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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Variations in electron density in the middle latitude D-region above Urbana, Illinois

Electron density measurements made with the partial reflections technique above Urbana, Illinois (44 deg 10 min N, 88 deg 10 min W) were analyzed for day-to-day variations, seasonal variations, magnetic storm aftereffects, and stratosphere-ionosphere coupling effects. As well as showing a winter anomaly, the electron densities near 76 km were significantly lower in fall than in spring. Magnetic storm aftereffects of the type predicted by models of energetic electron precipitation at middle latitudes were observed. No strong correlations were found between stratospheric and D-region time series, or between the occurrence of stratospheric warmings and D-region changes. It is likely that most of the electron density variation was due to variations in the transport of minor neutral constituents. The spring-fall differences were also probably caused by differences in minor constituent concentrations rather than the effect of temperature changes on the recombination coefficient.

Wratt, D. S.↗
NASA NTRS1977

Variable mid-latitude X-ray source 3U 0042+32

A celestial location with an error circle of radius one minute is reported for the mid-latitude X-ray source 3U 0042+32; comparison of observations from the Ariel-5 and Uhuru satellites with data obtained from two independent rotation modulation collimators yields the precise position. Studies to detect regular pulsations and energy spectra of the X-ray source are also discussed. Analysis of the peak X-ray flux in the error circle, as well as certain distance constraints, suggests that the source of the flux may be a neutron star in a distant galactic binary system having a companion that undergoes episodes of mass transfer due to eruption or orbital eccentricity.

Rappaport, S.↗
NASA NTRS1978

Analysis of daily latitude variations

The daily latitude measurements of the International polar motion service are analyzed. The results indicate that the annual polar oscillation is probably due to local phenomena with amplitudes varying from 0.05 to 0.15 min. Within the resolution of the residuals (150 cm), there is no indication of the sharp changes which might be associated with earthquake effects. Then, applying Schuster's test to a periodogram of the residuals indicates that there are probably several processes occurring at amplitudes between 0.007 and 0.03 min whose solution awaits a more precise measurement technique.

Graber, M. A.↗
NASA NTRS1978

Analysis of star pair latitudes

Star pair latitude observations forming the basis for the pole positions reported by the International Polar Motion Service (IPMS) are processed to produce a mean pole position. However, the time series of raw observations contains high frequency information which is lost in the calculation of the mean pole. Analysis of 2931 star pair observations reveals a possible large excitation at one cycle per solar day. The average power level in the frequency band of the tesseral tides is seen to be high, although the peaks do not occur at the expected tidal frequencies.

Graber, M. A.↗
NASA NTRS1977

Numerical model of the convecting F2 ionosphere at high latitudes

In previous work Knudsen (1974) presented a model for the convection field of the high latitude F layer and evaluated the time-dependent behavior of a tube of F layer plasma carried around the polar regions by the field. The present paper describes the initial results of a more detailed numerical study of the behavior of the F layer tubes, where it is assumed that the tubes are subjected to time-dependent ionization rates from both solar photons and precipitating energetic electrons. The numerical results are presented in the form of a map view of N-m F2 contours, electron concentration in vertical section over the magnetic pole from noon to midnight, and several vertical profiles of electron concentration for both convecting and nonconvecting flux tubes. The proposed convection field produced a tongue of F layer plasma extending from the dayside of the cleft over the polar cap with concentrations consistent with those observed by Isis 2.

Knudsen, W. C.↗
NASA NTRS1977

Wintertime density perturbations near 50 km in relation to latitude

Standard and reference atmospheres which depict the horizontal distribution of air density in the stratosphere and mesosphere are not realistic in that they do not provide information on the large departures from standard that may occur during a given month, nor on the time- and space-scales of atmospheric perturbations responsible for these departures. In the present paper, it is shown how this information can be obtained from a special analysis of satellite radiance measurements. Plots of the mean zonal radiance, obtained with the VTPR instrument, and the corresponding 50-km density show not only the expected strong poleward gradient of density, but also a strong density surge from late December to early January, affecting all latitudes.

Quiroz, R. S.↗
NASA NTRS1978

Diurnal and seasonal effects in E region low-latitude nitric oxide

Measurements of nitric oxide in the lower E region made by the ultraviolet nitric oxide experiment on Atmosphere Explorer C during 1974 are used to demonstrate diurnal and seasonal effects at low latitudes. At the equator, NO increases by about a factor of 2 between sunrise and the early afternoon: this is followed by a small decline toward sunset. Seasonally, NO shows an asymmetry about the equator with more NO on the summer side than on the winter side; at equinox the asymmetry vanishes. These effects are in qualitative accord with the current theoretical understanding of thermospheric nitric oxide.

Stewart, A. I.↗
NASA NTRS1978

A numerical model for low-latitude ionospheric TEC

A numerical model of total electron content (TEC) at low latitudes has been constructed from the Faraday rotation data recorded at a number of locations in India during the period Oct. 1975-July 1976 when the geostationary satellite ATS-6 was located at 35 deg E. In all, 36 coefficients for each season are required to represent the model. The model can be used for satellite tracking systems in estimating quickly the range, range rate and angular refraction errors. The present model is an improvement over the previously constructed model based on orbiting satellite data.

Sethia, G.↗
NASA NTRS1979

Ion velocity distributions in the high-latitude ionosphere

The theory and observations relating to ion velocity distributions in the high-latitude F region are reviewed. The review covers three basic aspects, including methods for calculating ion velocity distributions, experimental evidence for the existence of non-Maxwellian ion velocity distributions, and the ionospheric consequences of non-Maxwellian distributions. Specific topics covered include closed form solutions to Boltzmann's equation for a simple collision model, series solutions to the Boltzmann equation for more general collision models, retarding potential analyzer measurements, excitation of VLF electrostatic emissions, ion-neutral reaction rates, and transport effects.

St-Maurice, J.-P.↗
NASA NTRS1979

The latitude variation of O2 dayglow and O3 abundance on Mars

Spectroscopic observations of the Martian O2 dayglow near 1.27 microns directly show that the parent molecule, O3, has a strong latitude variation. These measurements give actual data on the equatorial concentrations, where Mariner gave only upper limits. The data also agree with a recent photochemical model, and the derived atmospheric temperature is in good agreement with this model.

Traub, W. A.↗
NASA NTRS1979

An intense soft high-latitude X-ray source H2156-304 - A new BL Lacertae object

The discovery of an intense high-latitude soft X-ray source (designated H2156-304) detected with the low-energy detectors of the HEAO A-2 experiment is reported. The error box of the source includes a 14th mag starlike object that may be coincident with the radio source PKS 2155-304 and has been suggested as a BL Lac candidate. Intensity variations of H2156-304 on time scales of about 1 sec to 1 day are discussed, along with a probable flare from the source. The derived energy spectrum of the source is shown to be well fitted by either a two-temperature thermal model with temperatures of 16 million and 1.6 million K or a single power-law model with a spectral index of 2.4 + or - 0.3. Hydrogen column densities of approximately 2.5 x 10 to the 20th and 2.0 x 10 to the 20th H atoms/sq cm are obtained for the two-temperature and power-law models, respectively. The emission mechanism of H2156-304 is considered, and the characteristics of this source are compared with those of three known soft X-ray-emitting BL Lac objects.

Agrawal, P. C.↗
NASA NTRS1979

High-latitude field-aligned current sources and induced electric fields

Using a simple, planar model of the high latitude ionosphere with an enhanced conductivity auroral ring, the electric potential is computed for a pair of field-aligned current sheets inferred from observations. The relationship of various characteristics of the electric potential pattern to features of the field-aligned current distribution are elucidated in the context of a generalized field-aligned current Fourier analysis. On the basis of the analysis and observations to date, it is concluded that boundary layer dynamo action is the prevalent mechanism in the solar wind/magnetosphere/ionosphere interaction.

Barbosa, D. D.↗
NASA NTRS1979

Analysis of star pair latitudes

Star pair latitude observations form the basis for the pole positions reported by the International Polar Motion Service (IMPS). The IPMS processes these observations to produce a mean pole position. However, the time series of observations contains high-frequency information which is lost in the calculation of the mean pole. In this study, 2931 star pair observations are analyzed. A possible large excitation at one cycle per solar day is observed. The average power level in the frequency band of the tesseral tides is seen to be high, although the peaks cannot be conclusively identified as tidal phenomena.

Graber, M. A.↗
NASA NTRS1980

Solar cycle changes in the high latitude solar wind

Measurements of the solar wind velocity during the period 1971-79 using the technique of interplanetary scintillation are discussed. The average wind speed was faster than 500 km/s at latitudes above 30 deg for most of 1973-77. The fast polar stream, observed to become much narrower in 1978-79 is examined. The narrowing of the polar streams coincided with the emergence of sunspots at midlatitudes, with the start of the new solar cycle, and with a corresponding contraction of the polar coronal holes. The theory that the solar magnetic field controls the large scale structure of the solar wind is discussed in relation to the results.

Rickett, B. J.↗
NASA NTRS1979

High-latitude E and F region ionospheric predictions

The physical processes and morphology of the high latitude E and F layers are discussed. The existence and adequacy of models, and features to be included are examined, as well as reliability of ionospheric predictions.

Hunsucker, R. D.↗
NASA NTRS1979

Morphology and phenomenology of the high-latitude E and F regions

Results obtained at high latitude observatories on the behavior of E and F region ionization are presented including a bibliography. Behavior of E and F region ionization during day and night for quiet and disturbed conditions in the auroral and polar regions is described. Daily, seasonal and sunspot variations are also outlined.

Hunsucker, R. D.↗