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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Global ozone long-term trends from satellite measurements and the response to solar activity variations

Analysis of global ozone variations for the period April 1970 to December 1975 was performed by using the reprocessed Nimbus 4 backscattered ultraviolet (BUV) measurements of total ozone. A correlation coefficient of 0.97 is found between the 6-month running mean of global mean total ozone (filtered for mean semiannual, annual, and quasibiennial variations) and the 10.7-cm solar activity index. Correcting ozone for a time-dependent latitudinal bias relative to Dobson ozone measurements reduces to 2-3% the global mean ozone variation over the solar cycle. The solar ultraviolet variability required in a one-dimensional time-dependent radiative photochemical model to account for the observed ozone variation appears to be consistent with recent solar UV observations.

Keating, G. M.↗
NASA NTRS1982

Short-term EUV flux variations from AE-E He/+/ abundances

The ionization rate of helium in the thermosphere is inferred from AE-E ion and neutral particle composition measurements made on 20 days from January 1979 to June 1980. The variations in the inferred rate are consistent with variations in the UV flux measured during the same period by the AE-E UV spectrometer. The approximately 27-day modulation of the calculated ionization rate is the result of cyclical variations in the UV flux, which are in turn coupled to the rotation period of the sun. Results indicate that the ionization structure of helium in the thermosphere is closely coupled to both the long and short term EUV flux variations.

Sternberg, A.↗
NASA NTRS1981

A model study of the diurnal variation of mesospheric O3

Diurnal variation of ozone between 50 to 80 km is studied for both oxygen-only and O-N-H-C atmospheres. The temporal variation of ozone density along the ray path as well as that due to the change in the local zenith angle are included in the model computations. The difference between cases with and without the temporal variation of ozone density, is examined. It is found that the inclusion of this variation reduces the ozone concentration at all altitudes. In addition, the greatest effect on the ozone concentration is during sunrise and sunset.

Wang, P. H.↗
NASA NTRS1982

Ion temperature variations in the daytime high-latitude F region

The Schunk and Sojka (1981a, b) high latitude ionospheric model is improved through the inclusion of thermal conduction and diffusion terms in the ion energy equation, permitting the study of daytime, high latitude F layer temperature variations in a region poleward of the auroral oval. It is found that ion temperature variation with solar cycle, season and geomagnetic activity closely follows the neutral atomic oxygen variation, and that meridional electric fields of more than 40 mV/m can cause larger ion temperature changes than those due to solar cycle, seasonal or geomagnetic activity variations. In the presence of meridional electric fields, there is an upward flow of heat from the lower ionosphere that also acts to raise ion temperatures at high altitudes. Zonal electric fields affect ion temperature indirectly, through electron density changes.

Schunk, R. W.↗
NASA NTRS1983

Minimal upper mantle temperature variations consistent with observed heat flow and plate velocities

Heat-flow and plate-velocity measurements are used to model upper-mantle temperature variations; the results are intended to form the basis for a gravity-field-variation model and are also applicable to the interpretation of petrological and seismological data. A 5-deg grid is used, a depth of 280 km is chosen as the fully convecting level, and it is assumed that 85 percent of the global heat production (4.0 x 10 to the 13th W) comes from below this level. The velocity field is calculated by integrating the momentum equations down to 280 km (assuming laterally homogeneous viscosity and density) and then used to determine the temperature fields. The results are presented in graphs, tables, and maps. The largest lateral temperature differences are about 1500 C and occur in the top 20 km, where the largest (about 200 C/Myr) nonlinear terms of the energy equation are also found. Below 50 km, heat transfer becomes more convective than conductive, and the most significant temperature variation appears in the form of negative 'tongues' as cold as -825 C at about 100 km. Temperature variations of at least + or - 180 C are calculated at the fully convecting level.

Kaula, W. M.↗
NASA NTRS1984

Interannual length-of-day variation with relation to the southern oscillation/El Nino

The atmospheric and oceanic mass transport associated with the southern oscillation/El Nino will inevitably induce an interannual variation in the length of day. An empirical correlation study is conducted by comparing the Southern Oscillation Index time series and the interannual length-of-day variation (obtained by removing the long-period and short-period variations from a BIH length-of-day series) for the period 1957-1983. The two series have an encouraging qualitative correlation, in particular with respect to El Nino events; and the linear correlation coefficient is found to be 0.55. It is believed that much, if not most, interannual length-of-day variation is caused by the southern oscillation, and the true correlation is considerably higher than its apparent value considering the fact that the Southern Oscillation Index is merely an indicator derived from two local atmospheric measurements.

Chao, B. F.↗
NASA NTRS1985

Probabilistic Finite Element: Variational Theory

The goal of this research is to provide techniques which are cost-effective and enable the engineer to evaluate the effect of uncertainties in complex finite element models. Embedding the probabilistic aspects in a variational formulation is a natural approach. In addition, a variational approach to probabilistic finite elements enables it to be incorporated within standard finite element methodologies. Therefore, once the procedures are developed, they can easily be adapted to existing general purpose programs. Furthermore, the variational basis for these methods enables them to be adapted to a wide variety of structural elements and to provide a consistent basis for incorporating probabilistic features in many aspects of the structural problem. Tasks concluded include the theoretical development of probabilistic variational equations for structural dynamics, the development of efficient numerical algorithms for probabilistic sensitivity displacement and stress analysis, and integration of methodologies into a pilot computer code.

Belytschko, T.↗
NASA NTRS1985

Long term changes in cosmic ray diurnal variations observed by ion chambers in Hong Kong and Japan

Yearly average solar diurnal variations of cosmic ray ion chamber data are inspected from a view point of the eleven and the 22 year solar activity cycle modulations. Ion chamber data and neutron data from various stations are added. From an inspection of observed data, a simple approximation that the 11 year and the 22 year variations of the solar diurnal variation are along 18-hour and 12-hour axes, respectively is proposed. The 18-hour component of diurnal variation in the 11 year cycle increases toward the solar active years. The 12-hour component is enhanced when the solar general magnetic field is parallel to the rotation vector, and is almost zero for the other state. The transition occurs when the amplitude of the 18-hour component is greater owing to the transition of the field during the maximum phase of solar activity. The 22 year shift is consistent with the drift modulation model in heliosphere.

Chuang, L. S.↗
NASA NTRS1984

Small-scale variations in the galactic magnetic field - The rotation measure structure function and birefringence in interstellar scintillations

The structure function of rotation measures of extragalactic sources and birefringence in interstellar scintillations are used to investigate variations in the interstellar magnetic field on length scales of about 0.01-100 pc and 10 to the 11th cm, respectively. Model structure functions are derived for the case of a power-law power spectrum of irregularities in the quantity (n(e)B), and an estimate for the structure function is computed for several regions of the sky using data on extragalactic sources. The results indicate an outer angular scale for rotation measure (RM) variations of not less than about 5 deg (a linear scale of about 9-90 pc at a distance of 0.1-1 kpc). There is also evidence for RM variations on angular scales as small as 1 arcmin, but it cannot be determined whether these are intrinsic to the source or caused by the interstellar medium. The effect of a random, Faraday-active medium on the diffraction of radio waves is derived, and an upper limit to the variations in n(e)B on a length scale of 10 to the 11th cm is obtained from available observations.

Simonetti, J. H.↗
NASA NTRS1985

Morphology of thermospheric composition variations in the quiet polar thermosphere from Dynamics Explorer measurements

Composition data obtained by the Neutral Atmosphere Composition Spectrometer carried aboard the Dynamics Explorer 2 satellite have been examined for variations in the polar regions during magnetically quiet conditions. A persistent enhancement of N2 density and a depletion of He density are present in the vicinity of the magnetic poles with maximum density response in the morning hours (magnetic) on average. A universal time (UT) variation in average density levels is evident near both the geographic and magnetic poles. There are systematic morphology changes with UT and between summer and winter which are qualitatively consistent with the shifting and spreading of thermospheric heating effects by the global circulation systems driven by EUV and magnetospheric sources. The magnitude of the UT variations is larger in the southern hemisphere on average, and the UT variations are larger in local winter than summer.

Hedin, A. E.↗
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.↗