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At least 1,099 records · Page 61

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NASA NTRS1991

Terrestrial weathering of Antarctic stone meteorites - Formation of Mg-carbonates on ordinary chondrites

Results are presented on the mineralogy, chemistry, and origin of white efflorescences on the surface of Lewis Cliff (Antarctica) 85320 (H5) chondrite (LEW 85320). Particular attention is given to determining the sources of the cations and anions of the evaporite, in order to establish the relative importance of the meteoritic element distribution and terrestrial contamination in the evaporite formation during the weathering process. The data on Na, K, Ca, and Rb abundances in efflorescence from LEW 85320 suggest that cations in evaporite minerals on Antarctic meteorites are not the products of contamination by terrestrial (marine) salts. It is suggested that the Mg in efflorescence on LEW 85320 originated from weathering of meteoritic olivine.

Velbel, Michael A.↗

NASA NTRS1990

Phase noise effects on turbulent weather radar spectrum parameter estimation

Accurate weather spectrum moment estimation is important in the use of weather radar for hazardous windshear detection. The effect of the stable local oscillator (STALO) instability (jitter) on the spectrum moment estimation algorithm is investigated. Uncertainty in the stable local oscillator will affect both the transmitted signal and the received signal since the STALO provides transmitted and reference carriers. The proposed approach models STALO phase jitter as it affects the complex autocorrelation of the radar return. The results can therefore by interpreted in terms of any source of system phase jitter for which the model is appropriate and, in particular, may be considered as a cumulative effect of all radar system sources.

Lee, Jonggil↗

NASA NTRS1991

Weathering of basaltic rocks under cold, arid conditions - Antarctica and Mars

The processes taking part in the chemical weathering of nonvesicular dolerite cobbles producing etch pits and secondary minerals including clays, under cold arid conditions of high-altitude ice-free areas of Victoria Land (Antarctica) are investigated as a possible analog to processes that produced the pitted rocks and clay minerals on Mars. Results suggest that the pits in the dolerite cobbles are formed by the dissolution of the rock by rare snow-melt water during the austral summer, followed by wind erosion of weathered material. The upper interior walls of the pits are lined with a yellow precipitate consisting of illite and quartz mixture, while the pit bottoms contain alteration products including Fe-rich clay minerals and soluble salts. A model is proposed for rock pitting on Mars analogous to that of the Antarctic dolerites.

Allen, C. C.↗

NASA NTRS1991

Cockpit display of hazardous weather information

Information transfer and display issues associated with the dissemination of hazardous weather warnings are studied in the context of wind shear alerts. Operational and developmental wind shear detection systems are briefly reviewed. The July 11, 1988 microburst events observed as part of the Denver Terminal Doppler Weather Radar (TDWR) operational evaluation are analyzed in terms of information transfer and the effectiveness of the microburst alerts. Information transfer, message content and display issues associated with microburst alerts generated from ground based sources (Doppler Radar, Low Level Wind Shear Alert System, and Pilot Reports) are evaluated by means fo pilot opinion surveys and part task simulator studies.

Hansman, R. John, Jr.↗

NASA NTRS1992

Micro weather stations for in situ measurements in the Martian planetary boundary layer

Viking Lander meteorology measurements show that the Martian planetary boundary layer (PBL) has large diurnal and seasonal variations in pressure, wind velocity, relative humidity, and airborne dust loading. An even larger range of conditions was inferred from remote sensing observations acquired by the Mariner 9 and Viking orbiters. Numerical models indicate that these changes may be accompanied by dramatic vertical and horizontal wind shears (100 m/s/km) and rapid changes in the static stability. In-situ measurements from a relatively small number surface stations could yield global constraints on the Martian climate and atmospheric general circulation by providing ground truth for remote sensing instruments on orbiters. A more complete understanding of the meteorology of the PBL is an essential precursor to manned missions to Mars because this will be their working environment. In-situ measurements are needed for these studies because the spatial and temporal scales that characterize the important meteorological processes near the surface cannot be resolved from orbit. The Mars Environmental Survey (MESUR) Program will provide the first opportunity to deploy a network of surface weather stations for a comprehensive investigation of the Martian PBL. The feasibility and utility of a network of micro-weather stations for making in-situ meteorological measurements in the Martian PBL are assessed.

Crisp, D.↗

NASA NTRS1992

Research relative to weather radar measurement techniques

Research relative to weather radar measurement techniques, which involves some investigations related to measurement techniques applicable to meteorological radar systems in Thailand, is reported. A major part of the activity was devoted to instruction and discussion with Thai radar engineers, technicians, and meteorologists concerning the basic principles of radar meteorology and applications to specific problems, including measurement of rainfall and detection of wind shear/microburst hazards. Weather radar calibration techniques were also considered during this project. Most of the activity took place during two visits to Thailand, in December 1990 and February 1992.

Smith, Paul L.↗

NASA NTRS1991

Future plans by the National Oceanic and Atmospheric Administration for operational geosynchronous weather satellites

The present status of the GOES program and plans for the GOES I-M system schedules for initial launch in 1992 are reviewed. Plans for improving NASA's capabilities to monitor weather patterns by using operational geosynchronous weather satellites are considered. The requirements for the imager, sounder, Space Environment Monitor, and Data Collection System of GOES-N are presented.

Gird, Ronald S.↗

NASA NTRS1992

Workshop on chemical weathering on Mars, part 2

The third Mars Surface and Atmosphere Through Time (MSATT) Workshop, which was held 10-12 Sep. 1992, at Cocoa Beach/Cape Kennedy, focused on chemical weathering of the surface of Mars. The 30 papers presented at the workshop described studies of Martian weathering processes based on results from the Viking mission experiments, remote sensing spectroscopic measurements, studies of the shergottite, nakhlite, and chassignite (SNC) meteorites, laboratory measurements of surface analog materials, and modeling of reaction pathways. A summary of the technical sessions is presented and a list of workshop participants is included.

Burns, Roger↗

NASA NTRS1993

Interactive Forecasting with the National Weather Service River Forecast System

The National Weather Service River Forecast System (NWSRFS) consists of several major hydrometeorologic subcomponents to model the physics of the flow of water through the hydrologic cycle. The entire NWSRFS currently runs in both mainframe and minicomputer environments, using command oriented text input to control the system computations. As computationally powerful and graphically sophisticated scientific workstations became available, the National Weather Service (NWS) recognized that a graphically based, interactive environment would enhance the accuracy and timeliness of NWS river and flood forecasts. Consequently, the operational forecasting portion of the NWSRFS has been ported to run under a UNIX operating system, with X windows as the display environment on a system of networked scientific workstations. In addition, the NWSRFS Interactive Forecast Program was developed to provide a graphical user interface to allow the forecaster to control NWSRFS program flow and to make adjustments to forecasts as necessary. The potential market for water resources forecasting is immense and largely untapped. Any private company able to market the river forecasting technologies currently developed by the NWS Office of Hydrology could provide benefits to many information users and profit from providing these services.

Smith, George F.↗

NASA NTRS1992

Implications for volcanogenic volatile release on the weathering of Mars

Volcanism on Mars has been widespread in both space and time. Notwithstanding important specific differences between the mantles of Earth and Mars, the similarities are such that the suite of gases emitted from martian volcanic activity surely includes gases such as H2O, CO2, S-containing gases (H2S, SO3, or SO2), and Cl-containing gases (e.g. Cl or HCl). Both H2O and CO2 are present in the atmosphere of Mars; both are also present as surface condensates. Spectroscopic observations of the martian atmosphere clearly show that the S- and Cl-containing gases are severely depleted. Likewise, there is no evidence of surface condensates of compounds of these elements. Within the soil, there is direct evidence of incorporation of H2O and some compounds of sulfur and chlorine. None of the resultant weathering products have been directly identified, but both clays and salts have been indirectly implicated. Other aspects of the implications for volcanogenic volatile release on the weathering of Mars are discussed.

Clark, Benton C.↗

NASA NTRS1993

Rates of oxidative weathering on the surface of Mars

A model of acid weathering is proposed for the iron-rich basalts on Mars. Aqueous oxidation of iron sulfides released SO4(2-) and H(+) ions that initiated the dissolution of basaltic ferromagnesian silicates and released Fe(2+) ions. The Fe(2+) ions eventually underwent ferrolysis reactions and produced insoluble hydrous ferric oxide phases. Measurements of the time-dependence of acid weathering reactions show that pyrrhotite is rapidly converted to pyrite plus dissolved ferrous iron, the rate of pyrite formation decreasing with rising pH and lower temperatures. On Mars, oxidation rates of dissolved Fe(2+) ions in equatorial melt-waters in contact with the atmosphere are estimated to lie in the range 0.3-3.0 ppb Fe/yr over the pH range 2 to 6. Oxidation of Fe(2+) ions is estimated to be extremely slow in brine eutectic solutions that might be present on Mars and to be negligible in the frozen regolith.

Burns, Roger G.↗

NASA NTRS1993

A comparison of the visible and near infrared reflectance of hydrovolcanic palagonite tuffs and Martian weathered soils

The visible and near infrared reflectance of Martian weathered soils, abundant in the bright regions, have been shown to resemble certain examples of the X-ray amorphous mineraloid palagonite. To date, most comparisons between terrestrial palagonites and Martian telescopic spectra have been done using palagonites that were formed under ambient semi-arid weathering conditions on Hawaiian volcanoes such as Mauna Kea. Here we examine palagonites associated with the tephra deposits that make up tuff rings and tuff cones. Tuff rings and tuff cones result from hydrovolcanic activity, defined as the interaction of magmas (in this instance, of basaltic composition) with surface or near-surface water. Tuff rings and tuff cones can contain variable amounts of country rock and juvenile crystals, but their primary constituent is fine grained sideromelane (basaltic glass). Sideromelane alters to palagonite. Unlike the aforementioned Hawaiian palagonites, the alteration of sideromelane to palagonite seems to occur relatively rapidly in tuff cones, on the order of days to months. In comparing the spectra of hydrovolcanically produced palagonites with telescopic spectra of Mars, one is struck by their similarity in the VNIR and dissimilarity in the SWIR.

Farrand, W. H.↗

NASA NTRS1993

Spectral evidence of size dependent space weathering processes on asteroid surfaces

Most compositional characterizations of the minor planets are derived from analysis of visible and near-infrared reflectance spectra. However, such spectra are derived from light which has only interacted with a very thin surface layer. Although regolith processes are assumed to mix all near-surface lithologic units into this layer, it has been proposed that space weathering processes can alter this surface layer to obscure the spectral signature of the bedrock lithology. It has been proposed that these spectral alteration processes are much less pronounced on asteroid surfaces than on the lunar surface, but the possibility of major spectral alteration of asteroidal optical surfaces has been invoked to reconcile S-asteroids with ordinary chondrites. The reflectance spectra of a large subset of the S-asteroid population have been analyzed in a systematic investigation of the mineralogical diversity within the S-class. In this sample, absorption band depth is a strong function of asteroid diameter. The S-asteroid band depths are relatively constant for objects larger than 100 km and increase linearly by factor of two toward smaller sizes (approximately 40 km). Although the S-asteroid surface materials includes a diverse variety of silicate assemblages, ranging from dunites to basalts, all compositional subtypes of the S-asteroids conform to this trend. The A-, R-, and V-type asteroids which are primarily silicate assemblages (as opposed to the metal-silicate mixtures of most S-asteroids) follow a parallel but displaced trend. Some sort of textural or regolith equilibrium appears to have been attained in the optical surfaces of asteroids larger than about 100 km diameter but not on bodies below this size. The relationships between absorption band depth, spectral slope, surface albedo and body size provide an intriguing insight into the nature of the optical surfaces of the S-asteroids and space weathering on these objects.

Gaffey, M. J.↗

NASA NTRS1993

Local topography of Mars and its relationship to surface weathering processes

There is a growing body of evidence in favor of the importance of aqueous sedimentary processes on Mars. It is important to understand the role that surface weathering processes have played in the development of the present morphology of the Martian surface. Such an understanding is important not only for its relevance to the study of volatile sources and sinks on Mars through time, but also for its relevance to Martian geologic and tectonic history. Starting in the fall of this year, the Mars Observer Laser Altimeter will begin sending back to Earth data on the topography of Mars that is of a higher quality than most of the topography data available for the Earth. This data will be invaluable, not only for understanding global and large-scale regional processes and landforms on Mars, but also for the study of local and smaller-scale regional processes and landforms. Digital topography is an important part of geologic and geomorphic studies, useful in distinguishing between different lithologies and between different types of weathering. Digital topography data may be used to study a wide variety of local and regional-scale landforms, including valleys, sand dunes, lava flows, landslides, and slopes. Topography data are also essential to the analysis of spectral response patterns, especially in areas of high topographic relief. Geomorphic classification can be significantly improved by the addition of topographic information.

Schaefer, M. W.↗

NASA NTRS1992

Managing an archive of weather satellite images

The author's experiences of building and maintaining an archive of hourly weather satellite pictures at NOAO are described. This archive has proven very popular with visiting and staff astronomers - especially on windy days and cloudy nights. Given access to a source of such pictures, a suite of simple shell and IRAF CL scripts can provide a great deal of robust functionality with little effort. These pictures and associated data products such as surface analysis (radar) maps and National Weather Service forecasts are updated hourly at anonymous ftp sites on the Internet, although your local Atsmospheric Sciences Department may prove to be a more reliable source. The raw image formats are unfamiliar to most astronomers, but reading them into IRAF is straightforward. Techniques for performing this format conversion at the host computer level are described which may prove useful for other chores. Pointers are given to sources of data and of software, including a package of example tools. These tools include shell and Perl scripts for downloading pictures, maps, and forecasts, as well as IRAF scripts and host level programs for translating the images into IRAF and GIF formats and for slicing & dicing the resulting images. Hints for displaying the images and for making hardcopies are given.

Seaman, R. L.↗

NASA NTRS1993

United States Weather Research Program (USWRP)

After more than a decade of development by a broad cross-section of the U.S. atmospheric research community involved in planning for the National STORM Program, the Subcommittee on Atmospheric Research (SAR) of the Committee on Earth and Environmental Science (CEES) led the development of a strategic plan to realize the objectives of STORM so as to improve our nation's capability to provide accurate short-term forecasts of weather. This strategic plan will guide the planning and implementation of what is now called the United States Weather Research Program (USWRP). The USWRP is charged with achieving operational atmospheric prediction based on mesoscale observations and model results and establishing the scientific and technological basis for global atmospheric mesoscale prediction by the year 2000. The key scientific questions that are addressed under USWRP are discussed.

Bhumralkar, Chandrakant↗

NASA NTRS1993

The influence of thermal inertia on Mars' seasonal pressure variation and the effect of the weather component

Using a Leighton-Murray type diurnal and seasonal Mars thermal model, we found that it is possible to reproduce the seasonal variation in daily-averaged pressures (approximately 680-890 Pa) measured by Viking Lander 1 (VL1), during years without global dust storms, with a standard deviation of less than 5 Pa. In this simple model, surface CO2, frost condensation, and sublimation rates at each latitude are determined by the net effects of radiation, latent heat, and heat conduction in subsurface soil layers. An inherent assumption of our model is that the seasonal pressure variation is due entirely to the exchange of mass between the atmosphere and polar caps. However, the results of recent Mars GCM modeling have made it clear that there is a significant dynamical contribution to the seasonal pressure variation. This 'weather' component is primarily due to large-scale changes in atmospheric circulation, and its magnitude depends somewhat on the dust content of the atmosphere. The overall form of the theoretical weather component at the location of VL1, as calculated by the AMES GCM, remains the same over the typical range of Mars dust opacities.

Wood, S. E.↗

NASA NTRS1994

Antarctic weathering of the CK chondrites EET90004, 90007, and 90022: Nickel and sulfur mobility

CK chondrites are a relatively new class of carbonaceous chondrite that have been described in the literature. Most meteorites that comprise the CK group are restricted to Antarctic finds; therefore terrestrial weathering processes can influence the geochemical records contained within these chondrites. The paired CK chondrites EET90004, 90007, and 90022 share not only a common heritage but similar weathering histories since all three meteorites were found on Antarctic ice covered with thick evaporative coatings. Additional material has grown on these samples during curation at the Antarctic Meteorite Lab at JSC, NASA. At present, efflorescence up to a millimeter thick coats the surface of EET90004 and 90022, with less material coating EET90007. The chemistry, mineralogy, and isotopic composition of efflorescence on EET90004 and 90022, described here, provide valuable information regarding the fate of meteoritic components in the Antarctic environment.

Romanek, C. S.↗