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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 469 records · Page 26
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NASA NTRS1991

Ground-based infrared measurements of HNO3 total column abundances - Long-term trend and variability

The long-term trend and variability of the total column amount of atmospheric nitric acid (HNO3) have been investigated. The study was based on time series of infrared solar absorption spectra recorded at two sites, the International Scientific Station of the Jungfraujoch (ISSJ) in the Swiss Alps (altitude 3.6 km, latitude 46.5 N, longitude 8.0 E) and the National Solar Observatory McMath solar telescope facility on Kitt Peak (altitude 2.1 km, latitude 31.9 N, longitude 111.6 W), Arizona. Measurements of HNO3 absorption features recorded at Kitt Peak between 1980 and 1990 and measurements of the same features in ISSJ solar spectra obtained in June 1951 and June 1986 to June 1990 provide quantitative estimates of the long-term trend in the HNO3 total vertical column. It is found that the trend deduced for each site is equal to zero within the measurement uncertainty. The modern ISSJ measurements show that the fitted trend is (-0.16 + or - 0.50) percent/yr, 2 sigma, which indicates that there has been no detectable change in HNO3 total column over three decades. The Kitt Peak measurements show marked variability in the HNO3 total column, but no obvious seasonal cycle is observed.

Rinsland, C. P.↗
NASA NTRS1991

Intensity variation and coherence of 3-6 day equatorial waves

Meridional wind oscillations of 3-6 day period are common in the equatorial lower stratosphere. Upper air data obtained from 32 equatorial stations, 1973-87, show that 70 mb wave intensity over the Maritime continent varied annually with largest amplitude in NH late winter and spring, but the seasonal cycle of intensity was not uniform in the tropics. Time series of meridional velocity and its spatial coherence suggest that 70 mb wave packets were local in longitude and episodic in time.

Dunkerton, Timothy J.↗
NASA NTRS1991

A Pacific Ocean general circulation model for satellite data assimilation

A tropical Pacific Ocean General Circulation Model (OGCM) to be used in satellite data assimilation studies is described. The transfer of the OGCM from a CYBER-205 at NOAA's Geophysical Fluid Dynamics Laboratory to a CRAY-2 at NASA's Ames Research Center is documented. Two 3-year model integrations from identical initial conditions but performed on those two computers are compared. The model simulations are very similar to each other, as expected, but the simulations performed with the higher-precision CRAY-2 is smoother than that with the lower-precision CYBER-205. The CYBER-205 and CRAY-2 use 32 and 64-bit mantissa arithmetic, respectively. The major features of the oceanic circulation in the tropical Pacific, namely the North Equatorial Current, the North Equatorial Countercurrent, the South Equatorial Current, and the Equatorial Undercurrent, are realistically produced and their seasonal cycles are described. The OGCM provides a powerful tool for study of tropical oceans and for the assimilation of satellite altimetry data.

Chao, Y.↗
NASA NTRS1990

Tropospheric hydroxyl concentrations and the lifetimes of hydrochlorofluorocarbons (HCFCs)

Three dimensional fields of modeled tropospheric OH concentrations are used to calculate lifetimes against destruction by OH for many hydrogenated halocarbons, including the CFC alternatives. The OH fields were taken from a 3-D chemical transport model (Spivakovsky et al. 1989) that accurately simulates the global measurements of methyl chloroform (derived lifetime of 5.5 years). The lifetimes of various hydro-halocarbons are shown to be insensitive to possible spatial variations and seasonal cycles. It is possible to scale the HCFC lifetimes to that of methyl chloroform or methane by using the ratio of the rate coefficients for reaction with OH at an appropriate temperature, about 277 K.

Prather, Michael J.↗
NASA NTRS1992

Astronomical variation experiments with a Mars general circulation model

In time scales of a hundred thousand to a million years, the eccentricity of Mars orbit varies in a quasi-periodic manner between extremes as large as 0.14 and as small as 0 and the tilt of its axis of rotation with respect to the orbit normal also varies quasi-periodically between extremes as large as 35 deg and as small as 15 deg. In addition, the orientation of the axis precesses on comparable time scales. These astronomical variations are much more extreme than those experienced by the Earth. These variations are thought to have strongly modulated the seasonal cycles of dust, carbon dioxide, and water. One manifestation of the induced quasiperiodic climate changes may be the layered terrain of the polar regions, with individual layers perhaps recording variations in the absolute and/or relative deposition rates of dust and water in the polar regions, most likely in association with the winter time deposition of carbon dioxide ice. In an attempt to understand the manner in which atmospheric temperatures and winds respond to the astronomical forcings, we have initiated a series of numerical experiments with the NASA/Ames general circulation model of the Martian Atmosphere.

Pollack, J. B.↗
NASA NTRS1992

Observed changes in limb clouds immediately prior to the onset of planet-encircling dust storms

Of the several size and nomenclature groupings of Martian dust storms, it is the plane-encircling or truly runaway dust storms that are of most concern to both the theoreticians and mission planners. Once believed to be regularly seasonal, it is now known that they are not annual occurrences and that the few we know about occurred within at least one-third of Mars' seasonal cycle. We cannot confirm that any were observed before 1956, and not one has been observed since 1982 (the classification of that event as 'encircling' is an interpretation of observation from a single point on the planet's surface). If these storms occur in cycles, we do not know the lengths or causes of the cycles. Regional and local dust storms occur more frequently and throughout the Martian year, but the underlying question is how do some become runaways, encircling the planet, while the others die out, usually within a few days. An investigation of this topic is presented.

Martin, L. J.↗
NASA NTRS1992

Short- and long-term climate changes on Mars

The present climate of Mars is dominated by the seasonal cycles of dust, water vapor, and carbon dioxide. Understanding these cycles represents a first step towards interpreting climate changes in the past. Past climates on Mars were probably different from the present one due to astronomical variations of orbital and axial properties, to major changes in atmospheric pressure and/or composition, and to long-term changes in solar luminosity.

Pollack, James B.↗
NASA NTRS1991

Model and observation comparison of the universal time and IMF by dependence of the ionospheric polar hole

The polar ionospheric F-region often exhibits regions of marked density depletion. These depletions have been observed by a variety of polar orbiting ionospheric satellites over a full range of solar cycle, season, magnetic activity, and universal time (UT). An empirical model of these observations has recently been developed to describe the polar depletion dependence on these parameters. Specifically, the dependence has been defined as a function of F10.7 (solar), summer or winter, Kp (magnetic), and UT. Polar cap depletions have also been predicted /1, 2/ and are, hence, present in physical models of the high latitude ionosphere. Using the Utah State University Time Dependent Ionospheric Model (TDIM) the predicted polar depletion characteristics are compared with those described by the above empirical model. In addition, the TDIM is used to predict the IMF By dependence of the polar hole feature.

Sojka, J. J.↗
NASA NTRS1991

Precipitation rates in the tropics based on the Q1-budget method - 1 June 1984-31 May 1987

The 'apparent' heat source method (Q1 budget) is used to compute the total derivative of dry static energy from 30 deg N to 30 deg S for the period June 1, 1984-May 31, 1987. The dataset is produced from the ECMWF global analyses and consists of twice-daily values of temperature, geopotential height, horizontal wind components, and vertical velocity at increments of 2.5 x 2.5 deg lat/long at seven pressure levels. Vertically integrated values of ds/dt, which are equal to total diabatic heating, Q1, are combined with estimates of net columnar radiation and surface sensible heat exchange to compute mean monthly precipitation rates, P0, as the residual in the Q1 budget. The accuracy of these P0 values is thoroughly examined, and it is suggested that the technique produces reliable estimates of precipitation over tropical oceanic areas on a monthly basis. Time series of mean monthly P0 for several geographic regions of the Southern Hemisphere tropics and the equatorial western Pacific (TOGA-COARE region) reveal that (1) the South Pacific convergence zone has the highest precipitation rates in the Southern Hemisphere; (2) a clear and distinct seasonal cycle is prominent in all regions; and (3) the 1986-87 ENSO event is easily identified, particularly in the TOGA-COARE region.

Vincent, Dayton G.↗
NASA NTRS1990

Mars Observer's global mapping mission

The objectives of the Mars Observer global mapping mission are to determine the global elemental and mineralogical character of the Martian surface material, define globally the topography and gravitational field of Mars, establish the nature of Mars's magnetic field, determine the time and space distribution, abundance, sources, and sinks of volatile Martian material and dust over a seasonal cycle, and explore the structure and aspects of the circulation of the Martian atmosphere. The experiments and instruments to be used in this mission are described, and the operations and data analysis are briefly considered.

Albee, A. L.↗
NASA NTRS1992

Triton - Voyager's finale

The investigation of the Neptunian satellite Triton by the Voyager 2 is described with interpretations of the object's nature and composition. The orbit, seasonal cycle, and southern-hemisphere solstice are described, and the composition of the satellite is discussed. Triton's mass and radius are known, and the objects is made up of about 70 percent rock and organics and 30 percent ice by mass. Triton's interior is warm and geologically active considering its distance from the sun, and large amounts of frozen methane and nitrogen are theorized to contribute to the object's high reflectivity. Also noted in the Voyager color images are creeping ice, cryogenic lava, and dark streaks on the south polar cap from nitrogen gas leaks driven by a type of greenhouse effect. Triton represents a class of satellite that has not been observed previously: a moon-sized body in a retrograde inclined orbit from the class of objects that coalesced to form Neptune.

Brown, R. H.↗
NASA NTRS1991

Observations of the late-summer to fall sea ice transition with the 14.6 GHz Seasat scatterometer

Seasat 14.6-GHz scatterometer data are used to investigate variations in the large area-averaged backscatter signature during the late summer to fall transition. The temporal evolution in the backscatter coefficient indicates general changes in the surface properties of the sea ice which are attributed to the seasonal cycle. Notable events in this typical cycle are the meltpond maximum, rapid drainage or disappearance of the meltponds, fall cooling and freeze-up, and ultimately snowfall. All are manifested in the signature record, and a simple empirical scattering model is used to infer the mean snow and ice properties and their temporal variation.

Drinkwater, Mark R.↗
NASA NTRS1988

NO2 column intercomparison between ground-based measurements at Lauder, New Zealand (45 deg S) and colocated SAGE II satellite measurements

NO2 columns measured at sunset from Lauder, New Zealand (45 deg S, 169.7 deg E) are compared with columns derived from colocated profiles measured by the SAGE II satellite instrument. The comparison period covers more than 3 yr of data since the launch of SAGE II in October 1984. The seasonal cycle is well reproduced in the SAGE II data, and there is reasonable agreement between it and the ground based data. Over the period from 1984 to 1988 the SAGE II NO2 columns show a definite decrease while the Lauder columns remain relatively constant.

Mckenzie, R. L.↗
NASA NTRS1991

Ocean circulation modeling by use of radar altimeter data

The project will investigate the use of radar altimetry (RA) data in the determination of the ocean circulation models. RA data will be used to verify prognostic experiments of the steady state and seasonal cycle of large-scale circulation models and the statistical steady state of eddy-resolving models. The data will serve as initial and update conditions in data assimilation experiments and as constraints in inverse calculations. The aim of the project is a better understanding of ocean physics, the determination and mapping of ocean currents, and a contribution to the establishment of ocean circulation models for climate studies. The goal of the project is to use satellite radar altimetry data for improving our knowledge of ocean circulation both in a descriptive sense and through the physics that govern the circulation state. The basic tool is a series of ocean circulation models. Depending on the model, different techniques will be applied to incorporate the RA data.

Olbers, Dirk↗
NASA NTRS1990

Analysis of AVHRR, CZCS and historical in situ data off the Oregon Coast

The original scientific objectives of this grant were to: (1) characterize the seasonal cycles and interannual variability for phytoplankton concentrations and sea surface temperature (SST) in the California Current using satellite data; and (2) to explore the spatial and temporal relationship between these variables and surface wind forcing. An additional methodological objective was to develop statistical methods for forming mean fields, which minimize the effects of random data gaps and errors in the irregularly sampled CZCS (Coastal Zone Color Scanner) and AVHRR (Advanced Very High Resolution Radiometer) satellite data. A final task was to evaluate the level of uncertainty in the wind fields used for the statistical analysis. Funding in the first year included part of the cost of an image processing system to enable this and other projects to process and analyze satellite data. This report consists of summaries of the major projects carried out with all or partial support from this grant. The appendices include a list of papers and professional presentations supported by the grant, as well as reprints of the major papers and reports.

Strub, P. Ted↗
NASA NTRS1992

The interannual variability of polar cap recessions as a measure of Martian climate and weather: Using Earth-based data to augment the time line for the Mars observer mapping mission

The recessions of the polar ice caps are the most visible and most studied indication of seasonal change on Mars. Circumstantial evidence links these recessions to the seasonal cycles of CO2, water, and dust. The possible advent of a planet encircling storm during the Mars Observer (MO) mission will provide a detailed correlation with a cap recession for that one Martian year. That cap recession will then be compared with other storm and nonstorm years. MO data will also provide a stronger link between cap recessions and the water and CO2 cycles. Cap recession variability might also be used to determine the variability of these cycles. After nearly a century of valiant attempts at measuring polar cap recessions, including Mariner 9 and Viking data, MO will provide the first comprehensive dataset. In contrast to MO, the older data are much less detailed and precise and could be forgotten, except that it will still be the only information on interannual variability. By obtaining simultaneous Earth-based observations (including those from Hubble) during the MO mission, direct comparisons can be made between the datasets.

Martin, L. J.↗
NASA NTRS1992

Comparative aspects of the climate of Mars - An introduction to the current atmosphere

The study reviews the historical perspective of the Martian climate, beginning with the early view of inexorable climate change on an older, but otherwise very earthlike, planet and continuing through the period when earth-based spectroscopy and the Mariner 4, 6, and 7 flyby missions portrayed a moonlike body, heavily cratered and almost airless by comparison with earth. The most general features of the earth and Mars are discussed and compared, with consideration given to the standard atmospheres, atmospheric circulation, seasonal cycles of carbon dioxide, water, and dust, and coupling between cycles.

Zurek, Richard W.↗
NASA NTRS1993

Present-day Antarctic climatology of the NCAR Community Climate Model Version 1

The ability of the NCAR Community Climate Model Version 1 (CCM1) with R 15 resolution to simulate the present-day climate of Antarctica was evaluated using the five-year seasonal cycle output produced by the CCM1 and comparing the model results with observed horizontal syntheses and point data. The results showed that the CCM1 with R 15 resolution can simulate to some extent the dynamics of Antarctic climate on the synoptic scale as well as some mesoscale features. The model can also simulate the phase and the amplitude of the annual and semiannual variation of the temperature, sea level pressure, and zonally averaged zonal (E-W) wind. The main shortcomings of the CCM1 model are associated with the model's anomalously large precipitation amounts at high latitudes, due to the tendency of the scheme to suppress negative moisture values.

Tzeng, Ren-Yow↗