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At least 649 records · Page 36

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NASA NTRS1975

Fluctuations and the radial variation of the interplanetary magnetic field

Correlations between fluctuations in the solar wind velocity and interplanetary magnetic field can influence the observed average interplanetary magnetic field and its variation with heliocentric radius. The average radial magnetic field still varies as inversely with the square of the radius, but, depending on the radial variation of the correlations, the average azimuthal field could depart from the 1/r dependence expected for an Archimedian spiral. This effect could account in part for those observations which indicate a steeper than 1/r dependence for the average azimuthal interplanetary magnetic field.

Jokipii, J. R.↗

NASA NTRS1975

Sasaki's variational optimization analysis of temperature and moisture advection in a severe storm environment

Temperature and moisture advection patterns of dry air intrusion were analyzed by a variational optimization method to relate mesoscale advection to a severe thunderstorm environment. The analysis results presented here were obtained from a case study, May 26, 1973, when a tornado squall line developed in Oklahoma in conjunction with a clearly delineated dry air intrusion. Observations from the synoptic upper air network were used for inputs of horizontal wind components, potential temperature, and mixing ratio at each 50 mb increment from 950 to 100 mb. An objective analysis was performed to assign values of the variables to grid points of a 15 x 14 horizontal grid with approximate 125 km grid spacing at each pressure level. After the analysis the data fields were smoothed using a variational formalism.

Mcfarland, M. J.↗

NASA NTRS1976

Diurnal and seasonal variations in atomic and molecular oxygen inferred from Atmosphere Explorer-C

Mass-spectrometer measurements of O and N2, obtained with the Atmosphere Explorer-C satellite during December 1974 and January 1975, are used to derive the O2 concentration near 250 km from several ionization reactions. In order to separate temperature effects from diffusion effects, the measured O and inferred O2 concentrations are employed to determine, under the assumption of diffusive equilibrium, the O/N2 and O2/N2 ratios at 120 km. It is found that the latitudinal and diurnal variations in the O concentration at 120 km are consistent with previous results obtained with OGO 6 and that the O2 concentration in the Northern (winter) Hemisphere is about twice as high as that in the Southern (summer) Hemisphere. The possible importance of photodissociation in the diurnal O2 variations is discussed.

Mayr, H. G.↗

NASA NTRS1975

IMP 6, 7 and 8 observations of the composition and time variations of low energy cosmic rays

The charge composition and time variations of quiet-time cosmic rays in the energy range 10 to 25 MeV/nucleon were studied to determine the source of the enhancement of quiet-time intensities of low energy nitrogen and oxygen nuclei observed by Pioneer 10. Time variations were established from data from IMPs 6, 7, and 8; the charge composition was obtained by summing data from IMP 7 and IMP 8. The neon to carbon ratio present in solar rays is too low to explain an observed enhancement of neon. Helium and oxygen have the same percentage modulation for a range of x5 in intensity. This can be explained within the framework of the field-force approximation and the selection mechanism based on the first ionization potential proposed by Fisk et al. (1974) if both oxygen and helium are singly charged.

Von Rosenvinge, T. T.↗

NASA NTRS1975

Variations in the charge composition of the July 2-12, 1974, solar particle event

Large temporal and spatial variations of alpha, M-group and heavy nuclei have been measured with two spacecraft. Variations of the M/H ratio associated with storm sudden commencements are reported and discussed. Large changes in composition of solar particle fluxes in periods of a few minutes may make the interpretation of long-time averaged spectra and composition measurements very difficult.

Armstrong, T. P.↗

NASA NTRS1975

Nucleosynthesis of He-3 in the sun and the variation of He-3/He-4 in solar wind

The time history of the variation of He-3/He-4 (R) on the surface of the sun as a result of nucleosynthesis in the solar interior has been studied for different empherical models of mixing. For homogeneous mixing with mixing periods between one million and 1,000 millions years, the expected value of R is very much larger than the observed solar wind value. On the other hand, the absolute value of R and its possible time variation in the solar wind are consistent with a model in which slow mixing with adjacent layers, equivalent to about 0.01 Mr, of the core takes place over a period of 100 million years. The possibility of explaining the He-3 rich solar flare events is discussed.

Stephens, S. A.↗

NASA NTRS1976

Diurnal variation of atomic nitrogen

When the perigee of the Atmospheric Explorer C satellite reached the northern latitudes (68 deg) by mid-April 1974, descending and ascending portions of the orbits stretched symmetrically across the Northern Hemisphere. Corresponding local solar times at altitudes above 400 km were 1700 hours and 0200 hours, respectively, thus providing the opportunity to study the diurnal variation of the neutral constituents. Atomic nitrogen densities, measured with the open-source neutral mass spectrometer, show a pronounced diurnal variation. At 400 km, the density ratios derived from measurements of the descending and ascending portions are 5.2 for N, 4.9 for N2, and 2.0 for O. Absolute densities of atomic nitrogen agree within a factor of 2 or 3 with densities derived from neutral-ion reactions. Measurements taken close to the geomagnetic pole show a decrease in atomic nitrogen densities when an increase in molecular nitrogen is observed.

Mauersberger, K.↗

NASA NTRS1976

Calcium abundance variations in diffuse interstellar clouds

Observations are discussed which show that the Na I/H2 column-density ratio is relatively constant among different clouds where H2 is optically thin, but the Na I/Ca II column-density ratio varies. This implies that the gas-phase abundance of calcium is variable. It is proposed that the wide variation in the gas-phase calcium abundance can be explained by small variations in the calcium content of grains. The observed enhancement of the Ca II/Na I column-density ratio with cloud velocity is attributed to grain destruction in grain-grain collisions within the same cloud. The structure of shock waves propagating through the interstellar gas is computed, and the grain-destruction model is compared with observational data.

Jura, M.↗

NASA NTRS1976

OTW noise correlation for variations in nozzle/wing geometry with 5:1 slot nozzles

Acoustic data obtained from a model-scale study with 5:1 slot nozzles are analyzed and correlated in terms of apparent noise sources. Variations in nozzle geometry include roof angle and sidewall cutback. In addition, geometry variations in wing size and flap deflection were included. Three dominant noise sources were evident in the data and correlated: fluctuating lift noise, trailing edge noise and a redirected jet mixing noise that included the effect of reflection of jet noise by the surface. Pertinent variables in the correlations included the shear layer thickness and peak jet flow velocity at the trailing edge.

Von Glahn, U.↗

NASA NTRS1976

The morphology of energetic O/+/ ions during two magnetic storms - Temporal variations

Results are presented for a statistical analysis of the temporal variations of precipitating O(+) and H(+) ions in the energy range 0.7-12 keV during the magnetic storms on Dec. 16-18, 1971. Emphasis is on the temporal variations of parameters describing the intensity, average energy, and spatial location of the precipitation zones of the two ionic species. It is shown that the intensity of the precipitating O(+) ions correlate well with the geomagnetic indices which measure the strength of magnetospheric substorm activity and the strength of the storm time ring current, indicating that a previously unknown strong coupling mechanism existed between the magnetosphere and the ionosphere during the storm period. Correlations are found between the locations of the O(+) and H(+) precipitation zones and between the average energies of the two ionic species. Precipitation is shown to be an important loss mechanism for ring current ions with energy less than 12 keV during the magnetic storm period studied.

Sharp, R. D.↗

NASA NTRS1976

Three-dimensional structure of the extended solar magnetic field and the sunspot cycle variation in cosmic ray intensity

A principal cause for the eleven-year sunspot cycle variation in the primary cosmic ray intensity observed at earth may be a variation in the solid angle of the heliosphere occupied by the extended solar polar magnetic field. Galactic cosmic rays have relatively easy access to the inner solar system through the regular extended solar polar fields, and relatively difficult access through the irregular extended solar sector structure fields.

Svalgaard, L.↗

NASA NTRS1977

The effect of variations in controls and displays on helicopter instrument approach capability

A flight investigation was conducted with a variable stability helicopter to determine the effects of variations in controls and displays on helicopter instrument approach capabilities. The baseline instrument approach task was a decelerating approach to a hover along a 6 deg glide slope. Pilot evaluations were obtained for both the constant speed part of the task and the deceleration and hover part of the task. The attitude stability augmentation system (SAS) was strongly preferred over the rate SAS because the aircraft had a divergent pitch response. From a display variation standpoint, it was not possible to decelerate to a hover in a consistent manner, regardless of the control system employed, with situation information only. In particular, the deceleration and hover part of the task was unacceptable without flight director command information.

Niessen, F. R.↗

NASA NTRS1977

Atomic oxygen between 80 and 120 km: Evidence for a rapid spatial variation in vertical transport near the ionosphere

Analysis of OGO-6 OI green line photometer results was carried out for 8 cases when the alignment of the spacecraft was such that local emission rates could be determined below the altitude of maximum emission and down to about 80 km. Results show a variation on a scale of 6 deg to 8 deg in latitude between regions where the emission rate increases rapidly between 90 and 95 km and regions where it increases slowly from 80 km to 95 km. Latitude-altitude maps of iso-emissivity contours and iso-density contours for oxygen concentration are presented. The latter are computed under 3 assumptions concerning excitation mechanisms. Comparisons of the spatial variations of oxygen density with the results of a time dependent theory suggest the regions of strong downward transport alternate on a scale of about 1000 km with regions of weak transport near 90 km. In the first case conversion of O to O3 at night appears to be overwhelmed by downward transport of O.

Donahue, T. M.↗

NASA NTRS1976

The ultraviolet variations of iota Cas

The Ap variable star iota Cas was observed with the photometers on OAO-2 covering the spectral range 1430-4250 A. The ultraviolet light curves show a double wave with primary minimum and maximum at phase ? 0.00 and 0.35, respectively. Secondary minimum light is at phase ? 0.65 with secondary maximum at phase ? 0.85. The light curves longward of 3150 A vary in opposition to those shortward of this 'null region'. Ground-based coude spectra show that the Fe II and Cr II line strengths have a double-wave variation such that maximum strength occurs at minimum ultraviolet light. We suggest that the strong ultraviolet opacities due to photoionization and line blanketing by these metals may cause the observed photometric variations. We have also constructed an oblique-rotator model which shows iron and chromium lying in a great circle band rather than in circular spots.

Molnar, M. R.↗

NASA NTRS1976

Quasi-biennial geomagnetic variation caused by the sun

Clear evidence for the existence of a quasi-biennial geomagnetic variation is shown by an analysis of annual averages of the horizontal (H) component of the geomagnetic field observed at five observatories. The analysis uses a numerical filter, which is equivalent to taking the second order time derivative of the time series. The cause for the variation is external to the earth because its amplitude depends on magnetic activity. The second order time derivative of H is well correlated with the corresponding time derivatives of the relative sunspot number and 10.7 cm solar flux. It is suggested that quasi-biennial oscillations observed in the geomagnetic field, cosmic rays, stratospheric zonal wind and temperature, total ozone, and other meteorological parameters could be produced by a common cause on the sun.

Sugiura, M.↗

NASA NTRS1976

Temperatures of the Martian surface and atmosphere - Viking observation of diurnal and geometric variations

Selected observations made with the Viking infrared thermal mapper after the first landing are reported. Atmospheric temperatures measured at the latitude of the Viking 2 landing site (48 deg N) over most of a Martian day reveal a diurnal variation of at least 15 K, with peak temperatures occurring near 2.2 hours after noon, implying significant absorption of sunlight in the lower 30 km of the atmosphere by entrained dust. The summit temperature of Arsia Mons varies by a factor of nearly two each day; large diurnal temperature variation is characteristic of the south Tharsis upland and implies the presence of low-thermal-inertia material. The thermal inertia of material on the floors of several typical large craters is found to be higher than for the surrounding terrain; this suggests that craters are somehow effective in sorting aeolian material. Brightness temperatures of the Viking 1 landing area decrease at large emissions angles; the intensity of reflected sunlight shows a more complex dependence on geometry than expected, implying atmospheric as well as surface scattering.

Kieffer, H. H.↗

NASA NTRS1977

Abundance variations in high-velocity interstellar gas

Based on line-of-sight models and profile fitting, abundance variations of Ca, Si, Fe, and Na in high-velocity interstellar clouds toward Mu Columbae, HD 28497, and HD 50896 are discussed. The correlation of larger ratios N(Ca II)/N(Na I) with increasing radial velocity in clouds with absolute values of radial velocity from 20 to 100 km/s, is shown to quite likely be due to abundance variations in Ca rather than an ionization effect. Copernicus UV data show that the ratios N(Fe II)/N(S II) and N(Si II)/N(S II) have the same velocity correlation as Ca II, and the ambiguity concerning the relative abundance of Na I to hydrogen is removed. Theories of grain disruption are discussed as they relate to the observed Ca, Si, and Fe enhancements and their correlation with cloud velocity.

Shull, J. M.↗

NASA NTRS1976

Observation of spatial and temporal variations in X-ray bright point emergence patterns

Observations of X-ray bright points (XBP) over a six-month interval in 1973 show significant variations in both the number density of XBP as a function of heliographic longitude and in the full-sun average number of XBP from one rotation to the next. The observed increases in XBP emergence are estimated to be equivalent to several large active regions emerging per day for several months. The number of XBP emerging at high latitudes varies in phase with the low-latitude variation and reaches a maximum approximately simultaneous with a major outbreak of active regions. The quantity of magnetic flux emerging in the form of XBP at high latitudes alone is estimated to be as large as the contribution from all active regions.

Golub, L.↗