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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.

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At least 271 records · Page 15
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NASA NTRS1981

High energy X-ray observations of CYG X-3 from from OSO-8: Further evidence of a 34.1 day period

The X-ray source Cyg X-3 (=4U2030+40) was observed with the high energy X-ray spectrometer on OSO-8 for two weeks in 1975 and in 1976 and for one week in 1977. No change in spectral shape and intensity above 23 keV was observed from year to year. No correlation is observed between the source's intensity and the phase of the 34.1 day period discovered by Molteni, et al. (1980). The pulsed fraction of the 4.8 hour light curve between 23 and 73 keV varies from week to week, however, and the magnitude of the pulsed fraction appears to be correlated with the 34.1 day phase. No immediate explanation of this behavior is apparent in terms of previously proposed models of the source.

Dolan, J. F.↗
NASA NTRS1982

Three-dimensional simulations of cumulus congestus clouds on GATE day 261

Schlesinger's (1978) three-dimensional cumulus model is applied to showering congestus clouds on day 261 of GATE. Model results are compared with each other and with observations to analyze the effects of varying shear and altered sounding. Relationships between shear, mesovortices and dynamic entrainment are examined, as well as the model clouds' impact on the environment as a function of shear. The simulations appear to resemble reality in many important aspects. Altostratus layers observed on day 261 are found to be a by-product of convection in three-dimensional shear. Rapid erosion of cloud base to 3.6 km is related to the ambient thermal structure, with wind shear and initial perturbation playing a secondary role. Some of the apparent conflict regarding lateral versus cloud-top entrainment is clarified, as well as some factors governing convective downdraft structure and intensity.

Simpson, J.↗
NASA NTRS1982

An 80 day X-ray light curve of 3C 371

The Large Area Sky Survey (LASS) experiment on HEAO 1 that monitored the N galaxy/BL Lacertae object 3C 371 from August 19 to November 7, 1977 is discussed, noting that statistically significant threefold or larger intensity variations were observed in the flux range 0.5-20 keV. It is found that the degree of variability depends on the time of observation, with the source sometimes appearing constant and sometimes changing on time scales of 1 to 2 weeks. Also observed was an X-ray flare that lasted approximately 25 days. The total 80-day X-ray light curve is seen as suggesting either a superposition of X-ray flares or a variable injection rate that changes on weekly time scales. The observed X-ray flux is found to be consistent with that expected by extrapolating the nonthermal optical spectrum, suggesting that the optical to X-ray flux could be synchrotron radiation, provided that it is possible to account for the patterns of variability seen at optical and X-ray wavelengths and to dispose of inverse Compton difficulties.

Snyder, W. A.↗
NASA NTRS1982

Short term /1 and 3 day/ cardiovascular adjustments to suspension antiorthostasis in rats

Antiorthostasis (AO) results in responses reflective of thoracic vessel loading. Initial findings included fluid and electrolyte shifts (diuresis and natriuresis) in AO but not in orthostatic (O) rats. This study aims at obtaining supportive evidence for cardiovascular responses, E.g., blood pressure and related parameters, in light of the original hypothesis. Tilting rats rapidly head-up from either horizontal (O) or head-down (AO) positions was used to assess cardiovascular sensitivities. O and AO rats were used after 1 or 3 days of suspension. Rats were controls (C), pre-tilted O and AO, tilted O and AO (rapid head-up 70-80 deg); post-tilted (to original postures). MAP in C rats was 108 +2 mmHg, in O, (117 + or - 1.02) and AO, (120 + or - 0.58). MAP, diastolic pressure (DP) and pulse pressure were consistently elevated in AO rats on day 3. With rapid head-up tilt, only MAP and DP showed significant increases. These changes were seen as cardiovascular responses to AO and support further use of this rat model for AO studies.

Musacchia, X. J.↗
NASA NTRS1983

Solar oscillations with 13-day period

Reference is made to the solar observations made by Claverie et al. (1982) over a three-month period in the summer of 1981 which show oscillatory velocity with a period of 13.1 days and amplitude of 6.6 m/s. These investigators reject the possibility that they see the Doppler shift from a radial oscillation, because the amplitude is implausibly large. They also do not believe that their signal was induced by solar magnetic fields, since typical mean solar fields are too small. Photo-electric drift-scan measurements of the solar diameter and full-disk magnetograms taken at Kitt Peak National Observatory are examined here for evidence of variations corresponding to the velocity oscillations of the 13.1-day period. An upper limit on radius variations is reported which is a factor of six below the amplitude needed to explain the velocity observations as a radial oscillation. Attention is also given to the possible role of the rotation of large-scale surface magnetic features.

Duvall, T. L., Jr.↗
NASA NTRS1983

A quasi-continuous record of atmospheric opacity at lambda = 1.1 mm over 34 days at Mauna Kea Observatory

A quasi-continuous record of atmospheric attenuation is obtained. The data were gathered during a 24-day period in September and October 1982 and a 10-day period in December of that year. The opacity is arrived at by measuring the thermal emission of the atmosphere over a bandwidth of approximately 300 MHz. Using an experimental relationship established by Zammit and Ade (1981), opacity measurements at 1.1 mm are converted to the precipitable water vapor column overhead. With the precipitable water vapor, estimates of opacity due to water vapor can be made for other mm and FIR wavelengths. These estimates require model absorption curves for the atmosphere.

De Zafra, R. L.↗
NASA NTRS1984

Hyperion - 13-day rotation from Voyager data

The rotation period of Hyperion is determined here on the basis of a light-curve derived from low-resolution Voyager images taken over a two-month span. The data indicate a coherent 13-day spin period over 61 days, with the spin axis nearly parallel to the orbital plane. Since Hyperion is not in synchronous rotation, it cannot be used to test the hypothesis that dark dust spiralling inward on retrograde orbits causes the pronounced leading side/trailing side albedo asymmetry observed on the surface of Iapetus.

Thomas, P.↗
NASA NTRS1984

Very slow classical Cepheids - Theoretical models with periods longer than 50 days

Systematics of the light curves of classical Cepheids with the longest known periods have been investigated with the help of full-amplitude models of pulsating stellar envelopes. For periods exceeding about 60 days, flat-topped light curves of the S Vul type are found to replace the smooth, asymmetric light curves characteristic of the slightly faster Cepheids. Predicted light and velocity amplitudes (although not the predicted radius amplitudes) agree well with observations. Variables with fluctuating light minima are observed to lie well off the mean period-luminosity relation, as are a few other (more stable?) variables with similarly long periods. The explanation for the long periods is probably low effective temperature rather than a low stellar mass. Because of the abnormal slowness of the classical Cepheids with periods longer than about 100 days, it is recommended that these variables not be used to calibrate the mean period-luminosity relation. Analogies between the slow classical Cepheids and the slow Population II Cepheids are drawn.

Carson, T. R.↗
NASA NTRS1985

Data on noise environments at different times of day around airports

Sources of information about noise environments at different times of the day at civilian and military airports are identified. Information about movements of scheduled flights are available in machine readable form from the Official Airline Guide. Information about permanent noise monitoring sites is readily obtained from individual airports. Limited data on the timing of flights are available at centralized locations for military airports. An examination of scheduled flights at commercial airports leads to the conclusion that differences between daytime and nighttime noise levels (measured in Equivalent Continuous Noise Level, LEQ) vary from 7 to 15 decibels. Data from 128 permanent noise monitoring sites at 11 airports are also examined. Differences between daytime and nighttime noise levels at these 128 noise monitoring sites vary from 3 to 17 decibels (LEQ). Preliminary analyses suggest that accurate estimates of time-of-day weights could not be obtained from conventional social surveys at existing airports.

Fields, J. M.↗
NASA NTRS1986

The relative effect of noise at different times of day: An analysis of existing survey data

This report examines survey evidence on the relative impact of noise at different times of day and assesses the survey methodology which produces that evidence. Analyses of the regression of overall (24-hour) annoyance on noise levels in different time periods can provide direct estimates of the value of the parameters in human reaction models which are used in environmental noise indices such as LDN and CNEL. In this report these analyses are based on the original computer tapes containing the responses of 22,000 respondents from ten studies of response to noise in residential areas. The estimates derived from these analyses are found to be so inaccurate that they do not provide useful information for policy or scientific purposes. The possibility that the type of questionnaire item could be biasing the estimates of the time-of-day weightings is considered but not supported by the data. Two alternatives to the conventional noise reaction model (adjusted energy model) are considered but not supported by the data.

Fields, J. M.↗
NASA NTRS1985

The 4-5 day mode oscillation in zonal winds of Indian middle atmosphere during MONEX-79

In the early studies based on time series of balloon observations, the existence of 4 to 5 day period waves and 10 to 20 day wind fluctuations were found in the tropical lower stratosphere, and they are identified theoretically as the mixed Rossby-gravity wave and the Kelvin wave, respectively. On the basis of these studies, it was established that the vertically propagating equatorial waves play an important role in producing the QBO (quasi-biennial oscillation) in the mean zonal wind through the mechanism of wave-zonal interaction. These studies are mainly concentrated over the equatorial Pacific and Atlantic Oceans. Similar prominent wave disturbances have been observed over the region east of the Indian Ocean during a quasi-biennial oscillation. Zonal winds in upper troposphere and lower stratosphere (10 to 20) km of the middle atmosphere over the Indian subcontinent may bear association with the activity of summer monsoon (June-September). Monsoon Experiment (MONEX-79) has provided upper air observations at Balasore (21 deg. 30 min.N; 85 deg. 56 min.E), during the peak of monsoon months July and August. A unique opportunity has, therefore, been provided to study the normal oscillations present in the zonal winds of lower middle atmosphere over India, which may have implication on large scale wave dynamics. This aspect is examined in the present study.

Reddy, R. S.↗
NASA NTRS1985

Aspects of the 40-50 day oscillation during the northern winter as inferred from outgoing longwave radiation

One-point correlation statistics and extended empirical orthogonal function analysis are used to show the existence of a principal mode of oscillation in the intraseasonal variability (ISV) of tropical convection. The data analyzed were derived from NOAA Outgoing Longwave Radiation data covering seven 6 mo periods from 1974-83. The data is filtered to remove fluctuations on time scales under 5 days and by subtracting a least-squares parabola to eliminate seasonal means. The previously-known 40-50 day oscillation is found to be the most prevalent component of the ISV of tropical convection. An E-W dipole forms and propagates over the equatorial Indian Ocean, then stalls and intensifies over Indonesia and the equatorial Indian Ocean, then stalls and intensifies over Indonesia and the equatorial central Pacific. Various anomalies generated in association with the dipole and dependent on its exact location when stalled are discussed.

Lau, K.-M.↗
NASA NTRS1985

Confirmation of a 152 day periodicity in the occurrence of solar flares inferred from microwave data

Evidence for a periodicity of about 155 + or - 5 days in the production of energetic solar flares was reported in 1984 by Rieger et al. and Kiplinger et al. To see whether this periodicity is a persistent phenomenon, the occurrences of flares inferred from microwave data, which are available for most of the present and previous solar cycles, were examined. Strong confirmation of a 152 day periodicity in the time interval previously studied is found, demonstrating that these flares are a useful indicator for the observed periodicity. Evidence is found for persistence of the periodicity in the previous cycle (cycle 20). In cycle 20 the periodic modulation of the flare occurrence rate was weaker than in cycle 21, but the phase has apparently remained coherent through both cycles.

Bogart, R. S.↗
NASA NTRS1986

A study of gravity-wave spectra in the troposphere and stratosphere at 5-min to 5-day periods with the Poker Flat MST radar

An analysis of frequency spectra at periods of about 5 days to 5 min from two 20-day sets of velocity measurements in the stratosphere and troposphere region obtained with the Poker Flat mesosphere-stratosphere-troposphere (MST) radar during January and June, 1984 is presented. A technique based on median filtering and averaged order statistics for automatic editing, smoothing and spectral analysis of velocity time series contaminated with spurious data points or outliers is outlined. The validity of this technique and its effects on the inferred spectral index was tested through simulation. Spectra obtained with this technique are discussed. The measured spectral indices show variability with season and height, especially across the tropopause. The discussion briefly outlines the need for obtaining better climatologies of velocity spectra and for the refinements of the existing theories to explain their behavior.

Bemra, R. S.↗
NASA NTRS1986

A preliminary theory of the origin of the 40-50 day oscillation

A theory of the 40 to 50 day oscillation in the tropical atmosphere which encompasses predominantly eastward propagation along the equator, spatial scales of wavenumber 1 and 2, slow time scales (20 to 70 days), and strong amplitude modulation in associated large-scale convective activity as a function of geographical location, i.e., pronounced convection is confined to the Indian Ocean and western Pacific, is presented. An initial disturbance generated near the equator disperses away from the source region, eastward by Kelvin waves and westward by Rossby waves. When the eastward disturbance passes over warm water it is expected to amplify by CISK due to enhanced supply of moisture from the ocean surface. Over cold water, its amplitude is expected to reduce due to decreased moisture supply. The climatological sea surface temperature contrast between the Indian Ocean/western Pacific and the eastern Pacific sets the spatial scale of the wave and its modulation to low wavenumbers and confines pronounced convection to the warm sector. If the eastward propagating wave can maintain itself over dissipation one circuit around the globe, it has a good chance to continue the process indefinitely, provided it is rejunvenated over the warm water with enough energy to go around for the next cycle.

Lau, K. M.↗
NASA NTRS1986

The origin of the 28- to 29-day recurrent patterns of the solar magnetic field

Numerical simulations of the sun's mean line-of-sight magnetic field suggest an origin for the 28- to 29-day recurrent patterns of the field and its associated interplanetary phenomena. The patterns are caused by longitudinal fluctuations in the eruption of new magnetic flux, the transport of this flux to mid latitudes by supergranular diffusion and meridional flow, and the slow rotation of the resulting flux distributions at the 28- to 29-day periods characteristic of those latitudes.

Sheeley, N. R., Jr.↗
NASA NTRS1987

Variations of the semi-diurnal tidal wind in the meteor region with periods of about 27 and 13.5 days

Daily values of sunspot number and solar radio emission at 10.7 cm wavelength show a well known strong modulation with a period of 27 days, the Sun's rotation period. Recent satellite measurements revealed the same modulation of the ultraviolet irradiance at wavelength below 300 nm. These UV variations can influence the thermal heating of the ozone layer by altering the chemical composition. Therefore, one can also expect a corresponding variation in the middle atmosphere of the semi-diurnal tide, which is thermally excited essentially by absorption of UV between 200 and 370 nm in the upper ozone layer. Results of radar meteor wind measurements were used to detect a presumable very weak 27 day modulation within the natural and artificial noise of the daily values of the semi-diurnal wind amplitude. The summer period was chosen because of its relatively steady conditions and the maximum amplitudes during the year. The results of this investigation are given and discussed.

Greisiger, K. M.↗
NASA NTRS1987

Chemical interactions between the present-day Martian atmosphere and surface minerals

Thermochemical and photochemical reactions between surface minerals and present-day atmospheric constituents are predicted to produce microscopic effects on the surfaces of mineral grains. Relevant reactions hypothesized in the literature include conversions of silicates and volcanic glasses to clay minerals, conversion of ferrous to ferric compounds, and formation of carbonates, nitrates, and sulfates. These types of surface-atmosphere interactions are important for addressing issues such as chemical weathering of minerals, biological potential of the surface environment, and atmospheric stability in both present and past Martian epochs. It is emphasized that the product of these reactions will be observable and interpretable on the microscopic surface layers of Martian surface rocks using modern techniques with obvious implications for sample return from Mars. Macroscopic products of chemical weathering reactions in past Martian epochs are also expected in Martian surface material. These products are expected not only as a result of reactions similar to those proceeding today but also due to aqueous reactions in past epochs in which liquid water was putatively present. It may prove very difficult or impossible however to determine definitively from the relic macroscopic product alone either the exact weathering process which led to its formation or the identity of its weathered parent mineral. The enormous advantages of studying Martian chemical weathering by investigating the microscopic products of present-day chemical reactions on sample surfaces are very apparent.

Prinn, Ronald↗