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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Gravity Waves Near 300 km Over the Polar Caps

Distinctive wave forms in the distributions of vertical velocity and temperature of both neutral particles and ions are frequently observed from Dynamics Explorer 2 at altitudes above 250 km over the polar caps. These are interpreted as being due to internal gravity waves propagating in the neutral atmosphere. The disturbances characterized by vertical velocity perturbations of the order of 100 m/s and horizontal wave lengths along the satellite path of about 500 km. They often extend across the entire polar cap. The associated temperature perturbations indicate that the horizontal phase progression is from the nightside to the dayside. Vertical displacements are inferred to be of the order of 10 km and the periods to be of the order of 10(exp 3) s. The waves must propagate in the neutral atmosphere, but they usually are most clearly recognizable in the observations of ion vertical velocity and ion temperature. By combining the neutral pressure calculated from the observed neutral concentration and temperature with the vertical component of the neutral velocity, an upward energy flux of the order of 0.04 erg/sq cm-s at 250 km has been calculated, which is about equal to the maximum total solar ultraviolet heat input above that altitude. Upward energy fluxes calculated from observations on orbital passes at altitudes from 250 to 560 km indicate relatively little attenuation with altitude.

Johnson, F. S.↗
NASA NTRS1998

Comparison of Energy Deposition in the Auroral Oval and Cap Regions for Cases Where Transpolar Structures Exist

For several cases where the full auroral zone is imaged and transpolar structures exist, we compare the total energy input to the auroral oval with the total energy input in the polar cap. This comparison is made for cases where auroral intensification near local midnight is and is not observed. Temporal evolution of the energy balance between the energy deposited in the oval and polar cap can be used to understand the mechanism that triggers substorms.

Spann, J. F., Jr.↗
NASA NTRS1998

Topography of Impact Structures on the Northern Polar Cap of Mars

The north polar residual ice deposits of mars are thought to be relatively young, based on the reported lack of any fresh impact craters in Viking Orbiter images. A handful of possible impact features were identified, but available data were inconclusive. Determining the number and current topographic characteristics of any craters on the polar residual ice surface is important in constraining the surface age, relative importance of polar cap resurfacing processes and ice flow dynamics, and the role of the cap deposits in the global volatile and climate cycles. Subsequent image processing advances and new Mars Orbiter Laser Altimeter (MOLA) data in the north polar region are now a considerable aid in impact feature identification. This study reconsiders the abundant Viking high-resolution polar images along with the new altimetry data. We examine possible impact features, compare their topography with known mars high-latitude impact features, and use their morphology as a constraint on crater modification processes.

Sakimoto, S. E. H.↗
NASA NTRS1998

Topography of the South Polar Cap and Layered Deposits of Mars: Viking Stereo Grametry at Regional and Local Scales

Layered deposits and residual polar caps on Mars may record the deposition of ice and sediment modulated by periodic climate change. Topographic information relating to layer thicknesses, erosional processes, and formation of dark spirals within these deposits has been sparce or unreliable until the arrival of MOLA in orbit in September 1997. To assist in evaluating these terrains prior to launch and to assess formation and erosion processes in the polar deposits, we have assembled Viking stereo mosaics of the region and have produced the first reliable DEM models of the south polar deposits using automated stereogrammetry tools. Here we report our preliminary topographic results, pending final image pointing updates. The maximum total thickness of the layered deposits in the south polar region is 2.5 km. The thick layered deposits consist of a series of megaterraces. Each terrace is several tens of kilometers wide and is flat or slopes very gently toward the pole. These terraces step downward from a central plateau near the south pole. Terraces are bounded by relatively steep scarps 100-500 meters high that face toward the equator. These scarps correspond to the pattern of dark spirals observed within the residual cap in southern summer, and are interpreted as ice or frost-free surfaces warmed by solar insolation. Several tongue-shaped troughs, with rounded cirquelike heads, are observed near the margins of the deposit. These troughs are 300-600 meters in deep and may be similar to troughs observed in the northern polar deposit.

Schenk, P.↗
NASA NTRS1998

Analysis of Daily, Seasonal, and Interannual Changes in Hofsjokull Ice Cap, Iceland, using Satellite Data

Analysis of a time series of European Remote Sensing Satellite (ERS)-1 and -2, RADARSAT ScanSAR synthetic aperture radar (SAR) and Landsat images from 1973 to 1998, shows daily to interannual changes in Hofsjokull, a 923 sq km ice cap in central Iceland. A digital elevation model of Hofsjokull was constructed using interferometry, and then SAR backscatter coefficient (d) was plotted with elevation, and air temperature along a transect across the ice cap. Most of the a' changes measured along the transect are caused by a change in the state (frozen or thawed) of the surficial snow or ice when air temperature rises above or below about -5 to O C. Seasonal (sigma)deg patterns are identified in a 4-year time series of 57 ERS-1 and -2 images. In addition, June 1997 ScanSAR images display rapid changes in brightness that are tied closely to daily meteorological events. SAR and Landsat data were also used to measure changes in the areal extent of Hofsjokull, from 1973 to 1997, and to locate (sigma)deg and reflectance boundaries that relate to the glacier facies. Late-summer 1997 (sigma)deg and reflectance boundaries agree and are coincident with the approximate location of the fim line, and the January 1998 position of the equilibrium line as determined from ERS-2 data.

Hall, D. K.↗
NASA NTRS1998

POLAR/TIDE Perigee Observations of Thermal O(+) Characteristics in the Polar Cap Region

We analyze in situ moment measurements of thermal O(+) from the Thermal Ion Dynamics Experiment (TIDE) on POLAR for April - May, 1996. These measurements were obtained near 5000 km altitude within the polar cap ionosphere - magnetosphere interface region. Su explored certain aspects of O(+) parameters in this region. In this report, we hope to expand our knowledge of the O(+) behavior by examining relationships of densities, parallel velocities, and temperatures to the convection velocities, IMF By and Bz components. Preliminary studies with the convection velocities currently require further analysis. In doing so, we are guided in part by the Cleft Ion Fountain paradigm and model developed by which involves downward O(+) flows in the polar magnetosphere. Initial results tend to indicate that in the extreme antisunward region of the polar cap, the density decreases with increasing convection velocity.

Stevenson, B. A.↗
NASA NTRS2000

Mechanical Property Allowables Generated for the Solid Rocket Booster Composite Note Cap

Mechanical property characterization was performed on AS4/3501-6 graphite/epoxy and SC350G syntactic foam for the SRB Composite Nose Cap Shuttle Upgrades Project. Lamina level properties for the graphite/epoxy were determined at room temperature, 240 F, 350 F, 480 F, 600 F, and 350 F after a cycle to 600 F. Graphite/epoxy samples were moisture conditioned prior to testing. The syntactic foam material was tested at room temperature, 350 F, and 480 F. A high-temperature test facility was developed at MSFC. Testing was performed with quartz lamp heaters and high resistance heater strips. The thermal history profile of the nose cap was simulated in order to test materials at various times during launch. A correlation study was performed with Southern Research Institute to confirm the test methodology and validity of test results. A-basis allowables were generated from the results of testing on three lots of material.

Hodge, A. J.↗
NASA NTRS2001

Solar Wind Influence on the Oxygen Content of Ion Outflow in the High-Altitude Polar Cap During Solar Minimum Conditions

We correlate solar wind and interplanetary magnetic field (IMF) properties with the properties of O(+) and H(+) during early 1996 (solar minimum) at altitudes between 5.5 and 8.9 R(sub E) geocentric using the Thermal Ion Dynamics Experiment (TIDE) on the Polar satellite. Throughout the high-altitude polar cap we observe H(+) to be more abundant than O(+). O(+) is found to be more abundant at lower latitudes when the solar wind speed is low (and Kp is low), while at higher solar wind speeds (and high Kp), O(+) is observed across most of the polar cap. The O(+) density and parallel flux are well organized by solar wind dynamic pressure, both increasing with solar wind dynamic pressure. Both the O(+) density and parallel flux have positive correlations with both V(sub SW)B(sub IMF) and E(sub SW). No correlation is found between O(+) density and IMF Bz, although a nonlinear relationship with IMF By is observed, possibly due to a strong linear correlation with the dynamic pressure. H(+) is not as highly correlated with solar wind and IMF parameters, although H(+) density and parallel flux are negatively correlated with IMF By and positively correlated with both V(sub SW)B(sub IMF) and E(sub SW). In this solar minimum data set, H(+) is dominant, so that contributions of this plasma to the plasma sheet would have very low O(+) to H(+) ratios.

Elliott, H. A.↗
NASA NTRS2001

Observation of Pollution Plume Capping by a Tropopause Fold

Airborne lidar measurements reveal a case in which a layer of high-ozone air extruding from a tropopause fold appears to cap a pollution plume and force it to spread out in the lower troposphere. The morphology of the high-ozone layer resembles a three-dimensional model of tropopause fold evolution that produces a low-altitude potential vorticity tube. This is a mechanism that can complete the irreversible transfer of air from the stratosphere, and can also affect pollution levels at the surface if the capping layer reaches the top of the boundary layer.

Cho, John Y. N.↗
NASA NTRS2001

CAP: A Computer Code for Generating Tabular Thermodynamic Functions from NASA Lewis Coefficients

For several decades the NASA Glenn Research Center has been providing a file of thermodynamic data for use in several computer programs. These data are in the form of least-squares coefficients that have been calculated from tabular thermodynamic data by means of the NASA Properties and Coefficients (PAC) program. The source thermodynamic data are obtained from the literature or from standard compilations. Most gas-phase thermodynamic functions are calculated by the authors from molecular constant data using ideal gas partition functions. The Coefficients and Properties (CAP) program described in this report permits the generation of tabulated thermodynamic functions from the NASA least-squares coefficients. CAP provides considerable flexibility in the output format, the number of temperatures to be tabulated, and the energy units of the calculated properties. This report provides a detailed description of input preparation, examples of input and output for several species, and a listing of all species in the current NASA Glenn thermodynamic data file.

Zehe, Michael J.↗
NASA NTRS2002

CAP: A Computer Code for Generating Tabular Thermodynamic Functions from NASA Lewis Coefficients

For several decades the NASA Glenn Research Center has been providing a file of thermodynamic data for use in several computer programs. These data are in the form of least-squares coefficients that have been calculated from tabular thermodynamic data by means of the NASA Properties and Coefficients (PAC) program. The source thermodynamic data are obtained from the literature or from standard compilations. Most gas-phase thermodynamic functions are calculated by the authors from molecular constant data using ideal gas partition functions. The Coefficients and Properties (CAP) program described in this report permits the generation of tabulated thermodynamic functions from the NASA least-squares coefficients. CAP provides considerable flexibility in the output format, the number of temperatures to be tabulated, and the energy units of the calculated properties. This report provides a detailed description of input preparation, examples of input and output for several species, and a listing of all species in the current NASA Glenn thermodynamic data file.

Zehe, Michael J.↗
NASA NTRS2002

Diurnal Albedo Variations of the Martian North Polar Water Ice Cap

Presentation of findings regarding diurnal variations in the north polar water ice cap of Mars as part of a larger study of the interannual and seasonal variations of the Martian north polar water ice cap. Additional information is contained in the original extended abstract.

Troy, R. F.↗
NASA NTRS1997

Three-Dimensional Analysis of Nuclear Size, Shape and Displacement in Clover Root Cap Statocytes from Space and a Clinostat

Under normal (l-g) conditions the statocytes of root caps have a characteristic polarity with the nucleus in tight association with the proximal cell wall; but, in altered gravity environments including microgravity (mu-g) and the clinostat (c-g) movement of the nucleus away from the proximal cell wall is not uncommon. To further understand the cause of gravity-dependent nuclear displacement in statocytes, three-dimensional cell reconstruction techniques were used to precisely measure the volumes, shapes, and positions of nuclei in white clover (Trifolium repens) flown in space and rotated on a clinostat. Seeds were germinated and grown for 72 hours aboard the Space Shuttle (STS-63) in the Fluid Processing Apparatus (BioServe Space Technologies, Univ. of Colorado, Boulder). Clinorotation experiments were performed on a two-axis clinostat (BioServe). Computer reconstruction of selected groups of statocytes were made from serial sections (0.5 microns thick) using the ROSS (Reconstruction Of Serial Sections) software package (Biocomputation Center, NASA Ames Research Center). Nuclei were significantly displaced from the tops of cells in mu-g (4.2 +/- 1.0 microns) and c-g (4.9 +/- 1.4 microns) when compared to l-g controls (3.4 +/- 0.8 gm); but, nuclear volume (113 +/- 36 cu microns, 127 +/- 32 cu microns and 125 +/- 28 cu microns for l-g, mu-g and c-g respectively) and the ratio of nuclear volume to cell volume (4.310.7%, 4.211.0% and 4.911.4% respectively) were not significantly dependent on gravity treatment (ANOVA; alpha = 0.05). Three-dimensional analysis of nuclear shape and proximity to the cell wall, however, showed that nuclei from l-g controls appeared ellipsoidal while those from space and the clinostat were more spherically shaped. This change in nuclear shape may be responsible for its displacement under altered gravity conditions. Since the cytoskeleton is known to affect nuclear polarity in root cap statocytes, those same cytoskeletal elements could also control nuclear shape. This alteration in nuclear shape and position in mu-g and c-g when compared to l-g may lead to functional differences in the gravity signaling systems of plants subjected to altered gravity environments.

Smith, J.D.↗
NASA NTRS2003

Modeling the Seasonal South Polar Cap Sublimation Rates at Dust Storm Conditions

Carbon dioxide is the principal component of the Martian atmosphere and its interaction with the polar caps forms the CO2 seasonal cycle on the planet. A significant fraction of the atmospheric constituent condenses on the surface during the polar winter and sublimes back during spring. The basic aspects of the CO2 cycle have been outlined by Leighton and Murray and a number of follow-up theoretical models ranging from energy balance to general circulation models have been used to study the physical processes involved in the cycle. This paper presents a modeling study on the seasonal south polar cap subliminiation rate under dust storm conditions. Mars Global Surveyor observations are also presented.

P P Bonev↗
NASA NTRS2003

A Case for Microorganisms on Comets, Europa and the Polar Ice Caps of Mars

Microbial extremophiles live on Earth wherever there is liquid water and a source of energy. Observations by ground-based observatories, space missions, and satellites have provided strong evidence that water ice exists today on comets, Europa, Callisto, and Ganymede and in the snow, permafrost, glaciers and polar ice caps of Mars. Studies of the cryoconite pools and ice bubble systems of Antarctica suggest that solar heating of dark rocks entrained in ice can cause localized melting of ice providing ideal conditions for the growth of microbial communities with the creation of micro-environments where trapped metabolic gasses produce entrained isolated atmospheres as in the Antarctic ice-bubble systems. It is suggested that these considerations indicate that several groups of microorganisms should be capable of episodic growth within liquid water envelopes surrounding dark rocks in cometary ices and the permafrost and polar caps of Mars. We discuss some of the types of microorganisms we have encountered within the permafrost and snow of Siberia, the cryoconite pools of Alaska, and frozen deep within the Antarctic ice sheet above Lake Vostok.

Hoover, Richard B.↗
NASA NTRS2003

Reevaluation of Tetrahydrophthalic Anhydride as an End Cap for Improved Oxidation Resistance in Addition Polyimides

Several substituted 1,2,3,6-tetrahydrophthalic anhydride end caps - including the 3-phenyl, 3-methoxy, 3-trimethylsilyloxy, and 3,6-diphenyl analogs - were synthesized via the Diels-Alder condensation of the corresponding butadienes and maleic anhydride. These anhydrides, as well as the commercially available 3-hydro and 4-methyl analogs, were each ground together with methylenedianiline in a 2:1 ratio and heated gradually from 204 C to 371 C, with the thermolysis followed by NMR. Generally speaking, a transformation via monoimide to bisimide was observed in the lower temperature range, followed by competition between crosslinking and aromatization. We believe that this competition produces a substantial percentage of aromatic product, with the concomitant lowering of the relative amount of crosslinking and is responsible for improving both thermal oxidative stability of tetrahydrophthalic end capped polyimides and their substantial frangibility. The thermolysis of the tetrahydrophthalimides under inert atmosphere dramatically lowers the amount of aromatization hence, the mechanism for aromatization is an oxidative one.

Meador, Mary Ann B.↗
NASA NTRS2004

Internal Structure of the Southern Polar Cap of Mars and Formation Implications

The surfaces of the Martian polar caps have been studied in detail but little is known about their internal structure. Exposures of the cap interior can be seen in the many troughs and scarps which incise them. The layered sequences visible in these topographic features have been known to exist for many years, however first order questions concerning the internal stratigraphy remain. We have identified a prominent bench forming layer near the top of the southern layered deposits. We have mapped its exposure in high-resolution MOC images on the eastern and western scarps. These images have been carefully registered to a MOLA derived DEM so topographic measurements along this bench can be extracted along with the location of each trace. What results are a set of measurements of the top of the bench forming layer in three dimensions. The top of this layer represents a distinct stratigraphic horizon. The prominent bench outcrops on both the eastern and western scarps which bound the highest portion of the southern layered deposits. Confirmation that these are two benches are indeed the same stratigraphic surface comes from the similarity of surrounding (nonbench forming) layers.

Byrne, S.↗
NASA NTRS2003

Constraints on the Within Season and Between Year Variability of the North Residual Cap from MGS-TES

There is a long history of telescopic and spacecraft observations of the polar regions of Mars. The finely laminated ice deposits and surrounding layered terrains are commonly thought to contain a record of past climate conditions and change. Understanding the basic nature of the deposits and their mineral and ice constituents is a continued focus of current and future orbited missions. Unresolved issues in Martian polar science include a) the unusual nature of the CO2 ice deposits ("Swiss Cheese", "slab ice" etc.) b) the relationship of the ice deposits to underlying layered units (which differs from the north to the south), c) understanding the seasonal variations and their connections to the finely laminated units observed in high-resolution images and d) the relationship of dark materials in the wind-swept lanes and reentrant valleys to the surrounding dark dune and surface materials. Our work focuses on understanding these issues in relationship to the north residual ice cap. Recent work using Mars Global Surveyor (MGS) data sets have described evolution of the seasonal CO2 frost deposits. In addition, the north polar residual ice cap exhibits albedo variations between Mars years and within the summer season. The Thermal Emission Spectrometer (TES) data set can augment these observations providing additional constraints such as temperature evolution and spectral properties associated with ice and rocky materials. Exploration of these properties is the subject of our current study.

Calvin, W. M.↗