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At least 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Influence of the Yukon River on the Bering Sea

Physical and biological oceanography of the northern Bering Sea including the influence of the Yukon River were studied. Satellite data acquired by the Advanced Very High Resolution Radiometer (AVHRR), the LANDSAT Multispectral Scanner (MSS) and the Thematic Mapper (TM) sensor were used to detect sea surface temperatures and suspended sediments. Shipboard measurements of temperature, salinity and nutrients were acquired through the Inner Shelf Transfer and Recycling (ISHTAR) project and were compared to digitally enhanced and historical satellite images. The satellite data reveal north-flowing, warm water along the Alaskan coast that is highly turbid with complex patterns of surface circulation near the Yukon River delta. To the west near the Soviet Union, cold water, derived from an upwelling, mixes with shelf water and also flows north. The cold and warm water coincide with the Anadyr, Bering Shelf and Alaskan coastal water masses. Generally, warm Alaskan coastal water forms near the coast and extends offshore as the summer progresses. Turbid water discharged by the Yukon River progresses in the same fashion but extends northward across the entrance to Norton Sound, attaining its maximum surface extent in October. The Anadyr water flows northward and around St. Lawrence Island, but its extent is highly variable and depends upon mesoscale pressure fields in the Arctic Ocean and the Bering Sea.

Dean, Kenneson G.↗
NASA NTRS1988

Effect of a uniform sea-level change on the earth's rotation and gravitational field

Global water redistriburtion between the oceans, atmosphere and continents causes changes in the earth's rotation and gravitational field. To conserve water mass, the effect of the small uniform change in sea-level must be considered. Explicit formulas are provided for these sea-level corrections to the gravitational Stokes coefficients, polar motion and length of day. In two recent publications, this sea-level correction term for polar motion was given incorrectly. These errors which arose from normalization conventions with the ocean function are corrected.

Chao, B. Fong↗
NASA NTRS1988

The relationship between large-scale vertical motion, highly reflective cloud, and sea surface temperature in the tropical Pacific region

Vertical motion fields at 850 mbar over the tropical Pacific region are calculated from the 1963-1973 mean wind fields for 4 months of the year and for October 1972, the peak month in the 1972-1973 El Nino event. These vertical motion fields are derived using the projective separation technique, which has the unique property of separating vertical motion into components due to meridional wind convergence and zonal wind convergence. This separation permits investigation of the response of the Hadley and Walker circulations to annual and interannual variation of the sea surface temperature in the tropical Pacific. The large-scale features of the computed vertical motion fields are in agreement with those of highly reflective clouds, which indicate the locations of deep convection. Examination of the annual cycle of the vertical motion and its components shows no strong variation of the Walker circulation with the east-west gradient of sea surface temperature. On the other hand, a strong correlation is found between meridional overturning in the eastern Pacific and the local equatorial sea surface temperature: during El Nino events, the eastern and central Pacific contribution to the Hadley circulation tends to increase.

Zimmermann, Peter H.↗
NASA NTRS1988

Late Eocene impact events recorded in deep-sea sediments

Raup and Sepkoski proposed that mass extinctions have occurred every 26 Myr during the last 250 Myr. In order to explain this 26 Myr periodicity, it was proposed that the mass extinctions were caused by periodic increases in cometary impacts. One method to test this hypothesis is to determine if there were periodic increases in impact events (based on crater ages) that correlate with mass extinctions. A way to test the hypothesis that mass extinctions were caused by periodic increases in impact cratering is to look for evidence of impact events in deep-sea deposits. This method allows direct observation of the temporal relationship between impact events and extinctions as recorded in the sedimentary record. There is evidence in the deep-sea record for two (possibly three) impact events in the late Eocene. The younger event, represented by the North American microtektite layer, is not associated with an Ir anomaly. The older event, defined by the cpx spherule layer, is associated with an Ir anomaly. However, neither of the two impact events recorded in late Eocene deposits appears to be associated with an unusual number of extinctions. Thus there is little evidence in the deep-sea record for an impact-related mass extinction in the late Eocene.

Glass, B. P.↗
NASA NTRS1988

The dependence of sea surface slope on atmospheric stability and swell conditions

A tower-mounted optical device is used to measure the two-orthogonal components of the sea surface slope. The results indicate that an unstable stratification at the air-sea interface tends to enhance the surface roughness. The presence of a long ocean swell system steers the primary direction of shortwave propagation away from wind direction, and may increase or reduce the mean square slope of the sea surface.

Hwang, Paul A.↗
NASA NTRS1988

Providing operational guidance for the development of sea breeze thunderstorms at the Kennedy Space Center - An experiment using a mesoscale numerical model

The effectiveness of a mesoscale numerical model to provide improved local forecast guidance is evaluated with respect to sea breeze convection storms at the Kennedy Space Center. The model and operational forecast guidance production are described. A case study is presented for sea breeze convection storms and lightning events on July 1, 1986. It is found that the mesoscale numerical model outperforms purely subjective predictions of sea breeze convection. The range of applications for the model are considered.

Lyons, Walter A.↗
NASA NTRS1989

A study of oceanic surface heat fluxes in the Greenland, Norwegian, and Barents Seas

This study examines oceanic surface heat fluxes in the Norwegian, Greenland, and Barents seas using the gridded Navy Fleet Numerical Oceanography Central surface analysis and the First GARP Global Experiment (FGGE) IIc cloudiness data bases. Monthly and annual means of net and turbulent heat fluxes are computed for the FGGE year 1979. The FGGE IIb data base consisting of individual observations provides particularly good data coverage in this region for a comparison with the gridded Navy winds and air temperatures. The standard errors of estimate between the Navy and FGGE IIb winds and air temperatures are 3.6 m/s and 2.5 C, respectively. The computations for the latent and sensible heat fluxes are based on bulk formulas with the same constant heat exchange coefficient of 0.0015. The results show extremely strong wintertime heat fluxes in the northern Greenland Sea and especially in the Barents Sea in contrast to previous studies.

Hakkinen, Sirpa↗
NASA NTRS1990

Analysis of altimetry over inland seas

Satellite-based altimetric data taken by GEOS-3 and SEASAT over the Black Sea and Caspian Sea are analyzed and a least squares collocation technique is used to predict the geoid undulation on a .25-degree by .25-degree grid and to transform these geoid undulations to free air gravity anomalies. This project entailed processing satellite altimeter data over inland seas for recovery of area mean gravity information. Gravity information in this area of the world is not readily available, so the possibility of obtaining it from the processing of altimeter observations is attractive. The principal objective was to complete and extend analyses done in a previous study, verify those results, and document the results and techniques. A secondary objective was to improve the algorithms and results, if possible. The approach used involved editing geoid height data to remove overland data; evaluating geoid height differences at crossover points; removing orbit errors from geoid heights using crossover differences; gridding geoid height data at .25-degree by .25-degree intervals; and estimating the gravity anomalies from gridded geoid heights using the collocation technique.

Au, A. Y.↗
NASA NTRS1989

User's guide: Programs for processing altimeter data over inland seas

The programs described were developed to process GEODYN-formatted satellite altimeter data, and to apply the processed results to predict geoid undulations and gravity anomalies of inland sea areas. These programs are written in standard FORTRAN 77 and are designed to run on the NSESCC IBM 3081(MVS) computer. Because of the experimental nature of these programs they are tailored to the geographical area analyzed. The attached program listings are customized for processing the altimeter data over the Black Sea. Users interested in the Caspian Sea data are expected to modify each program, although the required modifications are generally minor. Program control parameters are defined in the programs via PARAMETER statements and/or DATA statements. Other auxiliary parameters, such as labels, are hard-wired into the programs. Large data files are read in or written out through different input or output units. The program listings of these programs are accompanied by sample IBM job control language (JCL) images. Familiarity with IBM JCL and the TEMPLATE graphic package is assumed.

Au, A. Y.↗
NASA NTRS1990

SeaRISE: A Multidisciplinary Research Initiative to Predict Rapid Changes in Global Sea Level Caused by Collapse of Marine Ice Sheets

The results of a workshop held to discuss the role of the polar ice sheets in global climate change are reported. The participants agreed that the most important aspect of the ice sheets' involvement in climate change is the potential of marine ice sheets to cause a rapid change in global sea level. To address this concern, a research initiative is called for that considers the full complexity of the coupled atmosphere-ocean-cryosphere-lithosphere system. This initiative, called SeaRISE (Sea-level Response to Ice Sheet Evolution) has the goal of predicting the contribution of marine ice sheets to rapid changes in global sea level in the next decade to few centuries. To attain this goal, a coordinated program of multidisciplinary investigations must be launched with the linked objectives of understanding the current state, internal dynamics, interactions, and history of this environmental system. The key questions needed to satisfy these objectives are presented and discussed along with a plan of action to make the SeaRISE project a reality.

Bindschadler, Robert A.↗
NASA NTRS1989

A laboratory investigation into microwave backscattering from sea ice

The purpose of the research reported here was to determine the sources of scattering of artificial sea ice, to compare backscatter measurements semi-quantitatively with theoretical predictions, and to develop inexpensive polarimetric radars for sea ice backscatter studies. A brief review of the dielectric properties of sea ice and of commonly used surface and volume scattering theories is presented. We provide a description of the backscatter measurements performed and experimental techniques used. The development of inexpensive short-range polarimetric radars is discussed. We discuss limitations of this system and the development of a radar that avoids the oscillator instability problems of continuously tunable oscillators by doing measurements at discrete frequencies, using a synthesized frequency source. We present results of simple test of copolar phase capability and a simple method of doing phase calibrations. We discuss ice surface characterization data and techniques. We also present a method of estimating the standard deviation of rms height and correlation length for cases of few data points.

Bredow, Jonathan W.↗
NASA NTRS1989

A laboratory investigation into microwave backscattering from sea ice

The sources of scattering of artificial sea ice were determined, backscatter measurements semi-quantitatively were compared with theoretical predictions, and inexpensive polarimetric radars were developed for sea ice backscatter studies. A brief review of the dielectric properties of sea ice and of commonly used surface and volume scattering theories is presented. A description is provided of the backscatter measurements performed and experimental techniques used. The development of inexpensive short-range polarimetric radars is discussed. The steps taken to add polarimetric capability to a simple FM-W radar are considered as are sample polarimetric phase measurements of the radar. Ice surface characterization data and techniques are discussed, including computation of surface rms height and correlation length and air bubble distribution statistics. A method is also presented of estimating the standard deviation of rms height and correlation length for cases of few data points. Comparisons were made of backscatter measurements and theory. It was determined that backscatter from an extremely smooth saline ice surface at C band cannot be attributed only to surface scatter. It was found that snow cover had a significant influence on backscatter from extremely smooth saline ice at C band.

Bredow, Jonathan W.↗
NASA NTRS1989

Observations on electromagnetic bias in radar altimeter sea surface measurements

Because the relative radar cross section of the sea surface increases below mean sea level and decreases above it, the range measurements of satellite radar altimeters are biased toward the wave troughs. Published and unpublished direct measurements of this electromagnetic (EM) bias are examined as well as the predictions of theoretical developments. The EM bias is predominantly a function of the radar frequency used, averaging 1.2 percent of the wave height of Ka band and 3.3 percent of the wave height at X band. The airborne measurements present a consistent picture of the variation of the relative radar cross section as a function of deviation from mean sea level. A technique to measure EM bias at the Ku and C band operating frequencies of the Topex satellite altimeter is described.

Walsh, Edward J.↗
NASA NTRS1990

Mean sea surface and variability of the Gulf of Mexico using Geosat altimetry data

Geosat Exact Repeat Mission (ERM) altimetric measurements of the sea surface height in the Gulf of Mexico are used to determine the mean sea surface height with respect to the ellipsoid and mesoscale variability along Geosat ground tracks in the gulf for the time period from November 8, 1986 to November 25, 1988. A mean surface generated using the Geosat ERM along-track mean is calculated and contrasted with a previously derived mean surface determined using GEOS 3 and Seasat crossover differences. This provides a first look at the variability in the mean between the time periods of 1987-1988 and 1975-1978. In addition, the along-track mesoscale variability time series has been produced from the Geosat ERM data set by using a robust orbit-error removal algorithm to determine the variability of the sea-surface height with respect to the along-track mean. Good qualitative and quantitative agreement with previous in situ observations in the region is found. This study demonstrates the potential of satellite altimetry for oceanographic studies of the Gulf of Mexico.

Leben, Robert R.↗
NASA NTRS1990

Continuous assimilation of Geosat altimetric sea level observations into a numerical synoptic ocean model of the California Current

The Geosat altimetric sea level observations for the period from January to December 1987 were continuously assimilated into a realistic wind-driven numerical synoptic ocean model of the California Current in order to evaluate the effectiveness of using a realistic synoptic ocean model for interpolating (dynamically) real altimetric sea level observations onto a regular grid. The accuracy of dynamical interpolation was tested by comparing the gridded sea level residuals to ones estimated from in situ observations (by expendable bathythermographs) collected in the California Current region during the same period. The comparison yielded nearly exact agreement at low frequency (i.e., semiannual cycle), but less agreement on month-to-month time scales of variability, possibly due to the unfiltered nature of the in situ estimates.

White, Warren B.↗
NASA NTRS1990

Multilayer sea ice in the Arctic - Model- and satellite-derived

The behavior of sea ice is a strong function of ice strength which, in the central Arctic, depends on the relative fractions of multiyear and first-year ice coverage. A dynamic-thermodynamic sea ice model has been configured to include both multiyear and first-year ice. The model has been run for a 7-year period, 1979-1985, for which a satellite microwave record of multiyear sea ice coverage is available. The simulated concentrations of multiyear ice are slightly higher than the satellite-derived concentrations, although the total coverage of simulated multiyear ice agrees well with the satellite-derived coverage. Both the simulated and the satellite-derived coverages in the early 1980s show large interannual variations that represent potentially large perturbations in the mass balance of Arctic pack ice. These fluctuations are generally consistent in the model and satellite data, and they are generally consistent with year-to-year differences in the large-scale wind forcing. In at least some cases the wintertime distribution of multiyear ice is influenced by the pattern of ice drift as far back as the previous summer. The late December coverage of multiyear ice in the Alaskan region appears to foreshadow summer ice conditions in the same region. The short-term response to an intense synoptic system is considerably larger in the satellite data than in the model results.

Walsh, John E.↗
NASA NTRS1990

Dynamic sea surface topography, gravity, and improved orbit accuracies from the direct evaluation of Seasat altimeter data

A gravitational model incorporating Seasat altimetry, surface gravimetry, and satellite tracking data has been determined in terms of global spherical harmonics complete to degree and order 50. This model, PGS-3337, uses altimeter data as a dynamic observation of the satellite's height above the sea surface. A solution for the ocean's dynamic topography is recovered simultaneously with the orbit parameters, gravity, and ocean tidal terms. The recovered dynamic topography reveals the global long wavelength circulation of the oceans with a resolution of 2000 km and is very similar to the mean upper ocean dynamic height derived from historical ship observations. The PGS-3337 geoid has an uncertainty of 60 cm rms globally but 25 cm rms over the ocean because of the altimeter measurements. Seasat orbits determined in this solution have an estimated accuracy for the radial position of 20 cm rms. The difference between the altimeter observed sea height and the geoid plus dynamic topography model is 30 cm rms. Contained in these residuals are the sea height variability, as well as errors from the geoid, orbits, tidal models, and altimeter range measurement. This performance level is 2 to 3 times better than that achieved with previous Goddard gravitational models.

Marsh, J. G.↗
NASA NTRS1991

The influence of the hydrologic cycle on the extent of sea ice with climatic implications

The role was analyzed of the hydrologic cycle on the distribution of sea ice, and its influence on forcings and fluxes between the marine environment and the atmosphere. River discharge plays a significant role in degrading the sea ice before any melting occurs elsewhere along the coast. The influence is considered of river discharge on the albedo, thermal balance, and distribution of sea ice. Quantitative atmospheric-hydrologic models are being developed to describe these processes in the coastal zone. Input for the models will come from satellite images, hydrologic data, and field observations. The resulting analysis provides a basis for the study of the significance of the hydrologic cycle throughout the Arctic Basin and its influence on the regional climate as a result of possible climatic scenarios. The area offshore from the Mackenzie River delta was selected as the study area.

Dean, Ken↗