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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

The influence of variability in meridional over turning on global ocean circulation

The Atlantic Meridional Overturning circulation (AMOC) is an important global scale circulation and changes in AMOC can induce significant regional and global climate impacts. In this work, we study the stability of AMOC and its influence on global ocean circulation and the surface climate though analyzing a set of sensitivity experiments using the Community Climate System Model version 1 (CESM1). Results show that a collapsed AMOC can induce changes in global ocean circulation, such as reduced (or reversed) Bering Strait transport, weakened Indonesia throughflow and Agulhas current, but strengthened Drake Passage transport. It also changes the global wind pattern and surface temperature, such as a seesaw-like surface temperature change between Northern and Southern Hemispheres, a weakening of Indian-Australia summer monsoon, a southward shift of the Southern ocean westerlies, etc. We also found that AMOC and the Pacific deep meridional overturning circulation (or PMOC) do not form a natural seesaw under modern day climate and geography. A collapsed AMOC (active PMOC) is not stable under modern conditions if there is no additional freshwater (salt) input in the subpolar North Atlantic (Pacific), suggesting that the modern mean state of AMOC (PMOC) does not depend on local haline forcing although its variability and changes do.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1985

Atmospheric circulation of Venus

Observational data of Venus are utilized to study rotational effects on atmospheric circulations. The high surface temperature and planetary-scale turbulent motion at cloud tops, and the relation between energy and momentum budget are examined. The limited amount of data available on the vertical and horizontal distribution of net radiative heating, the zonal wind structure, and waves affects the study of the temperature and motion on Venus. The limitations of the scaling analysis used to estimate the properties of the circulation as regards the cyclostrophic balance, the extent of the Hadley circulation, large-scale wave transport, vertical propagation of waves, convection, and turbulence are considered. Hypotheses concerned with the deep, cloud-level, and upper atmospheres of Venus are proposed. Future research in the areas of propagating planetary- scale waves, zonal flow and planetary-scale wave instability processes, and convection is suggested.

Rossow, W. B.↗
NASA NTRS1998

Variations in Upper-Level Water Vapor Transport Diagnosed from Climatological Satellite Data

GOES-7 VAS measurements during the Pathfinder period (1987-88) have been analysed to reveal seasonal and interannual variations in moisture transport. Long term measurements of quality winds and humidity from satellite estimates show superior benefit in diagnosing middle and upper tropospheric large scale climate variations such as ENSO events and direct circulation systems such as the Hadley Cell. A water Vapor Transport Index (WVTI) has been developed to diagnose preferred regions of strong moisture transport and to gauge the seasonal and interannual intensities detected in the GOES viewing area. Second-order variables that may be derived from GOES winds will be also discussed on the poster.

Lerner, Jeffrey A↗
NASA NTRS1987

Application of digital holographic interferometry to pressure measurements of symmetric, supercritical and circulation-control airfoils in transonic flow fields

Six airfoil interferograms were evaluated using a semiautomatic image-processor system which digitizes, segments, and extracts the fringe coordinates along a polygonal line. The resulting fringe order function was converted into density and pressure distributions and a comparison was made with pressure transducer data at the same wind tunnel test conditions. Three airfoil shapes were used in the evaluation to test the capabilities of the image processor with a variety of flows. Symmetric, supercritical, and circulation-control airfoil interferograms provided fringe patterns with shocks, separated flows, and high-pressure regions for evaluation. Regions along the polygon line with very clear fringe patterns yielded results within 1% of transducer measurements, while poorer quality regions, particularly near the leading and trailing edges, yielded results that were not as good.

Torres, Francisco J.↗
NASA NTRS1986

An examination of vertical circulations associated with heavy snow events along the East Coast

Observational data are presented to show how a particular orientation of upper-level jet streaks (ULJS) associated with a diffluent trough near the East Coast of the U.S. can lead to heavy snowfalls. Surface fronts, precipitation and isobar maps, vertical motion vectors, and geostrophic wind streamlines preceding and during snowstorms on February 11, 1983, February 19, 1979, January 20, 1978, and January 13, 1964 are examined. The interaction of a direct vertical ageostrophic circulation within the confluent entrance of a ULJS over the northeastern U.S. or southeastern Canada and an indirect circulation within the exit region of a ULJS accompanying a trough nearing the East Coast are demonstrated to be conducive to heavy snowfall on the East Coast.

Kocin, Paul J.↗
NASA NTRS1986

Application of digital holographic interferometry to pressure measurements of symmetric, supercritical, and circulation control airfoils in transonic flow fields

Six airfoil interferograms were evaluated using a semiautomatic image-processor system which digitizes, segments, and extracts the fringe coordinates along a polygonal line. The resulting fringe order function was converted into density and pressure distributions and a comparison was made with pressure transducer data at the same wind tunnel test conditions. Three airfoil shapes were used in the evaluation to test the capabilities of the image processor with a variety of flows. Symmetric, supercritical, and circulation-control airfoil interferograms provided fringe patterns with shocks, separated flows, and high-pressure regions for evaluation. Regions along the polygon line with very clear fringe patterns yielded results within 1 percent of transducer measurements, while poorer quality regions, particularly near the leading and trailing edges, yielded results that were not as good.

Torres, Francisco J.↗
NASA NTRS1994

Simulations of Titan's Brightness by a Two-Dimensional Haze Model

We have used a 2-D microphysics model to study the effects of atmospheric motions on the albedo of Titan's thick haze layer. We compare our results to the observed variations of Titan's brightness with season and latitude. We use two wind fields. The first is an analytic solution to the simplified equations of motion. The second is based on the preliminary results of a Titan GCM. Seasonally varying wind fields, of typical horizontal velocity 1 cm/ s at optical depth unity, are capable of producing the observed change in geometric albedo of about 10% over the Titan year. Neither of the two wind fields can adequately reproduce the latitudinal distribution of the contrast seen by Voyager. At visible wavelengths, where only haze opacity is radiatively important, upwelling produces darkening by increasing the particle size at optical depth unity. This is due to the suspension of larger particles as well as the removal of smaller particles from the top of the atmosphere. From our results it can be inferred that the circulation on Titan just prior to the time of Voyager was upwelling in the northern hemisphere and downwelling in the southern hemisphere with broad regions of uniform wind separated by a sharp transition at 10 deg. S. At UV wavelengths and at 0.89 microns the albedo is determined by the competing effects of the gas and the haze material. Gas is bright in the UV and dark at 0.89 microns. Haze transport at high altitudes controls the UV albedo and transport at low altitude controls the 0.89 microns albedo. Comparisons between the hemispheric contrast at UV and IR wavelengths can be diagnostic of the vertical structure of the wind field on Titan. Infrared albedo features, which are in the lower atmosphere and persist for many rotations could reflect the haze distribution set up by a seasonally varying circulation rather than surface features as assumed in some observational studies.

Hutzell, W.↗
NASA NTRS1977

Significance of large-scale circulation in magnetic storm characteristics with application to AE-C neutral composition data

Theoretical analysis of a magnetic storm in February 1974 leads to the following conclusions: (1) Wind-induced diffusion leads to depletion of O and He and enhancements of Ar at high latitudes. (2) The same process increases O and He and decreases Ar at low latitudes. (3) There is substantial agreement between theory and neutral composition data from the AE-C closed source neutral mass spectrometer; the low-latitude enhancements of O and He, in magnitude comparable to or even larger than those of N2 and Ar, are observed, which is characteristic for the circulation mechanism. (4) To achieve agreement with the composition measurements, a heat input rate of 1.7 ergs/sq cm s is required above 120 km. (5) Changes in the neutral composition associated with the annual variations have significant effects on the magnetic storm dynamics.

Mayr, H. G.↗
NASA NTRS2005

Proceedings of the 2004 NASA/ONR Circulation Control Workshop, Part 1

As technological advances influence the efficiency and effectiveness of aerodynamic and hydrodynamic applications, designs and operations, this workshop was intended to address the technologies, systems, challenges and successes specific to Coanda driven circulation control in aerodynamics and hydrodynamics. A major goal of this workshop was to determine the 2004 state-of-the-art in circulation control and understand the roadblocks to its application. The workshop addressed applications, CFD, and experiments related to circulation control, emphasizing fundamental physics, systems analysis, and applied research. The workshop consisted of 34 single session oral presentations and written papers that focused on Naval hydrodynamic vehicles (e.g. submarines), Fixed Wing Aviation, V/STOL platforms, propulsion systems (including wind turbine systems), ground vehicles (automotive and trucks) and miscellaneous applications (e.g., poultry exhaust systems and vacuum systems). Several advanced CFD codes were benchmarked using a two-dimensional NCCR circulation control airfoil. The CFD efforts highlighted inconsistencies in turbulence modeling, separation and performance predictions.

Jones, Gregory S.↗
NASA NTRS2009

The Dynamics and Structure of Titan's Middle Atmosphere

Titan, after Venus, is the second example in the solar system of an atmosphere with a global cyclostrophic circulation. The origin and maintenance of these superrotating atmospheres is not well understood, but Titan has a strong seasonal modulation in the middle atmosphere, and the seasonal changes in the winds may offer clues. The pole in winter and early spring is characterized by temperatures 20-30 K cooler at 100-170 km than those at low latitudes, and strong circumpolar winds as high as 190 m/s at 200-250 km. At these levels the polar region is characterized by enhanced concentrations of several organic gases, and also detectable condensates. All this suggests that the polar vortex provides a mixing barrier between winter polar and lower-latitude air masses, analogous to the winter polar vortices on Earth. Because the concentrations of organic gases increase with altitude in the middle atmosphere, the observed enhancements suggest subsidence over the winter pole. Consistent with this are the observed temperatures approx.200 K at the winter-polar stratopause (280 km), making it the warmest part of the atmosphere. The warm stratopause likely results from adiabatic heating associated with the subsidence. Recent observations in late northern winter and early spring indicate that the warm anomaly at the winter-polar stratopause is weakening, and the strong zonal winds are weakening. Curiously, the stratospheric zonal winds and temperatures in both hemispheres are symmetric about a pole that is offset from the surface pole by 4 degrees. The cause of this is not well understood, but it may reflect the response of a cyclostrophic circulation to the offset between the equator, where the distance to the rotation axis is greatest, and the seasonally varying subsolar latitude.

Flasar, F. Michael↗
NASA NTRS2000

Active and Passive Microwave Determination of the Circulation and Characteristics of Weddell and Ross Sea Ice

A combination of satellite microwave data sets are used in conjunction with ECMWF (Medium Range Weather Forecasts) and NCEP (National Center for Environment Prediction) meteorological analysis fields to investigate seasonal variability in the circulation and sea-ice dynamics of the Weddell and Ross Seas. Results of sea-ice tracking using SSM/I (Special Sensor Microwave Imager), Scatterometer and SAR images are combined with in-situ data derived from Argos buoys and GPS drifters to validate observed drift patterns. Seasonal 3-month climatologies of ice motion and drift speed variance illustrate the response of the sea-ice system to seasonal forcing. A melt-detection algorithm is used to track the onset of seasonal melt, and to determine the extent and duration of atmospherically-led surface melting during austral summer. Results show that wind-driven drift regulates the seasonal distribution and characteristics of sea-ice and the intensity of the cyclonic Gyre circulation in these two regions.

Drinkwater, Mark R.↗
NASA NTRS2007

Inter-annual and Long-term Temperature Variations in the Mesopause Region at High Latitudes Generated by the Stratospheric QBO

The Numerical Spectral Model (NSM) simulates the Quasi-biennial Oscillation (QBO) that dominates the zonal circulation of the lower stratosphere at low latitudes. In the model, the QBO is generated with parameterized small-scale gravity waves (GW), which are partially augmented in 3D with planetary waves owing to baroclinic instability. Due to GW filtering, the QBO extends into the upper mesosphere, evident in UARS zonal wind and TIMED temperature measurements. While the QBO zonal winds are confined to equatorial latitudes, even in simulations with latitude-independent wave source, the associated temperature variations extend to high latitudes. The meridional circulation redistributes some of the QBO energy to focus it partially onto the Polar Regions. The resulting QBO temperature variations away from the equator tend to increase at higher altitudes to produce inter-annual variations that can exceed 5 K in the polar mesopause region -- and our 3D model simulations show that the effect is variable from year to year and can produce large differences between the two hemispheres, presumably due to interactions involving the seasonal variations. Modeling studies with the NSM have shown that long-term variations can also be generated by the QBO interacting with the seasonal cycles through OW node-filtering. A 30-month QBO, optimally synchronized by the 6-month Semi-Annual Oscillation (SAO), thus produces a 5-year or semi-decadal (SD) oscillation -- and observational evidence for that has been provided by a recent analysis of stratospheric NCEP data. In a simulation with the 2D version of the NSM, this SD oscillation extends into the upper mesosphere, and we present results to show that the related temperature variations could contribute significantly to the long-term variations of the polar mesopause region. Quasi-decadal variations could furthermore arise from the modeled solar cycle modulations of the QBO and 12-month annual oscillation. Our numerical results are discussed in the context of the observed low summer temperatures reproduced by the model, to demonstrate that the above interannual and long-term variations could contribute significantly to the climatology of Polar Mesospheric Clouds (PMC) investigated by the Aeronomy of Ice in the Mesosphere (AIM) mission.

Mayr, Hans G.↗
NASA NTRS1981

Equatorial superrotation in a thermally driven zonally symmetric circulation

Near the equator where the Coriolis force vanishes, the momentum balance for the axially symmetric circulation is established between horizontal and vertical diffusion, which, a priori, does not impose constraints on the direction or magnitude of the zonal winds. Solar radiation absorbed at low latitudes is a major force in driving large scale motions with air rising near the equator and falling at higher latitudes. In the upper leg of the meridional cell, angular momentum is redistributed so that the atmosphere tends to subrotate (or corotate) at low latitudes and superrotate at high latitudes. In the lower leg, however, the process is reversed and produces a tendency for the equatorial region to superrotate. The outcome depends on the energy budget which is closely coupled to the momentum budget through the thermal wind equation; a pressure (temperature) maximum is required to sustain equatorial superrotation. Such a condition arises in regions which are convectively unstable and the temperature lapse rate is superadiabatic. It should arise in the tropospheres of Jupiter and Saturn; planetary energy from the interior is carried to higher altitudes where radiation to space becomes important. Upward equatorial motions in the direct and indirect circulations (Ferrel-Thomson type) imposed by insolation can then trap dynamic energy for equatorial heating which can sustain the superrotation of the equatorial region.

Mayr, H. G.↗
NASA NTRS1996

Wind and pressure Fields Near Tropical Cyclone Oliver Derived From Scatterometer Observations

The results of this study demonstrate that the surface wind velocity and pressure fields derived from spaceborne scatterometers are useful in monitoring the location and intensity of tropical cyclones. Satellite-borne microwave scatterometers can penetrate the cloudy core regions of tropical cyclones to resolve the circulation in detail over data sparse regions. The location of the cyclone observed by the ERS-1 scatterometer is very close to that revealed in Geostationary Meteorological Satellite images. The surface winds provided by the ERS-1 scatterometer are used here with a modified two-layer planetary boundary layer model which includes effects of curvature, stability, and secondary flow to derive surface pressures near tropical cyclone Oliver. The curvature effect is found to be more significant than stability and secondary flow, which are crucial in deriving accurate surface pressure fields in midlatitudes.

Hsu, Carol S.↗
NASA NTRS1974

TRW A-type polyimide resin for filament winding

Studies were conducted to select a TRW A-type polyimide resin that would be suitable for fabrication of filament wound reinforced plastics structures. Several different formulations were evaluated after which the P105AC formulation was selected as the most promising. Procedures were developed for preparing P105AC/S-glass roving prepreg and for fabricating filament wound structural composites. Composites were fabricated and then tested in order to obtain tensile and shear strength information. Small, closed-end cylindrical pressure vessels then were fabricated using a stainless steel liner and end-fittings with a P105AC/S-glass polar-wound overwrap. These pressure vessels were cured in an air circulating oven without augmented pressure. It was concluded upon completion of this study that the P105AC resin system is suitable for filament winding; that low void content, high strength composites are obtained by the filament winding process; and that augmented pressure is not required to effect the fabrication of filament wound P105AC composites.

Vaughan, R. W.↗
NASA NTRS2002

Satellite Studies of Ionospheric Electric Fields and Neutral Winds

We have studied mid- and low-latitude electrodynamic and neutral thermospheric dynamic processes using measurements on board the AE-E, DE-2, and UARS (Upper Atmosphere Research Satellite) satellites, and global convection and general circulation models. These studies have determined the morphology of the equatorial zonal electric fields, the response of equatorial plasma irregularities to magnetospheric disturbances, and the time dependent response of the mid- and low latitude electric fields to magnetospheric disturbances. We have also used extensive F region zonal and meridional wind data obtained by Wind Imaging Interferometer (WINDII) instrument on board the UARS to study the latitudinal dependence of daytime disturbance winds during magnetically disturbed periods and the general characteristics of the global thermospheric disturbance wind system during geomagnetically active periods. This project has supported the PhD thesis research of John Emmert.

Fejer, Bela G.↗
NASA NTRS1976

Theoretical and experimental studies of atmospheric structure and dynamics, using high altitude chemical release, Radio meteor, and meteorological rocket network and other data

Data collected by the Georgia Tech Radio Meteor Wind Facility during the fall and winter of 1975 are analyzed indicating a relationship between lower thermospheric circulation at mid latitudes and polar stratospheric dynamics. Techniques of measurement of mixing processes in the upper atmosphere and the interpretation of those measurements are described along with a diffusion simulation program based on the Global Reference Atmosphere program.

Edwards, H. D.↗
NASA NTRS1986

Thermospheric nitric oxide and its role in thermospheric dynamics and composition

The global distribution of thermospheric nitric oxide has been measured under different geophysical conditions by the Atmosphere Explorer (AE) and Solar Mesosphere Explorer (SME) satellites. These observations show a great variability in the NO concentration but the existence of a latitudinal gradient is clearly evidenced by statistical maps of the NO meridional distribution. A two dimensional zonally averaged chemical-dynamical model was used to investigate the importance of nitric oxide 5.3 micrometer cooling and its role on thermospheric temperature, dynamics and major gas composition. For this purpose, a 2-D background atmosphere code and an odd nitrogen code were coupled and run to steady state. The NO distribution obtained is in good agreement with the AE-D global picture calculated at solstice for solar minimum activity. The importance of each term in the thermodynamic equation was studied spatially. It is found that the NO I.R. cooling term competes with conduction in the upper thermosphere and reaches its maximum value near 200 km at high summer latitudes. The primary effect of including the NO cooling term is to increase the temperature in the upper winter thermosphere and decrease it in the other hemisphere, if the global average temperature is fixed. In general, the strength of the circulation is decreased and the thermal gradient is smoother. As a consequence of these changes in the wind and temperature fields, the O2, N2 and O densities also react to the effect of the NO cooling. The importance of this process depends on the level of solar activity which controls the NO distribution.

Gerard, J. C.↗