particles constituting galactic cosmic rays; radiation biology entails careful consideration of the extremely nonuniform patterns of such particles' energy deposition. The ability to project such biological consequences of exposure to energetic particles as carcinogenicity currently involves great uncertainties from: (1) different regions of space; (2) the effects of spacecraft structures; and (3) the dose-effect relationships of single traversals of energetic particles.

Schimmerling, Walter↗

NASA NTRS1991

Interplanetary crew exposure estimates for the August 1972 and October 1989 solar particle events

Detailed exposure estimates for the bone marrow, ocular lens, and skin of astronauts on manned missions beyond the earth's magnetosphere have been made for the large solar particle events (SPE) of August 1972 and October 1989. The estimates were made using the coupled neutron-proton space radiation transport computer code BRYNTRN and the CAM model for the human body. It is found that at least 10 g/sq cm aluminum shielding is needed to keep estimated dose equivalent values below current space radiation exposure guidelines recommended for LEO missions. Space suits currently being designed will not provide adequate crew protection and may not even ensure crew survival in the event of exposure to a large SPE during extravehicular activity.

Townsend, Lawrence W.↗

NASA NTRS1991

Magnetic field-aligned electric potentials in nonideal plasma flows

The electric field component parallel to the magnetic field arising from plasma flows which violate the frozen-in field condition of ideal magnetohydrodynamics is discussed. The quantity of interest is the potential U = integral E parallel ds where the integral is extended along field lines. It is shown that U can be directly related to magnetic field properties, expressed by Euler potentials, even when time-dependence is included. These results are applicable to earth's magnetosphere, to solar flares, to aligned-rotator models of compact objects, and to galactic rotation. On the basis of order-of-magnitude estimates, these results support the view that parallel electric fields associated with nonideal plasma flows might play an important role in cosmic particle acceleration.

Schindler, K.↗

NASA NTRS1991

Theory and simulation of a high-frequency magnetic drift wave

The equilibrium of a nonneutral plasma in a toroidal vessel with a toroidal magnetic field is analyzed. In the zero inertia limit it is heuristically shown from force balance considerations that there is an electrostatic hoop force and a force due to diamagnetism along the major radius. The problem of equilibrium is formulated in terms of solutions of a 2D partial difference equation. This equation is solved in the large-aspect-ratio limit and a general expression for the shift of the potential axis is obtained which shows that the shift is approximately epsilon and that it depends solely on the internal capacitance of the cloud. The simulation study is based upon the modified MHD equations and the nonlocal nature of the mode is investigated. Applications to sub-Alfvenic plasma expansions, electromagnetic waves in the earth's magnetosphere, and plasma switches are discussed.

Huba, J. D.↗

NASA NTRS1992

Observed currents on the earth's high-latitude magnetopause

A survey of electrical currents of the earth's magnetosphere, principally at high latitudes, as inferred from magnetic vector data acquired by the Hawkeye 1 satellite, is reported. A total of 536 candidate crossings of the magnetopause were examined. A reduced data set of 139 selected cases was analyzed in detail though solar wind dynamic pressure data were available for only 117 of these cases. Inferred values of the lineal current densities on the magnetopause are in the range 5.5 to 157.5 mA/m over a wide range of solar wind dynamic pressure from 1.17 to 16.1 nPa. The apparent normal thickness of the magnetopause current sheet ranges from 30 to 850 km with mean and median values of 185 and 158 km, respectively. It is argued that the radial rate of motion of the magnetopause is of the order of 2 km/s and hence that its true thickness is of similar magnitude. The relationship of these results to models of the geomagnetic field and to other related work is discussed.

Van Allen, J. A.↗

NASA NTRS1992

The solar wind interaction with Venus

The Pioneer Venus Orbiter (PVO) mission has played a key role in establishing the nature of the solar wind interaction with Venus. Although earlier probes had determined that Venus presented an obstacle much smaller than the size of earth's magnetosphere to the solar wind, they did not carry out in situ measurements pertaining to solar wind interaction studies at low enough altitudes to determine why. They also did not provide datasets of sufficient duration to study the variability of the interaction of both short (one day) and long (solar cycle) timescales. The first 600 of the nearly 5000 orbits of PVO magnetometer data have been used to determine a very low upper limit on the intrinsic dipolar magnetic moment of Venus. The consequence of that low magnetic moment is that the solar wind interacts directly with the upper atmosphere and ionosphere. Relative to a dipolar field obstacle, the ionospheric obstacle is rather incompressible. A bow shock is observed to stand in front of the nearly Venus-sized ionospheric obstacle at a comparatively steady subsolar altitude of approximately 1.5 R(v) (Venus radii). This shock decelerates the supersonic solar wind plasma so that it can flow around the obstacle. It was found to change its average position in the terminator plane from about 2.4 R(v) to 2.1 R(v) as the solar cycle progressed from the 1978 orbit insertion near solar maximum through the 1986-87 solar minimum, and back again during the latest solar activity increase. Between the bow shock and the ionosphere proper, the slowed solar wind plasma flow diverges near the subsolar point and makes its way across the terminator where it reaccelerates and continues anti-Sunward. The solar wind magnetic field, which is in effect frozen into the flowing plasma, is distorted in this 'magnetosheath' region so that it appears to hang up or drape over the dayside ionosphere before it slips around with the flow. These features of the solar wind interaction are also seen when the obstacle is a dipole magnetic field, but there are two important distinctions. In the wake of the Venus obstacle one finds an induced magnetic tail composed of varying interplanetary fields rather than the constant fields of intrinsic origin. This magnetotail is further seen to be populated by Heavy (0+) ions that are evidently escaping from the planet at significant (approximately 10(exp -25) s(exp -1)) rates. These heavy ions are also observed in the dayside magnetosheath. The interpretation is that ions are produced by both photoionization and solar wind electron impact ionization of the upper neutral atmosphere that extends into the magnetosheath.

Luthmann, J. G.↗

NASA NTRS1992

Transfer Orbit Plasma Interaction Experiment (TROPIX)

Viewgraphs on the Transfer Orbit Plasma Interaction Experiment (TROPIX) are presented. Objectives of this research are (1) to map the charged particles in Earth's magnetosphere from LEO to GEO at high inclinations; (2) to measure plasma current collection and resulting shifts in vehicle electrical potential from LEO to GEO across range of orbital inclinations; (3) to study spacecraft interaction with plasma environment using solar electric propulsion (SEP) thrusters as plasma contactors; (4) to measure array degradation over mission duration; (5) to evaluate the potential of various microelectronics, spacecraft components, and instruments for future space missions; and (6) to demonstrate SEP technology applied to a flight vehicle. An overview of TROPIX is presented.

Hickman, Mark↗

NASA NTRS1992

Pc3 activity at low geomagnetic latitudes - A comparison with solar wind observations

On an hourly time-scale the different roles of the solar wind and interplanetary magnetic field (IMF) parameters on ground micropulsation activity can be better investigated than at longer time-scales. A long-term comparison between ground measurements made at L'Aquila and IMP 8 observations confirms the solar wind speed as the key parameter for the onset of pulsations even at low latitudes, although additional control of the energy transfer from the interplanetary medium to the earth's magnetosphere is clearly exerted by the cone angle. Above about 20 mHz the frequency of pulsations is confirmed to be closely related to the IMF magnitude while, in agreement with model predictions, the IMF magnitude is related to the amplitude of the local fundamental resonant mode. We provide an interesting example in which high resolution measurements simultaneously obtained in the foreshock region and on the ground show that external transversal fluctuations do not penetrate deep into the low latitude magnetosphere.

Villante, U.↗

NASA NTRS1992

Chemical-release mission of CRRES

The CRRES satellite was a dual-mission spacecraft to perform active experiments in the Earth's magnetosphere and ionosphere and to study the natural space environment and its effects on spacecraft electronics. The NASA chemical-release mission experiments were motivated by the need to address scientific questions in the areas of coupling between the ionosphere and magnetosphere, response of the magnetosphere system to injections of artificial ion clouds, and instabilities and structuring of the ionosphere in response to perturbations. The initial science results from the chemical-release experiments performed to date are (1) demonstration of critical velocity ionization over a narrow range of parameter space; (2) production of diamagnetic cavities by barium and lithium releases over a wide range of parameters; (3) demonstration of the chemical-release technique to study magnetosphere-ionosphere coupling; (4) modification of energetic electron distribution functions with barium injections; (5) stimulation of magnetospheric waves with barium injections; and (6) possible inducement of enhanced auroral activity.

Reasoner, David L.↗

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.↗