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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 127 records · Page 7
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NASA NTRS1976

Seasonal variation of neutral thermospheric constituents in the Northern Hemisphere

The Atmosphere Explorer-C satellite carries a large number of experiments including an open source neutral mass spectrometer. Among the measurements obtained with this instrument were ones of particle densities of N2, O, and He at northern latitudes in early February and late June 1974. The orbital geometry of the satellite was such that comparisons could be made between the winter and summer values at the same altitudes and latitudes and at similar local solar times. The helium density shows in midmorning a winter to summer enhancement of a factor of 29 at 400 km. The enhancement at other altitudes, both higher and lower, is less. At 250 km the winter/summer oxygen ratio is 1.7, whereas the winter/summer nitrogen ratio is 0.6. Both ratios decrease with increasing altitudes. The analysis identifies an oxygen enhancement at low altitudes in winter and at high altitudes in summer.

Mauersberger, K.↗
NASA NTRS1976

Diurnal and seasonal variations in atomic and molecular oxygen inferred from Atmosphere Explorer-C

Mass-spectrometer measurements of O and N2, obtained with the Atmosphere Explorer-C satellite during December 1974 and January 1975, are used to derive the O2 concentration near 250 km from several ionization reactions. In order to separate temperature effects from diffusion effects, the measured O and inferred O2 concentrations are employed to determine, under the assumption of diffusive equilibrium, the O/N2 and O2/N2 ratios at 120 km. It is found that the latitudinal and diurnal variations in the O concentration at 120 km are consistent with previous results obtained with OGO 6 and that the O2 concentration in the Northern (winter) Hemisphere is about twice as high as that in the Southern (summer) Hemisphere. The possible importance of photodissociation in the diurnal O2 variations is discussed.

Mayr, H. G.↗
NASA NTRS1976

Seasonal variations of the microwave scattering properties of deciduous trees as measured in the 1-18 GHz spectral range

The author has identified the following significant results. Employing two FM-CW radar spectrometers, scattering data were acquired from stands of deciduous trees during the spring and autumn. The data suggest that the trees act as a volume scatter target particularly in the 7-18 GHz region. A comparison of data collected in spring and autumn indicates that the radar scattering coefficient, sigma deg, as measured in spring can be substantially larger (as much as 10 dB) than sigma deg as measured in the autumn.

Ulaby, F. T.↗
NASA NTRS1978

Compatibility of seasonal variations in mid-latitude thermospheric models at solar maximum and low geomagnetic activity

Satellite drag data, in situ mass spectrometer data, Fabry Perot interferometer data, and incoherent scatter data were used to produce models of the concentration of atomic oxygen and molecular nitrogen in the thermosphere and of the exospheric temperature. Incoherent scatter data from two stations near 45 deg N were used. The three techniques provide similar patterns for the annual variations of the atomic oxygen concentration at 400 km, and the mean annual temperatures are within 20 K of each other for five of the six models involved. Four of the models are in good agreement concerning the annual temperature variation. There is fair agreement between incoherent scatter models and mass spectrometer models for the N2 concentrations at 400 km but disagreement between these models and the satellite drag model. It is shown that most disagreements can be resolved by changing both the vertical temperature profile and the lower-thermosphere oxygen concentration in the direction indicated by previous incoherent scatter measurements.

Alcayde, D.↗
NASA NTRS1979

Comparison of seasonal variations of upper stratospheric ozone concentrations revealed by Umkehr and Nimbus 4 BUV observations

This paper reports the results of a comparison between upper stratospheric ozone concentration profiles in the region between 22 and 1.4 mbar, as determined from surface-based Umkehr observations and satellite Nimbus 4 BUV observations. The Umkehr data, consisting of monthly averages of observations extending over several years or longer, were obtained at three stations located in the Northern Hemisphere and two in the Southern Hemisphere. The BUV data were obtained during the period from May 1970 to March 1971. Aside from some bias in the magnitudes of the Umkehr and BUV data, marked annual cycles of ozone concentration in the upper stratosphere are clearly revealed. Above 4 mbar the profiles show a summer minimum and a winter maximum, while below 4 mbar the annual variation is reversed from this pattern. In the Northern Hemisphere the winter maximum is accompanied by a secondary minimum of 1- to 2-month duration near 3 mbar. This short-term minimum is much less obvious in the Southern Hemisphere data. Some of the problem of attempting to monitor long-term changes in the upper stratosphere are discussed briefly.

Deluisi, J. J.↗
NASA NTRS1980

Seasonal variations in high-latitude ozone and metastable molecular oxygen emissions - A theoretical interpretation

Comparison of photochemical calculations of atmospheric ozone between 40 and 55 km with measurements from a satellite-borne remote sensor shows agreement in the high-latitude summer hemisphere. However, in the sunlit high-latitude winter, the available data imply either a smaller water vapor mixing ratio than generally accepted or a temperature 15 - 20 K colder than contained in published model atmospheres. As with the ozone data the infrared emission in winter implies an odd oxygen loss rate smaller than predicted on the basis of standard water vapor and temperature models. The magnitude of the 1.27 micron signals and their consistency with upper stratospheric ozone data cast doubt on the large mesospheric ozone abundances deduced in independent experiments.

Frederick, J. E.↗
NASA NTRS1982

Seasonal variation in the occurrence time of the equatorial midnight temperature bulge

Incoherent scatter radar data on electron and ion temperature from the Jicamarca Radar Observatory for the period 1967-68 and early 1969 are reexamined. Clear evidence is found of systematic nighttime temperature increases, presumably associated with the 'midnight pressure bulge' and the collapse of the middle latitude F region. An important new finding is that the temperature enhancements tend on the average to occur about two hours before midnight in the local summer and about one hour after midnight in the local winter.

Bamgboye, D. K.↗
NASA NTRS1984

Nimbus 7 SMMR Derived Seasonal Variations in the Water Vapor, Liquid Water and Surface Winds over the Global Oceans

Monthly mean distributions of water vapor and liquid water contained in a vertical column of the atmosphere and the surface wind speed were derived from Nimbus Scanning Multichannel Microwave Radiometer (SMMR) observations over the global oceans for the period November 1978 to November 1979. The remote sensing techniques used to estimate these parameters from SMMR are presented to reveal the limitations, accuracies, and applicability of the satellite-derived information for climate studies. On a time scale of the order of a month, the distribution of atmospheric water vapor over the oceans is controlled by the sea surface temperature and the large scale atmospheric circulation. The monthly mean distribution of liquid water content in the atmosphere over the oceans closely reflects the precipitation patterns associated with the convectively and baroclinically active regions. Together with the remotely sensed surface wind speed that is causing the sea surface stress, the data collected reveal the manner in which the ocean-atmosphere system is operating. Prominent differences in the water vapor patterns from one year to the next, or from month to month, are associated with anomalies in the wind and geopotential height fields. In association with such circulation anomalies the precipitation patterns deduced from the meteorological network over adjacent continents also reveal anomalous distributions.

Prabhakara, C.↗
NASA NTRS1985

Water-ice Clouds on Mars: Location and Seasonal Variation

Water-ice clouds were located on Mars using Viking infrared thermal mapper (IRTM) broadband spectral observations. The IRTM instrument had 5 thermal bands centered at 7, 9, 11, 15, and 20 microns. Clouds and hazes were consistently observed in four northern hemisphere regions centered over Tharsis, Arabia, Elysium, and along the boundary between the crater uplands and the northern plains. During the northern spring and summer when the atmosphere is relatively free of dust, there is a distinct difference between the cloud abundance in the Northern and Southern Hemispheres, with clouds and hazes being rare in the south. A second important class of water-ice clouds are those observed along the boundary of the retreating north polar cap. These clouds occur at all longitudes around the cap and are generally confined to within +/- 5 deg of the cap boundary. The cloud opacities can be estimated using a delta-Eddington radiative transfer model which incorporates Mie scattering and the electrical properties of water-ice. Assuming realistic, but non-unique, values for the ice particle size and cloud temperature, the derived opacities range from near-zero to 1.

Christensen, P. R.↗
NASA NTRS1983

Diurnal and seasonal variations of clouds from geostationary satellite data

Hourly 8-km visible (0.55-0.75 micron) and infrared (10.5-12.5 microns) data from the eastern Geostationary Operational Environmental Satellite were analyzed with a hybrid bispectral threshold method to yield total, low, middle, and high level cloud fractions and cloud radiative parameters for 250 x 250 sq km regions. These data were analyzed for the area between 45 deg N and 45 deg S, and longitudes 30 deg W and 125 deg W for the autumn of 1978 and the winter of 1979. Preliminary results for winter are presented in the present study. It is shown that diurnal variations of clouds may reveal diurnal variability in regional and large-scale circulation patterns. These diurnal cloud cycles may also have substantial effects on regional and large-scale radiation budgets and, therefore, influence circulation patterns at various spatial scales.

Minnis, P.↗