Engineering topics

Krimigis, S. M.

Publications and source records attributed to Krimigis, S. M..

At least 55 records · Page 3

NASA NTRS1989

Interplanetary energetic particle observations of the March 1989 events

The IMP-8 spacecraft placed in an elongated orbit of approximately R(sub E) x R(sub E) orbit around the Earth was the only monitor of the energetic particle environment of the near interplanetary space during the period of the solar particle events associated with the Active Region 5395 in March 1989. Measurements of energetic ion and electron intensities were obtained in a series of channels within the energy range: 0.3 to 440 MeV for photons, 0.6 to 52 MeV/nuc for alpha particles, 0.7 to 3.3 MeV/nuc for nuclei with Z greater than or equal to 3, 3 to 9 MeV/nuc with Z greater than or equal to 20, and 0.2 to 2.5 MeV for electrons. The responses of selected energy channels during the period 5 to 23 March 1989 are displayed. It is clearly noted that the most prominent energetic ion intensity enhancements in that time interval were associated with the interplanetary shock wave of March 13 (07:42 UT) as well as that of March 8 (17:56 UT), which have distinct particle acceleration signatures. These shock waves play a major role in determining the near Earth energetic ion intensities during the above period by accelerating and modulating the ambient solar energetic particle population, which was already present in high intensities in the interplanetary medium due to the superposition of a series of solar flare particle events originating in AR 5395. The differential ion intensities at the lowest energy channel of the CPME experiment, which were associated with the March 13 shock wave, reached the highest level in the life of the IMP-8 spacecraft at this energy. At high energies, the shock associated intensity peak was smaller by less than a factor of 3 than the maxima of solar flare particle intensities from some other major flares, in particular from those with sites well connected to the Earth's magnetic flux tubes.

Sarris, E. T.↗

NASA NTRS1989

The Advanced Composition Explorer

The Advanced Composition Explorer (ACE) was recently selected as one of two new Explorer-class missions to be developed for launch during the mid-1990's. ACE will observe particles of solar, interplanetary, interstellar, and galactic origins, spanning the energy range from that of the solar wind (approx. 1 keV/nucleon) to galactic cosmic ray energies (several hundred MeV/nucleon). Definitive studies will be made of the abundance of nearly all isotopes from H to Zn (1 less than or = Z less than or = 30), with exploratory isotope studies extending to Zr (Z = 40). To accomplish this, the ACE payload includes six high-resolution spectrometers, each designed to provide the optimum charge, mass, or charge-state resolution in its particular energy range, and each having a geometry factor optimized for the expected flux levels, so as to provide a collecting power a factor of 10 to 1000 times greater than previous or planned experiments. The payload also includes several instruments of standard design that will monitor solar wind and magnetic field conditions and energetic H, He, and electron fluxes. The scientific objectives, instrumentation, spacecraft, and mission approach that were defined for ACE during the Phase-A study period are summarized.

Stone, E. C.↗

NASA NTRS1988

Simultaneous energetic particle observations at geostationary orbit and in the upstream solar wind - Evidence for leakage during the magnetospheric compression event of November 1, 1984

The issue of accelertion and transport of particles in the upstream solar wind was investigated using the energetic ion and electron observations obtained simultaneously by three fortuitously positioned geostationary spececraft during a strong magnetospheric compression event of November 1, 1984. This compression event brought the subsolar magnetopause inward of the synchronous orbit. Data obtained indicate that, in the November 1 event, the process of magnetospheric ion escape was a very likely source for energetic particles both in the magnetosheath and the upstream solar wind.

Baker, D. N.↗

NASA NTRS1988

The magnetosphere as a sufficient source for upstream ions on November 1, 1984

The source of energetic particles in two upstream events which occurred during the great magnetospheric compression of November 1, 1984 were investigated. Ten tests, which could distinguish between the Fermi and the leakage sources for upstream diffuse ion events, were applied to simultaneous magnetospheric, magnetosheath, and upstream energetic particle observations obtained during the November-1 upstream events by several spacecraft. Results showed that magnetospheric leakage satisfactorily explains these observations, while in situ Fermi acceleration does not. It is concluded that, during these two events, magnetospheric leakage was a sufficient source for upstream particles.

Sibeck, D. G.↗

NASA NTRS1988

A case study of magnetotail current sheet disruption and diversion

On June 1, 1985 the AMPTE/CCE spacecraft (at a geocentric distance of about 8.8 earth radii at the midnight neutral sheet region) observed a dispersionless energetic particle injection and an increase in magnetic field magnitude, which are features commonly attributed to disruption of the near-earth cross-tail current sheet during substorm expansion onsets. An analysis based on high time-resolution measurements from the magnetometer and the energetic particle detector indicates that the current sheet disruption region exhibited localized (less than 1 earth radius) and transient (less than 1 min) particle intensity enhancements, accompanied by complex magnetic field changes with occasional development of a southward magnetic field component. Similar features are seen in other current disruption/diversion events observed by the CCE. The present analysis suggests that the current disruption region is quite turbulent, similar to laboratory experiments on current sheet disruption, with signatures unlike those expected from an X-type neutral line configuration. No clear indication of periodicity in any magnetic field parameter is discernible for this current disruption event.

Lui, A. T. Y.↗

NASA NTRS1988

Observational test of shock drift and Fermi acceleration on a seed particle population upstream of earth's bow shock

The efficiency of proposed shock acceleration mechanisms as they operate at the bow shock in the presence of a seed energetic particle population was examined using data from simultaneous observations of energetic solar-origin protons, carried out by the IMP 7 and 8 spacecraft in the vicinity of the quasi-parallel (dawn) and quasi-perpendicular (dusk) regions of the earth's bow shock, respectively. The results of observations (which include acceleration effects in the intensities of the energetic protons with energies as high as 4 MeV observed at the vicinity of the dusk bow shock, but no evidence for any particle acceleration at the energy equal to or above 50 keV at the dawn side of the bow shock) indicate that the acceleration of a seed particle population occurs only at the quasi-perpendicular bow shock through shock drift acceleration and that the major source of observed upstream ion populations is the leakage of magnetospheric ions of energies not less than 50 keV, rather than in situ acceleration.

Anagnostopoulos, G. C.↗

NASA NTRS1988

In situ acceleration and gradients of charged particles in the outer solar system observed by the Voyager spacecraft

Observations of interplanetary acceleration events from about 1 to about 25 AU are presented. It is shown that shock structures have a profound effect on high energy (greater than or equal to 70 MeV) cosmic rays, especially during solar minimum, when a negative latitudinal gradient was observed after early 1985 at all energies from about 70 MeV down to about 30 keV. The observations suggest that local acceleration to a few hundred MeV, and as high as a few GeV, is continually present throughout the heliosphere.

Krimigis, S. M.↗

NASA NTRS1988

Upstream energetic ions under radial IMF - A critical test of the Fermi model

Eight years of interplanetary magnetic field (IMF) and energetic particle observations obtained by the IMP-8 spacecraft upstream from the bow shock have been surveyed, and 63 cases when the upstream IMF remained radial for extended periods of time (greater than 1 hour) have been accumulated. Of these, two cases have been selected during which measurable fluxes of ambient solar or corotating energetic particle events were absent. These conditions provide an excellent test to the theories of the origin of upstream energetic ions. It is shown that there are extended periods with radial IMF when no upstream energetic ions were detected. It is further shown that energetic ions in the range E of between 50 keV and 1 MeV, inclusive, are not continuously present but appear in bursts of intensities varying by more than an order of magnitude under persistently radial IMF. These measurements contradict a fundamental prediction of the Fermi mechanism for the origin of the upstream energetic ions, namely that such ions should always be present on radial IMF lines. The observations are consistent with the hypothesis that energetic (greater than about 50 keV) ions leak out from, and appear in the upstream medium sporadically, following the onset of magnetic activity within the magnetosphere.

Sarris, E. T.↗

NASA NTRS1988

Observations of energetic ion enhancements and fast neutrals upstream and downstream of Uranus' bow shock by the Voyager 2 spacecraft

Measurements of energetic ions and electrons upstream and downstream from Uranus obtained during the low energy charged particle experiment on Voyager 2 are discussed. The results indicate that energetic ions were present upstream of Uranus' bow shock and that their charcteristics, in terms of anisotropies and energy spectra, are consistent with an Uranian magnetospheric origin and are inconsistent with predictions of in situ acceleration via the Fermi mechanism. An upper limit to the flux of energetic neutrals escaping the magnetosphere is established, and the volume-averaged neutral hydrogen density inside 5 Uranian radii is constrained.

Krimigis, S. M.↗

NASA NTRS1988

The latitude and radial dependence of shock acceleration in the heliosphere

Voyager 1 and 2 observations of ions accelerated at corotating shocks within about 13-28 AU are discussed. The ion spectra extend smoothly from at least 30 keV to an energy above about 3 MeV. However, these spectra are falling steeply at the other end. The event-avaraged energy spectra during 1984 are similar for both Voyagers, and the event-averaged spectra at Voyager 2 are of similar form both before and after the flux decrease in early 1985. The event-averaged intensities of about 1 MeV protons exhibit an about -3 percent per degree gradient before and after the early 1985 intensity decrease. The significance of these observations for interpreting the shock acceleration is addressed.

Gold, R. E.↗

NASA NTRS1988

The sun and the sun-earth connection

A discussion is presented of the elements comprising the field of solar-system space physics: the sun; the interplanetary medium; and the magnetosphere, ionosphere, and upper atmosphere of the earth and, to a leser extent, the planets. The principal entities in the interaction chain beginning at the center of the sun and extending through the interplanetary medium to earth's magnetosphere, ionosphere, and upper atmosphere are described with particular emphasis on solar variability and its manifestation in dynamical changes of the earth's environment. Solar variations range in time scales from less than 1 sec to over a century and can affect specific regions at earth within 8 min (solar X-ray bursts) and up to several decades (climatic variations).

Krimigis, S. M.↗

NASA NTRS1987

Effects of charged particles on the surfaces of the satellites of Uranus

Measurements of the ion and electron fluxes in the Uranian magnetosphere made by the low-energy charged-particle (LECP) instrument on the Voyager 2 spacecraft are used to discuss possible particle-induced modifications of the moons and rings of Uranus. The energy spectra of the orbit-integrated particle dosages expected on the major moons are derived from the LECP measurements of particle intensities and pitch-angle distributions. Laboratory-derived results on charged-particle-induced chemical and physical modifications of H2O, CH4, CO, and CO2 ions are used. The erosion rates of water ice and the darkening of organic ices on the surfaces of the moons are estimated from the orbit-integrated fluxes. Significant darkening of fresh organic ices to depths of the order of 1 micron is expected to occur for times as short as a few thousand years. Darkening at deeper depths will occur at increasingly longer times. The implications of these results for the interpretation of remote-sensing data are discussed.

Lanzerotti, L. J.↗

NASA NTRS1987

Whistler mode emissions in the Uranian radiation belts

Voyager 2 detected intense whistler mode emissions and fluxes of energetic electrons during the outbound pass through the region of auroral L shells. The observed energetic (E greater than 22 keV) electron distribution, a model warm (E less than 27.5 keV) electron distribution, and the cold plasma density profile deduced by Kurth et al. (1987) are used to calculate the ray path-integrated spatial amplification of whistlers which arrive at Voyager 2 from the magnetic equator. By matching the calculated amplification and the relative gains at different frequencies deduced from the observed whistler power spectrum, the pitch angle anisotropy parameters of the electron distributions are determined to within a fairly narrow range of values. The estimated bounce average pitch angle diffusion coefficient indicates that electrons are on strong diffusion over a wide range in energies. The electron precipitation energy flux is sufficient to produce the observed auroral light emissions.

Coroniti, F. V.↗

NASA NTRS1987

The hot plasma and radiation environment of the Uranian magnetosphere

A detailed account is given of the results of the Voyager 2 low-energy charged particle investigation of the Uranian magnetosphere. Data show that the encounter of the inbound bow shock was immediately preceded by intense upstream proton events characterized by bulk streaming pointing approximately tangentially to the magnetospheric boundaries. Observations are presented which suggest that substorm processes analogous to those occurring within the earth's magnetotail are occurring within the Uranian magnetotail.

Mauk, B. H.↗

NASA NTRS1987

Energetic ion and electron phase space densities in the magnetosphere of Uranus

Proton and electron phase space density profiles are constructed from an analysis of Voyager 2 low-energy charged particle data from the magnetosphere of Uranus. The Uranus proton profiles reveal an approximately exponential decline with decreasing radius for L less than about 9 in a relatively dense thermal plasma region with intense plasma wave activity. Among the distributed loss mechanisms at Uranus are satellite sweeping, wave-particle interactions, and charge exchange of protons with an extended hydrogen corona.

Cheng, Andrew F.↗

NASA NTRS1987

Magnetic field drift shell splitting - Cause of unusual dayside particle pitch angle distributions during storms and substorms

This paper presents a magnetic field drift shell-splitting model for the unusual butterfly and head-and-shoulder energetic (E greater than 25 keV) particle pitch angle distributions (PADs) which appear deep within the dayside magnetosphere during the course of storms and substorms. Drift shell splitting separates the high and low pitch angle particles in nightside injections as they move to the dayside magnetosphere, so that the higher pitch angle particles move radially away from earth. Consequently, butterfly PADs with a surplus of low pitch angle particles form on the inner edge of the injection, but head-and-shoulder PADs with a surplus of high pitch angle particles form on the outer edge. A similar process removes high pitch angle particles from the inner dayside magnetosphere during storms, leaving the remaining lower pitch angle particles to form butterfly PADs on the inner edge of the ring current. A detailed case and statistical study of Charge Composition Explorer/Medium-energy Particle Analyzer observations, as well as a review of previous work, shows most examples of unusual PADs to be consistent with the model.

Sibeck, D. G.↗

NASA NTRS1987

Simultaneous measurements of energetic ion (50 keV and above) and electron (220 keV and above) activity upstream of earth's bow shock and inside the plasma sheet - Magnetospheric source for the November 3 and December 3, 1977 upstream events

Simultaneous observations of energetic ions and electrons by the IMP 7 and 8 spacecraft are used here to separate temporal variations from spatial variations during the upstream ion events observed on December 3, 1977 and November 2-3, 1977, in order to determine the source of these particles. Analysis of the observations and comparison with theory shows that: (1) for each of the observed upstream enhancements, energetic ions and electrons were simultaneously present inside the plasma sheet; (2) the low-energy ion intensity profile inside the plasma sheet was relatively flat, while at higher energies there was considrable variability; (3) relativistic electron bursts were seen inside the plasma sheet and also upstream of the shock but at substantially reduced intensities; (4) the ion energy spectrum for the December 3 event, extended to energies of about 2 MeV, was identical in form with the plasma sheet and upstream of the shock; (5) ion anisotropies exhibited typically large dawn-dusk or dusk-dawn gradients and large field-aligned streaming away from the bow shock.

Sarris, E. T.↗

NASA NTRS1987

Energetic magnetospheric ions at the dayside magnetopause - Leakage or merging?

The leakage model for the escape of energetic magnetospheric particles into the magnetosheath is described, making comparisons with the merging model where possible. Reported observations of energetic particles at the dayside magnetopause are reexamined, and it is concluded that they do not conclusively support the merging model, either on a case-by-case basis or statistically. New observations made by the Charge Composition Explorer satellite during the Active Magnetospheric Particle Tracer Explorers program are presented. They indicate that magnetospheric ions of all species steadily escape into the magnetosheath and stream away from the magnetopause, regardless of the magnetosheath magnetic field orientation. It is concluded that the leakage model explains both the new and old observations at least as well as, or better than, the merging model.

Sibeck, D. G.↗