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in creator/contributor: "Elphic, R.C."

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Observations of flux transfer events: Are FTEs flux ropes, islands, or surface waves

Flux transfer events (FTEs) are widely regarded as a signature of transient magnetic reconnection between the solar wind and magnetospheric plasmas. However, there is disagreement on what form this reconnection takes: Are FTEs tearing islands, or time-varying single x-line reconnection We reexamine the evidence that first led to the suggestion that FTEs are related to a non-time-stationary reconnection process. In particular we discuss how the combination of field and plasma variations suggest … more

Date: January 1, 1989

Creator: Elphic, R. C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Magnetopause structure and dynamics: Issues for GEM (geospace environment modeling)

Recent multi-spacecraft observations of the magnetopause have allowed us to establish its structure and dynamical behavior. The magnetopause current sheet is thicker than expected, often ten magnetosheath ion gyroradii or more. One very important result has been the confirmation of magnetic reconnection in both its quasi- steady and transient forms. A boundary layer of magnetosheath-like plasma is often, but not always, observed earthward of the magnetopause current layer. There is considerable… more

Date: January 1, 1989

Creator: Elphic, R. C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Sensor fusion and nonlinear prediction for anomalous event detection

The authors consider the problem of using the information from various time series, each one characterizing a different physical quantity, to predict the future state of the system and, based on that information, to detect and classify anomalous events. They stress the application of principal components analysis (PCA) to analyze and combine data from different sensors. They construct both linear and nonlinear predictors. In particular, for linear prediction the authors use the least-mean-squar… more

Date: March 7, 1995

Creator: Hernandez, J. V.; Moore, K. R. & Elphic, R. C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Geosynchronous orbit magnetopause crossings

In this study we extend the analysis of magnetopause crossings observed with Magnetospheric Plasma Analyzer measurements to examine a much larger statistical data set. This study examines 39 maiznetosheath/LLBL intervals from 79 spacecraft-months of observations: these observations were taken from a survey of data from the start of each spacecraft mission and extending through March 1993. In contrast to the previous findings, we find no evidence for a significant dawn/dusk asymmetry in geosynch… more

Date: July 1, 1994

Creator: McComas, D. J.; Elphic, R. C.; Moldwin, M. B. & Thomsen, M. F.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Transport processes in space plasmas

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The project represents a comprehensive research effort to study plasma and field transport processes relevant for solar-terrestrial interaction, involving the solar wind and imbedded magnetic field and plasma structures, the bow shock of the Earth`s magnetosphere and associated waves, the Earth`s magnetopause with imbedded flux rope structures and t… more

Date: August 1, 1997

Creator: Birn, J.; Elphic, R. C. & Feldman, W. C.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Effects of an RTG power source on neutron spectroscopy measurements on the martian surface.

A continuing goal of Mars science is to identify the exact locations of near-surface water and/or hydrated minerals using in situ measurements. Recent data from the Mars Odyssey mission has used both neutron and gamma-ray spectroscopy to measure large amounts of water ice near both polar regions . Furthermore, these data have also determined that in the mid-latitude regions, there likely exist relatively large amounts of hydrogen (-4-7 equivalent H2O wt.%), although it is not certain in which f… more

Date: January 1, 2003

Creator: Lawrence, David J. (David Jeffery),; Elphic, R. C. (Richard C.) & Wiens, R. C. (Roger C.)

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Observations of cold magnetospheric ions at geosynchronous orbit during times of high activity

Flowing, cold magnetospheric ions have been observed in conjunction with geosynchronous orbit magnetopause crossings since the earliest ATS and OGO missions. The authors have reported on the occurrence and convection of low-energy (10-100 eV) ions seen by multiple satellites in association with geosynchronous orbit magnetopause and low-latitude boundary layer (LLBL) encounters. More generally, Los Alamos 3-D plasma instruments observe these ions following storm sudden commencements (SSCs), when… more

Date: October 1, 1994

Creator: Elphic, R. C.; Weiss, L. A.; Thomsen, M. F.; McComas, D. J. & Bame, S. J.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Study of a substorm on May 4, 1986

A substorm on May 4, 1986, midway through the PROMIS campaign of coordinated data acquisition, was uniquely well documented. Both in its aspects at earth and in its magnetotail aspects. The expansive phase onset was imaged by the Viking satellite at 20-second time resolution. Most of the expansive phase was also imaged by DE 1 at 6-minute time resolution. ISEE 1 and 2 were near the tail's axis 18.5 R/sub e/ from earth operating at high data rate and data were recorded by several geosynchronous … more

Date: January 1, 1988

Creator: Hones, E. W.; Craven, J. D.; Frank, L. A.; Galvin, A. B.; Murphree, J. S.; Elphinstone, R. D. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Mapping the elemental composition of the moon: Current results of the Lunar Prospector gamma ray spectrometer

One of the instruments on board the recently launched Lunar Prospector spacecraft is a Gamma-Ray Spectrometer (GRS) designed to map the surface elemental composition of the Moon. Specifically, the objectives of the GRS are to map abundances of Fe, Ti, U, Th, K, Si, O and if possible Mg, Al, and Ca. The GRS consists of a bismuth germanate (BGO) crystal placed within a well shaped borated plastic scintillator anti-coincidence (ACS) shield. Events triggering only the BGO are labeled as accepted ev… more

Date: December 1, 1998

Creator: Lawrence, D. J.; Feldman, W. C.; Barraclough, B. L.; Elphic, R. C.; Binder, A. B. & Maurice, S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The magnetospheric trough

The authors review the history of the concepts of the magnetospheric cold-ion trough and hot-electron trough and conclude that the two regions are actually essentially the same. The magnetospheric trough may be viewed as a temporal state in the evolution of convecting flux tubes. These flux tubes are in contact with the earth`s upper atmosphere which acts both as a sink for precipitating hot plasma sheet electrons and as a source for the cold ionospheric plasma leading to progressive depletion … more

Date: March 4, 1997

Creator: Thomsen, M. F.; McComas, D. J.; Elphic, R. C. & Borovsky, J. E.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Lunar prospector measurements of the distribution of incompatible elements gadolinium, samarium and thorium

Lunar Prospector neutron spectrometer (NS) and gamma ray spectrometer (GRS) observations have been used to map out the distribution of incompatible elements on the lunar surface. Specifically, the GRS data provide maps of the distribution of thorium and potassium while the NS data provide information on the distribution of iron and titanium, and the rare earth elements gadolinium and samarium. Using results of analysis of Celementine spectral reflectance (CSR) data, the Fe- and Ti-contributions… more

Date: April 1, 1999

Creator: Elphic, R. C.; Lawrence, D. J.; Feldman, W. C.; Barraclough, B. L.; Maurice, S.; Binder, A. B. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Delineating the major KREEP-bearing terranes on the moon with global measurements of absolute thorium abundances

The Lunar Prospector (LP) Gamma-Ray Spectrometer (GRS) has been used to map the global composition of thorium on the lunar surface. Previous LP results of relative thorium abundances demonstrated that thorium is highly concentrated in and around the nearside western maria and less so in the South Pole Aitken (SPA) basin. Using new detector modeling results and a larger data set, the authors present here a global map of absolute thorium abundances on a 2{degree} by 2{degree} equal-area pixel sca… more

Date: March 1, 1999

Creator: Lawrence, D. J.; Feldman, W. C.; Barraclough, B. L.; Elphic, R. C.; Prettyman, T. H.; Binder, A. B. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Regional elemental abundances within South Pole-Aitken basin as measured with lunar prospector gamma-ray spectrometer data.

South Pole-Aitken (SPA) basin has been a target of intense study since it is one of the largest impact basins in the solar system. It is thought that SPA basin excavated deep into the lunar crust and possibly even the mantle. Such conclusions have been supported by the observed mafic and thorium composition anomalies seen across the entire basin. One of the major goals of lunar and planetary science has been to measure and understand the composition of the non-mare materials within SPA basin. I… more

Date: January 1, 2003

Creator: Lawrence, David J. (David Jeffery),; Pieters, Carlé M.; Elphic, R. C. (Richard C.); Gasnault, O. M. (Olivier M.); Prettyman, T. H. (Thomas H.) & Feldman, W. C. (William C.)

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

In situ neutron spectroscopy on the martian surface: modeling the hydra instrument for different mission scenarios

Neutron spectroscopy has proven to be highly successful in remotely detecting and measuring the abundance of water on planetary surfaces such as Mars and the Moon. Because of the central role played by water on Mars and the need to make in situ measurements of water abundances for landed missions, neutron spectroscopy is being investigated as a technique for quickly determining the near-surface water abundance for fhture Mars missions, such as the Mars Smart Larider (MSL).

Date: January 1, 2003

Creator: Lawrence, David J. (David Jeffery),; Elphic, R. C. (Richard C.); Feldman, W. C. (William C.); Moore, K. R. (Kurt R.); Prettyman, T. H. (Thomas H.) & Weins, R. C. (Roger C.)

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Lunar surface outgassing and alpha particle measurements

The Lunar Prospector Alpha Particle Spectrometer (LP APS) searched for lunar surface gas release events and mapped their distribution by detecting alpha particle?; produced by the decay of gaseous radon-222 (5.5 MeV, 3.8 day half-life), solid polonium-2 18 (6.0 MeV, 3 minute half-life), and solid polonium-210 (5.3 MeV, 138 day half-life, but held up in production by the 21 year half-life of lead-210). These three nuclides are radioactive daughters from the decay of uranium-238.

Date: January 1, 2002

Creator: Lawson, S. L. (Stefanie L.); Feldman, W. C. (William C.); Lawrence, David J. (David Jeffery),; Moore, K. R. (Kurt R.); Elphic, R. C. (Richard C.); Maurice, S. (Sylvestre) et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Distribution of iron&titanium on the lunar surface from lunar prospector gamma ray spectra

Gamma ray pulse height spectra acquired by the Lunar Prospector (LP) Gamma-Ray Spectrometer (GRS) contain information on the abundance of major elements in the lunar surface, including O, Si, Ti, Al, Fe, Mg, Ca, K, and Th. With the exception of Th and K, prompt gamma rays produced by cosmic ray interactions with surface materials are used to determine elemental abundance. Most of these gamma rays are produced by inelastic scattering of fast neutrons and by neutron capture. The production of neu… more

Date: January 1, 2001

Creator: Prettyman, T. H. (Thomas H.); Feldman, W. C. (William C.); Lawrence, David J. (David Jeffery),; Elphic, R. C. (Richard C.); Gasnault, O. M. (Olivier M.); Maurice, S. (Sylvestre) et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Mid-latitude composition of mars from thermal and epithermal neutrons

Epithermal neutron data acquired by Mars Odyssey have been analyzed to determine global maps of water-equivalent hydrogen abundance. By assuming that hydrogen was distributed uniformly with depth within the surface, a map of minimum water abundance was obtained. The addition of thermal neutrons to this analysis could provide information needed to determine water stratigraphy. For example, thermal and epithermal neutrons have been used together to determine the depth and abundance of waterequiva… more

Date: January 1, 2003

Creator: Prettyman, T. H. (Thomas H.); Feldman, W. C. (William C.); Elphic, R. C. (Richard C.); Boynton, W. V. (William V.); Bish, D. L. (David L.); Vaniman, D. T. (David T.) et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department