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Sharp, R. D.

Publications and source records attributed to Sharp, R. D..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

ISEE observations of the plasma sheet boundary, plasma sheet, and neutral sheet. I - Electric field, magnetic field, plasma, and ion composition

The first simultaneous study of dc and ac electric and magnetic fields, E x B velocity, plasma flows, ratio of plasma to magnetic field pressure, total energy density, energetic particles, and ion composition from the ISEE satellites and ground and interplanetary magnetic fields has been made to determine (1) the relationship of the previously observed electric fields at the plasma sheet boundary and at the neutral sheet to plasma parameters, and (2) whether the phenomena occurring during quiet and active times were consistent with the formation of a near-earth neutral line during substorms or with the boundary layer model. Five observations made during the study of two substorms were seen to be in agreement with the neutral-line model. The observations are consistent with the satellite being located at varying distances from the neutral line and diffusion region where reconnection and plasma acceleration were occurring. Although the z component (into or out of the ecliptic plane) of E x B convection was generally toward the neutral sheet, there were examples when it was consistent with the inferred motion of the plasma sheet past the satellite. A synthesis of previous reports on large electric fields at the plasma sheet boundary and variable fields at the neutral sheet including the associated plasma flows is also described.

Cattell, C. A.↗
NASA NTRS1986

Observations of transverse and parallel acceleration of terrestrial ions at high latitudes

Selected S3-3 satellite ion-mass-spectrometer observations of upward-flowing 0.5-16-keV terrestrial ions in the auroral zones at altitudes 2000-8000 km are presented graphically and analyzed. The data are shown to support an interpretation in which ion conics are first formed at lower altitudes (by a mechanism which provides more energy to heavier ions) and then accelerated upward through a potential drop; outside these regions ion conics may be generated by mechanisms which are independent of ion mass.

Collin, H. L.↗
NASA NTRS1986

Ion specific differences in energetic field aligned upflowing ions at 1 earth radius

An ion-upflow event over the northern auroral zone during a small magnetic storm on August 24, 1976 is characterized on the basis of S3-3 satellite ion-mass-spectrometer observations at 0.5-16 keV. The data are presented in tables, graphs, and diagrams and analyzed in detail. The distributions of upward-flowing O(+) and H(+) associated with parallel electric fields below the satellite are shown to have transverse temperatures of about 1 keV and 0.1 keV, respectively, while the corresponding parallel temperatures were about 1 keV and 0.6 keV; the average energy of the O(+) ions is found to be 2-3 times greater than that of the H(+) ions in the acceleration regions. Possible interpretations of these findings are discussed.

Ghielmetti, A. G.↗
NASA NTRS1985

Study of storm time fluxes of heavy ions

Ion composition data sets from Lockheed instruments on a variety of spacecraft were used in combination with each other and with data from other instruments to address a variety of problems regarding plasma sources, energization and transport within the magnetosphere. The availability of data from several differing orbits has given a highly flexible approach to attacking the continually evolving questions of magnetospheric physics. This approach is very successful and should be continued in the future.

Sharp, R. D.↗
NASA NTRS1985

The ionospheric contribution to the plasma environment in near-earth space

SCATHA and ISEE 1 satellite ion mass spectrometer data on ion composition near GEO are reviewed. The data were gathered during and close to magnetic storm activity to assess the characteristics of ion composition variations in order to predict the effects of hot GEO plasma on spacecraft instruments. Attention is given to both substorms and storms, the former being associated, at high latitudes, with auroral activity, the latter with ring currents. The ionosphere was found to supply hot H(+), O(+) and He(+) ions to the GEO magnetosphere, while the solar wind carried H(+) and He(+) ions. The ionosphere was the dominant source in both quiet and storm conditions in the inner magnetosphere.

Sharp, R. D.↗
NASA NTRS1985

ISEE-1 data reduction and analysis plasma composition experiment

The plasma composition experiment covers energies from OeV to 17 keV/e and has a mass-per-charge range from less than 1 to about 150 amu. Measurements were made from the inner ring current region to the plasma sheet, magnetotail lobes, and the magnetopause boundary layers and beyond. Possibly the most significant results from the experiment are those related to energetic (0+) ions of terrestrial origin. These ions are found in every region of the magnetosphere reached by the spacecraft and can have energy and pitch-angle distributions that are similar to those traditionally associated with protons of solar wind origin. The (0+) ions are commonly the most numerous ions in the 0.1 - 17 keV/e energy range and are often a substantial part of the ion population at large distances as well, especially during geomagnetically disturbed conditions. An overview of results obtained for the (0+) and other ions with energies in the 0.1 - 17 keV/e range in the magnetosphere is given.

Lennartsson, W.↗
NASA NTRS1985

Substorm effects on the plasma sheet ion composition on March 22, 1979 (CDAW 6)

One of the potentially most useful aspects of mass spectroscopy in magnetospheric research is related to the ability to distinguish between ions of solar wind and terrestrial origins. Knowing the source of the plasmas in various regions and under various geomagnetic conditions is crucial in improving the understanding of particle flows in the magnetosphere. Sharp et al. (1982) found that the plasma sheet ions in the 0.1- to 16-keV/e range, were predominantly of solar wind origin during low geomagnetic activity, while there was a large terrestrial component during active times. This paper presents a set of data from March 22, 1979. The reported investigation represents the first detailed case study of the relation between geomagnetic substorm activity and the ion composition in the plasma sheet. A decrease in solar wind ion flow at ISEE 1 and the subsequent increase in the flow of ionospheric ions is interpreted as evidence of a fundamental change in the particle flow pattern following the start of substorm activity.

Lennartsson, W.↗
NASA NTRS1985

Counterstreaming hydrogen and oxygen ions observed in the magnetosphere on ISEE-1

Counterstreaming ions or ions travelling simultaneously both parallel and antiparallel to the magnetic field direction have been briefly noted in the literature but have not been studied previously in depth. Over 60 counterstreaming ion (CSI) events observed on the ISEE-1 satellite have been studied. They were found to occur at altitudes of about 2 to 8 earth radii on L shells of about 5 to 12 in the evening-to-morning sector from about 1700-0900 LT. Often both oxygen and hydrogen ions at a number of energy levels are counterstreaming but some events show only either oxygen or hydrogen ions involved. One particularly interesting event shows only counterstreaming oxygen ions with 417 eV energy; oxygen ions of lower energy (215 eV) and above (630-17,000 eV) and all the hydrogen ions between 215-17,000 eV energy have lower fluxes and/or nearly isotropic pitch angle distributions. This event correlates well with wave activity in the 17-100 Hz band and is also accompanied by 200 eV downgoing and 400 eV upgoing electrons. Details of this event and the other counterstreaming events are presented.

Horita, R. E.↗
NASA NTRS1984

Achievements of the plasma composition experiment on ISEE-1 during the IMS

The ISEE-1 spacecraft measured energetic ion composition over a wide radial range in the near-equatorial magnetosphere, from close to the Earth to a distance of 23 RE. The Plasma Composition Experiment covers energies from 0 eV/e to 17 keV/e. Results for energetic O+ ions of terrestrial origin show that these ions are found in every region of the magnetosphere reached by the spacecraft and can have energy and pitch-angle distributions very similar to those of H+ ions. The O+ ions are the most numerous ions in the 0.1 to 17 keV/e energy range at L 5 and are often a substantial part of the ion population at larger distances as well, especially during geomagnetically disturbed conditions.

Lennartsson, W.↗
NASA NTRS1983

The mass dependence of wave particle interactions as observed with the ISEE-1 energetic ion mass spectrometer

Simultaneous measurements of the O(+) and H(+) distributions from two transverse acceleration events in the high altitude auroral ionosphere are presented. The data were acquired from the energetic ion mass spectrometer on the ISEE-1 satellite, in the dusk sector, on auroral field lines (L = 8-9), at geocentric radial distances of about 3 earth radii. Temporal and/or spatial fluctuations during the measurement cycle resulted in some scatter of the data points, but the transverse velocity distributions are reasonably well represented by maxwellians at energies in the few hundred eV range. The transverse temperatures were about 60 eV in both cases and no significant differences were observed between the temperatures of the O(+) and H(+). The flux intensities of the two ion species were also generally comparable.

Sharp, R. D.↗
NASA NTRS1983

Hot plasma composition results from the S3-3 spacecraft

The S3-3 satellite discovered the principal auroral acceleration region at altitudes of about 1 R(E) over the auroral zone. Intense fluxes of upward flowing O(+) and H(+) ions with keV energies were commonly observed in this region of the magnetosphere. The detailed morphology of these upflowing ions is described, including their latitude, local time, altitude, and magnetic activity dependences and their relationship to the trapped keV electron population. The first measurements of the composition of the trapped keV ions in the radiation belts are also described, showing the importance of the ionospheric source term to the storm time population of ions with energies equal to or less than 16 keV/e.

Sharp, R. D.↗
NASA NTRS1983

Hot plasma composition results from the ISEE-1 spacecraft

The International Sun Earth Explorer (ISEE-1) was launched on Oct. 22, 1977 into a geocentric elliptical orbit. The energetic ion mass spectrometer on the satellite is employed in a study of the plasmas encountered by ISEE-1 in its orbits. The experiment is operating successfully and research is progressing in a number of areas. A review in the nature of a progress report on the energetic magnetospheric plasma results is provided. Attention is given to the plasma sheet and ion streams in the magnetotail, the inner magnetosphere, and magnetospheric boundary regions.

Sharp, R. D.↗
NASA NTRS1983

Initial hot plasma composition results from the Dynamics Explorer

Initial observations from the energetic ion composition spectrometer on the DE-1 spacecraft have found mass or charge dependent processes to be operating in the vicinity of an inverted-V event in the auroral acceleration region, above the polar cap ionosphere, and in the mid-altitude dayside cusp. Separate color spectrograms for the different ion species provide a synoptic picture of these processes that can contribute significantly to our understanding of both the solar wind and the ionosphere as sources of energetic magnetospheric ions.

Shelley, E. G.↗
NASA NTRS1982

The origins of the plasma in the distant plasma sheet

It is pointed out that ion mass spectrometers operating in the keV range have recently begun to provide a new class of information on magnetospheric processes. One of the principal motivations for the development of energetic ion mass spectrometers has been to investigate the origins of the hot plasma populations of the magnetosphere. Peterson et al. (1981) were able to estimate the fractional ion density of ionospheric origin in five intervals by intercomparing the He(++) and H(+) spectra and assuming the excess low-energy H(+) ions were from the ionosphere. They obtained values in the range from 0.1 to 0.65. The present investigation is concerned with an expansion of the previous study. A substantially larger data base is utilized, and a different set of assumptions is considered to infer the relative fractions of solar and ionospheric H(+) and to look for systematic changes in the relative source strengths with magnetic activity.

Sharp, R. D.↗
NASA NTRS1982

A comparison of the 0.1-17 keV/e ion composition in the near equatorial magnetosphere between quiet and disturbed conditions

Data from the near-equatorial magnetosphere are analyzed by comparing the plasma composition during storm conditions with the composition during extended periods of low magnetic activity. It is found that at L less than or equal to 5, the O(+) is typically comparable to the H(+) in density and is often the dominant species, particularly during quiet times and at the inner edge of the region of significant fluxes. The He(+) in most cases contributes a significant fraction of the density and is sometimes the second most abundant species, following the O(+). Another finding is that both the He(+)/H(+) and the O(+)/H(+) ratios peak at the lowest L values and are, on the average, higher during quiet times than they are during the early main phase of major magnetic storms; this is seen as suggesting that charge exchange may be a significant loss process at low L. It is pointed out that the mean energies of the H(+), He(+), and O(+) ions often decrease gradually with decreasing L toward the inner edge of the energetic particle population.

Lennartsson, W.↗
NASA NTRS1981

The small-scale structure of electrostatic shocks

It is noted that small-scale regions of large electric fields have been observed above the auroral zone by the S3-3 satellite. The data from five such electrostatic shocks are examined in great detail. The three higher altitude shocks (all above 5,700 km) are found to be associated with upward-going ion beams, indicating that the potential associated with the shock closed below the satellite to give rise to the parallel electric field required for the acceleration of the ion beam. In all these cases, electrostatic ion cyclotron waves are found to be adjacent to the shock and to extend throughout the upward-going ion beam region. The lack of noticeable Doppler shift in the electrostatic ion cyclotron waves in association with large convective drift velocities is seen as indicating that the wavelength of the electrostatic ion cyclotron wave can be several kilometers and that the potential difference within the wave can be on the order of 100 V.

Temerin, M.↗
NASA NTRS1981

Ion composition and energy distribution during 10 magnetic storms

Data from the plasma composition experiment of ISEE 1 are used to investigate the relative quantities and energy characteristics of H(+), He(++), He(+), and O(+) ions in the near-equatorial magnetosphere during magnetic storm conditions. The ions in the study had energies between 0.1 and 17 keV/e and pitch angles between 45 and 135 deg. The data were obtained during 10 storms, for the most part at or immediately following the peak Dst, covering all major local time sectors and geocentric distances between 2 and 15 earth radii. The ion fluxes are averaged over the spacecraft spin angle and over time for periods ranging from about 20 min close to the earth to more than an hour in most distant regions. The inferred 'isotropic' number densities are characterized by a large to dominant fraction of terrestrial ions throughout the energy range covered. The data are found to be consistent with a terrestrial origin for all of the O(+), most of the He(+), and a large but varying fraction of the H(+), whereas the He(++) and part of the H(+) appear to be of solar wind origin.

Lennartsson, W.↗