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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Systematic and random variations in Thematic Mapper digital radiance data

Studies are reported of the systematic and random variations in digital radiance data obtained by the Landsat-4 and Landsat-5 Thematic Mappers over an agricultural crop area which was apparently uniform and cloud-free. Systematic variations appeared to be time-dependent and bandpass-dependent. The predominant effect seemed to be random variations, which appeared to be in keeping with those expected from prior investigations. It is suggested that uncorrected variations will provide a limitation on the nonphotointerpretative analysis of images.

Duggin, M. J.↗
NASA NTRS1985

Irregularities in the secular variation and geodynamic implications; Proceedings of the Session, Cincinnati, OH, May 17, 1984

Consideration is given to: variations in the Gauss coefficients of the geomagnetic potential over the last several hundred years; eccentric geomagnetic dipole drift; and evidence for geomagnetic jerks from 1931 to 1971. Among other topics discussed are: models of the geomagnetic field in western Europe from 1960 to 1980; the external and internal parts of the geomagnetic jerk of 1970; secular variation of the magnetic mean energy density at the source layer depth; and motions at the core surface in the geostrophic approximation. Consideration is also given to: the unpredictability of geomagnetic secular variation; the use of short-term core-mantle coupling and geomagnetic variation impulses as Lagrangian tracers of core motions; and a comparison of two sequential geomagnetic polarity transitions in the upper Olduvai and the lower Jarmillio in the Southern Hemisphere.

Taylor, P.↗
NASA NTRS1985

The global response of stratospheric ozone to ultraviolet solar flux variations

The relation between rotational modulation of the ultraviolet solar irradiance and variations in atmospheric ozone has been investigated using Fourier transform harmonic analysis and cross-correlations. Ozone variations with the same period and phase as 13.5 day or 27-day solar flux variations occur at tropical and subtropical latitudes over a range of pressure levels centered about 3 mbar. The solar-forced oscillation is stronger in the summer hemisphere; as temperature-related variations would be stronger in winter. Changes in solar irradiance over the 11-year cycle can be estimated by scaling rotational modulation. Using this estimate and the ozone-sun relation obtained for rotational modulation yields solar cycle changes of 3.5 percent in 3 percent mixing ratio comparable to that predicted from halocarbons and 0.7 mbar in total ozone.

Heath, D. F.↗
NASA NTRS1986

Modification of a variational objective analysis model for new equations for pressure gradient and vertical velocity in the lower troposphere and for spatial resolution and accuracy of satellite data

Since late 1982 NASA has supported research to develop a numerical variational model for the diagnostic assimilation of conventional and space-based meteorological data. In order to analyze the model components, four variational models are defined dividing the problem naturally according to increasing complexity. The first of these variational models (MODEL I), the subject of this report, contains the two nonlinear horizontal momentum equations, the integrated continuity equation, and the hydrostatic equation. This report summarizes the results of research (1) to improve the way the large nonmeteorological parts of the pressure gradient force are partitioned between the two terms of the pressure gradient force terms of the horizontal momentum equations, (2) to generalize the integrated continuity equation to account for variable pressure thickness over elevated terrain, and (3) to introduce horizontal variation in the precision modulus weights for the observations.

Achtemeier, G. L.↗
NASA NTRS1986

Continuous measurement of nontidal variations of gravity

Records from seven superconducting gravimeters operated at five different locations in California and one in Boulder, CO, are examined after removal of tides and the gravitational attraction of the atmosphere. Fluctuations over periods between a few days and several months were observed at all sites with peak amplitudes of order 10 microgal. By contrast, a 640-day record obtained with one of the instruments in Germany showed peak fluctuations of only 2 microgal. In most of the records the causes of these aperiodic variations were not determined so that they serve to set limits on the vertical motion or displacement of mass at the respective locations. However, at The Geysers geothermal field, much of the gravity variation is correlated with seismic activity, reinjection rate, and rainfall. Measurements of this type were not possible prior to the development of the superconducting device. Consequently, these results provide the first evidence for the existence of gravity variations on the time scale and of the magnitude described here. Vertical crustal motion, motion related to seismic events, and hydrological phenomena can lead to variations on this scale. Unambiguous identification of causal relationships will require either special circumstances such as found at The Geysers or operation of the instruments in pairs.

Goodkind, John M.↗
NASA NTRS1986

Temporal variations of cosmic rays over a variety of time scales

The variation of the intensity of Galactic cosmic rays in the inner solar system over a wide variety of time scales is discussed, and the generally accepted physical model which can account quantitatively for these modulations is reviewed. The use of direct measurements and of nuclear reactions to study the temporal intensity variations is summarized. It is demonstrated that all of the observed variations could easily be the result of solar variations on long and short time scales.

Jokipii, J. R.↗
NASA NTRS1986

Solar cycle variations in the solar wind

The solar cycle variations of various solar wind parameters are reviewed. It is shown that there is a gradual decrease in the duration of high-speed streams from the declining phase of solar cycle 20 through the ascending phase of cycle 21 and a corresponding decrease in the annual average of the proton speed toward solar maximum. Beta, the ratio of the proton thermal pressure to magnetic pressure, undergoes a significant solar cycle variation, as expected from the variation in the IMF. Individual hourly averages of beta often exceed unity with 20 cases exceeding 10 and one case as high as 25. The Alfven Mach number shows a solar cycle variation similar to beta, lower aboard solar maximum. High-speed streams can be seen clearly in epsilon and the y component of the interplanetary magnetic field.

Freeman, John W.↗
NASA NTRS1987

Radial and latitudinal variations of the interplanetary magnetic field

This paper presents observations of the radial and latitudinal variations of the interplanetary magnetic field measured by the Voyager 1 (V1) and Voyager 2 (V2) spacecraft from mid-1977 to mid-1985. Observations of the radial variation of the large-scale magnetic field strength in the ecliptic agree with the predictions of Parker's (1958, 1963) model when temporal variations in the magnetic field and bulk speed are taken into account. The latitudinal variation of the magnetic field observed by V1 is in agreement with the predictions of Parker's model to first approximation. The magnetic field strength at higher latitudes is somewhat lower than expected on the basis of observations made in the ecliptic, but this could be due to an increase in bulk speed and/or a decrease of solar magnetic field strength with latitude. Fluctuations in the strength of the magnetic field are small compared to the large-scale field itself, and they decrease in amplitude with increasing distance approximately as R exp -1/4 . Fluctuations in the components are relatively large, and they make a significant contribution to the mean field that is not described by Parker's model.

Klein, Larry W.↗
NASA NTRS1988

Fast variations in the ultraviolet resonance lines of Alpha Camelopardalis (O9.5 Ia) - Evidence for blobs in the wind

The 72 IUE spectra of Alpha Cam and 19 IUE spectra of Kappa Cas, obtained during 72 hours of continuous IUE time in September 1978 were searched for variations in the profiles of the resonance lines of Si IV, C IV, and N V, and the results are discussed. The UV resonance lines in the spectra of Alpha Cam showed variations at the 2 percent level near -1800, -700, and +700 km/s. The first two variations can be explained by absorption components of outward-accelerated blobs or shells with an average acceleration of 1.5 cm/sq s. The characteristics of the blobs and shells are discussed, including the column densities and masses. No variations were found in the spectra of Kappa Cas.

Lamers, Henry J. G. L. M.↗
NASA NTRS1988

Observations of the stratospheric conductivity and its variation at three latitudes

Measurements from nine high-altitude balloon flights at altitudes ranging from 10 to 30 km have been obtained in order to study atmospheric conductivity variations on local and global scales. The conductivity profiles are not correlated with solar or cosmic ray activity, but they exhibit variations which appear to be dominated by local effects. Evidence is provided of stratospheric aerosol layers with number densities of the order of 1000/cu cm. It is suggested that global conductivity models employing latitudinal variations based on cosmic ray ionization alone may be improved by including the effects of latitudinal variations of temperature and aerosols.

Byrne, G. J.↗
NASA NTRS1988

Correlation of interannual length-of-day variation with El Nino/Southern Oscillation, 1972-1986

Correlation between interannual length-of-day (LOD) changes and an index representation of El Nino/Southern Oscillation (ENSO) for the period of 1972-1986 was examined in two ways: as the cross-correlation function in the time domain and as the complex coherence spectrum in the frequency domain. The ENSO representation was derived from barometric measurements from the Tahiti and Darwin, Australia, meteorological stations, as the difference of the sea-level pressure between the two locations. The cross correlation between this ENSO representation and LOD variation on the interannual time scale was found to have a maximum value of 0.68 and the LOD phase lag of 2 months, indicating that most of the interannual LOD variation is caused by ENSO, and that the transfer of ENSO's axial angular momentum to the solid earth lags behind the Tahiti-Darwin pressure variation by about 2 months. The corresponding coherence spectrum showed minimum correlation around biennial periods, indicating an influence of the stratospheric quasi-biennial oscillation on LOD variations.

Chao, B. Fong↗
NASA NTRS1988

Large time scale variation in hydrogen emission from Jupiter and Saturn

The IUE and Voyager spacecraft observations of Jupiter and Saturn were combined to obtain a consistent measurement of temporal variation of the equatorial subsolar hydrogen emission. The outer planets appear to have rather independent behavior over time scales of the order of 10 yr, particularly in emission from the H Ly alpha line. The time interval from 1978 to the present shows variation of mean equatorial H Ly alpha brightness of 2 at Jupiter and 5 at Saturn. The relative magnitudes of the variations is sufficiently different to suggest that response to input from the Sun is at least nonlinear. The brightness of H2 band emission appears to be relatively more stable than H Ly alpha. There is evidence in IUE observations of a moderate increase in H2 band brightness with increasing time at Jupiter, in opposition to the variation in H Ly alpha.

Shemansky, D. E.↗
NASA NTRS1988

Earth orbital variations and vertebrate bioevolution

Cause of the Pleistocene-Holocene transition mammalian extinctions at the end of the last age is the subject of debate between those advocating human predation and climate change. Identification of an ambient air temperature (AAT)-uterine blood flow (UBF) coupling phenomenon supports climate change as a factor in the extinctions, and couples the extinctions to earth orbital variations that drive ice age climatology. The AAT-UBF phenomenon couples mammalian bioevolution directly to climate change via effects of environmental heat upon blood flow to the female uterus and damage to developing embryos. Extinctions were in progress during climatic warming before the Younger Dryas event, and after, at times when the AAT-UBF couple would have been operative; however, impact of a sudden short-term cooling on mammals in the process of adapting to smaller size and relatively larger S/V would have been severe. Variations in earth's orbit, and orbital forcing of atmospheric CO2 concentrations, were causes of the succession of Pleistocene ice ages. Coincidence of mammalian extinctions with terminations of the more intense cold stages links mammalian bioevolution to variations in earth's orbit. Earth orbital variations are a driving source of vertebrate bioevolution.

Mclean, Dewey M.↗
NASA NTRS1989

On the interpretation of seasonal variations of stratospheric ozone

The causes of the annual and semiannual ozone oscillations were investigated. Using the middle-atmosphere model of Garcia and Solomon (1983), the monthly variations of the ozone mixing ratio were computed and Fourier-analyzed, with excellent agreement found between the computed values and those measured with the SBUV instrument. It was found that, at high latitudes and low altitudes, the modeled ozone abundances increased in the winter due to transport and decreased in the summer due to chemical destruction. In the middle stratosphere, the calculated annual ozone variation was found to be largely due to the annual variation in the odd-oxygen production rate, while in the upper stratosphere, the annual ozone variation was found to be caused by the large annual oscillation in temperature.

Perliski, Lori M.↗
NASA NTRS1990

Far-infrared intensity variations caused by 5 minute oscillations

Observations of solar IR intensity variations at 50, 100, and 200 microns were made simultaneously and cospatially with Doppler measurements in the sodium D1 line at 5896 A. Brightness temperature variations of several K in amplitude are highly correlated with five minute Doppler oscillations. The brightness variations are attributed to work done on the chromospheric medium by compression, driven by the five minute oscillations. The Doppler oscillations lead the brightness variations by about 47 deg in phase at 50 and 100 microns and by about 72 deg in phase at 200 microns.

Lindsey, C.↗
NASA NTRS1990

Directional variations in thermal emission from geologic surfaces

The directional emission properties of geologic surfaces were investigated using a ground-based, hand-held infrared radiometer and thermistor probe. Field sites involved surfaces ranging from smooth playa and sand surfaces to a very rough aa lava flow. Large directional variations in thermal emission were found; they result from the presence of surface roughness at large scales producing spatial variations in kinetic temperature and at small scales producing emissivity variations. These variations are important in remotely determining surface structure and understanding surface energy balance and emission spectra.

Jakosky, Bruce M.↗
NASA NTRS1991

Lateral variation in upper mantle temperature and composition beneath mid-ocean ridges inferred from shear-wave propagation, geoid, and bathymetry

Resolution of both the extent and mechanism of lateral heterogeneity in the upper mantle constraints the nature and scales of mantle convection. Oceanic regions are of particular interest as they are likely to provide the closest glimpse at the patterns of temperature anomalies and convective flow in the upper mantle because of their young age and simple crustal structure relative to continental regions. Lateral variations were determined in the seismic velocity and attenuation structure of the lithosphere and astenosphere beneath the oceans, and these seismological observations were combined with the data and theory of geoid and bathymetry anomalies in order to test and improve current models for seafloor spreading and mantle convection. Variations were determined in mantle properties on a scale of about 1000 km, comparable to the thickness of the upper mantle. Seismic velocity, geoid, and bathymetry anomalies are all sensitive to variations in upper mantle density, and inversions were formulated to combine quantitatively these different data and to search for a common origin. Variations in mantle density can be either of thermal or compositional origin and are related to mantle convection or differentiation.

Sheehan, Anne Francis↗
NASA NTRS1990

Global, seasonal cloud variations from satellite radiance measurements. II - Cloud properties and radiative effects

Cloud and surface radiative properties and their effects on the earth and surface radiation budgets are obtained based on global daily visible and IR radiance measurements. The magnitude of cloud property variations and their effects on radiation increase strongly with decreasing space/time scales. Cloud properties are systematically different between land and ocean, with ocean having larger cloud cover with somewhat larger optical thicknesses and lower cloud top altitudes. Although cloud variations appear to be the primary cause of regional radiation budget variability at 5-30 daytime scales, the effects of their seasonal variations at larger spatial scales are less important than the changes associated with changes in solar declination and atmospheric/surface temperatures. The largest seasonal variations in radiation occur in the 30-60 deg latitude band in each hemisphere. Although clouds have a net cooling effect on the global, annual mean radiation balance at both the top of the atmosphere and the surface, their net effect on regional, seasonal balances is much more varied.

Rossow, William B.↗