Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Latitude”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Mid-latitude VLF emissions observed in the topside ionosphere

Narrow-band VLF emissions observed on different days by Alouette-2 are described. It is found that narrow-band VLF hiss (3.5-7.0 kHz) occurs at midlatitudes (at 54 to 64 deg) in the topside ionosphere during both the geomagnetically disturbed and quiet periods, although the hiss region moves towards the auroral zone during the disturbed period. It is likely that the midlatitude hiss at around 5 kHz is the origin of the narrow-band hiss (5 plus or minus 1 kHz) often observed at ground stations at low latitudes, since no VLF emissions above 2 kHz appear in the auroral zone. The midlatitude VLF hiss observed in the topside ionosphere may be generated by the transverse (electron cyclotron) resonance instability in the magnetosphere.

Ondoh, T.↗
NASA NTRS1975

High-latitude ionospheric winds related to solar-interplanetary conditions

Treated jointly, two recent results imply that the distribution of winds in the polar ionosphere should change as a function of the direction of the interplanetary magnetic field. From the motions of chemically released ion and neutral clouds, it is apparent that neutral winds in the high-latitude ionosphere are driven principally by ion drag forces. OGO 6 electric field measurements demonstrate that there are definite relationships between the time/latitude distribution of ionospheric plasma convection and interplanetary magnetic field parameters, and also that the distribution is most sensitive to the azimuthal angle of the inter planetary field. Although direct neutral wind to interplanetary magnetic field comparisons are not available, logic clearly implies a close relationship. Observations of infrasonic waves following sudden ionization enhancements indicate the existence of momentum transfer.

Heppner, J. P.↗
NASA NTRS1976

Low latitude middle atmosphere ionization studies

Low latitude middle atmosphere ionization was studied with data obtained from three blunt conductivity probes and one Gerdien condenser. An investigation was conducted into the effects of various ionization sources in the 40 to 65 Km altitude range. An observed enhancement of positive ion conductivity taking place during the night can be explained by an atmsopheric effect, with cosmic rays being the only source of ionization only if the ion-ion recombination coefficient (alpha sub i) is small(10 to the -7 power cu cm/s) and varies greatly with altitude. More generally accepted values of alpha sub i ( approximately equal to 3x10 to the -7 power cu cm/s) require an additional source of ionization peaking at about 65 Km, and corresponding approximately to the integrated effect of an X-ray flux measured on a rocket flown in conjunction with the ionization measurements. The reasonable assumption of an alpha sub i which does not vary with altitude in the 50-70 Km range implies an even greater value alpha sub i and a more intense and harder X-ray spectrum.

Bassi, J. P.↗
NASA NTRS1976

A study of the conditions necessary for the onset of mid-latitude spread F

Ionospheric conditions associated with the initiation of spread F in the mid-latitude ionosphere were observed. The morphology of spread F at Puerto Rico was investigated. Data from 7 nights was examined for Arecibo, five with spread F and two without. The relative height of the F layer maximum and the vertically integreted Pedersen conductivity, the relation between E and F region conductivities, the coupling lengths between the E and F regions, and vertical and horizontal gradients of electron density were examined. At Millstone Hill 13 nights were examined for all of which spread F was observed. The EW and NS velocities and the vertical velocities and the electric ion temperature ratio were examined.

Zinchenko, G. N.↗
NASA NTRS1976

Empirical models of high latitude electric fields

Model cross sections of the high latitude dawn-dusk electric field based on OGO-6 data are presented for the signature profiles, most frequently encountered for both + and -Y orientations of the interplanetary magnetic field. Line integrals give a total potential of 76 keV in each case. To illustrate extremes, examples of model cross-sections with total potentials of 23 keV and 140 keV are also given. Model convection patterns are also presented utilizing OGO-6 data on boundary locations at other magnetic local times. When this information is combined with characteristic field geometries in the region of the Harang discontinuity, and is supplemented by data from Ba+ cloud motions in the polar cap, it becomes possible to construct realistic convection patterns on the nightside which deviate from the usual sun-aligned patterns. The observational models presented are of limited applicability as a consequence of the variability of observed distributions. These limitations are emphasized with particular attention given to several types of recurrent deviations which have not previously been discussed.

Heppner, J. P.↗
NASA NTRS1976

Dependence of the latitude of the cleft on the interplanetary magnetic field and substorm activity

The latitudinal motion of the cleft (the polar cusp) associated with the southward interplanetary magnetic field (IMF) and substorm activity is examined. The cleft location is identified on the basis of the location of midday auroras and of electron precipitation by the OGO 4 and ISIS 1 satellites. It is found that the IMF and substorm activity control independently the latitude of the cleft and that they can shift the cleft location by 3 or 4 deg under average conditions.

Kamide, Y.↗
NASA NTRS1976

A fast transient source of hard X-rays at high galactic latitude

An extremely short-lived transient X-ray source has been detected with the SAS-3 satellite at a high galactic latitude (about -51 deg). The source, designated MX 2346-65, had a duration of between 45 s and 2200 s as well as a very hard spectrum. This source had not been detected in previous sky surveys and was not seen again by SAS-3 in 7 days of further periodic observations. Possible explanations of this type of event are discussed.

Rappaport, S.↗
NASA NTRS1976

Electron temperature measurements in mid-latitude sporadic E layers

By using rocket-borne Langmuir probes, electron temperature profiles have been obtained in five mid-latitude sporadic E layers. The data show the electron temperature within the layers to be lower than the electron temperature at the adjacent altitudes. This is consistent with the layers' being maintained by a vertical redistribution of ionization. The magnitude of the observed electron temperature variation is, however, larger than expected.

Schutz, S. R.↗
NASA NTRS1976

Effects of electric fields and other processes upon the nighttime high-latitude F layer

The dynamics of the nighttime high-latitude F region is studied with special emphasis on the formation of the electron-density trough region which lies equatorward of the auroral oval. It is found that the absence of photoionization together with ordinary ionic recombination and slow plasma convection velocity can give a deep trough over a period of many hours. However, the normal global pattern of electric fields has regions of plasma convection sufficiently rapid to affect the rate of O(+) + N2 reactions and to speed the rate of ionospheric decay. In addition, the escape of thermal plasma via the polar winds as well as N2 vibrational excitation and enhanced N2 densities act to deplete the ionosphere. In combination, these destructive processes can readily account for the great variety of troughs found by experimentation. Thus, it appears that there is no single cause for the observed troughs, but that at various times, different processes act together to create density depressions of substantial magnitude.

Schunk, R. W.↗
NASA NTRS1976

High-latitude truncation errors of box-type primitive equation models

The 'box-type' finite-difference method includes a weighted average of the pressure gradient with weights proportional to the surface of the grid walls. It is shown that this averaging introduces first-order truncation errors near the poles. An example is shown in which the relative error is of zero order and the scheme produces large distortions in the solution at high latitudes.

Kalnay-Rivas, E.↗
NASA NTRS1977

A comparison between the current models of mid-latitude spread F and data from the Arecibo Observatory

The current models of mid-latitude F sub s are studied. The assumptions and derivations of the Reid model, the Scannapieco model, and the Perkins model are presented in detail. Incoherent-scatter data of the density profiles and velocity profiles were obtained in order that the models could be evaluated on the basis of experimental data. Initial studies indicated that the Perkins model was most representative of the data from Arecibo, so a detailed comparison of the predictions of the Perkins model and the data was made. Two of four nights studied are nights with F sub s. The Perkins model is derived in a frame of reference moving with the velocity of the neutral wind; the model is transformed to the rest frame to facilitate comparison with data. Several data handling techniques are introduced. In particular, an integration interval that remains constant in length, but follows the vertical motion of the peak of the F layer is used to obtain the field integrated quantities of the Perkins model.

Imel, G.↗
NASA NTRS1977

A model for simulating random atmospheres as a function of latitude, season, and time

An empirical stochastic computer model was developed with the capability of generating random thermodynamic profiles of the atmosphere below an altitude of 99 km which are characteristic of any given season, latitude, and time of day. Samples of temperature, density, and pressure profiles generated by the model are statistically similar to measured profiles in a data base of over 6000 rocket and high-altitude atmospheric soundings; that is, means and standard deviations of modeled profiles and their vertical gradients are in close agreement with data. Model-generated samples can be used for Monte Carlo simulations of aircraft or spacecraft trajectories to predict or account for the effects on a vehicle's performance of atmospheric variability. Other potential uses for the model are in simulating pollutant dispersion patterns, variations in sound propagation, and other phenomena which are dependent on atmospheric properties, and in developing data-reduction software for satellite monitoring systems.

Campbell, J. W.↗
NASA NTRS1976

Observations of high-latitude X-ray sources with the Uhuru satellite

Uhuru observations of 22 unidentified high-galactic-latitude X-ray sources over the period from December 1970 to April 1973 are analyzed. The results confirm the existence of at least 19 sources, improve the positions for several of them, and yield evidence that some are variable. Two sources, 3U 0042+32 and 3U 1809-50, are found to be variable at the 3-sigma level. The improved positions for 3U 1555+27 and 3U 0405+10 confirm that these sources are, respectively, the Abell galaxies A2142 and A478.

Murray, S. S.↗
NASA NTRS1976

Further evidence of a latitude gradient in the solar wind velocity

Simultaneous Mariner and Explorer data are used in the present paper to show that the large-scale gradient in the bulk velocity of the solar wind observed by Coles (1972) is a heliographic latitude gradient. A value of roughly 15 km/sec/deg for the gradient is derived by a correlation technique employed by Coleman and Rosenberg (1971). A simple model of the velocity/latitude dependence is developed and is shown to be consistent with a direct comparison of the observed Mariner and Explorer velocities. The gradient inferred from the Mariner and Explorer data is compared with values obtained from corresponding analyses of Vela and IPS data.

Rhodes, E. J., Jr.↗
NASA NTRS1977

High-latitude nitric oxide in the lower thermosphere

High-latitude observations of fluorescent nitric oxide gamma bands were made before and during a strong magnetic storm with the Ogo 4 ultraviolet spectrometer. Brightness measurements of the (1-0) gamma band of nitric oxide indicate a slow buildup of NO during the disturbed period. The NO column density reaches a value as high as a factor of 8 greater than the midlatitude value and shows no correlation with the brightness of the instantaneous aurora. A time-dependent model calculation indicates that the ionization and dissociation of N2 by auroral electrons can increase the NO and N(4-S) densities. This increase is dependent on the intensity and duration of the auroral precipitation and on the branching ratio of N(2-D) production by dissociation of N2. A steady state is not reached for NO until 100,000 sec in an aurora characterized by an energy flux of 10 ergs per sq cm sec. Dissociation by the solar ultraviolet radiation competes with horizontal and vertical transport as a loss process for the nitric oxide produced by the aurora. A high NO(plus)/O2(plus) ratio is to be expected in the period following a strong auroral precipitation.

Gerard, J.-C.↗
NASA NTRS1977

Empirical models of high-latitude electric fields

Observational models of high-latitude dawn-dusk electric fields, quantitatively based on Ogo 6 measurements, are presented for the two Northern Hemisphere (summer) distributions that occur, respectively, when the interplanetary magnetic field is in the -Y or +Y hemisphere in solar ecliptic coordinates. Both models are representative of conditions which produce magnetic disturbance levels corresponding to Kp of approximately 3. Model cross sections are also given for two selected time periods when the fields were exceptionally weak or strong and were accompanied by magnetic conditions corresponding to Kp of zero or AE of about 1000, respectively. An attempt is made to construct convection patterns resembling the original idealizations of Axford and Hines (1961) in order to obtain convective continuity within the observed boundaries. Since the result is not realistic in representing observations near the Harang discontinuity in the nightside auroral belt, the pattern is modified to fit typical conditions near that discontinuity.

Heppner, J. P.↗
NASA NTRS1977

Far-ultraviolet studies. II - Galactic-latitude dependence of the 1530 A interstellar radiation field

A 0.62-sq cm Geiger counter, sensitive between 1425 and 1640 A, was used to map the far-ultraviolet brightness of about half the sky, providing an experimental measurement of the far-ultraviolet interstellar radiation field. At 1530 A, the energy density is approximately 7.4 by 10 to the -17th power erg/cu cm per A. Comparison with integrations of star catalogs calibrated to the ultraviolet shows, as expected, that the bulk of the radiation comes directly from B- and A-type stars. The galactic-latitude dependence of the radiation is analyzed in an unsuccessful attempt to set limits on the absorbing and scattering properties of the interstellar grains in the far-ultraviolet. Excess radiation observed at the galactic pole is probably residual airglow from above the rocket altitude.

Henry, R. C.↗
NASA NTRS1977

The low-latitude circulation of Mars

A steady-state two-layer atmospheric model is used in an attempt to simulate the circulation of the equatorial regions of Mars, with consideration of both thermal and mechanical orographic effects. A steady-state solution is sought with the aim of producing mean seasonal circulations upon which tides can be superimposed, and the relative importance of orographic forcing at low latitudes is evaluated. It is assumed that the atmospheres over a topographic feature and over flat terrain possess the same radiative and convective properties, simple dissipation laws are introduced which represent a surface drag effect, and six first-order difference equations are obtained and then reduced to two linear complex second-order coupled difference equations. Analysis of the response of the equinoctial basic wind field to a Gaussian orographic feature situated at the equator and zero deg longitude reveals a number of similarities and differences between the Martian and terrestrial responses. Most of the similarities are explained in terms of the dynamics of a rotating atmosphere, while the major differences are at least partially explained by the different optical properties, lower boundaries, and smaller mass of the Martian atmosphere.

Webster, P. J.↗