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NASA NTRS1986

Observations of coherent transverse ion acceleration

DE-1 retarding ion mass spectrometer (RIMS) observations of transverse O(+) acceleration in the topside ionosphere are reported and analyzed. The operation and capabilities of RIMS are reviewed, and the data are presented graphically and characterized in detail. Torus or ring O(+) distributions with radii 10 km/s are observed, consistent with coherent transverse acceleration to 10-eV energies in the bulk-plasma reference frame, and conical hot tails at energies above the 50-eV RIMS maximum are noted. Possible mechanisms for these phenomena are discussed.

Moore, T. E.↗
NASA NTRS1986

Transport of accelerated low-energy ions in the polar magnetosphere

Recent satellite observations of low-energy (0-50 eV) ionospheric ions in the polar cap magnetosphere suggest that these ions are injected at the dayside cleft topside ionosphere. Using a two-dimensional kinetic model, several consequences of this ion flow from a narrow cleft source have been simulated and observed. These include: (1) the Kp/convection-dependent filling of the polar magnetosphere with ionospheric heavy ions, in which these ions are 'blown' further into the polar cap magnetosphere from the cleft during high Kp/convection; (2) the mass- and energy-dependent dispersion of these ions, as in a kind of 'geomagnetic spectrometer'; (3) the creation of 'supersonic' ion outflows as a natural velocity-filter effect of this geomagnetic spectrometer; and (4) the 'parabolic flow' of gravitationally bound heavy ions from the cleft ionosphere resulting in downward flow into the polar cap.

Horwitz, J. L.↗
NASA NTRS1986

Ion energization in upwelling ion events

A source of H(+), He(+), O(+), and N(+) outflow from the ionosphere has been identified near the polar cusp/cleft using the Dynamics Explorer/retarding ion mass spectrometer data set. This ion outflow termed 'upwelling ions' is characterized by large outfluxes of H(+) and O(+) ions and high transverse ion temperatures. This paper reports on the associated particle and field characteristics of one such upwelling ion event on March 12, 1982. Field-aligned currents and strong E x B convection channels are associated with the event as well as strong broadband plasma wave emission. One or all of these sources may play an important role in the ion energization in this region.

Waite, J. H., Jr.↗
NASA NTRS1986

Solar wind control of the Geomagnetic Mass Spectrometer

Evidence from Dynamics Explorer retarding-ion mass-spectrometer data collected between 1981 and 1983 for the mass dispersion of ionospheric plasma in the polar cap, known as the Geomagnetic Mass Spectrometer, is discussed, and implications of this new source of ionospheric ions for the magnetosphere are considered. A localized source of energization of ionspheric H(+), He(+), O(+) and N(+) ions in the polar cusp yields a source of upswelling plasma that is transported into the magnetosphere, and equal heating of the ion species results in field-aligned flow velocities which are inversely proportional to the square root of the ion mass. The present phenomenon is produced by the resulting velocity filter effect of solar-driven ExB ion convection. The influence of solar wind conditions on the outflow via the polar cap ExB convection pattern is also discussed.

Waite, J. H., Jr.↗
NASA NTRS1987

Interplanetary radial cosmic-ray gradients and their implication for a possible large modulation effect at the heliospheric boundary

It is proposed here that a large and time-variable part of the overall 11-year cosmic ray modulation in the heliosphere takes place near the heliosphere boundary itself. This conclusion is reached by examining interplanetary radial gradient measurements which show that out to 30-40 AU this gradient remains nearly independent of heliocentric distance throughout the solar cycle. Properties of the solar wind which suggest that the distance to the pressure balance boundary does not vary by more than + or - 25 percent over the solar cycle are also used in support of the proposal. The importance of the large modulation effect at the boundary could exceed that of interplanetary effects expected from present models.

Webber, W. R.↗
NASA NTRS1987

Thermoelectric properties of cerium monopnictides

Several cerium pnictides have been synthesized from the pure elements and hot pressed into test samples. Measurements of Seebeck coefficients and electrical resistivities were performed on these samples from room temperature to 1000 C. Cerium arsenide and cerium antimonide are n-type; cerium nitride changes from p-type to n-type conduction at 800 C. The materials are semimetals with resistivities below 1 mohm/cm. Cerium arsenide is the most favorable of the pnictides studied for high-temperature thermoelectric energy conversion, with an average power factor of 15 microW/cm K sq from 500 to 1000 C.

Danielson, L. R.↗
NASA NTRS1987

Effect of the microstructure on the thermoelectric properties of polycrystalline lanthanum chalcogenides

Small amounts of second phase materials can have important effects on the thermoelectric properties of polycrystalline gamma-La(3-x)X4 (X-S, Te; X in the range of 0 to 1/3). Microscopic examination by SEM of hot pressed La(3-x)Te4 samples has revealed from 1-5 vol. pct of La2O2Te, an amount which is not detected by X-ray powder diffraction measurements. This amount of La2O2Te resulting from oxygen contamination can reduce the concentration of electrons by as much as 10 to 75 percent below the electron concentration calculated for single phase La(3-x)Te4 in the composition range of greatest interest. Small amounts of second phase materials can also lower the lattice thermal conductivity by scattering low frequency phonons. These results indicate that microstructural effects should be considered when electrical and thermal properties of polycrystalline materials are analyzed.

Lockwood, A.↗
NASA NTRS1988

Observations related to the acceleration, injection, and interplanetary propagation of energetic protons during the solar cosmic ray event on February 16, 1984

This paper presents an analysis of data collected by the worldwide network of neutron monitors and from IMP-8 cosmic-ray telescopes, as well as by particle detectors on the GOES 5 and 6 and ICE satellites, on the solar cosmic ray event that took place on February 16, 1984. Using these data, the intensity-time (IT) profiles, the anisotropy-time profiles, the energy spectra, and the pitch angle distributions of the solar protons near earth were deduced. It was found that the solar protons propagated essentially scatter-free from the sun to the earth. The solar protons had easy access to the IMF lines to earth; the time from the onset to maximum intensity and the shape of the IT profiles at earth as a function of energy could be explained by the diffusion of the flare protons near the acceleration region. The energy spectrum of the solar flare protons injected into the undisturbed IMF at the sun was changing with time in both amplitude and shape. The observations suggest a shock acceleration process.

Debrunner, H.↗
NASA NTRS1988

Monitoring solar-type stars for luminosity variations

Since 1984, researchers have made more than 1500 differential photometric b (471 nm) and y (551 nm) measurements of three dozen solar-like lower main sequence stars whose chromospheric activity was previosly studied by O. C. Wilson. Here, researchers describe their methodology and the statistical tests used to distinguish intrinsic stellar variability from observational and instrument errors. The incidence of detected variability among the program and comparison stars is summarized. Among the 100 plus pairs of stars measured differentially, only a dozen were found that were unusually constant, with peak-to-peak amplitudes of seasonal mean brightness smaller than 0.3 percent (0.003 mag) over a two-to-three-year interval.

Lockwood, G. W.↗
NASA NTRS1989

Low-altitude signatures of the cusp and flux transfer events

Cusp-like ion injection was studied using DE-2 satellite data obtained during strongly southward IMF. Although magnetosheath ion injection signatures are detected, the satellite motion and convection are opposed, and it is suggested that the observed falling energy dispersion of the precipitating ions may have arisen from a static moving or growing source. The spatial scale of the flux is found to be typical of that of a flux transfer event (FTE). A simple model of the ionospheric signature of an FTE is able to reproduce the observed electric and magnetic field perturbations. Precipitating electrons with peak energies of about 100 eV lie on the predicted boundary of the newly opened tube and are similar to those noted on the edges of FTEs at the magnetopause.

Lockwood, Mike↗
NASA NTRS1989

The solar gamma ray and neutron capabilities of COMPTEL on the Gamma Ray Observatory

The imaging Compton telescope COMPTEL on the Gamma Ray Observatory (GRO) has unusual spectroscopic capabilities for measuring solar gamma-ray and neutron emission. The launch of the GRO is scheduled for June 1990 near the peak of the sunspot cycle. With a 30 to 40 percent probability for the Sun being in the COMPTEL field-of-view during the sunlit part of an orbit, a large number of flares will be observed above the 800 keV gamma-ray threshold of the telescope. The telescope energy range extends to 30 MeV with high time resolution burst spectra available from 0.1 to 10 MeV. Strong Compton tail suppression of instrumental gamma-ray interactions will facilitate improved spectral analysis of solar flare emissions. In addition, the high signal to noise ratio for neutron detection and measurement will provide new neutron spectroscopic capabilities. Specifically, a flare similar to that of 3 June 1982 will provide spectroscopic data on greater than 1500 individual neutrons, enough to construct an unambiguous spectrum in the energy range of 20 to 200 MeV. Details of the instrument and its response to solar gamma-rays and neutrons will be presented.

Ryan, James M.↗
NASA NTRS1990

The onset of the new solar modulation cycle in 1987-1988 as a function of heliocentric radius and latitude

The onset of a new solar modulation cycle were studied in 1987 and 1988, on the basis of data on counting rates of particles with E greater than 60 MeV, observed at the IMP, Voyager (V), and Pioneer (P) satellites. It was found that the decrease at earth was rapid after the intensity maximum in early 1987 and was closely correlated with the increase in the average tilt of the heliospheric current sheet. The initial rapid intensity decrease was found to be related to three small Forbush decreases which are superimposed on a more gradual decrease. By the end of 1988, the intensity decreased by about 40 percent at earth, 30 percent at V2, and 18 percent at P10. This overall decrease was accompanied by an increase in the average integral radial gradient as well as a decrease in the radial dependence of the gradient. The onset of the new solar modulation cycle seems to be related to the complete altering of the solar magnetic structure as observed on the surface of the sun.

Webber, W. R.↗
NASA NTRS1990

Differences in the solar modulation of E greater than 60 MeV cosmic rays at earth and 18 AU during a complete 11-year cycle from 1977 to 1988

The cosmic ray intensities for E greater than 60 MeV particles at a constant radius of 18 AU using data from the IMP, Voyager and Pioneer spacecraft. These intensities are compared with the intensities at earth for a complete 11-year cycle from 1977 to 1988. It is found that the variations at 1 AU and 18 AU track very closely during the decreasing portion of the cycle from 1977 to 1982 but during the recovery the intensity at 18 AU increases much less than at earth with the result that in 1987 the intensity is only 82 percent of that at the previous minimum in 1977. These results imply that the integral radial gradient between 1 and 18 AU is constant in time from 1977 to 1982 but decreases from 1982 to 1988. Thus, the amplitude of the 11-year variation observed at a fixed energy is quite strongly radially dependent, with the amplitude becoming less at larger radii.

Lockwood, J. A.↗
NASA NTRS1990

Effects of height acceleration on Geosat heights

A radar altimeter tracking loop, such as that utilized by Geosat, produces height errors in the presence of persistent height acceleration h(a). The correction factor for the height error is a function of both the loop feedback parameters and the height acceleration. The correction, in meters, to the sea-surface height (SSH) derived from Geosat is -0.16 h(a), where h(a) is in m/sec per sec. The errors induced by accelerations are produced primarily by changes in along-track geoid slopes. The nearly circular Geosat orbit and dynamic ocean topography produce small h(a) values. One area studied in detail encompasses the Marianas Trench and the Challenger Deep in the west central Pacific Ocean. Histograms of SSH corrections due to range accelerations have also been determined from 24-hour segments of Geosat global data. The findings are that 20 percent of the Geosat measurements have acceleration-induced errors of 2 cm or more, while 8 percent have errors of 3 cm or more.

Hancock, David W., III↗
NASA NTRS1990

Effects of islands in the Geosat footprint

The presence of land within a radar altimeter's footprint may contaminate its tracking performance and perturb the nadir oceanographic signal. A study has been performed which examines the effects of small mid-ocean islands on the Geosat tracker. The surface return waveforms, as well as the altimeter measurements, have been analyzed. Open-ocean waveforms have been compared with waveforms containing land reflections; they differ perceptibly. Computations could be performed, based on a combination of waveform data, altimeter signal strength, and sea surface heights, to detect contaminated sea-surface height values for subsequent editing.

Brooks, Ronald L.↗
NASA NTRS1990

The pulsating cusp

Recent observations at the magnetopause and of the high-latitude ionosphere suggest that the cusp may be pulzed in nature. Ground-based observations in the dayside auroral oval reveal transient optical features accompanied by bursts of enhanced plasma flow. Also, recent interpretation has shown cusp satellite data to be consistent with a burst of enhanced reconnection. These observations are used to produce a scenario in which both the satellite and ground-based observations can be fitted. The scenario developed is based on the flux transfer event (FTE) models of Southwood et al. (1988) and Scholer (1988) and shows that the signatures, at both low and high altitudes, can be interpreted in terms of FTEs.

Smith, M. F.↗
NASA NTRS1990

Some Insights on Solar Variability from Precision Stellar Astronomical Photometry

At Lowell Observatory, precision photoelectric photometry was directed toward the study of solar variability and the variability of sun-like stars beginning in 1949 and continuing until now. The ubiquity and range of low-level variability, including some that appears to be cyclic, among solar-type stars shows that recent solar variability may be unusual only in its present restraint.

Lockwood, G. W.↗
NASA NTRS1991

Development of a grid-independent approximate Riemannsolver

A grid-independent approximate Riemann solver for use with the Euler and Navier-Stokes equations was introduced and explored. The two-dimensional Euler and Navier-Stokes equations are described in Cartesian and generalized coordinates, as well as the traveling wave form of the Euler equations. The spatial and temporal discretization are described for both explicit and implicit time-marching schemes. The grid-aligned flux function of Roe is outlined, while the 5-wave grid-independent flux function is derived. The stability and monotonicity analysis of the 5-wave model are presented. Two-dimensional results are provided and extended to three dimensions. The corresponding results are presented.

Rumsey, Christopher Lockwood↗