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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

The Impacts of Daily Surface Forcing in the Upper Ocean over Tropical Pacific: A Numerical Study

Tropical Pacific Ocean is an important region that affects global climate. How the ocean responds to the atmospheric surface forcing (surface radiative, heat and momentum fluxes) is a major topic in oceanographic research community. The ocean becomes warm when more heat flux puts into the ocean. The monthly mean forcing has been used in the past years since daily forcing was unavailable due to the lack of observations. The daily forcing is now available from the satellite measurements. This study investigates the response of the upper ocean over tropical Pacific to the daily atmospheric surface forcing. The ocean surface heat budgets are calculated to determine the important processes for the oceanic response. The differences of oceanic responses between the eastern and western Pacific are intensively discussed.

Sui, C.-H.↗
NASA NTRS2001

A Modeling Study of Oceanic Response to Daily and Monthly Surface Forcing

The goal of this study is to investigate the effect of high-frequency surface forcing (wind stresses and heat fluxes) on upper-ocean response. We use the reduced-gravity quasi-isopycnal ocean model by Schopf and Loughe (1995) for this study. Two experiments are performed: one with daily and the other with monthly surface forcing. The two experiments are referred to as DD and MM, respectively. The daily surface wind stress is produced from the SSM/I wind data (Atlas et al. 1991) using the drag coefficient of Large and Pond (1982). The surface latent and sensible heat fluxes are estimated using the atmospheric mixed layer model by Seager et al. (1995) with the time-varying air temperature and specific humidity from the NCEP-NCAR reanalysis (Kalnay et al. 1996). The radiation is based on climatological shortwave radiation from the Earth Radiation Budget Experiment (ERBE) [Harrison et al. 1993] and the daily GEWEX SRB data. The ocean model domain is restricted to the Pacific Ocean with realistic land boundaries. At the southern boundary the model temperature and salinity are relaxed to the Levitus (1994) climatology. The time-mean SST distribution from MM is close to the observed SST climatology while the mean SST field from DD is about 1.5 C cooler. To identify the responsible processes, we examined the mean heat budgets and the heat balance during the first year (when the difference developed) in the two experiments. The analysis reveals that this is contributed by two factors. One is the difference in latent heat flux. The other is the difference in mixing processes. To further evaluate the responsible processes, we repeated the DD experiment by reducing the based vertical diffusion from 1e-4 to 0.5e-5. The resultant SST field becomes quite closer to the observed SST field. SST variability from the two experiments is generally similar, but the equatorial SST differences between the two experiments show interannual variations. We are investigating the possible mechanisms responsible for the different responses.

Sui, Chung-Hsiung↗
NASA NTRS1998

A Technique for Assimilating GOES-Derived Land Surface Products into Regional Models to Improve the Representation of Land Surface Forcing

As the parameterizations of surface energy budgets in regional models have become more complete physically, models have the potential to be much more realistic in simulations of coupling between surface radiation, hydrology, and surface energy transfer. Realizing the importance of properly specifying the surface energy budget, many institutions are using land-surface models to represent the lower boundary forcing associated with biophysical processes and soil hydrology. However, the added degrees of freedom due to inclusion of such land-surface schemes require the specification of additional parameters within the model system such as vegetative resistances, green vegetation fraction, leaf area index, soil physical and hydraulic characteristics, stream flow, runoff, and the vertical distribution of soil moisture. A technique has been developed for assimilating GOES-IR skin temperature tendencies into the surface energy budget equation of a mesoscale model so that the simulated rate of temperature change closely agrees with the satellite observations. A critical assumption of the technique is that the availability of moisture (either from the soil or vegetation) is the least known term in the model's surface energy budget. Therefore, the simulated latent heat flux, which is a function of surface moisture availability, is adjusted based upon differences between the modeled and satellite-observed skin temperature tendencies. An advantage of this technique is that satellite temperature tendencies are assimilated in an energetically consistent manner that avoids energy imbalances and surface stability problems that arise from direct assimilation of surface shelter temperatures. The fact that the rate of change of the satellite skin temperature is used rather than the absolute temperature means that sensor calibration is not as critical. An advantage of this technique for short-range forecasts is that it does not require a complex land-surface formulation within the atmospheric model. As a result, the need to specify poorly known soil and vegetative characteristics is eliminated. The GOES assimilation technique has been incorporated into the PSU/NCAR MM5. Results will be presented to demonstrate the ability of the assimilation scheme to improve short-term simulations of near-surface air temperature and mixing ratio during the warm season for several selected cases during June of 1995 and June 1997 which exhibit a variety of atmospheric and land-surface conditions. In addition, the simulations produced by the assimilation technique will be compared with those produced by the MM5/BATS coupled model initialized with soil water content derived from a soil hydrology model.

Lapenta, William M.↗
NASA NTRS1992

The modulation of the low-latitude radiation budget by cloud and surface forcing on interannual time scales

Regionally confined interannual perturbations in the tropical radiation budget associated with east-west circulations are examined along with the forcing mechanisms of these perturbations in relation to surface and cloudiness variability. A zonal harmonic analysis of emitted longwave radiation emphasizes that these variations are largely controlled at the planetary wave scale. The overall effect leads to an approximately 50 deg/yr propagation phase speed that is considerably slower than the oceanic Kelvin wave capable of driving east-west longwave (LW) anomalies through SST feedback. Examination of the time-dependent radiative energetics over the tropics reveals that the aforementioned anomaly LW propagation is mainly due to cloud forcing associated with east-west circulation changes. Diabatic heating associated with coupled ocean-atmosphere feedback appears to be larger responsible for the LW anomaly propagation.

Sohn, Byung-Ju↗
NASA NTRS1994

Satellite Observation of Surface Forcing Over the Warm Pool

Daily variations of wind and solar forcing derived from satellite data were compared with sea surface temperature and temperature tendency during the Tropical Ocean Global Atmosphere - Coupled Ocean Atmosphere Response Experiment.

sea surface temperature wind speed thermal respons↗
NASA NTRS2000

Force, Surface Pressure and Flowfield Measurements on Slender Missile Configurations at Supersonic Speeds

This paper describes a series of wind tunnel experiments carried out with the aim of providing data suitable for evaluating the performance of Computational Fluid Dynamics (CFD) codes. The configurations and flow conditions studied are most relevant to slender supersonic missiles. However, the data obtained, which includes forces and moments, surface pressures, flowfield surveys and a selection of flow visualization images, should he of interest to other CFD practitioners. Results for three test cases are presented and discussed in this paper. These cases have been the subject of a collaborative study concerned with the evaluation of Navier-Stokes solvers for missiles, carried out under the auspices of The Technical Cooperation Programme (TTCP).

Birch, T. J.↗
NASA NTRS2004

Force, Surface Pressure, and Flowfield Measurements on a Slender Missile Configuration with Square Cross-Section at Supersonic Speeds

A wind-tunnel investigation of a square cross-section missile configuration has been conducted to obtain force and moment measurements, surface pressure measurements, and vapor screen flow visualization photographs for comparison with computational fluid dynamics studies conducted under the auspices of The Technical Cooperation Program (TTCP). Tests were conducted on three configurations which included: (1) body alone, (2) body plus tail fins mounted on the missile corners, and (3) body plus tail fins mounted on the missile side. This test was conducted in test section #2 of the NASA Langley Unitary Plan Wind Tunnel at Mach numbers of 2.50 and 4.50 and at a Reynolds number of 4 million per ft. The data were obtained over an angle of attack range from -4 deg. to 24 deg. and roll angles from 0 deg. to 45 deg., i.e., from a diamond shape (as viewed from the rear) at a roll angle of 0 deg. to a square shape at 45 deg.

Wilcox, Floyd J., Jr.↗
NASA NTRS1995

Response of the Tropical Boundary Layer to Weak Surface Forcing

During the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE), a series of airborne thermal infrared observations and in situ atmospheric measurements were made near the sea surface through heights exceeding 4 km. Air movements associated with the sea surface temperature and the marine atmospheric boundary layer were studied.

TOGA COARE sea surface temperature tropical weathe↗
NASA NTRS1976

Saltation threshold on Mars - The effect of interparticle force, surface roughness, and low atmospheric density

Results are reported for wind-tunnel experiments performed to determine the threshold friction speed of particles with different densities. Experimentally determined threshold speeds are plotted as a function of particle diameter and in terms of threshold parameter vs particle friction Reynolds number. The curves are compared with those of previous experiments, and an A-B curve is plotted to show differences in threshold speed due to differences in size distributions and particle shapes. Effects of particle diameter are investigated, an expression for threshold speed is derived by considering the equilibrium forces acting on a single particle, and other approximately valid expressions are evaluated. It is shown that the assumption of universality of the A-B curve is in error at very low pressures for small particles and that only predictions which take account of both Reynolds number and effects of interparticle forces yield reasonable agreement with experimental data. Effects of nonerodible surface roughness are examined, and threshold speeds computed with allowance for this factor are compared with experimental values. Threshold friction speeds on Mars are then estimated for a surface pressure of 5 mbar, taking into account all the factors considered.

Iversen, J. D.↗
NASA NTRS1992

Surface forcing of the infrared cooling profile over the Tibetan Plateau. I - Influence of relative longwave radiative heating at high altitude. II - Cooling-rate variation over large-scale plateau domain during summer monsoon transition

The role of the Tibetan Plateau on the behavior of the surface longwave radiation budget is investigated, and the behavior of the vertical profile of longwave cooling over the plateau, including its diurnal variation, is quantified. A medium spectral-resolution IR radiative transfer model utilizing a simple modification for applications in idealized complex (valley) terrain is developed for the investigation. An understanding of how surface and elevation biophysical factors, which are highly variable over the large-scale plateau domain, regulate the spatial distribution of clear-sky IR cooling during the transition phase of the summer monsoon, is described.

Smith, Eric A.↗
NASA NTRS1995

Simulated interannual variability of the Greenland Sea deep water formation and its connection to surface forcing

A fully prognostic Arctic ice-ocean model is used to study the interannual variability of deepwater formation in the Greenland Sea Gyre based on the simulations for the Arctic ice-ocean system for the period 1955 and 1960 - 1985. The model uses monthly climatology for thermodynamic forcing components (such as air temperature and cloudiness), together with constant annual net precipitation and river runoff. The daily wind forcing is derived from analyzed sea level air pressures from the National Center for Atmospheric Research (NCAR). In summary, the model shows that the occurence of deep convection in the Greenland Sea Gyre is controlled by the extensive Fram Strait ice export and/or local wind conditions in the Greenland Sea. In the latter case the weakening of the local wind curl allows the Polar Front to move eastward. The movement of the Polar Front causes adverse ice conditions, often together with much larger than normal ice export from the Arctic, such as in 1968, which can block convection in the gyre. The density difference between upper and lower layers is investigated as an indication of water mass formation through convection, occurring as strong diffusion in the model. The model-simulated density difference between the average top 100 m and deep levels reveals that the period 1960 - 1985 had only a few distinct years with weak stratification, and, especially, the model predicts no deep convection since the nid-1970s. The common factor for the years of the weakest decrease of the model-predicted heat content of the upper 2000 m which can, to a high degree, be explained by local heat loss.

Haekkinen, Sirpa↗
NASA NTRS1999

The Impact of Surface Boundary Forcing on Simulation of the 1998 Summer Drought Over the US Midwest Using Factor Separation Technique

The factor separation (FS) technique has been utilized to evaluate quantitatively the impact of surface boundary forcings on simulation of the 1988 summer drought over the Midwestern part of the U.S. The four surface boundary forcings used are: (1)Sea Surface Temperature (SST), (2) soil moisture, (3) snow cover, and (4) sea ice. The Goddard Earth Observing System(GEOS) General Circulation Model (GCM) is used to simulate the 1988 U.S. drought. A series of sixteen simulations are performed with climatological and real 1988 surface boundary conditions. The major single and mutual synergistic factors/impacts are analyzed. The results show that SST and soil moisture are the major single pro-drought factors. The couple synergistic effect of SST and soil moisture is the major anti-drought factor. The triple synergistic impact of SST, soil moisture, and snow cover is the strongest pro-drought impact and is, therefore, the main contributor to the generation of the drought. The impact of the snow cover and sea ice anomalies for June 1988 on the drought is significant only when combined with the SST and soil moisture anomalies.

Stein, Uri↗
NASA NTRS1982

Capillary forces exerted by liquid drops caught between crossed cylinders. A 3-D meniscus problem with free contact line

The Young-Laplace equation is solved for three-dimensional menisci between crossed cylinders, with either the contact line fixed or the contact angle prescribed, by means of the Galerkin/finite element method. Shapes are computed, and with them the practically important quantities: drop volume, wetted area, capillary pressure force, surface tension force, and the total force exerted by the drop on each cylinder. The results show that total capillary force between cylinders increases with decreasing contact angle, i.e. with better wetting. Capillary force is also increases with decreasing drop volume, approaching an asymptotic limit. However, the wetted area on each cylinder decreases with decreasing drop volume, which raises the question of the optimum drop volume to strive for, when permanent bonding is sought from solidified liquid. For then the strength of the bond is likely to depend upon the area of contact, which is the wetted area when the bonding agent was introduced in liquid form.

Patzek, T. W.↗