Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Variational”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Compositional Variation in Lunar Regolith Samples: Vertical

Some techniques for measuring composition and mineralogy remotely detect only the upper few micrometers to millimeters of material. Is this a serious concern for lunar regolith studies? Here it is shown the centimeter-scale variation with depth in the composition of lunar regolith based on results of the studies of regolith cores taken on the Apollo missions. In short, the compositional variation of lunar regolith with depth over tens of centimeters is equivalent to that observed laterally at the surface over kilometers. On average, however, the composition of material in the upper half centimeter is probably reasonably representative of the upper half meter or more (the depth of most Apollo cores), particularly for measurements made from orbit that integrate over a large surface area.

Korotev, Randy L.↗
NASA NTRS1997

Long-term variations in total solar and UV irradiances

The variations of total solar and UV irradiances during solar cycles 21 and 22 are compared. The total solar irradiance data used were obtained by the SMM/active cavity radiometer irradiance monitoring (ACRIM) 1, upper atmosphere research satellite (UARS)/ACRIM 2 and ERBS experiments. The space-based irradiance observations are compared to the Mount Wilson Magnetic Plage and Photometric Sunspot Index, which is derived from the area and position of sunspots published by the NOAA World Data Center Solar Geophysical Data Catalog. It is found that the variations in solar UV irradiance were similar during the maximum and minimum of solar cycles 21 and 22. The possible reasons for the differences in the irradiance values during the minima of the two solar cylces are discussed.

Pap, J. M.↗
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 NTRS1999

The Yearly Variation in Fall-Winter Arctic Winter Vortex Descent

Using the change in HALOE methane profiles from early September to late March, we have estimated the minimum amount of diabatic descent within the polar which takes place during Arctic winter. The year to year variations are a result in the year to year variations in stratospheric wave activity which (1) modify the temperature of the vortex and thus the cooling rate; (2) reduce the apparent descent by mixing high amounts of methane into the vortex. The peak descent amounts from HALOE methane vary from l0km -14km near the arrival altitude of 25 km. Using a diabatic trajectory calculation, we compare forward and backward trajectories over the course of the winter using UKMO assimilated stratospheric data. The forward calculation agrees fairly well with the observed descent. The backward calculation appears to be unable to produce the observed amount of descent, but this is only an apparent effect due to the density decrease in parcels with altitude. Finally we show the results for unmixed descent experiments - where the parcels are fixed in latitude and longitude and allowed to descend based on the local cooling rate. Unmixed descent is found to always exceed mixed descent, because when normal parcel motion is included, the path average cooling is always less than the cooling at a fixed polar point.

Schoeberl, Mark R.↗
NASA NTRS1998

Effect of Helical Slow-Wave Circuit Variations on TWT Cold-Test Characteristics

Recent advances in the state of the art of computer modeling offer the possibility for the first time to evaluate the effect that slow-wave structure parameter variations, such as manufacturing tolerances, have on the cold-test characteristics of helical traveling-wave tubes (TWT's). This will enable manufacturers to determine the cost effectiveness of controlling the dimensions of the component parts of the TWT, which is almost impossible to do experimentally without building a large number of tubes and controlling several parameters simultaneously. The computer code MAFIA is used in this analysis to determine the effect on dispersion and on-axis interaction impedance of several helical slow-wave circuit parameter variations, including thickness and relative dielectric constant of the support rods, tape width, and height of the metallized films deposited on the dielectric rods. Previous computer analyzes required so many approximations that accurate determinations of the effect of many relevant dimensions on tube performance were practically impossible.

Kory, Carol L.↗
NASA NTRS1999

Evidence for the Absence of Conductivity Variations above Thunderstorms

In recent years, atmospheric conductivity and electric field measurements over thunderstorms have been made at 20 km with a high altitude aircraft. After compensating for the effects of aircraft charging induced by external electric fields no significant variations in ambient conductivity above thunderstorms have been found. These Gerdien results contrast strongly with the large (and frequent) conductivity variations reported in studies using relaxation probe techniques.

Bailey, Jeff C.↗
NASA NTRS1999

Evidence for the Absence of Conductivity Variations Above Thunderstorms

In recent years, atmospheric conductivity and electric field measurements over thunderstorms have been made at 20 km with a high altitude aircraft. After compensating for the effects of aircraft charging induced by external electric fields no significant variations in ambient conductivity above thunderstorms have been found. These Gerdien results contrast strongly with the large (and frequent) conductivity variations reported in studies using relaxation probe techniques.

Bailey, Jeff C.↗
NASA NTRS1999

The Spatial Variation of Water and Ammonia near Jupiter's Great Red Spot

The CSHELL spectrometer at NASA's Infrared Telescope Facility was used in August 1996 to observe Jupiter at 5.18 microns. This wavelength sounds the 3-8 bar region in Jupiter's deep troposphere. A 1-arcsec-wide slit was aligned east-west on Jupiter and stepped from north to south across the Great Red Spot (GRS). Within our spectral bandpass are absorption lines of NH3 and a hot band of CH4. Radiative transfer models indicate that the strength of the CH4 feature is anti-correlated with gaseous H2O between 3 and 6 bars. The CH4 feature is predicted to be very strong for H2O abundances less than 10ppm and it should vanish when H2O > 300ppm. The depths of the observed CH4 and NH3 absorption features varied dramatically near the GRS. The center and east side (planetocentric) of the GRS is dry in both volatiles as indicated by strong CH4 absorption and a weak NH3 line. The CH4 line vanishes and the NH3 feature grows stronger on the west side of the GRS. We interpret this as due to a real variation in both volatiles - H2O and NH3 - due to a common dynamical mechanism. Water clouds are expected to be accompanied by saturated gaseous H2O profiles between 3 and 5 bars. The Galileo imaging team (Banfield et al 1998 Icarus 135, p230) deduced the presence of a cloud near the 4-bar level northwest of the GRS. Our data indicate that this same region is volatile rich; thus the combination of the two datasets provides a compelling case for a water cloud at this location. The deep volatile abundance does not correlate with 5-micron continuum opacity near the GRS. This suggests that the spatial variation of the 5-micron flux near the GRS is due primarily to NH3 clouds, rather than H2O clouds.

Bjoraker, G. L.↗
NASA NTRS1999

Hurricane Directional Wave Spectrum Spatial Variation in the Open Ocean

The sea surface directional wave spectrum was measured for the first time in all quadrants of a hurricane in open water using the NASA airborne scanning radar altimeter (SRA) carried aboard one of the NOAA WP-3D hurricane hunter aircraft at 1.5 km height. The SRA measures the energetic portion of the directional wave spectrum by generating a topographic map of the sea surface. At 8 Hz, the SRA sweeps a radar beam of 1 deg half-power width (two-way) across the aircraft ground track over a swath equal to 0. 8 of the aircraft height, simultaneously measuring the backscattered power at its 36 GHz (8.3 mm) operating frequency and the range to the sea surface at 64 positions. These slant ranges are multiplied by the cosine of the incidence angles to determine the vertical distances from the aircraft to the sea surface. Subtracting these distances from the aircraft height produces the sea surface elevation map. The sea surface topography is interpolated to a uniform grid, transformed by a two-dimensional FFT, and Doppler corrected. The data presented were acquired on 24 August 1998 when hurricane Bonnie was east of the Bahamas and moving slowly to the north. Wave heights up to 18 m were observed and the spatial variation of the wave field was dramatic. The dominant waves generally propagated at significant angles to the downwind direction and at times there were wave fields traveling at right angles to each other. The NOAA aircraft spent over five hours within 180 km of the hurricane Bonnie eye, and made five eye penetrations. A 2-minute animation of the directional wave spectrum spatial variation over this period will be shown.

Wright, C. W.↗
NASA NTRS1999

Hurricane Directional Wave Spectrum Spatial Variation at Landfall

On 26 August 1998, hurricane Bonnie was making landfall near Wilmington, NC. The NASA airborne scanning radar altimeter (SRA) carried aboard one of the NOAA WP-3D hurricane hunter aircraft at 2.2 km height documented the sea surface directional wave spectrum in the region between Charleston, SC and Cape Hatteras, NC. The aircraft ground track included both segments along the shoreline and Pamlico Sound as well as far offshore. An animation of the directional wave spectrum spatial variation at landfall will be presented and contrasted with the spatial variation when Bonnie was in the open ocean on 24 August 1998.

Walsh, E. J.↗
NASA NTRS2000

Service Quality in the U.S. Airline Industry: Variations in Performance Within Airlines and Between Airlines and the Industry

This study examined the service quality of 25 U.S. airlines (1987-1996) using data from the Department of Transportation's Air Travel Consumer Report. After a total quality and total complaint rate was calculated for these airlines, a 95 percent confidence interval was placed around the yearly and company means calculated to examine those cases that were significantly different from the mean. Results indicate that while the major carriers are converging toward a higher level of quality, there continues to be significant yearly variation. The service quality of regional carriers was much lower than major carriers and showed much greater variation.

Rhoades, Dawna L.↗
NASA NTRS1999

Longitudinal and Seasonal Variations in Nighttime Plasma Temperatures in the Equatorial Topside Ionosphere During Solar Maximum

Latitude profiles of the ion and electron temperatures and total ion concentration across the equatorial region near 800 km altitude are routinely obtained from Defense Meteorological Satellite Program (DMSP) spacecraft. We have examined these profiles at 2100 hours local time to discover the influences of field-aligned plasma transport induced by F region neutral winds. Such dependencies are readily seen by contrasting observations at different seasons and different longitudes distinguished by different magnetic declinations. These data show strong evidence for adiabatic heating produced by interhemispheric plasma transport. This heating manifests itself as a local temperature maximum that appears in the winter hemisphere during the solstices and is generally absent during equinox. A longitudinal variation in the appearance of this maximum is consistent with the roles of meridional and zonal winds in modulating the field-aligned plasma velocities. The data also show a local temperature minimum near the dip equator. However, it is not so easy to attribute this minimum to adiabatic cooling since transport of plasma from below and the latitude variation in the flux tube content may also produce such a minimum.

Venkatraman, Sarita↗
NASA NTRS1996

Spatial Variation of the 3.29 and 3.40 Micron Emission Bands Within Reflection Nebulae and The Photochemical Evolution of Methylated Polycyclic Aromatic Hydrocarbons

Spectra of 3 microns emission features have been obtained at several positions within the reflection nebulae NGC 1333 SVS3 and NGC 2023. Strong variations of the relative intensities of the 3.29 microns feature and its most prominent satellite band at 3.40 microns are found. It is shown that: (1) the 3.40 microns band is too intense with respect to the 3.29 microns band at certain positions to arise from hot band emission alone, (2) the 3.40 microns band can be reasonably well matched by new laboratory spectra of gas-phase polycyclic aromatic hydrocarbons (PAHs) with alkyl (-CH3) side groups, and (3) the variations in the 3.40 microns to 3.29 microns band intensity ratios are consistent with the photochemical erosion of alkylated PAHs. We conclude that the 3.40 microns emission feature is attributable to -CH3 side groups on PAH molecules. We predict a value of 0.5 for the peak intensity ratio of the 3.40 and 3.29 microns emission bands from free PAHs in the diffuse interstellar medium, which would correspond to a proportion of one methyl group for four peripheral hydrogens. We also compare the 3 microns spectrum of the proto-planetary nebula IRAS 05341 + 0852 with the spectrum of the planetary nebula IRAS 21282 + 5050. We suggest that a photochemical evolution of the initial aliphatic and aromatic hydrocarbon mixture formed in the outflow is responsible for the changes observed in the 3 microns emission spectra of these objects.

Joblin, C.↗
NASA NTRS2000

SST Variation Due to Interactive Convective-Radiative Processes

The recent linking of Cloud-Resolving Models (CRMs) to Ocean-Mixed Layer (OML) models has provided a powerful new means of quantifying the role of cloud systems in ocean-atmosphere coupling. This is due to the fact that the CRM can better resolve clouds and cloud systems and allow for explicit cloud-radiation interaction. For example, Anderson (1997) applied an atmospheric forcing associated with a CRM simulated squall line to a 3-D OML model (one way or passive interaction). His results suggested that the spatial variability resulting from the squall forcing can last at least 24 hours when forced with otherwise spatially uniform fluxes. In addition, the sea surface salinity (SSS) variability continuously decreased following the forcing, while some of the SST variability remained when a diurnal mixed layer capped off the surface structure. The forcing used in the OML model, however, focused on shorter time (8 h) and smaller spatial scales (100-120 km). In this study, the 3-D Goddard Cumulus Ensemble Model (GCE; 512 x 512 x 23 cu km, 2-km horizontal resolution) is used to simulate convective active episodes occurring in the Western Pacific warm pool and Eastern Atlantic regions. The model is integrated for seven days, and the simulated results are coupled to an OML model to better understand the impact of precipitation and changes in the planetary boundary layer upon SST variation. We will specifically examine and compare the results of linking the OML model with various spatially-averaged outputs from GCE simulations (i.e., 2 km vs. 10-50 km horizontal resolutions), in order to help understand the SST sensitivity to multi-scale influences. This will allow us to assess the importance of explicitly simulated deep and shallow clouds, as well as the subgrid-scale effects (in coarse-model runs) upon SST variation. Results using both 1-D and 2-D OML models will be evaluated to assess the effects of horizontal advection.

Tao, W.-K.↗
NASA NTRS2000

Hurricane Directional Wave Spectrum Spatial Variation in the Open Ocean and at Landfall

The sea surface directional wave spectrum was measured for the first time in all quadrants of a hurricane in open water using the NASA airborne scanning radar altimeter (SRA) carried aboard one of the NOAA WP-3D hurricane hunter aircraft at 1.5 km height. The SRA measures the energetic portion of the directional wave spectrum by generating a topographic map of the sea surface. At 8 Hz, the SRA sweeps a radar beam of 1' half-power width (two-way) across the aircraft ground track over a swath equal to 0.8 of the aircraft height, simultaneously measuring the backscattered power at its 36 GHz (8.3 mm) operating frequency and the range to the sea surface at 64 positions. These slant ranges are multiplied by the cosine of the off-nadir angles to determine the vertical distances from the aircraft to the sea surface. Subtracting these distances from the aircraft height produces the sea surface elevation map. The sea surface topography is interpolated to a uniform grid, transformed by a two dimensional FFT, and Doppler corrected. The open-ocean data were acquired on 24 August 1998 when hurricane Bonnie was east of the Bahamas and moving toward 330 deg at about 5 m/s. Individual waves up to 18 m height were observed and the spatial variation of the wave field was dramatic. The dominant waves generally propagated at significant angles to the downwind direction. At some positions there were three different wave fields of comparable energy crossing each other. The NOAA aircraft spent over five hours within 180 km of the eye, and made five eye penetrations. On 26 August 1998, the NOAA aircraft flew at 2.2 km height when hurricane Bonnie was making landfall near Wilmington, NC, documenting the directional wave spectrum in the region between Charleston, SC and Cape Hatteras, NC. The aircraft flight lines included segments near and along the shoreline as well as far offshore. Animations of the directional wave spectrum spatial variation along the aircraft tracks on the two flights will be presented using a 100: 1 time compression.

Walsh, Edward J.↗
NASA NTRS2000

Hurricane Directional Wave Spectrum Spatial Variation at Landfall

On 26 August 1998, hurricane Bonnie was making landfall near Wilmington, NC. The NASA airborne scanning radar altimeter (SRA) carried aboard one of the NOAA WP-3D hurricane hunter aircraft at 2.2 km height documented the sea surface directional wave spectrum in the region between Charleston, SC and Cape Hatteras, NC. The aircraft ground track included both segments along the shoreline and Pamlico Sound as well as far offshore. An animation of the directional wave spectrum spatial variation at landfall will be presented and contrasted with the spatial variation when Bonnie was in the open ocean on 24 August 1998.

Walsh, Edward J.↗
NASA NTRS1997

Microwave Observations and Modeling of O2 (1-delta(sub g)) and O3 Diurnal Variation in the Mesosphere

The first microwave measurements of an electronically excited molecular species in the Earth's atmosphere are presented. Local thermodynamic equilibrium (LTE) rotational line emission from mesospheric O2(1-del(sub g)) was observed at a frequency of 255.01794 GHz (lambda is approx. 1.2 mm), employing the National Radio Astronomy Observatory (NRAO) millimeter facility at Kitt Peak, Arizona (32 N, 111 W). The pressure broadened line shapes of the O2(1-del(sub g)) spectra, which were obtained in January and April 1992 and in January and November 1993, are inverted to retrieve O2(1-del(sub g)) mixing profiles over the 50-70 km altitude region. The observed daytime abundances exceed ozone abundances in the lower mesosphere, which are separately retrieved with coincident O3 spectral line (249.7886 GHz) observations. The January and November 1993 observations are binned into 20-60 min time intervals to study O2(1-del(sub g)) diurnal behavior. Derived abundances of O2(1-del(sub g)) between 50 and 70 km for the four observation dates are 9%, 31%, 3%, and 26%, respectively, each +/- 10% higher than predicted, based on the simple photochemistry of lower mesospheric O2(1-del(sub g)). Modeled variation of [O2(1-del(sub g))] with time of day agrees with observed variation in that the observed difference between model and data abundances is constant throughout the daylight hours of each observation date. Model underprediction Of [02(lAg)] is consistent with similar model underprediction of mesospheric [O3]. A perturbation to the photochemical model that forces decreased ozone chemical loss brings brings both model [O3] and [O2(1-del(sub g))] into agreement with the observations. O2(1-del(sub g)) abundances derived from these 1.2 mm observations agree with [O2(1-del(sub g))] values derived from comparable SME observations of the 1.27 micrometers emission, with assumption of a 3880 sec O2(1-del(sub g)) radiative lifetime. The 6800 sec O2(1-del(sub g)) radiative lifetime proposed by Mlynczak and Nesbitt is ruled out by the similar comparison.

Sandor, Brad J.↗