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At least 469 records · Page 26
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NASA NTRS1985

Gamma-ray line emission from Al-26 produced by Wolf-Rayet stars

The recent satellite observations of the 1.8 MeV line from the decay of Al-26 has given a new impetus to the study of the nucleosynthesis of Al-26. The production and ejection of Al-26 by massive mass-losing stars (Of and WR stars) is discussed in the light of recent stellar models. The longitude distribution of the Al-26 gamma ray line emission produced by the galactic collection of WR stars is derived based on various estimates of their radial distribution. This longitude profile provides: (1) a specific signature of massive stars on the background of other potential Al-26 sources, as novae, supernovae, certain red giants and possibly AGB stars; and (2) a possible tool to improve the data analysis of the HEAO 3 and SMM experiments.

Prantzos, N.↗
NASA NTRS1984

Selection of a map grid for data analysis and archival

Arguments for selection of a map grid are reiterated by illustrating the quantitative effects on data quality caused by using different grids. It is shown that the use of the rectangular latitude-longitude grid actually degrades data quality, increases stored data volume, and increases the complexity of data manipulation. Use of an equal-area grid is shown to be a proper way to aggregate data, but such grids are thought to be inconvenient. A solution to this dilemma is proposed by showing that the analysis and archival map grids need not be the same. The results of a proper analysis of the data on an equal-area grid can be remapped to the more 'convenient' rectangular latitude-longitude grid without loss of quality.

Rossow, W. B.↗
NASA NTRS1984

Interplanetary field enhancements in the solar wind Statistical properties at 0.72 AU

A new class of disturbance in the interplanetary magnetic field has been discovered. This disturbance consists of an enhancement in the magnetic field strength lasting tens of minutes to hours. The strength of the enhancement is variable ranging up to over double the background field strength. The peak field pressure can be as high as 10 percent of the solar wind dynamic pressure. These events occur randomly with respect to the position of the spacecraft relative to Venus but not randomly with respect to Venus solar ecliptic longitude. There is a significant tendency for these events to cluster near certain ecliptic longitudes. The field distortion is often greater in the direction perpendicular to the solar wind flow rather than along it. These characteristics suggest that the source of the disturbances are weakly outgassing objects, possibly dispersed along their orbits such as in meteor streams.

Russell, C. T.↗
NASA NTRS1984

Io's sodium directional features - Evidence for a magnetospheric-wind-driven gas escape mechanism

Elongated features in Io's sodium cloud, directed away from Jupiter and inclined both to the north and to the south of the satellite's orbital plane, have been observed. The north/south directions of the features are correlated with Io's magnetic longitude, suggesting a formation mechanism involving the oscillating plasma torus. It is shown by means of a model analysis that the features can result from a source of high-velocity (about 20 km/s) sodium combined with the oscillating neutral sodium sink provided by the plasma. The phase relationship between the features' directions and Io's magnetic longitude can be understood if escaping sodium is initially directed at near right angles to Io's orbital motion. The directionality of the features requires that the sodium flux from equatorial regions be higher than that from the poles. The initial directions and speeds of sodium atoms escaping Io to form the directional features can be understood in terms of a magnetospheric-wind-driven escape mechanism. The one sequence of directional feature observations that has been analyzed in detail implies a high-speed sodium source rate of about 10 to the 26th atoms/s.

Pilcher, C. B.↗
NASA NTRS1985

Universal time dependence of nighttime F region densities at high latitudes

Coincident auroral-zone experiments using three incoherent-scatter radars at widely spaced longitudes are reported. The observational results demonstrate that, during the night, the F layer electron density is strongly dependent on the longitude of the observing site. Ionization patches were observed in the nighttime F region from the Chatanika and EISCAT radars, while densities observed from the Millstone radar were substantially smaller. The electron density within these maxima is larger at EISCAT than at Chatanika. When observed in the midnight sector auroral zone, these densities had a peak density at a high altitude of 360-475 km. The density was maximum when EISCAT was in the midnight sector and minimum when Millstone was in the midnight sector. A minimum in insolation in the auroral zone occurs at the UT when Millstone is in the midnight sector.

De La Beaujardiere, O.↗
NASA NTRS1985

Calculation of allowable orbital spacings for the fixed-satellite service

Minimum satellite separations are calculated which satisfy a given carrier-to-interference protection ratio for the Fixed-Satellite Service (FSS) on a single-entry basis, assuming circular antenna beams. The results are presented in the form of universal contour curves, in which antenna-centered angles are the coordinates, and also in terms of the more conventional longitude and latitude separations. It is shown that orbit capacity increases with decreasing service-area size and that, for practical service areas, capacity is increased if the longitude of a satellite does not differ too greatly from that of the service area it serves.

Yamamura, Y.↗
NASA NTRS1986

Radar altimetry of Mercury - A preliminary analysis

Altitude measurements derived from 2380 MHz radar observations of the equatorial zone of Mercury collected between 1978-1984 at Arecibo Observatory are analyzed. The altitude profiles, which span from 20-90 deg longitude at a resolution of 0.15 deg (longitude) by 2.5 deg (latitude), are compared with geologic maps of Mercury. The depths and shapes of the craters and basins are examined; it is observed that Mercurian craters are shallower than lunar craters. The plains of Tir Planitia, Caloris Basin, and circum-Caloris are studied and it is hypothesized that the plains are of a volanic origin. The ridges, scarps, and fault zones detected in the altimetry data are described.

Harmon, J. K.↗
NASA NTRS1986

Modeling the temporal and spatial variations of the vertical structure of Jupiter's atmosphere using observations of the 3-0 hydrogen quadrupole lines

An observational program was established in 1983 to monitor the spatial and temporal variations in the Jovian atmosphere over short and long time scales. The program involves tracking several different longitudes as they rotate around the planet from one limb to another. This tracking experiment was done at many different wavelengths including the 3-0 S(1) and S(0) hydrogen quadrupole lines as well as several broad band methane absorptions. The June 1983 hydrogen quadrupole data was reduced and equivalent widths were measured for approximately 25 east-west positions across the planet at 7 different latitudes for both wavelengths. The data for the South Tropical Zone (20 deg. S) was modeled extensively and the effects of the various model parameters on the value of the calculated equivalent widths of both lines was measured as a longitude rotated from the east (or morning) limb to the west (or evening) limb. The value of the equivalent width is also quite sensitive to the height of the NH3 cloud top and to the value used for the single scattering albedo. A combination of these parameters changing on a diurnal time scale could also explain these observations. This gradual increase from one limb to the other appears in the data for both the North and South Equatorial Belts as well as the equatorial region and the North Tropical Zone. Models that used only normal hydrogen and models that used only equilibrium hydrogen were studied.

Cunningham, C. C.↗
NASA NTRS1987

Gravity data analysis

Work on three different efforts related to gravity data analysis is discussed. The reduction of raw Doppler data from the Apollo 15 subsatellite to produce acceleration profiles as a function of latitude, longitude and altitude; an investigation related to fitting long arcs of Pioneer Venus Orbiter tracking data; and a study of gravity/topography ratios which were found to have a linear trend with longitude are discussed.

Sjogren, William L.↗
NASA NTRS1986

Preliminary analysis of the IRAS solar system dust data

The structure of the solar system dust cloud as revealed by IRAS all-sky survey data is discussed. Fourier analysis was used to separate the smooth, large-scale zodiacal background from the narrower dust lanes. The geometry of the background zodiacal cloud appears to show features associated with both the forced inclinations and the forced eccentricities of the dust particle orbits. The ecliptic latitude of the peak of the background zodiacal emission varies nearly sinusoidally with ecliptic longitude with an amplitude of 2.1 + or -0.2 degrees. However, there are marked displacements, both in latitude and longitude, between the leading or ascending curve and the trailing or descending curve, implying that the curves exhibit significant deviations from a simple sinusoidal variation. It is suggested that the plane of symmetry of the background cloud is inclined to the ecliptic by 1.47 + or -0.10 degrees with a descending node of 230 + or -4 degrees, and that the sun is not at the center of symmetry of the cloud.

Dermott, S. F.↗
NASA NTRS1986

Some observations on the role of planetary waves in determining the spring time ozone distribution in the Antarctic

Ozone measurements from 1970 to 1984 from the Nimbus 4 backscattered ultraviolet and the Nimbus 7 solar backscattered ultraviolet spectrometers show significant decrease in total ozone only after 1979. The downward trend is most apparent in October south of 70 deg S in the longitude zone 0 to 30 deg W where planetary wave activity is weak. Outside this longitude region, the trend in total ozone is much smaller due to strong interannual variability of wave activity. This paper gives a phenomenological description of ozone depletion in the Antarctic region based on vertical advection and transient planetary waves.

Chandra, S.↗
NASA NTRS1986

Periodic amplitude variations in Jovian continuum radiation

An analysis of periodic variations in the amplitude of continuum radiation near 3 kHz trapped in the Jovian magnetosphere shows structure with periods near both five and ten hours. Contrary to a plausible initial idea, the continuum amplitudes are not organized by position of the observer relative to the dense plasma sheet. Instead, there seem to be preferred orientations of system III longitude with respect to the direction to the sun which account for the peaks. This implies a clock-like modulation of the continuum radiation intensity as opposed to a searchlight effect. The importance of the dipole longitude-solar wind alignment to the amplitude of the continuum radiation implies the source region of the radiation is near the magnetopause and may indirectly tie the generation of the radio waves to the clocklike modulation of energetic electron fluxes from Jupiter.

Kurth, W. S.↗
NASA NTRS1987

Ray tracing of Jovian decametric radiation from Southern and Northern Hemisphere sources - Comparison with Voyager observations

The Voyager 1 and 2 Planetary Radio Astronomy observations of Io-dependent decametric (DAM) radiation originating from the Southern Hemisphere of Jupiter were compared with the results of three-dimensional model ray tracing calculations of the DAM radiation. The ray trajectories for sources located at constant sub-Io longitudes of 260 and 300 deg were computed for both the Northern and the Southern Jovian Hemisphere sources. The model results of wave propagation agree with the Voyager observations obtained with Io located at 260 and 300 deg in Jovian system III longitude. The agreement between the Voyager observations and the model ray tracings allows identification of the origin of several of the emission components.

Menietti, J. Douglas↗
NASA NTRS1987

The structure and evolution of seasonal wind anomalies over the near-equatorial eastern Indian and western Pacific Oceans

The longitude-height-time structure and evolution of near-equatorial wind variability over the eastern Indian and western Pacific Oceans are studied using data obtained from a network of eight radiosonde stations extending from southern India to the central Pacific Ocean. The seasonal zonal wind anomalies observed at the cross section beween Trivandrum and Majuro stations are analyzed using an empirical orthogonal function. The Walker Circulation fluctuations are described in terms of standing oscillations in the longitude-height plane, and it is determined that Southern Oscillation propagation anomaly best represents the wind fluctuations. A complex empirical orthogonal function (CEOF) analysis and an El Nino compositing methodology are applied to the seasonal zonal wind anomalies. It is determined that the composite El Nino anomalies correspond to the spatial structure and temporal evolution of anomalies implied by the CEOF analysis.

Gutzler, David S.↗
NASA NTRS1987

Solar activity and heliosphere-wide cosmic ray modulation in mid-1982

A plausible candidate flare is identified for each of the four major Forbush-like decrease events that were observed in the outer heliosphere in mid-1982. The associations are as follows: (1) FD 1 at P10 - backside flare at W152 deg on June 3; (2) FD 1 at P11 - 2B flare at E25 deg on June 6; (3) FD2 at P11 - 3B flare at E36 deg on July 12; and (4) FD 2 at P10 - 1N limb flare at W100 deg on July 22. In each case, the identified flare was 35 deg or less in ecliptic longitude from the affected satellite. There is no compelling evidence from near-sun spacecraft observations that the shocks from any of the four identified flares encompassed both P10 and P11. A significant fraction of the major near-sun interplanetary disturbances during June and July of 1982 arose in the relatively narrow range of Carrington longitude from 275-320 deg.

Cliver, E. W.↗
NASA NTRS1987

The Space Shuttle as a platform for observations of ground-based transmitter signals and whistlers

A preliminary global study of VLF transmitter signals and low-latitude whistlers received at 245 km altitude on the Space Shuttle is presented. The observations were made in a 5-day period during the STS 3 mission in March 1982. Direct signals from a 10-kW transmitter located at 28 deg S magnetic latitude were received in a roughly circular region with a diameter of 6000 km centered around the transmitter. Signals propagating through the magnetosphere from a 500-kW magnetically conjugate transmitter at 40 deg N magnetic latitude were received inside a region extending 5000 km in longitude and 2000 km in latitude. In addition, direct signals from a 1-MW transmitter at 31 deg S magnetic latitude were received in a region extending 22,000 km in longitude, while the latitudinal extent (5000 km) was limited by the Shuttle orbit and the day/night terminator.

Neubert, T.↗
NASA NTRS1987

The detection of global convection on the sun by an analysis of line shift data of the John M. Wilcox Solar Observatory at Stanford University

An analysis of the absorption line shift data of the John M. Wilcox Solar Observatory at Stanford University has yielded signatures of the existence of global convection on the sun. These include persistent periodic time variations in the east-west component of the velocity fields defined by fitting a slope to the line shift data in a certain longitude window at a specified latitude and longitude by the least squares method. The amplitude of the velocity fields estimated from these variations is of the order of 100 m/s. The results of the analysis also suggest that several modes of global convection coexist in the solar convection zone. Details of the analysis are given.

Yoshimura, Hirokazu↗
NASA NTRS1987

The effect of increased horizontal resolution on GLA Fourth Order model forecasts

A benchmark series of ten-day weather forecasts has been run with the GLA Fourth Order GCM with both a 4 deg latitude by 5 deg longitude resolution and a 2 deg latitude by 2.5 deg longitude resolution. Ensemble statistics of forecast skill and maps of systematic error fields have been generated for both resolutions. The enhanced resolution added 24 hours of useful predictive skill to the sea level pressure forecasts and 6 hours to the 500 mb height forecasts, but 5 to 6 days into the forecasts the advantage of the finer resolution was lost. The systematic error fields showed that by 8 days the 'climate drift' of the 2 x 2.5 deg forecasts had become pronounced and had caused the loss of predictive skill relative to the 4 x 5 deg forecasts. Additional results indicate that a gravity wave drag parameterization scheme might alleviate the climate drift problem.

Helfand, H. M.↗