Unloading Characteristics of Sand-drift in Wind-shallow Areas along Railway and the Effect of Sand Removal by Force of Wind

PubMed Central

Cheng, Jian-jun; Xin, Guo-Wei; Zhi, Ling-yan; Jiang, Fu-qiang

2017-01-01

Wind-shield walls decrease the velocity of wind-drift sand flow in transit. This results in sand accumulating in the wind-shadow zone of both windshield wall and track line, causing severe sand sediment hazard. This study reveals the characteristics of sand accumulation and the laws of wind-blown sand removal in the wind-shadow areas of three different types of windshield walls, utilizing three-dimensional numerical simulations and wind tunnel experiments and on-site sand sediment tests. The results revealed the formation of apparent vortex and acceleration zones on the leeward side of solid windshield walls. For uniform openings, the vortex area moved back and narrowed. When bottom-opening windshield walls were adopted, the track-supporting layer at the step became a conflux acceleration zone, forming a low velocity vortex zone near the track line. At high wind speeds, windshield walls with bottom-openings achieved improved sand dredging. Considering hydrodynamic mechanisms, the flow field structure on the leeward side of different types of windshield structures is a result of convergence and diffusion of fluids caused by an obstacle. This convergence and diffusion effect of air fluid is more apparent at high wind velocities, but not obvious at low wind velocities. PMID:28120915

Incident angle of saltating particles in wind-blown sand.

PubMed

Fu, Lin-Tao; Bo, Tian-Li; Gu, Hai-Hua; Zheng, Xiao-Jing

2013-01-01

Incident angle of saltating particles plays a very important role in aeolian events. In this paper, the incident angles of sand particles near the sand bed were measured in wind tunnel. It reveals that the incident angles range widely from 0° to 180° and thereby the means of angles are larger than published data. Surprisingly, it is found the proportion that angles of 5°-15° occupy is far below previous reports. The measuring height is probably the most important reason for the measurement differences between this study and previous investigations.

Incident Angle of Saltating Particles in Wind-Blown Sand

PubMed Central

Fu, Lin-Tao; Bo, Tian-Li; Gu, Hai-Hua; Zheng, Xiao-Jing

2013-01-01

Incident angle of saltating particles plays a very important role in aeolian events. In this paper, the incident angles of sand particles near the sand bed were measured in wind tunnel. It reveals that the incident angles range widely from 0° to 180° and thereby the means of angles are larger than published data. Surprisingly, it is found the proportion that angles of 5°–15° occupy is far below previous reports. The measuring height is probably the most important reason for the measurement differences between this study and previous investigations. PMID:23874470

A preliminary source-to-sink sediment budget for aeolian sands

NASA Astrophysics Data System (ADS)

Sebe, Krisztina; Csillag, Gábor; Timár, Gábor; Jámbor, Áron

2015-04-01

Source-to-sink sediment budgets are being intensively studied in fluvial systems. In contrast, sediment budget calculations are very rare for wind-transported material. This may be attributed to the fact that the exact delineation of both source and sink areas in aeolian systems can pose difficulties. In the Pannonian Basin, aeolian action by northwesterly to northerly winds exerted a thorough impact on landscape evolution during the Quaternary, testified among others by yardangs, wind corridors and numerous ventifacts as well as extensive blown sand fields. Wind erosion has been dated to be important since at least 1.5 Ma ago. Considering the sand fraction, the Pleistocene Pannonian Basin seems to be a nearly complete aeolian sedimentary system from source to sink, thus it provides a good opportunity to carry out sediment budget calculations. The largest blown sand accumulation occupies ~10 000 km2 in the central part of the Pannonian Basin, in the area called Kiskunság, and contains considerable volumes of aeolian sands extending down to the Lower Pleistocene. Its material is traditionally considered to originate from fluvial sediments of the Danube floodplain. However, recent studies on wind erosion and wind direction reconstructions have indicated that a considerable portion of the sand can have had a provenance in the extensive unconsolidated sediments of the Late Miocene Lake Pannon, which cover the uplifting Transdanubian Range and its surroundings. To gain data on this question, we carried out sediment budget calculations to assess if material volumes of the supposed source and sink areas are comparable. In the source area we reconstructed a paleotopography, practically a bounding envelope surface for the Pliocene/Pleistocene boundary using existing knowledge e.g. on the typical succession of Lake Pannon sediments and the evolution history of the area. The missing volume down to the present-day surface was then calculated, where the removed material was constituted dominantly by the Upper Miocene sediments, subordinately by older clastics. The final amount of sand possibly eroded by the wind from the area was calculated by reducing this volume through estimating the portion of sand in the lacustrine succession and the ratio of aeolian and fluvial erosion. Aeolian sand volumes of the sink were calculated using borehole data from publications and original borehole documentations. This approach contains several error sources, including uncertainties in the position of the envelope surface, varying quality of borehole documentations or the distribution of sampling points. As a result, the estimated error margin of the missing volume computation is up to 50% and the provided value is rather a minimum estimation. A similar value can be valid for the sink area. The calculations showed that sand volumes of the source and sink areas are comparable, with the eroded material being about one third to a half of that of the deposited amount (somewhere below 150 km3 and between 300-400 km3, respectively). This result supports the idea that Transdanubia is an important source area of the Kiskunság blown sand field. The portion of sand in the sink not accounted for by the present estimation can be derived from two sources. Probably more blown sand had been delivered to the sink from areas even more upwind from the Transdanubian Range (Danube Basin), now not included in the calculations. The floodplain of the Danube may have also provided sediments, but mostly only in the Late Pleistocene, when the river had already occupied its modern course upwind of the Kiskunság area. Work has been supported by the OTKA projects K 106197 and NK83400.

Opportunity Eastward View After Sol 2401 Drive

NASA Image and Video Library

2010-11-12

This mosaic of images from NASA Mars Exploration Rover Opportunity shows terrain that includes light-toned bedrock and darker ripples of wind-blown sand. Portions of Endeavour Crater rim are visible in the horizon of this scene.

Opportunity Surroundings After Sol 2363 Drive

NASA Image and Video Library

2010-09-29

This mosaic of images from the navigation camera on NASA Mars Exploration Rover Opportunity shows surroundings of the rover location following a drive on Sept. 16, 2010. The terrain includes light-toned bedrock and darker ripples of wind-blown sand.

Down in the Paleochannels

NASA Image and Video Library

2015-11-27

This whole area, located in Solis Planum, is an interesting, tectonic terrain south of Noctis Labrynthus which generally slopes toward the south as seen by NASA Mars Reconnaissance Orbiter spacecraft. Transverse aeolian ridges -- or TAR -- are mysterious, wind-blown features that are intermediate in size between ripples and much larger sand dunes. Ripples form from hopping sand grains, and dunes form from sand grains being blown over longer distances. One hypothesis for TAR formation is that larger grains like pebbles are rolled on top of smaller ripples; then, finer dust settles into the cracks, "inflating" the pebbles, making the TAR larger than typical ripples. Looking between the TAR, one sees a network of ancient, beaten-up channels that were carved by water, lava, or both. This whole area is located in Solis Planum, an interesting, tectonic terrain south of Noctis Labrynthus which generally slopes toward the south. http://photojournal.jpl.nasa.gov/catalog/PIA20157

Windblown Sand in West Candor

NASA Technical Reports Server (NTRS)

2004-01-01

23 December 2003

West Candor Chasma, a part of the vast Valles Marineris trough system, is known for its layered sedimentary rock outcrops. It is less known for dark fields of windblown sand, but that is what occurs in the north-central part of the chasm. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image, obtained in December 2003, shows the interplay of dark, wind-blown sand with buttes and mesas of layered rock in west Candor Chasma. Dark streamers of sand point toward the east/southeast (right/lower right), indicating that dominant winds blow from the west. This picture is located near 5.2oS, 75.7oW, and covers an area 3 km (1.9 mi) wide. Sunlight illuminates the scene from the lower left.

North Polar Gypsum Dunes in Olympia Undae

NASA Image and Video Library

2016-07-15

These sand dunes are a type of aeolian bedform and partly encircle the Martian North Pole in a region called Olympia Undae. Unlike most of the sand dunes on Mars that are made of the volcanic rock basalt, these are made of a type of sulfate mineral called gypsum. Whence the sand? Well, gypsum is a mineral that can often form from the evaporation of water that has sulfur and calcium dissolved in it. This sand was probably sourced from a northern region on Mars that used to be quite wet. The boxy gridding of the dunes indicates that the wind blows in multiple directions. Note: "Aeolian" means wind-blown and "bedform" means piles of sediment shaped by a flowing fluid (liquid or gas). http://photojournal.jpl.nasa.gov/catalog/PIA20743

Sand dune tracking from satellite laser altimetry

NASA Astrophysics Data System (ADS)

Dabboor, Mohammed

Substantial problems arise from sand movement in arid and semi-arid countries. Sand poses a threat to infrastructure, agricultural and urban areas. These issues are caused by the encroachment of sand on roads and railway tracks, farmland, towns and villages, and airports, to name a few. Sand movement highly depends on geomorphology including vegetation cover, shape and height of the terrain, and grain size of the sand. However, wind direction and speed are the most important factors that affect efficient sand movement. The direction of the movement depends on the main direction of the wind, but it has been shown that a minimum wind speed is required, e.g. wind gusts, to initiate sand transport. This fact prevents a simple calculation of sand transport from conventional wind data as wind records rarely contain sub-minute intervals masking out any wind gusts. An alternative of predicting sand transport is the direct observation of sand advance by in situ measurements or via satellite. Until recently, satellite imagery was the only means to compare dune shape and position for predicting dune migration over several years. In 2003, the NASA laser altimetry mission ICESat became operational and monitors elevations over all surface types including sand dunes with an accuracy of about 10-20 cm. In this study, ICESat observations from repeat tracks (tracks overlapping eachother within 50 m) are used to derive sand dune advance and direction. The method employs a correlation of the elevation profiles over several dunes and was sucessfully validated with synthetic data. The accuracy of this method is 5 meters of dune advance. One of the most active areas exhibiting sand and dune movement is the area of the Arabian Peninsula. Approximately one-third of the Arabian Peninsula is covered by sand dunes. Different wind regimes (Shamal, Kaus) cause sand dune movement in the selected study area in the eastern part of the Arabian Peninsula between 20-25 degrees North and 45-55 degrees East. Two different dune types can be distinguised which exhibit a 6 m and 26 m average dune advance over a 6 months time period. Wind speed/direction data and the observed dune advance agree well and indicate that dune tracking from space is a viable alternative to in situ or model data.

A continuously weighing, high frequency sand trap: Wind tunnel and field evaluations

NASA Astrophysics Data System (ADS)

Yang, Fan; Yang, XingHua; Huo, Wen; Ali, Mamtimin; Zheng, XinQian; Zhou, ChengLong; He, Qing

2017-09-01

A new continuously weighing, high frequency sand trap (CWHF) has been designed. Its sampling efficiency is evaluated in a wind tunnel and the potential of the new trap has been demonstrated in field trials. The newly designed sand trap allows fully automated and high frequency measurement of sediment fluxes over extensive periods. We show that it can capture the variations and structures of wind-driven sand transport processes and horizontal sediment flux, and reveal the relationships between sand transport and meteorological parameters. Its maximum sampling frequency can reach 10 Hz. Wind tunnel tests indicated that the sampling efficiency of the CWHF sand trap varies between 39.2 to 64.3%, with an average of 52.5%. It achieved a maximum sampling efficiency of 64.3% at a wind speed of 10 m s- 1. This is largely achieved by the inclusion of a vent hole which leads to a higher sampling efficiency than that of a step-like sand trap at high wind speeds. In field experiments, we show a good agreement between the mass of sediment from the CWHF sand trap, the wind speed at 2 m and the number of saltating particles at 5 cm above the ground surface. According to analysis of the horizontal sediment flux at four heights from the CWHF sand trap (25, 35, 50, and 100 cm), the vertical distribution of the horizontal sediment flux up to a height of 100 cm above the sand surface follows an exponential function. Our field experiments show that the new instrument can capture more detailed information on sediment transport with much reduced labor requirement. Therefore, it has great potential for application in wind-blown sand monitoring and process studies.

Saltation of Non-Spherical Sand Particles

PubMed Central

Wang, Zhengshi; Ren, Shan; Huang, Ning

2014-01-01

Saltation is an important geological process and the primary source of atmospheric mineral dust aerosols. Unfortunately, no studies to date have been able to precisely reproduce the saltation process because of the simplified theoretical models used. For example, sand particles in most of the existing wind sand movement models are considered to be spherical, the effects of the sand shape on the structure of the wind sand flow are rarely studied, and the effect of mid-air collision is usually neglected. In fact, sand grains are rarely round in natural environments. In this paper, we first analyzed the drag coefficients, drag forces, and starting friction wind speeds of sand grains with different shapes in the saltation process, then established a sand saltation model that considers the coupling effect between wind and the sand grains, the effect of the mid-air collision of sand grains, and the effect of the sand grain shape. Based on this model, the saltation process and sand transport rate of non-spherical sand particles were simulated. The results show that the sand shape has a significant impact on the saltation process; for the same wind speed, the sand transport rates varied for different shapes of sand grains by as much as several-fold. Therefore, sand shape is one of the important factors affecting wind-sand movement. PMID:25170614

Observations regarding the movement of barchan sand dunes in the Nazca to Tanaca area of southern Peru

NASA Astrophysics Data System (ADS)

Parker Gay, S.

1999-03-01

Significant studies of sand dunes and sand movement made in coastal southern Peru in 1959-1961 [Gay, S.P., 1962. Origen, distribución y movimiento de las arenas eólicas en el área de Yauca a Palpa. Boletin de la Sociedad Geologica del Perú 37, 37-58] have never been published in the English language and consequently have never been referred to in the standard literature. These studies contain valuable information, not developed by later workers in this field, that may be of broad general interest. For example, using airphotos of barchan dunes and plotting the rates of movement vs. dune widths, the author quantified the deduction of Bagnold [Bagnold, R.A., 1941. The Physics of Blown Sand and Desert Dunes. Methuen, London.] that the speed of barchan movement is inversely proportional to barchan size (as characterized by height or width). This led to the conclusion that all barchans in a given dune field, regardless of size, sweep out approximately equal areas in equal times. Another conclusion was that collisions between smaller, overtaking dunes and larger dunes in front of them do not result in destruction or absorption of the smaller dunes if the collision is a `sideswipe'. The dunes simply merge into a compound dune for a time, and the smaller dune then moves on intact, i.e., passes, the larger dune, whilst retaining its approximate original size and shape. Another result of the 1959-1961 studies was a map that documents the Pacific coast beaches as the source of the sand ( Fig. 1), which is then blown inland through extensive dune fields of barchans and other dune forms in great clockwise-sweeping paths, to its final resting place in huge sand masses, sometimes called `sand seas' [Lancaster, N., 1995. Geomorphology of Desert Dunes. Routledge, London], at higher elevations 20 to 60 km from the coast. A minor, but nevertheless interesting, discovery was a small heavy mineral dune located directly in the lee of a large barchan, evidently formed by the winnowing action of turbulent airflow streaming off the crest of the 20 m high slipface.

Soil Suitability for Forest Trees in the Thin Loess Area

Treesearch

W. M. Broadfoot; J. S. McKnight

1961-01-01

The Thin Loess soil belt lies east and adjacent to the Deep Loess area. Soils in the area's uplands developed in wind- blown silty deposits less than 4 feet thick. The terraces and bottoms are derived principally from sediments of the nearby loess hills, and mixed alluvium from loess and Coastal Plain sands and clays.

Lunar and Planetary Science XXXV: Martian Aeolian and Mass Wasting Processes: Blowing and Flowing

NASA Technical Reports Server (NTRS)

2004-01-01

The session Martian Aeolian and Mass Wasting Processes: BLowing and Flowing included the following topics: 1) Three Decades of Martian Surface Changes; 2) Thermophysical Properties of Isidis Basin, Mars; 3) Intracrater Material in Eastern Arabia Terra: THEMIS, MOC, and MOLA Analysis of Wind-blown Deposits and Possible High-Inertia Source Material; 4) Thermal Properties of Sand from TES and THEMIS: Do Martian Dunes Make a Good Control for Thermal Inertia Calculations? 5) A Comparative Analysis of Barchan Dunes in the Intra-Crater Dune Fields and the North Polar Sand Sea; 6) Diluvial Dunes in Athabasca Valles, Mars: Morphology, Modeling and Implications; 7) Surface Profiling of Natural Dust Devils; 8) Martian Dust Devil Tracks: Inferred Directions of Movement; 9) Numerical Simulations of Anastomosing Slope Streaks on Mars; 10) Young Fans in an Equatorial Crater in Xanthe Terra, Mars; 11) Large Well-exposed Alluvual Fans in Deep Late-Noachian Craters; 12) New Evidence for the Formation of Large Landslides on Mars; and 13) What Can We Learn from the Ages of Valles Marineris Landslides on Martian Impact History?

Aeolian processes over gravel beds: Field wind tunnel simulation and its application atop the Mogao Grottoes, China

NASA Astrophysics Data System (ADS)

Zhang, Weimin; Tan, Lihai; Zhang, Guobin; Qiu, Fei; Zhan, Hongtao

2014-12-01

The aeolian processes of erosion, transport and deposition are threatening the Mogao Grottoes, a world culture heritage site. A field wind tunnel experiment was conducted atop the Mogao Grottoes using weighing sensors to quantify aeolian processes over protective gravel beds. Results reveal that aeolian erosion and deposition over gravel beds are basically influenced by gravel coverage and wind speed. Erosion is a main aeolian process over gravel beds and its strength level is mainly determined by gravel coverage: strong (<30%), medium (30-50%) and slight (>50%). Aeolian deposition only occurs when gravel coverage is equal to or greater than 30% and wind speeds are between 8 and 12 m s-1, and this process continues until the occurrence of the equilibrium coverage. In addition, the change in conditions of external sand supply affects the transition between aeolian deposition and erosion over gravel beds, and the quantity of sand transport at the height of 0-24 mm is an important indicator of aeolian deposition and erosion over gravel beds. Our results also demonstrate that making the best use of wind regime atop the Mogao Grottoes and constructing an artificial gobi surface in staggered arrays, with 30% coverage and 30-mm-high gravels and in 40 mm spacing can trap westerly invading sand flow and enable the stronger easterly wind to return the deposited sand on the gravel surface back to the Mingsha Mountain so as to minimize the damage of the blown sand flux to the Mogao Grottoes.

The Changing Dunes of Wirtz Crater

NASA Image and Video Library

2017-01-19

The large dark feature is a classic Martian sand dune. Most sand on Earth is made from the mineral quartz, which is white and bright. On Mars, most sand is composed of dark basalt, a volcanic rock. For this reason, dunes on Mars are darker than those on Earth. The dunes in this observation, within Wirtz Crater, are known as "barchans." The steepest slope is on the eastern (right) side, partially in shadow, and represents the direction the dune is migrating as the sand is blown and transported by the wind. Small ripples are visible on much of the dune surface. The dark streaks on the dune are tracks left by passing vortices known to us as dust devils. These raise dust off the dune, revealing a darker substrate. http://photojournal.jpl.nasa.gov/catalog/PIA12289

Overview of the Spirit Mars Exploration Rover Mission to Gusev Crater: Landing Site to Backstay Rock in the Columbia Hills

NASA Technical Reports Server (NTRS)

Arvidson, R. E.; Squyres, S. W,; Anderson, R. C.; Bell, J. F., III; Blaney, D.; Brueckner, J.; Cabrol, N. A.; Calvin, W. M.; Carr, M. H.; Christensen, P. R.;

Relating sedimentary processes in the Bagnold Dunes to the development of crater basin aeolian stratification

NASA Astrophysics Data System (ADS)

Ewing, R. C.; Lapotre, M. G. A.; Lewis, K. W.; Day, M. D.; Stein, N.; Rubin, D. M.; Sullivan, R. J., Jr.; Banham, S.; Thomas, N. M.; Lamb, M. P.; Gupta, S.; Fischer, W. W.

2017-12-01

Wind-blown sand dunes are ubiquitous on the surface of Mars and are a recognized component of the martian stratigraphic record. Our current knowledge of the aeolian sedimentary processes that determine dune morphology, drive dune dynamics, and create aeolian cross-stratification are based upon orbital studies of ripple and dune morphodynamics, rover observations of stratification on Mars, Earth analogs, and experimental and theoretical studies of sand movement under martian conditions. Exploration of the Bagnold Dunes by the Curiosity Rover in Gale Crater, Mars provided the first opportunity to make in situ observations of martian dunes from the grain-to-dune scale. We used the suite of cameras on Curiosity, including Navigation Camera, Mast Camera, and Mars Hand Lens Imager. We measured grainsize and identified sedimentary processes similar to processes on terrestrial dunes, such as grainfall, grainflow, and impact ripples. Impact ripple grainsize had a median of 0.103 mm. Measurements of grainflow slopes indicate a relaxation angle of 29° and grainfall slopes indicate critical angles of at least 32°. Dissimilar to terrestrial dunes, large, meter-scale ripples form on all slopes of the dunes. The ripples form both sinuous and linear crestlines, have symmetric and asymmetric profiles, range in height between 12cm and 28cm, and host grainfall, grainflow, and impact ripples. The largest ripples are interpreted to integrate the annual wind cycle within the crater, whereas smaller large ripples and impact ripples form or reorient to shorter term wind cycling. Assessment of sedimentary processes in combination with dune type across the Bagnold Dunes shows that dune-field pattern development in response to a complex crater-basin wind regime dictates the distribution of geomorphic processes. From a stratigraphic perspective, zones of highest potential accumulation correlate with zones of wind convergence, which produce complex winds and dune field patterns thereby limiting the potential distribution of types of aeolian stratification preserved within crater basins.

Numerical simulation of wind-sand movement in the reversed flow region of a sand dune with a bridge built downstream.

PubMed

He, Wei; Huang, Ning; Xu, Bin; Wang, Wenbo

2018-04-23

A bridge built inside the reversed flow region of a sand dune will change the characteristics of wind-sand movement in this region. The Reynolds-averaged Navier-Stokes simulation and discrete particle tracing are used to simulate the wind-sand movement around a sand dune with a bridge built inside the reversed region. Three cases with different bridge positions are studied. The results show that 1) compared with the isolated dune case, a tall bridge built at the leeward toe leads to an increase in the deposition rate on the leeward slope and a longer reversed flow region downstream of the sand dune; meanwhile, the high speed of crosswind on the bridge indicates that some measures should be taken to protect trains from strong crosswind; 2) a low bridge at the leeward toe has little effect on the sand deposition and reversed flow region of the dune; however, low sand transport rate and crosswind speed on the bridge show that anti-crosswind/sand measures should be taken according to the actual situation and 3) a low bridge on the leeward slope has little effect on the length of reversed flow region, however, high crosswind speed and sand flux on the bridge reveal the need of anti-crosswind/sand measures on the bridge. Moreover, the bridges in the reversed flow region increase the sand flux near the leeward crest; as a result, the moving patterns of the sand dune are changed.

The effect of vegetation patterns on wind-blown mass transport at the regional scale: A wind tunnel experiment

NASA Astrophysics Data System (ADS)

Youssef, Feras; Visser, Saskia M.; Karssenberg, Derek; Erpul, Gunay; Cornelis, Wim M.; Gabriels, Donald; Poortinga, Ate

2012-07-01

Wind erosion is a global environmental problem. Re-vegetating land is a commonly used method to reduce the negative effects of wind erosion. However, there is limited knowledge on the effect of vegetation pattern on wind-blown mass transport. The objective of this study was to investigate the effect of vegetation pattern on this phenomenon within a land unit and at the border between land units. Wind tunnel experiments were conducted with artificial shrubs representing Atriplex halimus. Wind runs at a speed of 11 m s- 1 were conducted and sand translocation was measured after 200-230 s using a graph paper prepared for this purpose. This research showed that: 1) the transport within a land unit is affected by the neighboring land units and by the vegetation pattern within both the unit itself and the neighboring land units; 2) re-vegetation plans for degraded land can take into account the 'streets' effect (zones of erosion areas similar to streets); 3) the effect of neighboring land units includes sheltering effect and the regulation of sediment passing from one land unit to the neighboring land units and 4) in addition to investigation of the general effect of vegetation pattern on erosion and deposition within the region, it is important to investigate the redistribution of sediment at smaller scales depending on the scope of the project.

Terrain Dynamics Analysis Using Space-Time Domain Hypersurfaces and Gradient Trajectories Derived From Time Series of 3D Point Clouds

DTIC Science & Technology

2015-08-01

optimized space-time interpolation method. Tangible geospatial modeling system was further developed to support the analysis of changing elevation surfaces...Evolution Mapped by Terrestrial Laser Scanning, talk, AGU Fall 2012 *Hardin E, Mitas L, Mitasova H., Simulation of Wind -Blown Sand for...Geomorphological Applications: A Smoothed Particle Hydrodynamics Approach, GSA 2012 *Russ, E. Mitasova, H., Time series and space-time cube analyses on

Aeolian sedimentary processes at the Bagnold Dunes, Mars: Implications for modern dune dynamics and sedimentary structures in the aeolian stratigraphic record of Mars

NASA Astrophysics Data System (ADS)

Ewing, Ryan C.; Bridges, Nathan T.; Sullivan, Rob; Lapotre, Mathieu G. A.; Fischer, Woodward W.; Lamb, Mike P.; Rubin, David M.; Lewis, Kevin W.; Gupta, Sanjeev

2016-04-01

Wind-blown sand dunes are ubiquitous on the surface of Mars and are a recognized component of the martian stratigraphic record. Our current knowledge of the aeolian sedimentary processes that determine dune morphology, drive dune dynamics, and create aeolian cross-stratification are based upon orbital studies of ripple and dune morphodynamics, rover observations of stratification on Mars, Earth analogs, and experimental and theoretical studies of sand movement under Martian conditions. In-situ observations of sand dunes (informally called the Bagnold Dunes) by Curiosity Rover in Gale Crater, Mars provide the first opportunity to make observations of dunes from the grain-to-dune scale thereby filling the gap in knowledge between theory and orbital observations and refining our understanding of the martian aeolian stratigraphic record. We use the suite of cameras on Curiosity, including Navigation Camera (Navcam), Mast Camera (Mastcam) and Mars Hand Lens Imager (MAHLI), to make observations of the Bagnold Dunes. Measurements of sedimentary structures are made where stereo images are available. Observations indicate that structures generated by gravity-driven processes on the dune lee slopes, such as grainflow and grainfall, are similar to the suite of aeolian sedimentary structures observed on Earth and should be present and recognizable in Mars' aeolian stratigraphic record. Structures formed by traction-driven processes deviate significantly from those found on Earth. The dune hosts centimeter-scale wind ripples and large, meter-scale ripples, which are not found on Earth. The large ripples migrate across the depositional, lee slopes of the dune, which implies that these structures should be present in Mars' stratigraphic record and may appear similar to compound-dune stratification.The Mars Science Laboratory Curiosity Rover Team is acknowledged for their support of this work.

Comparison of Contributions of Wind-blown and Anthropogenic Fugitive Dust Particles to Atmospheric Particulate Matter

NASA Astrophysics Data System (ADS)

Park, S.; Gong, S.

2010-12-01

A new wind-blown-dust emissions module was recently implemented into AURAMS, a Canadian regional air quality model (Park et al., 2009; Park et al., 2007), to investigate the relative impact of wind-blown dust vs. anthropogenic fugitive dust on air quality in North America. In order to apply the wind-blown dust emissions module to the entire North American continent, a soil-grain-size-distribution map was developed using the outputs of four monthly runs of AURAMS for 2002 and available PM2.5 dust-content observations. The simulation results using the new soil-grain-size-distribution map showed that inclusion of wind-blown dust emissions is essential to predict the impact of dust aerosols on air quality in North America, especially in the western U.S.. The wind-blown dust emissions varied widely by season, whereas the anthropogenic fugitive dust emissions did not change significantly. In the spring (April), the continental monthly average emissions rate of wind-blown dust was much higher than that of anthropogenic fugitive dust. The total amount of wind-blown dust emissions in North America predicted by the model for 2002 was comparable to that of anthropogenic fugitive dust emissions. Even with the inclusion of wind-blown dust emissions, however, the model still had difficulty simulating dust concentrations. Further improvements are needed, in terms of both limitations of the wind-blown-dust emission module and uncertainties in the anthropogenic fugitive dust emissions inventories, for improved dust modelling. References Park, S.H., S.L. Gong, W. Gong, P.A. Makar, M.D. Moran, C.A. Stroud, and J. Zhang, Sensitivity of surface characteristics on the simulation of wind-blown dust source in North America, Atmospheric Environment, 43 (19), 3122-3129, 2009. Park, S.H., S.L. Gong, T.L. Zhao, R.J. Vet, V.S. Bouchet, W. Gong, P.A. Makar, M.D. Moran, C. Stroud, and J. Zhang, Simulation of entrainment and transport of dust particles within North America in April 2001 ("Red Dust Episode"), Journal of Geophysical Research, 112, D20209, doi:10.1029/2007JD008443, 2007.

Supernova remnant evolution in wind bubbles: A closer look at Kes 27

NASA Astrophysics Data System (ADS)

Dwarkadas, V. V.; Dewey, D.

2013-03-01

Massive Stars (>8M⊙) lose mass in the form of strong winds. These winds accumulate around the star, forming wind-blown bubbles. When the star explodes as a supernova (SN), the resulting shock wave expands within this wind-blown bubble, rather than the interstellar medium. The properties of the resulting remnant, its dynamics and kinematics, the morphology, and the resulting evolution, are shaped by the structure and properties of the wind-blown bubble. In this article we focus on Kes 27, a supernova remnant (SNR) that has been proposed by [1] to be evolving in a wind-blown bubble, explore its properties, and investigate whether the X-Ray properties could be ascribed to evolution of a SNR in a wind-blown bubble. Our initial model does not support the scenario proposed by [1], due to the fact that the reflected shock is expanding into much lower densities.

HST, flyaround of the telescope after deployment on this second servicing mission

NASA Image and Video Library

1997-02-19

STS082-746-071 (11-21 Feb. 1997) --- This nearly-vertical view, photographed from the Space Shuttle Discovery, shows the Hubble Space Telescope (HST) over Shark Bay. Shallowest parts of the bay appear light blue. In this view of Australia's arid west, sets of sand dunes are clearly visible on Peron Peninsula (lower center) from southwest to northeast (bottom left to top right), blown by the prevailing wind. Hartog Island lies bottom right.

Épisodes majeurs de la podzolisation en forêt de Fontainebleau (France). Essai de synthèse à l'aide du radiocarbone naturel

NASA Astrophysics Data System (ADS)

Robin, Anne-Marie

2005-04-01

The sandy materials underlying the Fontainebleau Forest (Paris Basin) are often podzolised. Several radiocarbon datings reveal different periods of podzolisation: during the first millenary before Christ (aliotic podzols, often humic, over Stampian sands, very quartzic and acid - certainly under heather and pines); from 10th to 12th centuries AD (humoferruginous podzols with Bh and Bs partially indurated, over blown sands, poor in fine particles - probably under heather); from 16th to 17th centuries AD (ochrepodzolic soils on blown sands, richer in fine particles than precedent, and humic podzols upon eroded Stampian sands); more recently, not precisely dated (ochrepodzolic soils or podzols with loose Bh over blown sands, relatively rich in fine particles, sometimes under leafed trees). To cite this article: A.-M. Robin, C. R. Geoscience 337 (2005).

Terrestrial Analogs to Wind-Related Features at the Viking and Pathfinder Landing Sites on Mars

NASA Technical Reports Server (NTRS)

Greeley, Ronald; Bridges, Nathan T.; Kuzmin, Ruslan O.; Laity, Julie E.

2002-01-01

Features in the Mojave Desert and Iceland provide insight into the characteristics and origin of Martian wind-related landforms seen by the Viking and Pathfinder landers. The terrestrial sites were chosen because they exhibit diverse wind features that are generally well understood. These features have morphologies comparable to those on Mars and include origins by deposition and erosion, with erosional processes modifying both soils and rocks. Duneforms and drifts are the most common depositional features seen at the Martian landing sites and indicate supplies of sand-sized particles blown by generally unidirectional winds. Erosional features include lag deposits, moat-like depressions around some rocks, and exhumed soil horizons. They indicate that wind can deflate at least some sediments and that this process is particularly effective where the wind interacts with rocks. The formation of ripples and wind tails involves a combination of depositional and erosional processes. Rock erosional features, or ventifacts, are recognized by their overall shapes, erosional flutes, and characteristic surface textures resulting from abrasion by windblown particles. The physics of saltation requires that particles in ripples and duneforms are predominantly sand-sized (60-2000 microns). The orientations of duneforms, wind tails, moats, and ventifacts are correlated with surface winds above particle threshold. Such winds are influenced by local topography and are correlated with winds at higher altitudes predicted by atmospheric models.

Eastern Sahara Geology from Orbital Radar: Potential Analog to Mars

NASA Technical Reports Server (NTRS)

Farr, T. G.; Paillou, P.; Heggy, E.

2004-01-01

Much of the surface of Mars has been intensely reworked by aeolian processes and key evidence about the history of the Martian environment seems to be hidden beneath a widespread layer of debris (paleo lakes and rivers, faults, impact craters). In the same way, the recent geological and hydrological history of the eastern Sahara is still mainly hidden under large regions of wind-blown sand which represent a possible terrestrial analog to Mars. The subsurface geology there is generally invisible to optical remote sensing techniques, but radar images obtained from the Shuttle Imaging Radar (SIR) missions were able to penetrate the superficial sand layer to reveal parts of paleohydrological networks in southern Egypt.

The dune effect on sand-transporting winds on Mars.

PubMed

Jackson, Derek W T; Bourke, Mary C; Smyth, Thomas A G

2015-11-05

Wind on Mars is a significant agent of contemporary surface change, yet the absence of in situ meteorological data hampers the understanding of surface-atmospheric interactions. Airflow models at length scales relevant to landform size now enable examination of conditions that might activate even small-scale bedforms (ripples) under certain contemporary wind regimes. Ripples have the potential to be used as modern 'wind vanes' on Mars. Here we use 3D airflow modelling to demonstrate that local dune topography exerts a strong influence on wind speed and direction and that ripple movement likely reflects steered wind direction for certain dune ridge shapes. The poor correlation of dune orientation with effective sand-transporting winds suggests that large dunes may not be mobile under modelled wind scenarios. This work highlights the need to first model winds at high resolution before inferring regional wind patterns from ripple movement or dune orientations on the surface of Mars today.

The dune effect on sand-transporting winds on Mars

PubMed Central

Jackson, Derek W. T.; Bourke, Mary C; Smyth, Thomas A. G.

2015-01-01

Wind on Mars is a significant agent of contemporary surface change, yet the absence of in situ meteorological data hampers the understanding of surface–atmospheric interactions. Airflow models at length scales relevant to landform size now enable examination of conditions that might activate even small-scale bedforms (ripples) under certain contemporary wind regimes. Ripples have the potential to be used as modern ‘wind vanes' on Mars. Here we use 3D airflow modelling to demonstrate that local dune topography exerts a strong influence on wind speed and direction and that ripple movement likely reflects steered wind direction for certain dune ridge shapes. The poor correlation of dune orientation with effective sand-transporting winds suggests that large dunes may not be mobile under modelled wind scenarios. This work highlights the need to first model winds at high resolution before inferring regional wind patterns from ripple movement or dune orientations on the surface of Mars today. PMID:26537669

Algerian Abstract

NASA Image and Video Library

2017-12-08

Algerian Abstract - April 8th, 1985 Description: What look like pale yellow paint streaks slashing through a mosaic of mottled colors are ridges of wind-blown sand that make up Erg Iguidi, an area of ever-shifting sand dunes extending from Algeria into Mauritania in northwestern Africa. Erg Iguidi is one of several Saharan ergs, or sand seas, where individual dunes often surpass 500 meters-nearly a third of a mile-in both width and height. Credit: USGS/NASA/Landsat 5 To learn more about the Landsat satellite go to: landsat.gsfc.nasa.gov/ NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Join us on Facebook

3D Airflow patterns over coastal foredunes: implications for aeolian sediment transport

NASA Astrophysics Data System (ADS)

Jackson, Derek W. T.; Cooper, Andrew G.; Baas, Andreas C. W.; Lynch, Kevin; Beyers, Meiring

2010-05-01

A fundamental criterion for the development of coastal sand dunes is usually highlighted as a significant onshore wind component of the local wind field. The presence of large sand dune systems on coasts where the predominant wind blows offshore is therefore difficult to explain and usually they are attributed to the past occurrence of onshore winds and, by implication, subsequent changes in climate. Recent studies have shown that offshore winds can be deflected or 'steered' by existing dunes so that their direction changes. This can occur to such an extent that a process known as 'flow reversal' can arise, whereby the initially offshore wind actually flows onshore at the beach. This process is important because it can cause sand to be blown from the beach and into the dunes, causing them to grow. This may be central in explaining the presence of extensive dunes on coasts where the dominant wind is offshore, but is also important in how dunes recover after periods of wave erosion during storms. Offshore winds have traditionally been excluded from sediment budget calculations for coastal dunes, but when they do transport sand onshore, this may have been an important oversight leading to significant underestimates of the volume of sand being transported by wind. This work investigates the controls on the processes and the mechanisms involved in deformation of the flow and resulting sediment transport at coastal foredunes in Northern Ireland. We use a combination of field measurement of wind and sediment transport coupled with state-of-the-art aerodynamic modelling using computational fluid dynamics (CFD) and 3-D sonic anemometry. Our working hypothesis is that offshore winds contribute substantially to foredune behaviour on leeside coasts. Preliminary results show strong reverse flow eddies in the seaward side of the foredunes during offshore wind events. These secondary flow reversals have been above velocity threshold and are transport capable. Using CFD modelling across a high resolution LIDAR surface of the dunes and beach we have isolated key areas of wind direction and velocity patterns which are important in aeolian transport budgets. Results are particularly important in post-storm recovery of foredunes damaged under wave action as offshore winds can initiate significant onshore transport, re-supplying the backbeach and foredune zones.

Seasonal geomorphic processes and rates of sand movement at Mount Baldy dune in Indiana, USA

NASA Astrophysics Data System (ADS)

Kilibarda, Zoran; Kilibarda, Vesna

2016-12-01

Winds are very strong, frequent, and have high energy (annual DP ∼800 VU) along the southern shores of Lake Michigan, allowing the coexistence of fixed and active dunes. Six years (2007-13) of monitoring Mount Baldy in the Indiana Dunes National Lakeshore reveals that this is the most active coastal dune in the Great Lakes region. This paper documents aeolian processes and changes in the dune's morphology that occur temporarily, following storms, or seasonally, due to weather (climate) variations. Most of the sand transport in this area takes place during strong storms with gale force (>17.5 m/s) winds, which occur in the autumn and winter months. A single storm, such as the October 28-31, 2013 event, can contribute 25% of the annual sand transport and dune movement inland. In its most active year (June 1, 2011 through May 31, 2012), Mount Baldy moved inland on average 4.34 m, with a maximum of 6.52 m along the blowout's axis (155° azimuth). During this particularly active season, there were six storms with sustained gale force winds, winter air temperatures were warmer than average, and shelf ice on Lake Michigan lasted only one day. The dune is least active during the summer season, when the winds are weakest. The late fall and winter winds are the strongest. But in a typical year, most of the dune's advance inland takes place during the spring thaw when sand is released from over-steepened and lumpy slip face, allowing it to avalanche to the toe of the slip face. However, with a warming air temperatures, a reduction in the duration of winter shelf ice, and rising Lake Michigan levels, the annual rates of sand transport and dune movement may increase. The recent Mount Baldy management strategy, which includes planting vegetation and installing wind barriers on the dune's stoss side in an effort to fix the dune and stop its further movement inland, may potentially cause the destruction of the mobile sand, open dune habitat, resulting in the extinction of rare plants, insects, lizards, birds, and mammals.

[Ecological benefits of planting winter rapeseed in western China].

PubMed

Wang, Xue-fang; Sun, Wan-cang; Li, Fang; Kang, Yan-li; Pu, Yuan-yuan; Liu, Hong-xia; Zeng, Chao-wu; Fan, Chong-xiu

2009-03-01

To evaluate the ecological benefits of popularizing winter rapeseed planting in western China, a wind tunnel simulation test was conducted with four kinds of farmland surface, i.e., winter rapeseed, winter wheat, wheat stubble, and bare field just after spring sowing, collected from west Gansu in April. The results showed that winter rapeseed surface had a roughness of 4.08 cm and a threshold wind velocity as high as 14 m x s(-1), being more effective in blown sand control than the other three surfaces. Under the same experimental conditions, the wind erosion modulus and sand transportation rate of winter rapeseed surface were only 4.1% and 485% of those of the bare field just after spring sowing, and the losses of soil organic matter, alkali-hydrolyzed N, available P and K, catalase, urease, alkaline phosphatase, invertase, and microbes of winter rapeseed surface due to wind erosion were only 1.4%, 5.1%, 1.6%, 2.7%, 9.7%, 3.6%, 6.3%, 6.7% and 1.5% of those of the bare field, respectively. It was suggested that popularizing winter rapeseed planting in west China could control wind erosion, retain soil water and nutrients, increase multicropping index, and improve economic benefits of farmland. In addition, it could benefit the regional desertification control and ecological environment improvement.

Estimation of saltation emission in the Kubuqi Desert, North China.

PubMed

Du, Heqiang; Xue, Xian; Wang, Tao

2014-05-01

The Kubuqi Desert suffered more severe wind erosion hazard. Every year, a mass of aeolian sand was blown in the Ten Tributaries that are tributaries of the Yellow River. To estimate the quantity of aeolian sediment blown into the Ten Tributaries from the Kubuqi Desert, it is necessary to simulate the saltation processes of the Kubuqi Desert. A saltation submodel of the IWEMS (Integrated Wind-Erosion Modeling System) and its accompanying RS (Remote Sensing) and GIS (Geographic Information System) methods were used to model saltation emissions in the Kubuqi Desert. To calibrate the saltation submodel, frontal area of vegetation, soil moisture, wind velocity and saltation sediment were observed synchronously on several points in 2011 and 2012. In this study, a model namely BEACH (Bridge Event And Continuous Hydrological) was introduced to simulate the daily soil moisture. Using the surface parameters (frontal area of vegetation and soil moisture) along with the observed wind velocities and saltation sediments for the observed points, the saltation model was calibrated and validated. To reduce the simulate error, a subdaily wind velocity program, WINDGEN was introduced in this model to simulate the hourly wind velocity of the Kubuqi Desert. By incorporating simulated hourly wind velocity, and model variables, the saltation emission of the Kubuqi Desert was modeled. The model results show that the total sediment flow rate was 1-30.99 tons/m over the last 10years (2001-2010). The saltation emission mainly occurs in the north central part of the Kubuqi Desert in winter and spring. Integrating the wind directions, the quantity of the aeolian sediment that deposits in the Ten Tributaries was estimated. Compared with the observed data by the local government and hydrometric stations, our estimation is reasonable. Copyright © 2014 Elsevier B.V. All rights reserved.

Disturbance of the inclined inserting-type sand fence to wind-sand flow fields and its sand control characteristics

NASA Astrophysics Data System (ADS)

Cheng, Jian-jun; Lei, Jia-qiang; Li, Sheng-yu; Wang, Hai-feng

2016-06-01

The inclined inserting-type sand fence is a novel sand retaining wall adopted along the Lanxin High-Speed Railway II in Xinjiang for controlling and blocking sand movement. To verify the effectiveness of the new fence structure for sand prevention, a wind tunnel test was used for flow field test simulation of the sand fence. The results indicate that the inclined inserting-type sand fence was able to deflect the flow of the sand and was able to easily form an upward slant acceleration zone on the leeward side of the sand fence. As shown by the percentage change in sand collection rates on the windward side and the leeward side of the sand fence, the sand flux per unit area at 4 m height in the slant upward direction increased on the leeward side of the inclined inserting-type sand fence. By comparing the flow fields, this site is an acceleration zone, which also reaffirms the correspondence of wind-sand flow fields with the spatial distribution characteristic of the wind-carried sand motion. The field sand collection data indicates that under the effects of the inclined inserting-type sand fence, the sandy air currents passing in front and behind the sand fence not only changed in quality, but the grain composition and particle size also significantly changed, suggesting that the inclined inserting-type sand fence has a sorting and filtering effect on the sandy air currents that passed through. The fence retained coarse particulates on the windward side and fine particulates within the shade of the wind on the leeward side.

Short-term changes in mobile dunes at Port Alfred, South Africa

NASA Astrophysics Data System (ADS)

Lubke, Roy A.; Sugden, Jean

1990-03-01

Development along the western beachfront of Port Alfred, which is situated along a sandy shoreline, increased markedly in the 1960s as the coastal town became a popular holiday resort. This development included the removal of coastal vegetation, which resulted in the destabilization of dunes and migration of sand westerly onto the road, West Beach parking lot, and lawns of the cabanas. Sand traps were constructed to collect sand blowing across the dunes over set periods, and the net sand movement along the mobile dune belt was calculated using Hunter's equation. The dunes show an easterly movement of sand at a rate of 3.5 m/yr, which is comparable with figures recorded along other areas of this coastline. Considering the wind regime and amount of sand movement along this coast, it is inappropriate to clear vegetation and develop within the dune region.

Layers and Fractures in Ophir Chasma

NASA Image and Video Library

2015-11-05

Ophir Chasma forms the northern portion of Valles Marineris, and this image from NASA Mars Reconnaissance Orbiter spacecraft features a small part of its wall and floor. The wall rock shows many sedimentary layers and the floor is covered with wind-blown ridges, which are intermediate in size between sand ripples and sand dunes. Rocks protruding on the floor could be volcanic intrusions of once-molten magma that have pushed aside the surrounding sedimentary layers and "froze" in place. Images like this can help geologists study the formation mechanisms of large tectonic systems like Valles Marineris. (The word "tectonics" does not mean the same thing as "plate tectonics." Tectonics simply refers to large stresses and strains in a planet's crust. Plate tectonics is the main type of tectonics that Earth has; Mars does not have plate tectonics.) http://photojournal.jpl.nasa.gov/catalog/PIA20044

Earth observation views of the Sahara Desert taken from OV-105 during STS-99

NASA Image and Video Library

2000-03-09

STS099-729-045 (11-22 February 2000) ---This Earth scene from the Space Shuttle Endeavour features linear dunes in the Algerian Saharan sand sea known as the Erg Chech. The dunes, according to NASA scientists, have been built up over thousands of years into masses elongated roughly parallel with the prevailing northeast winds. Dune chains in the northern (upper) half of the view are 5-8 kilometers apart. A slight change in orientation and an increase in the density of dunes appear across the middle of the view. Such changes usually relate to changes in sand supply, and also to topographic scarps over which the dunes pass. Obstacles like scarps and hills locally cause a leftward deflection (in the Northern Hemisphere) in wind direction, an effect that can be seen here in the dune orientation in the middle of the photo. Dunes in the lower part of the view are 2-5 kilometers apart. White patches are small dry lakes at low points in the underlying rock surface. The strong red color in some dunes near the edge of the dune field (left margin) is iron staining derived from sand particles blown into the dunes from the underlying iron-rich soils. A dune-free area appears in the lower left corner.

Glimpse of Bagnold Dunes Edging Mount Sharp

NASA Image and Video Library

2015-11-16

The dark band in the lower portion of this Martian scene is part of the "Bagnold Dunes" dune field lining the northwestern edge of Mount Sharp, inside Gale Crater. The view combines multiple images taken with the Mast Camera (Mastcam) on NASA's Curiosity Mars rover on Sept. 25, 2015, during the 1,115th Martian day, or sol, of Curiosity's work on Mars. The images are from Mastcam's right-eye camera, which has a telephoto lens. The view is toward south-southeast. Curiosity will visit examples of the Bagnold Dunes on the rover's route to higher layers of Mount Sharp. The informal name for the dune field is a tribute to British military engineer Ralph Bagnold (1896-1990), a pioneer in the study of how winds move sand particles of dunes on Earth. The dune field is evident as a dark band in orbital images of the area inside Gale Crater where Curiosity has been active since landing in 2012, such as a traverse map at PIA20162. Dunes are larger than wind-blown ripples of sand or dust that Curiosity and other rovers have visited previously. The scene is presented with a color adjustment that approximates white balancing, to resemble how the rocks and sand would appear under daytime lighting conditions on Earth. http://photojournal.jpl.nasa.gov/catalog/PIA19929

Numerical Study of Splash Detail Due to Grain Impact on Granular Bed

NASA Astrophysics Data System (ADS)

Tanabe, Takahiro; Niiya, Hirofumi; Awazu, Akinori; Nishimori, Hiraku

2017-04-01

Massive sediment transport phenomena, such as sand storm and drifting snow, pose a considerable threat to human life. Further, the formation of geomorphological patterns on sand-desert and snowfield surfaces as a result of sediment transport, such as dunes and ripples, is of considerable research interest. Because the major component of the grain entrainment into the air is caused by both the collision and ejection, it is necessary to focus on the collisions between wind-blown grains and surface of sand field along with the resultant ejection grains from the surfaces, which processes are, as a whole, called a splash process. However, because of complexity of jumping grains over the ground surface, detailed measurement is very hard. Therefore, to investigate the splash process, we simulate detailed process of splash caused by 1-grain impact onto a randomly packed granular bed using discrete element method. As a result, we obtained good correspondence between our numerical results and the findings of previous experiments for the movement of ejected grains. Furthermore, the distributions of the ejection angle and the vertical ejection speed for individual grains vary depending on the relative timing at which the grains are ejected after the initial impact. Obvious differences are observed between the distributions of grains ejected during the earlier and later splash periods: the form of the vertical ejection-speed distribution varies from a power-law form to a lognormal form with time, and this difference is related to the grain trajectory after ejection [1]. In addition, we focus on the bulk dynamics inside the granular bed to relate the ejected grains behavior to the force propagations from the first impact to the ejection of each grain. [1] T. Tanabe, T. Shimada, N. Ito, and, H. Nishimori, (submitted)

The Geodiversity in Drift Sand Landscapes of The Netherlands

NASA Astrophysics Data System (ADS)

van den Ancker, Hanneke; Jungerius, Pieter Dirk; Riksen, Michel

2015-04-01

The authors carried out detailed field studies of more than twelve drift sand landscapes in The Netherlands. The objective of these studies was to restore Natura-2000 values by restoring the wind activity. Active drift sands occur almost exclusively in The Netherlands, Natura 2000 habitat 2330 'Inland dunes with open Corynephorus and Agrostis grasslands', for which reason our country is largely responsible for this European landscape. Active drift sands had almost disappeared for two reasons: first, the stabilization of the drift sands by air pollution, mainly nitrogen, which stimulates the growth of algae and grasses that initiate soil formation, and second, by the growth of forests surrounding the sands, which decreases the wind force. The restoration studies revealed differences in the geodiversity between and within the drift sand areas. Whereas the drift sands on geological and soil maps show as almost homogenous areas, they have in fact highly variable geo-conditions of which examples will be given. These geodiversity aspects concern differences in geomorphological structure, origin, sediments and age of the drift sands. Differences in wind and water erosion, trampling and soil formation add to the geodiversity within the drift sand areas. Especially in the primary stages of succession the differences in geodiversity are relevant for the Natura-2000 values. We discerned three main types of active sands. Firstly, the impressive drift sands with large parabolic dune structures, often consisting of series of interlocking parabolic dunes. They developed from the northeast towards the southwest, against the direction of the dominant wind, and must have taken centuries to develop. Small parts of these systems are still active, other parts show different degrees of soil formation. Their origin is still unclear but probably dates from medieval times (Heidinga, 1985, Jungerius & Riksen, 2008). Second are the drift sand areas with irregular hills from 0.5 to about 2 metres high. They are common near villages. They originated through sand blown from fallow agricultural fields and local overgrazing. They vary in age from prehistoric to modern time and are now mostly planted with forests. Third are the linear drift sand areas with one to three metre high ridges that align old roads and originated through dust whirled up by horses and carriages over many centuries. They also occurs within drift sands of the first system. In the re-stabilization of reactivated drift sands, differences in geodiversity on a still more detailed scale are important (Ancker, Jungerius et al. 2013). Even a small change in slope can cause primary dunes to develop and stop wind erosion. Gradually the geodiversity aspects are recognized as relevant for the management of active and fossil drift sands, and also is becoming a management issue in itself. An important future research issue is the completion of the Drift Sand Atlas, a project that describes the geodiversity aspects of all drift sand areas of The Netherlands. This project has been retarded by lack of means. Knowledge of the geodiversity also is important for correct sampling of C14 and luminescence data. Other future research includes the processes that caused the formation of 'randwallen' (rim walls), rates of water and wind erosion and soil formation and links between flora, fauna and Natura 2000 species. References

Measurements of wind, aeolian sand transport, and precipitation in the Colorado River corridor, Grand Canyon, Arizona; January 2005 to January 2006

USGS Publications Warehouse

Draut, Amy E.; Rubin, David M.

2006-01-01

This report presents measurements of aeolian sediment-transport rates, wind speed and direction, and precipitation records from six locations that contain aeolian deposits in the Colorado River corridor through Grand Canyon, Grand Canyon National Park, Arizona. Aeolian deposits, many of which contain and preserve archaeological material, are an important part of the Grand Canyon ecosystem. This report contains data collected between January 2005 and January 2006, and is the second in a series; the first contained data that were collected between November 2003 and December 2004 (Draut and Rubin, 2005; http://pubs.usgs.gov/of/2005/1309/). Analysis of data collected in 2005 shows great spatial and seasonal variation in wind and precipitation patterns. Total annual rainfall can vary by more than a factor of two over distances ~ 10 km. Western Grand Canyon received substantially more precipitation than the eastern canyon during the abnormally wet winter of 2005. Great spatial variability in precipitation indicates that future sedimentary and geomorphic studies would benefit substantially from continued or expanded data collection at multiple locations along the river corridor, because rainfall records collected by NPS at Phantom Ranch (near river-mile 88) cannot be assumed to apply to other areas of the canyon. Wind velocities and sand transport in 2005 were greatest during May and June, with maximum winds locally as high as ~25 m s-1, and transport rates locally >100 g cm-1 d-1. This represents a later peak in seasonal aeolian sand transport compared to the previous year, in which transport rates were greatest in April and May 2004. Dominant wind direction varies with location, but during the spring windy season the greatest transport potential was directed upstream in Marble Canyon (eastern Grand Canyon). At all locations, rates of sand transport during the spring windy season were 5–15 times higher than at other times of year. This information has been used to evaluate the potential for aeolian reworking of new fluvial sand deposits, and restoration of higher-elevation aeolian deposits, following the 60-hour controlled flood release from Glen Canyon Dam in November 2004. Substantial deposition of new sand occurred at all study sites during this high-flow experiment, but most of the new sediment was eroded by high flow fluctuations between January and March 2005. Comparison of aeolian sand transport in the spring windy seasons of the preand post-flood years indicates that, where some of the flood-deposited sand remained by spring, aeolian sand transport was significantly higher than during the pre-flood spring. Gully incision in an aeolian dune field was observed to be partially ameliorated by deposition of wind-blown sand derived from a nearby 2004 flood deposit. These results imply that sediment-rich controlled floods can renew sand deposition in aeolian dune fields above the flood-stage elevation. The potential for restoration of archaeological sites in aeolian deposits can be maximized by using dam operations that maximize the open sand area on fluvial sandbars during spring, when aeolian sediment transport is greatest.

Planet-wide sand motion on mars

USGS Publications Warehouse

Bridges, N.T.; Bourke, M.C.; Geissler, P.E.; Banks, M.E.; Colon, C.; Diniega, S.; Golombek, M.P.; Hansen, C.J.; Mattson, S.; McEwen, A.S.; Mellon, M.T.; Stantzos, N.; Thomson, B.J.

2012-01-01

Prior to Mars Reconnaissance Orbiter data, images of Mars showed no direct evidence for dune and ripple motion. This was consistent with climate models and lander measurements indicating that winds of sufficient intensity to mobilize sand were rare in the low-density atmosphere. We show that many sand ripples and dunes across Mars exhibit movement of as much as a few meters per year, demonstrating that Martian sand migrates under current conditions in diverse areas of the planet. Most motion is probably driven by wind gusts that are not resolved in global circulation models. A past climate with a thicker atmosphere is only required to move large ripples that contain coarse grains. ?? 2012 Geological Society of America.

A High Resolution Look at Black Sand Particles from Sand Dunes of Saudi Arabia Using Electron Microscopy

NASA Astrophysics Data System (ADS)

Hussain, M. M.; Aburizaiza, O. S.; Siddique, A.; Hershey, D. L.; Guerrieri, D. A.; Qurashi, J.; Abbass, M.; Blake, D. R.; Khwaja, H. A.

2013-12-01

Particulate air pollution is a problem of health concern. The microscopic make-up of different varieties of sand particles found and collected at a sand dune site in Badr, Saudi Arabia has been determined. Primary emphasis is given to the use of multiple high resolution electron microscopy (viz., Scanning Electron Microscopy with Energy Dispersive X-ray spectrometry (SEM/EDS) and Laser Scanning Microscopy (LSM)) to study the morphologies, emission source types, size, and elemental composition of the particles, and to evaluate the presence of ';coatings or contaminants' adsorbed or carried on by the black sand particles. White sand contains natural coarse particles associated with wind-blown releases from crustal surfaces, weathering of an igneous/metamorphic rock source, and volcanic activities. Silicates (alumino-silicates) and quartz (clear, milky, rose) dominate white sand and rest appears to contain calcite, olivine, feldspar, and magnetite. Black sand particles exhibit very different morphologies and microstructures (surface roughness) compared with white sand and volcanic ash. Morphological analyses have shown that the black sand contain ultrafine particles. Black sand is strongly magnetic, which indicates the mineral magnetite (strongly magnetic) or elemental iron. Iron, C, O, Ti, Si, V, and S particles dominate the black sand. Natural and anthropogenic sources have been implicated for the observed particles. Analysis revealed that the surface of white sand particles is mainly covered with the fine particles. It is known that emissions from combustion contain carbon soot and other contaminants that are easily absorbed by soil particles during a long-range transport.

Earth Observations taken by the Expedition 13 crew

NASA Image and Video Library

2006-08-08

ISS013-E-65526 (8 Aug. 2006) --- Issaouane Dune Sea, Eastern Algeria is featured in this image photographed by an Expedition 13 crewmember on the International Space Station. This view from one of the smaller dune seas in the central Sahara shows the complex but regular patterns produced by winds in deserts where abundant sand is available. Geologists now know that dune seas (also called ergs) comprise at least three orders of dune size. In this image the largest and oldest appear here as chains oriented about 60 degrees apart, that is, one oriented almost north-south, the other southwest-northeast. The "streets" between the dune chains (also called mega-dunes) are swept clean of sand in places, revealing the original surface, with light colored muds and salt derived from very occasional rains. The chains have probably taken hundreds of thousands of years to accumulate, starting when the Sahara began to become significantly dry roughly 2.5 million years ago. Rivers became smaller, failed to reach the sea and deposited their sand load in the desert. Wind did the rest, blowing the sand into aerodynamic dune forms. According to scientists, chain trends coincide with two of the four major trends identified in the Great Eastern Sand Sea immediately to the north. Each trend likely implies a different formative wind direction--attesting to the climate shifts that have occurred since sand began to accumulate in the central Sahara. Smaller dunes are superimposed on the mega-dunes. Sinuous crest lines are the mesoscale (intermediate in size) forms, forming octopus-like crests, especially evident as the arms of star dunes. Whereas the mega-dunes are apparently stationary, studies based on aerial photographs in other parts of the world show that these dune crests move in the course of decades. The smallest dunes appear in patches on the eastern sides of the mega-dunes as a tracery of closely spaced crests. Small dunes move fast and reform quickly as stronger winds shift with the seasons. Sand grains are blown continuously from upwind dunes, across the dune-free flats. Small dunes form when the grains slow down and accumulate at the next large dune. The small dunes ride up and over the backs of the mega- and meso-dunes. Interestingly the crest orientation of the small dunes is different from that of the mesoscale dunes throughout the image. This is a common effect of wind direction shifting locally depending on dune height: the increased friction caused by larger dunes causes formative winds to blow to the left of the (weaker) winds that form the small dunes. The friction effect of larger dunes is to the right in the southern hemisphere, well illustrated on the coast of the Namib Desert.

Penetration and blown-air effect in sand

NASA Astrophysics Data System (ADS)

Clement, R.; Courrech du Pont, S.; Douady, S.

2012-04-01

Sand is known to show a variety of uncommon physical features that do not fit the behavior of liquid or solid state. A good example of the inherent difficulties encountered when trying to describe collective grains behavior is the penetration of an intruding object into a granular medium. Such problems involve large coordination numbers, and the medium response dramatically depends on the volume fraction. On the fringe of these studies, we consider here the penetration of a cylindrical shell (typically an upside down glass) into dry sand, and report what we called the "blown-air effect". The air initially trapped escapes when the shell is pushed into sand, flowing through the granular medium. This flow dilates the sand and considerably eases the penetration of the shell. This is very different from what happens in liquids: when pushing a top-closed shell into a liquid, the trapped air increases the buoyancy and opposes the penetration. We show that the air flow does not change the general dynamics of penetration, suggesting that fluidization only involves an effective smaller volume fraction. Despite its simplicity (only a glass and some sand are needed to observe the effect), this experiment nicely illustrates the sometimes counter-intuitive behavior of granular media. Penetration in sand is also a critical issue in industry, and this work may help improving burying methods. Ref: Penetration and blown air effect in granular media R. Clément, S. Courrech du Pont, M. Ould-Hamouda, D. Duveau, and S. Douady Phys. Rev. Lett. 2011 Science News: http://news.sciencemag.org/sciencenow/2011/02/convince-your-friends-youre-a-ge.html

STS-65 Earth observation of dust plumes from Rio Grande in Southern Bolivia

NASA Technical Reports Server (NTRS)

1994-01-01

STS-65 Earth observation taken aboard Columbia, Orbiter Vehicle (OV) 102, is of dust plumes from the Rio Grande in Southern Bolivia. A series of dust plumes can be seen rising from sand banks in the Rio Grande of southern Bolivia, bottom right of this northeast-looking view. The Rio Grande brings sediment from the Andes (foothills visible in the foreground, bottom left) and flows across the flat country of the northern Chaco plain. During the low-flow season, sand banks of this sediment are exposed to northerly winds which often blow dust into the surrounding forest. One of the significances of the dust plumes is that dust acts as a source of nutrient for the local soils. This is the most impressive example of dust ever recorded on Shuttle photography from this river. Such plumes have been seen on photographs from four previous missions (STS-31, STS-47, STS-48, STS-51I) emanating from the Rio Grande. The plumes are regularly space because the sand is blown only from those reaches of th

Periodic Trajectories in Aeolian Sand Transport

NASA Astrophysics Data System (ADS)

Valance, A.; Jenkins, J. T.

2014-12-01

Saltation is the primary mode of aeolian sand transport and refers to the hoping motion of grains over the bed [1]. We develop a simple model for steady, uniform transport in aeolian saltation over a horizontal bed that is based on the computation of periodic particle trajectories in a turbulent shearing flow [2]. The wind and the particles interact through drag, and the particles collide with the bed. We consider collisions with a rigid, bumpy bed, from which the particles rebound, and an erodible particle bed, for which a collision involves both rebound and particle ejection. The difference in the nature of the collisions results in qualitative differences in the nature of the solutions for the periodic trajectories and, in particular, to differences in the dependence of the particle flow rate on the strength of the turbulent shearing. We also discuss the pertinence of this model to describe bedload transport in water. References:[1] R. A. Bagnold, « The physics of blown sand and desert dunes » , Methuen, New York (1941).[2] J.T Jenkins and A. Valance. Periodic trajectories in Aeolian saltation transport. Physics of Fluids, 2014, 26, pp. 073301

Long-term sand supply to Coachella Valley Fringe-toed Lizard Habitat in the Northern Coachella Valley, California

USGS Publications Warehouse

Griffiths, Peter G.; Webb, Robert H.; Lancaster, Nicholas; Kaehler, Charles A.; Lundstrom, Scott C.

2002-01-01

The Coachella Valley fringe-toed lizard (Uma inornata) is a federally listed threatened species that inhabits active sand dunes in the vicinity of Palm Springs, California. The Whitewater Floodplain and Willow Hole Reserves provide some of the primary remaining habitat for this species. The sediment-delivery system that creates these active sand dunes consists of fluvial depositional areas fed episodically by ephemeral streams. Finer fluvial sediments (typically sand size and finer) are mobilized in a largely unidirectional wind field associated with strong westerly winds through San Gorgonio Pass. The fluvial depositional areas are primarily associated with floodplains of the Whitewater?San Gorgonio Rivers and Mission Creek?Morongo Wash; other small drainages also contribute fluvial sediment to the eolian system. The eolian dunes are transitory as a result of unidirectional sand movement from the depositional areas, which are recharged with fine-grained sediment only during episodic floods that typically occur during El Ni?o years. Eolian sand moves primarily from west to east through the study area; the period of maximum eolian activity is April through June. Wind speed varies diurnally, with maximum velocities typically occurring during the afternoon. Development of alluvial fans, alteration of stream channels by channelization, in-stream gravel mining, and construction of infiltration galleries were thought to reduce the amount of fluvial sediment reaching the depositional areas upwind of Uma habitat. Also, the presence of roadways, railroads, and housing developments was thought to disrupt or redirect eolian sand movement. Most of the sediment yield to the fluvial system is generated in higher elevation areas with little or no development, and sediment yield is affected primarily by climatic fluctuations and rural land use, particularly livestock grazing and wildfire. Channelization benefits sediment delivery to the depositional plains upwind of the reserves by minimizing in-channel sediment storage on the alluvial fans. The post-development annual sediment yield to the Whitewater and Mission Creek?Morongo Wash depositional areas are 3.5 and 1.5 million ft3/yr, respectively, covering each depositional area to a depth of 0.2 to 0.4 in. Given existing sand-transport rates, this material could be depleted by eolian processes in 8 to 16 months, a rate consistent with the presence of persistent sand dunes. However, these depletion times are likely minimum estimates, as some eolian sand is seen to persist in the immediate vicinity of depositional areas for longer time periods. Transport rates may be reduced by the presence of vegetation and other windbreaks. Because they are perpendicular to prevailing winds, the infiltration galleries on Whitewater River trap fluvial and eolian sediment, reducing sediment availability. Also, the presence of the railroad and Interstate 10 redirect eolian sand movement to the southeast along their corridors,potentially eliminating the Whitewater depositional area as a sand source for the Willow Hole Reserve. Using directional wind data, we discuss the potential for eolian sand transport from the Mission Creek?Morongo Wash depositional area to Willow Hole.

WIND CHARACTERISTICS OF MESQUITE STREETS IN THE NORTHERN CHIHUAHUAN DESERT, NEW MEXICO, USA

EPA Science Inventory

The most active areas for sand movement in the mesquite-dominated ecosystems in the northern part of the Chihuahuan Desert are elongated bare soil patches referred to as "streets." Wind properties were measured at two flat mesquite sites having highly similar sandy textures but...

Sporadic E movement followed with a pencil beam high frequency radar

NASA Astrophysics Data System (ADS)

From, W. R.

1983-12-01

Several types of sporadic E are observed using the 5.80 and 3.84-MHz Bribie Island pencil-beam high-frequency radar. Blanketing Es takes the form of large flat sheets with ripples in them. Non-blanketing Es is observed to be small clouds that drift across the field of view (40 deg). There is continuous gradation of sporadic E structure between these extremes. There are at least four different physical means by which sporadic E clouds may apparently move. It is concluded that non-blanketing sporadic E consists of separate clouds which follow the movement of the constructive interference between internal gravity waves rather than being blown by the background wind.

Correlation of aeolian sediment transport measured by sand traps and fluorescent tracers

NASA Astrophysics Data System (ADS)

Cabrera, Laura L.; Alonso, Ignacio

2010-03-01

Two different methods, fluorescent tracers and vertical sand traps, were simultaneously used to carry out an aeolian sediment transport study designed to test the goodness of fluorescent tracers in aeolian environments. Field experiments were performed in a nebkha field close to Famara beach at Lanzarote Island (Canary Islands, Spain) in a sector where the dunes were between 0.5 and 0.8 m height and 1-2 m wide and the vegetal cover was approximately 22%. In this dune field the sediment supply comes from Famara beach and is blown by trade winds toward the south, where the vegetation acts as natural sediment traps. Wind data were obtained by means of four Aanderaa wind speed sensors and one Aanderaa vane, all them distributed in a vertical array from 0.1 to 4 m height for 27 h. The average velocity at 1 m height during the experiment was 5.26 m s - 1 with the wind direction from the north. The tracer was under wind influence for 90 min at midday. During this period two series of sand traps (T1 and T2) N, S, E and W oriented were used. Resultant transport rates were 0.0131 and 0.0184 kg m - 1 min - 1 respectively. Tracer collection was performed with a sticky tape to sample only surface sediments. Tagged grains were visually counted under UV light. The transport rate was computed from the centroid displacement, that moved 0.875 m southwards, and the depth of the active layer considered was the size of one single grain. Taking into account these data the transport rate was 0.0072 kg m - 1 min - 1 . The discrepancy in results between both methods is related to several factors, such as the thickness of the active layer and the grain size difference between the tagged and the native material.

A Broad Continuum of Aeolian Impact Ripple Sizes on Mars is Allowed by Low Dynamic Wind Pressures

NASA Astrophysics Data System (ADS)

Sullivan, R. J., Jr.; Kok, J. F.; Yizhaq, H.

2017-12-01

Aeolian impact ripples are generated by impacts of wind-blown sand grains, and are common in environments with loose sand on Earth and Mars. Previous work has shown that, within a fully developed saltation cloud, impact ripple height grows upward into the boundary layer until limited by the effects of increasing wind dynamic pressure at the crest (e.g., lengthening of splash trajectories, or direct entrainment of grains by the wind). On Earth, this process limits ripples of well-sorted 250 µm dune sands to heights of millimeters, and strong winds can impose sufficient lateral dynamic pressure to flatten and erase these ripples. Rover observations show much larger ripple-like bedforms on Mars, raising questions about their formative mechanism. Here, we hypothesize that two factors allow impact ripples to grow much higher on Mars than on Earth: (1) previous work predicts a much larger difference between impact threshold and fluid threshold wind speeds on Mars than on Earth; and (2) recent analysis has revealed how low saltation flux can be initiated and sustained well below fluid threshold on Mars, allowing impact ripples to migrate entirely under prevailing conditions of relatively low wind speeds in the thin martian atmosphere. Under these circumstances, martian ripples would need to grow much larger than on Earth before reaching their maximum height limited by wind dynamic pressure effects. Because the initial size of impact ripples is similar on Mars and Earth, this should generate a much broader continuum of impact ripple sizes on Mars. Compared with Earth, far more time should be needed on Mars for impact ripples to achieve their maximum possible size. Consequently, in cases where wind azimuths are mixed but one azimuth is more dominant than others, martian impact ripples of all sizes can exist together in the same setting, with the largest examples reflecting the most common/formative wind azimuths. In cases where wind azimuth is not dominated by a single azimuth over others, ripple height should vary with orientation and the maximum possible height might never have the chance to be achieved. Our hypothesis could explain the wide range of observed ripple sizes on Mars having wavelengths from cm to several m, and suggests that the largest martian ripples are in fact large impact ripples.

Sand fences in the coastal zone: intended and unintended effects.

PubMed

Grafals-Soto, Rosana; Nordstrom, Karl

2009-09-01

Sand-trapping fences modify the character of the coastal landscape and change its spatial structure, image, and meaning. This paper examines the relationship between these changes and fence usage at the municipal level, where most decisions about fence deployment are made. Use of fences in 29 municipalities on the developed coast of New Jersey is examined over a 6-year period. Interviews with municipal officers indicate that wooden slat sand-trapping fences are used primarily to build dunes to provide protection against wave uprush and flooding, but they are also used to control pedestrian traffic and demarcate territory. These uses result in changes in landforms and habitats. An aerial video inventory of fences taken in 2002 indicates that 82% of the shoreline had fences and 72% had dunes. Single and double straight fence rows are the most commonly used. Fences are often built to accomplish a specific primary purpose, but they can cause many different and often unanticipated changes to the landscape. The effects of a sand fence change through time as the initial structure traps sand, creates a dune that is colonized by vegetation, and becomes integrated into the environment by increasing topographic variability and aesthetic and habitat value. Sand fences can be made more compatible with natural processes by not placing them in locations where sources of wind blown sand are restricted or in unnatural shore perpendicular orientations. Symbolic fences are less expensive, are easy to replace when damaged, are less visually intrusive, and can be used for controlling pedestrian access.

A Modified Bagnold-Type Wind Tunnel for Laboratory Use

ERIC Educational Resources Information Center

Logan, Alan

1975-01-01

Using the basic Bagnold design, a relatively inexpensive suction-type wind tunnel can be constructed for laboratory demonstration of sand-grain movement, ripple development, and other eolian processes. Its simple design provides no workshop problems and it can be made for a total cost in materials of approximately $225. (Author/CP)

Complexity confers stability: Climate variability, vegetation response and sand transport on longitudinal sand dunes in Australia's deserts

NASA Astrophysics Data System (ADS)

Hesse, Paul P.; Telfer, Matt W.; Farebrother, Will

2017-04-01

The relationship between antecedent precipitation, vegetation cover and sand movement on sand dunes in the Simpson and Strzelecki Deserts was investigated by repeated (up to four) surveys of dune crest plots (≈25 × 25 m) over a drought cycle (2002-2012) in both winter (low wind) and spring (high wind). Vegetation varied dramatically between surveys on vegetated and active dune crests. Indices of sand movement had significant correlations with vegetation cover: the depth of loose sand has a strong inverse relationship with crust (cyanobacterial and/or physical) while the area covered by ripples has a strong inverse relationship with the areal cover of vascular plants. However, the relationship between antecedent rainfall and vegetation cover was found to be complex. We tentatively identify two thresholds; (1) >10 mm of rainfall in the preceding 90 days leads to rapid and near total cover of crust and/or small plants <50 cm tall, and (2) >400 mm of rainfall in the preceding three years leads to higher cover of persistent and longer-lived plants >50 cm tall. These thresholds were used to predict days of low vegetation cover on dune crests. The combination of seasonality of predicted bare-crest days, potential sand drift and resultant sand drift direction explains observed patterns of sand drift on these dunes. The complex vegetation and highly variable rainfall regime confer meta-stability on the dunes through the range of responses to different intervals of antecedent rainfall and non-linear growth responses. This suggests that the geomorphic response of dunes to climate variation is complex and non-linear.

Supply-limited horizontal sand drift at an ephemerally crusted, unvegetated saline playa

USGS Publications Warehouse

Gillette, Dale A.; Niemeyer, T.C.; Helm, P.J.

2001-01-01

A site at Owens Dry Lake was observed for more than 4 years. The site was a vegetation-free saline playa where the surface formed "ephemeral crusts," crusts that form after rainfall. Sometimes these crusts were destroyed and often a layer of particles on the crust would engage in vigorous aeolian activity. Three "phases" of active sand drifting are defined as almost no movement (extreme supply limitation), loose particles on crust with some degree of sand drift (moderate supply limitation), and unlimited source movement corresponding to a destroyed surface crust (unlimited supply). These "phases" occurred 45, 49, and 6% of the time, respectively. The accumulation of loose particles on the crust was mostly the result of in situ formation. Crusted sediments with loose particles on top can exhibit mass flux rates about the same as for noncrusted sediments. Crusted sediments limit or eliminate sand drift in two conditions: for rough crusts that effect a sufficiently high threshold friction velocity (above the wind friction velocity) and for limited amounts of loose particles on the crust where particle supply is less than would be transported in normal saltation for a thick sandy surface. These "supply-limited" cases are similar to wind erosion of limited spilled material on a hard concrete surface. We quantified "supply limitation" by defining a "potential" or "supply unlimited" sand drift function Q = AG where A represents supply limitation that decreases as the particle source is depleted. Here Q is the mass of sand transported through a surface perpendicular to the ground and to the wind and having unit width during time period t, and G = ??? u*(u*2 - u*t2) dt for u* > u*t. G is integrated for the same time period t as for Q, u* is the friction velocity of the wind, and u*t is the threshold friction velocity of the wind. Hard crusts (usually formed in the summer) tended to show almost no change of threshold friction velocity with time and often gave total protection from wind erosion. Rough crusts provided sufficient protection expressed as high threshold friction velocities. For these high threshold friction velocities, aeolian activity was greatly reduced or practically prevented. The softest crusts, usually formed in the winter, provided much less protection and sometimes were destroyed by the wind. Following this destruction the "potential" or "supply unlimited" sand drift would be observed. Copyright 2000 by the American Geophysical Union.

Dune mobility and aridity at the desert margin of northern China at a time of peak monsoon strength

USGS Publications Warehouse

Mason, J.A.; Lu, H.; Zhou, Y.; Miao, X.; Swinehart, J.B.; Liu, Z.; Goble, R.J.; Yi, S.

2009-01-01

Wind-blown sands were mobile at many sites along the desert margin in northern China during the early Holocene (11.5-8 ka ago), based on extensive new numerical dating. This mobility implies low effective moisture at the desert margin, in contrast to growing evidence for greater than modern monsoon precipitation at the same time in central and southern China. Dry conditions in the early Holocene at the desert margin can be explained through a dynamic link between enhanced diabatic heating in the core region of the strengthened monsoon and increased subsidence in drylands to the north, combined with high evapotranspiration rates due to high summer temperatures. After 8 ka ago, as the monsoon weakened and lower temperatures reduced evapotranspiration, eolian sands were stabilized by vegetation. Aridity and dune mobility at the desert margin and a strengthened monsoon can both be explained as responses to high summer insolation in the early Holocene. ?? 2009 Geological Society of America.

Aeolian sedimentation in the middle buntsandstein in the eifel north-south depression zone: Summary of the variability of sedimentary processes in a buntsandstein erg as a base for evaluation of the mutual relationships between aeolian sand seas and fluvial river systems in the mid-european buntsandstein

NASA Astrophysics Data System (ADS)

Mader, Detlef

The spectrum of aeolian depositional subenvironments in the upper Middle Buntsandstein Karlstal-Schichten sequence in the Eifel North-South-zone at the western margin of the Mid-European Triassic Basin comprises trains of larger and higher narrowly-spaced dunes in sand seas, isolated smaller and lower widely-spaced dunes in floodplains and interdune playas, dry interdune sheet sands, damp interdune adhesive sandflats, wet interdune playa lakes, rainfall runoff watercourses and ephemeral channels cutting through the dune belt, and deflation gravel lag veneers. Distinction of aeolian and fluvial sediments within the succession of closely intertonguing wind- and water-laid deposits is possible by independent analysis of the conventional criteria and the more modern stratification styles. Thick cross-bedded aeolian sand sequences originate as barchanoid-type dunes which accumulate and migrate in the regime of narrow to wide unimodal southeasterly to southwesterly trade winds in low northern palaeolatitude in summer when the intertropical convergence zone is shifted to the north. The predominantly transverse-ridge dunes accrete mainly by grainfall and subcritical climbing of wind ripples, subordinately also by grainflow interfingering with grainfall. Horizontal-laminated aeolian sands form as sand sheets in dry interdune playas by subcritical migration of wind ripple trains, rarely also by plane bed accretion. Thin cross-bedded dune sands or horizontal-laminated aeolian sands capping fluvial cyclothems originate by deflation of emerged alluvial bar sands during low-water stages and subsequent accumulation of the winnowed sand as widely-spaced dunelets or chains of wind ripples in desiccated parts of the adjoining floodplain. The aeolian sand layers at the base of lacustrine cyclothems record migration of isolated little dunes across the dry playa floor at the beginning of a wetting-upwards cyclothem, with the sand deriving from deflation of fluvial incursions or representing residual sand not having been incorporated into larger dunes of the surrounding sand sea. Damp interdune deposits originate by trapping of loose sand that is blown across a moist playa surface as adhesion ripples and warts. The adhesion structures form both in aeolian sheet sand environments with increasing moisture of the substrate and on fluvial channel bars and stream bottoms with declining dampness during subaerial exposure. Wet interdune deposits originate by settling of suspension fines in periodic shallow lakes between the dunes following heavy ephemeral rainfall or forming by rising ground water table, and by aquatic redeposition of aeolian sand due to washout after atmospheric precipitation and alluvial invasion. Deflationary interdune deposits form by winnowing of the sandy matrix from fluvial sheet or bar conglomerates thereby leaving the dispersed gravel as more or less tightly-packed residual veneer on the degradation surface providing bed armour against further aeolian or aquatic erosion. Aeolian deposition is at the top of the Middle Buntsandstein rather rapidly terminated by fluvial inundation of the erg, erosion and partial resedimentation of dune sands and burial of the more or less degraded aeolian bedforms under a carpet of alluvial deposits. At the beginning of the Upper Buntsandstein, a change to semi-arid climate results in stabilization of emerging overbank plains and channels by palaeosol formation and plant growth thus completely inhibiting further accumulation of aeolian sands. The range of modes of origin of dune sands and interdune deposits, the spatial and temporal variability of their accumulation and preservation and the distribution of water-laid intercalations provide a base for independent evaluation of the dynamics of the aeolian system and its controls as well as for comparative assessment of the behaviour of the aeolian environment and the fluvial milieu in a system of intertonguing sand sea and river belt and of the mechanisms triggering and governing the interference pattern.

Airflow reversal and alternating corkscrew vortices in foredune wake zones during perpendicular and oblique offshore winds

NASA Astrophysics Data System (ADS)

Jackson, Derek W. T.; Beyers, Meiring; Delgado-Fernandez, Irene; Baas, Andreas C. W.; Cooper, Andrew J.; Lynch, Kevin

2013-04-01

On all sandy coastlines fringed by dunes, understanding localised air flow allows us to examine the potential sand transfer between the beach and dunes by wind-blown (Aeolian) action. Traditional thinking into this phenomenon had previously included only onshore winds as effective drivers of this transfer. Recent research by the authors, however, has shown that offshore air-flow too can contribute significantly, through lee-side back eddies, to the overall windblown sediment budget to coastal dunes. Under rising sea levels and increased erosion scenarios, this is an important process in any post-storm recovery of sandy beaches. Until now though, full visualisation in 3D of this newly recognised mechanism in offshore flows has not been achieved. Here, we show for the first time, this return flow eddy system using 3D computational fluid dynamics modelling, and reveal the presence of complex corkscrew vortices and other phenomena. The work highlights the importance of relatively small surface undulations in the dune crest which act to induce the spatial patterns of airflow (and transport) found on the adjacent beach.

Dune-slope activity due to frost and wind throughout the north polar erg, Mars

PubMed Central

DINIEGA, SERINA; HANSEN, CANDICE J.; ALLEN, AMANDA; GRIGSBY, NATHAN; LI, ZHEYU; PEREZ, TYLER; CHOJNACKI, MATTHEW

2018-01-01

Repeat, high-resolution imaging of dunes within the Martian north polar erg have shown that these dune slopes are very active, with alcoves forming along the dune brink each Mars year. In some areas, a few hundred cubic metres of downslope sand movement have been observed, sometimes moving the dune brink ‘backwards’. Based on morphological and activity-timing similarities of these north polar features to southern dune gullies, identifying the processes forming these features is likely to have relevance for understanding the general evolution/modification of dune gullies. To determine alcove-formation model constraints, we have surveyed seven dune fields, each over 1–4 Mars winters. Consistent with earlier reports, we found that alcove-formation activity occurs during the autumn–winter seasons, before or while the stable seasonal frost layer is deposited. We propose a new model in which alcove formation occurs during the autumn, and springtime sublimation activity then enhances the feature. Summertime winds blow sand into the new alcoves, erasing small alcoves over a few Mars years. Based on the observed rate of alcove erasure, we estimated the effective aeolian sand transport flux. From this, we proposed that alcove formation may account for 2–20% of the total sand movement within these dune fields. PMID:29731538

Dune-slope activity due to frost and wind throughout the north polar erg, Mars.

PubMed

Diniega, Serina; Hansen, Candice J; Allen, Amanda; Grigsby, Nathan; Li, Zheyu; Perez, Tyler; Chojnacki, Matthew

2017-01-01

Repeat, high-resolution imaging of dunes within the Martian north polar erg have shown that these dune slopes are very active, with alcoves forming along the dune brink each Mars year. In some areas, a few hundred cubic metres of downslope sand movement have been observed, sometimes moving the dune brink 'backwards'. Based on morphological and activity-timing similarities of these north polar features to southern dune gullies, identifying the processes forming these features is likely to have relevance for understanding the general evolution/modification of dune gullies. To determine alcove-formation model constraints, we have surveyed seven dune fields, each over 1-4 Mars winters. Consistent with earlier reports, we found that alcove-formation activity occurs during the autumn-winter seasons, before or while the stable seasonal frost layer is deposited. We propose a new model in which alcove formation occurs during the autumn, and springtime sublimation activity then enhances the feature. Summertime winds blow sand into the new alcoves, erasing small alcoves over a few Mars years. Based on the observed rate of alcove erasure, we estimated the effective aeolian sand transport flux. From this, we proposed that alcove formation may account for 2-20% of the total sand movement within these dune fields.

The Partition Between Terminal Speed and Mass Loss: Thin, Thick, and Rotating Line-Driven Winds

NASA Astrophysics Data System (ADS)

Gayley, K. G.; Onifer, A. J.

2003-01-01

Steady-state supersonic line-driven winds are important contributors to wind-blown bubbles in star forming regions. The key input to the bubble in the energy-conserving phase is the wind kinetic-energy flux, which involves both the mass-loss rate and the terminal speed. However, these quantities are themselves self-consistent parameters of the line-driving process, so relate to each other and to the resulting wind optical depth. This complex interrelation between optical depth, mass-loss, and wind speed lies at the heart of line-driven wind theory. Drawing on the successes and insights of ``CAK'' theory, I will convey a simplified view of how to unite these processes using the concept of effective opacity, with attention to the ramifications for nonspherical nebular and wind-blown structures. Recent extensions to nongray optically thick environments such as Wolf-Rayet winds and supernovae are also discussed.

A study of morphology, provenance, and movement of desert sand seas in Africa, Asia, and Australia

NASA Technical Reports Server (NTRS)

Mckee, E. D.; Breed, C. S.

1973-01-01

A description and classification of major types of sand seas on the basis of morphological pattern and lineation are discussed. The steps involved in analyzing the patterns of deposits on ERTS-1 imagery, where the visible forms are mostly dune complexes rather than individual dunes are outlined. After completion of thematic maps portraying the pattern and lineation of the sand bodies, data on directions and intensity of prevailing and other winds are plotted on corresponding bases, as a preliminary to determination of internal structures through ground truth.

Image motion environments: background noise for movement-based animal signals.

PubMed

Peters, Richard; Hemmi, Jan; Zeil, Jochen

2008-05-01

Understanding the evolution of animal signals has to include consideration of the structure of signal and noise, and the sensory mechanisms that detect the signals. Considerable progress has been made in understanding sounds and colour signals, however, the degree to which movement-based signals are constrained by the particular patterns of environmental image motion is poorly understood. Here we have quantified the image motion generated by wind-blown plants at 12 sites in the coastal habitat of the Australian lizard Amphibolurus muricatus. Sampling across different plant communities and meteorological conditions revealed distinct image motion environments. At all locations, image motion became more directional and apparent speed increased as wind speeds increased. The magnitude of these changes and the spatial distribution of image motion, however, varied between locations probably as a function of plant structure and the topographic location. In addition, we show that the background motion noise depends strongly on the particular depth-structure of the environment and argue that such micro-habitat differences suggest specific strategies to preserve signal efficacy. Movement-based signals and motion processing mechanisms, therefore, may reveal the same type of habitat specific structural variation that we see for signals from other modalities.

Earth Observations taken by the Expedition 22 Crew

NASA Image and Video Library

2009-12-24

ISS022-E-015154 (24 Dec. 2009) --- Tsauchab River and Sossus Vlei Lakebed, Namibia are featured in this image photographed by an Expedition 22 crew member on the International Space Station. Taken on Christmas Eve of 2009, this image shows the lower 45 kilometers of the Tsauchab River, a famous landmark for Namibians, tourists, and for orbiting astronauts. The Tsauchab River bed is seen jutting into the sea of red dunes near Namibia?s hyper arid coast, where it ends in a series of light-toned silty muds of the dry lake floor, known locally as Sossus Vlei (small lake). Because of the present arid climate, few people have ever seen the Tsauchab River with flowing water or a lake in Sossus Vlei. In times past, however, the Tsauchab appears to have reached the Atlantic coast, another 55 kilometers further west. Like several other rivers of the coastal Namib Desert, the Tsauchab brings sediment down from the hinterland to the coastal lowland. According the scientists, this sediment is then blown from the river beds, and over probably tens of millions of years, has accumulated as the red dunes of the impressive Namib Sand Sea. In this view the sand is heaped up in the form of numerous ?star dunes,? each characterized by long arms extending in several directions. These compare with the better-known barchan dunes (not present in image) that display two horns pointing downwind, which form in areas where winds generally blow from one direction only. By contrast, star dunes are apparently generated in a variable wind regime. In this part of the Sand Sea, winds are mainly from the south, but easterly winds, channeled along the Tsauchab valley, provide another component. And warm dry winter winds?similar to the Santa Ana winds of California, which can cause the hottest annual temperatures to occur briefly on winter days?blow from the northeast. These northeasterly winds are likely responsible for the regular dune arms that point into the valley from both sides. These large dunes facing the river valley are promoted as the highest dunes in the world. Although continuous dune slopes allow hikers to gain more than 300 meters of altitude from the river bottom, this could be misleading since the main base of the dunes lies on a terrace 180 meters above the river.

Recent Aeolian Dune Change on Mars

NASA Technical Reports Server (NTRS)

Bourke, M. C.; Edgett, K. S.; Cantor, B. A.

2007-01-01

Previous comparisons of Martian aeolian dunes in satellite images have not detected any change in dune form or position. Here, we show dome dunes in the north polar region that shrank and then disappeared over a period of 3.04 Mars years (5.7 Earth years), while larger, neighboring dunes showed no erosion or movement. The removal of sand from these dunes indicates that not only is the threshold wind speed for saltation exceeded under present conditions on Mars, but that any sand that is available for transport is likely to be moved. Dunes that show no evidence of change could be crusted, indurated. or subject to infrequent episodes of movement.

2008 Weather and Aeolian Sand-Transport Data from the Colorado River Corridor, Grand Canyon, Arizona

USGS Publications Warehouse

Draut, Amy E.; Sondossi, Hoda A.; Hazel, Joseph E.; Andrews, Timothy; Fairley, Helen C.; Brown, Christopher R.; Vanaman, Karen M.

2009-01-01

This report presents measurements of weather parameters and aeolian (windblown) sand transport made in 2008 near selected archaeological sites in the Colorado River corridor through Grand Canyon, Ariz. The quantitative methods and data discussed here form a basis for monitoring ecosystem processes that affect archeological-site stability. Combined with forthcoming work to evaluate landscape evolution at nearby archaeological sites, these data can be used to document the relationship between physical processes, including weather and aeolian sand transport, and their effects on the physical integrity of archaeological sites. Data collected in 2008 reveal event- and seasonal-scale variations in rainfall, wind, temperature, humidity, and barometric pressure. Broad seasonal changes in aeolian sediment flux are also apparent at most study sites. The continuation of monitoring that began in 2007, and installation of equipment at several new sites in early 2008, allowed evaluation of the effects of the March 2008 high-flow experiment (HFE) on aeolian sand transport. At two of the nine sites studied, spring and summer winds reworked 2008 HFE sandbars to form new aeolian dunes, at which sand moved inland toward larger, well-established dune fields. At the other seven study sites, neither dune formation nor enhanced sand transport after the HFE were observed. At several of those sites, dominant wind directions in spring 2008 were not oriented such that much HFE sand would have moved inland; at other sites, lack of increased inland sand flux is attributable to lack of sandbar enlargement near the study sites or to inhibition of sand movement by vegetation or local topography.

Western Edge of Mars Marth Crater, a Movie Location

NASA Image and Video Library

2015-10-05

In the best-selling novel "The Martian" and the movie based on it, stranded astronaut Mark Watney's adventures take him to the rim of Mawrth Crater. This image from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter shows the nature of this terrain. The crater rim is not very distinct, and from the Martian surface it would be quite difficult to tell that you are even on the rim of a crater. The terrain is hummocky and rolling, punctuated by smaller impact craters and wind-blown drifts of sand or dust. This view is one image product from HiRISE observation ESP_042252_1930, taken Aug. 1, 2015, at 12.6 degrees north latitude, 355.7 degrees east longitude. http://photojournal.jpl.nasa.gov/catalog/PIA19915

Aeolian responses to climate variability during the past century on Mesquite Lake Playa, Mojave Desert

USGS Publications Warehouse

Whitney, John W.; Breit, George N.; Buckingham, S.E.; Reynolds, Richard L.; Bogle, Rian C.; Luo, Lifeng; Goldstein, Harland L.; Vogel, John M.

2015-01-01

The erosion and deposition of sediments by wind from 1901 to 2013 have created large changes in surface features of Mesquite Lake playa in the Mojave Desert. The decadal scale recurrence of sand-sheet development, migration, and merging with older dunes appears related to decadal climatic changes of drought and wetness as recorded in the precipitation history of the Mojave Desert, complemented by modeled soil-moisture index values. Historical aerial photographs, repeat land photographs, and satellite images document the presence and northward migration of a mid-20th century sand sheet that formed during a severe regional drought that coincided with a multi-decadal cool phase of the Pacific Decadal Oscillation (PDO). The sand sheet slowly eroded during the wetter conditions of the subsequent PDO warm phase (1977–1998) due to a lack of added sediment. Sand cohesion gradually increased in the sand sheet by seasonal additions of salt and clay and by re-precipitation of gypsum, which resulted in the wind-carving of yardangs in the receding sand sheet. Smaller yardangs were aerodynamically shaped from coppice dunes with salt-clay crusts, and larger yardangs were carved along the walls and floor of trough blowouts. Evidence of a 19th century cycle of sand-sheet formation and erosion is indicated by remnants of yardangs, photographed in 1901 and 1916, that were found buried in the mid-20th century sand sheet. Three years of erosion measurements on the playa, yardangs, and sand sheets document relatively rapid wind erosion. The playa has lowered 20 to 40 cm since the mid-20th century and a shallow deflation basin has developed since 1999. Annually, 5–10 cm of surface sediment was removed from yardang flanks by a combination of wind abrasion, deflation, and mass movement. The most effective erosional processes are wind stripping of thin crusts that form on the yardang surfaces after rain events and the slumping of sediment blocks from yardang flanks. These wind-eroded landforms persist several decades to a century before eroding away or being buried by younger sands. On Mesquite Lake playa the climatic history of alternating PDO phases of multi-decadal drought and wetness is recorded twice by the presence of yardangs formed nearly a century apart.

Dusty Ejecta Blanket

NASA Technical Reports Server (NTRS)

2004-01-01

[figure removed for brevity, see original site]

The large crater in this nighttime IR image had its ejecta emplaced in a semifluidized state, creating an outer rampart at the distal ends of the ejecta blanket. This wall can act as a trap for fine wind blown materials. It is likely that part of the darker/cooler materials surrounding the crater are wind blown materials such as dust and sand. This crater is located north of the Meridiani region of Mars.

Image information: IR instrument. Latitude 1.9, Longitude 359.1 East (0.89999999999998 West). 100 meter/pixel resolution.

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

Origin and Evolution of the Layered Sulfate-Rich Rocks in Meridiani Planum, Mars

NASA Astrophysics Data System (ADS)

Arvidson, R. E.

2007-12-01

Opportunity rover observations show that Meridiani Planum has extensive exposures of sulfate-rich dirty sandstones partially covered by a mix of wind-blown basaltic sand, dust, and a lag deposit of 1 to 5 mm diameter hematitic concretions. The dirty sandstones are interpreted to have formed in an acid-sulfate evaporative lacustrine system that left behind sulfate-rich muds with a siliciclastic component. Erosion by wind and water produced sandstones that were then cemented and diagenetically altered by rising groundwater. Subsequent wind erosion of these deposits and associated advection of basaltic sand onto the outcrops produced the surfaces encountered during the rover's traverses. On a regional scale these sulfate-rich deposits are up to several kilometers in thickness, extend over several hundred thousand square kilometers, and unconformably overlie the fluvially dissected Noachian cratered terrain. Both OMEGA and CRISM hyperspectral data show clear evidence for the presence of phyllosilicate minerals in the cratered terrains adjacent to the sulfate deposits, but not within the sulfate section proper. The ensemble of evidence indicates a change in Meridiani Planum from fluvial erosion and formation of phyllosilicate minerals to deposition of evaporite deposits associated with an acid-sulfate aqueous system. This change is interpreted to be due to a major climatic shift in which a relatively vigorous hydrologic system with extensive neutral rain and snowfall changed to more arid conditions in which a regional-scale acid sulfate groundwater system emerged in Meridiani Planum with enough of a hydrostatic head to produce and retain 1 to 3 km of sulfate-rich deposits.

Investigating Mars: Arabia Terra Dunes

NASA Image and Video Library

2018-03-20

The bottom of this image shows the hills and mesas within the crater. The dunes at the top of the image are engulfing and covering the hills. In some locations the hills are still a substantial obstacle to the wind. In these cases the wind is blowing sand up against the windward side, but the hill is causing chaotic wind flow around the hill and rather than depositing sand, the wind is actually removing sand on the leeward side of the hill. With continued winds and sand movement the deposition of material will eventually build up along the leeward side of the hill and then engulf the hill on all sides. Located in eastern Arabia is an unnamed crater, 120 kilometers (75 miles) across. The floor of this crater contains a large exposure of rocky material, a field of dark sand dunes, and numerous patches of what is probably fine-grain sand. The shape of the dunes indicate that prevailing winds have come from different directions over the years. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 11781 Latitude: 26.3693 Longitude: 62.693 Instrument: VIS Captured: 2004-08-10 10:40 https://photojournal.jpl.nasa.gov/catalog/PIA22299

Earth Observations taken by the Expedition 31 Crew

NASA Image and Video Library

2012-05-11

ISS031-E-030783 (11 May 2012) --- Linear dunes in the Great Sand Sea in southwest Egypt are featured in this image photographed by an Expedition 31 crew member on the International Space Station. In southwestern Egypt, deep in the Sahara Desert, the action of wind dominates landscapes today much as it has done for the past several thousand years. Winds blowing from the north have fashioned sands into large dunes, aligned parallel with these winds. The so-called linear dunes?shown here in the Great Sand Sea?are easily seen from space and local maps show that they rise 20?30 meters above the surrounding flat plains. The distance between individual linear dunes is interestingly regular, at 1.5?2.5 kilometers, suggesting some equilibrium exists between the formative wind strength and the sand supply. It is possible that linear dunes may relate to earlier times when winds were stronger than they are today, or sand more plentiful. The dark patch of rock outcrop at upper right sticks up above the surface on which the dunes lie by as much as 150 meters. The north winds have been deflected around this high zone, and smaller secondary linear dunes can be seen along the right side of the image, aligned with local winds that become ever more northeasterly with nearness to the outcrops. A dune-free zone on the protected downwind (south-southeast) side of the outcrop gives a sense of the sand movement (generally from the bottom of the image towards the top). At first glance, the large linear dunes appear to be the major landform in the image; however a complex pattern of even smaller dunes can be seen perched on top of the largest dunes (inset). The sand that comprises many dune fields usually, according to scientists, derives from some larger river not very distant upwind, supplied from the dry river bed (exposed to the wind during dry seasons of low river flow, or regional change to a more arid climate). Inland dune fields thus lie downwind of the source river. A large, unnamed river once flowed to the Mediterranean Sea situated west of the dunes shown in this picture, dumping its sand load 300 kilometers northwest of the area shown. It is likely that this river, the evidence of which is now almost completely obliterated, was the source of the sand in the linear dunes, the scientists say.

IRAS 18153-1651: an H II region with a possible wind bubble blown by a young main-sequence B star

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.; Mackey, J.; Kniazev, A. Y.; Langer, N.; Chené, A.-N.; Castro, N.; Haworth, T. J.; Grebel, E. K.

2017-04-01

We report the results of spectroscopic observations and numerical modelling of the H II region IRAS 18153-1651. Our study was motivated by the discovery of an optical arc and two main-sequence stars of spectral type B1 and B3 near the centre of IRAS 18153-1651. We interpret the arc as the edge of the wind bubble (blown by the B1 star), whose brightness is enhanced by the interaction with a photoevaporation flow from a nearby molecular cloud. This interpretation implies that we deal with a unique case of a young massive star (the most massive member of a recently formed low-mass star cluster) caught just tens of thousands of years after its stellar wind has begun to blow a bubble into the surrounding dense medium. Our 2D, radiation-hydrodynamics simulations of the wind bubble and the H II region around the B1 star provide a reasonable match to observations, both in terms of morphology and absolute brightness of the optical and mid-infrared emission, and verify the young age of IRAS 18153-1651. Taken together our results strongly suggest that we have revealed the first example of a wind bubble blown by a main-sequence B star.

Robotic Measurement of Aeolian Processes

NASA Astrophysics Data System (ADS)

Roberts, S.; Duperret, J. M.; Jerolmack, D. J.; Lancaster, N.; Nikolich, G.; Shipley, T. F.; Van Pelt, R. S.; Zobeck, T. M.; Koditschek, D. E.

2015-12-01

Local and regional measurements of sand transport and dust emission in complex natural settings presently lack spatiotemporal resolution adequate to inform models relevant for land management, climate policy, and the basic science of geomorphology. Deployments of wind, sand and dust sensors sophisticated enough to begin unpacking the complex relations among wind turbulence, surface roughness, sand flux and dust emission remain largely stationary. Aerial observations from satellites, planes and even UAVs help fill in, but none of these modalities offer the hope of "capturing the action" by being at the right place at the right time relative to the highly localized nature of sediment transport during wind storms. We have been developing a legged robot capable of rapidly traversing desert terrain, and are now adapting it to serve as a platform for scientific instrumentation. We aim to field a semi-autonomous, reactive mobile sensory package suited to the needs of aeolian science that can address the limitations of existing alternatives. This presentation reports on early trials in the Jornada LTER and White Sands National Monument aimed at gathering measurements of airflow and rates of sand transport on a dune face, assessing the role of roughness elements such as vegetation in modifying the wind shear stresses incident on the surface, and estimating erosion susceptibility in a natural arid soil. We will solicit ideas from the audience about other potentially interesting and viable measurement targets. Future close collaboration between aeolian, cognitive and robotics scientists such as we hope to promote through this presentation may yield machines with scientifically relevant sensory suites possessing sufficient autonomy to operate in-situ at the most intense episodes of wind and sediment movement under conditions far too uncomfortable and hazardous for human presence.

Trouvelot Crater Deposit

NASA Image and Video Library

2002-12-04

Like many of the craters in the Oxia Palus region of Mars, Trouvelot Crater, shown in this NASA Mars Odyssey image, hosts an eroded, light-toned, sedimentary deposit on its floor. Compared with the much larger example in Becquerel Crater to the NE, the Trouvelot deposit has been so eroded by the scouring action of dark, wind-blown sand that very little of it remains. Tiny outliers of bright material separated from the main mass attest to the once, more really extensive coverage by the deposit. A similar observation can be made for White Rock, the best known example of a bright, crater interior deposit. The origin of the sediments in these deposits remains enigmatic but they are likely the result of fallout from ash or dust carried by the thin martian atmosphere. http://photojournal.jpl.nasa.gov/catalog/PIA04017

Lunar and Planetary Science XXXV: Mars: Wind, Dust Sand, and Debris

NASA Technical Reports Server (NTRS)

2004-01-01

The session "Mars: Wind, Dust Sand, and Debris" included: Mars Exploration Rovers: Laboratory Simulations of Aeolian Interactions; Thermal and Spectral Analysis of an Intracrater Dune Field in Amazonis Planitia; How High is that Dune? A Comparison of Methods Used to Constrain the Morphometry of Aeolian Bedforms on Mars; Dust Devils on Mars: Scaling of Dust Flux Based on Laboratory Simulations; A Close Encounter with a Terrestrial Dust Devil; Interpretation of Wind Direction from Eolian Features: Herschel Crater, Mars Erosion Rates at the Viking 2 Landing Site; Mars Dust: Characterization of Particle Size and Electrostatic Charge Distributions; Simple Non-fluvial Models of Planetary Surface Modification, with Application to Mars; Comparison of Geomorphically Determined Winds with a General Circulation Model: Herschel Crater, Mars; Analysis of Martian Debris Aprons in Eastern Hellas Using THEMIS; Origin of Martian Northern Hemisphere Mid-Latitude Lobate Debris Aprons; Debris Aprons in the Tempe/Mareotis Region of Mars;and Constraining Flow Dynamics of Mass Movements on Earth and Mars.

Estimation of wind erosion from construction of a railway in arid northwest China

USDA-ARS?s Scientific Manuscript database

A state-of-the-art wind erosion simulation model, the Wind Erosion Prediction System and the United States Environmental Protection Agency’s AP-42 emission factors formula, were combined together to evaluate wind-blown dust emissions from various construction units from a railway construction projec...

A study of morphology, provenance, and movement of desert sand seas in Africa, Asia, and Australia

NASA Technical Reports Server (NTRS)

Mckee, E. D. (Principal Investigator); Breed, C. S.

1973-01-01

The author has identified the following significant results. Recent acquisition of generally high quality color prints for most of the test sites has enabled the project to make significant advances in preparing mosaics of sand desert areas under study. Computer enhancement of imagery of selected sites, where details of complex dune forms need to be determined, has been achieved with arrival of computer-compatible ERTS-1 tapes. Further, a comparator, recently received, gives precise visual measurements of width, length, and spacing of sand bodies and so improves comparison of patterns in various test sites. Considerable additional meteorological data recently received on sand-moving winds in China, Pakistan, Libya and other areas enabled much progress to be made in developing overlays for the dune mosaics. These data show direction, speed, and frequency of winds. Other new data for use in preparing overlays used with ERTS-1 image mosaics include ground truth on moisture control, geologic settings, and plant distribution. With the addition of visual observation data and prints from hand-held photography now being obtained by the Skylab mission, much progress in interpreting the patterns of sand seas for 17 desert sites is anticipated.

A study of morphology, provenance, and movement of desert sand seas in Africa, Asia, and Australia

NASA Technical Reports Server (NTRS)

Mckee, E. D. (Principal Investigator); Breed, C. S.

1974-01-01

The author has identified the following significant results. Recent acquisition of generally high quality color prints for most of the test sites has enabled this project to make significant advances in preparing mosaics of sand desert areas under study. Computer enhancement of imagery, where details of complex dune forms need to be determined, has been achieved with arrival of computer-compatible ERTS-1 tapes. Further, a comparator, recently received, gives precise visual measurements of width, length, and spacing of sand bodies and so improves comparison of patterns in various test sites. Considerable additional meteorological data recently received on sand-moving winds in China, Pakistan, Libya, and other study areas enabled much progress to be made in developing overlays for the dune mosaics. These data show direction, speed, and frequency of winds. Other new data for use in preparing overlays used with ERTS-1 image mosaics include ground truth on moisture control, geologic settings, and plant distribution. With the addition of visual observation data and prints from hand-held photography now being obtained by the Skylab 4 mission, much progress in interpreting the patterns of sand seas for 17 desert sites is anticipated.

Large-scale wind-tunnel investigation of the noise characteristics of a semispan wing equipped with an externally blown jet flap

NASA Technical Reports Server (NTRS)

Falarski, M. D.

1972-01-01

A wind tunnel investigation was made of the noise characteristics of a 4.42 m(14.5 foot) semispan, externally-blown jet flap model. The model was equipped with a single 76.2 cm(30 inch) diameter, ducted fan with a 1.03 pressure ratio. The effects of flap size, fan vertical location, and forward speed on the noise characteristics were studied. The data from the investigation is presented in the form of tabulated one-third octave band frequency spectrums and perceived noise levels for each test condition.

Impact of grazing intensity on seasonal variations in soil organic carbon and soil CO2 efflux in two semiarid grasslands in southern Botswana

PubMed Central

Thomas, Andrew D.

2012-01-01

Biological soil crusts (BSCs) are an important source of organic carbon, and affect a range of ecosystem functions in arid and semiarid environments. Yet the impact of grazing disturbance on crust properties and soil CO2 efflux remain poorly studied, particularly in African ecosystems. The effects of burial under wind-blown sand, disaggregation and removal of BSCs on seasonal variations in soil CO2 efflux, soil organic carbon, chlorophyll a and scytonemin were investigated at two sites in the Kalahari of southern Botswana. Field experiments were employed to isolate CO2 efflux originating from BSCs in order to estimate the C exchange within the crust. Organic carbon was not evenly distributed through the soil profile but concentrated in the BSC. Soil CO2 efflux was higher in Kalahari Sand than in calcrete soils, but rates varied significantly with seasonal changes in moisture and temperature. BSCs at both sites were a small net sink of C to the soil. Soil CO2 efflux was significantly higher in sand soils where the BSC was removed, and on calcrete where the BSC was buried under sand. The BSC removal and burial under sand also significantly reduced chlorophyll a, organic carbon and scytonemin. Disaggregation of the soil crust, however, led to increases in chlorophyll a and organic carbon. The data confirm the importance of BSCs for C cycling in drylands and indicate intensive grazing, which destroys BSCs through trampling and burial, will adversely affect C sequestration and storage. Managed grazing, where soil surfaces are only lightly disturbed, would help maintain a positive carbon balance in African drylands. PMID:23045706

Adjoint Sensitivity Analyses Of Sand And Dust Storms In East Asia

NASA Astrophysics Data System (ADS)

Kay, J.; Kim, H.

2008-12-01

Sand and Dust Storm (SDS) in East Asia, so called Asian dust, is a seasonal meteorological phenomenon. Mostly in spring, dust particles blown into atmosphere in the arid area over northern China desert and Manchuria are transported to East Asia by prevailing flows. Three SDS events in East Asia from 2005 to 2008 are chosen to investigate how sensitive the SDS forecasts to the initial condition uncertainties and thence to suggest the sensitive regions for adaptive observations of the SDS events. Adaptive observations are additional observations in sensitive regions where the observations may have the most impact on the forecast by decreasing the forecast error. Three SDS events are chosen to represent different transport passes from the dust source regions to the Korean peninsula. To investigate the sensitivities to the initial condition, adjoint sensitivities that calculate gradient of the forecast aspect (i.e., response function) with respect to the initial condition are used. The forecast aspects relevant to the SDS transport are forecast error of the surface pressure, surface pressure perturbation, and steering vector of winds in the lower troposphere. Because the surface low pressure system usually plays an important role for SDS transport, the forecast error of the surface pressure and the surface pressure perturbation are chosen as the response function of the adjoint calculation. Another response function relevant to SDS transport is the steering flow over the downstream region (i.e., Korean peninsula) because direction and intensity of the prevailing winds usually determine the intensity and occurrence of the SDS events at the destination. The results show that the sensitive regions for the forecast error of the surface pressure and surface pressure perturbation are initially located in the vicinity of the trough and then propagate eastward as the low system moves eastward. The vertical structures of the adjoint sensitivities are upshear tilted structures, which are typical structures of extratropical cyclones. The adjoint sensitivities for lower tropospheric steering flow are also located near the trough, which confirms that the accurate forecast on the location and movement of the trough is essential to have better forecasts of Asian dust events. More comprehensive results and discussions of the adjoint sensitivity analyses for Asian dust events will be presented in the meeting.

Supernova Remnant Evolving in Wind-Blown Bubbles: A Case Study of Kes 27

NASA Astrophysics Data System (ADS)

Li, Jiangtao

2013-10-01

Mixed-morphology (MM) SNRs represent SN explosion in wind-blown bubbles. They are thus good places to study the interaction between massive stellar winds, SNRs, and the surrounding ISM. We propose a 50ks XMM-Newton observation of a peculiar MM SNR, Kes 27. We will map out the spectral parameters in tessellated meshes and construct EW maps of some emission lines with our newly developed spatially-resolved spectroscopy method. These analyses will help us to understand the unusual properties of this MM SNR, such as the X-ray bright outer shell, shell-like interior, and strong NE-SW asymmetry in morphology. We will also search for evidence of over-ionization state plasma and coherent X-ray features associated with the shell of the HI cavity.

Origin of the late quaternary dune fields of northeastern Colorado

USGS Publications Warehouse

Muhs, D.R.; Stafford, T.W.; Cowherd, S.D.; Mahan, S.A.; Kihl, R.; Maat, P.B.; Bush, C.A.; Nehring, J.

1996-01-01

Stabilized eolian deposits, mostly parabolic dunes and sand sheets, cover much of the landscape of northeastern Colorado and adjacent parts of southwestern Nebraska in four geographically distinct dune fields. Stratigraphic and soil-geomorphic relations and accelerator radiocarbon dating indicate that at least three episodes of eolian sand movement occurred between 27 ka and 11 ka, possibly between 11 ka and 4 ka, and within the past 1.5 ka. Thus, eolian sand deposition took place under both glacial and interglacial climatic conditions. In the youngest episodes of eolian sand movement, Holocene parabolic dunes partially buried Pleistocene sand sheet deposits. Late Holocene sands in the Fort Morgan and Wray dune fields, to the south of the South Platte River, have trace element ratios that are indistinguishable from modern South Platte River sands, but different from Ogallala Formation bedrock, which has previously been cited as the main source of dune sand on the Great Plains. Sands in the Greeley dune field, to the north of the South Platte River, have trace element concentrations that indicate a probable Laramie Formation source. Measurements of parabolic dunes indicate paleowinds from the northwest in all dune fields, in good agreement with resultant drift directions calculated for nearby weather stations. Thus, paleowinds were probably not significantly different from present-day winds, and are consistent with a South Platte River source for the Fort Morgan and Wray dune fields, and a Laramie Formation source for the Greeley dune field. Sand accumulated downwind of the South Platte River to form the Fort Morgan dune field. In addition, sand was also transported farther downwind over the upland formed by the calcrete caprock of the Ogallala Formation, and deposited in die lee of the upland on the southeast side. Because of high wind energy, the upland itself served as a zone of sand transport, but little or no sand accumulation took place on this surface. These studies, which demonstrate the importance of fluvial-source sediments for dune fields in Colorado, may be applicable to other dune fields in North America. Because modern drift potentials in northeastern Colorado are among the highest in the world, the present stability of dunes in the region may be in part a function of the dunes being supply-limited rather than solely transport-limited. Extensive (??? 7700 km2) late Holocene dunes document that eolian sand in northeastern Colorado is very sensitive to small changes in climate or fluvial source conditions.

The Unitary Plan Wind Tunnel(UPWT) Test 1891 Space Launch System

NASA Image and Video Library

2014-10-15

Stage Separation Test of the Space Launch System(SLS) in the Langley Unitary Plan Wind Tunnel (UPWT). The model used High Pressure air blown through the solid rocket boosters. (SRB) to simulate the booster separation motors (BSM) firing.

The Unitary Plan Wind Tunnel(UPWT) Test 1891 Space Launch System

NASA Image and Video Library

2014-10-14

Stage Separation Test of the Space Launch System(SLS) in the Langley Unitary Plan Wind Tunnel (UPWT). The model used High Pressure air blown through the solid rocket boosters. (SRB) to simulate the booster separation motors (BSM) firing.

Cerberus Wind Streaks

NASA Technical Reports Server (NTRS)

2002-01-01

(Released 6 May 2002) The Science Cerberus is a dark region on Mars that has shrunk down from a continuous length of about 1000 km to roughly three discontinuous spots a few 100 kms in length in less than 20 years. There are two competing processes at work in the Cerberus region that produce the bright and dark features seen in this THEMIS image. Bright dust settles out of the atmosphere, especially after global dust storms, depositing a layer just thick enough to brighten the dark surfaces. Deposition occurs preferentially in the low wind 'shadow zones' within craters and downwind of crater rims, producing the bright streaks. The direction of the streaks clearly indicates that the dominant winds come from the northeast. Dust deposition would completely blot out the dark areas if it were not for the action of wind-blown sand grains scouring the surface and lifting the dust back into the atmosphere. Again, the shadow zones are protected from the blowing sand, preserving the bright layer of dust. Also visible in this image are lava flow features extending from the flanks of the huge Elysium volcanoes to the northwest. Two shallow channels and a raised flow lobe are just barely discernable. The lava channel in the middle of the image crosses the boundary of the bright and dark surfaces without any obvious change in its morphology. This demonstrates that the bright dust layer is very thin in this location, perhaps as little as a few millimeters. The Story Mars is an ever-changing land of spectacular contrasts. This THEMIS image shows the Cerberus region of Mars, a dark area located near the Elysium volcanoes and fittingly named after the three-headed, dragon-tailed dog who guards the door of the underworld. Two opposing processes are at work here: a thin layer of dust falling from the atmosphere and/or dust storms creating brighter surface areas (e.g. the top left portion of this image) and dust being scoured away by the action of the Martian wind disturbing the sand grains and freeing the lighter dust to fly away once more (the darker portions of this image). There are, however, some darker areas that are somewhat shielded and protected from the wind that have yielded bright, dusty crater floors and wind streaks that trail out behind the craters. These wind streaks tell a story all their own as to the prevailing wind direction coming from the northeast. This, added to the fact that this dark region was once 1000 km in length and has dwindled to just a few isolated dark splotches of 100 kilometers in the past 20 years, help us to see that the Martian environment is still quite dynamic and capable of changing. Finally, this being a volcanic region, a lobe of a lava flow from the immense Elysium volcanoes to the northwest is visible stretching across the bottom one-quarter of the image.

The Colorado Plateau III: integrating research and resources management for effective conservation

USGS Publications Warehouse

Sogge, Mark K.; van Riper, Charles

2008-01-01

Roughly centered on the Four Corners region of the southwestern United States, the Colorado Plateau covers an area of 130,000 square miles. The relatively high semi-arid province boasts nine national parks, sixteen national monuments, many state parks, and dozens of wilderness areas. With the highest concentration of parklands in North America and unique geological and ecological features, the area is of particular interest to researchers. Derived from the Eighth Biennial Conference of Research on the Colorado Plateau, this third volume in a series of research on the Colorado Plateau expands upon the previous two books. This volume focuses on the integration of science into resource management issues, summarizes what criteria make a successful collaborative effort, outlines land management concerns about drought, provides summaries of current biological, sociological, and archaeological research, and highlights current environmental issues in the Four Corner States of Arizona, New Mexico, Colorado, and Utah. With broad coverage that touches on topics as diverse as historical aspects of pronghorn antelope movement patterns through calculating watershed prescriptions to the role of wind-blown sand in preserving archaeological sites on the Colorado River, this volume stands as a compendium of cuttingedge management-oriented research on the Colorado Plateau. The book also introduces, for the first time, tools that can be used to assist with collaboration efforts among landowners and managers who wish to work together toward preserving resources on the Colorado Plateau and offers a wealth of insights into land management questions for many readers, especially people interested in the natural history, biology, anthropology, wildlife, and cultural management issues of the region.

Small scale wind tunnel model investigation of hybrid high lift systems combining upper surface blowing with the internally blown flap

NASA Technical Reports Server (NTRS)

Waites, W. L.; Chin, Y. T.

1974-01-01

A small-scale wind tunnel test of a two engine hybrid model with upper surface blowing on a simulated expandable duct internally blown flap was accomplished in a two phase program. The low wing Phase I model utilized 0.126c radius Jacobs/Hurkamp flaps and 0.337c radius Coanda flaps. The high wing Phase II model was utilized for continued studies on the Jacobs/Hurkamp flap. Principal study areas included: basic data both engines operative and with an engine out, control flap utilization, horizontal tail effectiveness, spoiler effectiveness, USB nacelle deflector study and USB/IBF pressure ratio effects.

Archaeological Investigations on the San Antonio Terrace, Vandenberg Air Force Base, California, in Connection with MX Facilities Construction.

DTIC Science & Technology

1984-01-01

different subsistence-settlement contexts: agriculturalists living in permanent villages and hunter-gatherers subsisting on highly productive wild food...peoples on the terrace (especially at the upwind extremities) may --- have resulted in an increase in the occurance of wild fires and an increase in...sand. The charcoal was probably generated in a wild fire upwind, blown across the surface and then covered by the sands freed by the burning of the

Using rare earth elements to trace wind-driven dispersion of sediments from a point source

NASA Astrophysics Data System (ADS)

Van Pelt, R. Scott; Barnes, Melanie C. W.; Strack, John E.

2018-06-01

The entrainment and movement of aeolian sediments is determined by the direction and intensity of erosive winds. Although erosive winds may blow from all directions, in most regions there is a predominant direction. Dust emission causes the removal preferentially of soil nutrients and contaminants which may be transported tens to even thousands of kilometers from the source and deposited into other ecosystems. It would be beneficial to understand spatially and temporally how the soil source may be degraded and depositional zones enriched. A stable chemical tracer not found in the soil but applied to the surface of all particles in the surface soil would facilitate this endeavor. This study examined whether solution-applied rare earth elements (REEs) could be used to trace aeolian sediment movement from a point source through space and time at the field scale. We applied erbium nitrate solution to a 5 m2 area in the center of a 100 m diameter field 7854 m2 on the Southern High Plains of Texas. The solution application resulted in a soil-borne concentration three orders of magnitude greater than natively found in the field soil. We installed BSNE sampler masts in circular configurations and collected the trapped sediment weekly. We found that REE-tagged sediment was blown into every sampler mast during the course of the study but that there was a predominant direction of transport during the spring. This preliminary investigation suggests that the REEs provide a viable and incisive technique to study spatial and temporal variation of aeolian sediment movement from specific sources to identifiable locations of deposition or locations through which the sediments were transported as horizontal mass flux and the relative contribution of the specific source to the total mass flux.

Nourishment of perched sand dunes and the issue of erosion control in the Great Lakes

NASA Astrophysics Data System (ADS)

Marsh, William M.

1990-09-01

Although limited in coverage, perched sand dunes situated on high coastal bluffs are considered the most prized of Great Lakes dunes. Grand Sable Dunes on Lake Superior and Sleeping Bear Dunes on Lake Michigan are featured attractions of national lakeshores under National Park Service management. The source of sand for perched dunes is the high bluff along their lakeward edge. As onshore wind crosses the bluff, flow is accelerated upslope, resulting in greatly elevated levels of wind stress over the slope brow. On barren, sandy bluffs, wind erosion is concentrated in the brow zone, and for the Grand Sable Bluff, it averaged 1 m3/yr per linear meter along the highest sections for the period 1973 1983. This mechanism accounts for about 6,500 m3 of sand nourishment to the dunefield annually and clearly has been the predominant mechanism for the long-term development of the dunefield. However, wind erosion and dune nourishment are possible only where the bluff is denuded of plant cover by mass movements and related processes induced by wave erosion. In the Great Lakes, wave erosion and bluff retreat vary with lake levels; the nourishment of perched dunes is favored by high levels. Lake levels have been relatively high for the past 50 years, and shore erosion has become a major environmental issue leading property owners and politicians to support lake-level regulation. Trimming high water levels could reduce geomorphic activity on high bluffs and affect dune nourishment rates. Locally, nourishment also may be influenced by sediment accumulation associated with harbor protection facilities and by planting programs aimed at stabilizing dunes.

Provenance and recycling of Arabian desert sand

NASA Astrophysics Data System (ADS)

Garzanti, Eduardo; Vermeesch, Pieter; Andò, Sergio; Vezzoli, Giovanni; Valagussa, Manuel; Allen, Kate; Kadi, Khalid; Al-Juboury, Ali

2013-04-01

This study seeks to determine the ultimate origin of aeolian sand in Arabian deserts by high-resolution petrographic and heavy-mineral techniques combined with zircon U-Pb geochronology. Point-counting is used here as the sole method by which unbiased volume percentages of heavy minerals can be obtained. A comprehensive analysis of river and wadi sands from the Red Sea to the Bitlis-Zagros orogen allowed us to characterize all potential sediment sources, and thus to quantitatively constrain provenance of Arabian dune fields. Two main types of aeolian sand can be distinguished. Quartzose sands with very poor heavy-mineral suites including zircon occupy most of the region comprising the Great Nafud and Rub' al-Khali Sand Seas, and are largely recycled from thick Lower Palaeozoic quartzarenites with very minor first-cycle contributions from Precambrian basement, Mesozoic carbonate rocks, or Neogene basalts. Instead, carbonaticlastic sands with richer lithic and heavy-mineral populations characterize coastal dunes bordering the Arabian Gulf from the Jafurah Sand Sea of Saudi Arabia to the United Arab Emirates. The similarity with detritus carried by the axial Tigris-Euphrates system and by transverse rivers draining carbonate rocks of the Zagros indicates that Arabian coastal dunes largely consist of far-travelled sand, deposited on the exposed floor of the Gulf during Pleistocene lowstands and blown inland by dominant Shamal northerly winds. A dataset of detrital zircon U-Pb ages measured on twelve dune samples and two Lower Palaeozoic sandstones yielded fourteen identical age spectra. The age distributions all show a major Neoproterozoic peak corresponding to the Pan-African magmatic and tectonic events by which the Arabian Shield was assembled, with minor late Palaeoproterozoic and Neoarchean peaks. A similar U-Pb signature characterizes also Jafurah dune sands, suggesting that zircons are dominantly derived from interior Arabia, possibly deflated from the Wadi al-Batin fossil alluvial fan or even from Mesozoic sandstones of the Arabian margin accreted to the Cenozoic Zagros orogen. Due to extensive recycling and the fact that zircon is so resistant to weathering and erosion, the U-Pb age signatures are much less powerful a tracer of sedimentary provenance than framework petrography and heavy minerals. Actualistic provenance studies of dune fields at subcontinental scale shed light on the generation and homogenization of aeolian sand, and allow us to trace complex pathways of multistep sediment transport, thus providing crucial independent information for accurate palaeogeographic and palaeoclimatic reconstructions.

Provenance and recycling of Arabian desert sand

NASA Astrophysics Data System (ADS)

Garzanti, Eduardo; Vermeesch, Pieter; Andò, Sergio; Vezzoli, Giovanni; Valagussa, Manuel; Allen, Kate; Kadi, Khalid A.; Al-Juboury, Ali I. A.

2013-05-01

This study seeks to determine the ultimate origin of aeolian sand in Arabian deserts by high-resolution petrographic and heavy-mineral techniques combined with zircon U-Pb geochronology. Point-counting is used here as the sole method by which unbiased volume percentages of heavy minerals can be obtained. A comprehensive analysis of river and wadi sands from the Red Sea to the Bitlis-Zagros orogen allowed us to characterize all potential sediment sources, and thus to quantitatively constrain provenance of Arabian dune fields. Two main types of aeolian sand can be distinguished. Quartzose sands with very poor heavy-mineral suites including zircon occupy most of the region comprising the Great Nafud and Rub' al-Khali Sand Seas, and are largely recycled from thick Lower Palaeozoic quartzarenites with very minor first-cycle contributions from Precambrian basement, Mesozoic carbonate rocks, or Neogene basalts. Instead, carbonaticlastic sands with richer lithic and heavy-mineral populations characterize coastal dunes bordering the Arabian Gulf from the Jafurah Sand Sea of Saudi Arabia to the United Arab Emirates. The similarity with detritus carried by the axial Tigris-Euphrates system and by transverse rivers draining carbonate rocks of the Zagros indicates that Arabian coastal dunes largely consist of far-travelled sand, deposited on the exposed floor of the Gulf during Pleistocene lowstands and blown inland by dominant Shamal northerly winds. A dataset of detrital zircon U-Pb ages measured on twelve dune samples and two Lower Palaeozoic sandstones yielded fourteen identical age spectra. The age distributions all show a major Neoproterozoic peak corresponding to the Pan-African magmatic and tectonic events by which the Arabian Shield was assembled, with minor late Palaeoproterozoic and Neoarchean peaks. A similar U-Pb signature characterizes also Jafurah dune sands, suggesting that zircons are dominantly derived from interior Arabia, possibly deflated from the Wadi al-Batin fossil alluvial fan or even from Mesozoic sandstones of the Arabian margin accreted to the Cenozoic Zagros orogen. Due to extensive recycling and the fact that zircon is so resistant to weathering and erosion, the U-Pb age signatures are much less powerful a tracer of sedimentary provenance than framework petrography and heavy minerals. Actualistic provenance studies of dune fields at subcontinental scale shed light on the generation and homogenization of aeolian sand, and allow us to trace complex pathways of multistep sediment transport, thus providing crucial independent information for accurate palaeogeographic and palaeoclimatic reconstructions.

Aeolian saltation on Mars at low wind speeds

NASA Astrophysics Data System (ADS)

Sullivan, R.; Kok, J. F.

2017-10-01

Laboratory experiments indicate that the fluid threshold friction speed, u*tf, required to initiate fully developed aeolian saltation is much higher on Mars than on Earth. A discrepancy exists between Mars climate models that do not predict winds this strong and observations that sand-sized particles are indeed moving. This paper describes how wind friction speeds well below u*tf, but above the impact threshold, u*ti, required to sustain saltation, can initiate sustained saltation on Mars, but at relatively low flux. Numerical experiments indicate that a sand grain on Mars mobilized sporadically between u*ti and u*tf will develop, over fetch lengths longer than generally available within low-pressure wind tunnels, trajectories capable of splashing grains that propagate saltation and collectively form a cluster of saltating grains that migrate downwind together. The passage of a saltation cluster should leave behind a narrow zone of affected surface grains. The cumulative effect of many clusters represents a low-flux phenomenon that should produce slow changes to aeolian bedforms over periods in which winds remain close to u*ti and never or rarely reach u*tf. Field evidence from small impact ripples along rover traverses is consistent with effects of saltation at these low friction speeds, without obvious evidence for events ≥u*tf. The potential utility of this grain mobility process is that it can operate entirely at more common winds well below u*tf and so help explain widespread sand movements observed on Mars wherever evidence might be mostly absent for u*tf being exceeded.

A study of morphology, provenance, and movement of desert sand seas in Africa, Asia, and Australia

NASA Technical Reports Server (NTRS)

Mckee, E. D.; Breed, C. S.; Harris, L. F. (Principal Investigator)

1973-01-01

The author has identified the following significant results. The assembling of photomosaics from color prints of ERTS images has made possible the recognition and description of san patterns, and these are to be the basis of a worldwide classification of sand bodies. Progress has been as rapid as the acquisition of the bulk composite images will permit and for some areas the mosaics are now nearly complete. A second step, which consists of the accumulation and analysis of regional wind data, to be plotted as overlays for the dune patterns, is now underway and should soon give tangible results. Other aspects of the project include the gathering of ground truth in the form of air photographs, needed to interpret geomorphic forms and the sampling of sand deposits for analyzing the texture and composition of sand bodies. A start has been made on these studies in several selected areas.

Windblown Snow

NASA Image and Video Library

2011-04-11

On April 11, 2011, IceBridge finally got the clear weather necessary to fly over glaciers in southeast Greenland, but with clear skies came winds of up to 70 knots. What looks like clouds is actually wind-blown snow. The data could help scientists to evaluate the impact of wind-blown snow on satellite-based laser altimetry measurements. Operation IceBridge, now in its third year, makes annual campaigns in the Arctic and Antarctic where science flights monitor glaciers, ice sheets and sea ice. Credit: NASA/GSFC/Michael Studinger To learn more about Ice Bridge go to: www.nasa.gov/mission_pages/icebridge/news/spr11/index.html NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Join us on Facebook

Threshold for sand mobility on Mars calibrated from seasonal variations of sand flux.

PubMed

Ayoub, F; Avouac, J-P; Newman, C E; Richardson, M I; Lucas, A; Leprince, S; Bridges, N T

2014-09-30

Coupling between surface winds and saltation is a fundamental factor governing geological activity and climate on Mars. Saltation of sand is crucial for both erosion of the surface and dust lifting into the atmosphere. Wind tunnel experiments along with measurements from surface meteorology stations and modelling of wind speeds suggest that winds should only rarely move sand on Mars. However, evidence for currently active dune migration has recently accumulated. Crucially, the frequency of sand-moving events and the implied threshold wind stresses for saltation have remained unknown. Here we present detailed measurements of Nili Patera dune field based on High Resolution Imaging Science Experiment images, demonstrating that sand motion occurs daily throughout much of the year and that the resulting sand flux is strongly seasonal. Analysis of the seasonal sand flux variation suggests an effective threshold for sand motion for application to large-scale model wind fields (1-100 km scale) of τ(s)=0.01±0.0015 N m(-2).

Intertidal sand body migration along a megatidal coast, Kachemak Bay, Alaska

USGS Publications Warehouse

Adams, P.N.; Ruggiero, P.; Schoch, G.C.; Gelfenbaum, G.

2007-01-01

Using a digital video-based Argus Beach Monitoring System (ABMS) on the north shore of Kachemak Bay in south central Alaska, we document the timing and magnitude of alongshore migration of intertidal sand bed forms over a cobble substrate during a 22-month observation period. Two separate sediment packages (sand bodies) of 1-2 m amplitude and ???200 m wavelength, consisting of well-sorted sand, were observed to travel along shore at annually averaged rates of 278 m/yr (0.76 m/d) and 250 m/ yr (0.68 m/d), respectively. Strong seasonality in migration rates was shown by the contrast of rapid winter and slow summer transport. Though set in a megatidal environment, data indicate that sand body migration is driven by eastward propagating wind waves as opposed to net westward directed tidal currents. Greatest weekly averaged rates of movement, exceeding 6 m/d, coincided with wave heights exceeding 2 m suggesting a correlation of wave height and sand body migration. Because Kachemak Bay is partially enclosed, waves responsible for sediment entrainment and transport are locally generated by winds that blow across lower Cook Inlet from the southwest, the direction of greatest fetch. Our estimates of sand body migration translate to a littoral transport rate between 4,400-6,300 m3/yr. Assuming an enclosed littoral cell, minimal riverine sediment contributions, and a sea cliff sedimentary fraction of 0.05, we estimate long-term local sea cliff retreat rates of 9-14 cm/yr. Applying a numerical model of wave energy dissipation to the temporally variable beach morphology suggests that sand bodies are responsible for enhancing wave energy dissipation by ???13% offering protection from sea cliff retreat. Copyright 2007 by the American Geophysical Union.

A COMBINED MODELING AND MEASUREMENT TECHNIQUE FOR ESTIMATING WIND-BLOWN DUST EMISSIONS AT OWENS (DRY) LAKE, CA

EPA Science Inventory

A refined method of modeling atmospheric dust concentrations due to wind erosion was developed using real-time saltation flux measurements and ambient dust monitoring data at Owens Lake, California. This modeling method may have practical applications for modeling the atmospheric...

1D gasdynamics of wind-blown bubbles: effects of thermal conduction

NASA Astrophysics Data System (ADS)

Zhekov, S. A.; Myasnikov, A. V.

1998-03-01

Gasdynamic properties of the wind-blown bubbles are considered in the framework of the 1D spherically symmetric flow. The model self-consistently takes into account the optically-thin-plasma cooling and the electron thermal conduction. The numerical method used in calculations is described in details. A comparison with the existing self-similar solution is provided. It is shown that the self-similar solution gives a relatively well representation of the hot-bubble interior and could be used for estimations of some of its spectral characteristics. However, it is also shown that the thermal conduction in combination with the cooling may cause additional multiple shocks to appear in the interaction region and the analysis of the nature of these shocks is provided.

Electrostatic Charging of Polymers by Particle Impact at Low Pressures

NASA Technical Reports Server (NTRS)

Calle, Carlos I.; Mantovani, J. G.; Buhler, C. R.; Hogue, M. D.; Nowicki, A. W.; Groop, E. E.; Thompson, Karen (Technical Monitor)

2001-01-01

Studies of the electrostatic interaction between micrometer-sized particles and polymer surfaces are of great interest to NASA's planetary exploration program. The unmanned landing missions to Mars planned for this decade as well as the possible manned missions that might take place during the second decade of this century require a better understanding of the electrostatic response of the materials used in landing crafts and equipment when exposed to wind-blown dust or to surface dust and sand particles. We report on preliminary experiments designed to measure the electrostatic charge developed on five polymer surfaces as they are impacted simultaneously by Mars simulant particles less than 5 micrometers in diameter moving at 20 m/s. Experiments were performed in a CO2 atmosphere at 10 mbars of pressure using a particle delivery method that propels the particles with contact. Experiments were also performed in dry air at atmospheric pressures using a pressurized particle delivery system. The five polymer surfaces, commonly used in space applications, were chosen so that they span the triboelectric series.

Annual monsoon rains recorded by Jurassic dunes.

PubMed

Loope, D B; Rowe, C M; Joeckel, R M

2001-07-05

Pangaea, the largest landmass in the Earth's history, was nearly bisected by the Equator during the late Palaeozoic and early Mesozoic eras. Modelling experiments and stratigraphic studies have suggested that the supercontinent generated a monsoonal atmospheric circulation that led to extreme seasonality, but direct evidence for annual rainfall periodicity has been lacking. In the Mesozoic era, about 190 million years ago, thick deposits of wind-blown sand accumulated in dunes of a vast, low-latitude desert at Pangaea's western margin. These deposits are now situated in the southwestern USA. Here we analyse slump masses in the annual depositional cycles within these deposits, which have been described for some outcrops of the Navajo Sandstone. Twenty-four slumps, which were generated by heavy rainfall, appear within one interval representing 36 years of dune migration. We interpret the positions of 20 of these masses to indicate slumping during summer monsoon rains, with the other four having been the result of winter storms. The slumped lee faces of these Jurassic dunes therefore represent a prehistoric record of yearly rain events.

Aerodynamic excitation and sound production of blown-closed free reeds without acoustic coupling: the example of the accordion reed.

PubMed

Ricot, Denis; Caussé, René; Misdariis, Nicolas

2005-04-01

The accordion reed is an example of a blown-closed free reed. Unlike most oscillating valves in wind musical instruments, self-sustained oscillations occur without acoustic coupling. Flow visualizations and measurements in water show that the flow can be supposed incompressible and potential. A model is developed and the solution is calculated in the time domain. The excitation force is found to be associated with the inertial load of the unsteady flow through the reed gaps. Inertial effect leads to velocity fluctuations in the reed opening and then to an unsteady Bernoulli force. A pressure component generated by the local reciprocal air movement around the reed is added to the modeled aerodynamic excitation pressure. Since the model is two-dimensional, only qualitative comparisons with air flow measurements are possible. The agreement between the simulated pressure waveforms and measured pressure in the very near-field of the reed is reasonable. In addition, an aeroacoustic model using the permeable Ffowcs Williams-Hawkings integral method is presented. The integral expressions of the far-field acoustic pressure are also computed in the time domain. In agreement with experimental data, the sound is found to be dominated by the dipolar source associated by the strong momentum fluctuations of the flow through the reed gaps.

Aerodynamic excitation and sound production of blown-closed free reeds without acoustic coupling: The example of the accordion reed

NASA Astrophysics Data System (ADS)

Ricot, Denis; Caussé, René; Misdariis, Nicolas

2005-04-01

The accordion reed is an example of a blown-closed free reed. Unlike most oscillating valves in wind musical instruments, self-sustained oscillations occur without acoustic coupling. Flow visualizations and measurements in water show that the flow can be supposed incompressible and potential. A model is developed and the solution is calculated in the time domain. The excitation force is found to be associated with the inertial load of the unsteady flow through the reed gaps. Inertial effect leads to velocity fluctuations in the reed opening and then to an unsteady Bernoulli force. A pressure component generated by the local reciprocal air movement around the reed is added to the modeled aerodynamic excitation pressure. Since the model is two-dimensional, only qualitative comparisons with air flow measurements are possible. The agreement between the simulated pressure waveforms and measured pressure in the very near-field of the reed is reasonable. In addition, an aeroacoustic model using the permeable Ffowcs Williams-Hawkings integral method is presented. The integral expressions of the far-field acoustic pressure are also computed in the time domain. In agreement with experimental data, the sound is found to be dominated by the dipolar source associated by the strong momentum fluctuations of the flow through the reed gaps. .

The influence of food supply on foraging behaviour in a desert spider.

PubMed

Lubin, Y; Henschel, J

1996-01-01

We tested the alternative hypotheses that foraging effort will increase (energy maximizer model) or decrease (due to increased costs or risks) when food supply increased, using a Namib desert burrowing spider, Seothyra henscheli (Eresidae), which feeds mainly on ants. The web of S. henscheli has a simple geometrical configuration, comprising a horizontal mat on the sand surface, with a variable number of lobes lined with sticky silk. The sticky silk is renewed daily after being covered by wind-blown sand. In a field experiment, we supplemented the spiders' natural prey with one ant on each day that spiders had active webs and determined the response to an increase in prey. We compared the foraging activity and web geometry of prey-supplemented spiders to non-supplemented controls. We compared the same parameters in fooddeprived and supplemented spiders in captivity. The results support the "costs of foraging" hypothesis. Supplemented spiders reduced their foraging activity and web dimensions. They moulted at least once and grew rapidly, more than doubling their mass in 6 weeks. By contrast, food-deprived spiders increased foraging effort by enlarging the diameter of the capture web. We suggest that digestive constraints prevented supplemented spiders from fully utilizing the available prey. By reducing foraging activities on the surface, spiders in a prey-rich habitat can reduce the risk of predation. However, early maturation resulting from a higher growth rate provides no advantage to S. henscheli owing to the fact that the timing of mating and dispersal are fixed by climatic factors (wind and temperature). Instead, large female body size will increase fitness by increasing the investiment in young during the period of extended maternal care.

Influence of Surface Roughness on Polymer Drag Reduction

DTIC Science & Technology

2007-11-30

paint (High Build Semi-Gloss 97-130, Aquapon ) with glass bead grit. The particles were tightly packed producing a sand grain type roughness. Based on the... Aquapon High Build Semi-Gloss Epoxy 97-130) with glass bead grit blown into the epoxy. The particles were tightly packed giving an average roughness height

Mesoscale and Synoptic Summertime Circulations and Their Impact on Visibility in the Arabian Gulf

NASA Astrophysics Data System (ADS)

Eleuterio, D. P.; Walker, A. L.

2005-12-01

Although frequently characterized as a region of relatively persistent northwesterly winds, often referred to as the 40-day shamal, several researchers have recognized significant temporal and spatial variability in the summer low level winds in the Arabian Gulf. In addition to the synoptically driven gradient between the subtropical high to the north and the monsoon trough across the Gulf of Oman and Northern Arabian Sea, there are complex interactions between the Saudi Arabian and Pakistani heat lows, land-sea breeze circulations, and coastal terrain influence due to the proximity of the Zagros Mountains. These interactions frequently result in several distinct wind regimes within the Arabian Gulf, to include weak thermally and dynamically forced southerlies in the southern Gulf, a diurnally varying region of convergence/ divergence across the central Gulf, and northwesterly shamal type flow in the northern Gulf. The relative orientation and strength of these wind regimes and the strength of the subsidence inversion at the top of the marine boundary layer greatly impact the aerosol loading over water and resulting visibility due to wind-blown sand, dust, and smoke. Several case studies are examined to explore the interaction between mesoscale and synoptic forcing and the resulting spatial and temporal variability in visibility and aerosol optical depth. Conditions range from two to three day periods of rapid and persistent regional clearing with freshening northwesterly winds, to persistent periods of moderate to poor visibility in marine haze under light winds, to large scale events that create a distinct wind and dust front, severely reducing visibility through much of Iraq, Kuwait, and Saudi Arabia, and extending well into the Arabian Gulf. These strong, widespread events may be correlated with synoptically forced conditions farther north. Alternatively, smaller scale regional plumes of mobilized dust are often created by mesoscale events which, in conjunction with oil smoke and industrial pollution, can rapidly reduce visibility in localized regions for periods of 1-2 days and are relatively difficult to forecast because of their mesoscale nature.

Development and testing of a unique carousel wind tunnel to experimentally determine the effect of gravity and the interparticle force on the physics of wind-blown particles

NASA Technical Reports Server (NTRS)

Leach, R. N.; Greeley, Ronald; White, Bruce R.; Iversen, James D.

1987-01-01

In the study of planetary aeolian processes the effect of gravity is not readily modeled. Gravity appears in the equations of particle motion along with the interparticle forces but the two are not separable. A wind tunnel that perimits multiphase flow experiments with wind blown particles at variable gravity was built and experiments were conducted at reduced gravity. The equations of particle motion initiation (saltation threshold) with variable gravity were experimentally verified and the interparticle force was separated. A uniquely design Carousel Wind Tunnel (CWT) allows for the long flow distance in a small sized tunnel since the test section if a continuous loop and develops the required turbulent boundary layer. A prototype model of the tunnel where only the inner drum rotates was built and tested in the KC-135 Weightless Wonder 4 zero-g aircraft. Future work includes further experiments with walnut shell in the KC-135 which sharply graded particles of widely varying median sizes including very small particles to see how interparticle force varies with particle size, and also experiments with other aeolian material.

Static and wind tunnel model tests for the development of externally blown flap noise reduction techniques

NASA Technical Reports Server (NTRS)

Pennock, A. P.; Swift, G.; Marbert, J. A.

1975-01-01

Externally blown flap models were tested for noise and performance at one-fifth scale in a static facility and at one-tenth scale in a large acoustically-treated wind tunnel. The static tests covered two flap designs, conical and ejector nozzles, third-flap noise-reduction treatments, internal blowing, and flap/nozzle geometry variations. The wind tunnel variables were triple-slotted or single-slotted flaps, sweep angle, and solid or perforated third flap. The static test program showed the following noise reductions at takeoff: 1.5 PNdB due to treating the third flap; 0.5 PNdB due to blowing from the third flap; 6 PNdB at flyover and 4.5 PNdB in the critical sideline plane (30 deg elevation) due to installation of the ejector nozzle. The wind tunnel program showed a reduction of 2 PNdB in the sideline plane due to a forward speed of 43.8 m/s (85 kn). The best combination of noise reduction concepts reduced the sideline noise of the reference aircraft at constant field length by 4 PNdB.

Improvements in Fabrication of Sand/Binder Cores for Casting

NASA Technical Reports Server (NTRS)

Bakhitiyarov, Sayavur I.; Overfelt, Ruel A.; Adanur, Sabit

2005-01-01

Three improvements have been devised for the cold-box process, which is a special molding process used to make sand/binder cores for casting hollow metal parts. These improvements are: The use of fiber-reinforced composite binder materials (in contradistinction to the non-fiber-reinforced binders used heretofore), The substitution of a directed-vortex core-blowing subprocess for a prior core-blowing process that involved a movable gassing plate, and The use of filters made from filtration-grade fabrics to prevent clogging of vents. For reasons that exceed the scope of this article, most foundries have adopted the cold-box process for making cores for casting metals. However, this process is not widely known outside the metal-casting industry; therefore, a description of pertinent aspects of the cold-box process is prerequisite to a meaningful description of the aforementioned improvements. In the cold-box process as practiced heretofore, sand is first mixed with a phenolic resin (considered to be part 1 of a three-part binder) and an isocyanate resin (part 2 of the binder). Then by use of compressed air, the mixture is blown into a core box, which is a mold for forming the core. Next, an amine gas (part 3 of the binder) that acts as a catalyst for polymerization of parts 1 and 2 is blown through the core box. Alternatively, a liquid amine that vaporizes during polymerization can be incorporated into the sand/resin mixture. Once polymerization is complete, the amine gas is purged from the core box by use of compressed air. The finished core is then removed from the core box.

Effects of sand burial and wind disturbances on moss soil crusts in a revegetated area of the Tennger Desert, Northern China

NASA Astrophysics Data System (ADS)

Jia, R. L.; Li, X. R.; Liu, L. C.; Gao, Y. H.

2012-04-01

Sand burial and wind are two predominant natural disturbances in the desert ecosystems worldwide. However, the effects of sand burial and wind disturbances on moss soil crusts are still largely unexplored. In this study, two sets of experiments were conducted separately to evaluated the effects of sand burial (sand depth of 0, 1, 2, 3 and 4 mm) and wind blowing (wind speed of 0.2, 3, 6 and 9ms-1) on ecophysiological variables of two moss soil crusts collected from a revegetated area of the Tengger Desert, Northern China. Firstly, the results from the sand burial experiment revealed that respiration rate was significantly decreased and that moss shoot elongation was significantly increased after burial. In addition, Bryum argenteum crust showed the fastest speed of emergence and highest tolerance index, followed by Didymodon vinealis crust. This sequence was consistent with the successional order of the two moss crusts that happened in our study area, indicating that differential sand burial tolerance explains their succession sequence. Secondly, the results from the wind experiment showed that CO2 exchange, PSII photochemical efficiency, photosynthetic pigments, shoot upgrowth, productivity and regeneration potential of the two moss soil crust mentioned above were all substantially depressed. Furthermore, D. vinealis crust exhibited stronger wind resistance than B. argenteum crust from all aspects mentioned above. And this is comparison was identical with their contrasting microhabitats with B. argenteum crust being excluded from higher wind speed microsites in the windward slopes, suggesting that the differential wind resistance of moss soil crusts explains their microdistribution pattern. In conclusion, the ecogeomorphological processes of moss soil crusts in desert ecosystems can be largely determined by natural disturbances caused by sand burial and wind blowing in desert ecosystems.

KC-46A Third Main Operating Base (MOB 3) Beddown Environmental Impact Statement (EIS)

DTIC Science & Technology

2017-04-01

conflict with military activities. Applicants are required to conduct a preliminary evaluation to ensure that proposed wind turbines will not pose...the amount of disturbed ground area at a given time; • Suspension of all soil disturbance activities when winds exceed 25 miles per hour or when...are derived from glacial till and some wind -blown loess that was deposited 12,000 years ago. This area is dissected by stream channels that separate

The contribution of Corynephorus canescens to the geodiversity of inland drift sands

NASA Astrophysics Data System (ADS)

Jungerius, Pieter Dirk; Riksen, Michel; van den Ancker, Hanneke; Kooistra, Maja

2016-04-01

Most dunes in the Netherlands are phytogenic, which means that plants are essential in their formation. This applies also to the dunes of the inland drift sand areas, which are nicknamed Atlantic deserts on account of their extreme climatic conditions. Daily temperatures on the bare sand surfaces may run up to 60° C on sunny summer days, dropping as low as below freezing point at night. Apart from blue and green algae, Corynephorus canescens, Grey hair-grass, it is the first conqueror of these active sands and plays an important role in the geomorphological development of the inland drift sands. C. canescens is a rapid colonizer and flourishes when it receives a regular supply of fresh sand, but is soon succeeded by competitor species. Like Ammophila arenaria (Marram grass), its vigour declines after some time, because its roots are affected. Therefore the plant requires a regular supply of fresh sand to outgrow the affected root zone. The growth of C. canescens is stimulated by two different geomorphological processes: aeolian and pluvial processes. Aboveground, the tussock architecture of the plant helps to trap sand and form small initial dunes. When formed by wind, these are called nabkahs; when formed by splash bush mounds. In a micro-morphological thin section both processes can often be recognized in one dune. The decline of C. canescens is caused by two soil-forming processes: reduction of permeability and accumulation of organic matter. Poor aeration and compaction restrict the growth of its roots. Increase in organic matter hampers the rate of root respiration and promotes conditions for the establishment of competitor species. In the nabkahs, thin slides show on the positive side for C. canescens there is little blown-in organic matter, but on the negative side that the grains upon aging develop a colourless organic coating formed by cyanobacteria (algae. For splashed sands on the positive side for Grey hairgrass there are few organic coatings, but on the negative side there are many organic fragments. So although different both sediments have the same effect. Under the present climate and level of air pollution, the phase of C. canescens is short-lived. Its disappearance marks the end of dune formation and after its decline slope development changes drastically. In conclusion, the interaction between Corynephorus canescens and the geomorphological and soil processes are important in the development and the geodiversity of inland drift sands.

Storm of Stars in the Trifid Nebula

NASA Image and Video Library

2014-01-29

Radiation and winds from massive stars have blown a cavity into the surrounding dust and gas, creating the Trifid nebula, as seen here in infrared light by NASA Wide-field Infrared Survey Explorer, or WISE.

Lidar observations of wind- and wave-driven morphological evolution of coastal foredunes

NASA Astrophysics Data System (ADS)

Spore, N.; Brodie, K. L.; Kershner, C. M.

2016-02-01

Coastal foredunes are continually evolving geomorphic features that are slowly built up by wind-blown sand and rapidly eroded during storms by large waves and swash. Landward aeolian transport removes sediment from the active beach and surf-zone, trapping it in the dune, where as coastal erosion both removes sediment from the dune and can decrease the overall fetch and sediment supply available to the dune. Understanding how wave and wind-driven process interact with each other and the dune-beach system itself is a critical component of improving predictions of coastal evolution. To investigate these processes, two 50 m alongshore by 25 m cross-shore patches of dune along an open coast beach fronting the Atlantic Ocean in Duck, NC were scanned with a high resolution terrestrial lidar scanner ( 5000 points per m^2) every three weeks over the last year to observe detailed morphological evolution of the dune and upper beach. Sequential scans were co-registered to each other using fixed objects in the field of view, significantly increasing precision and accuracy of the observations. The north study site featured a 7.5 m tall scarped foredune system, where as the southern study site featured a 6 m tall, hummocky, prograding foredune. Initial analyses show large accretion events on the southern prograding site. For example, during one three week period in February, portions of the site accreted over 40 cm. In contrast, during the same three week period at the northern site (less than 1 km away), response was alongshore variable with erosion and accretion of roughly 10 cm on the foredune face. Further analysis will focus on separating wind vs. wave driven evolution of these sites. Funded by the USACE Coastal Inlets Research Program.

Digital data sets that describe aquifer characteristics of the alluvial and terrace deposits along the North Canadian River from Canton Lake to Lake Overholser in Central Oklahoma

USGS Publications Warehouse

Adams, G.P.; Rea, Alan; Runkle, D.L.

1997-01-01

ARC/INFO export and nonproprietary format files This diskette contains digitized aquifer boundaries and maps of of hydraulic conductivity, recharge, and ground-water level elevation contours for the alluvial and terrace deposits along the alluvial and terrace deposits along the North Canadian River from Canton Lake to Lake Overholser in central Oklahoma. Ground water in approximately 400 square miles of Quaternary-age alluvial and terrace aquifer is an important source of water for irrigation, industrial, municipal, stock, and domestic supplies. The aquifer consists of clay, silt, sand, and gravel. Sand-sized sediments dominate the poorly sorted, fine to coarse, unconsolidated quartz grains in the aquifer. The hydraulically connected alluvial and terrace deposits unconformably overlie Permian-age formations. The aquifer is overlain by a layer of wind-blown sand in parts of the area. Most of the lines in the aquifer boundary, hydraulic conductivity, and recharge data sets were extracted from published digital surficial geology data sets based on a scale of 1:250,000. The ground-water elevation contours and some of the lines for the aquifer boundary, hydraulic conductivity, and recharge data sets were digitized from a ground-water modeling report about the aquifer published at a scale of 1:250,000. The hydraulic conductivity values and recharge rates also are from the ground-water modeling report. Ground-water flow models are numerical representations that simplify and aggregate natural systems. Models are not unique; different combinations of aquifer characteristics may produce similar results. Therefore, values of hydraulic conductivity and recharge used in the model and presented in this data set are not precise, but are within a reasonable range when compared to independently collected data.

Fluvial sedimentary styles and associated depositional environments in the buntsandstein west of river rhine in saar area and pfalz (F.R. Germany) and vosges (France)

NASA Astrophysics Data System (ADS)

Dachroth, Wolfgang

The Buntsandstein west of river Rhine in Saar area, Pfalz and Vosges consists of three fluvial magnacycles which are characterized by different associated non-alluvial environments. The stratigraphic sequence is divided by several unconformities reflecting tectonic movements which were connected with periods of extension of the depositional area. Two major phases and two minor events are recognized by the evaluation of the Pfalz unconformity and the Lothringen unconformity, and the Leuter unconformity and the Saar unconformity, respectively. The Lower Buntsandstein (including Zechstein) compries the first magnacycle and is built up of alluvial-fan deposits, fluvial braidplain sediments and marine to lagoonal deposits. Some aeolian sands as well as several palaeosols are also present. The palaeolandscape consists of alluvial fans seaming the margin of the basin and fluvial braidplains reaching from the toes of the fan belt to the centre of the depositional area which is occupied by a lagoonal sea that partially evolves into a playa-lake with progressive refreshment. The Middle Buntsandstein comprises the second magnacycle and is composed of an alternation of aeolian Dünnschichten and fluvial Felsbänke. The third facies are alluvial-fan deposits of palaeogeographically restricted distribution along the margins of the basin. The aeolian Dünnschichten originate in the marginal parts of chott-type depressions (in comparison with the recent Chott Djerid in Tunesia) where rising ground water moistens the dry sediments that are laid down on the playa floor and thus allows their enhanced preservation. In dry periods, wind-blown sand is spread out as plane sheets or as migrating wind ripple trains, or accumulates to barchanoid-type dunes that advance across the flat. Depending on supply of sand, all stages of transition between dune fields with only narrow interdune corridors between the ridges and interdune playas with isolated widely-spaced dunes are developed. The individual sand storms operating in the erg are recorded in a mm-scale graded grain-size lamination. The desert-type setting is divided into depositional sand ergs where aeolian bedforms migrate, and deflationary gravel serirs where pebbly fluvial sediments are winnowed, resulting in concentration of the gravel to residual lags and in abundant grinding of clasts to ventifacts. During time of flooding of the chotts by atmospheric precipitation, fluvial incursions or rising ground water level, lacustrine playa deposits settle out in shallow stagnant water. The fluvial Felsbänke originate in wadi-type braided river systems intersecting the erg and serir zones and often redepositing aeolian sand which is derived from undercutting during abandonment and displacement of the watercourses. The stream complexes are partially fed at their proximal ends by runoff from local alluvial fans which are aligned along parts of the margins of the basin. The Upper Buntsandstein comprises the third magnacycle which is split into three megacycles that in turn are divided into several phases. A change from generally arid to primarily semi-arid climate along with tectonical up-lift in the source area results in extinction of aeolian deposition and gives rise to formation of Violette Horizonte calcrete palaeosols which are widespread throughout the Upper Buntsandstein, if their origin was not inhibited by the dynamics of the fluvial systems. The palaeosols occur in different evolutionary stages and are mainly characterized by the typical blue-violet colour, presence of root tubes, carbonate nodules and carbonate crusts, destratification and polyedric jointing. The fluvial fining-upwards cyclothems are formed in braided river systems which partially pass into meandering stream complexes. At the top of the Upper Buntsandstein, the alluvial inland plain is converted into a delta complex in the coastal plain along the approaching sea, and with a sequence of alternating progradation and recession events, the Muschelkalk transgression finally inundates the continental setting.

Geomorphology and drift potential of major aeolian sand deposits in Egypt

NASA Astrophysics Data System (ADS)

Hereher, Mohamed E.

2018-03-01

Aeolian sand deposits cover a significant area of the Egyptian deserts. They are mostly found in the Western Desert and Northern Sinai. In order to understand the distribution, pattern and forms of sand dunes in these dune fields it is crucial to analyze the wind regimes throughout the sandy deserts of the country. Therefore, a set of wind data acquired from twelve meteorological stations were processed in order to determine the drift potential (DP), the resultant drift potential (RDP) and the resultant drift direction (RDD) of sand in each dune field. The study showed that the significant aeolian sand deposits occur in low-energy wind environments with the dominance of linear and transverse dunes. Regions of high-energy wind environments occur in the south of the country and exhibit evidence of deflation rather than accumulation with the occurrence of migratory crescentic dunes. Analysis of the sand drift potentials and their directions help us to interpret the formation of major sand seas in Egypt. The pattern of sand drift potential/direction suggests that the sands in these seas might be inherited from exogenous sources.

Phase diagrams of dune shape and orientation depending on sand availability

PubMed Central

Gao, Xin; Narteau, Clément; Rozier, Olivier; du Pont, Sylvain Courrech

2015-01-01

New evidence indicates that sand availability does not only control dune type but also the underlying dune growth mechanism and the subsequent dune orientation. Here we numerically investigate the development of bedforms in bidirectional wind regimes for two different conditions of sand availability: an erodible sand bed or a localized sand source on a non-erodible ground. These two conditions of sand availability are associated with two independent dune growth mechanisms and, for both of them, we present the complete phase diagrams of dune shape and orientation. On an erodible sand bed, linear dunes are observed over the entire parameter space. Then, the divergence angle and the transport ratio between the two winds control dune orientation and dynamics. For a localized sand source, different dune morphologies are observed depending on the wind regime. There are systematic transitions in dune shape from barchans to linear dunes extending away from the localized sand source, and vice-versa. These transitions are captured fairly by a new dimensionless parameter, which compares the ability of winds to build the dune topography in the two modes of dune orientation. PMID:26419614

Improving the performance of roadside vegetation.

DOT National Transportation Integrated Search

2011-02-01

Vegetation along roadways can be aesthetically pleasing and helps to stabilize the soil, which reduces wind-blown soil : and soil erosion. While products containing chloride salts have proven to be very effective in helping to provide safe road : sur...

Saco Bay, Maine: Sediment Budget for Late Twentieth Century to Present

DTIC Science & Technology

2016-02-01

determined that sediment flux was variable, depending on bathymetry and input wave conditions. Despite these variations in conditions, there is no obvious...DETAILS, SACO BAY, MAINE V3. Last update: 11 September 2014 Units are yd3/year. Source1 = bluffs, river influx, wind . Sink1 = wind -blown loss or...Beach05 (B05), Pine Point QSource1 1,600 Wind transport (from Kelley et al. 2005). DeltaV 1,600 Dune accumulation 1859–1991 (from Kelley et al. 2005

Low-speed wind tunnel investigation of a semispan STOL jet transport wing body with an upper surface blown jet flap

NASA Technical Reports Server (NTRS)

Phelps, A. E., III; Letko, W.; Henderson, R. L.

1973-01-01

An investigation of the static longitudinal aerodynamic characteristics of a semispan STOL jet transport wing-body with an upper-surface blown jet flap for lift augmentation was conducted in a low-speed wind tunnel having a 12-ft octagonal test section. The semispan swept wing had an aspect ratio of 3.92 (7.84 for the full span) and had two simulated turbofan engines mounted ahead of and above the wing in a siamese pod equipped with an exhaust deflector. The purpose of the deflector was to spread the engine exhaust into a jet sheet attached to the upper surface of the wing so that it would turn downward over the flap and provide lift augmentation. The wing also had optional boundary-layer control provided by air blowing through a thin slot over a full-span plain trailing-edge flap.

Linear Relation for Wind-blown Bubble Sizes of Main-sequence OB Stars in a Molecular Environment and Implication for Supernova Progenitors

NASA Astrophysics Data System (ADS)

Chen, Yang; Zhou, Ping; Chu, You-Hua

2013-05-01

We find a linear relationship between the size of a massive star's main-sequence bubble in a molecular environment and the star's initial mass: R b ≈ 1.22 M/M ⊙ - 9.16 pc, assuming a constant interclump pressure. Since stars in the mass range of 8 to 25-30 M ⊙ will end their evolution in the red supergiant phase without launching a Wolf-Rayet wind, the main-sequence wind-blown bubbles are mainly responsible for the extent of molecular gas cavities, while the effect of the photoionization is comparatively small. This linear relation can thus be used to infer the masses of the massive star progenitors of supernova remnants (SNRs) that are discovered to evolve in molecular cavities, while few other means are available for inferring the properties of SNR progenitors. We have used this method to estimate the initial masses of the progenitors of eight SNRs: Kes 69, Kes 75, Kes 78, 3C 396, 3C 397, HC 40, Vela, and RX J1713-3946.

Earth Observations taken by the Expedition 17 Crew

NASA Image and Video Library

2008-09-15

ISS017-E-016521 (15 Sept. 2008) --- Sandy Cape and Fraser Island, Australia are featured in this image photographed by an Expedition 17 crewmember on the International Space Station. Fraser Island, the world's largest sand island, includes Great Sandy National Park and is located along the coastline of Queensland, Australia. The island was designated a World Heritage site in 1992, in part due to its outstanding preservation of geological processes related to sand dune formation. According to scientists, the island's dune fields preserve a record of sand deposition and movement related to sea level rise and fall extending back over 700,000 years. In addition to sand dunes, the island also preserves an interesting range of vegetation -- including vine rainforest, stands of eucalypt trees, and mangroves -- and diverse fauna including crabs, parrots, sugar gliders and flying foxes. This view highlights the northernmost portion of the island, known as Sandy Cape. Active white sand dunes contrast with dark green vegetation that anchors older dune sets. Irregular patches of sand dunes surrounded by vegetation are known as sand blows (or blowouts), formed when the vegetation cover is disturbed -- by wind, fire, or human activities. The exposed underlying sand can then move and form new dunes, sometimes at rates of up to one meter per year. Coastal sand dune fields -- such as the one located along the eastern side of Sandy Cape (center) -- will remain active until anchored by vegetation, or until no more sand is available to form new dunes.

Mars Reconnaissance Orbiter and Opportunity observations of the Burns formation: Crater hopping at Meridiani Planum

NASA Astrophysics Data System (ADS)

Arvidson, R. E.; Bell, J. F., III; Catalano, J. G.; Clark, B. C.; Fox, V. K.; Gellert, R.; Grotzinger, J. P.; Guinness, E. A.; Herkenhoff, K. E.; Knoll, A. H.; Lapotre, M. G. A.; McLennan, S. M.; Ming, D. W.; Morris, R. V.; Murchie, S. L.; Powell, K. E.; Smith, M. D.; Squyres, S. W.; Wolff, M. J.; Wray, J. J.

2015-03-01

Compact Reconnaissance Imaging Spectrometer for Mars hyperspectral (1.0-2.65 μm) along-track oversampled observations covering Victoria, Santa Maria, Endeavour, and Ada craters were processed to 6 m/pixel and used in combination with Opportunity observations to detect and map hydrated Mg and Ca sulfate minerals in the Burns formation. The strongest spectral absorption features were found to be associated with outcrops that are relatively young and fresh (Ada) or preferentially scoured of dust, soil, and coatings by prevailing winds. At Victoria and Santa Maria, the scoured areas are on the southeastern rims and walls, opposite to the sides where wind-blown sands extend out of the craters. At Endeavour, the deepest absorptions are in Botany Bay, a subdued and buried rim segment that exhibits high thermal inertias, extensive outcrops, and is interpreted to be a region of enhanced wind scour extending up and out of the crater. Ada, Victoria, and Santa Maria outcrops expose the upper portion of the preserved Burns formation and show spectral evidence for the presence of kieserite. In contrast, gypsum is pervasive spectrally in the Botany Bay exposures. Gypsum, a relatively insoluble evaporative mineral, is interpreted to have formed close to the contact with the Noachian crust as rising groundwaters brought brines close to and onto the surface, either as a direct precipitate or during later diagenesis. The presence of kieserite at the top of the section is hypothesized to reflect precipitation from evaporatively concentrated brines or dehydration of polyhydrated sulfates, in both scenarios as the aqueous environment evolved to very arid conditions.

Mars Reconnaissance Orbiter and Opportunity observations of the Burns formation: crater hopping at Meridiani Planum

USGS Publications Warehouse

R.E. Arvidson,; Bell, J.F.; Catalano, J.G.; Clark, B. C.; Fox, V.K.; Gellert, Ralf; Grotzinger, J.P.; Guinness, E.A.; Herkenhoff, Kenneth E.; Knoll, A.H.; Lapotre, M.G.A.; McLennan, S.M.; Ming, D. W.; Morris, R.V.; Murchie, S.L.; Powell, K. E.; Smith, M.D.; Squyres, S. W.; Wolff, M.J.; J.J. Wray,

2015-01-01

Compact Reconnaissance Imaging Spectrometer for Mars hyperspectral (1.0–2.65 µm) along-track oversampled observations covering Victoria, Santa Maria, Endeavour, and Ada craters were processed to 6 m/pixel and used in combination with Opportunity observations to detect and map hydrated Mg and Ca sulfate minerals in the Burns formation. The strongest spectral absorption features were found to be associated with outcrops that are relatively young and fresh (Ada) or preferentially scoured of dust, soil, and coatings by prevailing winds. At Victoria and Santa Maria, the scoured areas are on the southeastern rims and walls, opposite to the sides where wind-blown sands extend out of the craters. At Endeavour, the deepest absorptions are in Botany Bay, a subdued and buried rim segment that exhibits high thermal inertias, extensive outcrops, and is interpreted to be a region of enhanced wind scour extending up and out of the crater. Ada, Victoria, and Santa Maria outcrops expose the upper portion of the preserved Burns formation and show spectral evidence for the presence of kieserite. In contrast, gypsum is pervasive spectrally in the Botany Bay exposures. Gypsum, a relatively insoluble evaporative mineral, is interpreted to have formed close to the contact with the Noachian crust as rising groundwaters brought brines close to and onto the surface, either as a direct precipitate or during later diagenesis. The presence of kieserite at the top of the section is hypothesized to reflect precipitation from evaporatively concentrated brines or dehydration of polyhydrated sulfates

Navier-Stokes Analysis of a High Wing Transport High-Lift Configuration with Externally Blown Flaps

NASA Technical Reports Server (NTRS)

Slotnick, Jeffrey P.; An, Michael Y.; Mysko, Stephen J.; Yeh, David T.; Rogers, Stuart E.; Roth, Karlin; Baker, M.David; Nash, S.

2000-01-01

Insights and lessons learned from the aerodynamic analysis of the High Wing Transport (HWT) high-lift configuration are presented. Three-dimensional Navier-Stokes CFD simulations using the OVERFLOW flow solver are compared with high Reynolds test data obtained in the NASA Ames 12 Foot Pressure Wind Tunnel (PWT) facility. Computational analysis of the baseline HWT high-lift configuration with and without Externally Blown Flap (EBF) jet effects is highlighted. Several additional aerodynamic investigations, such as nacelle strake effectiveness and wake vortex studies, are presented. Technical capabilities and shortcomings of the computational method are discussed and summarized.

Kuwait City, Kuwait as seen from STS-59

NASA Technical Reports Server (NTRS)

1994-01-01

The radiating transportation pattern of this 20th-Century urban plan is nicely displayed in this high-resolution photograph. Light-toned spots in the desrt mark oil well sites; along the south edge of the scene, some dark residue remains from the fires set during the recent Gulf War. Blown sand has nearly hidden the soot and thick oil that were deposited on the surface.

3 CFR 9071 - Proclamation 9071 of December 16, 2013. Wright Brothers Day, 2013

Code of Federal Regulations, 2014 CFR

2014-01-01

... seconds of flight. Wilbur and Orville Wright's airplane soared above the wind-blown banks of Kitty Hawk... proud tradition, we must give them the tools to translate energy and creativity into concrete results...

77 FR 30953 - Approval and Promulgation of State Implementation Plans; State of Wyoming; Regional Haze Rule...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-05-24

... the problem of visibility impairment in Class I areas, states need to develop strategies in... air corridors (CACs), mobile sources, and wind-blown dust, among other things. The EPA codified these...

77 FR 28825 - Approval, Disapproval and Promulgation of State Implementation Plans; State of Utah; Regional...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-05-16

... transported over long distances, even hundreds of kilometers. Therefore, to effectively address the problem of... air corridors (CACs), mobile sources, and wind-blown dust, among other things. The EPA codified these...

77 FR 36043 - Approval and Promulgation of State Implementation Plans; New Mexico; Regional Haze Rule...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-06-15

.... Therefore, to address effectively the problem of visibility impairment in Class I areas, states need to... development; and provisions to manage clean air corridors, mobile sources, and wind-blown dust, among other...

77 FR 24767 - Approval and Promulgation of State Implementation Plans; City of Albuquerque-Bernalillo County...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-04-25

... of kilometers. Therefore, to address effectively the problem of visibility impairment in Class I... sources, and wind-blown dust, among other things. The EPA codified these recommendations as part of the...

Desertification in Russia: Problems and solutions (an example in the Republic of Kalmykia-Khalmg Tangch).

PubMed

Zonn, I S

1995-01-01

During the second half of the 20th century Kalmykia has undergone severe desertification. Under Soviet rule, rangelands were increasingly devoted to animal production, and pastures were converted to cropland in a campaign to increase crops. Pastures were grazed two to three times their sustainable production, saiga populations and habitat greatly decreased, more than 17 million ha were subjected to wind erosion, 380,000 ha were transformed into moving sands, and 106,000 ha were ruined by secondary salinization and waterlogging. By the 1990s almost 80% of the Republic had undergone desertification, and 13% had been transformed into a true desert. In 1986 the General Scheme of Desertification Control was formulated. The scheme called for rotating pastures, reclaiming blown sand using silviculture, tilling overgrazed pastures and sowing fodder plants, and developing water supplies for pastures. In its early years the scheme has been successful. But the management of restored pastures usually reverts to the same farms responsible for the poor conditions, and there is great apprehension that degradation could reoccur. This case study concludes that the general cattle and agriculture development in Kalmykia is unviable for ecological and economic reasons, that Kalmykia should implement an adaptive policy oriented toward conservation and accommodating the interrelation and variability of land resources, that the desertification problem can be solved only by changing agrarian policy as a whole, and that a desertification control program must become an integral part of economic and social development of the Republic.

The sand-deposition impact of artificial gravel beds on the protection of the Mogao Grottoes

PubMed Central

Li, Guo Shuai; Qu, Jian Jun; Li, Xu Zhi; Wang, Wan Fu

2014-01-01

Gravel beds can prevent sand-dust emission and weaken sand-dust flux. We used wind-tunnel experiments and field observations on artificial gravel beds above the Mogao Grottoes to quantify their impact. In the report, we identified a significant correlation between gravel roughness and its ability to trap wind-transported sand. The optimal combinations of gravel diameter and coverage were determined. The greatest roughness is achieved when small gravel coverage is 75%, medium 40% and large 45%. We found that initial wind speed and gravel coverage are the key factors controlling the amount of sand trapped by the gravel beds. PMID:24614183

Quantifying Post-Fire Aeolian Sediment Transport Using Rare Earth Element Tracers.

NASA Astrophysics Data System (ADS)

Dukes, D.; Ravi, S.; Grandstaff, D. E.; Gonzales, H. B.; Li, J. J.; Sankey, J. B.; Wang, G.; Van Pelt, R. S.

2016-12-01

Grasslands and rangelands in arid and semi-arid regions of the world, which provide fundamental ecosystem services, are undergoing rapid increases in fire activity and are highly susceptible to post-fire accelerated soil erosion by wind. A quantitative assessment that integrates fire-wind erosion feedbacks is therefore critically needed in understanding vegetation change, soil biogeochemical cycling, air quality, and landscape evolution. We investigated the applicability of a novel tracer technique - the use of rare earth element (REE) tracers - to quantify soil erosion by wind and to identify sources and sinks of wind-blown sediments in both a burned and unburned shrub-grass transition zone within the Chihuahuan desert (New Mexico, USA). At the beginning of the windy season, March 2016, silt and sand sized particles in shrub, grass, and bare microsites were each tagged with a unique REE oxide, Ho, Eu, and Yb respectively. Samples were then taken directly after application prior to a prescribed fire and again at the end of the windy season in June 2016. All REE tracers showed signs of depletion and mixing, with the depletion in the burned site up to 20% greater than the unburned. REE concentration comparisons between the burned and unburned plots reveal a shift in the source and sink dynamics of sediment post fire. In unburned plots, changes in microsite REE concentrations indicate that sediment moved from the bare to vegetated microsites, whereas the opposite occurred in burned plots. However, burned plot grass microsites acted as a sink for sediment from shrub microsites, whereas unburned plot grass microsites exhibited no enrichment from shrub microsite-sourced sediment. Though fires are known to immediately increase aeolian sediment transport, accompanying changes in the sources and sinks of wind borne sediment may influence biogeochemical cycling and vegetation shifts possibly providing a feedback mechanism for land degradation in dryland ecosystems.

Morphologic characteristics and migration rate assessment of barchan dunes in the Southeastern Western Desert of Egypt

NASA Astrophysics Data System (ADS)

Hamdan, M. A.; Refaat, A. A.; Abdel Wahed, M.

2016-03-01

This work explores the morphologic characteristics of aeolian dune sand in the southeastern part of Western Desert of Egypt. It aims to assess the movement of barchan dunes and evaluate their environmental influence on the Toshka Project. Morphometric investigation of barchan dunes in the Toshka area revealed that most barchans have high length/width (a/c) ratios (fat to pudgy), while one-fifth of the studied barchans have lower a/c ratios and so appear normal in their morphologic forms. Statistical analysis of the main parameters of barchan dunes in Toshka and other desert regions in the Kharga (Egypt), Kuwait, Southern Morocco, California and Southern Peru demonstrates that barchans of the Toshka area are distinctive in their appearance. They are characterized by distinct aspect with higher values of length and width and greater growth in height. The high-energy wind environment in addition to the large amount of drifting sand are principal factors responsible for the unique shape of Toshka barchans. The migration rate of barchan dunes in four chosen test locations, within the central and western Toshka area, ranges from about 3 to 10.82 m/year. The calculated average migration rate of these dunes is about 6 m/year in a SSW direction. Sand encroachment is more extensive in the central and western parts of the investigated Toshka area. Risk evaluation of sand dune movements in the southeastern part of the Western Desert points to medium to high sand encroachment risk values. These may represent serious hazards to the newly-established Toshka Project, threatening roads, as well as cultivated lands in the area.

Development of Advanced High Lift Leading Edge Technology for Laminar Flow Wings

NASA Technical Reports Server (NTRS)

Bright, Michelle M.; Korntheuer, Andrea; Komadina, Steve; Lin, John C.

2013-01-01

This paper describes the Advanced High Lift Leading Edge (AHLLE) task performed by Northrop Grumman Systems Corporation, Aerospace Systems (NGAS) for the NASA Subsonic Fixed Wing project in an effort to develop enabling high-lift technology for laminar flow wings. Based on a known laminar cruise airfoil that incorporated an NGAS-developed integrated slot design, this effort involved using Computational Fluid Dynamics (CFD) analysis and quality function deployment (QFD) analysis on several leading edge concepts, and subsequently down-selected to two blown leading-edge concepts for testing. A 7-foot-span AHLLE airfoil model was designed and fabricated at NGAS and then tested at the NGAS 7 x 10 Low Speed Wind Tunnel in Hawthorne, CA. The model configurations tested included: baseline, deflected trailing edge, blown deflected trailing edge, blown leading edge, morphed leading edge, and blown/morphed leading edge. A successful demonstration of high lift leading edge technology was achieved, and the target goals for improved lift were exceeded by 30% with a maximum section lift coefficient (Cl) of 5.2. Maximum incremental section lift coefficients ( Cl) of 3.5 and 3.1 were achieved for a blown drooped (morphed) leading edge concept and a non-drooped leading edge blowing concept, respectively. The most effective AHLLE design yielded an estimated 94% lift improvement over the conventional high lift Krueger flap configurations while providing laminar flow capability on the cruise configuration.

Opportunity's 'Rub al Khali' Panorama

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site] Click on the image for Opportunity's 'Rub al Khali' Panorama (QTVR)

This panoramic image, dubbed 'Rub al Khali,' was acquired by NASA's Mars Exploration Rover Opportunity on the plains of Meridiani during the period from the rover's 456th to 464th sols on Mars (May 6 to May 14, 2005). Opportunity was about 2 kilometers (1.2 miles) south of 'Endurance Crater' at a place known informally as 'Purgatory Dune.'

The rover was stuck in the dune's deep fine sand for more than a month. 'Rub al Khali' (Arabic translation: 'the empty quarter') was chosen as the name for this panorama because it is the name of a similarly barren, desolate part of the Saudi Arabian desert on Earth.

The view spans 360 degrees. It consists of images obtained in 97 individual pointings of the panoramic camera. The camera took images with five camera filters at each pointing. This 22,780-by-6,000-pixel mosaic is an approximately true-color rendering generated using the images acquired through filters admitting light wavelengths of 750, 530, and 480 nanometers.

Lighting varied during the nine sols it took to acquire this panorama, resulting in some small image seams within the mosaic. These seams have been smoothed in sky parts of the mosaic to better simulate the vista that a person would see if able to view it all at the same time on Mars.

Opportunity's tracks leading back to the north (center of the panorama) are a reminder of the rover's long trek from Endurance Crater. The deep ruts dug by Opportunity's wheels as it became stuck in the sand appear in the foreground. The crest and trough of the last ripple the rover crossed before getting stuck is visible in the center. These wind-formed sand features are only about 10 to 15 centimeters (4 to 6 inches) tall. The crest of the actual ripple where the rover got stuck can be seen just to the right of center. The tracks and a few other places on and near ripple crests can be seen in this color image to be dustier than the undisturbed or 'normal' plains soils in Meridiani. Since the time these ruts were made, some of the dust there has been blown away by the wind, reaffirming the dynamic nature of the martian environment, even in this barren, ocean-like desert of sand.

STS-32 Earth observation of the southern Sand Sea, Namibia, Atlantic Ocean

NASA Technical Reports Server (NTRS)

1990-01-01

STS-32 Earth observation taken onboard Columbia, Orbiter Vehicle (OV) 102, is of the southern Sand Sea. Low sun angles on this south-looking view of the sand dunes of the southern Sand Sea (foreground) shows the many subtle patterns produced by winds. Along the coast very strong southerly winds have generated a zone of ribbed, transverse dunes. Further inland, different patterns appear, which may relate to present winds, or perhaps to winds which blew in different directions at times in the geological past. Strong Santa Ana-type winds blow from inland (left) during the winter which may explain the small patterns (center left). The small fishing port of Luderitz occupies the main bay on the coastline. Otherwise the area is empty of inhabitants on the very dry and windy coast. Railways connect the post with inland centers.

Data report for the geologic and scenic quality evaluation of selected sand and gravel sites on the Wind River Indian Reservation, Wyoming

USGS Publications Warehouse

Langer, William H.; Van Gosen, Bradley S.; Arbogast, Belinda; Lindsey, David A.

2011-01-01

In April 2005, the U.S. Geological Survey (USGS) conducted field studies on the Wind River Indian Reservation, Wyoming, to inventory and evaluate sand and gravel deposits underlying river terraces on tribal lands along the Wind River. This report contains the results for 12 sites of sand and gravel deposits evaluated for their potential use as aggregate in Portland cement concrete, asphalt, and base course. The report provides the results of: * The USGS geologic studies and engineering tests. * A conclusion and recommendation for the best use of sand and gravel materials. * Calculations of available sand and gravel materials. * A scenic quality landscape inventory and evaluation.

Seed bank dynamics of blowout penstemon in relation to local patterns of sand movement on the Ferris Dunes, south-central Wyoming

Treesearch

Kassie L. Tilini; Susan E. Meyer; Phil S. Allen

2017-01-01

Plants restricted to active sand dunes possess traits that enable both survival in a harsh environment and local migration in response to a shifting habitat mosaic. We examined seed bank dynamics of Penstemon haydenii S. Watson (blowout penstemon) in relation to local sand movement. We measured within-year sand movement along a 400 m transect and examined plant density...

Aerodynamic characteristics of a large-scale hybrid upper surface blown flap model having four engines

NASA Technical Reports Server (NTRS)

Carros, R. J.; Boissevain, A. G.; Aoyagi, K.

1975-01-01

Data are presented from an investigation of the aerodynamic characteristics of large-scale wind tunnel aircraft model that utilized a hybrid-upper surface blown flap to augment lift. The hybrid concept of this investigation used a portion of the turbofan exhaust air for blowing over the trailing edge flap to provide boundary layer control. The model, tested in the Ames 40- by 80-foot Wind Tunnel, had a 27.5 deg swept wing of aspect ratio 8 and 4 turbofan engines mounted on the upper surface of the wing. The lift of the model was augmented by turbofan exhaust impingement on the wind upper-surface and flap system. Results were obtained for three flap deflections, for some variation of engine nozzle configuration and for jet thrust coefficients from 0 to 3.0. Six-component longitudinal and lateral data are presented with four engine operation and with the critical engine out. In addition, a limited number of cross-plots of the data are presented. All of the tests were made with a downwash rake installed instead of a horizontal tail. Some of these downwash data are also presented.

Trajectories of saltating sand particles behind a porous fence

NASA Astrophysics Data System (ADS)

Zhang, Ning; Lee, Sang Joon; Chen, Ting-Guo

2015-01-01

Trajectories of aeolian sand particles behind a porous wind fence embedded in a simulated atmospheric boundary layer were visualized experimentally, to investigate the shelter effect of the fence on sand saltation. Two sand samples, one collected from a beach (d = 250 μm) and the other from a desert (d = 100 μm), were tested in comparison with the previous studies of a 'no-fence' case. A wind fence (ε = 38.5%) was installed on a flat sand bed filled with each sand sample. A high-speed photography technique and the particle tracking velocimetry (PTV) method were employed to reconstruct the trajectories of particles saltating behind the fence. The collision processes of these sand particles were analyzed, momentum and kinetic energy transfer between saltating particles and ground surface were also investigated. In the wake region, probability density distributions of the impact velocities agree well with the pattern of no-fence case, and can be explained by a log-normal law. The horizontal component of impact velocity for the beach sand is decreased by about 54%, and about 76% for the desert sand. Vertical restitution coefficients of bouncing particles are smaller than 1.0 due to the presence of the wind fence. The saltating particles lose a large proportion of their energy during the collision process. These results illustrate that the porous wind fence effectively abates the further evolution of saltating sand particles.

Exploratory studies of the cruise performance of upper surface blown configurations: Program analysis and conclusions

NASA Technical Reports Server (NTRS)

Braden, J. A.; Hancock, J. P.; Hackett, J. E.; Lyman, V.

1979-01-01

The experimental data encompassing surface pressure measurements, and wake surveys at static and wind-on conditions are analyzed. Cruise performance trends reflecting nacelle geometric variations, and nozzle operating conditions are presented. Details of the modeling process are included.

Granular Mechanics and Surface Systems Lab

NASA Technical Reports Server (NTRS)

Randle, Leah

2007-01-01

The cratering of sand under gas jets is observed to further understanding of soil in hopes to further understand lunar soil. Lunar soil is important to understand because it is causing problems with the materials taken into space including the shuttle. Lunar soil is not rounded like beach sand. Lunar soil is sharp like little particles of glass, and some times when blown they can hook on to one another and become bigger particles. The experiments are designed to help to understand some of the basic physics in how the shuttle jets will interact with lunar soil and how to control the lunar soil. These experiments investigate the diameter of the gas jet and the size of the sand grains to determine how these parameters affect the erosion rate and the cratering processes. Therefore, the experiments preformed will point out what is dependent and what is independent.

Why do seif dunes meander?

NASA Astrophysics Data System (ADS)

Kryger, Mateusz; Bubenzer, Olaf; Parteli, Eric

2017-04-01

Seif dunes - which develop in the absence of vegetation and elongate in the resultant sand transport direction - are the prevailing dune type in many deserts of Earth and Mars and display a meandering shape that has challenged geomorphologists for decades. Understanding the factors controlling seif dune morphology may have impact for a broad range of scientific areas, in particular in the investigation of planetary wind regimes, as dune shape is primarily affected by wind directionality. Sand roses of areas hosting seif dunes display, in general, two main wind directions that form a divergence angle larger than 90˚ . Indeed, theory of dune formation predicts that longitudinal alignment of aeolian bedforms occurs under obtuse bimodal winds, a prediction that has been confirmed by field observations and numerical simulations of aeolian dunes, as well as by experiments on subaqueous bedforms. However, numerical simulations and water tank experiments performed under conditions of bimodal flows could never reproduce one of the most salient characteristics of the seif dune shape, which is its meandering. Instead, longitudinal dunes produced in such simulations and experiments display an unrealistic straight shape, which elongates into the resultant transport trend without developing the sinuous morphology of the seif dunes. Here we show, by means of morphodynamic modeling of aeolian sediment transport and dune formation under directionally varying flows, that the meandering shape of seif dunes can be explained by the action of subordinated sand-moving winds, which occur in addition to both main wind components of the bimodal wind. Because such subordinated winds - inherent to most measured sand roses of seif dune fields - are associated with transport rates much smaller than the sand flux values of the main bimodal wind components - they have been long thought to be negligible for dune shape. However, our simulations show that meandering may be caused by a single secondary wind component in the sand rose with transport rate of about 1/5 of the flux due to the bimodal wind components. To verify our model we calculate dune formation using the sand rose of the seif dune field in Bir Lahfan, Sinai, and find good quantitative agreement between the shape of seif dunes in this field and the dune morphology obtained in the simulations. Our simulations suggest that meandering seif dunes constitute a dune type produced by multimodal wind systems and cannot form under (strictly) bimodal wind regimes.

Space Shuttle Radar Images of Terrestrial Impact Structures: SIR-C/X-SAR

NASA Astrophysics Data System (ADS)

McHone, J. F.; Blumberg, D. G.; Greeley, R.; Underwood, J. R., Jr.

1995-09-01

The Spaceborne Radar Laboratory (SRL) orbited Earth in April and October of 1994 operating two imaging radars: X-SAR, an X-band (3 cm lambda) instrument, and the polarimetric SIR-C, a combination L-band/C-band (24 cm and 5.6 cm lambda). More than 150 terrestrial meteorite craters and astroblemes are presently known. Three of these, Wolfe Creek in Australia; Roter Kamm in Namibia; and Zhamanshin in Kazakhstan, were planned targets and were imaged successfully with multiple passes and look directions. Several other impact sites were fortuitously imaged while radar data were being collected for other purposes. These sites include B.P. and Oasis structures in Libya, Aourounga multi-ring feature in Chad, Amguid crater in Algeria, and the Spider astrobleme and Henbury crater field in Australia. Wolfe Creek (19 degrees 10'S; 127 degrees 47'E; 875 m dia) Both the elevated rim and the inner floor of this crater appear as radar bright features. Strong radar returns are due to blocky rubble textures in the rim and desert vegetation within the central bowl. Associated linear sand dunes show differential penetration properties in the various radar wavelengths and polarization. Roter Kamm (27 degrees 46'S; 016 degrees 18'E; 2.5 km dia) This bowl-shaped crater is mostly buried by wind-blown sands. Comparison of differential radar penetration patterns due to changes in wavelength and look direction reveal concealed target rocks and a buried possible ejecta unit. Zhamanshin (48 degrees 24'N; 060 degrees 48'E; 14 km dia) This unusual impact structure, first detected by the presence of glassy impact melt products [1], has very little topographic relief and is nearly invisible on survey-quality radar imagery. Fully processed images, however, enhance subtle vegetation patterns which highlight regional streams. These drainage patterns are now being analyzed in detail to better delineate boundaries and internal structure of this feature. B.P. Structure (25 degrees 19'N; 024 degrees 20'E; 2.8 km dia) Wind-blown sands which cover much of this relatively small feature make it difficult to distinguish from numerous dark sandstone outcrops using only optical images. Radar, however, penetrates the shallow sand mantle to reveal a nearly complete radar-bright bullseye pattern typical of central-uplift style impact structure. Oasis Structure (24 degrees 35'N; 24 degrees 24'E; >11.5 km dia) Oasis astrobleme was originally described as an elevated ring of sandstone some 5.1 km wide in desert sands. Examination of optical satellite images detected subtle concentric patterns more than 11 km across [2]. SIR-C images reveal strong arcuate reflectors buried beneath the sand at an even larger diameter of greater than 17 km. Aurounga (19 degrees 06'N; 019 degrees 15'E; 12.6 km dia) Although this highly circular depression has been noticed in numerous remote sensing studies, eg.[3], it usually has been associated with a large volcanic field and attributed to endogenic forces. Recent reports of shatter cones [4] and microscopic shock metamorphic effects [5] now demonstrate an impact origin. The radar-dark ring is a sand-filled trough which interupts a regional pattern of yardangs, wind-cut parallel ridges and grooves, developed in surrounding sandstones. Amguid (26 degrees 05'N; 004 degrees 23'E; 450 m dia) Situated in elevated rocky highlands [6], the small Amguid crater is nearly overprinted by surrounding radar backscatter. A dry central bowl is partially filled with smoothly surfaced fine-grained playa deposits which absorb radar energy and/or reflect it away from the spacecraft. The result is a distinct radar-dark disk within a bright regional ground clutter. Spider (16 degrees 44'S; 126 degrees 05'E; 13 km dia) Named for a radially splayed fault system in its center, Spider is the exposed root structure of a central-uplift impact feature [7]. Radar slope effects on processed data clearly delineate its size and internal complexity. Henbury craters (24 degrees 35'S; 133 degrees 09'E; largest ca.150 m dia) Although quite small, Henbury crater field [8] appears distinctly radar bright on survey -qualilty imagery. Strong radar backscatter may be due to a combination of impact-disrupted sedimentary horizons and of soil dielectrical properties altered by a significant meteoritic iron content [9]. References: [1] Garvin J. B. and Schnetzler C. C. (1994) GSA Spec. Pap. 293, 249-257. [2] Dietz R. S. and McHone J. F. (1979) Apollo Soyuz Test Proj. Summary Sci. Rept. (2) NASA SP-412, 183-192. [3] Roland N. W. (1976) Geol. Jahrb., Reihe A, 33, 117-131. [4] Becq-Giraudon J. F. et al. (1992) Comptes Rendus de l'Academ. des Sciences, Ser.2, 315, 83-88. [5] Grieve R. A. F. and Therriault A. M. (1995) LPS XXVI, 515-516. [6] Lambert P. et al. (1980) Meteoritics, 15, 157-159. [7] Harms et al. (1980) Nature, 286, 704-706. [8] Milton D. J. (1968) Geol. Surv. Prof. Pap. 599-C, C1-C16. [9] Hodge P. W. and Wright F. W. (1971) JGR, 76, 3880-3895.

Investigation of the Airflow around a Sail.

ERIC Educational Resources Information Center

Gray, Rachel P.

1986-01-01

Shows how air flows around a sail, explaining why a dinghy is able to move toward the wind rather than be blown backwards. Also illustrates the effects of alternating the angle of a sail, using different sail shapes and using a rig consisting of two sails. (JN)

Comparison of the acoustic characteristics of large-scale models of several propulsive-lift concepts

NASA Technical Reports Server (NTRS)

Falarski, M. D.; Aiken, T. N.; Aoyagi, K.; Koenig, D. G.

1974-01-01

Wind-tunnel acoustic investigations were performed to determine the acoustic characteristics and the effect of forward speed on the over-the-wing externally blown jet flap (OTW), the under-the-wing externally blown jet flap (UTW), the internally blown jet flap (IBF), and the augmentor wing (AW). The data presented represent the basic noise generated by the powered-lift system without acoustic treatment, assuming all other noise sources, such as the turbofan compressor noise, have been suppressed. Under these conditions, when scaled to a 100,000-lb aircraft, the OTW concept exhibited the lowest perceived noise levels, because of dominant low-frequency noise and wing shielding of the high-frequency noise. The AW was the loudest configuration, because of dominant high-frequency noise created by the high jet velocities and small nozzle dimensions. All four configurations emitted noise 10 to 15 PNdB higher than the noise goal of 95 PNdB at 500 ft.

Dust storms on Mars: Considerations and simulations

NASA Technical Reports Server (NTRS)

Greeley, R.; White, B. R.; Pollack, J. B.; Iverson, J. D.; Leach, R. N.

1977-01-01

Aeolian processes are important in modifying the surface of Mars at present, and appear to have been significant in the geological past. Aeolian activity includes local and global dust storms, the formation of erosional features such as yardangs and depositional features such as sand dunes, and the erosion of rock and soil. As a means of understanding aeolian processes on Mars, an investigation is in progress that includes laboratory simulations, field studies of earth analogs, and interpretation of spacecraft data. This report describes the Martian Surface Wind Tunnel, an experimental facility established at NASA-Ames Research Center, and presents some results of the general investigation. Experiments dealing with wind speeds and other conditions required for the initiation of particle movement on Mars are described and considerations are given to the resulting effectiveness of aeolian erosion.

Aeolian Landscapes of Titan from Cassini RADAR Reveal Winds, Elevation Constraints and Sediment Characteristics

NASA Astrophysics Data System (ADS)

Radebaugh, J.; Lewis, R. C.; Bishop, B.; Christiansen, E. H.; Kerber, L.; Rodriguez, S.; Narteau, C.; Le Gall, A. A.; Lucas, A.; Malaska, M.

2017-12-01

Similar to terrestrial bodies with atmospheres, a significant portion of the surface of Titan is covered in aeolian landscapes, now imaged by Cassini RADAR at close to 50% coverage. While the compositions of the wind-carried and wind-carved sediments are under discussion, their characteristics, such as being rounded, loose and capable of being saltated, or being fine, soft and forming easily erodible deposits, can be discerned from the geomorphology. Large duneforms are similar to those in Earth's big deserts, formed by particles in strict size and shape limits, and steep, badlands-like morphologies of yardang regions indicate soft rocks with armored features. Shapes and orientations of dunes and yardangs can also reveal wind directions and effects of elevation and topographic obstacles. Recent studies of dunes in the Belet Sand Sea of Titan's equatorial trailing hemisphere reveal dunes are generally wider and with greater spacing near the center, similar to dunes in the Namib Sand Sea of Earth. Dune-to-interdune ratios decrease toward higher latitudes, as was previously observed, and are slightly higher in regions of low elevation, which may relate to elevation affecting winds and sand transport capacity. However, this relationship is not as strong for the Namib. Furthermore, the effects of the location of dunes with respect to sand sea margins on dune parameter values has only begun to be explored. The European ERA-Interim (observations plus model) wind results for the Namib reveal vector sum winds are several degrees away from down the dune long axis, consistent with the fingering mode of dune growth, and allowing for down-axis sand transport. We assume similar model winds for the dunes of Titan. Model winds for the yardangs of the Lut desert of Earth are directly down axis, which means wind directions should be able to be determined in the isolated yardang fields of Titan's northern midlatitudes. Further studies of dune parameters on Titan from Cassini can help reveal the reasons for the extent of the sand seas and how (and whether) sands are transported across them. Further studies of winds and sediment properties of yardangs on Earth will reveal expected winds, material requirements and relative ages of the yardangs with respect to other landforms of Titan.

Role of natural and human factors in the degradation of the environment in central, eastern, and northern Saudi Arabia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alwelaie, A.N.A.

1985-01-01

The roles of natural and human factors in the arid lands have long been a matter of concern to many researchers. This study tries to find out the causes of degradation of natural environments in the central, eastern, and northern parts of Saudi Arabia. The decrease in rainfall leads to increasing aridity and, thus paves the way for greater deterioration of the environment as the carrying capacity of the arid lands decreases. This study determines that human activities have had adverse effects on the arid lands of Saudi Arabia. Causes of degradation of environment in the study area include: (1)more » drought: (2) agricultural malpractice and soil degradation; (3) use of wood for fuel; (4) water wastage; (5) wind-blown sand; (6) pressure of locusts; (7) hunting; (8) societal instability; (9) oil rush and population pressure; (10) management of the environment; (11) overgrazing of pastures. An analysis of people's attitudes towards their environment in relation to their beliefs finds that the attitude of people towards the idea of conservation is not as positive as the attitude of Islam.« less

Geologic map of the Boulder-Fort Collins-Greeley Area, Colorado

USGS Publications Warehouse

Colton, Roger B.

1978-01-01

This digital map shows the geographic extent of rock stratigraphic units (formations) as compiled by Colton in 1976 under the Front Range Urban Corridor Geology Program. Colton used his own geologic mapping and previously published geologic maps to compile one map having a single classification of geologic units. The resulting published color paper map (USGS Map I-855-G, Colton, 1978) was intended for land-use planning and to depict the regional geology. In 1997-1999, another USGS project designed to address urban growth issues was undertaken. This project, the USGS Front Range Infrastructure Resources Project, undertook to digitize Colton's map at 1:100,000 scale, making it useable in Geographical Information Systems (GIS). That product is described here. In general, the digitized map depicts in its western part Precambrian igneous and metamorphic rocks, Pennsylvanian and younger sedimentary rock units, major faults, and brecciated zones along an eastern strip (5-20 km wide) of the Front Range. The central and eastern parts of the map (Colorado Piedmont) show a mantle of Quaternary unconsolidated deposits and interspersed outcrops of sedimentary rock of Cretaceous or Tertiary age. A surficial mantle of unconsolidated deposits of Quaternary age is differentiated and depicted as eolium (wind-blown sand and silt), alluvium (river gravel, sand, and silt of variable composition), colluvium, and a few landslide deposits. At the mountain front, north-trending, Paleozoic and Mesozoic formations of sandstone, shale, and minor limestone dip mostly eastward and form folds, fault blocks, hogbacks and intervening valleys. Local dikes and sills of Tertiary rhyodacite and basalt intrude rocks near the range front, mostly in the Boulder area.

Theory of advection-driven long range biotic transport

USDA-ARS?s Scientific Manuscript database

We propose a simple mechanistic model to examine the effects of advective flow on the spread of fungal diseases spread by wind-blown spores. The model is defined by a set of two coupled non-linear partial differential equations for spore densities. One equation describes the long-distance advectiv...

EXACERBATION OF ATHEROSCLEROSIS FOLLOWING EXPOSURE TO VARIOUS COMBUSTION SOURCE PARTICLES

EPA Science Inventory

Exposure of ApoE knockout (ApoE^-/-) mice to concentrated ambient particles (CAPs) has been shown to increase arterial plaque area and size. CAPs are a complex aerosol mixture consisting of wind-blown dust, emissions from the combustion of fossil fuels, and secondary tr...

CONCENTRATED COARSE AIR PARTICLE EXPOSURE PRODUCES MILD TOXICOLOGICAL EFFECTS IN HEALTHY VOLUNTEERS

EPA Science Inventory

Epidemiological studies have shown that the adverse health effects of ambient particulate matter (PM) exposure to be in general more strongly associated with "fine" PM (<2.5 µM) originating from combustion processes than for "coarse" PM (>2.5 µM) from wind-blown dust, mechanical ...

Quantitative detection of mass concentration of sand-dust storms via wind-profiling radar and analysis of Z- M relationship

NASA Astrophysics Data System (ADS)

Wang, Minzhong; Ming, Hu; Ruan, Zheng; Gao, Lianhui; Yang, Di

2018-02-01

With the aim to achieve quantitative monitoring of sand-dust storms in real time, wind-profiling radar is applied to monitor and study the process of four sand-dust storms in the Tazhong area of the Taklimakan Desert. Through evaluation and analysis of the spatial-temporal distribution of reflectivity factor, it is found that reflectivity factor ranges from 2 to 18 dBz under sand-dust storm weather. Using echo power spectrum of radar vertical beams, sand-dust particle spectrum and sand-dust mass concentration at the altitude of 600 ˜ 1500 m are retrieved. This study shows that sand-dust mass concentration reaches 700 μg/m3 under blowing sand weather, 2000 μg/m3 under sand-dust storm weather, and 400 μg/m3 under floating dust weather. The following equations are established to represent the relationship between the reflectivity factor and sand-dust mass concentration: Z = 20713.5 M 0.995 under floating dust weather, Z = 22988.3 M 1.006 under blowing sand weather, and Z = 24584.2 M 1.013 under sand-dust storm weather. The retrieval results from this paper are almost consistent with previous monitoring results achieved by former researchers; thus, it is implied that wind-profiling radar can be used as a new reference device to quantitatively monitor sand-dust storms.

Coastal dune dynamics in response to excavated foredune notches

NASA Astrophysics Data System (ADS)

Ruessink, B. G.; Arens, S. M.; Kuipers, M.; Donker, J. J. A.

2018-04-01

Dune management along developed coasts has traditionally focussed on the suppression of the geomorphic dynamics of the foredune to improve its role in sea defence. Because a stabilized foredune acts as an almost total barrier to aeolian transport from the beach, the habitat diversity in the more landward dunes has degraded. With the overarching objective to mitigate this undesirable loss in biodiversity, dune management projects nowadays increasingly intend to restore aeolian dynamics by reconnecting the beach-dune system with notches excavated through the foredune. Here, we use repeat topographic survey data to examine the geomorphic response of a coastal dune system in the Dutch National Park Zuid-Kennemerland to five notches excavated in 2012-2013 within an 850-m stretch of the 20-m high established foredune. The notches were dug in a V-shape (viewed onshore), with a width between approximately 50 and 100 m at the top, a (cross-dune) length between 100 and 200 m, and excavation depths between 9 and 12.5 m. The 1 × 1 m digital terrain models, acquired with airborne Lidar and UAV photogrammetry, illustrate that during the 3-year survey period the notches developed into a U-shape because of wall deflation, and that up to 8-m thick and 150-m long depositional lobes formed landward of the notches. Sand budget computations showed that the sand volume of the entire study area increased by about 22,750 m3/year, which, given the 850-m width of the study area, corresponds to an aeolian input from the beach of approximately 26.5 m3/m/year. Between 2006 and 2012 all wind-blown beach sand deposited on the seaward side of the foredune; since 2013, the notches have caused 75% of the sand to be deposited landward of the foredune. This highlights that the notches are highly effective conduits for aeolian transport into the back dunes. Future monitoring is required to determine for how long the notches will stimulate aeolian dynamics and if (and when) vegetation eventually starts to regrow and enforces the degeneration of the notches.

The role of interfacial water layer in atmospherically relevant charge separation

NASA Astrophysics Data System (ADS)

Bhattacharyya, Indrani

Charge separation at interfaces is important in various atmospheric processes, such as thunderstorms, lightning, and sand storms. It also plays a key role in several industrial processes, including ink-jet printing and electrostatic separation. Surprisingly, little is known about the underlying physics of these charging phenomena. Since thin films of water are ubiquitous, they may play a role in these charge separation processes. This talk will focus on the experimental investigation of the role of a water adlayer in interfacial charging, with relevance to meteorologically important phenomena, such as atmospheric charging due to wave actions on oceans and sand storms. An ocean wave generates thousands of bubbles, which upon bursting produce numerous large jet droplets and small film droplets that are charged. In the 1960s, Blanchard showed that the jet droplets are positively charged. However, the charge on the film droplets was not known. We designed an experiment to exclusively measure the charge on film droplets generated by bubble bursting on pure water and aqueous salt solution surfaces. We measured their charge to be negative and proposed a model where a slight excess of hydroxide ions in the interfacial water layer is responsible for generating these negatively charged droplets. The findings from this research led to a better understanding of the ionic disposition at the air-water interface. Sand particles in a wind-blown sand layer, or 'saltation' layer, become charged due to collisions, so much so, that it can cause lightning. Silica, being hydrophilic, is coated with a water layer even under low-humidity conditions. To investigate the importance of this water adlayer in charging the silica surfaces, we performed experiments to measure the charge on silica surfaces due to contact and collision processes. In case of contact charging, the maximum charge separation occurred at an optimum relative humidity. On the contrary, in collisional charging process, no humidity effect was observed. We proposed an ion transfer mechanism in case of contact charging. However, an electron transfer mechanism explained the collisional charging process. The effects of temperature, surface roughness, and chemical nature of surface were also studied for both contact and collisional charging processes.

Difference in the wind speeds required for initiation versus continuation of sand transport on mars: implications for dunes and dust storms.

PubMed

Kok, Jasper F

2010-02-19

Much of the surface of Mars is covered by dunes, ripples, and other features formed by the blowing of sand by wind, known as saltation. In addition, saltation loads the atmosphere with dust aerosols, which dominate the Martian climate. We show here that saltation can be maintained on Mars by wind speeds an order of magnitude less than required to initiate it. We further show that this hysteresis effect causes saltation to occur for much lower wind speeds than previously thought. These findings have important implications for the formation of dust storms, sand dunes, and ripples on Mars.

Earth observations taken by the STS-59 crew

NASA Image and Video Library

1994-04-14

STS059-306-034 (9-20 April 1994) --- The radiating transportation pattern of this 20th-Century urban plan is nicely displayed in this high-resolution photograph. Light-toned spots in the desert mark oil well sites; along the south edge of the scene, some dark residue remains from the fires set during the recent Gulf War. Blown sand has nearly hidden the soot and thick oil that were deposited on the surface. Nikon photograph, 300mm lens.

Morphodynamics of Planetary Deserts: A Laboratory Approach

NASA Astrophysics Data System (ADS)

Garcia, A.; Courrech Du Pont, S.; Rodriguez, S.

2014-12-01

Earth deserts show a rich variety of dune shapes from transverse to barchan, star and linear dunes depending on the history of wind regimes (strength and variability) and sand availability [1]. In desert, exposed to one wind direction, dunes perpendicular to the wind direction are found to be transverse or barchans, only sand availability plays a key role on their formation and evolution. However, the evolution time scale of such structures (several years) limits our investigation of their morphodynamics understanding. We use here, a laboratory experiment able to considerably reduce space and time scales by reproducing millimeter to centimeter subaqueous dunes by controlling environmental parameters such as type of wind (multi-winds, bimodal, quasi-bimodal or unidirectional wind) and amount of sediment [2,3]. This set up allows us to characterize more precisely the different modes of dune formation and long-term evolution, and to constrain the physics behind the morphogenesis and dynamics of dunes. Indeed, the formation, evolution and transition between the different dune modes are better understood and quantified thanks to a new setting experiment able to give a remote sediment source in continuous (closer to what happens in terrestrial desert): a sand distributor that controls the input sand flow. Firstly, in a one wind direction conditions, we managed to follow and quantify the growth of the instability of transverse dunes that break into barchans when the sand supply is low and reversely when the sand supply is higher, barchan fields evolve to bars dunes ending to form transverse. The next step will be to perform experiments under two winds conditions in order to better constrain the formation mode of linear dunes, depending also only on the input sand flux. Previous experiments shown that linear "finger" dunes can be triggered by the break of transverse dunes and then the elongating of one barchan's arm [4]. These studies can farther explain more precisely in different wind history and sand supply, these patterns state that should emerge and, by applying the relevant scale law, to apply this laboratory work to terrestrial and planetary (Mars and Titan) desert dynamics. [1] Bagnold R.A. (1941). [2] Hersen P. (2004). [3] Reffet E. (2010). [4] Courrech Du Pont S. et al. (2014).

The effects of psammophilous plants on sand dune dynamics

NASA Astrophysics Data System (ADS)

Bel, Golan; Ashkenazy, Yosef

2014-07-01

Mathematical models of sand dune dynamics have considered different types of sand dune cover. However, despite the important role of psammophilous plants (plants that flourish in moving-sand environments) in dune dynamics, the incorporation of their effects into mathematical models of sand dunes remains a challenging task. Here we propose a nonlinear physical model for the role of psammophilous plants in the stabilization and destabilization of sand dunes. There are two main mechanisms by which the wind affects these plants: (i) sand drift results in the burial and exposure of plants, a process that is known to result in an enhanced growth rate, and (ii) strong winds remove shoots and rhizomes and seed them in nearby locations, enhancing their growth rate. Our model describes the temporal evolution of the fractions of surface cover of regular vegetation, biogenic soil crust, and psammophilous plants. The latter reach their optimal growth under either (i) specific sand drift or (ii) specific wind power. The model exhibits complex bifurcation diagrams and dynamics, which explain observed phenomena, and it predicts new dune stabilization scenarios. Depending on the climatological conditions, it is possible to obtain one, two, or, predicted here for the first time, three stable dune states. Our model shows that the development of the different cover types depends on the precipitation rate and the wind power and that the psammophilous plants are not always the first to grow and stabilize the dunes.

Space Radar Image of Pinacate Volcanic Field, Mexico

NASA Technical Reports Server (NTRS)

1994-01-01

This spaceborne radar image shows the Pinacate Volcanic Field in the state of Sonora, Mexico, about 150 kilometers (93 miles) southeast of Yuma, Arizona. The United States/Mexico border runs across the upper right corner of the image. More than 300 volcanic vents occur in the Pinacate field, including cinder cones that experienced small eruptions as recently as 1934. The larger circular craters seen in the image are a type of volcano known as a 'maar', which erupts violently when rising magma encounters groundwater, producing highly pressurized steam that powers explosive eruptions. The highest elevations in the volcanic field, about 1200 meters (4000 feet), occur in the 'shield volcano' structure shown in bright white, occupying most of the left half of the image. Numerous cinder cones dot the flanks of the shield. The yellow patches to the right of center are newer, rough-textured lava flows that strongly reflect the long wavelength radar signals. Along the left edge of the image are sand dunes of the Gran Desierto. The dark areas are smooth sand and the brighter brown and purple areas have vegetation on the surface. Radar data provide a unique means to study the different types of lava flows and wind-blown sands. This image was acquired by Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) onboard the space shuttle Endeavour on April 18, 1994. The image is 57 kilometers by 48 kilometers (35 miles by 30 miles) and is centered at 31.7 degrees north latitude, 113.4 degrees West longitude. North is toward the upper right. The colors are assigned to different radar frequencies and polarizations of the radar as follows: red is L-band, horizontally transmitted and received; green is L-band, horizontally transmitted, vertically received; and blue is C-band, horizontally transmitted, vertically received. SIR-C/X-SAR, a joint mission of the German, Italian, and United States space agencies, is part of NASA's Mission to Planet Earth.

A hydrodynamical model of the circumstellar bubble created by two massive stars

NASA Astrophysics Data System (ADS)

van Marle, A. J.; Meliani, Z.; Marcowith, A.

2012-05-01

Context. Numerical models of the wind-blown bubble of massive stars usually only account for the wind of a single star. However, since massive stars are usually formed in clusters, it would be more realistic to follow the evolution of a bubble created by several stars. Aims: We develop a two-dimensional (2D) model of the circumstellar bubble created by two massive stars, a 40 M⊙ star and a 25 M⊙ star, and follow its evolution. The stars are separated by approximately 16 pc and surrounded by a cold medium with a density of 20 particles per cm3. Methods: We use the MPI-AMRVAC hydrodynamics code to solve the conservation equations of hydrodynamics on a 2D cylindrical grid using time-dependent models for the wind parameters of the two stars. At the end of the stellar evolution (4.5 and 7.0 million years for the 40 and 25 M⊙ stars, respectively), we simulate the supernova explosion of each star. Results: Each star initially creates its own bubble. However, as the bubbles expand they merge, creating a combined, aspherical bubble. The combined bubble evolves over time, influenced by the stellar winds and supernova explosions. Conclusions: The evolution of a wind-blown bubble created by two stars deviates from that of the bubbles around single stars. In particular, once one of the stars has exploded, the bubble is too large for the wind of the remaining star to maintain and the outer shell starts to disintegrate. The lack of thermal pressure inside the bubble also changes the behavior of circumstellar features close to the remaining star. The supernovae are contained inside the bubble, which reflects part of the energy back into the circumstellar medium. Movies are available in electronic form at http://www.aanda.org

A study of global sand seas

USGS Publications Warehouse

McKee, Edwin D.

1979-01-01

The birth of the idea that led to this publication on "Global Sand Seas" dates back to the late 1920's. At that time I was engaged in a study of the Coconino Sandstone of Arizona's Grand Canyon. Considerable controversy existed then as to whether this sandstone was a subaqueous deposit or was composed of wind-formed dunes. It became apparent that definitive literature was sparse or lacking on types of dunes, global distribution of these types, the mechanics of their development, the precise nature of their internal structure of cross-stratificiation, and the relation of wind systems to these sand forms. Especially lacking were data on criteria that could confidently be used in the recognition of ancient dunes. The common denominator in this publication is eolian sand bodies. Although the book is concerned primarily with desert sand seas, the subject matter is not restricted to deserts; it includes many references to deposits of coastal sand and to sand bodies in humid climates. Nor does the book deal exclusively with dunes, which, according to most definitions, involve mounds or hills. Many references are made to sand sheets, sand stringers, and other types of sand deposits that have no prominent topographic expression. All sand bodies accumulated by the action of wind are discussed. Chapters A-J of this publication are primarily topical. Chapters cover the grain texture, the color, and the structure of modern dunes and other eolian sands. Special treatment is given to the relation of wind data to dune interpretation, the evolution of form in current-deposited sand bodies as determined from experimental studies, and the discriminant analysis technique for differentiating between coastal and inland desert sands. This topical part of the publication also includes an analysis of criteria used in ancient deposits to interpret their eolian genesis and a consideration of economic application of the principles described, including a discussion of potentials and problems associated with eolian hydrocarbon reservoirs. The final chapters present a discussion of the morphology and distribution of dunes as determined largely from Landsat images.Chapter K of the publication is devoted to descriptions of major sand seas based largely on thematic maps derived from Landsat (ERTS) mosaics. Although inclusion herein of the actual mosaics proved to be impractical, the maps derived from them do show the distribution and abundance of various dune types and the relations of these types to certain associated features, such as bedrock, water bodies, and juxtaposed dunes. Furthermore, sand roses included with each of these maps enable the user to draw conclusions on the probable relations of wind strength and direction to dune type in a particular area.Regional studies (chapter K) were a team effort. Analysis of the Landsat (ERTS) mosaics and mapping boundaries of individual dune types were by Carol Breed. Synthesis of the rather voluminous literature and preparation of abstracts covering it was by Camilla MacCauley. Actual preparation of maps was by Franci Lennartz and later by Sarah Andrews. The gathering of data on wind, the calculation of wind roses, and the interpretation of their relations to sand bodies were by Steven Fryberger, assisted by Gary Dean.

An efficient, self-orienting, vertical-array, sand trap

NASA Astrophysics Data System (ADS)

Hilton, Michael; Nickling, Bill; Wakes, Sarah; Sherman, Douglas; Konlechner, Teresa; Jermy, Mark; Geoghegan, Patrick

2017-04-01

There remains a need for an efficient, low-cost, portable, passive sand trap, which can provide estimates of vertical sand flux over topography and within vegetation and which self-orients into the wind. We present a design for a stacked vertical trap that has been modelled (computational fluid dynamics, CFD) and evaluated in the field and in the wind tunnel. The 'swinging' trap orients to within 10° of the flow in the wind tunnel at 8 m s-1, and more rapidly in the field, where natural variability in wind direction accelerates orientation. The CFD analysis indicates flow is steered into the trap during incident wind flow. The trap has a low profile and there is only a small decrease in mass flow rate for multiple traps, poles and rows of poles. The efficiency of the trap was evaluated against an isokinetic sampler and found to be greater than 95%. The centre pole is a key element of the design, minimally decreasing trap efficiency. Finally, field comparisons with the trap of Sherman et al. (2014) yielded comparable estimates of vertical sand flux. The trap described in this paper provides accurate estimates of sand transport in a wide range of field conditions.

Maps Showing Composition of Surficial Sediments on the Insular Shelf of Southwestern Puerto Rico

USGS Publications Warehouse

Shideler, Gerald L.

1980-01-01

The limited availability of onshore sand deposits for use in construction appears to be a future major problem in Puerto Rico (U.S. Bureau of Mines, 1972; Committee on Puerto Rico and the Sea, 1974). Consequently, the mining of offshore sand deposits as supplemental sources of construction aggregate may becom e necessary. For this reason, the U.S. Geological Survey and the Department of Natural Resources of the Commonwealth of Puerto Rico have conducted investigations of potential offshore sand deposits on the Puerto Rico insular shelf. This report provides information on the composition of surficial sediments on the southwestern Puerto Rico shelf (fig. 1), an area that may be one of the more favorable potential sites for offshore sand resources. Water depths over most of the study area are less than 22 meters (m). The sea floor is composed of live and dead patch and fringing reefs, areas of rock exposures, and sedim ent-covered areas. The adjacent coastline includes prominent embaym ents and a conspicuous rock promontory (Cabo Rojo) connected by a tombolo to the mainland of Puerto Rico. The study area is in the belt of northeast trade winds. Waves approach the coast predominantly from the southeast, resulting in a predominantly westward littoral drift along the south coast (Grove and Trumbull, 1978). Local sand movement on the southern shelf is shown by an active sand wave field south of Bah1a Sucia in which the sand wave crests have migrated toward the southwest (Grove and Trumbull, 1978). The presence of the sand wave field suggests that large volumes of sand having potential for mining are locally present in the study area.

Lower Jurassic Navaho-Aztec-Equivalent Sandstones in southern Arizona and their paleogeographic significance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bilodeau, W.L.; Keith, S.B.

1986-06-01

Thick sequences of Lower Jurassic rhyolitic and andesitic volcanic rocks in several mountain ranges of southern Arizona contain interbedded quartzarenites. Locally up to 250 m thick, these sandstone lenses, composed of well-sorted and well-rounded quartz grains, commonly contain large-scale cross-stratification and are considered to be eolian sand deposits. The eolian sands were blown up against the continental side of the Early Jurassic volcanic arc that trended northwest-southeast across the southwestern margin of the North American continent and/or plate at that time. Paleocurrent data suggest southerly eolian transport of the sands from the Colorado Plateau area. Correlation of these sandstones withmore » the Lower Jurassic Navaho and Aztec Sandstones is indicated by the paleocurrent data as well as radiometric dating of the interbedded volcanics. Eolian sand transport southward across central Arizona in the Early Jurassic indicates that the Mogollon highlands either did not then exist, or were merely low, discontinuous inselbergs on a broad back-arc ramp, more appropriately called the Mogollon slope.« less

Formation of Bipolar Lobes by Jets

NASA Astrophysics Data System (ADS)

Soker, Noam

2002-04-01

I conduct an analytical study of the interaction of jets, or a collimated fast wind (CFW), with a previously blown asymptotic giant branch (AGB) slow wind. Such jets (or CFWs) are supposedly formed when a compact companion, a main-sequence star, or a white dwarf accretes mass from the AGB star, forms an accretion disk, and blows two jets. This type of flow, which I think shapes bipolar planetary nebulae (PNs), requires three-dimensional gasdynamical simulations, which are limited in the parameter space they can cover. By imposing several simplifying assumptions, I derive simple expressions which reproduce some basic properties of lobes in bipolar PNs and which can be used to guide future numerical simulations. I quantitatively apply the results to two proto-PNs. I show that the jet interaction with the slow wind can form lobes which are narrow close to, and far away from, the central binary system, and which are wider somewhere in between. Jets that are recollimated and have constant cross section can form cylindrical lobes with constant diameter, as observed in several bipolar PNs. Close to their source, jets blown by main-sequence companions are radiative; only further out they become adiabatic, i.e., they form high-temperature, low-density bubbles that inflate the lobes.

Hydrological change during the last 600 years as observed from landscape analysis and historical maps: a case study from the Nete catchment, Campine area, NE-Belgium

NASA Astrophysics Data System (ADS)

Beerten, Koen; Leterme, Bertrand

2015-04-01

Reliably predicting the future state of the hydrological system under transient climate and land use conditions is a major challenge. Hydrological models are usually calibrated and validated for a short time period (e.g. 30 years), for conditions that are similar to today's. In order to test model performance for future (unverifiable) projections, palaeohydrological modelling is first needed to build confidence in model output under different conditions. One of the major challenges of palaeohydrological modelling is the acquisition of verification data that is representative for the past state(s) of the hydrological system. Here, we present the reconstructed evolution of the groundwater table depth over the last six centuries, in a sandy interfluvium (20 km² with altitude varying between 16 m and 28 m a.s.l.) of the Nete catchment. For periods before 1770 AD, the altitude (depth) of blown-out surfaces in the drift sand landscape is used as a proxy for the average highest groundwater level. These surfaces are generally interpreted as the lower limit for wind erosion. Soil profiles investigations where these surfaces are overblown by younger drift sand show that they were created in the time period between ca. 1400 AD and 1600 AD. For younger periods, historical maps were analysed for the presence of surface water features, such as fens (shallow lakes that are groundwater fed in this sandy landscape under temperate climate), marshes and wetlands. The results clearly show declining water levels in the second half of the 19th century, i.e., between 1854 AD and 1909 AD. The decline is most pronounced for the higher areas of the interfluve (drift sand landscape) and becomes less clear towards the floodplains. The amount of groundwater level decline is 1-2 m on average. The cause for the synchronous groundwater level drop seems to be linked to land use and land cover changes during that period. In the time interval between 1854 AD and 1909 AD, the total length of drains increased from 2 km to 25 km, while land cover changed from 80% heathland and almost no trees to only 20% heathland and 50% coniferous forest. Available palaeoclimate records suggest that there is no correlation between groundwater level change and average annual temperature or precipitation. Furthermore, population density seems to be uncorrelated with the observed hydrological changes. Internal consistency checks are performed and found satisfactory. For example, the high groundwater levels predicted by the blown-out surfaces for 1400-1600 AD are confirmed by surface water features on younger historical maps (~1770 AD and ~1850 AD). Indeed, pollen analysis, topographical maps and climate records show that land cover and climate did not change significantly throughout the period 1400 AD to 1850 AD. We conclude that the proposed methods are useful tools to gather verification data (i.e., groundwater table depth) for palaeohydrological modelling in the European sand belt during the last millenium.

Vegetated dune morphodynamics during recent stabilization of the Mu Us dune field, north-central China

NASA Astrophysics Data System (ADS)

Xu, Zhiwei; Mason, Joseph A.; Lu, Huayu

2015-01-01

The response of dune fields to changing environmental conditions can be better understood by investigating how changing vegetation cover affects dune morphodynamics. Significant increases in vegetation and widespread dune stabilization over the years 2000-2012 are evident in high-resolution satellite imagery of the Mu Us dune field in north-central China, possibly a lagged response to changing wind strength and temperature since the 1970s. These trends provide an opportunity to study how dune morphology changes with increasing vegetation stabilization. Vegetation expansion occurs mainly by expansion of pre-existing patches in interdunes. As vegetation spreads from interdunes onto surrounding dunes, it modifies their shapes in competition with wind-driven sand movement, primarily in three ways: 1) vegetation anchoring horns of barchans transforms them to parabolic dunes; 2) vegetation colonizes stoss faces of barchan and transverse dunes, resulting in lower dune height and an elongated stoss face, with shortening of barchan horns; and 3) on transverse dunes, the lee face is fixed by plants that survive sand burial. Along each of these pathways of stabilization, dune morphology tends to change from more barchanoid to more parabolic forms, but that transformation is not always completed before full stabilization. Artificial stabilization leads to an extreme case of "frozen" barchans or transverse dunes with original shapes preserved by rapid establishment of vegetation. Observations in the Mu Us dune field emphasize the point that vegetation growth and aeolian sand transport not only respond to external factors such as climate but also interact with each other. For example, some barchans lose sand mass during vegetation fixation, and actually migrate faster as they become smaller, and vegetation growth on a barchan's lower stoss face may alter sand transport over the dune in a way that favors more rapid stabilization. Conceptual models were generalized for the development of vegetation-stabilized dunes, which should be helpful in better understanding of vegetated dune morphology, model verification and prediction, and guiding practical dune stabilization efforts.

The many sides of RCW 86: a Type Ia supernova remnant evolving in its progenitor's wind bubble

NASA Astrophysics Data System (ADS)

Broersen, Sjors; Chiotellis, Alexandros; Vink, Jacco; Bamba, Aya

2014-07-01

We present the results of a detailed investigation of the Galactic supernova remnant RCW 86 using the XMM-Newton X-ray telescope. RCW 86 is the probable remnant of SN 185 A.D., a supernova that likely exploded inside a wind-blown cavity. We use the XMM-Newton Reflection Grating Spectrometer to derive precise temperatures and ionization ages of the plasma, which are an indication of the interaction history of the remnant with the presumed cavity. We find that the spectra are well fitted by two non-equilibrium ionization models, which enables us to constrain the properties of the ejecta and interstellar matter plasma. Furthermore, we performed a principal component analysis on EPIC MOS and pn data to find regions with particular spectral properties. We present evidence that the shocked ejecta, emitting Fe K and Si line emission, are confined to a shell of approximately 2 pc width with an oblate spheroidal morphology. Using detailed hydrodynamical simulations, we show that general dynamical and emission properties at different portions of the remnant can be well reproduced by a Type Ia supernova that exploded in a non-spherically symmetric wind-blown cavity. We also show that this cavity can be created using general wind properties for a single degenerate system. Our data and simulations provide further evidence that RCW 86 is indeed the remnant of SN 185, and is the likely result of a Type Ia explosion of single degenerate origin.

Soft Soil Mobility

DTIC Science & Technology

2016-02-11

Wind speed ± 2 knots (kts), 3 km/hr, 1 meter per second (m/s), or ± 5% of reading (whichever is higher) Wind direction ± 7 degrees NOTE: Values...longitudinal sand grades are located in an alluvial plain that lies next to Highway 95. The course material is, soft, loose, dry, wind sorted beach...particles. These soils are easily moved by wind action and tend to build extensive low dunes. The sand dynamometer terrain is described as sandy

Comparative dose-response assessment of various combustion source particles to indcue acute lung-injury and exacerbate atherosclerosis in ApoE-Mice

EPA Science Inventory

Exposure to concentrated ambient particles (CAPs) has been shown to increase arterial plaque area and size in atherosclerosis susceptible mice. CAPs are a complex aerosol mixture consisting of wind-blown dust. emissions from the combustion of fossil fuels, and secondary transform...

The Plains are Not Plain

NASA Image and Video Library

2016-06-01

This image from NASA Mars Reconnaissance Orbiter spacecraft covers some of the plains south of Capri Chasma in eastern Valles Marineris. Where the aeolian (wind-blown) sedimentary cover has been stripped away, we see diverse colors indicative of of a variety of altered minerals formed in Mars' wetter past. http://photojournal.jpl.nasa.gov/catalog/PIA20730

Orographic precipitation, wind-blown snow, and landscape evolution in glaciated mountain ranges

NASA Astrophysics Data System (ADS)

Brocklehurst, S. H.; Rowan, A. V.; Plummer, M. A.; Foster, D.; Schultz, D. M.; MacGregor, K. R.

2011-12-01

Orographic precipitation and wind-blown snow appear to significantly influence the evolution of glaciated mountain ranges, and in narrow ranges the effect is opposite from orographic precipitation in non-glaciated ranges. While fluvially-eroded ranges tend to be exhumed more on the windward side, glacially-eroded ranges can experience greater erosion on the leeward side. On the timescale of an individual glaciation, the distribution of precipitation and settling is a key component of glacier mass balance and ice extent, while on longer timescales, the interaction of precipitation and topography can play a major role in landscape evolution and range morphology. Numerical modelling of last glacial maximum (LGM) ice extents for catchments on the eastern side of the Southern Alps, New Zealand, highlights the importance of the distribution of precipitation. The accumulation areas of the glaciers would have experienced much greater precipitation than lower elevations, because of the pronounced orographic precipitation gradient, so glacier length is very sensitive to the precipitation distribution employed for any given temperature change. This is particularly challenging given the lack of modern snow monitoring at high altitudes within the Southern Alps, the likelihood of steep accumulation gradients amongst high topography, below the resolution of current datasets, and the difficulty of extrapolating modern values to the LGM. The Sangre de Cristo Range, southern Colorado, and the Bitterroot Range on the Idaho-Montana border both run close to north-south, cross-cutting the prevailing westerly winds. Drainage basins on both sides of the ranges cover similar areas, but moraines are much more substantial on the eastern sides, indicating greater glacial incision, which we suggest at least partly reflects snow blown over the range crest. The Uinta Mountains, Utah, run west-east, parallel to prevailing winds, and show topographic asymmetry across individual catchments, rather than at the range scale. Rapid rock uplift and significant glacial erosion of the north-south Teton Range, Wyoming, has created some of the highest relief in the conterminous US. While an initial topographic asymmetry would have arisen from the tectonic gradient imposed by the extensional Teton Fault on the east side of the range, the topographic asymmetry would have been exaggerated by feedbacks associated with glacial erosion. Slowly-falling snow would have been advected further into the range by prevailing westerlies, which would also have redistributed fallen snow from the subdued topography typical of the headwaters of west-draining basins. Greater topographic shading and cover by rock debris would have mitigated ablation of eastern glaciers bounded by high valley walls. Glacier size, ice flux and erosion would therefore have been enhanced in eastern-draining basins, though only the largest glaciers were capable of eroding at rates that kept pace with rock uplift. Preliminary numerical modelling results are consistent with these inferences of the importance of orographic precipitation and wind-blown snow based on topographic analysis.

Vector thrust induced lift effects for several ejector exhaust locations on a V/STOL wind tunnel model at forward speed

NASA Technical Reports Server (NTRS)

Sharon, A. D.

1975-01-01

The results and analysis of aerodynamic force data obtained from a small scale model of a V/STOL research vehicle in a low speed wind tunnel are presented. The analysis of the data includes the evaluation of aerodynamic-propulsive lift performance when operating twin ejector nozzles with thrust deflected. Three different types of thrust deflector systems were examined: 90 deg downward deflected nozzle, 90 deg slotted nozzle with boundary layer control, and an externally blown flap configuration. Several nozzle locations were tested, including over and underwing positions. The interference lift of the nacelle and model due to jet exhaust thrust is compared and results show that 90 deg turned nozzles located over the wing (near the trailing edge) produce the largest interference lift increment for an untrimmed aircraft, and that the slotted nozzle located under the wing near the trailing edge (in conjunction with a BLC flap) gives a comparable interference lift in the trimmed condition. The externally blown flap nozzle produced the least interference lift and significantly less total lift due to jet thrust effects.

Acoustic characteristics of a large-scale wind tunnel model of an upper-surface blown flap transport having two engines

NASA Technical Reports Server (NTRS)

Falarski, M. D.; Aoyagi, K.; Koenig, D. G.

1973-01-01

The upper-surface blown (USB) flap as a powered-lift concept has evolved because of the potential acoustic shielding provided when turbofan engines are installed on a wing upper surface. The results from a wind tunnel investigation of a large-scale USB model powered by two JT15D-1 turbofan engines are-presented. The effects of coanda flap extent and deflection, forward speed, and exhaust nozzle configuration were investigated. To determine the wing shielding the acoustics of a single engine nacelle removed from the model were also measured. Effective shielding occurred in the aft underwing quadrant. In the forward quadrant the shielding of the high frequency noise was counteracted by an increase in the lower frequency wing-exhaust interaction noise. The fuselage provided shielding of the opposite engine noise such that the difference between single and double engine operation was 1.5 PNdB under the wing. The effects of coanda flap deflection and extent, angle of attack, and forward speed were small. Forward speed reduced the perceived noise level (PNL) by reducing the wing-exhaust interaction noise.

Low Albedo Surfaces and Eolian Sediment: Mars Orbiter Camera Views of Western Arabia Terra Craters and Wind Streaks

NASA Technical Reports Server (NTRS)

Edgett, Kenneth S.

2001-01-01

High spatial resolution (1.5 to 12 m/pixel) Mars Global Surveyor Mars Orbiter Camera images obtained September 1997 through June 2001 indicate that the large, dark wind streaks of western Arabia Terra each originate at a barchan dune field on a crater floor. The streaks consist of a relatively thin coating of sediment deflated from the dune fields and their vicinity. This sediment drapes a previous mantle that more thickly covers nearly all of western Arabia Terra. No dunes or eolian bedforms are found within the dark wind streaks, nor do any of the intracrater dunes climb up crater walls to provide sand to the wind streaks. The relations between dunes, wind streak, and subjacent terrain imply that dark-toned grains finer than those which comprise the dunes are lifted into suspension and carried out of the craters to be deposited on the adjacent terrain. Such grains are most likely in the silt size range (3.9-62.5 micrometers). The streaks change in terms of extent, relative albedo, and surface pattern over periods measured in years, but very little evidence for recent eolian activity (dust plumes, storms, dune movement) has been observed.

Steam and air co-injection in removing residual TCE in unsaturated layered sandy porous media.

PubMed

Peng, Sheng; Wang, Ning; Chen, Jiajun

2013-10-01

Steam and air co-injection is a promising technique for volatile and semi-volatile organic contaminant remediation in heterogeneous porous media. In this study, removal of trichloroethene (TCE) with steam-air co-injection was investigated through a series of 2D sandbox experiments with different layered sand structures, and through numerical simulations. The results show that a layered structure with coarse sand, in which steam and air convection are relatively rapid, resulted in a higher removal rate and a larger removal ratio than those observed in an experiment using finer sand; however, the difference was not significant, and the removal ratios from three experiments ranged from 85% to 94%. Slight downward movement of TCE was observed for Experiment 1 (TCE initially in a fine sand zone encased in a coarse sand), while no such movement was observed for Experiment 2 (TCE initially in two fine sand layers encased in a coarse sand) or 3 (TCE initially in a silty sand zone encased in a coarse sand). Simulations show accumulation of TCE at the interface of the layered sands, which indicates a capillary barrier effect in restraining the downward movement of TCE. This effect is illustrated further by a numerical experiment with homogeneous coarse sand, in which continuous downward TCE movement to the bottom of the sandbox was simulated. Another numerical experiment with higher water saturation was also conducted. The results illustrate a complicated influence of water saturation on TCE removal in a layered sand structure. Published by Elsevier B.V.

Deceleration efficiencies of shrub windbreaks in a wind tunnel

NASA Astrophysics Data System (ADS)

Wu, Xiaoxu; Zou, Xueyong; Zhou, Na; Zhang, Chunlai; Shi, Sha

2015-03-01

Artemisia and Salix are dominant shrub species for windbreaks in arid areas of China, and they show similar features to shrubs in other arid areas of the world. We compared the mean velocity fields and shelter effects of two shrub windbreaks with different layouts. For a single plant of Artemisia, the higher the free airflow velocity is, the more the wind velocity around two sides of the plant increases. The velocity gradient around a single plant of Salix is smaller than that around an Artemisia plant due to the difference in the plant shapes. Seven new velocity zones in the horizontal direction appear when airflow passes through an Artemisia windbreak, including four deceleration zones and three acceleration zones. The mean velocity field that is affected by a Salix windbreak can be divided into a deceleration zone in the front, an acceleration zone above, a vortex zone behind and a restoration zone downwind of the vortex zone. Shelter effects of the shrub windbreaks vary with the wind velocity and are influenced by the construct of the windbreaks. Shrub windbreaks that have a complex construction have better shelter effects than simple ones. The shelter effects of plant windbreaks are also influenced by the growth features of the plants. Considering the plant characteristics and the shelter effects of Salix and Artemisia windbreaks, it is optimal to plant these two windbreaks together in a sand-control system. This research is intended to be useful for sand movement control in arid areas.

Barchan Pac-Man

NASA Image and Video Library

2018-05-14

This image from NASA's Mars Reconnaissance Orbiter shows barchan sand dunes, common on Mars and often forming vast dune fields within very large (tens to hundreds of kilometers) impact basins. The regions upwind of barchans are usually devoid of sandy bedforms, so if you were walking in a downwind direction, then the barchans would seem to appear out of nowhere. As you walk downwind, you would notice the barchans link up ("joining arms") and eventually slope into featureless sand sheets. We call this progression of dunes a "Herschel-type dune field" named after the first place this sequence was described: Herschel Crater. But here is something interesting: a barchan dune filling the upwind portion of a small impact crater in a Pac-Man-like shape. This "dune-in-a-crater" is nearly at the highest extent of the field. It is also probably a rare configuration, and over the next few tens of thousands of years the sand will be blown out of the crater. https://photojournal.jpl.nasa.gov/catalog/PIA22456

Eolian features in the Western Desert of Egypt and some applications to Mars.

USGS Publications Warehouse

El-Baz, F.; Breed, C.S.; Grolier, M.J.; McCauley, J.F.

1979-01-01

Relations of landform types to wind regimes, bedrock composition, sediment supply, and topography are shown by field studies and satellite photographs of the Western Desert. This desert provides analogs of Martian wind-formed features and sand dunes, alternating light and dark streaks, knob 'shadows' and yardangs. Surface particles have been segregated by wind into dunes, sand sheets, and light streaks, that can be differentiated by their grain size distributions, surface shapes, and colors. Throughgoing sand of mostly fine to medium grain size is migrating S in longitudinal dune belts and barchan chains whose long axes lie parallel to the prevailing W winds, but topographic variations such as scarps and depressions strongly influence the zones of deposition and dune morphology. -from Authors

Collimated Outflow Formation via Binary Stars: Three-Dimensional Simulations of Asymptotic Giant Branch Wind and Disk Wind Interactions

NASA Astrophysics Data System (ADS)

García-Arredondo, F.; Frank, Adam

2004-01-01

We present three-dimensional hydrodynamic simulations of the interaction of a slow wind from an asymptotic giant branch (AGB) star and a jet blown by an orbiting companion. The jet or ``collimated fast wind'' is assumed to originate from an accretion disk that forms via Bondi accretion of the AGB wind or Roche lobe overflow. We present two distinct regimes in the wind-jet interaction determined by the ratio of the AGB wind to jet momentum flux. Our results show that when the wind momentum flux overwhelms the flux in the jet, a more disordered outflow results with the jet assuming a corkscrew pattern and multiple shock structures driven into the AGB wind. In the opposite regime, the jet dominates and will drive a highly collimated, narrow-waisted outflow. We compare our results with scenarios described by Soker & Rappaport and extrapolate to the structures observed in planetary nebulae (PNs) and symbiotic stars.

Research of wind erosion intensity in the region of Subotica-Horgos sands

Treesearch

Velizar Velasevic; Ljubomir Letic

1991-01-01

Wind is an important erosional process in the areas of steppe-savanna climate in Europe as typified by the Bojvodina plain in Yugoslavia. Cultivated and forested plots on the Subotica-Horgos Sands were used to study aeolian erosion processes. Wind erosion on the cultivated plot was 3-29 times greater than that occurring on a plot planted to forest trees. That erosion...

Flowing Dunes of Shangri-La Denoised

NASA Image and Video Library

2016-09-07

This radar image of the Shangri-La Sand Sea on Titan from NASA's Cassini spacecraft shows hundreds of sand dunes are visible as dark lines snaking across the surface. These dunes display patterns of undulation and divergence around elevated mountains (which appear bright to the radar), thereby showing the direction of wind and sand transport on the surface. Sands being carried from left to right (west to east) cannot surmount the tallest obstacles; instead, they are directed through chutes and canyons between the tall features, evident in thin, blade-like, isolated dunes between bright some features. Once sands have passed around the obstacles, they resume their downwind course, at first collecting into small, patchy dunes and then organizing into larger, more pervasive linear forms, before being halted once again by obstacles. These patterns reveal the effects not only of wind -- perhaps even modern winds if the dunes are actively moving today -- but also the effects of underlying bedrock and surrounding topography. Dunes across the solar system aid in our understanding of underlying topography, winds and climate, past and present. Similar patterns can be seen in dunes of the Great Sandy Desert in Australia, where dunes undulate broadly across the uneven terrain and are halted at the margins of sand-trapping lakes. The dune orientations correlate generally with the direction of current trade winds, and reveal that winds must have been similar back when the dunes formed, during the Pleistocene glacial and interglacial periods. The image was taken by the Cassini Synthetic Aperture radar (SAR) on July 25, 2016 during the mission's 122nd targeted Titan encounter. The image has been modified by the denoising method described in A. Lucas, JGR:Planets (2014). http://photojournal.jpl.nasa.gov/catalog/PIA20711

Flowing Dunes of Shangri-La

NASA Image and Video Library

2016-09-07

The Shangri-La Sand Sea on Titan is shown in this image from the Synthetic Aperture radar (SAR) on NASA's Cassini spacecraft. Hundreds of sand dunes are visible as dark lines snaking across the surface. These dunes display patterns of undulation and divergence around elevated mountains (which appear bright to the radar), thereby showing the direction of wind and sand transport on the surface. Sands being carried from left to right (west to east) cannot surmount the tallest obstacles; instead, they are directed through chutes and canyons between the tall features, evident in thin, blade-like, isolated dunes between bright some features. Once sands have passed around the obstacles, they resume their downwind course, at first collecting into small, patchy dunes and then organizing into larger, more pervasive linear forms, before being halted once again by obstacles. These patterns reveal the effects not only of wind -- perhaps even modern winds if the dunes are actively moving today -- but also the effects of underlying bedrock and surrounding topography. Dunes across the solar system aid in our understanding of underlying topography, winds and climate, past and present. Similar patterns can be seen in dunes of the Great Sandy Desert in Australia, where dunes undulate broadly across the uneven terrain and are halted at the margins of sand-trapping lakes. The dune orientations correlate generally with the direction of current trade winds, and reveal that winds must have been similar back when the dunes formed, during the Pleistocene glacial and interglacial periods. An annotated version of this radar image is also available.at the Photojournal. North on Titan is up in the image. Radar illuminates the scene from upper right at a 27-degree incidence angle. http://photojournal.jpl.nasa.gov/catalog/PIA20710

Modern sedimentary facies, depositional environments, and major controlling processes on an arid siliciclastic coast, Al qahmah, SE Red Sea, Saudi Arabia

NASA Astrophysics Data System (ADS)

Nabhan, Abdullah I.; Yang, Wan

2018-04-01

The facies and environments along the arid siliciclastic coast of Red Sea in Al Qahmah, Saudi Arabia are studied to establish a depositional model for interpretation of ancient rocks deposited in rift settings. Field and petrographic studies of 151 sediment samples in an area of 20 km2 define seven main facies types: beach, washover fan, tidal channel, dune, sabkha, delta, and wadi (seasonal stream). The wadi and delta facies are composed of poorly to moderately well-sorted, gravelly, medium-to-fine sands. Delta-front sands are redistributed by southward longshore currents to form a beach. Beach facies is composed of well-to-moderately sorted fine sands with minor gravels, which contain high concentrations of magnetite, ilmenite, garnet, pyroxene, amphibole, epidote, titanite, and apatite grains, indicating strong winnowing. Crabs and other burrowers destroy primary sedimentary structures and mix sediments in foreshore and backshore of the beaches. Wind and storm surge rework foreshore and backshore sediments to form washover fans. Sabkha facies occurs extensively in supratidal depressions behind beach, are flooded by rainstorms and spring tide, and capped by a 5-cm-thick crust composed of interlaminated halite, quartz, albite, minor gypsum and biotite, and rarely calcium carbonate. Halite occurs as thin sheets and gypsum as nodules with a chicken-wire structure. Clastic fraction in sabkha sediments ranges from coarse silt to coarse sand with moderate sorting, and is transported by currents and wind. Tidal inlets and tidal creeks assume abandoned wadis and are filled by muddy sand. Sand dunes and sand sheets are 1-7 m high and widely distributed due to variable wind directions. Fine-grained dune sands are moderately well sorted, whereas sheet sands are coarser and poorly sorted due to vegetation baffling. Most eolian sands are sourced from beach deposits. This suite of complex riverine, wave, tidal, wind, chemical, and biological processes form the facies mosaic along the arid Al Qahmah coast, which is strongly affected by climate-driven evaporation and wind action.

Things Aren't Always What They Seem

NASA Technical Reports Server (NTRS)

2004-01-01

This mosaic was assembled from images taken by the panoramic camera on the Mars Exploration Rover Spirit at a region dubbed 'site 31.' Spirit is looking at 'Missoula Crater.' From orbit, the features within the crater appeared to be ejecta from the younger 'Bonneville Crater,' but Spirit's closer look revealed wind-blown drift deposits, not ejecta, within Missoula Crater.

Two year performance of a 10 kW CPV system installed in two areas of Saudi Arabia

NASA Astrophysics Data System (ADS)

Khonkar, Hussam; Alowais, Abdullah; Sheikho, Ayman; Alyahya, Abdulaziz; Alghamdi, Ahmed; Alsaedan, Abdullah; Eugenio, Nunilo N.; Alalweet, Fahad; Halawani, Mohammad; Alsaferan, Abdulrahman

2014-09-01

The three year KACST/IBM collaboration in solar technology research led to the design and development of a 10kW CPV system. The system is comprised of 81 PV modules, inverters and a tracking system and is grid connected. A primary and secondary optics were employed to reach 1600x concentration on multijunction solar cells. Two CPV trackers were installed in the city of Riyadh and one in the eastern coastal city of Al Khafji. These two areas differ in climatic conditions. Riyadh is mostly dry and very often hit by very strong sand storms while Al Khafji is very humid with sand storms. Very fine dusts and dirt carried by the storms hits the surface of the primary optics, Fresnel lens, of the system. In Riyadh, the particles stick to the lenses but accumulation in the surface is not much since it is blown away by wind. However, the humid condition of the coastal areas wets the dusts and makes it sticky, cumulating more dusts and dirt. This paper discusses in details the parts of the 10kW CPV system. It presents a comprehensive analysis of the system's performance since the time they were installed and operated. CPV systems are operated with the least number of personnel and supervision. However, dust and dirt lessens the amount of sunlight passing through the primary optics. It requires periodic cleaning of the Fresnel lens. Different methods of cleaning were tried to identify the efficient way to clean the system that results to a higher power generation. Corrections and modifications of the system to further increase power production are presented.

υ-driven winds from the remnant of binary neutron star mergers

NASA Astrophysics Data System (ADS)

Perego, A.

2018-01-01

We present a 3D hydrodynamic study of the neutrino-driven winds that emerge from the remnant of a neutron star merger, represented by a thick accretion disc orbiting around a massive neutron star. This strong baryonic wind is blown out by neutrino absorption on free baryons inside the disc. It expands within a few tens of ms along the original binary rotation axis. If the central object survives for at least 200ms, the mass ejected in the wind can reach 5% of the initial mass of the accretion disc. Due to the intense neutrino irradiation, matter ejected in the wind increases its electron fraction between 0.3 and 0.4, producing weak r-process nucleosynthesis yields. We predict a distinct UV/optical transient associated with the wind ejecta that peaks from a few hours to a few days after the merger.

Ion movement in acidified, low base saturated sand soils.

Treesearch

A. Ray Harris; Douglas M. Stone

1992-01-01

Describes factors causing cation export in leachate in low base saturated forested sand soils. Reports the effects of varying acid precipitation and litter-humus treatments on ion movement and interaction.

An Overview of Wind-Driven Rovers for Planetary Exploration

NASA Technical Reports Server (NTRS)

Hajos, Gregory A.; Jones, Jack A.; Behar, Alberto; Dodd, Micheal

2005-01-01

The use of in-situ propulsion is considered enabling technology for long duration planetary surface missions. Most studies have focused on stored energy from chemicals extracted from the soil or the use of soil chemicals to produce photovoltaic arrays. An older form of in-situ propulsion is the use of wind power. Recent studies have shown potential for wind driven craft for exploration of Mars, Titan and Venus. The power of the wind, used for centuries to power wind mills and sailing ships, is now being applied to modern land craft. Efforts are now underway to use the wind to push exploration vehicles on other planets and moons in extended survey missions. Tumbleweed rovers are emerging as a new type of wind-driven science platform concept. Recent investigations by the National Aeronautics and Space Administration (NASA) and Jet Propulsion Laboratory (JPL) indicate that these light-weight, mostly spherical or quasi-spherical devices have potential for long distance surface exploration missions. As a power boat has unique capabilities, but relies on stored energy (fuel) to move the vessel, the Tumbleweed, like the sailing ships of the early explorers on earth, uses an unlimited resource the wind to move around the surface of Mars. This has the potential to reduce the major mass drivers of robotic rovers as well as the power generation and storage systems. Jacques Blamont of JPL and the University of Paris conceived the first documented Mars wind-blown ball in 1977, shortly after the Viking landers discovered that Mars has a thin CO2 atmosphere with relatively strong winds. In 1995, Jack Jones, et al, of JPL conceived of a large wind-blown inflated ball for Mars that could also be driven and steered by means of a motorized mass hanging beneath the rolling axis of the ball. A team at NASA Langley Research Center started a biomimetic Tumbleweed design study in 1998. Wind tunnel and CFD analysis were applied to a variety of concepts to optimize the aerodynamic characteristics of the Tumbleweed Rovers. Bare structures, structures carrying sails and a tumbleweed plant (of the Salsola genus) were tested in Langley's wind tunnels. Thomas Estier of the Swiss Federal Institute of Technology developed a memory metal collapsible structure, the Windball. Numerous other researchers have also suggested spherical rovers.

Wind-Driven Erosion and Exposure Potential at Mars 2020 Rover Candidate-Landing Sites.

PubMed

Chojnacki, Matthew; Banks, Maria; Urso, Anna

2018-02-01

Aeolian processes have likely been the predominant geomorphic agent for most of Mars' history and have the potential to produce relatively young exposure ages for geologic units. Thus, identifying local evidence for aeolian erosion is highly relevant to the selection of landing sites for future missions, such as the Mars 2020 Rover mission that aims to explore astrobiologically relevant ancient environments. Here we investigate wind-driven activity at eight Mars 2020 candidate-landing sites to constrain erosion potential at these locations. To demonstrate our methods, we found that contemporary dune-derived abrasion rates were in agreement with rover-derived exhumation rates at Gale crater and could be employed elsewhere. The Holden crater candidate site was interpreted to have low contemporary erosion rates, based on the presence of a thick sand coverage of static ripples. Active ripples at the Eberswalde and southwest Melas sites may account for local erosion and the dearth of small craters. Moderate-flux regional dunes near Mawrth Vallis were deemed unrepresentative of the candidate site, which is interpreted to currently be experiencing low levels of erosion. The Nili Fossae site displayed the most unambiguous evidence for local sand transport and erosion, likely yielding relatively young exposure ages. The downselected Jezero crater and northeast Syrtis sites had high-flux neighboring dunes and exhibited substantial evidence for sediment pathways across their ellipses. Both sites had relatively high estimated abrasion rates, which would yield young exposure ages. The downselected Columbia Hills site lacked evidence for sand movement, and contemporary local erosion rates are estimated to be relatively low.

Wind-Driven Erosion and Exposure Potential at Mars 2020 Rover Candidate-Landing Sites

PubMed Central

Chojnacki, Matthew; Banks, Maria; Urso, Anna

2018-01-01

Aeolian processes have likely been the predominant geomorphic agent for most of Mars’ history and have the potential to produce relatively young exposure ages for geologic units. Thus, identifying local evidence for aeolian erosion is highly relevant to the selection of landing sites for future missions, such as the Mars 2020 Rover mission that aims to explore astrobiologically relevant ancient environments. Here we investigate wind-driven activity at eight Mars 2020 candidate-landing sites to constrain erosion potential at these locations. To demonstrate our methods, we found that contemporary dune-derived abrasion rates were in agreement with rover-derived exhumation rates at Gale crater and could be employed elsewhere. The Holden crater candidate site was interpreted to have low contemporary erosion rates, based on the presence of a thick sand coverage of static ripples. Active ripples at the Eberswalde and southwest Melas sites may account for local erosion and the dearth of small craters. Moderate-flux regional dunes near Mawrth Vallis were deemed unrepresentative of the candidate site, which is interpreted to currently be experiencing low levels of erosion. The Nili Fossae site displayed the most unambiguous evidence for local sand transport and erosion, likely yielding relatively young exposure ages. The downselected Jezero crater and northeast Syrtis sites had high-flux neighboring dunes and exhibited substantial evidence for sediment pathways across their ellipses. Both sites had relatively high estimated abrasion rates, which would yield young exposure ages. The downselected Columbia Hills site lacked evidence for sand movement, and contemporary local erosion rates are estimated to be relatively low. PMID:29568719

Wind-Driven Erosion and Exposure Potential at Mars 2020 Rover Candidate-Landing Sites

NASA Astrophysics Data System (ADS)

Chojnacki, Matthew; Banks, Maria; Urso, Anna

2018-02-01

Aeolian processes have likely been the predominant geomorphic agent for most of Mars' history and have the potential to produce relatively young exposure ages for geologic units. Thus, identifying local evidence for aeolian erosion is highly relevant to the selection of landing sites for future missions, such as the Mars 2020 Rover mission that aims to explore astrobiologically relevant ancient environments. Here we investigate wind-driven activity at eight Mars 2020 candidate-landing sites to constrain erosion potential at these locations. To demonstrate our methods, we found that contemporary dune-derived abrasion rates were in agreement with rover-derived exhumation rates at Gale crater and could be employed elsewhere. The Holden crater candidate site was interpreted to have low contemporary erosion rates, based on the presence of a thick sand coverage of static ripples. Active ripples at the Eberswalde and southwest Melas sites may account for local erosion and the dearth of small craters. Moderate-flux regional dunes near Mawrth Vallis were deemed unrepresentative of the candidate site, which is interpreted to currently be experiencing low levels of erosion. The Nili Fossae site displayed the most unambiguous evidence for local sand transport and erosion, likely yielding relatively young exposure ages. The downselected Jezero crater and northeast Syrtis sites had high-flux neighboring dunes and exhibited substantial evidence for sediment pathways across their ellipses. Both sites had relatively high estimated abrasion rates, which would yield young exposure ages. The downselected Columbia Hills site lacked evidence for sand movement, and contemporary local erosion rates are estimated to be relatively low.

Eta Carinae: Viewed from Multiple Vantage Points

NASA Technical Reports Server (NTRS)

Gull, Theodore

2007-01-01

The central source of Eta Carinae and its ejecta is a massive binary system buried within a massive interacting wind structure which envelops the two stars. However the hot, less massive companion blows a small cavity in the very massive primary wind, plus ionizes a portion of the massive wind just beyond the wind-wind boundary. We gain insight on this complex structure by examining the spatially-resolved Space Telescope Imaging Spectrograph (STIS) spectra of the central source (0.1") with the wind structure which extends out to nearly an arcsecond (2300AU) and the wind-blown boundaries, plus the ejecta of the Little Homunculus. Moreover, the spatially resolved Very Large Telescope/UltraViolet Echelle Spectrograph (VLT/UVES) stellar spectrum (one arcsecond) and spatially sampled spectra across the foreground lobe of the Homunculus provide us vantage points from different angles relative to line of sight. Examples of wind line profiles of Fe II, and the.highly excited [Fe III], [Ne III], [Ar III] and [S III)], plus other lines will be presented.

Earth-like sand fluxes on Mars.

PubMed

Bridges, N T; Ayoub, F; Avouac, J-P; Leprince, S; Lucas, A; Mattson, S

2012-05-09

Strong and sustained winds on Mars have been considered rare, on the basis of surface meteorology measurements and global circulation models, raising the question of whether the abundant dunes and evidence for wind erosion seen on the planet are a current process. Recent studies showed sand activity, but could not determine whether entire dunes were moving--implying large sand fluxes--or whether more localized and surficial changes had occurred. Here we present measurements of the migration rate of sand ripples and dune lee fronts at the Nili Patera dune field. We show that the dunes are near steady state, with their entire volumes composed of mobile sand. The dunes have unexpectedly high sand fluxes, similar, for example, to those in Victoria Valley, Antarctica, implying that rates of landscape modification on Mars and Earth are similar.

Scratching technique for the study and analysis of soil surface abrasion mechanism

NASA Astrophysics Data System (ADS)

Ta, Wanquan

2007-11-01

Aeolian abrasion is the most fundamental and active surface process that takes place in arid and semi-arid environments. Its nature is a wear process for wind blown grains impinging on a soil or sediment surface, which causes particles and aggregates to fracture from the soil surface through a series of plastic and brittle cracking deformation such as cutting, ploughing and brittle fracturing. Using a Universal Micro-Tribometer (UMT), a scratching test was carried out on six soil surfaces (sandy soil, sand loam, silt loam, loam, silt clay loam, and silt clay). The results indicate that traces of normal and tangential force vs. time show a jagged curve, which can reflect the plastic deformation and brittle fracturing of aggregates and particles of various sizes fractured from the soil surfaces. The jagged curve peaks, and the area enclosed underneath, may represent the bonding forces and bonding energies of some aggregates and grains on the soil surface, respectively. Connecting the scratching test with an impact abrasion experiment furthermore demonstrates that soil surface abrasion rates are proportional to the square of speeds of impacting particles and to the 2.6 power of mean soil grain size, and inversely proportional to the 1.5 power of specific surface abrasive energy or to the 1.7 power of specific surface hardness.

Weather resistance of CaSO4 ṡ 1/2H2O-based sand-fixation material

NASA Astrophysics Data System (ADS)

Liu, Xin; Tie, Shengnian

2017-07-01

Searching for an economical and effective sand-fixing material and technology is of great importance in Northwest China. This paper described the use of a semihydrated gypsum-(CaSO4 ṡ 1/2H2O-)based composite as a sand-fixing material. Its morphology and composition were characterized by SEM, and its water resistance, freezing-thawing resistance and wind erosion resistance were tested in the field. The results indicated that semihydrated gypsum-(CaSO4 ṡ 1/2H2O-)based sand-fixing composite has good water resistance and water-holding capacity. Its strength is maintained at 1.42 MPa after 50 freezing and thawing cycles, and its wind erosion increases with increasing wind speed and slope. Its compressive strength starts to decrease after nine months of field tests with no change in appearance, but it still satisfies the requirements of fixation technology. This sand-fixing material should have wide application owing to its good weather resistance.

Aeolian Sediment Transport Pathways and Aerodynamics at Troughs on Mars

NASA Technical Reports Server (NTRS)

Bourke, Mary C.; Bullard, Joanna E.; Barnouin-Jha, Olivier S.

2004-01-01

Interaction between wind regimes and topography can give rise to complex suites of aeolian landforms. This paper considers aeolian sediment associated wit11 troughs on Mars and identifies a wider range of deposit types than has previously been documented. These include wind streaks, falling dunes, "lateral" dunes, barchan dunes, linear dunes, transverse ridges, sand ramps, climbing dunes, sand streamers, and sand patches. The sediment incorporated into these deposits is supplied by wind streaks and ambient Planitia sources as well as originating within the trough itself, notably from the trough walls and floor. There is also transmission of sediment between dneTsh. e flow dynamics which account for the distribution of aeolian sediment have been modeled using two-dimensional computational fluid dynamics. The model predicts flow separation on the upwind side of the trough followed by reattachment and acceleration at the downwind margin. The inferred patterns of sediment transport compare well with the distribution of aeolian forms. Model data indicate an increase of wind velocity by approx. 30 % at the downwind trough margin. This suggests that the threshold wind speed necessary for sand mobilization on Mars will be more freqentmlye t in these inclined locations.

Estimating the change of porosity in the saturated zone during air sparging.

PubMed

Tsai, Yih-jin; Kuo, Yu-chia; Chen, Tsu-chi; Chou, Feng-chih

2006-01-01

Air sparging is a remedial method for groundwater. The remedial region is similar to the air flow region in the saturated zone. If soil particles are transported during air sparging, the porosity distributions in the saturated zone change, which may alter the flow path of the air. To understand better the particle movement, this study performed a sandbox test to estimate the soil porosity change during air sparging. A clear fracture was formed and the phenomenon of particle movement was observed when the air injection was started. The moved sand filled the porous around the fracture and the reparked sand filled the fracture, reducing the porosity around the fracture. The results obtained from the photographs of the sandbox, the current measurements and the direct sand sample measurements were close to each other and are credible. Therefore, air injection during air sparging causes sand particle movement of sand, altering the characteristic of the sand matrix and the air distribution.

Dust Storm Monitoring Using Satellite Observatory and Numerical Modeling Analysis

NASA Astrophysics Data System (ADS)

Taghavi, Farahnaz

In recent years, the frequency of dust pollution events in the Iran Southwest are increased which caused huge damage and imposed a negative impacts on air quality, airport traffic and people daily life in local areas. Dust storms in this area usually start with the formation of a low-pressure center over the Arabian Peninsula. The main objectives of this study is to asses and monitor the movement of aerosols and pollutions from origin source to local areas using satellite imagery and numerical modeling analysis. Observational analyses from NCEP such as synoptic data (Uwind,Vwind,Vorticity and Divergence Fields), upper air radiosonde, measured visibility distributions, land cover data are also used in model comparisons to show differences in occurrence of dust events. The evolution and dynamics of this phenomena are studied on the based a method to modify the initial state of NWP output using discrepancies between dynamic fields and WV imagery in a grid. Results show that satellite images offers a means to control the behavior of numeric models and also the model using land cover data improving the wind-blown dust modeling.

Sheet Flows, Avalanches, and Dune Evolution on Earth and Mars

NASA Technical Reports Server (NTRS)

2003-01-01

This investigation is a collaboration between researchers at Cornell University, the University of Florida, and the University of Rennes 1, France. Flow modeling at Cornell University focused on mechanisms for the suspension and transport of wind-blown sand that are important in both terrestrial and Martian environments. These mechanisms include the saltation (or jumping) of grains, collisions between grains, and the interaction of grains with the velocity fluctuations of the turbulent wind. Of particular interest are sheet flows; these are relatively thin, highly concentrated regions of grains flowing near the ground under the influence of a strong turbulent wind. In them, the grains are suspended by interparticle collisions. Sheet flows may be relatively rare events, but they have the capacity to move great amounts of sand. In order to describe sheet flows, a turbulent mixture theory was formulated for particles in a fluid in which fluctuations in the volume fiaction of the particles take place on the scale of the turbulent eddies. Ensemble averaged equations for particle and fluid mass, momentum, and energy and fluid rate of dissipation were expressed in terms of Farve (concentration) averaged velocities and the associated velocity fluctuations. Correlations that describe the turbulent suspension of particles and dissipation of turbulent energy of both phases due to fluid particle interactions were modeled and boundary conditions at the bed and at the upper surface of the collisional flow were formulated. The boundary conditions at the upper surface were tested in a numerical simulation developed at the University of Florida. Steady and unsteady solutions for steady and unsteady fully-developed flows were obtained over a range of wind speeds fiom the lowest for which collisional between particles occurred to at which turbulent suspension is found to dominate collisional suspension. Below the value of the wind speed at which collisions between particles were unimportant, numerical solutions were obtained for the velocity distribution function and the resulting fields of concentration, particle and gas mean velocity, and particle shear stress for the steady two-dimensional saltation of spherical sand particles driven by a turbulent wind over a bed characterized by a simple relationship (the splash function) between the properties of incoming particles and those of the rebounding particles and other particles ejected fiom the bed. At the University of Rennes 1, experiments devoted to the characterization of the splash function for beds consisting of either random or ordered arrays of spheres in two- dimensions were completed. These indicated the role played by the packing geometry in the rebound and ejection of grains. Preliminary experiments on response of a three- dimensional collision bed to a collision with a single particle were performed. Data was taken with a single camera focused on the plane of collision. Here, for example, the decrease of the effective coefficient of restitution of the bed with an increase of the angle of incidence of the incoming particle has been measured. Other experiments on avalanches at Rennes studied the properties of the flows of particles that are responsible for the motion of the leeward side of a dune. In these, the dependence of the initiation of avalanches on the packing and depth of the particles was measured. Particle migration was studied in inclined flows of a binary mixture of disks and the mechanisms of diffision and segregation were isolated and characterized. The influence of side wall on dense, rapid inclined flows was measured and shown to be the reason why the angle of the free surface in such flows can exceed the static angle of repose. Future research will be devoted to a better understanding the transition between saltating (collisionless) and collisional flows as the wind speed the increases. This will involve the understanding of the evolution of the splash function as clisions with the bed become more numerous, more frequent, and more violent.

Blown Away

ERIC Educational Resources Information Center

Scott, Alan

2014-01-01

On Aug. 13, 2011, at 8:45 p.m. country music fans were eagerly awaiting the band Sugarland to make its entry onto the main stage at the Indiana State Fairgrounds. Also competing for the fans' attention was an approaching storm. Sugarland never made their entrance. At 8:49 p.m. the stage rigging was hit by 59 mile/h (94 km/h) winds causing it to…

[Process study on hysteresis of vegetation cover influencing sand-dust events].

PubMed

Xu, Xing-Kui; Wang, Xiao-Tao; Zhang, Feng

2009-02-15

Data analysis from satellite and weather stations during 1982-2000 shows nonlinear relationship between vegetation cover and sand-dust events is present in most part of China. Vegetation cover ratio in summer can impact significantly on the frequency of sand-dust storms from winter to spring in the source regions of sand-dust events. It is not quite clear about the hysteresis that vegetation cover in summer influence sand-dust events during winter and spring. A quasi-geostrophic barotropic model is used under the condition of 3 magnitude of frictional coefficient to investigate the cause of the hysteresis. Wind velocity shows a greatest decline at 90% during 72 h as initial wind velocity is 10 m/s for magnitude of frictional coefficient between atmosphere and water surface, greatest decline at 100% during 18 h for magnitude of frictional coefficient between atmosphere and bare soil and a 100% reduction of wind speed during 1 h for magnitude of frictional coefficient between atmosphere and vegetation cover. Observation and simulation prove that residual root and stem from summervegetation are one of factors to influence sand-dust events happened during winter and spring. Air inhibition from residual root and stem is a most important reason for hysteresis that vegetation cover influence sand-dust events.

Aeolian transport in the field: A comparison of the effects of different surface treatments

NASA Astrophysics Data System (ADS)

Dong, Zhibao; Lv, Ping; Zhang, Zhengcai; Qian, Guangqiang; Luo, Wanyin

2012-05-01

Aeolian transport represents the result of wind-surface interactions, and therefore depends strongly on variations in the characteristics of the sediment surface. We conducted field observations of aeolian transport of typical dune sand in three 80 m × 80 m plots with different surface treatments: gravel-covered sand, enclosed shifting sand, and open (unprotected) shifting sand. The study was performed at the Shapotou Aeolian Experiment Site in the southeastern part of China's Tengger Desert to compare the effects of these different surface treatments on aeolian transport. To do so, we analyzed the flux density profiles and transport rates above each surface. The flux density profiles for all three treatments followed the exponential decay law that was proposed by most previous researchers to describe the saltation flux density profiles. Coefficients of the exponential decay function were defined as a function of the surface and the wind velocity. The enclosed and open plots with shifting sand had similar flux density profiles, but the flux density above gravel-covered plots showed that transport decayed more slowly with increasing height, producing flux density profiles with a higher average saltation height. The transport rate above the three treatment plots tended to increase proportionally with the cube of the mean wind velocity and with the maximum wind velocity during the observation period, but was more strongly correlated with the square of drift potential. Transport rates above the plot with open shifting sand were greater than those above the plots with enclosed shifting sand and the gravel-covered plot.

Surprises from the field: Novel aspects of aeolian saltation observed under natural turbulence

NASA Astrophysics Data System (ADS)

Martin, R. L.; Kok, J. F.; Chamecki, M.

2015-12-01

The mass flux of aeolian (wind-blown) sediment transport - critical for understanding earth and planetary geomorphology, dust generation, and soil stability - is difficult to predict. Recent work suggests that competing models for saltation (the characteristic hopping of aeolian sediment) fail because they do not adequately account for wind turbulence. To address this issue, we performed field deployments measuring high-frequency co-variations of aeolian saltation and near-surface winds at multiple sites under a range of conditions. Our observations yield several novel findings not currently captured by saltation models: (1) Saltation flux displays no significant lag relative to horizontal wind velocity; (2) Characteristic height of the saltation layer remains constant with changes in shear velocity; and (3) During saltation, the vertical profile of mean horizontal wind velocity is steeper than expected from the Reynolds stress. We examine how the interactions between saltation and turbulence in field settings could explain some of these surprising observations.

Earth Observations taken by the Expedition 13 crew

NASA Image and Video Library

2006-09-02

ISS013-E-75141 (2 Sept. 2006) --- Erg Oriental, Algeria is featured in this image photographed by an Expedition 13 crewmember onboard the International Space Station. One of the main interests of rainless regions like the Sahara Desert to landscape science is that the work of flowing water--mainly streams and rivers--becomes less important than the work of wind. According to scientists, over millennia, and if enough sand is available, winds can generate dunes of enormous size, arranged in regular patterns. Long, generally north-south trending linear dunes stretch across much of northeast Algeria covering a vast tract (approximately 140,000 kilometers square) of the Sahara Desert known as the Erg Oriental. Erg means dune sea in Arabic, and the term has been adopted into modern geology. Spanning this image diagonally are a series of two kilometer-wide linear dunes, comprised of red sand, from a point on the southwest margin of the erg (center point 28.9N 4.8W). The dune chains are more than 100 meters high. The "streets" between the dunes are grayer areas free of sand. Linear dune chains are usually generated roughly parallel with the dominant winds. It also seems to be true that linear dunes are built by stronger winds. This detailed view shows that smaller dunes, known as star dunes, are built on top of the linear dunes. By contrast, star dunes seem to form in weak wind regimes, with winds from different directions in each season -- resulting in characteristic "arms" snaking away from a central point. Some scientists therefore think the dunes in this image were generated in two earlier climatic phases, different from that of today. (1) During a phase when winds were stronger and dominantly from one direction (the south), major linear sand masses accumulated. (2) Later, when wind strengths declined, the star dunes formed. Modern features--known as wind streaks--on the edge of the present erg (not shown), younger than either the linear or star dunes, show that present-day sand-moving winds blow from the southwest.

WIND VELOCITIES AND SAND FLUXES IN MESQUITE DUNE-LANDS IN THE NORTHERN CHIHUAHUAN DESERT: A COMPARISON BETWEEN FIELD MEASUREMENTS AND THE QUIC (QUICK URBAN AND INDUSTRIAL COMPLEX) MODEL

EPA Science Inventory

The poster shows comparisons of wind velocities and sand fluxes between field measurements and a computer model, called QUIC (Quick Urban & Industrial Complex). The comparisons were made for a small desert region in New Mexico.

Earth Observations taken by the Expedition 27 Crew

NASA Image and Video Library

2011-05-16

ISS027-E-034290 (16 May 2011) --- Ar Rub al Khali Sand Sea, Arabian Peninsula is featured in this image photographed by an Expedition 27 crew member on the International Space Station. The Ar Rub al Khali, also known as the “Empty Quarter”, is a large region of sand dunes and interdune flats known as a sand sea (or erg). This photograph highlights a part of the Ar Rub al Khali located close to its southeastern margin in the Sultanate of Oman. Reddish-brown, large linear sand dunes alternate with blue-gray interdune salt flats known as sabkhas at left. The major trend of the linear dunes is transverse to northwesterly trade winds that originate in Iraq (known as the Shamal winds). Formation of secondary barchan (crescent-shaped) and star dunes (dune crests in several directions originating from a single point, looking somewhat like a starfish from above) on the linear dunes is supported by southwesterly winds that occur during the monsoon season (Kharif winds). The long linear dunes begin to break up into isolated large star dunes to the northeast and east (right). This is likely a result of both wind pattern interactions and changes in the sand supply to the dunes. The Empty Quarter covers much of the south-central portion of the Arabian Peninsula, and with an area of approximately 660,000 square kilometers it is the largest continuous sand desert on Earth. The Empty Quarter is so called as the dominantly hyperarid climate and difficulty of travel through the dunes has not encouraged permanent settlement within the region. There is geological and archeological evidence to support cooler and wetter past climates in the region together with human settlement. This evidence includes exposed lakebed sediments, scattered stone tools, and the fossils of hippopotamus, water buffalo, and long-horned cattle.

Aeolian sand transport over complex intertidal bar-trough beach topography

NASA Astrophysics Data System (ADS)

Anthony, Edward J.; Ruz, Marie-Hélène; Vanhée, Stéphane

2009-04-01

Aeolian sand transport on macrotidal beaches with complex intertidal bar-trough topography (ridge-and-runnel beaches) was assessed from experiments in northern France that involved measurements of wind speed, saltation, surface moisture contents, and rates of sand trapping across surveyed portions of the upper beach profile. Beaches exhibiting intertidal bars and troughs are much more complex, topographically, than simple reflective or dissipative beaches. Furthermore, the intertidal bar-trough morphology commonly exhibits strong cross-shore variations in the moisture contents of the beach surface and in patterns of bedform development. The results of four 30-minute experiments, conducted along topographically surveyed portions of the upper beach-dune toe profile, show that troughs act as extremely efficient sand interceptors, because of their permanently saturated state, which also inhibits sand mobilisation. Troughs, thus, limit or segment the dry fetch during conditions of intermittent saltation. Flow lines, inferred from the wind profiles, suggest that complex interactions at the boundary layer are generated by the bar-trough topography. Troughs systematically appear to be characterised by air expansion, while bar faces generate ramp wind acceleration for onshore winds, and sometimes immediate downwind deceleration for offshore winds. These effects may also contribute to cross-shore variations in the rates of sand trapping. Finally, a simple conceptual model of effective fetch development, integrating the effects of the spring-neap tidal range and of gross bar-trough morphological variability over time, is proposed for bar-trough beaches. The model highlights the key theme of fetch segmentation induced by cross-shore differentiation in the moisture contents of the beach surface hinged on the complex topography of multiple bars and troughs.

Investigation of Reversing Sand Dunes at the Bruneau Dunes, Idaho, as Analogs for Features on Mars

NASA Astrophysics Data System (ADS)

Zimbelman, J. R.; Scheidt, S. P.

2012-12-01

The Bruneau Dunes in south-central Idaho include several large reversing sand dunes located within a cut-off meander of the Snake River. These dunes include the largest single-structured sand dune present in North America. Wind records from the Remote Automated Weather Station (RAWS) installation at the Mountain Home Air Force Base, which is ~21 km NW of the Bruneau Dunes, have proved to be very helpful in assessing the regional wind patterns at this section of the western Snake River Plains province; a bimodal wind regime is present, with seasonal changes of strong (sand-moving) winds blowing from either the northwest or the southeast. During April of 2011, we obtained ten precision topographic surveys across the southernmost reversing dune using a Differential Global Positioning System (DGPS). The DGPS data document the shape of the dune going from a low, broad sand ridge at the southern distal end of the dune to the symmetrically shaped 112-m-high central portion of the dune, where both flanks of the dune consist of active slopes near the angle of repose. These data will be useful in evaluating the reversing dune hypothesis proposed for enigmatic features on Mars called Transverse Aeolian Ridges (TARs), which could have formed either as large mega-ripples or small sand dunes. The symmetric profiles across TARs with heights greater than 1 m are more consistent with measured profiles of reversing sand dunes than with measured profiles of mega-ripples (whose surfaces are coated by large particles ranging from coarse sand to gravel, moved by saltation-induced creep). Using DGPS to monitor changes in the three-dimensional location of the crests of the reversing dunes at the Bruneau Dunes should provide a means for estimating the likely timescale for changes of TAR crests if the Martian features are indeed formed in the same manner as reversing sand dunes on Earth.

Beach erosion control study at Pass Christian. [using remote sensors and satellite observation

NASA Technical Reports Server (NTRS)

1978-01-01

The methods of measuring the existence of erosion and the effects of sand stabilization control systems are described. The mechanics of sand movement, the nature of sand erosion, and the use of satellite data to measure these factors and their surrogates are discussed using the locational and control aspects of aeolian and litoral erosion zones along the sand beach of the Mississippi coast. The aeolian erosion is highlighted due to the redeposition of the sand which causes high cleanup costs, property damage, and safety and health hazards. The areas of differential erosion and the patterns of beach sand movement are illustrated and the use of remote sensing methods to identify the areas of erosion are evaluated.

Caught in the Draft

ERIC Educational Resources Information Center

Edge, Ron

2007-01-01

We've all seen (in movies, newscasts, or perhaps in person) the violent effect of the downwash that occurs when a helicopter hovers over the ground. Leaves, grass, and debris are dramatically blown about. We've also sat in front of circulating room fans and felt a large draft, whereas there seems to be very little air movement behind the fan. The…

Dune growth under multidirectional wind regimes

NASA Astrophysics Data System (ADS)

Gadal, C.; Rozier, O.; Claudin, P.; Courrech Du Pont, S.; Narteau, C.

2017-12-01

Under unidirectional wind regimes, flat sand beds become unstable to produce periodic linear dunes, commonly called transverse dunes because their main ridges are oriented perpendicular to the air flow. In areas of low sediment availability, the same interactions between flow, transport and topography produce barchan dunes, isolated sand-pile migrating over long distances with a characteristic crescentic shape. For the last fifteen years, barchan dunes and the instability at the origin of transverse dunes have been the subject of numerous studies that have identified a set of characteristic length and time scales with respect to the physical properties of both grains and fluid. This is not the case for dunes developing under multidirectional wind regimes. Under these conditions, dune orientation is measured with respect to the direction of the resultant sand flux. Depending on the wind regime, dunes do not always line up perpendicularly to the resultant sand flux, but can also be at an oblique angle or even parallel to it. These oblique and longitudinal dunes are ubiquitous in all deserts on Earth and planetary bodies because of the seasonal variability of wind orientation. They are however poorly constrained by observations and there is still no complete theoretical framework providing a description of their orientation and initial wavelength. Here, we extend the linear stability analysis of a flat sand of bed done in two dimensions for a unidirectional flow to three dimensions and multidirectional flow regimes. We are able to recover transitions from transverse to oblique or longitudinal dune patterns according to changes in wind regimes. We besides give a prediction for the initial dune wavelength. Our results compare well to previous theory of dune orientation and to field, experimental and numerical data.

The importance of humans in the dispersal and spread of Phytophthora ramorum at local, landscape, and regional scales

Treesearch

J. Hall Cushman; Ross Meentemeyer

2006-01-01

Determining how Phytophthora ramorum is dispersed across the landscape is critical for understanding the ecology and epidemiology of this influential pathogen. To date, researchers have shown that abiotic factors – such as rain-splash, wind-blown rain and down-stream transport of inoculum – are critical mechanisms for the dispersal of this pathogen....

Survivability of Microbes in Mars Wind Blown Dust Environment

NASA Technical Reports Server (NTRS)

Mancinelli, Rocco L.; Klovstad, Melisa R.; Fonda, Mark L.; DeVincenzi, Donald (Technical Monitor)

2000-01-01

Although the probability of Earth microbes growing (dividing) in the Martian environment is extremely low, the probability of their survival on the Martian surface is unknown. During the course of landed missions to Mars terrestrial microbes may reach the surface of Mars via inadequately sterilized spacecraft landers, rovers, or through accidental impact of orbiters. This investigation studied the potential for Earth microbes to survive in the windblown dust on the surface of Mars. The rationale for the study comes from the fact that Mars regularly has huge dust storms that engulf the planet, shading the surface from solar UV radiation. These storms serve as a mechanism for global transfer of dust particles. If live organisms were to be transported to the surface of Mars they could be picked up with the dust during a dust storm and transported across the planet. Washed, dried spores of Bacillus subtilis strain HA 101 were aseptically mixed with sterile sieved (size range of 1-5microns) Mars soil standard (obtained from NASA Johnson Space Center, Houston, Texas, USA), or Fe-montmorillonite such that the number of microbes equals 5 x 10(exp 6)/g dry wt soil. The microbe soil mixture was placed in a spherical 8 L Mars simulation chamber equipped with a variable speed rotor, gas ports and an Oriel deuterium UV lamp emitting light of wave lengths 180-400 nm. The chamber was sealed, flushed with a simulated Martian atmosphere (96.9% CO2, 3% O2, 0.1% H2O), and the pressure brought to 10 torr. The lamp and rotor were switched on to begin the experiment. Periodically samples were collected from the chamber, and the numbers of microbial survivors g soil was determined using plate counts and the most probable number method (MPN). The data indicate that Bacillus subtilis spores dispersed with Mars analog soil in a Mars atmosphere (wind blown dust) survive exposure to 5.13 KJ m-2 UV radiation, suggesting that Mars wind blown dust has potential to the protect microbes from solar UV radiation.

Surface and airborne evidence for plumes and winds on triton

USGS Publications Warehouse

Hansen, C.J.; McEwen, A.S.; Ingersoll, A.P.; Terrile, R.J.

1990-01-01

Aeolian features on Triton that were imaged during the Voyager Mission have been grouped. The term "aeolian feature" is broadly defined as features produced by or blown by the wind, including surface and airborne materials. Observations of the latitudinal distributions of the features probably associated with current activity (known plumes, crescent streaks, fixed terminator clouds, and limb haze with overshoot) all occur from latitude -37?? to latitude -62??. Likely indicators of previous activity (dark surface streaks) occur from latitude -5?? to -70??, but are most abundant from -15?? to -45??, generally north of currently active features. Those indicators which give information on wind direction and speed have been measured. Wind direction is a function of altitude. The predominant direction of the surface wind streaks is found to be between 40?? and 80?? measured clockwise from north. The average orientation of streaks in the northeast quadrant is 59??. Winds at 1- to 3-kilometer altitude are eastward, while those at >8 kilometers blow west.

Movement analysis of upper limb during resistance training using general purpose robot arm "PA10"

NASA Astrophysics Data System (ADS)

Morita, Yoshifumi; Yamamoto, Takashi; Suzuki, Takahiro; Hirose, Akinori; Ukai, Hiroyuki; Matsui, Nobuyuki

2005-12-01

In this paper we perform movement analysis of an upper limb during resistance training. We selected sanding training, which is one type of resistance training for upper limbs widely performed in occupational therapy. Our final aims in the future are to quantitatively evaluate the therapeutic effect of upper limb motor function during training and to develop a new rehabilitation training support system. For these purposes, first of all we perform movement analysis using a conventional training tool. By measuring upper limb motion during the sanding training we perform feature abstraction. Next we perform movement analysis using the simulated sanding training system. This system is constructed using the general purpose robot arm "PA10". This system enables us to measure the force/torque exerted by subjects and to easily change the load of resistance. The control algorithm is based on impedance control. We found these features of the upper limb motion during the sanding training.

Application of the Gillette model for windblown dust at Owens Lake, CA

NASA Astrophysics Data System (ADS)

Ono, Duane

Windblown dust can have significant impacts on local air pollution levels, and in cases such as dust from Africa or Asia, can have global impacts on our environment. Models to estimate particulate matter emissions from windblown dust are generally based on the local wind speed, the threshold wind speed to initiate erosion, and the soil texture of a given surface. However, precipitation, soil crusting, and soil disturbance can dramatically change the threshold wind speed and erosion potential of a surface, making modeling difficult. A low-cost sampling and analysis method was developed to account for these surface changes in a wind erosion model. Windblown dust emissions measured as PM 10 (particulate matter less than a nominal 10 μm aerodynamic diameter) have been found to be generally proportional to sand flux (also known as saltation flux). In this study, a model was used to estimate sand flux using the relationship Q=AρG/g, where Q is horizontal sand flux, A is a surface erosion potential factor, ρ is air density, g is the gravitational constant, and G=∫ u*(u*2-u*t2)dt, where u* is friction velocity and u is the threshold friction velocity of the surface. The variable A in the model was derived by comparing the measured sand flux for a given period and area to G for the same period. Sand flux was monitored at Owens Lake, CA using low-cost Cox Sand Catchers (CSCs) for monthly measurements, and more expensive electronic sensors (Sensits) to measure hourly flux rates and u. Monitors were spaced 1 km apart at 114 sites, covering one clay and three sand-dominated soil areas. Good model results relied primarily on the erosion potential A, which could be determined from CSC measurements and wind speed data. Annual values for A were found to range from 1.3 to 3.5 in the three sand areas. The value of A was an order of magnitude lower (0.2) in the less erodible clay area. Previous studies showed similar values for A of 0.7 and 2.9 for a sandy site at Owens Lake, and 1.1 for a site in the Chihuahuan desert in New Mexico. The model performed well using annual values for A and better with monthly values, with R2 ranging from 0.74 to 0.87 for hourly sand flux rates in the four study areas. Monthly changes in A accounted for temporal surface changes, such as precipitation and surface crusting in the model predictions. This study demonstrated that low-cost periodic sand flux sampling using CSCs can provide a practical method to determine values for A in a simple wind erosion model, and that this model can provide good hourly and monthly estimates of sand flux rates in windblown dust areas.

Dunes with Frost

NASA Technical Reports Server (NTRS)

2004-01-01

31 May 2004 Springtime for the martian northern hemisphere brings defrosting spots and patterns to the north polar dune fields. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows an example located near 76.7oN, 250.4oW. In summer, these dunes would be darker than their surroundings. However, while they are still covered by frost, they are not any darker than the substrate across which the sand is slowly traveling. Dune movement in this case is dominated by winds that blow from the southwest (lower left) toward the northeast (upper right). The picure covers an area about 3 km (1.9 mi) across and is illuminated by sunlight from the lower left.

Ripples or Dunes?

NASA Technical Reports Server (NTRS)

2004-01-01

This approximate true-color image taken by the Mars Exploration Rover Spirit's panoramic camera shows the windblown waves of soil that characterize the rocky surface of Gusev Crater, Mars. Scientists were puzzled about whether these geologic features were 'ripples' or 'dunes.' Ripples are shaped by gentle winds that deposit coarse grains on the tops or crests of the waves. Dunes are carved by faster winds and contain a more uniform distribution of material. Images taken of these features by the rover's microscopic imager on the 41st martian sol, or day, of the rover's mission revealed their identity to be ripples. This information helps scientists better understand the winds that shape the landscape of Mars. This image was taken early in Spirit's mission.

[figure removed for brevity, see original site] Click on image for larger view [Image credit: NASA/JPL/ASU]

This diagram illustrates how windblown sediments travel. There are three basic types of particles that undergo different motions depending on their size. These particles are dust, sand and coarse sand, and their sizes approximate flour, sugar, and ball bearings, respectively. Sand particles move along the 'saltation' path, hitting the surface downwind. When the sand hits the surface, it sends dust into the atmosphere and gives coarse sand a little shove. Mars Exploration Rover scientists are studying the distribution of material on the surface of Mars to better understand how winds shaped the landscape.

The Carolina Sandhills: Quaternary eolian sand sheets and dunes along the updip margin of the Atlantic Coastal Plain province, southeastern United States

USGS Publications Warehouse

Swezey, Christopher; Fitzwater, Bradley A.; Whittecar, G. Richard; Mahan, Shannon; Garrity, Christopher P.; Aleman Gonzalez, Wilma B.; Dobbs, Kerby M.

2016-01-01

The Carolina Sandhills is a physiographic region of the Atlantic Coastal Plain province in the southeastern United States. In Chesterfield County (South Carolina), the surficial sand of this region is the Pinehurst Formation, which is interpreted as eolian sand derived from the underlying Cretaceous Middendorf Formation. This sand has yielded three clusters of optically stimulated luminescence ages: (1) 75 to 37 thousand years ago (ka), coincident with growth of the Laurentide Ice Sheet; (2) 28 to 18 ka, coincident with the last glacial maximum (LGM); and (3) 12 to 6 ka, mostly coincident with the Younger Dryas through final collapse of the Laurentide Ice Sheet. Relict dune morphologies are consistent with winds from the west or northwest, coincident with modern and inferred LGM January wind directions. Sand sheets are more common than dunes because of effects of coarse grain size (mean range: 0.35–0.59 mm) and vegetation. The coarse grain size would have required LGM wind velocities of at least 4–6 m/sec, accounting for effects of colder air temperatures on eolian sand transport. The eolian interpretation of the Carolina Sandhills is consistent with other evidence for eolian activity in the southeastern United States during the last glaciation.

Crew Earth Observations (CEO) taken during Expedition Five on the ISS

NASA Image and Video Library

2002-08-25

ISS005-E-11189 (25 August 2002) --- Calanscio Sand Sea, Libya is featured in this digital image photographed by an Expedition 5 crewmember on the International Space Station (ISS). A plume of black smoke blowing westward is silhouetted against yellow linear dunes in the great sand sea of northeast Libya. Smoke from flares at remote well heads is commonly seen by astronauts flying over the Sahara Desert. NASA scientists studying the Station imagery had the following observations about the image. The plume dispersal pattern visible at the left edge of the image may be due to upper-level winds or gravitational settling of heavier particulates. The regular pattern of linear dunes is generated by two major winds: the dominant north wind (north is towards the top right) determines the orientation of the sand dunes. Gentler easterly winds, as were blowing when this view was taken, make the dunes asymmetric, with a gentle windward (west) slope and an over steeped downwind slope. Some over steepened slopes even cast shadows in the early morning light. One mound of sand (top right), due north of the well head, does not fit the pattern of linear dunes. This type is known as a star dune.

Ocean Surface Winds Drive Dynamics of Transoceanic Aerial Movements

PubMed Central

Felicísimo, Ángel M.; Muñoz, Jesús; González-Solis, Jacob

2008-01-01

Global wind patterns influence dispersal and migration processes of aerial organisms, propagules and particles, which ultimately could determine the dynamics of colonizations, invasions or spread of pathogens. However, studying how wind-mediated movements actually happen has been hampered so far by the lack of high resolution global wind data as well as the impossibility to track aerial movements. Using concurrent data on winds and actual pathways of a tracked seabird, here we show that oceanic winds define spatiotemporal pathways and barriers for large-scale aerial movements. We obtained wind data from NASA SeaWinds scatterometer to calculate wind cost (impedance) models reflecting the resistance to the aerial movement near the ocean surface. We also tracked the movements of a model organism, the Cory's shearwater (Calonectris diomedea), a pelagic bird known to perform long distance migrations. Cost models revealed that distant areas can be connected through “wind highways” that do not match the shortest great circle routes. Bird routes closely followed the low-cost “wind-highways” linking breeding and wintering areas. In addition, we found that a potential barrier, the near surface westerlies in the Atlantic sector of the Intertropical Convergence Zone (ITCZ), temporally hindered meridional trans-equatorial movements. Once the westerlies vanished, birds crossed the ITCZ to their winter quarters. This study provides a novel approach to investigate wind-mediated movements in oceanic environments and shows that large-scale migration and dispersal processes over the oceans can be largely driven by spatiotemporal wind patterns. PMID:18698354

Ocean surface winds drive dynamics of transoceanic aerial movements.

PubMed

Felicísimo, Angel M; Muñoz, Jesús; González-Solis, Jacob

2008-08-13

Global wind patterns influence dispersal and migration processes of aerial organisms, propagules and particles, which ultimately could determine the dynamics of colonizations, invasions or spread of pathogens. However, studying how wind-mediated movements actually happen has been hampered so far by the lack of high resolution global wind data as well as the impossibility to track aerial movements. Using concurrent data on winds and actual pathways of a tracked seabird, here we show that oceanic winds define spatiotemporal pathways and barriers for large-scale aerial movements. We obtained wind data from NASA SeaWinds scatterometer to calculate wind cost (impedance) models reflecting the resistance to the aerial movement near the ocean surface. We also tracked the movements of a model organism, the Cory's shearwater (Calonectris diomedea), a pelagic bird known to perform long distance migrations. Cost models revealed that distant areas can be connected through "wind highways" that do not match the shortest great circle routes. Bird routes closely followed the low-cost "wind-highways" linking breeding and wintering areas. In addition, we found that a potential barrier, the near surface westerlies in the Atlantic sector of the Intertropical Convergence Zone (ITCZ), temporally hindered meridional trans-equatorial movements. Once the westerlies vanished, birds crossed the ITCZ to their winter quarters. This study provides a novel approach to investigate wind-mediated movements in oceanic environments and shows that large-scale migration and dispersal processes over the oceans can be largely driven by spatiotemporal wind patterns.

On the origin of the system PSR B 1757-24/SNR G 5.4-1.2

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.

2004-03-01

A scenario for the origin of the system PSR B 1757-24/supernova remnant (SNR) G 5.4-1.2 is proposed. It is suggested that both objects are the remnants of a supernova (SN) that exploded within a pre-existing bubble blown-up by a runaway massive star (the SN progenitor) during the final (Wolf-Rayet) phase of its evolution. This suggestion implies that (a) the SN blast centre was significantly offset from the geometric centre of the wind-blown bubble (i.e. from the centre of the future SNR), (b) the bubble was surrounded by a massive wind-driven shell, and (c) the SN blast wave was drastically decelerated by the interaction with the shell. Therefore, one can understand how the relatively young and low-velocity pulsar PSR B 1757-24 was able to escape from the associated SNR G 5.4-1.2 and why the inferred vector of pulsar transverse velocity does not point away from the geometric centre of the SNR. A possible origin of the radio source G 5.27-0.9 (located between PSR B 1757-24 and the SNR G 5.4-1.2) is proposed. It is suggested that G 5.27-0.9 is a lobe of a low Mach number (≃1.7) jet of gas outflowing from the interior of G 5.4-1.2 through the hole bored in the SNR's shell by the escaping pulsar. It is also suggested that the non-thermal emission of the comet-shaped pulsar wind nebula originates in the vicinity of the termination shock and in the cylindric region of subsonically moving shocked pulsar wind. The role of magnetized wind-driven shells (swept-up during the Wolf-Rayet phase from the ambient interstellar medium with the regular magnetic field) in formation of elongated axisymmetric SNRs is discussed.

Earth Observations taken by Expedition 26 Crewmember

NASA Image and Video Library

2011-02-13

ISS026-E-026761 (13 Feb. 2011) --- Medano Blanco coastal dunes in Buenos Aires Province, Argentina are featured in this image photographed by an Expedition 26 crew member on the International Space Station. The Medano Blanco (White Dunes) are a well known recreational area 35 kilometers west of the twin cities of Nicochea-Quequen, one of the biggest ports in the province of Buenos Aires, central Argentina. The Medano Blanco dunes separate the Atlantic Ocean from intensive sunflower agricultural cropland, visible as the angular pattern of green and brown fields at left. The dune field extends 3.5 kilometers at its widest part. Narrow cordons of coastal dunes stretch along this part of Argentina’s coastline for hundreds of kilometers. Small streams, oriented towards the coast, cross the farmland at upper left. Water from these is dammed behind the dunes, and even within the dunes, where wetlands flourish. This is the drier southern part of Buenos Aires province near the more arid and windier border with Patagonia—one of the windiest places on Earth. The effect of strong westerly winds (blowing bottom to top in this slightly oblique image) can be seen everywhere in this detailed photograph. The dune sand is blown from local beaches onshore where it forms the dunes. The prominent dune ridge crests are oriented at right angles to the prevailing wind. Geologists suspect that erosion by wind has excavated numerous hollows which now dot the farmland as small shallow lakes. A stand of dark green trees has been planted on the upwind side of a health spa—located at the white dot (center left) which is the roof of a stately building—as a protective barrier against the wind. The white fringe along the seashore is formed from lines of breaking waves. Crossing swell trains can be seen offshore in the Atlantic Ocean. The curvature of the swell pattern offshore also shows the effect of the westerly wind, and indeed drives the local sea current in this area—slightly more prominent onshore swells approach the coast from the southeast. The light brown tint of seawater nearer the shore is the fine muddy fraction of the coastal sediment being washed seaward (after being stirred up by wave action) and then east by the current.

Aerodynamic characteristics of a small-scale straight and swept-back wing with knee-blown jet flaps

NASA Technical Reports Server (NTRS)

Morehouse, G. G.; Eckert, W. T.; Boles, R. A.

1977-01-01

Two sting-mounted, 50.8 cm (20 in.) span, knee-blown, jet-flap models were tested in a large (2.1- by 2.5-m (7- by 10-ft) subsonic wind tunnel. A straight- and swept-wing model were tested with fixed flap deflection with various combinations of full-span leading-edge slats. The swept-wing model was also tested with wing tip extensions. Data were taken at angles-of-attack between 0 deg and 40 deg, at dynamic pressures between 143.6 N/sq m (3 lb/sq ft) and 239.4 N/sq m (5 lb/sq ft), and at Reynolds numbers (based on wing chord) ranging from 100,000 to 132,000. Jet flap momentum blowing coefficients up to 10 were used. Lift, drag, and pitching-moment coefficients, and exit flow profiles for the flap blowing are presented in graphical form without analysis.

A wind tunnel investigation of the wake near the trailing edge of a deflected externally blown flap. [on a jet powered STOL transport aircraft

NASA Technical Reports Server (NTRS)

Johnson, W. G., Jr.; Kardas, G. E.

1974-01-01

The model tested was a general research model of a swept-wing, jet-powered STOL transport with externally blown flaps. The model was tested with four engine simulators mounted on pylons under the wing. Tests were conducted in the V/STOL tunnel over an angle of attack range of 0 deg to 16 deg and a thrust coefficient range from 0 to approximately 4 at a Reynolds number of 0.461 x 1 million based on the wing reference chord. The results of this investigation are presented primarily as plots of the individual velocity vectors obtained from the wake survey. These data are used to extend an earlier analysis to isolate the effects of the engine thrust on the behavior of the flow at the flap trailing edge. Results of a comparison with a jet-flap theory are also shown.

Spontaneous neonatal pneumomediastinum: the "spinnaker sail" sign.

PubMed

Lawal, T A; Glüer, S; Reismann, M; Dördelmann, M; Schirg, E; Ure, B

2009-02-01

Spontaneous pneumomediastinum is a rare condition in the newborn, not associated with identifiable trauma or mechanical ventilation. It is diagnosed by a combination of physical examination and confirmatory chest radiograph, with various recognized signs identifiable in this condition. We report the case of a male neonate, who had pneumomediastinum confirmed by the presence of a wind blown spinnaker sail sign and was managed conservatively. We also reviewed the literature.

Equilibrium configuration of a stratus floating above accretion disks: Full-disk calculation

NASA Astrophysics Data System (ADS)

Itanishi, Yusuke; Fukue, Jun

2017-06-01

We examine floating strati above a luminous accretion disk, supported by the radiative force from the entire disk, and calculate the equilibrium locus, which depends on the disk luminosity and the optical depth of the stratus. Due to the radiative transfer effect (albedo effect), the floating height of the stratus with a finite optical depth generally becomes high, compared with the particle case. In contrast to the case of the near-disk approximation, moreover, the floating height becomes yet higher in the present full-disk calculation, since the intense radiation from the inner disk is taken into account. As a result, when the disk luminosity normalized by the Eddington luminosity is ˜0.3 and the stratus optical depth is around unity, the stable configuration disappears at around r ˜ 50 rg, rg being the Schwarzschild radius, and the stratus would be blown off as a cloudy wind consisting of many strati with appropriate conditions. This luminosity is sufficiently smaller than the Eddington one, and the present results suggest that the radiation-driven cloudy wind can be easily blown off from the sub-Eddington disk, and this can explain various outflows observed in ultra-fast outflow objects as well as in broad-absorption-line quasars.

Cobbles in Troughs Between Meridiani Ripples

NASA Technical Reports Server (NTRS)

2006-01-01

As NASA's Mars Exploration Rover Opportunity continues to traverse from 'Erebus Crater' toward 'Victoria Crater,' the rover navigates along exposures of bedrock between large, wind-blown ripples. Along the way, scientists have been studying fields of cobbles that sometimes appear on trough floors between ripples. They have also been studying the banding patterns seen in large ripples.

This view, obtained by Opportunity's panoramic camera on the rover's 802nd Martian day (sol) of exploration (April 27, 2006), is a mosaic spanning about 30 degrees. It shows a field of cobbles nestled among wind-driven ripples that are about 20 centimeters (8 inches) high.

The origin of cobble fields like this one is unknown. The cobbles may be a lag of coarser material left behind from one or more soil deposits whose finer particles have blown away. The cobbles may be eroded fragments of meteoritic material, secondary ejecta of Mars rock thrown here from craters elsewhere on the surface, weathering remnants of locally-derived bedrock, or a mixture of these. Scientists will use the panoramic camera's multiple filters to study the rock types, variability and origins of the cobbles.

This is an approximately true-color rendering that combines separate images taken through the panoramic camera's 753-nanometer, 535-nanometer and 432-nanometer filters.

How to make a wind-movement recorder from any spare drum-type recorder

Treesearch

Irvin C. Reigner

1964-01-01

The automatic recording of wind movement is sometimes essential to experiments in forestry and watershed-management research. Wind-movement data are often obtained by periodic reading of the anemometer dial, but occasionally data are required for variable intervals and at times when observations cannot be made easily. Instruments designed to record wind movement are...

Sand sagebrush response to fall and spring prescribed burns

Treesearch

Lance T. Vermeire; Robert B. Mitchell; Samuel D. Fuhlendorf

2001-01-01

Sand sagebrush (Artemisia filifolia) is a dominant shrub on sandy soils throughout the Great Plains and Southwest. Sand sagebrush is reported to reduce wind erosion and provides valuable forage and cover to numerous wildlife species. However, the fire ecology of sand sagebrush is not well understood. Our objectives were to evaluate fire-induced mortality, occurrence of...

A wind tunnel study of aeolian sediment transport response to unsteady winds

NASA Astrophysics Data System (ADS)

Li, Bailiang; McKenna Neuman, Cheryl

2014-06-01

Although moderate attention has been paid to the response of the aeolian mass transport rate to wind gusts, it is still unclear how the particle size and volumetric concentration affect this relation. Very little is known about the response time of the particle speed, and specifically, how the sensor scale and elevation affect measurements of this variable. The present study addresses this knowledge gap through a series of wind tunnel experiments in which a gusty wind was generated by programming the fan motor to adjust to a randomly selected rpm every 10 s. Beds consisting of either medium or coarse sand were investigated through synchronous, co-located measurements of the local wind speed and particle speed/count rate obtained via a customized laser Doppler anemometry (LDA) system. The vertically integrated sand transport rate (Q) and the wind speed in the freestream were quantified using a passive sand trap and pitot tube, respectively. The results of the experiments indicate that the response of the aeolian transport system to wind gusts is generally faster in terms of the particle speed than the mass transport rate, while the degree of correlation is found to vary with the sensor elevation, as well as with the particle size and volumetric concentration. In essence, the coupling within the transport system is demonstrated to be strongly scale dependent.

Sand Transport under Highly Turbulent Airflow on a Beach Surface

NASA Astrophysics Data System (ADS)

Baas, A. C. W.; Jackson, D. W. T.; Cooper, J. A. G.; Lynch, K.; Delgado-Fernandez, I.; Beyers, J. H. M.

2012-04-01

The past decade has seen a growing body of research on the relation between turbulence in the wind and the resultant transport of sediment over active sand surfaces. Widespread use of sonic anemometry and high-frequency sand transport sensors and traps have facilitated recent field studies over dunes and beach surfaces, to move beyond monitoring of mean wind speed and bulk transport to more detailed measurements at much higher spatio-temporal resolutions. In this paper we present results of a field study conducted in the recirculation flow and re-attachment zone on a beach behind a foredune at Magilligan Strand, Northern Ireland. The offshore winds over the foredune at this site are associated with flow separation and reversal located over the beach surface in the lee of the dune row, often strong enough to induce sand transport toward the toe of the foredune ('against' the overall offshore flow). The re-attachment and recirculation zone are associated with strongly turbulent fluid flow and complex streamlines that do not follow the underlying topography. High frequency (25 Hz) wind and sand transport data were collected at a grid of point locations distributed over the beach surface between 35 m to 55 m distance from the 10 m high dune crest, using ultrasonic anemometers at 0.5 m height and co-located load cell traps and Safires at the bed surface. The wind data are used to investigate the role of Reynolds shear stresses and quadrant analysis techniques for identifying burst-sweep events in relation to sand transport events. This includes an assessment of the issues involved with data rotations for yaw, pitch, and roll corrections relative to complex flow streamlines, and the subsequently derived turbulence parameters based on fluctuating vector components (u', v', w'). Results illustrate how transport may exist under threshold mean velocities because of the role played by coherent flow structures, and the findings corroborate previous findings that shear velocity obtained using traditional wind profile approaches does not correlate with transport as additional stresses are generated due to turbulent structures.

All Along the Fractures

NASA Image and Video Library

2015-09-30

This image from NASA Mars Reconnaissance Orbiter spacecraft provides information about erosion and movement of surface material, about wind and weather patterns, even about the soil grains and grain sizes. However, looking past the dunes, these images also reveal the nature of the substrate beneath. Within the spaces between the dunes, a resistant and highly fractured surface is revealed. The fractured ground is resistant to erosion by the wind, and suggests the material is bedrock that is now shattered by a history of bending stresses or temperature changes, such as cooling, for example. Alternately, the surface may be a sedimentary layer that was once wet and shrunk and fractured as it dried, like gigantic mud cracks. In either case, the relative small and indistinct fractures have trapped the dark dune sand marching overhead. Now the fractures have become quite distinct, allowing us to examine the orientation and spacing of the fractures to learn more about the processes that formed them. http://photojournal.jpl.nasa.gov/catalog/PIA19958

Microbial hitchhikers on intercontinental dust: catching a lift in Chad

PubMed Central

Favet, Jocelyne; Lapanje, Ales; Giongo, Adriana; Kennedy, Suzanne; Aung, Yin-Yin; Cattaneo, Arlette; Davis-Richardson, Austin G; Brown, Christopher T; Kort, Renate; Brumsack, Hans-Jürgen; Schnetger, Bernhard; Chappell, Adrian; Kroijenga, Jaap; Beck, Andreas; Schwibbert, Karin; Mohamed, Ahmed H; Kirchner, Timothy; de Quadros, Patricia Dorr; Triplett, Eric W; Broughton, William J; Gorbushina, Anna A

2013-01-01

Ancient mariners knew that dust whipped up from deserts by strong winds travelled long distances, including over oceans. Satellite remote sensing revealed major dust sources across the Sahara. Indeed, the Bodélé Depression in the Republic of Chad has been called the dustiest place on earth. We analysed desert sand from various locations in Chad and dust that had blown to the Cape Verde Islands. High throughput sequencing techniques combined with classical microbiological methods showed that the samples contained a large variety of microbes well adapted to the harsh desert conditions. The most abundant bacterial groupings in four different phyla included: (a) Firmicutes—Bacillaceae, (b) Actinobacteria—Geodermatophilaceae, Nocardiodaceae and Solirubrobacteraceae, (c) Proteobacteria—Oxalobacteraceae, Rhizobiales and Sphingomonadaceae, and (d) Bacteroidetes—Cytophagaceae. Ascomycota was the overwhelmingly dominant fungal group followed by Basidiomycota and traces of Chytridiomycota, Microsporidia and Glomeromycota. Two freshwater algae (Trebouxiophyceae) were isolated. Most predominant taxa are widely distributed land inhabitants that are common in soil and on the surfaces of plants. Examples include Bradyrhizobium spp. that nodulate and fix nitrogen in Acacia species, the predominant trees of the Sahara as well as Herbaspirillum (Oxalobacteraceae), a group of chemoorganotrophic free-living soil inhabitants that fix nitrogen in association with Gramineae roots. Few pathogenic strains were found, suggesting that African dust is not a large threat to public health. PMID:23254516

Sequence of infilling events in Gale Crater, Mars: Results from morphology, stratigraphy, and mineralogy

NASA Astrophysics Data System (ADS)

Le Deit, Laetitia; Hauber, Ernst; Fueten, Frank; Pondrelli, Monica; Rossi, Angelo Pio; Jaumann, Ralf

2013-12-01

Crater is filled by sedimentary deposits including a mound of layered deposits, Aeolis Mons. Using orbital data, we mapped the crater infillings and measured their geometry to determine their origin. The sediment of Aeolis Mons is interpreted to be primarily air fall material such as dust, volcanic ash, fine-grained impact products, and possibly snow deposited by settling from the atmosphere, as well as wind-blown sands cemented in the crater center. Unconformity surfaces between the geological units are evidence for depositional hiatuses. Crater floor material deposited around Aeolis Mons and on the crater wall is interpreted to be alluvial and colluvial deposits. Morphologic evidence suggests that a shallow lake existed after the formation of the lowermost part of Aeolis Mons (the Small yardangs unit and the mass-wasting deposits). A suite of several features including patterned ground and possible rock glaciers are suggestive of periglacial processes with a permafrost environment after the first hundreds of thousands of years following its formation, dated to ~3.61 Ga, in the Late Noachian/Early Hesperian. Episodic melting of snow in the crater could have caused the formation of sulfates and clays in Aeolis Mons, the formation of rock glaciers and the incision of deep canyons and valleys along its flanks as well as on the crater wall and rim, and the formation of a lake in the deepest portions of Gale.

Sands at Gusev Crater, Mars

NASA Astrophysics Data System (ADS)

Cabrol, Nathalie A.; Herkenhoff, Kenneth; Knoll, Andrew H.; Farmer, Jack; Arvidson, Raymond; Grin, Edmond; Li, Ronxing; Fenton, Lori; Cohen, Barbara; Bell, James F.; Aileen Yingst, R.

2014-05-01

Processes, environments, and the energy associated with the transport and deposition of sand at Gusev Crater are characterized at the microscopic scale through the comparison of statistical moments for particle size and shape distributions. Bivariate and factor analyses define distinct textural groups at 51 sites along the traverse completed by the Spirit rover as it crossed the plains and went into the Columbia Hills. Fine-to-medium sand is ubiquitous in ripples and wind drifts. Most distributions show excess fine material, consistent with a predominance of wind erosion over the last 3.8 billion years. Negative skewness at West Valley is explained by the removal of fine sand during active erosion, or alternatively, by excess accumulation of coarse sand from a local source. The coarse to very coarse sand particles of ripple armors in the basaltic plains have a unique combination of size and shape. Their distribution display significant changes in their statistical moments within the ~400 m that separate the Columbia Memorial Station from Bonneville Crater. Results are consistent with aeolian and/or impact deposition, while the elongated and rounded shape of the grains forming the ripples, as well as their direction of origin, could point to Ma'adim Vallis as a possible source. For smaller particles on the traverse, our findings confirm that aeolian processes have dominated over impact and other processes to produce sands with the observed size and shape patterns across a spectrum of geologic (e.g., ripples and plains soils) and aerographic settings (e.g., wind shadows).

Sands at Gusev Crater, Mars

USGS Publications Warehouse

Cabrol, Nathalie A.; Herkenhoff, Kenneth E.; Knoll, Andrew H.; Farmer, Jack D.; Arvidson, Raymond E.; Grin, E.A.; Li, Ron; Fenton, Lori; Cohen, B.; Bell, J.F.; Yingst, R. Aileen

2014-01-01

Processes, environments, and the energy associated with the transport and deposition of sand at Gusev Crater are characterized at the microscopic scale through the comparison of statistical moments for particle size and shape distributions. Bivariate and factor analyses define distinct textural groups at 51 sites along the traverse completed by the Spirit rover as it crossed the plains and went into the Columbia Hills. Fine-to-medium sand is ubiquitous in ripples and wind drifts. Most distributions show excess fine material, consistent with a predominance of wind erosion over the last 3.8 billion years. Negative skewness at West Valley is explained by the removal of fine sand during active erosion, or alternatively, by excess accumulation of coarse sand from a local source. The coarse to very coarse sand particles of ripple armors in the basaltic plains have a unique combination of size and shape. Their distribution display significant changes in their statistical moments within the ~400 m that separate the Columbia Memorial Station from Bonneville Crater. Results are consistent with aeolian and/or impact deposition, while the elongated and rounded shape of the grains forming the ripples, as well as their direction of origin, could point to Ma'adim Vallis as a possible source. For smaller particles on the traverse, our findings confirm that aeolian processes have dominated over impact and other processes to produce sands with the observed size and shape patterns across a spectrum of geologic (e.g., ripples and plains soils) and aerographic settings (e.g., wind shadows).

Assessment of sand encroachment in Kuwait using GIS

NASA Astrophysics Data System (ADS)

Al-Helal, Anwar B.; Al-Awadhi, Jasem M.

2006-04-01

Assessment of sand encroachment in Kuwait using Geographical Information System (GIS) technology has been formulated as a Multi-Criteria Decision Making problem. The Delphi method and Analytical Hierarchy Process were adopted as evaluating techniques, in which experts’ judgments were analyzed for objectively estimating and weighting control factors. Seven triggering factors, depicted in the form of maps, were identified and ordered according to their priority. These factors are (1) wind energy; (2) surface sediment; (3) vegetation density; (4) land use; (5) drainage density; (6) topographic change and (7) vegetation type. The factor maps were digitized, converted to raster data and overlaid to determine their possible spatial relationships. Applying a susceptibility model, a map of sand encroachment susceptibility in Kuwait was developed. The map showed that the areas of very high and high sand encroachment susceptibility are located within the main corridor of sand pathway that coincides with the northwesterly dominant wind direction.

Using Large-Scale Roughness Elements to Control Sand and Dust Flux at the Keeler Dunes, Keeler, CA

NASA Astrophysics Data System (ADS)

Gillies, John; McCarley-Holder, Grace

2014-05-01

Controlling dust emission from areas that subsequently degrade air quality and threaten human and animal health and reduce the quality of life for people residing in proximity to such sources is necessary, but also challenging. Recent research has indicated that arrays of large roughness elements (height >0.3 m) can be used effectively to modulate sand transport and the associated dust emissions. Prediction of the rate of sand flux reduction as a function of downwind distance upon entering an array of roughness elements, and the equilibrium flux reduction in the interior of the array is possible using the known geometric properties of the roughness elements, their number, and published relationships. Air quality in the town of Keeler, CA (36 deg 29' 17.92" N, 117 deg 52' 24.62" W) is degraded by levels of particulate matter <10 µm aerodynamic diameter (PM10) during periods of elevated wind speeds due to sand transport and dust emissions in the nearby Keeler Dunes. A demonstration project was designed to evaluate the effectiveness of an array of roughness elements composed of solid elements and managed vegetation to meet sand and dust flux reduction criteria. This project has two major goals: 1) to demonstrate that solid roughness elements placed on areas of the Keeler Dunes immediately arrest sand movement to specified levels (target of 85% reduction), and 2) to assess whether native plant species, planted in the sheltered area of the solid roughness elements can effectively thrive and subsequently replace the solid roughness to achieve the desired sand flux reduction control efficiency. This poster describes the results related mostly to objective one, as considerable time has to pass before sufficient data will be obtained to evaluate the success of the planted and managed vegetation to achieve a control level provided by the solid element roughness array.

Eolian sand transport pathways in the southwestern United States: Importance of the Colorado River and local sources

USGS Publications Warehouse

Muhs, D.R.; Reynolds, R.L.; Been, J.; Skipp, G.

2003-01-01

Geomorphologists have long recognized that eolian sand transport pathways extend over long distances in desert regions. Along such pathways, sediment transport by wind can surmount topographic obstacles and cross major drainages. Recent studies have suggested that three distinct eolian sand transport pathways exist (or once existed) in the Mojave and Sonoran Desert regions of the southwestern United States. One hypothesized pathway is colian sand transport from the eastern Mojave Desert of California into western Arizona, near Parker, and would require sand movement across what must have been at least a seasonally dry Colorado River valley. We tested this hypothesis by mineralogical, geochemical and magnetic analyses of eolian sands on both sides of the Colorado River, as well as sediment from the river itself. Results indicate that dunes on opposite sides of the Colorado River are mineralogically distinct: eastern California dunes are feldspar-rich whereas western Arizona dunes are quartz-rich, derived from quartz-rich Colorado River sediments. Because of historic vegetation changes, little new sediment from the Colorado River is presently available to supply the Parker dunes. Based on this study and previous work, the Colorado River is now known to be the source of sand for at least three of the major dune fields of the Sonoran Desert of western Arizona and northern Mexico. On the other hand, locally derived alluvium appears to be a more important source of dune fields in the Mojave Desert of California. Although many geomorphologists have stressed the importance of large fluvial systems in the origin of desert dune fields, few empirical data actually exist to support this theory. The results presented here demonstrate that a major river system in the southwestern United States is a barrier to the migration of some dune fields, but essential to the origin of others. Published by Elsevier Science Ltd.

Atmospheric trace metals measured at a regional background site (Welgegund) in South Africa

NASA Astrophysics Data System (ADS)

Venter, Andrew D.; van Zyl, Pieter G.; Beukes, Johan P.; Josipovic, Micky; Hendriks, Johan; Vakkari, Ville; Laakso, Lauri

2017-03-01

Atmospheric trace metals can cause a variety of health-related and environmental problems. Only a few studies on atmospheric trace metal concentrations have been conducted in South Africa. Therefore the aim of this study was to determine trace metal concentrations in aerosols collected at a regional background site, i.e. Welgegund, South Africa. PM1, PM1-2. 5 and PM2. 5-10 samples were collected for 13 months, and 31 atmospheric trace metal species were detected. Atmospheric iron (Fe) had the highest concentrations in all three size fractions, while calcium (Ca) was the second-most-abundant species. Chromium (Cr) and sodium (Na) concentrations were the third- and fourth-most-abundant species, respectively. The concentrations of the trace metal species in all three size ranges were similar, with the exception of Fe, which had higher concentrations in the PM1 size fraction. With the exception of titanium (Ti), aluminium (Al) and manganese (Mg), 70 % or more of the trace metal species detected were in the smaller size fractions, which indicated the influence of industrial activities. However, the large influence of wind-blown dust was reflected by 30 % or more of trace metals being present in the PM2. 5-10 size fraction. Comparison of trace metals determined at Welgegund to those in the western Bushveld Igneous Complex indicated that at both locations similar species were observed, with Fe being the most abundant. However, concentrations of these trace metal species were significantly higher in the western Bushveld Igneous Complex. Fe concentrations at the Vaal Triangle were similar to levels thereof at Welgegund, while concentrations of species associated with pyrometallurgical smelting were lower. Annual average Ni was 4 times higher, and annual average As was marginally higher than their respective European standard values, which could be attributed to regional influence of pyrometallurgical industries in the western Bushveld Igneous Complex. All three size fractions indicated elevated trace metal concentrations coinciding with the end of the dry season, which could partially be attributed to decreased wet removal and increases in wind generation of particulates. Principal component factor analysis (PCFA) revealed four meaningful factors in the PM1 size fraction, i.e. crustal, pyrometallurgical-related and Au slimes dams. No meaningful factors were determined for the PM1-2. 5 and PM2. 5-10 size fractions, which was attributed to the large influence of wind-blown dust on atmospheric trace metals determined at Welgegund. Pollution roses confirmed the influence of wind-blown dust on trace metal concentrations measured at Welgegund, while the impact of industrial activities was also substantiated.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shaikhislamov, I. F.; Prokopov, P. A.; Berezutsky, A. G.

The interaction of escaping the upper atmosphere of a hydrogen-rich non-magnetized analog of HD 209458b with a stellar wind (SW) of its host G-type star at different orbital distances is simulated with a 2D axisymmetric multi-fluid hydrodynamic (HD) model. A realistic Sun-like spectrum of X-ray and ultraviolet radiation, which ionizes and heats the planetary atmosphere, together with hydrogen photochemistry, as well as stellar-planetary tidal interaction are taken into account to generate self-consistently an atmospheric HD outflow. Two different regimes of the planetary and SW interaction have been modeled. These are: (1) the “ captured by the star ” regime, whenmore » the tidal force and pressure gradient drive the planetary material beyond the Roche lobe toward the star, and (2) the “ blown by the wind ” regime, when sufficiently strong SW confines the escaping planetary atmosphere and channels it into the tail. The model simulates in detail the HD interaction between the planetary atoms, protons and the SW, as well as the production of energetic neutral atoms (ENAs) around the planet due to charge exchange between planetary atoms and stellar protons. The revealed location and shape of the ENA cloud, either as a paraboloid shell between the ionopause and bowshock (for the “ blown by the wind ” regime), or a turbulent layer at the contact boundary between the planetary stream and SW (for the “ captured by the star ” regime) are of importance for the interpretation of Ly α absorption features in exoplanetary transit spectra and characterization of the plasma environments.« less

Geochemical evidence for a complex origin for the Kelso dunes, Mojave National Preserve, California USA

USGS Publications Warehouse

Muhs, Daniel; Lancaster, Nicholas; Skipp, Gary L.

2017-01-01

The Kelso Dune field in southern California is intriguing because although it is of limited areal extent (~ 100 km2), it has a wide variety of dune forms and contains many active dunes (~ 40 km2), which is unusual in the Mojave Desert. Studies over the past eight decades have concluded that the dunes are derived primarily from a single source, Mojave River alluvium, under a dominant, westerly-to-northwesterly wind regime. The majority of these studies did not, however, present data to support the Mojave River as the only source. We conducted mineralogical and geochemical studies of most of the 14 geomorphically defined dune groups of the Kelso Dune field as well as potential sand sources, alluvial sediments from the surrounding mountain ranges. Results indicate that sands in the nine western dune groups have K/Rb and K/Ba (primarily from K-feldspar) compositions that are indistinguishable from Mojave River alluvium (westerly/northwesterly winds) and Budweiser Wash alluvium (southwesterly winds), permitting an interpretation of two sources. In contrast, sands from the five eastern dune groups have K/Rb and K/Ba values that indicate significant inputs from alluvial fan deposits of the Providence Mountains. This requires either rare winds from the east or southeast or, more likely, aeolian reworking of distal Providence Mountain fan sediments by winds from the west, at a rate greater than input from the Mojave River or other western sources. The results indicate that even a small dune field can have a complex origin, either from seasonally varying winds or complex alluvial-fan-dune interaction. Application of K/Rb and K/Ba in K-feldspar as a provenance indicator could be used in many of the world's ergs or sand seas, where dune origins are still not well understood or are controversial. Four examples are given from Africa and the Middle East where such an approach could yield useful new information about dune sand provenance.

A complex origin for the Kelso Dunes, Mojave National Preserve, California, USA: A case study using a simple geochemical method with global applications

NASA Astrophysics Data System (ADS)

Muhs, Daniel R.; Lancaster, Nicholas; Skipp, Gary L.

2017-01-01

The Kelso Dune field in southern California is intriguing because although it is of limited areal extent ( 100 km2), it has a wide variety of dune forms and contains many active dunes ( 40 km2), which is unusual in the Mojave Desert. Studies over the past eight decades have concluded that the dunes are derived primarily from a single source, Mojave River alluvium, under a dominant, westerly-to-northwesterly wind regime. The majority of these studies did not, however, present data to support the Mojave River as the only source. We conducted mineralogical and geochemical studies of most of the 14 geomorphically defined dune groups of the Kelso Dune field as well as potential sand sources, alluvial sediments from the surrounding mountain ranges. Results indicate that sands in the nine western dune groups have K/Rb and K/Ba (primarily from K-feldspar) compositions that are indistinguishable from Mojave River alluvium (westerly/northwesterly winds) and Budweiser Wash alluvium (southwesterly winds), permitting an interpretation of two sources. In contrast, sands from the five eastern dune groups have K/Rb and K/Ba values that indicate significant inputs from alluvial fan deposits of the Providence Mountains. This requires either rare winds from the east or southeast or, more likely, aeolian reworking of distal Providence Mountain fan sediments by winds from the west, at a rate greater than input from the Mojave River or other western sources. The results indicate that even a small dune field can have a complex origin, either from seasonally varying winds or complex alluvial-fan-dune interaction. Application of K/Rb and K/Ba in K-feldspar as a provenance indicator could be used in many of the world's ergs or sand seas, where dune origins are still not well understood or are controversial. Four examples are given from Africa and the Middle East where such an approach could yield useful new information about dune sand provenance.

Wind-driven particle mobility on Mars: Insights from Mars Exploration Rover observations at "El Dorado" and surroundings at Gusev Crater

USGS Publications Warehouse

Sullivan, R.; Arvidson, R.; Bell, J.F.; Gellert, Ralf; Golombek, M.; Greeley, R.; Herkenhoff, K.; Johnson, J.; Thompson, S.; Whelley, P.; Wray, J.

2008-01-01

The ripple field known as 'El Dorado' was a unique stop on Spirit's traverse where dust-raising, active mafic sand ripples and larger inactive coarse-grained ripples interact, illuminating several long-standing issues of Martian dust mobility, sand mobility, and the origin of transverse aeolian ridges. Strong regional wind events endured by Spirit caused perceptible migration of ripple crests in deposits SSE of El Dorado, erasure of tracks in sandy areas, and changes to dust mantling the site. Localized thermal vortices swept across El Dorado, leaving paths of reduced dust but without perceptibly damaging nearly cohesionless sandy ripple crests. From orbit, winds responsible for frequently raising clay-sized dust into the atmosphere do not seem to significantly affect dunes composed of (more easily entrained) sand-sized particles, a long-standing paradox. This disparity between dust mobilization and sand mobilization on Mars is due largely to two factors: (1) dust occurs on the surface as fragile, low-density, sand-sized aggregates that are easily entrained and disrupted, compared with clay-sized air fall particles; and (2) induration of regolith is pervasive. Light-toned bed forms investigated at Gusev are coarse-grained ripples, an interpretation we propose for many of the smallest linear, light-toned bed forms of uncertain origin seen in high-resolution orbital images across Mars. On Earth, wind can organize bimodal or poorly sorted loose sediment into coarse-grained ripples. Coarse-grained ripples could be relatively common on Mars because development of durable, well-sorted sediments analogous to terrestrial aeolian quartz sand deposits is restricted by the lack of free quartz and limited hydraulic sediment processing. Copyright 2008 by the American Geophysical Union.

Bonestell Crater

NASA Image and Video Library

2018-04-17

Bonestell Crater is a relatively young crater located in Acidalia Planitia. The grooved surface of the ejecta blanket is evident in this VIS image. Dust blown into the crater and the downslope movement of fine materials from the rim are slowly modifying the crater features. Orbit Number: 71230 Latitude: 36.398 Longitude: 329.708 Instrument: VIS Captured: 2018-01-04 05:31 https://photojournal.jpl.nasa.gov/catalog/PIA22371

Application of a combined measurement and modeling method to quantify windblown dust emissions from the exposed playa at Mono Lake, California.

PubMed

Ono, Duane; Kiddoo, Phill; Howard, Christopher; Davis, Guy; Richmond, Kenneth

2011-10-01

Particulate matter < or =10 microm (PM10) emissions due to wind erosion can vary dramatically with changing surface conditions. Crust formation, mechanical disturbance, soil texture, moisture, and chemical content of the soil can affect the amount of dust emitted during a wind event. A refined method of quantifying windblown dust emissions was applied at Mono Lake, CA, to account for changing surface conditions. This method used a combination of real-time sand flux monitoring, ambient PM10 monitoring, and dispersion modeling to estimate dust emissions and their downwind impact. The method identified periods with high emissions and periods when the surface was stable (no sand flux), even though winds may have been high. A network of 25 Cox sand catchers (CSCs) was used to measure the mass of saltating particles to estimate sand flux rates across a 2-km2 area. Two electronic sensors (Sensits) were used to time-resolve the CSC sand mass to estimate hourly sand flux rates, and a perimeter tapered element oscillating microbalance (TEOM) monitor measured hourly PM10 concentrations. Hourly sand flux rates were related by dispersion modeling to hourly PM10 concentrations to back-calculate the ratio of vertical PM10 flux to horizontal sand flux (K-factors). Geometric mean K-factor values (K(f)) were found to change seasonally, ranging from 1.3 x 10(-5) to 5.1 x 10(-5) for sand flux measured at 15 cm above the surface (q15). Hourly PM10 emissions, F, were calculated by applying seasonal K-factors to sand flux measurements (F = K(f) x q15). The maximum hourly PM10 emission rate from the study area was 76 g/m2 x hr (10-m wind speed = 23.5 m/sec). Maximum daily PM10 emissions were estimated at 450 g/m2 x day, and annual emissions at 1095 g/m2 x yr. Hourly PM10 emissions were used by the U.S. Environmental Protection Agency (EPA) guideline AERMOD dispersion model to estimate downwind ambient impacts. Model predictions compared well with monitor concentrations, with hourly PM10 ranging from 16 to over 60,000 microg/m3 (slope = 0.89, R2 = 0.77).

Scale-dependent effects of habitat on movements and path structure of reef sharks at a predator-dominated atoll.

PubMed

Papastamatiou, Yannis P; Lowe, Christopher G; Caselle, Jennifer E; Friedlander, Alan M

2009-04-01

The effects of habitat on the ecology, movements, and foraging strategies of marine apex predators are largely unknown. We used acoustic telemetry to quantify the movement patterns of blacktip reef sharks (Carcharhinus melanopterus) at Palmyra Atoll National Wildlife Refuge, in the Pacific Ocean. Sharks had relatively small home ranges over a timescale of days to weeks (0.55 +/- 0.24 km2) and showed strong site fidelity to sand-flat ledges within the west lagoon over a three-year period. Sharks showed evidence of diel and tidal movements, and they utilized certain regions of the west lagoon disproportionately. There were ontogenetic shifts in habitat selection, with smaller sharks showing greater selection for sand-flat habitats, and pups (total length 35-61 cm) utilizing very shallow waters on sand-flats, potentially as nursery areas. Adult sharks selected ledge habitats and had lower rates of movement when over sand-flats and ledges than they did over lagoon waters. Fractal analysis of movements showed that over periods of days, sharks used patches that were 3-17% of the scale of their home range. Repeat horizontal movements along ledge habitats consisted of relatively straight movements, which theoretical models consider the most efficient search strategy when forage patches may be spatially and temporally unpredictable. Although sharks moved using a direct walk while in patches, they appeared to move randomly between patches. Microhabitat quantity and quality had large effects on blacktip reef shark movements, which have consequences for the life-history characteristics of the species and potentially the spatial distribution of behaviorally mediated effects on lower trophic levels throughout the Palmyra ecosystem.

Overview of Initial Results From Studies of the Bagnold Dune Field on Mars by the Curiosity Rover

NASA Astrophysics Data System (ADS)

Bridges, Nathan; Ehlmann, Bethany; Ewing, Ryan; Newman, Claire; Sullivan, Robert; Conrad, Pamela; Cousin, Agnes; Edgett, Kenneth; Fisk, Martin; Fraeman, Abigail; Johnson, Jeffrey; Lamb, Michael; Lapotre, Mathieu; Le Mouélic, Stéphane; Martinez, German; Meslin, Pierre-Yves; Thompson, Lucy; van Beek, Jason; Vasavada, Ashwin; Wiens, Roger

2016-04-01

The Curiosity Rover is currently studying the Bagnold Dunes in Gale Crater. Here we provide a general overview of results and note that other EGU presentations will focus on specific aspects. The in situ activities have not yet occurred as of this writing, but other analyses have been performed approaching and within the dunefield. ChemCam passive spectra of Bagnold Dune sands are consistent with the presence of olivine. Two APXS spots on the High Dune stoss slope margin, and two others in an engineering test sand patch, show less inferred dust, greater Si, and higher Fe/Mn than other "soils" in Gale Crater. ChemCam analyses of more than 300 soils along the Curiosity traverse show that both fine and coarse soils have increasing iron and alkali content as the Bagnold Dunes are approached, a trend that may reflect admixtures of local rocks (alkalis + iron) to the fines, but also a contribution of Bagnold-like sand (iron) that increases toward the dunefield. MAHLI images of sands on the lower east stoss slope of High Dune show medium and coarse sand in ripple forms, and very fine and fine sand in ripple troughs. Most grains are dark gray, but some are also brick-red/brown, white, green translucent, yellow, brown" colorless translucent, or vitreous spheres HiRISE orbital images show that the Bagnold Dunes migrate on the order of decimeters or more per Earth year. Prior to entering the dune field, wind disruption of dump piles and grain movement was observed over multi-sol time spans, demonstrating that winds are of sufficient strength to mobilize unconsolidated material, either through direct aerodynamic force or via the action of smaller impacting grains. Within the dune field, we are, as of this writing, engaged in change detection experiments with Mastcam and ChemCam's RMI camera. Data we have so far, spanning 8 sols from the same location, shows no changes. Mastcam and RMI images of the stoss sides of Namib, Noctivaga, and High Dune show that the "ripples" seen with HiRISE are more akin to ˜1 m scale wavelength bedforms that exhibit clear stoss slopes, sinuous crests, slip faces, and grain flow and fall features. One interpretation is that these are fluid drag bedforms that form in an aeolian regime distinct from that on Earth due to the large viscous sub-layer in the low density Martian atmosphere. Superimposed on these bedforms are more definitive ripples of ˜10 cm wavelength, similar to impact dune ripples on Earth. The slipface of Namib Dune shows distinct flow lobes, bounded at the top by alcoves and at the bottom by lobate toes, with prominent detachment scars. Ripples upon and oriented orthogonal to the slipface indicate sand transport from winds within the dune recirculation zone. Some of the flow lobes have few ripples, indicating recent avalanching. The internal structure and stratigraphy of the edge Namib Dunes will likely be forthcoming in the trenching at the first in situ stop and will be reported at EGU.

Development of Yellow Sand Image Products Using Infrared Brightness Temperature Difference Method

NASA Astrophysics Data System (ADS)

Ha, J.; Kim, J.; Kwak, M.; Ha, K.

2007-12-01

A technique for detection of airborne yellow sand dust using meteorological satellite has been developed from various bands from ultraviolet to infrared channels. Among them, Infrared (IR) channels have an advantage of detecting aerosols over high reflecting surface as well as during nighttime. There had been suggestion of using brightness temperature difference (BTD) between 11 and 12¥ìm. We have found that the technique is highly depends on surface temperature, emissivity, and zenith angle, which results in changing the threshold of BTD. In order to overcome these problems, we have constructed the background brightness temperature threshold of BTD and then aerosol index (AI) has been determined from subtracting the background threshold from BTD of our interested scene. Along with this, we utilized high temporal coverage of geostationary satellite, MTSAT, to improve the reliability of the determined AI signal. The products have been evaluated by comparing the forecasted wind field with the movement fiend of AI. The statistical score test illustrates that this newly developed algorithm produces a promising result for detecting mineral dust by reducing the errors with respect to the current BTD method.

Analytical mesoscale modeling of aeolian sand transport

NASA Astrophysics Data System (ADS)

Lämmel, Marc; Kroy, Klaus

2017-11-01

The mesoscale structure of aeolian sand transport determines a variety of natural phenomena studied in planetary and Earth science. We analyze it theoretically beyond the mean-field level, based on the grain-scale transport kinetics and splash statistics. A coarse-grained analytical model is proposed and verified by numerical simulations resolving individual grain trajectories. The predicted height-resolved sand flux and other important characteristics of the aeolian transport layer agree remarkably well with a comprehensive compilation of field and wind-tunnel data, suggesting that the model robustly captures the essential mesoscale physics. By comparing the predicted saturation length with field data for the minimum sand-dune size, we elucidate the importance of intermittent turbulent wind fluctuations for field measurements and reconcile conflicting previous models for this most enigmatic emergent aeolian scale.

Water movement in the unsaturated zone at a low-level radioactive-waste burial site near Barnwell, South Carolina

USGS Publications Warehouse

Dennehy, Kevin F.; McMahon, Peter B.

1989-01-01

Four unsaturated-zone monitoring sites and a meteorologic station were installed at the low-level radioactive-waste burial site near Barnwell, S.C., to investigate the geohydrologic and climatologic factors affecting water movement in the unsaturated zone. The study site is located in the Atlantic Coastal Plain. The unsaturated zone consists of a few centimeters to more than 1 meter of surface sand, underlain by up to 15 meters of clayey sand. Two monitoring sites were installed in experimental trenches, and two were installed in radioactive-waste trenches. Two different trench designs were evaluated at the monitoring sites. A meteorologic station was used to measure precipitation and to calculate actual evapotranspiration using the Bowen ratio method. Soil-moisture tensiometers, soil-moisture conductance probes, and temperature sensors were used to monitor soil-water movement in and adjacent to the trenches. Tracer tests using sodium chloride were conducted at each monitoring site. Hydrologic properties of unsaturated-zone materials were also determined. Data collection at the monitoring sites began in January 1982 and continued until early May 1984. Tensiometer data show that the unsaturated materials had their highest percent saturations in winter and spring. Saturations in the backfill sand varied from 20 to 100 percent, and in the adjacent undisturbed and overlying compacted clayey sand, from about 75 to 100 percent. The same pattern generally was observed at all four monitoring sites. The tracer-test data indicate that water movement occurred mainly during the recharge period, winter and spring. The tracer-test results enabled computation of rates of unsaturated flow in the compacted clayey-sand cap, the compacted clayey-sand barrier, and the backfill sand. A micro-scale hydrologic budget was determined for an undisturbed part of the site from July 1983 through June 1984.Total precipitation was 144 centimeters, and actual evapotranspiration was 101 centimeters. Additionally, because tensiometer data indicate negligible water-storage changes in the unsaturated zone, it is estimated that approximately 43 centimeters of recharge reached the water table. During 1984, the rise and fall of ponded water in an experimental trench was continuously monitored with a digital recorder. This water-level record was used to compute the rate of leakage of ponded water from that trench--1 x 10 -5 centimeter per second. A cross-sectional finite-element model of variably saturated flow was used to test the conceptual model of water movement in the unsaturated zone and to illustrate the effect of trench design on water movement into the experimental trenches. Monitoring and model results show that precipitation on trenches infiltrated the trench cap and moved vertically into the trench backfill material. Precipitation on the undisturbed material adjacent to the trenches moved vertically through the surface sand and continued either downward into undisturbed clayey sand or laterally along the sand/clayey-sand interface into the backfill sand, depending on trench design. The trench construction practice of placing a compacted clayey-sand barrier around the trench greatly inhibits soil water from entering the trench.

Defense Coastal/Estuarine Research Program (DCERP) Baseline Monitoring Plan

DTIC Science & Technology

2007-09-19

climatological stress (e.g., temperature, drought) and shorter-term air pollutant stress (oxidants and metals ). Heavy metals of fine PM have been...speciation of the fine and coarse PM fractions will allow distinction between different PM sources such as wind blown soil dust, including dust...emitting 12% of the total PM2.5 mass (U.S. EPA, 2004b). Source apportionment modeling of PM2.5 mass concentrations from 24 Speciation Defense Coastal

Effects of simulated rain acidified with sulfuric acid on host-parasite interactions

Treesearch

D. S. Shriner

1976-01-01

Wind-blown rain, rain splash, and films of free moisture play important roles in the epidemiology of many plant diseases. The effects of simulated rain acidified with sulfuric acid were studied on several host-parasite systems. Plants were exposed, in greenhouse or field, to simulated rain of pH 3.2 ? 0.1 or pH 6.0 ? 0.2. Simulated "rain" of pH 3.2 resulted...

Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Eastern Mountains and Piedmont Region (Version 2.0)

DTIC Science & Technology

2012-04-01

are the Blue Ridge Province and the Piedmont Plateau, composed mainly of highly eroded Precambrian metamorphic rocks . The Piedmont Plateau extends...older igneous and metamorphic rocks (Atwood 1940; Hunt 1974; USGS 2004). Caverns and karst features are found in marble formations in the Piedmont...colluvium derived from sandstone, shale, limestone, and metamorphic and igneous rocks . Other parent materials include deposits of wind-blown loess

A field study of flow turbulence and sediment transport dynamics on a beach surface in the lee of a coastal foredune under offshore winds

NASA Astrophysics Data System (ADS)

Baas, A. C.; Jackson, D.; Cooper, J. A.; Lynch, K.; Delgado-Fernandez, I.; Beyers, M.; Lee, Z. S.

2010-12-01

The past decade has seen a growing body of research on the relation between turbulence in the wind and the resultant transport of sediment over active sand surfaces. Widespread use of sonic anemometry and high-frequency sand transport sensors and traps have facilitated recent field studies over dunes and beach surfaces, to move beyond monitoring of mean wind speed and bulk transport to more detailed measurements at much higher spatio-temporal resolutions. In this paper we present results of a field study conducted in the recirculation flow and re-attachment zone on a beach behind a foredune at Magilligan Strand, Northern Ireland. The offshore winds over the foredune at this site are associated with flow separation and reversal located over the beach surface in the lee of the dune row, often strong enough to induce sand transport toward the toe of the foredune (‘against’ the overall offshore flow). The re-attachment and recirculation zone are associated with strongly turbulent fluid flow and complex streamlines that do not follow the underlying topography. High frequency (25 Hz) wind and sand transport data were collected at a grid of point locations distributed over the beach surface between 35 m to 55 m distance from the 10 m high dune crest, using ultrasonic anemometers at 0.5 m height and co-located load cell traps and Safires at the bed surface. The wind data are used to investigate the role of Reynolds shear stresses and quadrant analysis techniques for identifying burst-sweep events in relation to sand transport events. This includes an assessment of the issues involved with data rotations for yaw, pitch, and roll corrections relative to complex flow streamlines, and the subsequently derived turbulence parameters based on fluctuating vector components (u’, v’, w’). Results illustrate how transport may exist under threshold mean velocities because of the role played by coherent flow structures, and the findings corroborate previous findings that shear velocity obtained using traditional wind profile approaches does not correlate with transport as additional stresses are generated due to turbulent structures.

Aeolian transport of biota with dust: A wind tunnel experiment

NASA Astrophysics Data System (ADS)

Rivas, J. A., Jr.; Gill, T. E.; Van Pelt, R. S.; Walsh, E.

2015-12-01

Ephemeral wetlands are ideal sources for dust emission, as well as repositories for dormant stages of aquatic invertebrates. An important component of invertebrate dispersal and colonization to new areas is the ability to be entrained into the atmosphere. Aquatic invertebrate eggs fall within the size of dust and sand grains (30-600μm), are less dense and aerodynamically shaped. We have shown previously that aquatic invertebrates can be dispersed long distances in dust storms but the extent of transport of taxa based on diapausing egg size/morphology has not been investigated. Here, we control the wind erosion process in a wind tunnel to test entrainment of diapausing stages of brine shrimp, clam shrimp, tadpole shrimp, fairy shrimp, Daphnia, and the rotifers Brachionus plicatilis and B. calyciflorus into the air by saltation. Diapausing eggs were mixed with sterilized wind-erodible soil. The soil/egg mixture was moistened with distilled water and air dried to form a crust. Dust was generated in a wind tunnel by releasing sand grains that act as saltator material similar to wind-entrained natural sands. Maximum wind velocity was 10m/s and entrained particles were sampled through an isokinetic horizontal intake opening. Aeolian sediment was collected from three points in the system; transfer section for coarse sediment, the pan subtending a settling chamber for finer saltation-sized sediment, and two paper filters for suspension-sized sediment. Samples were then passed through 250 and 350 μm sieves to remove abrader sand and rehydrated with various sterile media depending on the type of organism. We retrieved viable brine, fairy, and tadpole shrimp, ostracods, Daphnia, and diapausing eggs of the rotifers after hydration. This experiment demonstrates that resting stages of many invertebrates can be wind-eroded due to size and egg morphology and remain viable under controlled conditions mimicking dust emission.

Aeolian features and processes at the Mars Pathfinder landing site

USGS Publications Warehouse

Greeley, Ronald; Kraft, Michael; Sullivan, Robert; Wilson, Gregory; Bridges, Nathan; Herkenhoff, Ken; Kuzmin, Ruslan O.; Malin, Michael; Ward, Wes

1999-01-01

The Mars Pathfinder landing site contains abundant features attributed to aeolian, or wind, processes. These include wind tails, drift deposits, duneforms of various types, ripplelike features, and ventifacts (the first clearly seen on Mars). Many of these features are consistant with formation involving sand-size particles. Although some features, such as dunes, could develop from saltating sand-size aggregates of finer grains, the discovery of ventifact flutes cut in rocks strongly suggests that at least some of the grains are crystalline, rather than aggregates. Excluding the ventifacts, the orientations of the wind-related features correlate well with the orientations of bright wind steaks seen on Viking Orbiter images in the general area. They also correlate with wind direction predictions from the NASA-Ames General Circulation Model (GCM) which show that the strongest winds in the area occur in the northern hemisphere winter and are directed toward 209°. Copyright 1999 by the American Geophysical Union.

Dunes and microdunes on Venus: Why were so few found in the Magellan data?

NASA Technical Reports Server (NTRS)

Weitz, Catherine M.; Plaut, Jeffrey J.; Greeley, Ronald; Saunders, R. Steven

1994-01-01

A search through cycle 1, 2, and 3 Magellan radar data covering 98% of the surface of Venus revealed very few dunes. Only two possible dune fields and several areas that may contain microdunes smaller than the resolution of the images (75 m) were identified. The Aglaonice dune field was identified in the cycle 1 images by the specular returns characteristic of dune faces oriented perpendicular to the radar illumination. Cycle 1 and 2 data of the Fortuna-Meshkenet dune field indicate that there has been no noticeable movement of the dunes over an 8-month period. The dunes, which are oriented both parallel and perpendicular to the radar illumination, appear to be dark features on a brighter substrate. Bright and dark patches that were visible in either cycle 1 or 2 data, but not both, allowed identification of several regions in the southern part of Venus that may contain microdunes. The microdunes are associated with several parabolic crater deposits in the region and are probably similar to those formed in wind tunnel experiments under Venus-like conditions. Bragg scattering and/or subpixel relfections from the near-normal face on asymmetric microdunes may account for these bright and dark patches. Look-angle effects and the lack of sufficient sand-size particles seem to be most likely reasons so few dunes were identified in Magellan data. Insufficient wind speeds, thinness of sand cover, and difficulty in identifying isolated dunes may also be contributors to the scarcity of dunes.

Dunes and Microdunes on Venus: Why Were So Few Found in the Magellan Data?

NASA Technical Reports Server (NTRS)

Weitz, Catherine M.; Plaut, Jeffrey J.; Greeley, Ronald; Saunders, R. Steven

1994-01-01

A search through cycle 1, 2, and 3 Magellan radar data covering 98% of the surface of Venus revealed very few dunes. Only two possible dune fields and several areas that may contain microdunes smaller than the resolution of the images (75 m) were identified. The Aglaonice dune field was identified in the cycle I images by the specular returns characteristic of dune faces oriented perpendicular to the radar illumination. Cycle 1 and 2 data of the Fortuna-Meshkenet dune field indicate that there has been no noticeable movement of the dunes over an 8-month period. The dunes, which are oriented both parallel and perpendicular to the radar illumination, appear to be dark features on a brighter substrate. Bright and dark patches that were visible in either cycle 1 or 2 data, but not both, allowed identification of several regions in the southern part of Venus that may contain microdunes. The microdunes are associated with several parabolic crater deposits in the region and are probably similar to those formed in wind tunnel experiments under Venus-like conditions. Bragg scattering and/or subpixel reflections from the near-normal face on asymmetric microdunes may account for these bright and dark patches. Look-angle effects and the lack of sufficient sand-size particles seem to be the most likely reasons so few dunes were identified in Magellan data. Insufficient wind speeds, thinness of sand cover, and difficulty in identifying isolated dunes may also be contributors to the scarcity of dunes.

Windy Mars: A Dynamic Planet as Seen by the HiRISE Camera

NASA Technical Reports Server (NTRS)

Bridges, N. T.; Geissler, P. E.; McEwen, A. S.; Thomson, B. J.; Chuang, F. C.; Herkenhoff, K. E.; Keszthelyi, L. P.; Martnez-Alonso, S.

2007-01-01

With a dynamic atmosphere and a large supply of particulate material, the surface of Mars is heavily influenced by wind-driven, or aeolian, processes. The High Resolution Imaging Science Experiment (HiRISE) camera on the Mars Reconnaissance Orbiter (MRO) provides a new view of Martian geology, with the ability to see decimeter-size features. Current sand movement, and evidence for recent bedform development, is observed. Dunes and ripples generally exhibit complex surfaces down to the limits of resolution. Yardangs have diverse textures, with some being massive at HiRISE scale, others having horizontal and cross-cutting layers of variable character, and some exhibiting blocky and polygonal morphologies. 'Reticulate' (fine polygonal texture) bedforms are ubiquitous in the thick mantle at the highest elevations.

Are They Telltale Ripples?

NASA Technical Reports Server (NTRS)

2004-01-01

This false-color image from the Mars Exploration Rover Spirit's panoramic camera shows peak-like formations on the martian terrain at Gusev Crater. Scientists have been analyzing these formations, which have coarse particles accumulating on their tops, or crests. This characteristic classifies them as ripples instead of dunes, which have a more uniform distribution of particle sizes. Scientists are looking further into such formations, which can give insight to the wind direction and velocity on Mars, as well as the material that is being moved by the wind. This image was taken on the 40th martian day, or sol, of Spirit's mission.

[figure removed for brevity, see original site] Click on image for larger view [Image credit: NASA/JPL/ASU]

This diagram illustrates how windblown sediments travel. There are three basic types of particles that undergo different motions depending on their size. These particles are dust, sand and coarse sand, and their sizes approximate flour, sugar, and ball bearings, respectively. Sand particles move along the 'saltation' path, hitting the surface downwind. When the sand hits the surface, it sends dust into the atmosphere and gives coarse sand a little shove. Mars Exploration Rover scientists are studying the distribution of material on the surface of Mars to better understand how winds shaped the landscape.

Geomorphic change on the Missouri River during the flood of 2011: Chapter I in 2011 Floods of the Central United States

USGS Publications Warehouse

Schenk, Edward R.; Skalak, Katherine J.; Benthem, Adam J.; Dietsch, Benjamin J.; Woodward, Brenda K.; Wiche, Gregg J.; Galloway, Joel M.; Nustad, Rochelle A.; Hupp, Cliff R.

2014-01-01

The 2011 flood on the Missouri River was one of the largest floods since the river became regulated by a series of high dams in the mid-20th century (greater than 150,000 cubic feet per second during the peak). The flood persisted through most of the summer, eroding river banks, adding sand to sandbars, and moving the thalweg of the channel in many places. The U.S. Geological Survey monitored and assessed the changes in two reaches of the Missouri River: the Garrison Reach in North Dakota, bounded by the Garrison Dam and the Lake Oahe Reservoir, and the Recreational Reach along the boundary of South Dakota and Nebraska bounded upstream by the Gavins Point Dam and extending downstream from Ponca, Nebraska. Historical cross-section data from the Garrison Dam closure until immediately before the flood indicate that the upper reaches of the river near the dam experienced rapid erosion, channel incision, and island/sandbar loss following the dam closure. The erosion, incision, and land loss lessened with time. Conversely, the lower reach near the Lake Oahe Reservoir slackwaters became depositional with channel in-filling and sandbar growth through time as the flow slowed upon reaching the reservoir. Preliminary post-flood results in the Garrison Reach indicate that the main channel has deepened at most cross-sections whereas sandbars and islands have grown vertically. Sandbars and the thalweg migrated within the Recreational Reach, however net scouring and aggradation was minimal. Changes in the two-dimensional area of sandbars and islands are still being assessed using high-resolution satellite imagery. A sediment balance can be constructed for the Garrison Reach using cross-sections, bathymetric data, sand traps for wind-blown material, a quasi-three-dimensional numerical model, and dating of sediment cores. Data collection and analysis for a reach-scale sediment balance and a concurrent analysis of the effects of riparian and island vegetation on sediment deposition currently (2014) is ongoing.

A Window into the Past

NASA Image and Video Library

2017-10-23

The layered sedimentary deposits inside the giant canyons of Mars have puzzled scientists for decades. These light toned deposits have fine, horizontal laminations that are unlike the rugged rim rock of the Valles Marineris as seen by NASA's Mars Reconnaisance Orbiter (MRO). Various ideas for the origin of the layered sediments have suggested lake deposits, wind blown dust and sand, or volcanic materials that erupted after the canyon was formed, and possibly filled with water. One particular layered deposit, called Ceti Mensa, attracted attention because its deep red color in images collected by the Viking Orbiter mission during the 1970s. Located in west Candor Chasma in the north of the Valles Marineris, Ceti Mensa is an undulating plateau that rises 3 kilometers above the canyon floor and is bounded by steep scarps up to 1.5 kilometers in height. Deep red hues are on the west-facing scarp in particular. The red tint may be due to the presence of crystalline ferric oxide, suggesting that the material may have been exposed to heat or water, or both. Spectral measurements by the Mars Express OMEGA and MRO CRISM instruments confirm the presence of hydrated sulfate salts, such as gypsum and kieserite . These minerals are important for two reasons. On Earth, they typically form in wet environments, suggesting that the deposits in Ceti Mensa may have formed under water. On Mars, these deposits could be valuable to future Martian colonists as fertilizer for growing crops. In a view of the colorful west-facing scarp of Ceti Mensa, we see the interior layers of the deposit, giving us a window into the past history of the sediments as they accumulated over time. We also see layers that were previously too small to view, and a surface that is thoroughly fractured, eroded into knobs, and partially covered by young dark sand dunes. https://photojournal.jpl.nasa.gov/catalog/PIA22051

Aeolian Sand Transport with Collisional Suspension

NASA Technical Reports Server (NTRS)

Jenkins, James T.; Pasini, Jose Miguel; Valance, Alexandre

2004-01-01

Aeolian transport is an important mechanism for the transport of sand on Earth and on Mars. Dust and sand storms are common occurrences on Mars and windblown sand is responsible for many of the observed surface features, such as dune fields. A better understanding of Aeolian transport could also lead to improvements in pneumatic conveying of materials to be mined for life support on the surface of the Moon and Mars. The usual view of aeolian sand transport is that for mild winds, saltation is the dominant mechanism, with particles in the bed being dislodged by the impact of other saltating particles, but without in-flight collisions. As the wind becomes stronger, turbulent suspension keeps the particles in the air, allowing much longer trajectories, with the corresponding increase in transport rate. We show here that an important regime exists between these two extremes: for strong winds, but before turbulent suspension becomes dominant, there is a regime in which in-flight collisions dominate over turbulence as a suspension mechanism, yielding transport rates much higher than those for saltation. The theory presented is based on granular kinetic theory, and includes both turbulent suspension and particle-particle collisions. The wind strengths for which the calculated transport rates are relevant are beyond the published strengths of current wind tunnel experiments, so these theoretical results are an invitation to do experiments in the strong-wind regime. In order to make a connection between the regime of saltation and the regime of collisional suspension, it is necessary to better understand the interaction between the bed and the particles that collide with it. This interaction depends on the agitation of the particles of the bed. In mild winds, collisions with the bed are relatively infrequent and the local disturbance associated with a collision can relax before the next nearby collision. However, as the wind speed increases, collision become more frequent and the agitation need not decay completely. In the regime of collisional suspension, the particles near the surface of the bed are assumed to be in a state of constant agitation. We indicate the conditions at the bed corresponding to the limits of saltation and collisional suspension and outline experiments, simulations, and modeling that have been undertaken to bridge these limits.

The influence of wave-, wind- and tide-forced currents on headland sand bypassing - Study case: Santa Catarina Island north shore, Brazil

NASA Astrophysics Data System (ADS)

Vieira da Silva, Guilherme; Toldo, Elírio E., Jr.; Klein, Antonio H. da F.; Short, Andrew D.

2018-07-01

Investigations of headland sand bypassing are still an under-reported subject in the literature. This paper aims to understand the contribution of currents forced by different mechanisms such as tides, winds (i.e. local wind acting over the ocean surface generating currents, without considering wave generation) and waves (as they approach/break on the coast) to headland sand bypassing. The study was carried out in an area comprising a series of seven headlands with varying wave exposure due to changes in shoreline orientation and increasing tidal influence close to a relatively large bay. This paper uses a calibrated and validated process-based model (Delft3D) to simulate a series of scenarios including spring and neap tides during flood and ebb conditions and a range of wind and wave scenarios that encompass both average and extreme conditions. The results indicate that waves are the main driving force for the headland bypassing as they transport sand at rates two orders of magnitude higher than tide- or wind-driven sediment transport. The tide-driven currents can only transport sediment during spring tides in locations where the currents are intensified. It is also demonstrated that the wave direction plays an important role in sediment transport. In exposed areas with larger headlands a combination of wave directions is required to first transport sediment offshore (out of the beach) and secondly to transport sediment alongshore and back to the next beach. Whereas in areas with little variation in wave direction exposure, the same oblique wave direction is responsible for the entire headland bypassing process. This is the first time the contribution of tide-, winds- and wave-generated sediment transport to headland bypassing have been studied.

The Karakum and Kyzylkum sand seas dynamics; mapping and palaeoclimatic interpretations

NASA Astrophysics Data System (ADS)

Maman, Shimrit; Blumberg, Dan G.; Tsoar, Haim; Porat, Naomi

2015-04-01

Sand seas are large basins in deserts that are mantled by wind-swept sand and that exhibit varying degrees of vegetation cover. Wilson (1973) was the first to globally map and classify sand seas. Beyond Wilson's maps, however, little research has been published regarding the Karakum and Kyzylkum sand seas of Central Asia. Wilson's maps delineate active ergs from inactive ergs based solely on precipitation. His assumption of annual average rainfall as a factor determining mobility vs. stability of sand seas is too simplistic and does not take into consideration other factors such as biogenic soil crusts and wind power, both of which are known to have major effects on the dynamics of sand dunes. Literature related to mapping and classifying the Central Asian ergs by remote sensing or sand sea classification state (stable/active) is lacking. Moreover, the palaeoclimatic significance of dunes in Central Asia is difficult to assess, as there has been few studies of dune stratigraphy and numerical ages are lacking. Optically stimulated luminescence (OSL) is a firm optical dating method that is used to determine the elapsed time since quartz grains were last exposed to sunlight, thus, their burial. Yet, absolute ages indicating mobilization and stabilization of these sands, are still inadequately known and are here under discussion. The broad concern of this research was to determine the dynamics of the Central Asian sand seas and study the palaeoclimatic changes that brought to their stabilization. As there are no reliable maps or aeolian discussion of these sands, establishment of a digital data base was initially conducted, focusing on identifying and mapping these sand seas. The vast area and inaccessibility make traditional mapping methods virtually impossible. A variety of space-borne imagery both optical and radar, with varying spectral and spatial resolutions was used. These images provided the basis for mapping sand distribution, dune forms, and vegetation cover. GIS analysis was performed in parallel with field work to obtain validation and verification. The remote sensing and GIS results show that these ergs are mostly stabilized, with the estimated sand mantled area for the Karakum desert ~260,000 km2, and for the Kyzylkum it is ~195,500 km2. Meteorological analysis of wind and precipitation data indicate a low wind power environment (DP< 200) and sufficient rainfall (>100 mm) to support vegetation. Thus, these sands are indicative of past periods during which the climate in this region was different than today, enabling aeolian sand activity. Optically stimulated luminescence ages derived from the upper meter of the interdune of 14 exposed sections from both ergs, indicate sand stabilization during the mid-Holocene. This stabilization is understood to reflect a transition to a warmer, wetter, and less windy climate that generally persisted until today. The OSL ages, coupled with a compilation of regional palaeoclimatic data, corroborate and reinforce the previously proposed Mid-Holocene Liavliakan phase, known to reflect a warmer, wetter, and less windy climate that persists until today and resulted in dune stabilization around the Mid-Holocene.

[Influence of climate change on mosaic landscape of sand land-wetland in middle-east Inner Mongolia].

PubMed

Li, Xing-hua; Han, Fang; Zhang, Cun-hou; Na, Ri-su; Liu, Peng-tao

2009-01-01

By using wavelet transform and remote sensing techniques, the influence of climate change on the unique mosaic landscape of sand land-wetland in middle-east Inner Mongolia in 1961 -2005 was studied. The results showed that in 1961-2005, the annual air temperature in study area had an increment of 0.32 degrees C x (10 a)(-1), the annual precipitation fluctuated with a cycle of 30 years and of 15 years, and the annual average wind speed decreased by 0.26 m x s(-1) x (10 a)(-1). In the southeast part of study area, which located in the places between Hunshandake sand land and Keerqin Deserts, there was a district, in which, the climatic characteristics did not change evidently. Until 2010, the study area would still have an increasing air temperature, lesser precipitation, and decreasing wind speed. Under the influence of warming and drying, the total area of Hunshandake sand land and the wetland around reduced year after year, and, with the vegetation degradation on sand land, wetland shrunk and lake dried up, moving sand land enlarged ceaselessly, while immovable and semi-moving sand lands reduced obviously.

Probe into the origin, development and evolution model of shelf desertizational environment in the last stage of Late Pleistocene

NASA Astrophysics Data System (ADS)

Yu, Hong-Jun; Liu, Jing-Pu; Shan, Qiu-Mei

1998-12-01

Based on study of China's shelf paleoenvironment, this paper summarises the definition of shelf desertization that occurred in the last stage of Late Pleistocene, and discusses the background of its formation and evolution process. Study of shallow layer profiler records and core data revealed that cold-dry aeolian erosion was the major exogenic force on the exposed shelf. Under the prevailing paleo-winter monsoon, part of the exposed marine stratum disintegrated into sand and then desertization occurred. The fine sediments were blown away and deposited on the leeward to form derivative loess deposits.

Sand-wave movement on Little Georges Bank

USGS Publications Warehouse

Twichell, David C.

1983-01-01

A 1-x-1.5-km area on Little Georges Bank (centered at 41?08?N., 68?04?W.) was mapped three times during a ten-month period by sidescan sonar and echo-sounding techniques to assess the morphology and mobility of sand waves on Georges Bank. Sand-wave amplitudes in the survey area ranged from 1-11 m although most were 5-7 m. Wavelengths were not constant as the crests were sinuous and in places, even bifurcated. The sand waves are asymmetrical with their steepest sides facing northwest; however, gradients of their steep sides mostly are 4?-10? which is well below the angle of repose for sand in water. Sand waves tended to have greater relief and a sharper asymmetry during the survey in September than during those in June or April. During the survey period the sand waves moved but the direction and rate of motion was variable. Even along an individual sand wave some parts moved as much as 60 m between surveys while other parts apparently remained stationary. The sand waves were asymmetrical, but movement was not consistently in the direction that the steep sides faced. Along the same sand wave, parts moved to the northwest while other parts moved to the southeast. Despite the complex pattern of sand motion, the mean displacement of the sand waves was below the resolution of the survey technique; to resolve it, a longer survey is needed.

Earth Observations taken during Expedition 16 / STS-120 Joint Operations

NASA Image and Video Library

2007-10-26

ISS016-E-006986 (26 Oct. 2007) --- Great Sand Dunes National Park and Preserve, Colorado is featured in this image photographed by an Expedition 16 crewmember on the International Space Station. The Sangre de Cristo Mountains of south-central Colorado stretch dramatically from top left to lower right of this image, generally outlined by the dark green of forests with white snow-capped peaks on the highest elevations. Dun-colored dunes, covering an area of 80 square kilometers, are banked up on the west side of the mountains and comprise the Great Sand Dunes National Park and Preserve. Originally established in 1932 as a National Monument, it was reauthorized as a National Park in 2004. The park contains dunes over 750 feet (227 meters) high -- among the highest in North America. Sand grains that make up the dunes are small enough to be moved along by the wind (a process known as saltation), although much of the dunefield is now anchored by vegetation. Predominant winds blow broadly to the east, so that sand in the San Luis valley (part of which appears at lower left) is driven towards and piled against the Sangre de Cristo Mts. The sand of the dunes is mostly derived from ancient exposed lakebed sediments - now the floor of the San Luis valley - formed by erosion of rocks in the Sangre de Cristo and San Juan Mountains (located to the west). The action of streams and occasional storms today returns some of the impounded sand back to the valley, where the prevailing winds begin the sand's migration to the dunefield anew. Interestingly, the specific location of the sand field appears to be related to a locally lower altitude sector of the Sangre de Cristo Mts. Altitudes can be inferred from the distribution of snow cover on the day this image was taken. Areas to the north (Cleveland Peak and northward) of the dunefield, and to the south around Blanca Peak, are higher than the ridgeline next to the dune field where almost no snow is visible. Since winds are preferentially channeled over the lower parts of any range (hundreds of meters lower here than ridgelines to north and south), sand grains are carried up to (but not over) the low point of the range.

Tambora Caldera, Sumbawa Island, Indonesia

NASA Technical Reports Server (NTRS)

1988-01-01

Tambora caldera on the island of Sumbawa, Indonesia (8.5S, 118.0E) is a large crater formed in 1815 when a huge volcanic eruption ejected millions of tons debris high into the atmosphere. The particulate matter was blown around the globe by winds, masking much of the Earth's surface from sunlight, lowering global temperatures. Snow fell in New England in June and freezes occurred in the summer of 1816 which became known as the year without a summer.

Overview and Evaluation of the Community Multiscale Air ...

EPA Pesticide Factsheets

The Community Multiscale Air Quality (CMAQ) model is a state-of-the-science air quality model that simulates the emission, transport and fate of numerous air pollutants, including ozone and particulate matter. The Computational Exposure Division (CED) of the U.S. Environmental Protection Agency develops the CMAQ model and periodically releases new versions of the model that include bug fixes and various other improvements to the modeling system. In late 2016 or early 2017, CMAQ version 5.2 will be released. This new version of CMAQ will contain important updates from the current CMAQv5.1 modeling system, along with several instrumented versions of the model (e.g. decoupled direct method and sulfur tracking). Some specific model updates include the implementation of a new wind-blown dust treatment in CMAQv5.2, a significant improvement over the treatment in v5.1 which can severely overestimate wind-blown dust under certain conditions. Several other major updates to the modeling system include an update to the calculation of aerosols; implementation of full halogen chemistry (CMAQv5.1 contains a partial implementation of halogen chemistry); the new carbon bond 6 (CB6) chemical mechanism; updates to cloud model in CMAQ; and a new lightning assimilation scheme for the WRF model which significant improves the placement and timing of convective precipitation in the WRF precipitation fields. Numerous other updates to the modeling system will also be available in v5.2.

Cobbles in Troughs Between Meridiani Ripples (False Color)

NASA Technical Reports Server (NTRS)

2006-01-01

As NASA's Mars Exploration Rover Opportunity continues to traverse from 'Erebus Crater' toward 'Victoria Crater,' the rover navigates along exposures of bedrock between large, wind-blown ripples. Along the way, scientists have been studying fields of cobbles that sometimes appear on trough floors between ripples. They have also been studying the banding patterns seen in large ripples.

This view, obtained by Opportunity's panoramic camera on the rover's 802nd Martian day (sol) of exploration (April 27, 2006), is a mosaic spanning about 30 degrees. It shows a field of cobbles nestled among wind-driven ripples that are about 20 centimeters (8 inches) high.

The origin of cobble fields like this one is unknown. The cobbles may be a lag of coarser material left behind from one or more soil deposits whose finer particles have blown away. The cobbles may be eroded fragments of meteoritic material, secondary ejecta of Mars rock thrown here from craters elsewhere on the surface, weathering remnants of locally-derived bedrock, or a mixture of these. Scientists will use the panoramic camera's multiple filters to study the rock types, variability and origins of the cobbles.

This is a false-color rendering that combines separate images taken through the panoramic camera's 753-nanometer, 535-nanometer and 432-nanometer filters. The false color is used to enhance differences between types of materials in the rocks and soil.

Seasonal movement change of sediments using RFID tracer monitoring in composite gravel beach, west coast of Korea

NASA Astrophysics Data System (ADS)

Han, M.; Yu, J.; Yang, D. Y.; Kim, J. W.

2017-12-01

The purpose of this study is to investigate seasonal movement patterns of gravel movements on the west coast of Korean peninsula. This study aims improve understanding of the process of coastal sediments movement and contribute to coastal erosion management. The study site is Taean Bangpo Beach, which is characterized by its macro tide and composite gravel beach (CGB). In this study, we carried out a radio frequency identifier (RFID) tracer movement monitoring experiment. Four hundred tracers, similar in size and shape to beach sediment, were inserted into the beach in February and December 2015. From the results, it was confirmed that generally, gravel moved southward in the winter and northward in the summer. It was also confirmed that the gravel moved long distances in the summer and winter, but much shorter distances in the spring. At the end of the results, it is confirmed that the tracer recovery rate in summer is lower than in winter. Bangpo Beach was influenced by strong wind and wave energy driven by the East Asian winter monsoon, and by normal tidal energy during the other seasons. It means that seasonal variation of gravel movement in the beach is attributed to the difference of seasonal energy conditions. In addition, it is interpreted that the sand at the intertidal zone cannot be removed in the summer when the wave energy is weak, causing the tracer to be buried. This study is expected to contribute to the study of composite gravel beach and coastal coarse sediment movement which have been lacking in research.

Determination of the effect of wind velocity and direction changes on turbidity removal in rectangular sedimentation tanks.

PubMed

Khezri, Seyed Mostafa; Biati, Aida; Erfani, Zeynab

2012-01-01

In the present study, a pilot-scale sedimentation tank was used to determine the effect of wind velocity and direction on the removal efficiency of particles. For this purpose, a 1:20 scale pilot simulated according to Frude law. First, the actual efficiency of total suspended solids (TSS) removal was calculated in no wind condition. Then, the wind was blown in the same and the opposite directions of water flow. At each direction TSS removal was calculated at three different velocities from 2.5 to 7 m/s. Results showed that when the wind was in the opposite direction of water flow, TSS removal efficiency initially increased with the increase of wind velocity from 0 to 2.5 m/s, then it decreased with the increase of velocity to 5 m/s. This mainly might happen because the opposite direction of wind can increase particles' retention time in the sedimentation tank. However, higher wind velocities (i.e. 3.5 and 5.5 m/s) could not increase TSS removal efficiency. Thus, if sedimentation tanks are appropriately exposed to the wind, TSS removal efficiency increases by approximately 6%. Therefore, energy consumption will be reduced by a proper site selection for sedimentation tank unit in water and waste water treatment plants.

Radar remote sensing of wind-driven land degradation processes in northeastern Patagonia.

PubMed

del Valle, H F; Blanco, P D; Metternicht, G I; Zinck, J A

2010-01-01

Wind-driven land degradation negatively impacts on rangeland production and infrastructure in the Valdes Peninsula, northeastern Patagonia. The Valdes Peninsula has the most noticeable dunefields of the Patagonian drylands. Wind erosion has been assessed at different scales in this region, but often with limited data. In general, terrain features caused by wind activity are better discriminated by active microwaves than by sensors operating in the visible and infrared regions of the electromagnetic spectrum. This paper aims to analyze wind-driven land degradation processes that control the radar backscatter observed in different sources of radar imagery. We used subsets derived from SIR-C, ERS-1 and 2, ENVISAT ASAR, RADARSAT-1, and ALOS PALSAR data. The visibility of aeolian features on radar images is mostly a function of wavelength, polarization, and incidence angle. Stabilized sand deposits are clearly observed in radar images, with defined edges but also signals of ongoing wind erosion. One of the most conspicuous features corresponds to old track sand dunes, a mixture of active and inactive barchanoid ridges and parabolic dunes. This is a clear example of deactivation of migrating dunes under the influence of vegetation. The L-band data reveal details of these sand ridges, whereas the C-band data only allow detecting a few of the larger tracks. The results of this study enable us to make recommendations about the utility of some radar sensor configurations for wind-driven land degradation reconnaissance in mid-latitude regions.

Limited change in dune mobility in response to a large decrease in wind power in semi-arid northern China since the 1970s

USGS Publications Warehouse

Mason, J.A.; Swinehart, J.B.; Lu, H.; Miao, X.; Cha, P.; Zhou, Y.

2008-01-01

The climatic controls on dune mobility, especially the relative importance of wind strength, remain incompletely understood. This is a key research problem in semi-arid northern China, both for interpreting past dune activity as evidence of paleoclimate and for predicting future environmental change. Potential eolian sand transport, which is approximately proportional to wind power above the threshold for sand entrainment, has decreased across much of northern China since the 1970s. Over the same period, effective moisture (ratio of precipitation to potential evapotranspiration) has not changed significantly. This "natural experiment" provides insight on the relative importance of wind power as a control on dune mobility in three dunefields of northern China (Mu Us, Otindag, and Horqin), although poorly understood and potentially large effects of human land use complicate interpretation. Dune forms in these three regions are consistent with sand transport vectors inferred from weather station data, suggesting that wind directions have remained stable and the stations adequately represent winds that shaped the dunes. The predicted effect of weaker winds since the 1970s would be dune stabilization, with lower sand transport rates allowing vegetation cover to expand. Large portions of all three dunefields remained stabilized by vegetation in the 1970s despite high wind power. Since the 1970s, trends in remotely sensed vegetation greenness and change in mobile dune area inferred from sequential Landsat images do indicate widespread dune stabilization in the eastern Mu Us region. On the other hand, expansion of active dunes took place farther west in the Mu Us dunefield and especially in the central Otindag dunefield, with little overall change in two parts of the Horqin dunes. Better ground truth is needed to validate the remote sensing analyses, but results presented here place limits on the relative importance of wind strength as a control on dune mobility in the study areas. High wind power alone does not completely destabilize these dunes. A large decrease in wind power either has little short-term effect on the dunes, or more likely its effect is sufficiently small that it is obscured by human impacts on dune stability in many parts of the study areas. ?? 2008 Elsevier B.V. All rights reserved.

The Late Quaternary peat, vegetation and climate history of the Southern Oceanic Islands of New Zealand

NASA Astrophysics Data System (ADS)

McGlone, M. S.

2002-02-01

Seven oceanic island groups (Chatham, Bounty, Snares, Antipodes, Auckland, Campbell and Macquarie) lie to the south and east of the southern New Zealand mainland between the Subtropical Convergence and the Antarctic Convergence. They are highly oceanic, experiencing moist, cool, cloudy and windy climates. Deep peat soils cover most of the islands, except for steep slopes and exposed high altitude sites. The three large island groups (Chatham, Auckland and Campbell) support forest and tall scrub in the lowlands, in the latter two grading with altitude through shrubland and grassland to upland tundra. Macrophyllous forbs create luxuriant herbfields in nutrient-rich coastal sites and also, as stunted forms, dominate upland tundra associations. The southernmost island, Macquarie has no woody species, and is covered with tussock grassland, herbfield and tundra. Vegetation cover is highly sensitive to soil saturation and exposure to the strong westerly winds of this region. Extensive oligotrophic bogs occur where drainage is poor and exposure high, and forest and tall scrub are abundant only in sheltered, well-drained lowland sites. Glacial cirque levels indicate mean annual temperatures fell by 5-6°C during the Last Glacial Maximum. A depression of 6-10°C in sea surface temperatures is suggested by deep-sea core analyses, but this seems incompatible with terrestrial evidence. Auckland and Campbell Islands were extensively glaciated, and grassland, herbfield and tundra landscapes prevailed. Glaciers retreated by 15,000 yr BP, and landscapes had stabilised and peat soils begun forming by 12,000 yr BP. By the beginning of the Holocene, oligotrophic bog, grassland and shrubland were dominant. Scrub and low forest spread slowly during the early Holocene in the Chatham, Auckland and Campbell Islands, inhibited by cloudy, moist climates, low insolation and wet soils. Maximum extent of forest and scrub occurred between 6000 and 2000 yr BP, most probably linked with a drying of the soils and increasing summer insolation. Upland sites and those exposed to westerly gales on Auckland and Campbell Islands remained in grassland, herbfield and bog throughout the Holocene. Wind-blown sand and stones in cliff edge peat profiles on Auckland and Campbell Island from 8000 yr BP suggest strengthening westerly winds.

Protection of surface assets on Mars from wind blown jettisoned spacecraft components

NASA Astrophysics Data System (ADS)

Paton, Mark

2017-07-01

Jettisoned Entry, Descent and Landing System (EDLS) hardware from landing spacecraft have been observed by orbiting spacecraft, strewn over the Martian surface. Future Mars missions that land spacecraft close to prelanded assets will have to use a landing architecture that somehow minimises the possibility of impacts from these jettisoned EDLS components. Computer modelling is used here to investigate the influence of wind speed and direction on the distribution of EDLS components on the surface. Typical wind speeds encountered in the Martian Planetary Boundary Layer (PBL) were found to be of sufficient strength to blow items having a low ballistic coefficient, i.e. Hypersonic Inflatable Aerodynamic Decelerators (HIADs) or parachutes, onto prelanded assets even when the lander itself touches down several kilometres away. Employing meteorological measurements and careful characterisation of the Martian PBL, e.g. appropriate wind speed probability density functions, may then benefit future spacecraft landings, increase safety and possibly help reduce the delta v budget for Mars landers that rely on aerodynamic decelerators.

Interpretation of gypsy moth frontal advance using meteorology in a conditional algorithm.

PubMed

Frank, K L; Tobin, P C; Thistle, H W; Kalkstein, Laurence S

2013-05-01

The gypsy moth, Lymantria dispar, is a non-native species that continues to invade areas in North America. It spreads generally through stratified dispersal where local growth and diffusive spread are coupled with long-distance jumps ahead of the leading edge. Long-distance jumps due to anthropogenic movement of life stages is a well-documented spread mechanism. Another mechanism is the atmospheric transport of early instars and adult males, believed to occur over short distances. However, empirical gypsy moth population data continue to support the possibility of alternative methods of long-range dispersal. Such dispersal events seemed to have occurred in the mid- to late-1990s with spread across Lake Michigan to Wisconsin. Such dispersal would be against the prevailing wind flow for the area and would have crossed a significant physical barrier (Lake Michigan). The climatology of the region shows that vigorous cyclones can result in strong easterly winds in the area at the time when early instars are present. It is hypothesized that these storms would enable individuals to be blown across the Lake and explain the appearance of new population centers observed at several locations on the western shore of Lake Michigan nearly simultaneously. A synoptic climatology model coupled with population dynamics data from the area was parameterized to show an association between transport events and population spread from 1996 to 2007. This work highlights the importance of atmospheric transport events relative to the invasion dynamics of the gypsy moth, and serves as a model for understanding this mechanism of spread in other related biological invasions.

A wind proxy based on migrating dunes at the Baltic coast: statistical analysis of the link between wind conditions and sand movement

NASA Astrophysics Data System (ADS)

Bierstedt, Svenja E.; Hünicke, Birgit; Zorita, Eduardo; Ludwig, Juliane

2017-07-01

We statistically analyse the relationship between the structure of migrating dunes in the southern Baltic and the driving wind conditions over the past 26 years, with the long-term aim of using migrating dunes as a proxy for past wind conditions at an interannual resolution. The present analysis is based on the dune record derived from geo-radar measurements by Ludwig et al. (2017). The dune system is located at the Baltic Sea coast of Poland and is migrating from west to east along the coast. The dunes present layers with different thicknesses that can be assigned to absolute dates at interannual timescales and put in relation to seasonal wind conditions. To statistically analyse this record and calibrate it as a wind proxy, we used a gridded regional meteorological reanalysis data set (coastDat2) covering recent decades. The identified link between the dune annual layers and wind conditions was additionally supported by the co-variability between dune layers and observed sea level variations in the southern Baltic Sea. We include precipitation and temperature into our analysis, in addition to wind, to learn more about the dependency between these three atmospheric factors and their common influence on the dune system. We set up a statistical linear model based on the correlation between the frequency of days with specific wind conditions in a given season and dune migration velocities derived for that season. To some extent, the dune records can be seen as analogous to tree-ring width records, and hence we use a proxy validation method usually applied in dendrochronology, cross-validation with the leave-one-out method, when the observational record is short. The revealed correlations between the wind record from the reanalysis and the wind record derived from the dune structure is in the range between 0.28 and 0.63, yielding similar statistical validation skill as dendroclimatological records.

The Sand Yacht Challenge...Inspires Lots of Science

ERIC Educational Resources Information Center

James, Robin

2018-01-01

In this article, Robin James describes the Sand Yacht Challenge. The race took place on sand between small, wind-powered land yachts made by groups of children from four local schools. The project provided a term of collaborative opportunities at the designing and testing stage, followed by a competition when the students raced them. It was…

Nonlinear dynamics of Aeolian sand ripples.

PubMed

Prigozhin, L

1999-07-01

We study the initial instability of flat sand surface and further nonlinear dynamics of wind ripples. The proposed continuous model of ripple formation allowed us to simulate the development of a typical asymmetric ripple shape and the evolution of a sand ripple pattern. We suggest that this evolution occurs via ripple merger preceded by several soliton-like interaction of ripples.

An Old-Growth Definition for Sand Pine Forests

Treesearch

Kenneth W. Outcalt

1997-01-01

Sand pine scrub, Society of American Foresters cover type 69 (Eyre 1980), grows on deep, droughty, infertile sands of marine and aeolian origin. Water and wind formed these features as sea levels fluctuated during past glacial and interglacial periods (Kurz 1942, Laessle 1958, Brooks 1972). Because of washing and sorting during transport and deposition, soil parent...

78 FR 11981 - Special Regulations; Areas of the National Park System, Sleeping Bear Dunes National Lakeshore...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-02-21

... complex of coastal sand dunes, the Lakeshore features white sand beaches, steep bluffs reaching as high as... most notable feature--the ancient sand dunes--are products of wind, ice, and water action over... National Lakeshore'' (NPS Environmental Quality Division--May 2012), available for review at http://www.nps...

On Release of Microbe-Laden Particles from Mars Landers

NASA Technical Reports Server (NTRS)

Bellan, Josette; Harstad, Kenneth

2006-01-01

A paper presents a study in which rates of release of small particles from Mars lander spacecraft into the Martian atmosphere were estimated from first principles. Because such particles can consist of, or be laden with, terrestrial microbes, the study was undertaken to understand their potential for biological contamination of Mars. The study included taking account of forces and energies involved in adhesion of particles and of three mechanisms of dislodgement of particles from the surface of a Mars lander: wind shear, wind-driven impingement of suspended dust, and impingement of wind-driven local saltating sand particles. Wind shear was determined to be effective in dislodging only particles larger than about 10 microns and would probably be of limited interest because such large particles could be removed by pre-flight cleaning of the spacecraft, and their number on the launched spacecraft would thus be relatively small. Dislodgement by wind-driven dust was found to be characterized by an adhesion half-life of the order of 10,000 years judged to be too long to be of concern. Dislodgement by saltating sand particles, including skirts of dust devils, was found to be of potential importance, depending on the sizes of the spacecraft-attached particles and characteristics of both Mars sand-particle and spacecraft surfaces.

Simulation model of erosion and deposition on a barchan dune

NASA Technical Reports Server (NTRS)

Howard, A. D.; Morton, J. B.; Gal-El-hak, M.; Pierce, D. B.

1977-01-01

Erosion and deposition over a barchan dune near the Salton Sea, California, are modeled by bookkeeping the quantity of sand in saltation following streamlines of transport. Field observations of near surface wind velocity and direction plus supplemental measurements of the velocity distribution over a scale model of the dune are combined as input to Bagnold type sand transport formulas corrected for slope effects. A unidirectional wind is assumed. The resulting patterns of erosion and deposition compare closely with those observed in the field and those predicted by the assumption of equilibrium (downwind translation of the dune without change in size or geometry). Discrepancies between the simulated results and the observed or predicted erosional patterns appear to be largely due to natural fluctuations in the wind direction. The shape of barchan dunes is a function of grain size, velocity, degree of saturation of the oncoming flow, and the variability in the direction of the oncoming wind. The size of the barchans may be controlled by natural atmospheric scales, by the age of the dunes, or by the upwind roughness. The upwind roughness can be controlled by fixed elements or by sand in the saltation. In the latter case, dune scale is determined by grain size and wind velocity.

Cosmic Ray Acceleration from Multiple Galactic Wind Shocks

NASA Astrophysics Data System (ADS)

Cotter, Cory; Bustard, Chad; Zweibel, Ellen

2018-01-01

Cosmic rays still have an unknown origin. Many mechanisms have been suggested for their acceleration including quasars, pulsars, magnetars, supernovae, supernova remnants, and galactic termination shocks. The source of acceleration may be a mixture of these and a different mixture in different energy regimes. Using numerical simulations, we investigate multiple shocks in galactic winds as potential cosmic rays sources. By having shocks closer to the parent galaxy, more particles may diffuse back to the disk instead of being blown out in the wind, as found in Bustard, Zweibel, and Cotter (2017, ApJ) and also Merten, Bustard, Zweibel, and Tjus (to be submitted to ApJ). Specifically, this flux of cosmic rays could contribute to the unexplained "shin" region between the well-known "knee" and "ankle" of the cosmic ray spectrum. We would like to acknowledge support from the National Science Foundation (NSF) Graduate Research Fellowship Program under grant No. DGE-125625 and NSF grant No. AST-1616037.

Earth Observations taken by the Expedition 22 Crew

NASA Image and Video Library

2009-12-01

ISS022-E-005258 (1 Dec. 2009) --- This detailed hand-held digital camera?s image recorded from the International Space Station highlights sand dunes in the Fachi-Bilma erg, or sand sea, which is part of the central eastern Tenere Desert. The Tenere occupies much of southeastern Niger and is considered to be part of the larger Sahara Desert that stretches across northern Africa. Much of the Sahara is comprised of ergs ? with an area of approximately 150,000 square kilometers, the Fachi-Bilma is one of the larger sand seas. Two major types of dunes are visible in the image. Large, roughly north-south oriented transverse dunes fill the image frame. This type of dune tends to form at roughly right angles to the dominant northeasterly winds. The dune crests are marked in this image by darker, steeper sand accumulations that cast shadows. The lighter-toned zones between are lower interdune ?flats?. The large dunes appear to be highly symmetrical with regard to their crests. This suggests that the crest sediments are coarser, preventing the formation of a steeper slip face on the downwind side of the dune by wind-driven motion of similarly-sized sand grains. According to NASA scientists, this particular form of transverse dune is known as a zibar, and is thought to form by winnowing of smaller sand grains by the wind, leaving the coarser grains to form dune crests. A second set of thin linear dunes oriented at roughly right angles to the zibar dunes appears to be formed on the larger landforms and is therefore a younger landscape feature. These dunes appear to be forming from finer grains in the same wind field as the larger zibars. The image was taken with digital still camera fitted with a 400 mm lens, and is provided by the ISS Crew Earth Observations experiment and Image Science & Analysis Laboratory, Johnson Space Center.

Mid-Holocene stabilization of the Karakum and Kyzylkum sand seas, central Asia - evidence from OSL ages

NASA Astrophysics Data System (ADS)

Maman, Shimrit; Tsoar, Haim; Blumberg, Dan G.; Porat, Naomi

2013-04-01

Sand seas (ergs) are large areas of deserts covered by wind-swept sand with varying degrees of vegetation cover. The Kyzylkum and Karakum ergs have accumulated in the Turan basin, northwest of the Hindu Kush range, and span from south Turkmenistan to the Syrdarya River in Kazakhstan. These ergs are dissected by the Amudarya River; To the north lies the Kyzylkum (red sands) and to the south the Karakum (black sands). This area is understudied, and little information has been published regarding the sands stabilization processes and deposition ages. This research focuses on identifying and mapping the ergs of Central Asia and analyzing the climate factors that set the dunes into motion and that stabilized them. A variety of spaceborne imagery with varying spectral and spatial resolutions was used. These images provide the basis for mapping sand distribution, dune forms, and vegetation cover. Wilson (1973) defined these ergs as active based on precipitation. Our results show that they are mostly stabilized, with an estimated area of ~260,000 sq. Km for Kara-Kum , and ~195,500 sq. Km for the Kyzyl-Kum . Meteorological analysis of wind and precipitation data indicate a low wind energy environment (DP<200) and sufficient rainfall (>100 mm) to which is essential for vegetation cover. We present the first optically stimulated luminescence (OSL) ages from the upper meter of 14 exposed sections from both ergs. The age of the sand samples was determined as ~Mid-Holocene by OSL, which provides an insight into past climate characteristics. These ages indicate extensive sand and dune stabilization during the Mid-Holocene. GIS analysis was performed in parallel with field work to validate and verify the results. The OSL ages, coupled with a compilation of regional palaeoclimatic data, corroborate and reinforce the previously proposed Mid-Holocene Liavliakan phase, known to reflect a warmer, wetter, less windy climate than persists today and that resulted in dune stabilization around Mid-Holocene. This study emphasizes the importance of regional climatic control on aeolian activity and is the first to show when these vast sand seas were stabilized.

Coprates Chasma

NASA Technical Reports Server (NTRS)

2002-01-01

(Released 21 June 2002) The Science This image covers a portion of Coprates Chasma, located near 15.5S, 57.8W, which is part of the Valles Marineris system of canyons that stretch for thousands of kilometers. This image displays clearly the contrast between bedrock, sand, and dust surfaces. The steepest slopes, such as on the canyon walls, appear to be free of the mantle of dust and sand that is nearly ubiquitous elsewhere in the image. Layering is clearly present in the bedrock unit, but it is not clear if that layering is due to sedimentary deposits or volcanic lava flows. Superimposed on the slopes is a mantle of dust in a manner that appears similar to snow covered mountains on Earth. This is because in both situations, fine-grained dry, particulate material is settling on a sloped surface. Collecting in the valleys and, in some cases, climbing up the slopes are several sand sheets. The amount of cover and the apparent thickness of these sands give some indication to the huge volume of material that is collected here. The orientation of the slip faces of the dunes in this image can be used to deduce the prevalent wind patterns in the region. In this case, the prevalent wind direction is towards the east but there are areas where the winds indicate a more complex system, perhaps indicating topographic control of the local winds. The Story The canyon walls of Coprates, the old name for the Persian River Ab-I-Diz, descend clearly at the top of this image, without being obscured by the dust that covers much of this region. Coprates Chasma is part of Valles Marineris, the largest canyon system in the solar system. In addition to the hard bedrock and dust, sand dunes also appear on the floor of the canyon. They almost look as though they've been raked by a Zen gardener, but the eastward-blowing wind is really responsible for their rows. Scientists can tell the direction of the wind by looking at the slip faces of the dunes -- that is, by identifying the steep, downward slope formed from loose, cascading sand. Some areas seem to have been formed by more complex wind patterns that may have emerged due to the topography of the area. This region is, in fact, pretty complex. The sand in this area looks like it is thick and abundant. Not only has it collected in the valleys, it has also built up enough to begin to 'climb up' the slopes. There is also layering in the bedrock, but who knows if this layering is made of deposits of 'dirt' and rock or from lava. Finally, at the bottom of this image, dust-covered slopes appear like snow-covered mountain s on Earth. This similar look occurs because both dust and snow are fine-grained particles and cover the slopes in comparable ways.

The NASA Langley Mars Tumbleweed Rover Prototype

NASA Technical Reports Server (NTRS)

Antol, Jeffrey; Chattin, Richard L.; Copeland, Benjamin M.; Krizann, Shawn A.

2005-01-01

Mars Tumbleweed is a concept for an autonomous rover that would achieve mobility through use of the natural winds on Mars. The wind-blown nature of this vehicle make it an ideal platform for conducting random surveys of the surface, scouting for signs of past or present life as well as examining the potential habitability of sites for future human exploration. NASA Langley Research Center (LaRC) has been studying the dynamics, aerodynamics, and mission concepts of Tumbleweed rovers and has recently developed a prototype Mars Tumbleweed Rover for demonstrating mission concepts and science measurement techniques. This paper will provide an overview of the prototype design, instrumentation to be accommodated, preliminary test results, and plans for future development and testing of the vehicle.

Abrasion by aeolian particles: Earth and Mars

NASA Technical Reports Server (NTRS)

Greeley, R.; Marshall, J. R.; White, B. R.; Pollack, J. B.; Marshall, J.; Krinsley, D.

1984-01-01

Estimation of the rate of aeolian abrasion of rocks on Mars requires knowledge of: (1) particle flux, (2) susceptibilities to abrasion of various rocks, and (3) wind frequencies on Mars. Fluxes and susceptibilities for a wide range of conditions were obtained in the laboratory and combined with wind data from the Viking meteorology experiment. Assuming an abundant supply of sand-sized particles, estimated rates range up to 2.1 x 10 to the minus 2 power cm of abrasion per year in the vicinity of Viking Lander 1. This rate is orders of magnitude too great to be in agreement with the inferred age of the surface based on models of impact crater flux. The discrepancy in the estimated rate of abrasion and the presumed old age of the surface cannot be explained easily by changes in climate or exhumation of ancient surfaces. The primary reason is thought to be related to the agents of abrasion. At least some sand-sized (approx. 100 micrometers) grains appear to be present, as inferred from both lander and orbiter observations. High rates of abrasion occur for all experimental cases involving sands of quartz, basalt, or ash. However, previous studies have shown that sand is quickly comminuted to silt- and clay-sized grains in the martian aeolian regime. Experiments also show that these fine grains are electrostatically charged and bond together as sand-sized aggregates. Laboratory simulations of wind abrasion involving aggregates show that at impact velocities capable of destroying sand, aggregates from a protective veneer on the target surface and can give rise to extremely low abrasion rates.

The surface of Mars - The view from the Viking 1 lander

NASA Technical Reports Server (NTRS)

Mutch, T. A.; Patterson, W. R.; Binder, A. B.; Huck, F. O.; Taylor, G. R.; Levinthal, E. C.; Liebes, S., Jr.; Morris, E. C.; Pollack, J. B.; Sagan, C.

1976-01-01

Imagery of the surface of Mars obtained by Viking 1 is analyzed. The lander is situated on the western slopes of the 5-km deep Chryse Planitia depression, about 2 km higher than the floor. The topography is gently rolling. Angular rocks and small sand dunes are visible. There are very few craters; initial evaluations indicate that crater area densities are several orders of magnitude below saturation for crater sizes less than about 50 m. The presence of scour marks and of fine-grained deposits in some boulders indicates that some aeolian activity has occurred. Almost all the sky brightness can be attributed to scattering by particles present in the atmosphere. No signs of movement have been detected, consistent with the low seasonal winds recorded by meteorological instruments.

Windy Mars: A dynamic planet as seen by the HiRISE camera

USGS Publications Warehouse

Bridges, N.T.; Geissler, P.E.; McEwen, A.S.; Thomson, B.J.; Chuang, F.C.; Herkenhoff, K. E.; Keszthelyi, L.P.; Martinez-Alonso, S.

2007-01-01

With a dynamic atmosphere and a large supply of particulate material, the surface of Mars is heavily influenced by wind-driven, or aeolian, processes. The High Resolution Imaging Science Experiment (HiRISE) camera on the Mars Reconnaissance Orbiter (MRO) provides a new view of Martian geology, with the ability to see decimeter-size features. Current sand movement, and evidence for recent bedform development, is observed. Dunes and ripples generally exhibit complex surfaces down to the limits of resolution. Yardangs have diverse textures, with some being massive at HiRISE scale, others having horizontal and cross-cutting layers of variable character, and some exhibiting blocky and polygonal morphologies. "Reticulate" (fine polygonal texture) bedforms are ubiquitus in the thick mantle at the highest elevations. Copyright 2007 by the American Geophysical Union.

Ring nebulae around Wolf-Rayet stars in M33

NASA Technical Reports Server (NTRS)

Drissen, Laurent; Shara, Michael M.; Moffat, Anthony F. J.

1991-01-01

Results of a systematic search for H II ring nebulae surrounding Wolf-Rayet (WR) stars in M33 are presented. Eleven objects are found to be good candidates, while eight others are classified as possible WR ring nebulae. The WR rings in M33 are larger on average than their Galactic counterparts, but the H-alpha luminosity of most of them is comparable to the bright Galactic wind-blown bubbles. The rings are associated with WC as well as with WN stars.

Detection of sand encroachment patterns in desert oases. The case of Erg Chebbi (Morocco).

PubMed

Puy, Arnald; Herzog, Manuel; Escriche, Pedro; Marouche, Amou; Oubana, Yousef; Bubenzer, Olaf

2018-06-11

Desert oases are fragile agrarian areas, very vulnerable to sand encroachment by wind. Ensuring their conservation highly depends on our capacity to identify sand encroachment patterns, e.g. the origin of sand and its spatial distribution in the irrigated plots. Here we show how to tackle this issue using the case study of Erg Chebbi (Morocco), where two oases (Hassilabiad and Merzouga) are surrounded by dunes, Hamada and alluvial sediments from the Wadi Ziz. We combine field interviews with the study of wind dynamics, sediment sampling, Particle Size Distribution (PSD) tests and End-Member Modelling Analysis (EMMA). We observe that the most relevant contributor to sand encroachment is the Wadi Ziz (30%), followed by the Hamada (28%), an undetermined source of dust (25%), and the Erg dunes (16%). These genetically different sediments cluster unevenly in the oases, indicating the existence of areas with contrasting degrees of exposure to sedimentary sources. The results allow to define on solid grounds which sand source areas should be stabilized first in order to obtain the greatest reduction in sand encroachment. Our approach also provides policy-makers with better tools to identify which spots are specially vulnerable to accumulate a specific sediment, thus allowing for a more nuanced management of sand in oasis environments. Copyright © 2018 Elsevier B.V. All rights reserved.

Spatiotemporal surface moisture dynamics on a coastal beach

NASA Astrophysics Data System (ADS)

Smit, Y.; Donker, J.; Ruessink, G.

2017-12-01

Surface moisture strongly controls aeolian transport on a beach and, accordingly, understanding its spatiotemporal variability will aid in developing a predictive model for the aeolian input of wind-blown beach sand into the foredune. In our earlier work (Smit et al., 2017, Aeolian Research) we have illustrated that the reflectance signal of a near-infrared Terrestrial Laser Scanner (TLS) corresponds well to gravimetric surface moisture content (in %) over its full range. Here, we analyze TLS-derived surface moisture maps with a 1x1 m spatial and a 15-min temporal resolution and concurrent groundwater measurements collected during a falling and rising tide at Egmond beach, the Netherlands. The maps show that the beach can be conceptualized into three surface moisture zones. First, the swash zone: 18% - 25%. Second, the intertidal zone: 5% - 25% (large fluctuations). A striking result for this zone is that surface moisture can decrease with a rate varying between 2.5% - 4% per hour, and cumulatively 16% during a single falling tide. And third, the back beach zone: 3% - 7%. During falling tide surface moisture fluctuations are strongly linked to the behavior of groundwater depth. A clear `Van Genuchten-type' retention curve can describe the relation between the two. Furthermore, no anticipated processes by capillary forces were observed in advance of the rising tide and no hysteresis was observed over de complete tidal cycle. Concluding, the TLS-derived moisture maps and the groundwater measurements clearly show that groundwater depth is the key control on spatiotemporal surface moisture variations.

Windblown Sand from the Rocknest Drift

NASA Image and Video Library

2012-12-03

NASA Mars rover Curiosity acquired close-up views of sands in the Rocknest wind drift to document the nature of the material that the rover scooped, sieved and delivered to the CheMin and SAM instruments in October and November 2012.

Small Dunes

NASA Image and Video Library

2011-06-06

As wind is the only active geologic process on Mars today, sand and dust continue to be moved around the surface. Most craters host a sand dune or two, like this unnamed crater in Tyrrhena Terra. This image is from NASA 2001 Mars Odyssey.

Turbulent Flow and Sand Dune Dynamics: Identifying Controls on Aeolian Sediment Transport

NASA Astrophysics Data System (ADS)

Weaver, C. M.; Wiggs, G.

2007-12-01

Sediment transport models are founded on cubic power relationships between the transport rate and time averaged flow parameters. These models have achieved limited success and recent aeolian and fluvial research has focused on the modelling and measurement of sediment transport by temporally varying flow conditions. Studies have recognised turbulence as a driving force in sediment transport and have highlighted the importance of coherent flow structures in sediment transport systems. However, the exact mechanisms are still unclear. Furthermore, research in the fluvial environment has identified the significance of turbulent structures for bedform morphology and spacing. However, equivalent research in the aeolian domain is absent. This paper reports the findings of research carried out to characterise the importance of turbulent flow parameters in aeolian sediment transport and determine how turbulent energy and turbulent structures change in response to dune morphology. The relative importance of mean and turbulent wind parameters on aeolian sediment flux was examined in the Skeleton Coast, Namibia. Measurements of wind velocity (using sonic anemometers) and sand transport (using grain impact sensors) at a sampling frequency of 10 Hz were made across a flat surface and along transects on a 9 m high barchan dune. Mean wind parameters and mass sand flux were measured using cup anemometers and wedge-shaped sand traps respectively. Vertical profile data from the sonic anemometers were used to compute turbulence and turbulent stress (Reynolds stress; instantaneous horizontal and vertical fluctuations; coherent flow structures) and their relationship with respect to sand transport and evolving dune morphology. On the flat surface time-averaged parameters generally fail to characterise sand transport dynamics, particularly as the averaging interval is reduced. However, horizontal wind speed correlates well with sand transport even with short averaging times. Quadrant analysis revealed that turbulent events with a positive horizontal component, such as sweeps and outward interactions, were responsible for the majority of sand transport. On the dune surface results demonstrate the development and modification of turbulence and sediment flux in key regions: toe, crest and brink. Analysis suggests that these modifications are directly controlled by streamline curvature and flow acceleration. Conflicting models of dune development, morphology and stability arise when based upon either the dynamics of measured turbulent flow or mean flow.

Sand and Dust on Mars

NASA Technical Reports Server (NTRS)

Greeley, Ronald; Haberle, Robert M.

1991-01-01

Mars is a planet of high scientific interest. Various studies are currently being made that involve vehicles that have landed on Mars. Because Mars is known to experience frequent wind storms, mission planners and engineers require knowledge of the physical and chemical properties of Martian windblown sand and dust, and the processes involved in the origin and evolution of sand and dust storms.

Yardangs near Olympus Mons

NASA Image and Video Library

2002-12-16

In this region of the Olympus Mons aureole, located to the SW of the volcano, the surface has been eroded by the wind into linear landforms called yardangs. These ridges generally point in direction of the prevailing winds that carved them, in this case winds from the southeast. Yardangs typically occur on surfaces that are easily erodable, such as wind-blown dust or volcanic ash. The northeast - southwest trending ridges and valleys in the northwest corner of the image are typical of the Olympus Mons aureole. The varying concentration and shape of the yardangs in this area may be controlled by the motion of winds around these topographic features. Some crater outlines are visible near the top of this image. The rims of these craters appear to have been stripped away - indicating that the wind erosion is younger than these craters. There are two round knobs in the image, one on the bottom on the right side of the image and another about midway down on the left. These may be inverted craters, formed because the impacts caused materials underneath the crater to become harder to erode than the surrounding materials. http://photojournal.jpl.nasa.gov/catalog/PIA04036

Wind erosion of waste impoundments in arid climates and mitigation of dust pollution.

PubMed

Blight, G E

2008-12-01

Wind can erode and disperse fine-grained material from an impoundment of mining, industrial or municipal waste that stands above the level of its surroundings. Such dust dispersion can be a serious nuisance as well as a health hazard to inhabitants and animals in nearby settlements. It can also degrade crops, making them less marketable, and pollute soil, surface water and ground water. Wind can seasonally erode waste impoundments in all types of climate, but the erosion intensifies and persists for more of each year as regional aridity increases. As clouds of dust are often observed billowing across the top surfaces of waste impoundments in dry windy weather, there is a common misconception that dust arises from erosion of the top surface of an impoundment, resulting in much effort and money being misspent on top treatments when in fact the sloped sides of the impoundments are the true source of blown dust. This paper offers a brief review of general waste impoundment wind erosion issues and then focuses in more detail on the mechanics of how wind erodes surfaces of waste impoundments. Recommendations are offered for mitigating the effects of wind-eroded dust.

Wind speed and sediment transport recovery in the lee of a vegetated and denuded nebkha within a nebkha dune field

NASA Astrophysics Data System (ADS)

Gillies, John A.; Nield, Joanna M.; Nickling, William G.

2014-03-01

Field observations of scaled wind speed and sand transport recovery in the lee of a nebka within a field of nebkhas and then subsequently for the nebkha denuded of its vegetation cover were collected. The measurements of wind speed at 0.4 times the element height indicate that for both conditions wind speed recovery in the lee is exponential. The porous vegetation cover influences the rate of this recovery being more gradual for the vegetated form. The return to equilibrium wind speed occurs in both cases at approximately eight element heights. For either case the recovery of shear stress and the return to a constant value occurs much closer to the bluff body form than has been described for porous fences. The recovery of sand transport in the lee appears to be more rapid for the un-vegetated condition, which corresponds to the observed faster rate of wind speed increase. The observations did not show a continual increase in saltation flux with increasing downwind distance due to the increasing shear stress downwind and the increase that may be expected due to the fetch effect. The change in saltation flux with downwind distance was controlled by the sediment supply, which diminished with downwind distance. The interaction of a changing shear stress and the zone of influence created by the wind as it interacts with the roughness dimensions, along with the distribution of sediment available for transport bring increased complexity to modeling sand flux for this type of environment over different temporal scales.

Morphodynamics of dome dunes under unimodal wind regimes

NASA Astrophysics Data System (ADS)

Gao, Xin; Narteau, Clement; Rozier, Olivier

2017-04-01

Dome dunes are isolated sand piles with a rounded shape and no slip face. They are not only incipient or disappearing dunes, they can also reach a giant size and form dome-dune fields. Nevertheless, unlike other types of dunes, they have not been the subject of intense research, certainly because they result from complex multidirectional wind regimes. Here we analyze the morphodynamics of dome dunes under unimodal wind regimes. From numerical modeling using a normal distribution of sand flux orientation, we show that the transition from barchan to dome dunes occur when the standard deviation is larger than 40°. As confirmed by sand flux roses of dome-dune fields in arid deserts on Earth, it corresponds to RDP/DP-value of 0.8 (RDP/DP is the ratio between the resultant drift potential and the drift potential). Both in the field and in the numerical model, the transition from barchan to dome-dunes can also be captured from the coefficient of variation of the planar dune shape. Not surprisingly, smaller dome dunes are faster than larger ones. However, the dependence of dune migration rate on the RDP-value changes according to the presence or absence of slip faces because of the speed-up effect. Transient finger dunes may develop in dome-dune fields, but they rapidly break-up into smaller bodies. This shows that, contrary to bidirectional wind regimes, a large dispersion of sand flux orientation is not efficient in building longitudinal dunes.

Changes in wind erosion over a 25-year restoration chronosequence on the south edge of the Tengger Desert, China: implications for preventing desertification.

PubMed

Ma, Quanlin; Fehmi, Jeffrey S; Zhang, Dekui; Fan, Baoli; Chen, Fang

2017-08-23

Wind erosion is a primary cause of desertification as well as being a serious ecological problem in arid and semi-arid areas across the world. To determine mechanisms for restoring desertified lands, an unrestored shifting sand dune and three formerly shifting sand dunes (desertified lands) that had been enclosed and afforested for 5, 15, and 25 years were selected for evaluation on the south edge of the Tengger Desert, China. Based on sampling heights between 0.2 and 3 m, the critical threshold average wind speed was 6.5 m s -1 at 2 m where the sand transport rate was reduced from 285.9 kg m -2  h -1 on the unrestored dunes to 9.1 and 1.8 kg m -2  h -1 on the sites afforested and enclosed for 5 and 15 years, respectively. The percentage of wind eroded area was reduced from 99.9% on the unrestored dune to 94.5, 9.0, and 0.5% on the sites afforested and enclosed for 5, 15, and 25 years, respectively. Wind erosion was effectively reduced after 15 years. Although there were different driving factors for wind erosion mitigation on the different restoration stages, an increase in the vegetation cover, surface roughness, soil shear strength, soil clay content, organic matter, and reduction in the near-surface wind speed were the primary variables associated with the restoration chronosequence. We conclude that reducing the wind speed and developing a biological crust through vegetation restoration were the critical components for restoration of desertified land.

Plants and ventifacts delineate late Holocene wind vectors in the Coachella Valley, USA

USGS Publications Warehouse

Griffiths, P.G.; Webb, R.H.; Fisher, M.; Muth, Allan

2009-01-01

Strong westerly winds that emanate from San Gorgonio Pass, the lowest point between Palm Springs and Los Angeles, California, dominate aeolian transport in the Coachella Valley of the western Sonoran Desert. These winds deposit sand in coppice dunes that are critical habitat for several species, including the state and federally listed threatened species Uma inornata, a lizard. Although wind directions are generally defined in this valley, the wind field has complex interactions with local topography and becomes more variable with distance from the pass. Local, dominant wind directions are preserved by growth patterns of Larrea tridentata (creosote bush), a shrub characteristic of the hot North American deserts, and ventifacts. Exceptionally long-lived, Larrea has the potential to preserve wind direction over centuries to millennia, shaped by the abrasive pruning of windward branches and the persistent training of leeward branches. Wind direction preserved in Larrea individuals and clones was mapped at 192 locations. Compared with wind data from three weather stations, Larrea vectors effectively reflect annual prevailing winds. Ventifacts measured at 24 locations record winds 10° more westerly than Larrea and appear to reflect the direction of the most erosive winds. Based on detailed mapping of local wind directions as preserved in Larrea, only the northern half of the Mission-Morongo Creek floodplain is likely to supply sand to protected U. inornata habitat in the Willow Hole ecological reserve.

Kuwait City and Fire Scars in the Oil Fields

NASA Image and Video Library

1992-08-08

This view of the northern Persian Gulf shows Kuwait City and the Tigris and Euphrates River Deltas (29.5N, 48.5E). The oil laden sands and oil lakes of the Kuwait Oil Fields to the north and south of the city are clearly visible as dark patches surrounded by oil free desert sands. Comparison with earlier photos indicate that the oil laden sands are slowly being covered with clean sand carried by strong NW winds called Shmals.

Kuwait Oil Fields as seen from STS-58

NASA Image and Video Library

1993-10-20

STS058-73-054 (18 Oct-1 Nov 1993) --- A clear view of the northern Kuwaiti coast shows the southern part of Kuwait City, and the major oil fields to the south. Oil-laden sands, where wells were set ablaze during the Gulf War in 1991, are visible south of Kuwait City as a dark, elongated patch surrounded by light-colored sand. Oil-stained sand between well sites (dots) and criss-crossing roads is gradually being covered by clean sand carried by strong, seasonal northwest winds.

Investigating Mars: Olympia Undae

NASA Image and Video Library

2018-03-16

This VIS image was collected at the height of summer. It is during this season that winds are able to move sand sized particles, slowly modifying the dunes. Olympia Undae is a vast dune field in the north polar region of Mars. It consists of a broad sand sea or erg that partly rings the north polar cap from about 120° to 240°E longitude and 78° to 83°N latitude. The dune field covers an area of approximately 470,000 km2 (bigger than California, smaller than Texas). Olympia Undae is the largest continuous dune field on Mars. Olympia Undae is not the only dune field near the north polar cap, several other smaller fields exist in the same latitude, but in other ranges of longitude, e.g. Abolos and Siton Undae. Barchan and transverse dune forms are the most common. In regions with limited available sand individual barchan dunes will form, the surface beneath and between the dunes is visible. In regions with large sand supplies, the sand sheet covers the underlying surface, and dune forms are found modifying the surface of the sand sheet. In this case transverse dunes are more common. Barchan dunes "point" down wind, transverse dunes are more linear and form parallel to the wind direction. The "square" shaped transverse dunes in Olympia Undae are due to two prevailing wind directions. The density of dunes and the alignments of the dune crests varies with location, controlled by the amount of available sand and the predominant winds over time. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 13475 Latitude: 80.7459 Longitude: 177.171 Instrument: VIS Captured: 2004-12-27 21:44 https://photojournal.jpl.nasa.gov/catalog/PIA22297

Correlating seabird movements with ocean winds: linking satellite telemetry with ocean scatterometry.

USGS Publications Warehouse

Adams, Josh; Flora, Stephanie

2010-01-01

Satellite telemetry studies of the movements of seabirds are now common and have revealed impressive flight capabilities and extensive distributions among individuals and species at sea. Linking seabird movements with environmental conditions over vast expanses of the world's open ocean, however, remains difficult. Seabirds of the order Procellariiformes (e.g., petrels, albatrosses, and shearwaters) depend largely on wind and wave energy for efficient flight. We present a new method for quantifying the movements of far-ranging seabirds in relation to ocean winds measured by the SeaWinds scatterometer onboard the QuikSCAT satellite. We apply vector correlation (as defined by Crosby et al. in J Atm Ocean Tech 10:355-367, 1993) to evaluate how the trajectories (ground speed and direction) for five procellariiform seabirds outfitted with satellite transmitters are related to ocean winds. Individual seabirds (Sooty Shearwater, Pink-footed Shearwater, Hawaiian Petrel, Grey-faced Petrel, and Black-footed Albatross) all traveled predominantly with oblique, isotropic crossing to quartering tail-winds (i.e., 105-165 degrees in relation to birds' trajectory). For all five seabirds, entire track line trajectories were significantly correlated with co-located winds. Greatest correlations along 8-day path segments were related to wind patterns during birds' directed, long-range migration (Sooty Shearwater) as well as movements associated with mega-scale meteorological phenomena, including Pacific Basin anticyclones (Hawaiian Petrel, Grey-faced Petrel) and eastward-propagating north Pacific cyclones (Black-footed Albatross). Wind strength and direction are important factors related to the overall movements that delineate the distribution of petrels at sea. We suggest that vector correlation can be used to quantify movements for any marine vertebrate when tracking and environmental data (winds or currents) are of sufficient quality and sample size. Vector correlation coefficients can then be used to assess population--or species-specific variability and used to test specific hypotheses related to how animal movements are associated with fluid environments.

Connecting meteorology to surface transport in aeolian landscapes: Peering into the boundary layer with Doppler lidar

NASA Astrophysics Data System (ADS)

Gunn, A.; Jerolmack, D. J.; Edmonds, D. A.; Ewing, R. C.; Wanker, M.; David, S. R.

2017-12-01

Aolian sand dunes grow to 100s or 1000s of meters in wavelength by sand saltation, which also produces dust plumes that feed cloud formation and may spread around the world. The relations among sediment transport, landscape dynamics and wind are typically observed at the limiting ends of the relevant range: highly resolved and localized ground observations of turbulence and relevant fluxes; or regional and synoptic-scale meteorology and satellite imagery. Between the geostrophic winds aloft and shearing stress on the Earth's surface is the boundary layer, whose stability and structure determines how momentum is transferred and ultimately entrains sediment. Although the literature on atmospheric boundary layer flows is mature, this understanding is rarely applied to aeolian landscape dynamics. Moreover, there are few vertically and time-resolved datasets of atmospheric boundary layer flows in desert sand seas, where buoyancy effects are most pronounced. Here we employ a ground-based upward-looking doppler lidar to examine atmospheric boundary layer flow at the upwind margin of the White Sands (New Mexico) dune field, providing continuous 3D wind velocity data from the surface to 300-m aloft over 70 days of the characteristically windy spring season. Data show highly resolved daily cyles of convective instabilty due to daytime heating and stable stratification due to nightime cooling which act to enhance or depress, respectively, the surface wind stresses for a given free-stream velocity. Our data implicate convective instability in driving strong saltation and dust emission, because enhanced mixing flattens the vertical velocity profile (raising surface wind speed) while upward advection helps to deliver dust to the high atmosphere. We also find evidence for Ekman spiralling, with a magnitude that depends on atmospheric stability. This spiralling gives rise to a deflection in the direction between geostrophic and surface winds, that is significant for the orientation of dunes.

Electrification of particulate entrained fluid flows-Mechanisms, applications, and numerical methodology

NASA Astrophysics Data System (ADS)

Wei, Wei; Gu, Zhaolin

2015-10-01

Particulates in natural and industrial flows have two basic forms: liquid (droplet) and solid (particle). Droplets would be charged in the presence of the applied electric field (e.g. electrospray). Similar to the droplet charging, particles can also be charged under the external electric field (e.g. electrostatic precipitator), while in the absence of external electric field, tribo-electrostatic charging is almost unavoidable in gas-solid two-phase flows due to the consecutive particle contacts (e.g. electrostatic in fluidized bed or wind-blown sand). The particle charging may be beneficial, or detrimental. Although electrostatics in particulate entrained fluid flow systems have been so widely used and concerned, the mechanisms of particulate charging are still lack of a thorough understanding. The motivation of this review is to explore a clear understanding of particulate charging and movement of charged particulate in two-phase flows, by summarizing the electrification mechanisms, physical models of particulate charging, and methods of charging/charged particulate entrained fluid flow simulations. Two effective methods can make droplets charged in industrial applications: corona charging and induction charging. The droplet charge to mass ratio by corona charging is more than induction discharge. The particle charging through collisions could be attributed to electron transfer, ion transfer, material transfer, and/or aqueous ion shift on particle surfaces. The charges on charged particulate surface can be measured, nevertheless, the charging process in nature or industry is difficult to monitor. The simulation method might build a bridge of investigating from the charging process to finally charged state on particulate surface in particulate entrained fluid flows. The methodology combining the interface tracking under the action of the applied electric with the fluid flow governing equations is applicable to the study of electrohydrodynamics problems. The charge distribution and mechanical behaviors of liquid surface can be predicted by using this method. The methodology combining particle charging model with Computational Fluid Dynamics (CFD) and Discrete element method (DEM) is applicable to study the particle charging/charged processes in gas-solid two phase flows, the influence factors of particle charging, such as gas-particle interaction, contact force, contact area, and various velocities, are described systematically. This review would explore a clear understanding of the particulate charging and provide theoretical references to control and utilize the charging/charged particulate entrained fluid system.

The Moving Sands of Lobo Vallis

NASA Image and Video Library

2018-04-02

NASA's Mars Reconnaissance Orbiter shows bright ripples line the topography in this region, formed within a past climate. Dark dunes and sand streaks (composed of basaltic sand) have moved and filled lower areas, pushed by more recent winds from the top towards the bottom of this image. Lobo Vallis is named for a river on the Ivory Coast. https://photojournal.jpl.nasa.gov/catalog/PIA22346

A Wireless Sensor Network for the Real-Time Remote Measurement of Aeolian Sand Transport on Sandy Beaches and Dunes

PubMed Central

Cappelli, Irene; Mecocci, Alessandro; Alquini, Fernanda

2018-01-01

Direct measurements of aeolian sand transport on coastal dunes and beaches is of paramount importance to make correct decisions about coast management. As most of the existing studies are mainly based on a statistical approach, the solution presented in this paper proposes a sensing structure able to orient itself according to wind direction and directly calculate the amount of wind-transported sand by collecting it and by measuring its weight. Measurements are performed remotely without requiring human action because the structure is equipped with a ZigBee radio module, which periodically sends readings to a local gateway. Here data are processed by a microcontroller and then transferred to a remote data collection centre, through GSM technology. The ease of installation, the reduced power consumption and the low maintenance required, make the proposed solution able to work independently, limiting human intervention, for all the duration of the expected experimental campaign. In order to analyze the cause-effect relationship between the transported sand and the wind, the sensing structure is integrated with a multi-layer anemoscope-anemometer structure. The overall sensor network has been developed and tested in the laboratory, and its operation has been validated in field through a 48 h measurement campaign. PMID:29518060

A Wireless Sensor Network for the Real-Time Remote Measurement of Aeolian Sand Transport on Sandy Beaches and Dunes.

PubMed

Pozzebon, Alessandro; Cappelli, Irene; Mecocci, Alessandro; Bertoni, Duccio; Sarti, Giovanni; Alquini, Fernanda

2018-03-08

Direct measurements of aeolian sand transport on coastal dunes and beaches is of paramount importance to make correct decisions about coast management. As most of the existing studies are mainly based on a statistical approach, the solution presented in this paper proposes a sensing structure able to orient itself according to wind direction and directly calculate the amount of wind-transported sand by collecting it and by measuring its weight. Measurements are performed remotely without requiring human action because the structure is equipped with a ZigBee radio module, which periodically sends readings to a local gateway. Here data are processed by a microcontroller and then transferred to a remote data collection centre, through GSM technology. The ease of installation, the reduced power consumption and the low maintenance required, make the proposed solution able to work independently, limiting human intervention, for all the duration of the expected experimental campaign. In order to analyze the cause-effect relationship between the transported sand and the wind, the sensing structure is integrated with a multi-layer anemoscope-anemometer structure. The overall sensor network has been developed and tested in the laboratory, and its operation has been validated in field through a 48 h measurement campaign.

Evaluation of the Community Multiscale Air Quality (CMAQ) ...

EPA Pesticide Factsheets

The Community Multiscale Air Quality (CMAQ) model is a state-of-the-science air quality model that simulates the emission, transport and fate of numerous air pollutants, including ozone and particulate matter. The Computational Exposure Division (CED) of the U.S. Environmental Protection Agency develops the CMAQ model and periodically releases new versions of the model that include bug fixes and various other improvements to the modeling system. In the fall of 2016, CMAQ version 5.1.1 will be released. This new version of CMAQ will contain important bug fixes to several issues that were identified in CMAQv5.1 (the current public release version of the CMAQ model), and additionally include updates to other portions of the code. Some specific model updates include a new implementation of the wind-blown dust calculation in CMAQv5.1.1 which fixes several bugs that were identified in the current implementation of wind-blown dust in CMAQv5.1. Several other major updates to the model include an update to the calculation of aerosols; implementation of full halogen chemistry (CMAQv5.1 contains a partial implementation of halogen chemistry), which is particularly important for hemispheric applications of the CMAQ model, as halogen chemistry is need to accurately simulation the destruction of ozone over the ocean; and the new carbon bond 6 (CB6) chemical mechanism. Several annual, and numerous episodic, CMAQv5.1.1 simulations will be performed to assess the impact of these

Take-Off and Landing Characteristics of a 0.13-Scale Model of the Convair XFY-1 Vertically Rising Airplane in Steady Winds, TED No. NACA DE 368

NASA Technical Reports Server (NTRS)

Schade, Robert O.; Smith, Charles C., Jr.; Lovell, P. M., Jr.

1954-01-01

An experimental investigation has been conducted to determine the stability and control characteristics of a 0.13-scale free-flight model of the Convair XFY-1 airplane during take-offs and landings in steady winds. The tests indicated that take-offs in headwinds up to at least 20 knots (full scale) will be fairly easy to perform although the airplane may be blown downstream as much as 3 spans before a trim condition can be established. The distance that the airplane will be blown down-stream can be reduced by restraining the upwind landing gear until the instant of take-off. The tests also indicated that spot landings in headwinds up to at least 30 knots (full scale) and in crosswinds up to at least 20 knots (full scale) can be accomplished with reasonable accuracy although, during the landing approach, there will probably be an undesirable nosing-up tendency caused by ground effect and by the change in angle of attack resulting from vertical descent. Some form of arresting gear will probably be required to prevent the airplane from rolling downwind or tipping over after contact. This rolling and tipping can be prevented by a snubbing line attached to the tip of the upwind' wing or tail or by an arresting gear consisting of a wire mesh on the ground and hooks on the landing gear to engage the mesh.

Possibility of star (pyramid) dune development in the area of bimodal wind regime

NASA Astrophysics Data System (ADS)

Biejat, K.

2012-04-01

Star (pyramid) dunes are the largest aeolian landforms. They can occur in three types - simple, complex and compound. Development of this type of dunes is usually connected with multidirectional or complex wind regimes. The aim of this study was to verify a hypothesis that the star dunes can also develop by a bimodal wind regime and by local modifications of nearsurface wind flow directions. Field study was performed on Erg Chebbi, in southern Morocco. Several star and transverse dunes were selected for the study of their shape. The star dunes were analysed concerning their type and position in the dune field. This erg contains all of three types of star dunes together with transverse dunes. The regional wind data show that there are two dominant wind directions - NE (Chergui) and SW (Saheli). To determine the difference in shape of star dunes, we performed topographic surveying by GPS RTK. The results allowed to create 3D models of star dunes. The models were used to determine metric characteristics of star dunes, including area of dune basis, volume, and slope angles. On the basis of 3D models, primary, secondary and, on the compound dunes, tertiary arms were determined. Primary arms on each type of star dunes, as well as crestlines of transverse dunes, have dominant orientation NW-SE, perpendicular to two dominant wind directions. This clearly confirms that star dunes of Erg Chebbi develop by a bimodal wind regime In contrast to primary arms, subsidiary (secondary and tertiary) arms are not connected to general wind regime. The secondary arms of star dunes occur to be differentially developer. There are more subsidiary arms on SW sides in comparison to the E sides of the dunes where inclination of slopes is constant. It can be therefore inferred that sand has been supplied predominantly from SW direction. This is supported by distribution of the dunes on the erg. Most compound star dunes compose a chain along the E margin of the erg. Comparison of compound star dunes located in E and W parts of the erg allow inferring that there must have been differences in supply of the aeolian sand. Eastern slopes of compound star dunes developed in the W part of the erg are inclined 10-15°. This shows that significant delivery of the sand must have occurred also from NE. Eastern slopes of compound star dunes located in the E part of the erg are inclined 20-30°. It can be therefore inferred that they have functioned mainly as lee slopes and the sand was delivery from SW. This proves that location of the dunes within the erg plays a significant role in shaping wind directions responsible for delivery of the sand. Orientation of subsidiary arms does not show any relationship with general wind regime, which leads to conclusion that the subsidiary arms develop due to local diversified regime of nearsurface wind flow. This is governed by barriers such as the star dunes themselves and not by other topographic obstacles.

Controls on desert dune activity - a geospatial approach

NASA Astrophysics Data System (ADS)

Lancaster, N.; Hesse, P. P.

2017-12-01

Desert and other inland dunes occur on a wide spectrum of activity (defined loosely as the proportion of the surface area subject to sand movement) from unvegetated to sparsely vegetated "active" dunes through discontinuously vegetated inactive dunes to completely vegetated and degraded dunes. Many of the latter are relicts of past climatic conditions. Although field studies and modeling of the interactions between winds, vegetation cover, and dune activity can provide valuable insights, the response of dune systems to climate change and variability past, present, and future has until now been hampered by the lack of pertinent observational data on geomorphic and climatic boundary conditions and dune activity status for most dune areas. We have developed GIS-based approach that permits analysis of boundary conditions and controls on dune activity at a range of spatial scales from dunefield to global. In this approach, the digital mapping of dune field and sand sea extent has been combined with systematic observations of dune activity at 0.2° intervals from high resolution satellite image data, resulting in four classes of activity. 1 km resolution global gridded datasets for the aridity index (AI); precipitation, satellite-derived percent vegetation cover; and estimates of sand transport potential (DP) were re-sampled for each 0.2° grid cell, and dune activity was compared to vegetation cover, sand transport potential, precipitation, and the aridity index. Results so far indicate that there are broad-scale relationships between dunefield mean activity, climate, and vegetation cover. However, the scatter in the data suggest that other local factors may be at work. Intra-dune field patterns are complex in many cases. Overall, much more work needs to be done to gain a full understanding of controls at different spatial and temporal scales, which can be faciliated by this spatial database.

Geochemical variations in aeolian mineral particles from the Sahara-Sahel Dust Corridor.

PubMed

Moreno, Teresa; Querol, Xavier; Castillo, Sonia; Alastuey, Andrés; Cuevas, Emilio; Herrmann, Ludger; Mounkaila, Mohammed; Elvira, Josep; Gibbons, Wes

2006-10-01

The Sahara-Sahel Dust Corridor runs from Chad to Mauritania and expels huge amounts of mineral aerosols into the Atlantic Ocean. Data on samples collected from Algeria, Chad, Niger, and Western Sahara illustrate how corridor dust mineralogy and chemistry relate to geological source and weathering/transport history. Dusts sourced directly from igneous and metamorphic massifs are geochemically immature, retaining soluble cations (e.g., K, Na, Rb, Sr) and accessory minerals containing HFSE (e.g., Zr, Hf, U, Th) and REE. In contrast, silicate dust chemistry in desert basins (e.g., Bodélé Depression) is influenced by a longer history of transport, physical winnowing (e.g., loss of Zr, Hf, Th), chemical leaching (e.g., loss of Na, K, Rb), and mixing with intrabasinal materials such as diatoms and evaporitic salts. Mineral aerosols blown along the corridor by the winter Harmattan winds mix these basinal and basement materials. Dusts blown into the corridor from sub-Saharan Africa during the summer monsoon source from deeply chemically weathered terrains and are therefore likely to be more kaolinitic and stripped of mobile elements (e.g., Na, K, Mg, Ca, LILE), but retain immobile and resistant elements (e.g., Zr, Hf, REE). Finally, dusts blown southwestwards into the corridor from along the Atlantic Coastal Basin will be enriched in carbonate from Mesozoic-Cenozoic marine limestones, depleted in Th, Nb, and Ta, and locally contaminated by uranium-bearing phosphate deposits.

The sand seas of titan: Cassini RADAR observations of longitudinal dunes

USGS Publications Warehouse

Lorenz, R.D.; Wall, S.; Radebaugh, J.; Boubin, G.; Reffet, E.; Janssen, M.; Stofan, E.; Lopes, R.; Kirk, R.; Elachi, C.; Lunine, J.; Mitchell, Ken; Paganelli, F.; Soderblom, L.; Wood, C.; Wye, L.; Zebker, H.; Anderson, Y.; Ostro, S.; Allison, M.; Boehmer, R.; Callahan, P.; Encrenaz, P.; Ori, G.G.; Francescetti, G.; Gim, Y.; Hamilton, G.; Hensley, S.; Johnson, W.; Kelleher, K.; Muhleman, D.; Picardi, G.; Posa, F.; Roth, L.; Seu, R.; Shaffer, S.; Stiles, B.; Vetrella, S.; Flamini, E.; West, R.

2006-01-01

The most recent Cassini RADAR images of Titan show widespread regions (up to 1500 kilometers by 200 kilometers) of near-parallel radar-dark linear features that appear to be seas of longitudinal dunes similar to those seen in the Namib desert on Earth. The Ku-band (2.17-centimeter wavelength) images show ???100-meter ridges consistent with duneforms and reveal flow interactions with underlying hills. The distribution and orientation of the dunes support a model of fluctuating surface winds of ???0.5 meter per second resulting from the combination of an eastward flow with a variable tidal wind. The existence of dunes also requires geological processes that create sand-sized (100- to 300-micrometer) particulates and a lack of persistent equatorial surface liquids to act as sand traps.

The sand seas of Titan: Cassini RADAR observations of longitudinal dunes.

PubMed

Lorenz, R D; Wall, S; Radebaugh, J; Boubin, G; Reffet, E; Janssen, M; Stofan, E; Lopes, R; Kirk, R; Elachi, C; Lunine, J; Mitchell, K; Paganelli, F; Soderblom, L; Wood, C; Wye, L; Zebker, H; Anderson, Y; Ostro, S; Allison, M; Boehmer, R; Callahan, P; Encrenaz, P; Ori, G G; Francescetti, G; Gim, Y; Hamilton, G; Hensley, S; Johnson, W; Kelleher, K; Muhleman, D; Picardi, G; Posa, F; Roth, L; Seu, R; Shaffer, S; Stiles, B; Vetrella, S; Flamini, E; West, R

2006-05-05

The most recent Cassini RADAR images of Titan show widespread regions (up to 1500 kilometers by 200 kilometers) of near-parallel radar-dark linear features that appear to be seas of longitudinal dunes similar to those seen in the Namib desert on Earth. The Ku-band (2.17-centimeter wavelength) images show approximately 100-meter ridges consistent with duneforms and reveal flow interactions with underlying hills. The distribution and orientation of the dunes support a model of fluctuating surface winds of approximately 0.5 meter per second resulting from the combination of an eastward flow with a variable tidal wind. The existence of dunes also requires geological processes that create sand-sized (100- to 300-micrometer) particulates and a lack of persistent equatorial surface liquids to act as sand traps.

Aeolian processes in Proctor Crater on Mars: Sedimentary history as analyzed from multiple data sets

USGS Publications Warehouse

Fenton, L.K.; Bandfield, J.L.; Ward, A.W.

2003-01-01

Proctor Crater is a 150 km diameter crater in Noachis Terra, within the southern highlands of Mars. The analysis leading to the sedimentary history incorporates several data sets including imagery, elevation, composition, and thermal inertia, mostly from the Mars Global Surveyor mission. The resulting stratigraphy reveals that the sedimentary history of Proctor Crater has involved a complex interaction of accumulating and eroding sedimentation. Aeolian features spanning much of the history of the crater interior dominate its surface, including large erosional pits, stratified beds of aeolian sediment, sand dunes, erosional and depositional streaks, dust devil tracks, and small bright bed forms that are probably granule ripples. Long ago, up to 450 m of layered sediment filled the crater basin, now exposed in eroded pits on the crater floor. These sediments are probably part of an ancient deposit of aeolian volcaniclastic material. Since then, some quantity of this material has been eroded from the top layers of the strata. Small, bright dune forms lie stratigraphically beneath the large dark dune field. Relative to the large dark dunes, the bright bed forms are immobile, although in places, their orientations are clearly influenced by the presence of the larger dunes. Their prevalence in the crater and their lack of compositional and thermal distinctiveness relative to the crater floor suggests that these features were produced locally from the eroding basin fill. Dust devil tracks form during the spring and summer, following a west-southwesterly wind. Early in the spring the dust devils are largely restricted to dark patches of sand. As the summer approaches, dust devil tracks become more plentiful and spread to the rest of the crater floor, indicating that the entire region acquires an annual deposit of dust that is revealed by seasonal dust devils. The dark dunes contain few dust devil tracks, suggesting that accumulated dust is swept away directly by saltation, rather than by the passage of dust devils. Spectral deconvolution indicates that the dark dunes have infrared spectra consistent with basalt-like materials. The average thermal inertia calculated from Thermal Emission Spectrometer bolometric temperatures is 277 ?? 17 J m-2 s-0.5 K-1, leading to an effective grain size of 740 ?? 170 ??m, which is consistent with coarse sand and within the range expected for Martian sand. The coarse sand that composes the large dune field may have originated from outside the crater, saltating in from the southwest. Most of the transport pathway that delivered this sand to the dune field has since been eroded away or buried. The sand was transported to the east center of the crater floor, where beneath the present-day dunes a 50 m high mound of sand has accumulated. Dune slip faces indicate a wind regime consisting of three opposing winds. Some of these wind directions are correlated with the orientations of dust devil tracks and bright bed forms. The combination of a tall mound of sand and three opposing winds is consistent with a convergent wind regime, which produces the large reversing transverse and star dunes that dominate the dune field. The dark dunes have both active slip faces and seemingly inactive slip faces, suggesting that the dunes vary spatially in their relative activity. Nevertheless, the aeolian activity that has dominated the history of Proctor Crater still continues today. Copyright 2003 by the American Geophysical Union.

The role of streamline curvature in sand dune dynamics: evidence from field and wind tunnel measurements

NASA Astrophysics Data System (ADS)

Wiggs, Giles F. S.; Livingstone, Ian; Warren, Andrew

1996-09-01

Field measurements on an unvegetated, 10 m high barchan dune in Oman are compared with measurements over a 1:200 scale fixed model in a wind tunnel. Both the field and wind tunnel data demonstrate similar patterns of wind and shear velocity over the dune, confirming significant flow deceleration upwind of and at the toe of the dune, acceleration of flow up the windward slope, and deceleration between the crest and brink. This pattern, including the widely reported upwind reduction in shear velocity, reflects observations of previous studies. Such a reduction in shear velocity upwind of the dune should result in a reduction in sand transport and subsequent sand deposition. This is not observed in the field. Wind tunnel modelling using a near-surface pulse-wire probe suggests that the field method of shear velocity derivation is inadequate. The wind tunnel results exhibit no reduction in shear velocity upwind of or at the toe of the dune. Evidence provided by Reynolds stress profiles and turbulence intensities measured in the wind tunnel suggest that this maintenance of upwind shear stress may be a result of concave (unstable) streamline curvature. These additional surface stresses are not recorded by the techniques used in the field measurements. Using the occurrence of streamline curvature as a starting point, a new 2-D model of dune dynamics is deduced. This model relies on the establishment of an equilibrium between windward slope morphology, surface stresses induced by streamline curvature, and streamwise acceleration. Adopting the criteria that concave streamline curvature and streamwise acceleration both increase surface shear stress, whereas convex streamline curvature and deceleration have the opposite effect, the relationships between form and process are investigated in each of three morphologically distinct zones: the upwind interdune and concave toe region of the dune, the convex portion of the windward slope, and the crest-brink region. The applicability of the model is supported by measurements of the rate of sand transport and the change of the dune surface in the field.

Bahamian Pleistocene model for some Mississippian oolites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bain, R.J.

1989-08-01

San Salvador Island, unlike most Bahamian islands, is a narrow isolated platform surrounded by deep ocean. Therefore, sedimentary deposits on San Salvador must be explained in terms of processes and settings on this narrow, isolated shelf. Pleistocene oolite occurs between Illinoian and Wisconsinan paleosols. Dune ridges of up to 120 ft are composed of Pleistocene cross-bedded oolitic grainstone, whereas interdunal deposits are bioclastic packstone and wackestone containing abundant Chione cancellata. In lower dunal deposits, bioclastic content increases and the degree of sorting decreases. A fenestral porosity zone occurs approximately 5 ft above present-day sea level. In several ridges, oolite drapesmore » over older paleosol-capped bioclastic ridges. During the Sangamonian, sea water flooded the platform, however some remnant Aftonian ridges remained above sea level. As cold water from the surrounding deep ocean warmed on the shelf, ooids were generated and were washed onto beaches and blown into dunes. Remnant ridges restricted water movement and acted as nucleii for eolian ooid dunes. As sea level continued to rise, ooids were replaced by lagoonal bioclastic deposits. Ooid production was restricted to the swash zone along beaches resulting in the mixture of ooids and bioclastic sand in later Sangamonian deposits. Numerous Mississippian oolites display features similar to the Pleistocene oolite of San Salvador Island. Possible comparisons include thick lenses of Ste. Genevieve and Bangor limestones, paleosols in the Ste. Genevieve halo-shaped bodies of Greenbrier oolite, and the relationship of nearly all olites with bioclastic facies.« less

Wind-invariant saltation heights imply linear scaling of aeolian saltation flux with shear stress.

PubMed

Martin, Raleigh L; Kok, Jasper F

2017-06-01

Wind-driven sand transport generates atmospheric dust, forms dunes, and sculpts landscapes. However, it remains unclear how the flux of particles in aeolian saltation-the wind-driven transport of sand in hopping trajectories-scales with wind speed, largely because models do not agree on how particle speeds and trajectories change with wind shear velocity. We present comprehensive measurements, from three new field sites and three published studies, showing that characteristic saltation layer heights remain approximately constant with shear velocity, in agreement with recent wind tunnel studies. These results support the assumption of constant particle speeds in recent models predicting linear scaling of saltation flux with shear stress. In contrast, our results refute widely used older models that assume that particle speed increases with shear velocity, thereby predicting nonlinear 3/2 stress-flux scaling. This conclusion is further supported by direct field measurements of saltation flux versus shear stress. Our results thus argue for adoption of linear saltation flux laws and constant saltation trajectories for modeling saltation-driven aeolian processes on Earth, Mars, and other planetary surfaces.

Wind-invariant saltation heights imply linear scaling of aeolian saltation flux with shear stress

PubMed Central

Martin, Raleigh L.; Kok, Jasper F.

2017-01-01

Wind-driven sand transport generates atmospheric dust, forms dunes, and sculpts landscapes. However, it remains unclear how the flux of particles in aeolian saltation—the wind-driven transport of sand in hopping trajectories—scales with wind speed, largely because models do not agree on how particle speeds and trajectories change with wind shear velocity. We present comprehensive measurements, from three new field sites and three published studies, showing that characteristic saltation layer heights remain approximately constant with shear velocity, in agreement with recent wind tunnel studies. These results support the assumption of constant particle speeds in recent models predicting linear scaling of saltation flux with shear stress. In contrast, our results refute widely used older models that assume that particle speed increases with shear velocity, thereby predicting nonlinear 3/2 stress-flux scaling. This conclusion is further supported by direct field measurements of saltation flux versus shear stress. Our results thus argue for adoption of linear saltation flux laws and constant saltation trajectories for modeling saltation-driven aeolian processes on Earth, Mars, and other planetary surfaces. PMID:28630907

Sedimentation and lithofacies relations in the Holocene Pahang Delta Complex, East Coast Malay Peninsula, Malaysia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farshori, M.Z.; Jantan, A.

1994-07-01

A detailed study of the Pahang River Delta was undertaken in order to understand the development, architecture, geometrical characteristics, and structural sequential organization of the sand bodies on the east coast of the Malay Peninsula. The present delta indicates that although marine wave regimes are dominant, as exhibited by the cuspate-shaped delta, fluvial and tidal influences are substantial, as evident from the bedforms and sand bars morphology. The Pahang Delta system provides a unique case study for a tropical fluvio-marine windwave-dominated delta, which was profoundly influenced by seasonal storms. The deltaic sand is coarse and moderately sorted, and contains abundantmore » clay clasts. The southern coastline of the Pahang Delta is continuously modified by the erosive attack of the storm waves. The delta is subjected to extremely high-energy storm waves and fluvially formed sand bodies, such as channel mouth bars, dominant in other types of deltas that have been replaced by strand plains, sand bars and sand flats. The combination of high wave energy and strong littoral drift along the east coast of the Malay Peninsula results in changing the orientation of the sand bodies in the Pahang Delta. No modern wind-dominated delta is comparable to the Pahang Delta system. However, some modern deltas show many similarities in general morphology and sand distribution. The authors have developed a comprehensive sedimentological model of fluvio-marine sand-body variability in tropical wind-dominated deltas. The results of the studies will enlarge the applicability of geometrical studies to subsurface exploration of hydrocarbons.« less

Slaves of the environment: the movement of herbivorous insects in relation to their ecology and genotype

PubMed Central

Loxdale, H. D.

1999-01-01

The majority of insect species do not show an innate behavioural migration, but rather populations expand into favourable new habitats or contract away from unfavourable ones by random changes of spatial scale. Over the past 50 years, the scientific fascination with dramatic long-distance and directed mass migratory events has overshadowed the more universal mode of population movement, involving much smaller stochastic displacement during the lifetime of the insects concerned. This may be limiting our understanding of insect population dynamics. In the following synthesis, we provide an overview of how herbivorous insect movement is governed by both abiotic and biotic factors, making these animals essentially 'slaves of their environment'. No displaced insect or insect population can leave a resource patch, migrate and flourish, leaving descendants, unless suitable habitat and/or resources are reached during movement. This must have constrained insects over geological time, bringing about species-specific adaptation in behaviour and movements in relation to their environment at a micro- and macrogeographical scale. With insects that undergo long-range spatial displacements, e.g. aphids and locusts, there is presumably a selection against movement unless overruled by factors, such as density-dependent triggering, which cause certain genotypes within the population to migrate. However, for most insect species, spatial changes of scale and range expansion are much slower and may occur over a much longer time-scale, and are not innate (nor directed). Ecologists may say that all animals and plants are figuratively speaking 'slaves of their environments', in the sense that their distribution is defined by their ecology and genotype. But in the case of insects, a vast number must perish daily, either out at sea or over other hostile habitats, having failed to find suitable resources and/or a habitat on which to feed and reproduce. Since many are blown by the vagaries of the wind, their chances of success are serendipitous in the extreme, especially over large distances. Hence, the strategies adopted by mass migratory species (innate pre-programmed flight behaviour, large population sizes and/or fast reproduction), which improve the chances that some of these individuals will succeed. We also emphasize the dearth of knowledge in the various interactions of insect movement and their environment, and describe how molecular markers (protein and DNA) may be used to examine the details of spatial scale over which movement occurs in relation to insect ecology and genotype.

Sand-grain micromorphology used as a sediment-source indicator for Kharga Depression dunes (Western Desert, S Egypt)

NASA Astrophysics Data System (ADS)

Woronko, B.; Dłużewski, M.; Woronko, D.

2017-12-01

Roundness and surface-feature characteristics of sand grains collected from two dune ridges in Kharga Depression (southern Egypt) were tested for potential use as source-to-sink indicators of dunes movement. Grain examination was accommodated through Scanning Electron Microscope (SEM) analysis. Five grain types were distinguished: A) fresh; B) sheet precipitated with ;raindrop; structures; C) platy precipitated; D) broken; and E) with chemically etched surfaces-each type diagnostic of a specific geomorphic inheritance. Regarding the level of sphericity, these grains were subdivided into nine roundness classes (0.1-0.9), where angular grains are marked by 0.1 and very well-rounded grains by 0.9. Significant roundness and grain-type surface variations are observed both along dune ridges and between them. Poorly and medium-rounded grain populations dominate, along with sheet-precipitated grains. The contribution of well- and very well-rounded grains is low. The northern part of both eastern and western dune ridges is characterized by grains that represent high-energy aqueous environments with well-rounded grains, whereas platy precipitated grains with a lower level of roundness are concentrated in the middle part of the dune ridges. The southern part of the Kharga Depression is again characterized by sheet-precipitated grains. Our results indicate that the northern part of dune ridges in the Kharga Depression is mainly built of sands that originate from beyond the depression (e.g., Ghard Abu-Maharik) and the weathered deposits of the Nubian and Moghra Sandstones. The dunes in central and southern part of the Kharga Depression also derive sand from a local depression bottom comprised of playa and fluvial deposits. The growing importance of the local sand source may be explained by the lowering of the local groundwater table, which resulted in playa drying. This groundwater loss resulted in the degradation of the vegetation cover, facilitating an increase in wind entrainment of playa sediments.

Review Report on Design Study and Economic Assessment of Multi-Unit Offshore Wind Energy Conversion Systems Applications,

DTIC Science & Technology

1977-03-21

meter turbine . Available from NTIS; $6.50. 113 pages. 7. SAND-76-0130 Wind Tunnel Performance Data for the Darrieus Wind Tur- bine with NACA-0012...2-meter-diameter Darrieus wind turbine have been tested in a low speed wind tunnel. The airfoil section for all configurations was NACA 0012. The... Darrieus Vertical-Axis Wind Turbine Program at Sandia Laboratories, Kadlec, E.G., published by Sandia Laboratories 1976. Contract No. AT(29-1)-789. From

The viability of photovoltaics on the Martian surface

NASA Technical Reports Server (NTRS)

Gaier, James R.; Perez-Davis, Marla E.

1994-01-01

The viability of photovoltaics (PV) on the Martian surface may be determined by their ability to withstand significant degradation in the Martian environment. Probably the greatest threat is posed by fine dust particles which are continually blown about the surface of the planet. In an effort to determine the extent of the threat, and to investigate some abatement strategies, a series of experiments were conducted in the Martian Surface Wind Tunnel (MARSWIT) at NASA Ames Research Center. The effects of dust composition, particle size, wind velocity, angle of attack, and protective coatings on the transmittance of light through PV coverglass were determined. Both initially clear and initially dusted samples were subjected both to clear winds and simulated dust storms in the MARSWIT. It was found that wind velocity, particle size, and angle of attack are important parameters affecting occlusion of PV surfaces, while dust composition and protective coatings were not. Neither induced turbulence nor direct current biasing up to 200 volts were effective abatement techniques. Abrasion diffused the light impinging on the PV cells, but did not reduce total coverglass transmittance by more than a few percent.

Age and effects of the Odessa meteorite impact, western Texas, USA

NASA Astrophysics Data System (ADS)

Holliday, Vance T.; Kring, David A.; Mayer, James H.; Goble, Ronald J.

2005-12-01

The Odessa meteorite craters (Texas, United States) include a main crater (˜160 m diameter, ˜30 m deep) plus four smaller meteorite craters. The main crater was sampled by coring (to 22 m depth) to better understand its origin and history. Dating by optically stimulated luminescence indicates that it was produced immediately prior to ca. 63.5 ± 4.5 ka. Sediment filling the crater includes impact breccias produced at the time of impact; wind-dominated silts with minor amounts of pond sediments deposited ca. 63.5 ka, probably just after the impact, and ca. 53 ± 2 ka; wind-dominated silt ca. 38 ± 1.7 ka; and playa muds with a wind-blown silt component younger than 36 ka. The environment was arid or semiarid at the time of impact based on characteristics of soils on the surrounding landscape. The impact caused severe damage within 2 km and produced >1000 km/hr winds and thermal pulse. Animals within a 1 1.5-km-diameter area were probably killed. This is only the second well-dated Pleistocene hypervelocity impact crater in North America.

Something Old, Something New

NASA Technical Reports Server (NTRS)

2006-01-01

20 September 2006 When it was launched in 1996, the plan was that Mars Global Surveyor (MGS) would wrap up its mission in 2000. Damage to a hinge connected to a solar panel slowed the orbit insertion aerobraking process by a year, so in 1997 the spacecraft team determined that MGS's mission would end in early 2001. However, the spacecraft and its instruments remained healthy, and its mission was extended. And extended. And extended again. And again. MGS has now been orbiting the red planet for just over nine years. Throughout the mission, data from the Mars Orbiter Camera (MOC) have emphasized details about some of the very oldest and the very newest features exposed on the planet's surface.

The very ancient and the modern come together in this small, approximately 3 km by 3 km (1.9 mi by 1.9 mi) area on the floor of an unnamed impact crater in western Arabia Terra.

Old are the light-toned, layered mounds scattered across the image. The layers form stair-steps leading to the top of each mound. In most cases, the 'steps' are not clean, but are instead covered with debris eroded from the next layer, or step, above. The mounds are remnants of layered rock that once covered the entire scene. They were deposited as sediment in the large, unnamed crater in which these landforms occur. Their regular thickness and repeated character suggest that episodic, or perhaps cyclic, processes brought sediment to the crater floor. If the crater contained water at the time the sediments were deposited, then they represent lakebed materials. The processes that (a) brought sediment to this site, (b) cemented the sediment to form rock, and (c) eroded the sediment to form the mounds we see today, all occurred at some time in the distant past.

New are the dark-toned sand dunes and intermediate-toned ripples. The dark dunes were formed of sand that in relatively recent times has been blown by wind from the northeast (upper right) toward the southwest (lower left). The dunes have slowly encroached upon the older, light-toned, layered mounds. Surrounding each mound is a suite of intermediate-toned ripples. These are large ripples, relative to counterparts on Earth, and are most likely made up of grains somewhat coarser than sand, typically of several millimeters in size. The ripples form a pattern that is generally radial to each mound, indicating that they formed in winds that interacted with these topographic obstacles. The dark dunes are generally younger than the ripples, as dark sand has encroached upon and over-ridden some of the ripples.

This image is one of the favorites of the MOC operations team at Malin Space Science Systems, because it is not only pretty, it also emphasizes aspects of both the ancient and modern sedimentary processes and materials on Mars. Sediments, sedimentary rocks, and the environments in which they were deposited have been a key theme of the MOC science investigation from the beginning, more than 20 years ago, when MOC was selected by NASA to be built and sent to Mars. The first MOC was aboard Mars Observer when it was lost in 1993; the second MOC was built for MGS and is still operating today.

Location near: 8.8oN, 1.2oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Winter

Windflow circulation patterns in a coastal dune blowout, south coast of Lake Michigan

USGS Publications Warehouse

Fraser, G.S.; Bennett, S.W.; Olyphant, G.A.; Bauch, N.J.; Ferguson, V.; Gellasch, C.A.; Millard, C.L.; Mueller, B.; O'Malley, P. J.; Way, J.N.; Woodfield, M.C.

1998-01-01

The windflow patterns in a large active blowout in a coastal dune on the southern shore of Lake Michigan were intensively monitored during a two-day period when the predominant winds shifted from onshore (Day 1) to offshore (Day 2). The wind data were used in conjunction with mapped geomorphic features and sedimentologic characteristics to infer the following aspects of blowout evolution: (1) Prevailing winds are transformed considerably once they enter the blowout. Flow separation occurs when offshore winds enter the blowout over the steep back wall. Separated flows may, in turn, induce countercurrent flows within the trough. Flow expansion and deceleration occur when onshore winds enter over gently sloping walls at the front of the blowout. (2) Maximum erosion occurs along the deflationary floor near the entrance to the blowout, and lateral extensional lobes are also expanding the blowout to the east. Sand avalanches down the eastern and western lateral walls toward the deflationary floor where it is moved toward the rear of the blowout and up the ramp at the south end. Sand leaves the blowout as a series of depositional lobes prograding out onto the surface of the host dune along the south and east walls. (3) Vegetation prevents expansion of the blowout in certain directions and impediments to flow, such as slump blocks, alter circulation patterns and sand transport paths. (4) Prevailing onshore winds deflate the floor and promote eastward expansion of lateral erosional lobes, whereas strong flows from the southwest apparently are the main cause of transport up the transportational ramp and over the south wall of the blowout.

[Functions of different cultivation modes in oasis agriculture on soil wind erosion control and soil moisture conservation].

PubMed

Su, Peixi; Zhao, Aifen; Du, Mingwu

2004-09-01

During 2001-2002, the effects of different cultivation modes including winter irrigation and zero tillage, crop-grass intercropping, and early spring film mulching on sand entrainment, wind velocity gradient and soil moisture conservation were studied in the middle reaches of the Heihe River in the Hexi Corridor region. The results showed that all these modes could reduce soil wind erosion and halt sand entrainment to different degrees. Compared with the bare fields exposed by spring plowing, early spring film mulching could increase soil moisture storage by 35.6%. At present, spring plowing and sowing was a main factor responsible to the occurrence of sand storms and the increase in suspended dust content. Farmlands in the upper and middle reaches of the Heihe River generally produced a dust transport up to 4.8-6.0 million tons per year, which was higher than that of sandy desert in the same region. In the Hexi Corridor region, the suspended dust amount produced from 1 hm2 farmland was equivalent to that of 1.5 hm2 desert.

Earth observations taken from the shuttle Challenger during STS-41C

NASA Image and Video Library

2009-06-25

41C-31-990 (6-13 April 1984) --- Southwestern Algeria's Erg Chech shows long lines of parallel sand dunes called siefs. The Erg (sand desert) is in a remote (26.5 degrees north by 1.5 degrees west) of harsh desert, uninhabited and rarely visited. These parallel sand dunes are about 100 miles in length and 5 to 10 miles apart and are found in very few areas of the Earth. Most sand dunes are traverse dunes, or perpendicular to the general direction of the wind.

Fine-Branched Ridges

NASA Image and Video Library

2015-10-14

This image from NASA Mars Reconnaissance Orbiter spacecraft shows numerous branching ridges with various degrees of sinuosity. These branching forms resemble tributaries funneling and draining into larger channel trunks towards the upper portion of the scene. The raised relief of these branching ridges suggests that these are ancient channels are inverted due to lithification and cementation of the riverbed sediment, which made it more resistant to erosion than the surrounding material. Wind-blown bedforms are abundant and resemble small ridges that are aligned in an approximately north-south direction. http://photojournal.jpl.nasa.gov/catalog/PIA20006

Exploration of Victoria crater by the mars rover opportunity

USGS Publications Warehouse

Squyres, S. W.; Knoll, A.H.; Arvidson, R. E.; Ashley, James W.; Bell, J.F.; Calvin, W.M.; Christensen, P.R.; Clark, B. C.; Cohen, B. A.; De Souza, P.A.; Edgar, L.; Farrand, W. H.; Fleischer, I.; Gellert, Ralf; Golombek, M.P.; Grant, J.; Grotzinger, J.; Hayes, A.; Herkenhoff, K. E.; Johnson, J. R.; Jolliff, B.; Klingelhofer, G.; Knudson, A.; Li, R.; McCoy, T.J.; McLennan, S.M.; Ming, D. W.; Mittlefehldt, D. W.; Morris, R.V.; Rice, J. W.; Schroder, C.; Sullivan, R.J.; Yen, A.; Yingst, R.A.

2009-01-01

The Mars rover Opportunity has explored Victoria crater, a ???750-meter eroded impact crater formed in sulfate-rich sedimentary rocks. Impact-related stratigraphy is preserved in the crater walls, and meteoritic debris is present near the crater rim. The size of hematite-rich concretions decreases up-section, documenting variation in the intensity of groundwater processes. Layering in the crater walls preserves evidence of ancient wind-blown dunes. Compositional variations with depth mimic those ???6 kilometers to the north and demonstrate that water-induced alteration at Meridiani Planum was regional in scope.

Exploration of Victoria crater by the Mars rover Opportunity.

PubMed

Squyres, S W; Knoll, A H; Arvidson, R E; Ashley, J W; Bell, J F; Calvin, W M; Christensen, P R; Clark, B C; Cohen, B A; de Souza, P A; Edgar, L; Farrand, W H; Fleischer, I; Gellert, R; Golombek, M P; Grant, J; Grotzinger, J; Hayes, A; Herkenhoff, K E; Johnson, J R; Jolliff, B; Klingelhöfer, G; Knudson, A; Li, R; McCoy, T J; McLennan, S M; Ming, D W; Mittlefehldt, D W; Morris, R V; Rice, J W; Schröder, C; Sullivan, R J; Yen, A; Yingst, R A

2009-05-22

The Mars rover Opportunity has explored Victoria crater, an approximately 750-meter eroded impact crater formed in sulfate-rich sedimentary rocks. Impact-related stratigraphy is preserved in the crater walls, and meteoritic debris is present near the crater rim. The size of hematite-rich concretions decreases up-section, documenting variation in the intensity of groundwater processes. Layering in the crater walls preserves evidence of ancient wind-blown dunes. Compositional variations with depth mimic those approximately 6 kilometers to the north and demonstrate that water-induced alteration at Meridiani Planum was regional in scope.

Effect of sand and rubber surface on the lying behavior of lame dairy cows in hospital pens.

PubMed

Bak, A S; Herskin, M S; Jensen, M B

2016-04-01

Housing lame cows in designated hospital pens with a soft surface may lessen the pain the animals feel when lying and changing position. This study investigated the effect of the lying surface on the behavior of lame cows in hospital pens. Thirty-two lame dairy cows were kept in individual hospital pens, provided with either 30-cm deep-bedded sand or 24-mm rubber mats during 24 h in a crossover design. On each surface, the lying behavior of each cow was recorded during 18 h. On deep-bedded sand, cows lay down more and changed position more often than when housed on the rubber surface. Furthermore, a shorter duration of lying down and getting up movements and a shorter duration of lying intention movements were observed. These results suggest that lame dairy cows are more reluctant to change position on rubber compared with sand, and that sand is more comfortable to lie on. Thus, deep bedding such as sand may provide better lying comfort for lame cows than an unbedded rubber surface. Copyright © 2016 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Dust dynamics in off-road vehicle trails: Measurements on 16 arid soil types, Nevada, USA.

PubMed

Goossens, Dirk; Buck, Brenda

2009-08-01

Soil analyses and measurements with the Portable In Situ Wind Erosion Laboratory (PI-SWERL) were conducted on 16 soil types in an area heavily affected by off-road vehicle (ORV) driving. Measurements were performed in ORV trails as well as on undisturbed terrain to investigate how ORV driving affects the vulnerability of a soil to emit PM10 (particles<10microm), during the driving as well as during episodes of wind erosion. Particular attention is paid to how the creation of a new trail affects those properties of the topsoil that determine its capability to emit PM10. Also, recommendations are given for adequate management of ORV-designed areas. The type of surface (sand, silt, gravel, drainage) is a key factor with respect to dust emission in an ORV trail. Trails in sand, defined in this study as the grain size fraction 63-2000microm, show higher deflation thresholds (the critical wind condition at which wind erosion starts) than the surrounding undisturbed soil. Trails in silt (2-63microm) and in drainages, on the other hand, have lower deflation thresholds than undisturbed soil. The increase in PM10 emission resulting from the creation of a new ORV trail is much higher for surfaces with silt than for surfaces with sand. Also, the creation of a new trail in silt decreases the supply limitation in the top layer: the capacity of the reservoir of emission-available PM10 increases. For sand the situation is reversed: the supply limitation increases, and the capacity of the PM10 reservoir decreases. Finally, ORV trails are characterized by a progressive coarsening of the top layer with time, but the speed of coarsening is much lower in trails in silt than in trails in sand or in drainages. The results of this study suggest that, to minimize emissions of PM10, new ORV fields should preferably be designed on sandy terrain rather than in silt areas or in drainages.

Constraints on aeolian sediment transport to foredunes within an undeveloped backshore enclave on a developed coast

NASA Astrophysics Data System (ADS)

Kaplan, Kayla L.; Nordstrom, Karl F.; Jackson, Nancy L.

2016-10-01

Landforms present in undeveloped beach enclaves located between properties developed with houses and infrastructure are often left to evolve naturally but are influenced by the human structures near them. This field study evaluates how buildings and sand-trapping fences change the direction of wind approach, reduce wind speed, and restrict fetch distances for sediment entrainment, thereby reducing the potential for aeolian transport and development of dunes in enclaves. Field data were gathered in an 80 m long, 44 m deep beach enclave on the ocean shoreline of New Jersey, USA. Comparison of wind characteristics in the enclave with a site unaffected by buildings revealed that offshore winds in the enclave are reduced in strength and altered in direction by landward houses, increasing the relative importance of longshore winds. Vertical arrays of anemometers on the foredune crest, foredune toe and berm crest in the enclave revealed increasing wind speed with distance offshore, with strongest winds on the berm crest. Vertical cylindrical traps on the foredune crest, foredune toe, mid-backshore, berm crest and upper foreshore revealed the greatest rate of sediment transport on the berm crest. Sediment samples from the beach and from traps revealed limited potential for aeolian transport because of coarse grain sizes. Strong oblique onshore winds are common in this region and are normally important for transporting sand to dunes. The length of an enclave and the setback distance on its landward side determine the degree to which sediment delivered by oblique winds contributes to dune growth. The landward edge of the enclave (defined by a sand fence near the dune toe) is sheltered along its entire length from winds blowing at an angle to the shoreline of 25° or less. A foredune set back this distance in an enclave the length of an individual lot (about 20 m) would be sheltered at an angle of 57° or less, reducing the opportunity for dune building by onshore winds. Reduced potential for aeolian transport in enclaves implies that human actions may be required to build dunes artificially to protect buildings and roads from storm overwash.

The provenance of Taklamakan desert sand

NASA Astrophysics Data System (ADS)

Rittner, Martin; Vermeesch, Pieter; Carter, Andrew; Bird, Anna; Stevens, Thomas; Garzanti, Eduardo; Andò, Sergio; Vezzoli, Giovanni; Dutt, Ripul; Xu, Zhiwei; Lu, Huayu

2016-03-01

Sand migration in the vast Taklamakan desert within the Tarim Basin (Xinjiang Uyghur Autonomous region, PR China) is governed by two competing transport agents: wind and water, which work in diametrically opposed directions. Net aeolian transport is from northeast to south, while fluvial transport occurs from the south to the north and then west to east at the northern rim, due to a gradual northward slope of the underlying topography. We here present the first comprehensive provenance study of Taklamakan desert sand with the aim to characterise the interplay of these two transport mechanisms and their roles in the formation of the sand sea, and to consider the potential of the Tarim Basin as a contributing source to the Chinese Loess Plateau (CLP). Our dataset comprises 39 aeolian and fluvial samples, which were characterised by detrital-zircon U-Pb geochronology, heavy-mineral, and bulk-petrography analyses. Although the inter-sample differences of all three datasets are subtle, a multivariate statistical analysis using multidimensional scaling (MDS) clearly shows that Tarim desert sand is most similar in composition to rivers draining the Kunlun Shan (south) and the Pamirs (west), and is distinctly different from sediment sources in the Tian Shan (north). A small set of samples from the Junggar Basin (north of the Tian Shan) yields different detrital compositions and age spectra than anywhere in the Tarim Basin, indicating that aeolian sediment exchange between the two basins is minimal. Although river transport dominates delivery of sand into the Tarim Basin, wind remobilises and reworks the sediment in the central sand sea. Characteristic signatures of main rivers can be traced from entrance into the basin to the terminus of the Tarim River, and those crossing the desert from the south to north can seasonally bypass sediment through the sand sea. Smaller ephemeral rivers from the Kunlun Shan end in the desert and discharge their sediment there. Both river run-off and wind intensity are strongly seasonal, their respective transport strength and opposing directions maintain the Taklamakan in its position and topography.

Aeolian Processes at the Mars Exploration Rover Opportunity Landing Site

NASA Technical Reports Server (NTRS)

Sullivan, R.; Bell, J. F., III; Calvin, W.; Fike, D.; Golombek, M.; Greeley, R.; Grotzinger, J.; Herkenhoff, K.; Jerolmack, D.; Malin, M.

2005-01-01

The traverse of the Mars Exploration Rover Opportunity across its Meridiani Planum landing site has shown that wind has affected regolith by creating drifts, dunes, and ubiquitous ripples, by sorting grains during aeolian transport, by forming bright wind streaks downwind from craters seen from orbit, and by eroding rock with abrading, wind-blown material. Pre-landing orbiter observations showed bright and dark streaks tapering away from craters on the Meridiani plains. Further analysis of orbiter images shows that major dust storms can cause bright streak orientations in the area to alternate between NW and SE, implying bright wind streak materials encountered by Opportunity are transient, potentially mobilized deposits. Opportunity performed the first in situ investigation of a martian wind streak, focusing on a bright patch of material just outside the rim of Eagle crater. Data from Pancam, the Miniature Thermal Emission Spectrometer (Mini-TES), the Alpha-Particle X-Ray Spectrometer (APXS), and the Mossbauer spectrometer either are consistent with or permit an air fall dust interpretation. We conclude that air fall dust, deposited in the partial wind shadow of Eagle crater, is responsible for the bright streak seen from orbit, consistent with models involving patchy, discontinuous deposits of air fall dust distributed behind obstacles during periods of atmospheric thermal stability during major dust storms.

Voyager Approaches Final Frontier Artist Concept

NASA Image and Video Library

2003-12-12

An artist's concept illustrates the positions of the Voyager spacecraft in relation to structures formed around our Sun by the solar wind. Also illustrated is the termination shock, a violent region the spacecraft must pass through before reaching the outer limits of the solar system. At the termination shock, the supersonic solar wind abruptly slows from an average speed of 400 kilometers per second to less than 100 kilometer per second (900,000 to less than 225,000 miles per hour). Beyond the termination shock is the solar system's final frontier, the heliosheath, a vast region where the turbulent and hot solar wind is compressed as it presses outward against the interstellar wind that is beyond the heliopause. A bow shock likely forms as the interstellar wind approaches and is deflected around the heliosphere, forcing it into a teardrop-shaped structure with a long, comet-like tail. The exact location of the termination shock is unknown, and it originally was thought to be closer to the Sun than Voyager 1 currently is. As Voyager 1 cruised ever farther from the Sun, it confirmed that all the planets are inside an immense bubble blown by the solar wind and the termination shock was much more distant. http://photojournal.jpl.nasa.gov/catalog/PIA04927

Aleutian Pribilof Islands Wind Energy Feasibility Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bruce A. Wright

2012-03-27

Under this project, the Aleutian Pribilof Islands Association (APIA) conducted wind feasibility studies for Adak, False Pass, Nikolski, Sand Point and St. George. The DOE funds were also be used to continue APIA's role as project coordinator, to expand the communication network quality between all participants and with other wind interest groups in the state and to provide continued education and training opportunities for regional participants. This DOE project began 09/01/2005. We completed the economic and technical feasibility studies for Adak. These were funded by the Alaska Energy Authority. Both wind and hydro appear to be viable renewable energy optionsmore » for Adak. In False Pass the wind resource is generally good but the site has high turbulence. This would require special care with turbine selection and operations. False Pass may be more suitable for a tidal project. APIA is funded to complete a False Pass tidal feasibility study in 2012. Nikolski has superb potential for wind power development with Class 7 wind power density, moderate wind shear, bi-directional winds and low turbulence. APIA secured nearly $1M from the United States Department of Agriculture Rural Utilities Service Assistance to Rural Communities with Extremely High Energy Costs to install a 65kW wind turbine. The measured average power density and wind speed at Sand Point measured at 20m (66ft), are 424 W/m2 and 6.7 m/s (14.9 mph) respectively. Two 500kW Vestas turbines were installed and when fully integrated in 2012 are expected to provide a cost effective and clean source of electricity, reduce overall diesel fuel consumption estimated at 130,000 gallons/year and decrease air emissions associated with the consumption of diesel fuel. St. George Island has a Class 7 wind resource, which is superior for wind power development. The current strategy, led by Alaska Energy Authority, is to upgrade the St. George electrical distribution system and power plant. Avian studies in Nikolski and Sand Point have allowed for proper wind turbine siting without killing birds, especially endangered species and bald eagles. APIA continues coordinating and looking for funding opportunities for regional renewable energy projects. An important goal for APIA has been, and will continue to be, to involve community members with renewable energy projects and energy conservation efforts.« less

Exploring the Sandy Province of Herschel Crater

NASA Image and Video Library

2017-09-04

This view from NASA's Mars Reconnaissance Orbiter shows the downwind stretches of a sand sheet in central part of the much larger Herschel Crater. This sandy province began kilometers upwind in a string of barchan sand dunes. As the north-to-south blowing wind weakened downwind, it could no longer fashion the sand into dunes but rather into amorphously-shaped sand sheets. While perhaps not awe-inspiringly beautiful, sand sheets can tell us about Mars' current and past environmental conditions as a piece of the puzzle for understanding habitability. Having dunes upwind of sheets is the opposite situation Earth has, where upwind sand sheets evolve downwind into sand dunes. This mystery is receiving ongoing research to to understand these sandy differences between Earth and Mars. https://photojournal.jpl.nasa.gov/catalog/PIA21933

Fertilisation of the Southern Atlantic: Ephemeral River Valleys as a replenishing source of nutrient-enriched mineral aerosols

NASA Astrophysics Data System (ADS)

Dansie, Andrew; Wiggs, Giles; Thomas, David

2016-04-01

Oceanic dust deposition provides biologically important iron and macronutrients (Phosphorus (P) and Nitrogen-based (N) compounds) that contribute to phytoplankton growth, marine productivity and oceanic atmospheric CO2 uptake. Research on dust emission sources to date has largely focused on the northern hemisphere and on ephemeral lakes and pans. Our work considers the ephemeral river valleys of the west coast of Namibia as an important yet overlooked source of ocean-fertilizing dust. Dust plumes are frequently emitted from the river valleys by strong easterly winds during the Southern Hemisphere winter, when the upwelling of the Benguela Current is at its weakest. We present field data from dust emission source areas along the main river channels near the coastal termini of the Huab, Kuiseb and Tsauchab river valleys. Collected data include erodible surface sediment, wind-blown flux, and associated meteorological data. Extensive surface sediment sampling was also undertaken throughout the combined 34,250 km2 extent of each river valley catchment with samples collected from within the main river channels, the main branches of each river system, selected tributaries, and into the upper watersheds. Geochemical data show valley sediment and wind-blown flux material have high concentrations of bioavailable Fe, P and N, exceeding that measured at the major dry lake basin dust sources in southern Africa. The contribution of fertilising deposition material is enhanced by both the spatial proximity of the source areas to the ocean and enrichment of source material by ephemeral fluvial accumulation and desiccation. Results show that geographical factors within each watershed play a key role in the nutrient composition of the emitting fluvial deposits in the river valleys. Analysis explores potential relationships between land use, geology, climate and precipitation in the upper watersheds and their influence on bioavailability of Fe, P and N compounds in wind-erodible valley sediments. MODIS data for dust plume identification and chlorophyll concentration in the southern Atlantic is utilised to investigate associations between recorded dust emission events and phytoplankton growth in the ocean surface waters.

High frequency observations of Iapetus on the Green Bank Telescope aided by improvements in understanding the telescope response to wind

NASA Astrophysics Data System (ADS)

Ries, Paul A.

2012-05-01

The Green Bank Telescope is a 100m, fully steerable, single dish radio telescope located in Green Bank, West Virginia and capable of making observations from meter wavelengths to 3mm. However, observations at wavelengths short of 2 cm pose significant observational challenges due to pointing and surface errors. The first part of this thesis details efforts to combat wind-induced pointing errors, which reduce by half the amount of time available for high-frequency work on the telescope. The primary tool used for understanding these errors was an optical quadrant detector that monitored the motion of the telescope's feed arm. In this work, a calibration was developed that tied quadrant detector readings directly to telescope pointing error. These readings can be used for single-beam observations in order to determine if the telescope was blown off-source at some point due to wind. With observations with the 3 mm MUSTANG bolometer array, pointing errors due to wind can mostly be removed (> ⅔) during data reduction. Iapetus is a moon known for its stark albedo dichotomy, with the leading hemisphere only a tenth as bright as the trailing. In order to investigate this dichotomy, Iapetus was observed repeatedly with the GBT at wavelengths between 3 and 11 mm, with the original intention being to use the data to determine a thermal light-curve. Instead, the data showed incredible wavelength-dependent deviation from a black-body curve, with an emissivity as low as 0.3 at 9 mm. Numerous techniques were used to demonstrate that this low emissivity is a physical phenomenon rather than an observational one, including some using the quadrant detector to make sure the low emissivities are not due to being blown off source. This emissivity is the among the lowest ever detected in the solar system, but can be achieved using physically realistic ice models that are also used to model microwave emission from snowpacks and glaciers on Earth. These models indicate that the trailing hemisphere contains a scattering layer of depth 100 cm and grain size of 1-2 mm. The leading hemisphere is shown to exhibit a thermal depth effect.

KSC-2014-2566

NASA Image and Video Library

2014-03-11

HAMPTON, Va. – NASA technician Ricky Hall works inside the Unitary Plan Wind Tunnel at NASA's Langley Research Center in Virginia to affix grains of sand to a precise scale model of the Dream Chaser spacecraft. Sierra Nevada Corporation is developing the Dream Chaser in partnership with NASA's Commercial Crew Program. The sand creates turbulence at key points to simulate the conditions the real spacecraft will encounter during its return to Earth. The data gathered from the wind tunnel was used to further test the design through the company's Commercial Crew Integrated Capability agreement with NASA. Photo credit: NASA/ David C. Bowman

KSC-2014-2567

NASA Image and Video Library

2014-03-11

HAMPTON, Va. – NASA technician Ricky Hall works inside the Unitary Plan Wind Tunnel at NASA's Langley Research Center in Virginia to affix grains of sand to a precise scale model of the Dream Chaser spacecraft. Sierra Nevada Corporation is developing the Dream Chaser in partnership with NASA's Commercial Crew Program. The sand creates turbulence at key points to simulate the conditions the real spacecraft will encounter during its return to Earth. The data gathered from the wind tunnel was used to further test the design through the company's Commercial Crew Integrated Capability agreement with NASA. Photo credit: NASA/ David C. Bowman

Pedestal Crater and Yardangs

NASA Technical Reports Server (NTRS)

2003-01-01

MGS MOC Release No. MOC2-444, 6 August 2003

This April 2003 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a small meteor impact crater that has been modified by wind erosion. Two things happened after the crater formed. First, the upper few meters of surface material into which the meteor impacted was later eroded away by wind. The crater ejecta formed a protective armor that kept the material under the ejecta from been blown away. This caused the crater and ejecta to appear as if standing upon a raised platform--a feature that Mars geologists call a pedestal crater. Next, the pedestal crater was buried beneath several meters of new sediment, and then this material was eroded away by wind to form the array of sharp ridges that run across the pedestal crater's surface. These small ridges are known as yardangs. This picture is illuminated by sunlight from the upper left; it is located in west Daedalia Planum near 14.6oS, 131.9oW.

Wind Streaks on Venus: Clues to Atmospheric Circulation

NASA Technical Reports Server (NTRS)

Greeley, Ronald; Schubert, Gerald; Limonadi, Daniel; Bender, Kelly C.; Newman, William I.; Thomas, Peggy E.; Weitz, Catherine M.; Wall, Stephen D.

1994-01-01

Magellan images reveal surface features on Venus attributed to wind processes. Sand dunes, wind-sculpted hills, and more than 5830 wind streaks have been identified. The streaks serve as local "wind vanes," representing wind direction at the time of streak formation and allowing the first global mapping of near-surface wind patterns on Venus. Wind streaks are oriented both toward the equator and toward the west. When streaks associated with local transient events, such as impact cratering, are deleted, the westward component is mostly lost but the equatorward component remains. This pattern is consistent with a Hadley circulation of the lower atmosphere.

Design and laboratory testing of a new flow-through directional passive air sampler for ambient particulate matter.

PubMed

Lin, Chun; Solera Garcia, Maria Angeles; Timmis, Roger; Jones, Kevin C

2011-03-01

A new type of directional passive air sampler (DPAS) is described for collecting particulate matter (PM) in ambient air. The prototype sampler has a non-rotating circular sampling tray that is divided into covered angular channels, whose ends are open to winds from sectors covering the surrounding 360°. Wind-blown PM from different directions enters relevant wind-facing channels, and is retained there in collecting pools containing various sampling media. Information on source direction and type can be obtained by examining the distribution of PM between channels. Wind tunnel tests show that external wind velocities are at least halved over an extended area of the collecting pools, encouraging PM to settle from the air stream. Internal and external wind velocities are well-correlated over an external velocity range of 2.0-10.0 m s⁻¹, which suggests it may be possible to relate collected amounts of PM simply to ambient concentrations and wind velocities. Measurements of internal wind velocities in different channels show that velocities decrease from the upwind channel round to the downwind channel, so that the sampler effectively resolves wind directions. Computational fluid dynamics (CFD) analyses were performed on a computer-generated model of the sampler for a range of external wind velocities; the results of these analyses were consistent with those from the wind tunnel. Further wind tunnel tests were undertaken using different artificial particulates in order to assess the collection performance of the sampler in practice. These tests confirmed that the sampler can resolve the directions of sources, by collecting particulates preferentially in source-facing channels.

Aggregative group behavior in insect parasitic nematode disperal

USDA-ARS?s Scientific Manuscript database

Movement behavior is critical to determination of spatial ecology and success of foraging in predators and parasites. In this study movement behavior of entomopathogenic nematodes was explored. Movement patterns in sand were investigated when nematodes were applied to a specific locus or when the ne...

Earth observation taken by the Expedition 20 crew

NASA Image and Video Library

2009-07-25

ISS020-E-026195 (25 July 2009) --- Aorounga Impact Crater is featured in this image photographed by an Expedition 20 crew member on the International Space Station. Aorounga Impact Crater is located in the Sahara Desert of north-central Chad and is one of the best preserved impact structures in the world. According to scientists, the crater is thought to be middle or upper Devonian to lower Mississippian (approximately 345 ? 370 million years old) based on the age of the sedimentary rocks deformed by the impact. Spaceborne Imaging Radar (SIR) data collected in 1994 suggests that Aorounga is one of a set of three craters formed by the same impact event. The other two suggested impact structures are buried by sand deposits. The concentric ring structure of the Aorounga crater ? renamed Aorounga South in the multiple-crater interpretation of SIR data ? is clearly visible in this detailed photograph. The central highland, or peak, of the crater is surrounded by a small sand-filled trough; this in turn is surrounded by a larger circular trough. Linear rock ridges alternating with light orange sand deposits cross the image from upper left to lower right; these are called yardangs by geomorphologists. Yardangs form by wind erosion of exposed rock layers in a unidirectional wind field. The wind blows from the northeast at Aorounga, and sand dunes formed between the yardangs are actively migrating to the southwest.

Predictability of dune activity in real dune fields under unidirectional wind regimes

NASA Astrophysics Data System (ADS)

Barchyn, Thomas E.; Hugenholtz, Chris H.

2015-02-01

We present an analysis of 10 dune fields to test a model-derived hypothesis of dune field activity. The hypothesis suggests that a quantifiable threshold exists for stabilization in unidirectional wind regimes: active dunes have slipface deposition rates that exceed the vegetation deposition tolerance, and stabilizing dunes have the opposite. We quantified aeolian sand flux, slipface geometry, and vegetation deposition tolerance to directly test the hypothesis at four dune fields (Bigstick, White Sands Stable, White Sands Active, and Cape Cod). We indirectly tested the hypothesis at six additional dune fields with limited vegetation data (Hanford, Año Nuevo, Skagen Odde, Salton Sea, Oceano Stable, and Oceano Active, "inverse calculation sites"). We used digital topographic data and estimates of aeolian sand flux to approximate the slipface deposition rates prior to stabilization. Results revealed a distinct, quantifiable, and consistent pattern despite diverse environmental conditions: the modal peak of prestabilization slipface deposition rates was 80% of the vegetation deposition tolerance at stabilized or stabilizing dune fields. Results from inverse calculation sites indicate deposition rates at stabilized sites were near a hypothesized maximum vegetation deposition tolerance (1 m a-1), and active sites had slipface deposition rates much higher. Overall, these results confirm the hypothesis and provide evidence of a globally applicable, simple, and previously unidentified predictor for the dynamics of vegetation cover in dune fields under unidirectional wind regimes.

United States Air Force Academy (USAFA) Vertical Axis Wind Turbine.

DTIC Science & Technology

1980-09-01

Rotors, SAND76-0131. Albuquerque: July 1977. 10. Oliver, R.C. and P.R. Nixon. "Design Procedure for Coupling Savonius and Darrieus Wind Turbines ", Air...May 17-20, 1976. -65- 16. Blackwell, B.F., R.E. Sheldahl, and L.V. Feltz. Wind Tunnel Performance Data for the Darrieus Wind Turbine with NACA 0012...a 5.8 m/s (13 mph) wind . At 100 rpm, the Darrieus turbine would be fully self-sustaining and acceleration would continue to an operating tip speed

Analysis of the Contribution of Wind Drift Factor to Oil Slick Movement under Strong Tidal Condition: Hebei Spirit Oil Spill Case

PubMed Central

Kim, Tae-Ho; Yang, Chan-Su; Oh, Jeong-Hwan; Ouchi, Kazuo

2014-01-01

The purpose of this study is to investigate the effects of the wind drift factor under strong tidal conditions in the western coastal area of Korea on the movement of oil slicks caused by the Hebei Spirit oil spill accident in 2007. The movement of oil slicks was computed using a simple simulation model based on the empirical formula as a function of surface current, wind speed, and the wind drift factor. For the simulation, the Environmental Fluid Dynamics Code (EFDC) model and Automatic Weather System (AWS) were used to generate tidal and wind fields respectively. Simulation results were then compared with 5 sets of spaceborne optical and synthetic aperture radar (SAR) data. From the present study, it was found that highest matching rate between the simulation results and satellite imagery was obtained with different values of the wind drift factor, and to first order, this factor was linearly proportional to the wind speed. Based on the results, a new modified empirical formula was proposed for forecasting the movement of oil slicks on the coastal area. PMID:24498094

Assessing the impact of marine wind farms on birds through movement modelling.

PubMed

Masden, Elizabeth A; Reeve, Richard; Desholm, Mark; Fox, Anthony D; Furness, Robert W; Haydon, Daniel T

2012-09-07

Advances in technology and engineering, along with European Union renewable energy targets, have stimulated a rapid growth of the wind power sector. Wind farms contribute to carbon emission reductions, but there is a need to ensure that these structures do not adversely impact the populations that interact with them, particularly birds. We developed movement models based on observed avoidance responses of common eider Somateria mollissima to wind farms to predict, and identify potential measures to reduce, impacts. Flight trajectory data that were collected post-construction of the Danish Nysted offshore wind farm were used to parameterize competing models of bird movements around turbines. The model most closely fitting the observed data incorporated individual variation in the minimum distance at which birds responded to the turbines. We show how such models can contribute to the spatial planning of wind farms by assessing their extent, turbine spacing and configurations on the probability of birds passing between the turbines. Avian movement models can make new contributions to environmental assessments of wind farm developments, and provide insights into how to reduce impacts that can be identified at the planning stage.

Colloquium: Biophysical principles of undulatory self-propulsion in granular media

NASA Astrophysics Data System (ADS)

Goldman, Daniel I.

2014-07-01

Biological locomotion, movement within environments through self-deformation, encompasses a range of time and length scales in an organism. These include the electrophysiology of the nervous system, the dynamics of muscle activation, the mechanics of the skeletal system, and the interaction mechanics of such structures within natural environments like water, air, sand, and mud. Unlike the many studies of cellular and molecular scale biophysical processes, movement of entire organisms (like flies, lizards, and snakes) is less explored. Further, while movement in fluids like air and water is also well studied, little is known in detail of the mechanics that organisms use to move on and within flowable terrestrial materials such as granular media, ensembles of small particles that collectively display solid, fluid, and gaslike behaviors. This Colloquium reviews recent progress to understand principles of biomechanics and granular physics responsible for locomotion of the sandfish, a small desert-dwelling lizard that "swims" within sand using undulation of its body. Kinematic and muscle activity measurements of sand swimming using high speed x-ray imaging and electromyography are discussed. This locomotion problem poses an interesting challenge: namely, that equations that govern the interaction of the lizard with its environment do not yet exist. Therefore, complementary modeling approaches are also described: resistive force theory for granular media, multiparticle simulation modeling, and robotic physical modeling. The models reproduce biomechanical and neuromechanical aspects of sand swimming and give insight into how effective locomotion arises from the coupling of the body movement and flow of the granular medium. The argument is given that biophysical study of movement provides exciting opportunities to investigate emergent aspects of living systems that might not depend sensitively on biological details.

Evidence of Cold Climate Slope Processes from the New Jersey Coastal Plain: Debris Flow Stratigraphy at Haines Corner, Camden County, New Jersey

USGS Publications Warehouse

Newell, Wayne L.

2005-01-01

Excavations through surficial deposits across the New Jersey Coastal Plain commonly reveal homogenized surficial sediments, deformed sedimentary structures, chaotically rearranged bed-forms, and wedge-shaped cracks filled with sand from the top-most layers of extant soil profiles. As a whole, these abundant, broadly distributed phenomena are best explained as artifacts of an era of frozen ground during the last Pleistocene glacial maximum. Vigorous freeze-thaw processes and abundant seasonal rainfall created a landscape of low relief covered by highly mobile surficial deposits. The surficial deposits are at grade into broad, flat bottomed valleys now drained by small, tightly meandering, under-fit streams. Modern fluvial, aeolian, and slope processes are ineffectual in either creating or modifying these landscapes. One particularly brief exposure of complex slope deposits was documented at Haines Corner, Camden County, during the field work (1986) for the Surficial Geologic Map of southern and central New Jersey. The exposure, now presented and interpreted here, provides previously unavailable details of a system of freeze-thaw driven processes that unfolded upon a frozen, impermeable substrate 80 miles south of the southern margin of the Wisconsinan glacial advance to Long Island, N.Y. At the time of these extreme processes, the presently sub-aerial New Jersey Coastal Plain was not proximal to moderating effects of the Atlantic Ocean, being about 100 miles inland and 300 feet above the lowered sea level. Current studies of analogous deposits across the mid-Atlantic Coastal Plain now benefit from dating techniques that were not available during the geologic mapping field work (1985-'92). During the mapping in New Jersey, hundreds of exposures failed to produce datable carbon remains within the stratigraphy of the surficial deposits. Recently reported TL dates from wind-blown sand filling frost wedges, exposed elsewhere in New Jersey, indicate that the widely distributed surficial deposits of the New Jersey Coastal Plain were active during the maximum cold period of the late Pleistocene (around 18,000 years ago).

Geology and ground-water hydrology of the Angostura irrigation project, South Dakota, with a section on the mineral quality of the waters

USGS Publications Warehouse

Littleton, Robert T.; Swenson, Herbert A.

1949-01-01

The lands to be irrigated from water stored in the Angostura Reservoir are situated on the lover of two terraces along the southeast side of the Cheyenne River in northeastern Fall River County and on the terrace known as Harrison Plat in southeastern Custer County, S. Dak. The terrace deposits are composed of relatively permeable sands and gravels that rest on a shale bedrock platform. The terrace surfaces are mantled in part by slope wash derived from higher shale slopes and by wind-blown sand. Ground water occurs under water-table conditions in the river alluvium and in terraces above the river. Although the zone of saturation in the terrace deposits is 6enerally thin, it is essentially continuous in the area southeast of the river, and the water issues as springs in the terrace faces along the inner valley of the river and along the valleys of tributary streams cuttin6 back into the terraces. A zone of saturation is present only in part of the Harrison Plat area, and it extends to the terrace face only along Cottonwood Creek. Wells in the unconsolidated mantle rock supply water for domestic and stock purposes, but yields are small. Abundant supplies of artesian water are available at depths ranging up to 3,000 feet but are not now utilized except at the extreme western end of the area where the bedrock aquifer is close below the surface. The effect of applying irrigation water on the terrace lands will depend on the character of the underlying material and on the measures taken to forestall waterlogging and other undesirable effects. Terrace areas that are mantled by slope wash will be especially susceptible to waterlogging, as will valley-bottom areas mantled by colluvium that are adjacent to irrigated terracea. Periodic measurements of water levels in observation wells will give warning of potential waterlogging in time to permit taking preventive measures. Analyses of samples of both ground water and surface water indicate a high mineral content. In general, samples from the Cheyenne River are higher in total dissolved solids and lower in percent sodium than the ground water.

A Jurassic Shock-Aftershock Earthquake Sequence Recorded by Small Clastic Pipes and Dikes within Dune Cross-Strata, Zion National Park, Utah

NASA Astrophysics Data System (ADS)

Loope, D. B.; Zlotnik, V. A.; Kettler, R. M.; Pederson, D. T.

2012-12-01

Eolian sandstones of south-central and southeast Utah contain large volumes of contorted cross-strata that have long been recognized as products of liquefaction caused by seismic shaking. Unlike most sites where Navajo Sandstone is exposed, in Zion National Park (southwestern Utah), the Navajo contains very, very few contorted strata. We have, however, mapped the distribution of more than 1,000 small-scale, vertical pipes and dikes in uncontorted cross-strata of the Navajo at two small study sites in Zion. Pipes are 2-5 cm in diameter and up to 3 m long; dikes are ~6 cm wide. Clusters of the water-escape structures lie directly above and below numerous, near-horizontal bounding surfaces. Dikes are restricted to the wind-ripple strata that lie above the bounding surfaces. Pipes are common both above and below the bounding surfaces. In map view, most pipes are arranged in lines. Near the bounding surfaces, pipes merge upward with shallow dikes trending parallel to the lines of pipes. Pipes formed in grainflows—homogeneous, well-sorted sand lacking cohesion. Dikes formed above the bounding surface, in more-cohesive, poorly sorted, wind-ripple strata. As liquefaction began, expansion of subsurface sand caused spreading within the unliquified (capping) beds near the land surface. Dikes intruded cracks in the wind-ripple strata, and pipes rose from the better-sorted sand to interdune surfaces, following trends of cracks. Because the wind-ripple strata had low cohesive strength, a depression formed around each rupture, and ejected sand built upward to a flat-topped surface rather than forming the cone of a classic sand volcano. In one 3 m2 portion of the map area, a cluster of about 20 pipes and dikes, many with truncated tops, record eight stratigraphically distinct seismic events. The large dunes that deposited the Navajo cross-strata likely moved ~1m/yr. When, in response to seismic shaking, a few liters of fluidized sand erupted onto the lowermost portion of the dune lee slope through a pipe, the erupted sand dried and was buried by climbing wind-ripple strata as the large dune continued to advance downwind. The mapped cluster recording eight distinct seismic events lies within thin-laminated sediment that was deposited by wind ripples during 1 m (~ 1 year) of southeastward dune migration. We conclude that the small pipes and dikes of our study sites are products of numerous >MM 5 earthquakes, some of which recurred at intervals of less than 2 months. We interpret one small cluster of pipes and dikes with well-defined upward terminations as a distinct shock-aftershock sequence. Because the largest modern earthquakes can produce surface liquefaction only up to about 175 km from their epicenters, the Jurassic epicenters must have been well within that distance. The tendency of modern plate boundaries to produce high-frequency aftershocks suggests that the epicenter for this Jurassic sequence lay to the southwest, within the plate boundary zone (not within continental rocks to the east). As eolian dunes steadily migrate over interdune surfaces underlain by water-saturated dune cross-strata, the thin, distinct laminae produced by the wind ripples that occupy dune toes can faithfully record high-frequency seismic events.

A new turbulence-based model for sand transport

NASA Astrophysics Data System (ADS)

Mayaud, Jerome; Wiggs, Giles; Bailey, Richard

2016-04-01

Knowledge of the changing rate of sediment flux in space and time is essential for quantifying surface erosion and deposition in desert landscapes. While many aeolian studies have relied on time-averaged parameters such as wind velocity (U) and wind shear velocity (u*) to determine sediment flux, there is increasing evidence that high-frequency turbulence is an important driving force behind the entrainment and transport of sand. However, turbulence has yet to be incorporated into a functional sand transport model that can be used for predictive purposes. In this study we present a new transport model (the 'turbulence model') that accounts for high-frequency variations in the horizontal (u) and vertical (w) components of wind flow. The turbulence model is fitted to wind velocity and sediment transport data from a field experiment undertaken in Namibia's Skeleton Coast National Park, and its performance at three temporal resolutions (10 Hz, 1 Hz, 1 min) is compared to two existing models that rely on time-averaged wind velocity data (Radok, 1977; Dong et al., 2003). The validity of the three models is analysed under a variety of saltation conditions, using a 2-hour (1 Hz measurement resolution) dataset from the Skeleton Coast and a 5-hour (1 min measurement resolution) dataset from the southwestern Kalahari Desert. The turbulence model is shown to outperform the Radok and Dong models when predicting total saltation count over the three experimental periods. For all temporal resolutions presented in this study (10 Hz-10 min), the turbulence model predicted total saltation count to within at least 0.34%, whereas the Radok and Dong models over- or underestimated total count by up to 5.50% and 20.53% respectively. The strong performance of the turbulence model can be attributed to a lag in mass flux response built into its formulation, which can be adapted depending on the temporal resolution of investigation. This accounts for the inherent lag within the physical saltation system that has been reported in previous studies. Whilst the inclusion of both the u and w flow components is a key conceptual element of our new model, similar to recent field studies (e.g. Schönfeldt & von Löwis, 2003; Wiggs & Weaver, 2012; Chapman et al., 2013), we find that fluctuations in w are relatively unimportant for driving saltation, because wind-driven flux is more strongly associated with a positive u component. The best predictions of total sand transport are achieved using our turbulence model at a temporal resolution of 4 s in cases of partially developed saltation, and at a resolution of 1 min in cases of well-developed saltation. The proposed approach could prove to be significant for integrating turbulent transport processes into long-term, macro-scale landscape modelling of drylands References Chapman, C., Walker, I. J., Hesp, P. A., Bauer, B. O., Davidson-Arnott, R. G. D., & Ollerhead, J. (2013). Reynolds stress and sand transport over a foredune. Earth Surface Processes and Landforms, 38(14), 1735-1747. Dong, Z., Liu, X., Wang, H. & Wang, X. (2003). Aeolian sand transport: a wind tunnel model. Sedimentary Geology, 161, 71-83. Radok, U. (1977). Snow drift. Journal of Glaciology, 19, 123-139. Schönfeldt, H. J., & von Löwis, S. (2003). Turbulence-driven saltation in the atmospheric surface layer. Meteorologische Zeitschrift, 12(5), 257-268. Wiggs, G. F. S. & Weaver, C. M. (2012). Turbulent flow structures and aeolian sediment transport over a barchan sand dune. Geophysical Research Letters, 39(5), 1-7.

Wind tunnel experimental study on the effect of PAM on soil wind erosion control.

PubMed

He, Ji-Jun; Cai, Qiang-Guo; Tang, Ze-Jun

2008-10-01

In recent years, high-molecular-weight anionic polyacrylamide (PAM) have been widely tested on a variety of soils, primarily in water erosion control. However, little information is available regarding the effectiveness of PAM on preventing soil loss from wind erosion. The research adopted room wind tunnel experiment, two kinds of soils were used which were from the agro-pastoral area of Inner Mongolia, the northwest of China, the clay content of soils were 22.0 and 13.7%, respectively. For these tests, all the treatments were performed under the condition of wind velocity of 14 m s(-1) and a blown angle of 8.75%, according to the actual situation of experimented area. The study results indicated that using PAM on the soil surface could enhance the capability of avoiding the wind erosion, at the same time, the effect of controlling wind soil erosion with 4 g m(-2) PAM was better than 2 g m(-2) PAM's. Economically, the 2 g m(-2) PAM used in soil surface can control wind erosion effectively in this region. The prophase PAM accumulated in soil could not improve the capability of avoiding the wind erosion, owing to the degradation of PAM in the soil and the continual tillage year after year. The texture of soil is a main factor influencing the capability of soil avoiding wind erosion. Soil with higher clay content has the higher capability of preventing soil from wind erosion than one with the opposite one under the together action of PAM and water.

Estimation of bare soil evaporation for different depths of water table in the wind-blown sand area of the Ordos Basin, China

NASA Astrophysics Data System (ADS)

Chen, Li; Wang, Wenke; Zhang, Zaiyong; Wang, Zhoufeng; Wang, Qiangmin; Zhao, Ming; Gong, Chengcheng

2018-04-01

Soil surface evaporation is a significant component of the hydrological cycle, occurring at the interface between the atmosphere and vadose zone, but it is affected by factors such as groundwater level, soil properties, solar radiation and others. In order to understand the soil evaporation characteristics in arid regions, a field experiment was conducted in the Ordos Basin, central China, and high accuracy sensors of soil moisture, moisture potential and temperature were installed in three field soil profiles with water-table depths (WTDs) of about 0.4, 1.4 and 2.2 m. Soil-surface-evaporation values were estimated by observed data combined with Darcy's law. Results showed that: (1) soil-surface-evaporation rate is linked to moisture content and it is also affected by air temperature. When there is sufficient moisture in the soil profile, soil evaporation increases with rising air temperature. For a WTD larger than the height of capillary rise, the soil evaporation is related to soil moisture content, and when air temperature is above 25 °C, the soil moisture content reduces quickly and the evaporation rate lowers; (2) phreatic water contributes to soil surface evaporation under conditions in which the WTD is within the capillary fringe. This indicates that phreatic water would not participate in soil evaporation for a WTD larger than the height of capillary rise. This finding developed further the understanding of phreatic evaporation, and this study provides valuable information on recognized soil evaporation processes in the arid environment.

Sedimentary processes of the Bagnold Dunes: Implications for the eolian rock record of Mars

NASA Astrophysics Data System (ADS)

Ewing, R. C.; Lapotre, M. G. A.; Lewis, K. W.; Day, M.; Stein, N.; Rubin, D. M.; Sullivan, R.; Banham, S.; Lamb, M. P.; Bridges, N. T.; Gupta, S.; Fischer, W. W.

2017-12-01

The Mars Science Laboratory rover Curiosity visited two active wind-blown sand dunes within Gale crater, Mars, which provided the first ground-based opportunity to compare Martian and terrestrial eolian dune sedimentary processes and study a modern analog for the Martian eolian rock record. Orbital and rover images of these dunes reveal terrestrial-like and uniquely Martian processes. The presence of grainfall, grainflow, and impact ripples resembled terrestrial dunes. Impact ripples were present on all dune slopes and had a size and shape similar to their terrestrial counterpart. Grainfall and grainflow occurred on dune and large-ripple lee slopes. Lee slopes were 29° where grainflows were present and 33° where grainfall was present. These slopes are interpreted as the dynamic and static angles of repose, respectively. Grain size measured on an undisturbed impact ripple ranges between 50 μm and 350 μm with an intermediate axis mean size of 113 μm (median: 103 μm). Dissimilar to dune eolian processes on Earth, large, meter-scale ripples were present on all dune slopes. Large ripples had nearly symmetric to strongly asymmetric topographic profiles and heights ranging between 12 cm and 28 cm. The composite observations of the modern sedimentary processes highlight that the Martian eolian rock record is likely different from its terrestrial counterpart because of the large ripples, which are expected to engender a unique scale of cross stratification. More broadly, however, in the Bagnold Dune Field as on Earth, dune-field pattern dynamics and basin-scale boundary conditions will dictate the style and distribution of sedimentary processes.

The case for a southeastern Australian Dust Bowl, 1895-1945

NASA Astrophysics Data System (ADS)

Cattle, Stephen R.

2016-06-01

Australia has an anecdotal history of severe wind erosion and dust storm activity, but there has been no lasting public perception of periods of extreme dust storm activity in this country, such as that developed in the USA following the Dust Bowl of the 1930s. Newspaper accounts of droughts and dust storms in southeastern (SE) Australia between 1895 and 1945 suggest that, at various times, the scale of these events was comparable to those experienced in the USA Dust Bowl. During this 50-year period, average annual rainfall values in this region were substantially below long-term averages, air temperatures were distinctly warmer, marginal lands were actively cropped and grazed, and rabbits were a burgeoning grazing pest. From the beginning of the Federation Drought of 1895-1902, dust storm activity increased markedly, with the downwind coastal cities of Sydney and Melbourne experiencing dust hazes, dust storms and falls of red rain relatively regularly. Between 1935 and 1945, Sydney and Melbourne received ten and nine long-distance dust events, respectively, with the years of 1938 and 1944/45 being the most intensely dusty. Entire topsoil horizons were blown away, sand drift was extreme, and crops and sheep flocks were destroyed. Although these periods of extreme dust storm activity were not as sustained as those experienced in the USA in the mid-1930s, there is a strong case to support the contention that SE Australia experienced its own extended, somewhat episodic version of a Dust Bowl, with a similar combination of causal factors and landscape effects.

Giant saltation on Mars

PubMed Central

Almeida, Murilo P.; Parteli, Eric J. R.; Andrade, José S.; Herrmann, Hans J.

2008-01-01

Saltation, the motion of sand grains in a sequence of ballistic trajectories close to the ground, is a major factor for surface erosion, dune formation, and triggering of dust storms on Mars. Although this mode of sand transport has been matter of research for decades through both simulations and wind tunnel experiments under Earth and Mars conditions, it has not been possible to provide accurate measurements of particle trajectories in fully developed turbulent flow. Here we calculate the motion of saltating grains by directly solving the turbulent wind field and its interaction with the particles. Our calculations show that the minimal wind velocity required to sustain saltation on Mars may be surprisingly lower than the aerodynamic minimal threshold measurable in wind tunnels. Indeed, Mars grains saltate in 100 times higher and longer trajectories and reach 5-10 times higher velocities than Earth grains do. On the basis of our results, we arrive at general expressions that can be applied to calculate the length and height of saltation trajectories and the flux of grains in saltation under various physical conditions, when the wind velocity is close to the minimal threshold for saltation. PMID:18443302

Kuwait Oil Fields as seen from STS-58

NASA Technical Reports Server (NTRS)

1993-01-01

A clear view of the northern Kuwait coast shows the southern part of Kuwait City, and the major oil fields to the south. Oil laden sands, where wells were set ablaze during the Gulf War in 1991, are visible south of Kuwait City as a dark, elongated patch surrounded by light-colored sand. Oil-stained sandbetween well sites (dots) and criss-crossing roads is gradually being covered by clean sand carried by strong, seasonal northwest winds.

Sand Dunes with Frost

NASA Technical Reports Server (NTRS)

2004-01-01

9 May 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a suite of frost-covered sand dunes in the north polar region of Mars in early spring, 2004. The dunes indicate wind transport of sand from left to right (west to east). These landforms are located near 78.1oN, 220.8oW. This picture is illuminated by sunlight from the lower left and covers an area about 3 km (1.9 mi) across.

Mechanistic Drifting Forecast Model for A Small Semi-Submersible Drifter Under Tide-Wind-Wave Conditions

NASA Astrophysics Data System (ADS)

Zhang, Wei-Na; Huang, Hui-ming; Wang, Yi-gang; Chen, Da-ke; Zhang, lin

2018-03-01

Understanding the drifting motion of a small semi-submersible drifter is of vital importance regarding monitoring surface currents and the floating pollutants in coastal regions. This work addresses this issue by establishing a mechanistic drifting forecast model based on kinetic analysis. Taking tide-wind-wave into consideration, the forecast model is validated against in situ drifting experiment in the Radial Sand Ridges. Model results show good performance with respect to the measured drifting features, characterized by migrating back and forth twice a day with daily downwind displacements. Trajectory models are used to evaluate the influence of the individual hydrodynamic forcing. The tidal current is the fundamental dynamic condition in the Radial Sand Ridges and has the greatest impact on the drifting distance. However, it loses its leading position in the field of the daily displacement of the used drifter. The simulations reveal that different hydrodynamic forces dominate the daily displacement of the used drifter at different wind scales. The wave-induced mass transport has the greatest influence on the daily displacement at Beaufort wind scale 5-6; while wind drag contributes mostly at wind scale 2-4.

On the Beauty of Yardangs

NASA Image and Video Library

2015-05-06

Some geological materials (like solid rock) are incredibly tough, but others (like piles of volcanic ash) are quite soft. Some materials are soft enough that they can be eroded by the wind alone and yield landscapes that look like what we see in this HiRISE image. The long straight ridges seen here are called yardangs and they form on Mars (and Earth) when the wind strips away the inter-ridge material. This process is greatly aided when the wind is also blowing sand along. The sand grains do an effective job at stripping away loose material: these ridges are literally being sandblasted. Yardangs are useful features to recognize because the tell us the direction the wind is blowing in. They take a long time to form so this direction is the dominant wind orientation averaged over a long period of time (which might be quite different that the winds on Mars today). These yardangs also tell us that the surface here is made up of loose weak material and this information, in conjunction with other data, can tell us what the material is composed of and what the history of this particular site on Mars has been. http://photojournal.jpl.nasa.gov/catalog/PIA19457

Windscapes and olfactory foraging in a large carnivore

PubMed Central

Togunov, Ron R.; Derocher, Andrew E.; Lunn, Nicholas J.

2017-01-01

The theoretical optimal olfactory search strategy is to move cross-wind. Empirical evidence supporting wind-associated directionality among carnivores, however, is sparse. We examined satellite-linked telemetry movement data of adult female polar bears (Ursus maritimus) from Hudson Bay, Canada, in relation to modelled winds, in an effort to understand olfactory search for prey. In our results, the predicted cross-wind movement occurred most frequently at night during winter, the time when most hunting occurs, while downwind movement dominated during fast winds, which impede olfaction. Migration during sea ice freeze-up and break-up was also correlated with wind. A lack of orientation during summer, a period with few food resources, likely reflected reduced cross-wind search. Our findings represent the first quantitative description of anemotaxis, orientation to wind, for cross-wind search in a large carnivore. The methods are widely applicable to olfactory predators and their prey. We suggest windscapes be included as a habitat feature in habitat selection models for olfactory animals when evaluating what is considered available habitat. PMID:28402340

Radiotelemetric analysis of the effects of prevailing wind direction on Mormon cricket migratory band movement.

PubMed

Sword, G A; Lorch, P D; Gwynne, D T

2008-08-01

During outbreaks, flightless Mormon crickets [Anabrus simplex Haldeman (Orthoptera: Tettigoniidae)] form large mobile groups known as migratory bands. These bands can contain millions of individuals that march en masse across the landscape. The role of environmental cues in influencing the movement direction of migratory bands is poorly understood and has been the subject of little empirical study. We examined the effect of wind direction on Mormon cricket migratory band movement direction by monitoring the local weather conditions and daily movement patterns of individual insects traveling in bands over the same time course at three close, but spatially distinct sites. Although weather conditions were relatively homogeneous across sites, wind directions tended to be more variable across sites during the morning hours, the period during which directional movement begins. Migratory bands at different sites traveled in distinctly different directions. However, we failed to find any evidence to suggest that the observed variation in migratory band movement direction was correlated with local wind direction at any time during the day. These results support the notion that the cues mediating migratory band directionality are likely to be group specific and that a role for landscape-scale environmental cues such as wind direction is unlikely.

Social movement heterogeneity in public policy framing: A multi-stakeholder analysis of the Keystone XL pipeline

NASA Astrophysics Data System (ADS)

Wesley, David T. A.

In 2011, stakeholders with differing objectives formed an alliance to oppose the Keystone XL heavy oil pipeline. The alliance, which came to be known as "Tar Sands Action," implemented various strategies, some of which were more successful than others. Tar Sands Action was a largely heterogeneous alliance that included indigenous tribes, environmentalists, ranchers, landowners, and trade unions, making it one of the more diverse social movement organizations in history. Each of these stakeholder categories had distinct demographic structures, representing an array of racial, ethnic, educational, occupational, and political backgrounds. Participants also had differing policy objectives that included combating climate change and protecting jobs, agricultural interests, water resources, wildlife, and human health. The current dissertation examines the Tar Sands Action movement to understand how heterogeneous social movement organizations mobilize supporters, maintain alliances, and create effective frames to achieve policy objectives. A multi-stakeholder analysis of the development, evolution and communication of frames concerning the Keystone XL controversy provides insight into the role of alliances, direct action, and the news media in challenging hegemonic frames. Previous research has ignored the potential value that SMO heterogeneity provides by treating social movements as culturally homogenous. However, diversity has been shown to affect performance in business organizations. The current study demonstrates that under some circumstances, diversity can also improve policy outcomes. Moreover, policy frames are shown to be more effective in sustaining news media and public interest through a process the author calls dynamic frame sequencing (DFS). DFS refers to a process implementing different stakeholder frames at strategically opportune moments. Finally, Tar Sands Action was one of the first SMOs to rely heavily on social media to build alliances, disseminate information, and mobilize support. This study adds to a growing body of research that considers the emerging role of social media in protest movements.

Inland aeolian deposits of the Iberian Peninsula: Sand dunes and clay dunes of the Duero Basin and the Manchega Plain. Palaeoclimatic considerations

NASA Astrophysics Data System (ADS)

Bernat Rebollal, M.; Pérez-González, A.

2008-12-01

This paper describes the latest research on the geomorphological characteristics, formation environment and chronology of the main inland aeolian deposits from the south-eastern Duero Basin (DB) and the Manchega Plain (MP) of the Iberian Peninsula. Similarities and differences between the aeolian deposits of these two locations are summarised. Wind deflation from the Guadiana and Júcar alluvial systems created the aeolian deposits of the MP. These deposits are mainly composed of quartz sands. However, in the San Juan alluvial plain (MP) there is a large extent of clay dunes formed by exposure to prevalent winds of seasonal playa-lakes with salt and clay sediments. In the DB, wind remobilisation of the small particles from Quaternary terraces and Tertiary arkosic sediments left aeolian deposits of quartz-feldspar sands. Textural parameters of the aeolian deposits show large variations depending on the location and the original deposit. Thus, in the DB the aeolian sands derived from the deflation of fluvial sediments are better sorted and smaller in grain size than those created by the deflation of arkosic sediments. Morphologically, simple and compound parabolic dunes (U-V forms, hemicyclic, lobate and elongate), crescentic and linear dunes, climbing dunes and blowout dunes have been recognized at both sites. Barchan and dome dunes are present only in the DB while "lunette lunette-clay dunes" are found only in the MP. In both locations, the large extent of aeolian sand sheets and the predominance of simple and compound parabolic dunes indicates the active role of sparse vegetation cover in the formation of this aeolian system. In the DB, dunes were formed by southwest and west winds, while in the MP the aeolian morphologies indicate that the prevalent winds were west and northwest. The chronology of the dune deposits is being determined with luminescence (TL-OSL) dating and Mass Spectrometry Analysis ( 14C-AMS). In this way, the aeolian activity and stabilisation stages can be established, the latter well marked in the DB through soil A horizon development. Thus, the main sand dune formation in the DB and the eastern regions of the MP occurred between 13.5 and 7 ka BP, during the cold and arid Younger Dryas episode and the Early Holocene. The clay dunes of the MP accumulated mainly from 29 to 19 ka BP that corresponds with Heinrich events HE-3 and HE-2 and the Last Glacial Maximum. However, clay dunes were also formed between 13.5 and 7 ka BP. In both locations, there have been reactivations of some sand deposits in the recent Holocene, with maximum activity around 5-2 ka BP and 0.5-0.2 ka BP. On the other hand, three marked stages of stabilisation of the DB aeolian system have been established with 14C-AMS, around 10.2, 6.2 and 1.2 ka BP. Finally, the main winds contributing to dune construction were also responsible for the deflation processes with the formation of erosional depressions.

Agglomeration of a comprehensive model for the wind-driven sand transport at the Belgian Coast

NASA Astrophysics Data System (ADS)

Strypsteen, Glenn; Rauwoens, Pieter

2016-04-01

Although a lot of research has been done in the area of Aeolian transport, it is only during the last years that attention has been drawn to Aeolian transport in coastal areas. In these areas, the physical processes are more complex, due to a large number of transport limiting parameters. In this PhD-project, which is now in its early stage, a model will be developed which relates the wind-driven sand transport at the Belgian coast with physical parameters such as the wind speed, humidity and grain size of the sand, and the slope of beach and dune surface. For the first time, the interaction between beach and dune dynamics is studied at the Belgian coast. The Belgian coastline is only 67km long, but densely populated and therefore subject to coastal protection and safety. The coast mostly consists of sandy beaches and dikes. Although, still 33km of dunes exist, whose dynamics are far less understood. The overall research approach consists of three pathways: (i) field measurements, (ii) physical model tests, and (iii) numerical simulations. Firstly and most importantly, several field campaigns will provide accurate data of meteo-marine conditions, morphology, and sand transport events on a wide beach at the Belgian Coastline. The experimental set-up consists of a monitoring station, which will provide time series of vegetation cover, shoreline position, fetch distances, surficial moisture content, wind speed and direction and transport processes. The horizontal and vertical variability of the event scale Aeolian sand transport is analyzed with 8 MWAC sand traps. Two saltiphones register the intensity and variations of grain impacts over time. Two meteo-masts, each with four anemometers and one wind vane, provide quantitative measurements of the wind flow at different locations on the beach. Surficial moisture is measured with a moisture sensor. The topography measurements are typically done with laser techniques. To start, two sites are selected for measurement campaigns: one consists of the typical beach - dike system, a second site involves the dunes. First results of the measured data will be presented at the conference, together with a comparison to empirical correlations available in literature. Next to the field measurements, we propose physical model tests to provide data that is difficult to measure in the field. They will be used to determine the shear velocity and critical shear velocity in function of the transport flux. The effect of surficial moisture, vegetation and morphologic landforms will also be investigated in the model tests. Numerical simulations will provide a better insight in the physical processes of the Aeolian events and will be validated with the experimental results from the field campaigns and the physical model tests. The ultimate goal of the PhD is to obtain a sand transport model for the Belgian Coast, which can be used to assess the stability of nourishments in a quantitative matter, but it also will gain a better insight in the beach and dune interactions with the changing climate.

The South Carolina Coastal Erosion Study: Numerical modeling of circulation and sediment transport in Long Bay, SC

NASA Astrophysics Data System (ADS)

Warner, J. C.; Sullivan, C.; Voulgaris, G.; Work, P.; Haas, K.; Hanes, D. M.

2004-12-01

Long Bay, South Carolina, is a heavily populated coastal region that supports a large tourism industry. Sand resources are important for both recreation and coastal habitat. Earlier geological framework studies have identified a large sand deposit oblique to the shoreline, oriented clockwise in the offshore direction. This sand feature is ~ 10 km long, 2 km wide, and in excess of 3m thick, possibly providing a source for beach nourishment material. Objectives of this study are to describe the physical processes that control the transport of sediment in Long Bay, specifically off the coast of Myrtle Beach, South Carolina. Specifically we seek to 1) measure and model the oceanographic circulation in the region, 2) identify the processes that maintain the presence of the offshore sand feature, 3) quantify the control that the shoal exerts on the nearshore through changes in wave energy propagation, and 4) identify consequences of removal of the offshore sand feature. Both observational and numerical experiments are used to study the oceanographic circulation and transport of sediment. The observational study is described in an accompanying poster and consists of eight sites that measured tides, surface waves, currents, salinity, temperature, suspended sediment concentrations, and bed forms from October 2003 to April 2004. Numerical modeling for circulation and sediment transport in the study region uses a new version of ROMS (v2.1) that now includes transport of multiple grain sizes, coupling of sediment transport to wave bottom boundary layer models, and evolution of the bottom morphology. The SWAN model is used to compute wave propagation. Results indicate that currents in the study area are strongly influenced by both tidal motion and wind driven setup / setdown. The presence of the offshore sand feature alters the residual flows in the region. Sediment transport is more significant during periods of sustained strong winds that generate local waves. Wind direction plays a key role in determining the direction and magnitude of sediment transport.

Airflow Dynamics and Sand Transport over a Coastal Foredune with Large Woody Debris.

NASA Astrophysics Data System (ADS)

Grilliot, M. J.; Walker, I. J.; Bauer, B. O.

2016-12-01

Airflow dynamics and sand transport patterns over beach-foredune systems are complex due to the effects of topographic forcing and varied surface roughness elements. The role of large woody debris (LWD) as a roughness element in foredune dynamics is understudied compared to the effects of plant cover. Unlike plants, non-porous objects like LWD impose bluff body effects and induce secondary flow circulation that varies with LWD size, density, and arrangement. It is hypothesized that modified flow patterns over LWD can influence beach-dune sediment budgets and dune geometry via changes to mean near-surface flow patterns, turbulence, sand transport pathways and sedimentation patterns. In turn, LWD may act as an accretion anchor and store appreciable amounts of aeolian sand that subsequently may provide an enhanced buffer against coastal and/or wind erosion. This study examines turbulent airflow dynamics and related sand transport patterns for oblique onshore flow conditions over a mesotidal beach and scarped dune on Calvert Island, British Columbia, Canada. Abundant exposed LWD fronting the foredune enhances turbulent Reynolds stress (RS) and turbulence intensity (TI) near the surface. During low, yet competent wind speeds (6.54 m s-1), RS and TI are not competent enough in the sheltered flow regions within the LWD matrix and sediment deposition occurs. However, small zones of localized acceleration were observed with sand transport. Higher wind speeds, well above the entrainment threshold, increase RS and TI over LWD relative to the beach, facilitating sediment transport through and over the LWD matrix, with localized pockets of deposition in sheltered areas. The majority of LWD deposits on beaches in the region are anthropogenic logging debris and are known to be decreasing since the 1950s, but likely earlier. Thus, it is important to understand how non-porous roughness elements, like LWD, affect beach-dune sediment budgets and evolution, particularly in light of increasing storminess and sea level rise.

Becquerel Crater Deposit

NASA Technical Reports Server (NTRS)

2002-01-01

(Released 28 May 2002) The finely layered deposit in Becquerel crater, seen in the center of this THEMIS image, is slowly being eroded away by the action of windblown sand. Dark sand from a source north of the bright deposit is collecting along its northern edge, forming impressive barchan style dunes. These vaguely boomerang-shaped dunes form with their two points extending in the downwind direction, demonstrating that the winds capable of moving sand grains come from the north. Grains that leave the dunes climb the eroding stair-stepped layers, collecting along the cliff faces before reaching the crest of the deposit. Once there, the sand grains are unimpeded and continue down the south side of the deposit without any significant accumulation until they fall off the steep cliffs of the southern margin. The boat-hull shaped mounds and ridges of bright material called yardangs form in response to the scouring action of the migrating sand. To the west, the deposit has thinned enough that the barchan dunes extend well into the deeply eroded north-south trending canyons. Sand that reaches the south side collects and reforms barchan dunes with the same orientation as those on the north side of the deposit. Note the abrupt transition between the bright material and the dark crater floor on the southern margin. Steep cliffs are present with no indication of rubble from the obvious erosion that produced them. The lack of debris at the base of the cliffs is evidence that the bright material is readily broken up into particles that can be transported away by the wind. The geological processes that are destroying the Becquerel crater deposit appear active today. But it is also possible that they are dormant, awaiting a particular set of climatic conditions that produces the right winds and perhaps even temperatures to allow the erosion to continue.

Enhanced Gravitational Drainage of Crude Oil Through Alabama Beach Sand Caused by the Dispersant Corexit 9500A

NASA Astrophysics Data System (ADS)

Steffy, D. A.; Nichols, A.; Hobbs, K.

2017-12-01

Oil spill material released by the 2010 Deepwater Horizon accident contaminated a majority of the 60 miles of Alabama coastline. In response to the oil spill, BP sprayed a dispersant, Corexit 9500A, as an initial remediation effort. An unforeseen impact of the saltwater-dispersant mixture includes the mobilization of oil-spilled material into the underlying beach sand. This study investigated the effect of the dispersant to promote gravitational drainage by measuring the physical characteristics of the sand, saltwater, crude oil, and the dispersant solution. The saltwater-dispersant mixture promoted the downward movement of oil mass 20 times greater extent than just saltwater. These tests are meant to simulate spill material on the beach being exposed to a low-energy, 1-meter mixed tide occurring along the Alabama coastline. A separate test simulated oilwet sand exposed to saltwater and a saltwater-dispersant mixture. The oil-wet sand impeded the vertical movement of saltwater, but allowed a saltwater-dispersant solution to mobilize the oil to migrate downward. The mobilization of oil in this three phase system of saltwater, oil, and air is controlled by: the pressure-saturation profile of the sand; interfacial tension with saltwater; and its surface tension with air.

Soil nutrients losses by wind erosion in a citrus crop at southeast Spain

NASA Astrophysics Data System (ADS)

Segovia, C.; Gómez, J. D.; Gallardo, P.; Lozano, F. J.; Asensio, C.

2017-06-01

The purpose of this study was to analyze the influence of wind erosion on the productivity of citric crops over gypsiric Fluvisols in Gador area (Almeria, SE Spain) by blowing air through a wind tunnel. Wind erosion varies considerably depending on time since the last tillage. This is because a physical crust forms after tilling which protects the soil from wind. Crust formation in the study area is strongly favored by dew, which causes them to form in around a week. The repeated measurements ANOVA, as a nonparametric alternative to the ANOVA, using the Geiiser method and the Friedman test shows significant differences ( P ≤ 0.05) in the fractions of very fine sand and coarse silt, which confirmed that very fine sand and coarse silt are the fractions most susceptible to loss from wind. The same statistical analysis for fertility showed smaller differences in organic carbon and K2O content, while N and P2O5 increased. Nutrients lost from wind imply an additional fertilization cost for a crop to be economically feasible. The cost of this restoration of nutrients lost from the soil because of wind erosion was based on experimental data taken in crusted soil and immediately after tilling. Losses in organic matter (O.M.), N, P2O5 and K2O were estimated based on the cost of fertilizers most commonly used in the area.

Surtsey and Mount St. Helens: a comparison of early succession rates

NASA Astrophysics Data System (ADS)

del Moral, R.; Magnússon, B.

2014-04-01

Surtsey and Mount St. Helens are celebrated but very different volcanoes. Permanent plots allow for comparisons that reveal mechanisms that control succession and its rate and suggest general principles. We estimated rates from structure development, species composition using detrended correspondence analysis (DCA), changes in Euclidean distance (ED) of DCA vectors, and by principal components analysis (PCA) of DCA. On Surtsey, rates determined from DCA trajectory analyses decreased as follows: gull colony on lava with sand > gull colony on lava, no sand ≫ lava with sand > sand spit > block lava > tephra. On Mount St. Helens, plots on lahar deposits near woodlands were best developed. The succession rates of open meadows declined as follows: Lupinus-dominated pumice > protected ridge with Lupinus > other pumice and blasted sites > isolated lahar meadows > barren plain. Despite the prominent contrasts between the volcanoes, we found several common themes. Isolation restricted the number of colonists on Surtsey and to a lesser degree on Mount St. Helens. Nutrient input from outside the system was crucial. On Surtsey, seabirds fashioned very fertile substrates, while on Mount St. Helens wind brought a sparse nutrient rain, then Lupinus enhanced fertility to promote succession. Environmental stress limits succession in both cases. On Surtsey, bare lava, compacted tephra and infertile sands restrict development. On Mount St. Helens, exposure to wind and infertility slow succession.

Surtsey and Mount St. Helens: a comparison of early succession rates

NASA Astrophysics Data System (ADS)

del Moral, R.; Magnússon, B.

2013-12-01

Surtsey and Mount St. Helens are celebrated, but very different volcanoes. Permanent plots allow comparisons that reveal mechanisms that control succession and its rate and suggest general principles. We estimated rates from structure development, species composition using detrended correspondence analysis (DCA), changes in Euclidean distance (ED) of DCA vectors and by principal components analysis (PCA) of DCA. On Surtsey, rates determined from DCA trajectory analyses decreased as follows: gull colony on lava with sand > gull colony on lava, no sand ≫ lava with sand > sand spit > block lava > tephra. On Mount St. Helens, plots on lahar deposits near woodlands were best developed. The succession rates of open meadows declined as follows: Lupinus-dominated pumice > protected ridge with Lupinus > other pumice and blasted sites > isolated lahar meadows > barren plain. Despite the prominent contrasts between the volcanoes, common themes were revealed. Isolation restricted the number of colonists on Surtsey and to a lesser degree on Mount St. Helens. Nutrient input from outside the system was crucial. On Surtsey, seabirds fashioned very fertile substrates, while on Mount St. Helens wind brought a sparse nutrient rain, then Lupinus enhanced fertility to promote succession. Environmental stress limits succession in both cases. On Surtsey, bare lava, compacted tephra and infertile sands restrict development. On Mount St. Helens, exposure to wind and infertility slow succession.

Investigating the Impacts of Particle Size and Wind Speed on Brownout

DTIC Science & Technology

2015-03-26

mixture of sand, silt, clay , and organic material, classified based on its size and texture. Sand is the largest of the particle materials, with...smallest soil component is clay , with particle sizes less than 0.002 mm. Ultra-fine in texture, clay feels sticky when wet, is extremely cohesive, and does...not allow air to move through it easily. Clay makes a soil dense and is hard as concrete when dry. Loam is a nearly even mixture of sand and silt

Variable Camber Morphing Wings

DTIC Science & Technology

2016-02-02

devices and wind turbines , but also it is present in fixed wings, which can vibrate at high frequencies during flight, and in the most fascinating...way to delay dynamic stall to control periodic vortex generation and improve the performance of rotorcrafts and wind turbines (McCroskey, 1982). As...Axis Wind Turbines , Sandia National Laboratories Energy Report, SAND80-2114. 7. RESPONSIBILITY NOTICE “The authors are the only responsible for

Subsurface Assessment at McMurdo Station, Antarctica

DTIC Science & Technology

2017-02-01

collected at the T-site for design and construction of a foundation for a wind turbine (after Oswell et al. 2010...foundation for a wind turbine (after Oswell et al. 2010). 5.3 Surface snowmelt and frost susceptibility The gravelly sand with silts found in this...maximum unfrozen density with low moisture content. Compaction of fill materials for con- structing wind turbine foundations at the T-site commenced

How fragmentation and corridors affect wind dynamics and seed dispersal in open habitats

PubMed Central

Damschen, Ellen I.; Baker, Dirk V.; Bohrer, Gil; Nathan, Ran; Orrock, John L.; Turner, Jay R.; Brudvig, Lars A.; Haddad, Nick M.; Levey, Douglas J.; Tewksbury, Joshua J.

2014-01-01

Determining how widespread human-induced changes such as habitat loss, landscape fragmentation, and climate instability affect populations, communities, and ecosystems is one of the most pressing environmental challenges. Critical to this challenge is understanding how these changes are affecting the movement abilities and dispersal trajectories of organisms and what role conservation planning can play in promoting movement among remaining fragments of suitable habitat. Whereas evidence is mounting for how conservation strategies such as corridors impact animal movement, virtually nothing is known for species dispersed by wind, which are often mistakenly assumed to not be limited by dispersal. Here, we combine mechanistic dispersal models, wind measurements, and seed releases in a large-scale experimental landscape to show that habitat corridors affect wind dynamics and seed dispersal by redirecting and bellowing airflow and by increasing the likelihood of seed uplift. Wind direction interacts with landscape orientation to determine when corridors provide connectivity. Our results predict positive impacts of connectivity and patch shape on species richness of wind-dispersed plants, which we empirically illustrate using 12 y of data from our experimental landscapes. We conclude that habitat fragmentation and corridors strongly impact the movement of wind-dispersed species, which has community-level consequences. PMID:24567398

Assessing the impact of marine wind farms on birds through movement modelling

PubMed Central

Masden, Elizabeth A.; Reeve, Richard; Desholm, Mark; Fox, Anthony D.; Furness, Robert W.; Haydon, Daniel T.

2012-01-01

Advances in technology and engineering, along with European Union renewable energy targets, have stimulated a rapid growth of the wind power sector. Wind farms contribute to carbon emission reductions, but there is a need to ensure that these structures do not adversely impact the populations that interact with them, particularly birds. We developed movement models based on observed avoidance responses of common eider Somateria mollissima to wind farms to predict, and identify potential measures to reduce, impacts. Flight trajectory data that were  collected post-construction of the Danish Nysted offshore wind farm were used to parameterize competing models of bird movements around turbines. The model most closely fitting the observed data incorporated individual variation in the minimum distance at which birds responded to the turbines. We show how such models can contribute to the spatial planning of wind farms by assessing their extent, turbine spacing and configurations on the probability of birds passing between the turbines. Avian movement models can make new contributions to environmental assessments of wind farm developments, and provide insights into how to reduce impacts that can be identified at the planning stage. PMID:22552921

How fragmentation and corridors affect wind dynamics and seed dispersal in open habitats.

PubMed

Damschen, Ellen I; Baker, Dirk V; Bohrer, Gil; Nathan, Ran; Orrock, John L; Turner, Jay R; Brudvig, Lars A; Haddad, Nick M; Levey, Douglas J; Tewksbury, Joshua J

2014-03-04

Determining how widespread human-induced changes such as habitat loss, landscape fragmentation, and climate instability affect populations, communities, and ecosystems is one of the most pressing environmental challenges. Critical to this challenge is understanding how these changes are affecting the movement abilities and dispersal trajectories of organisms and what role conservation planning can play in promoting movement among remaining fragments of suitable habitat. Whereas evidence is mounting for how conservation strategies such as corridors impact animal movement, virtually nothing is known for species dispersed by wind, which are often mistakenly assumed to not be limited by dispersal. Here, we combine mechanistic dispersal models, wind measurements, and seed releases in a large-scale experimental landscape to show that habitat corridors affect wind dynamics and seed dispersal by redirecting and bellowing airflow and by increasing the likelihood of seed uplift. Wind direction interacts with landscape orientation to determine when corridors provide connectivity. Our results predict positive impacts of connectivity and patch shape on species richness of wind-dispersed plants, which we empirically illustrate using 12 y of data from our experimental landscapes. We conclude that habitat fragmentation and corridors strongly impact the movement of wind-dispersed species, which has community-level consequences.

Water movement in the unsaturated zone at a low-level radioactive-waste burial site near Barnwell, South Carolina

USGS Publications Warehouse

Dennehy, K.F.; McMahon, P.B.

1987-01-01

Four unsaturated zone monitoring sites and a meteorologic station were installed at the low level radioactive waste burial site near Barnwell, South Carolina, to investigate the geohydrologic and climatologic factors affecting water movement in the unsaturated zone. The study site is located in the Atlantic Coastal Plain. The unsaturated zone consists of a few centimeters to > 1 m of surface sand, underlain by up to 15 m of clayey sand. Two monitoring sites were installed in experimental trenches and two were installed in radioactive waste trenches. Two different trench designs were evaluated at the monitoring sites. A meteorologic station was used to measure precipitation and to calculate actual evapotranspiration using the Bowen ratio method. Soil-moisture tensiometers, soil-moisture conductance probes, and temperature sensors were used to monitor soil-water movement in and adjacent to the trenches. Tracer tests using sodium chloride were conducted at each monitoring site. Data collection at the monitoring sites began in January 1982 and continued until early May 1984. Tensiometer data show that the unsaturated materials had their highest percent saturations in the winter and spring. Saturations in the backfill sand varied from 20 to 100%. They varied from about 75 to 100% in the adjacent undisturbed and overlying compacted clayey sand. Additionally, because tensiometer data indicate negligible water storage changes in the unsaturated zone, it is estimated that approximately 43 cm of recharge reached the water table. During 1984, the rise and fall of ponded water in an experimental trench was continuously monitored with a digital recorder. A cross-sectional finite element model of variably saturated flow was used to test the conceptual model of water movement in the unsaturated zone and to illustrate the effect of trench design on water movement into the experimental trenches. Monitoring and model results show that precipitation on trenches infiltrated the trench cap and moved vertically into the trench backfill material. The trench construction practice of placing a compacted clayey-sand barrier around the trench greatly inhibits soil water from entering the trench. (Author 's abstract)

Observations of transport of bacterial-like microspheres through beach sand

NASA Astrophysics Data System (ADS)

Gast, Rebecca J.; Elgar, Steve; Raubenheimer, Britt

2015-04-01

Often, there is an order of magnitude more fecal indicator bacteria (enterococci) in beach sand than in nearby water. Consequently, sand is considered a reservoir for these bacteria, potentially contributing to poor water quality, and raising questions regarding the human health risks associated with sand exposure. An integral aspect of the distribution and persistence of sand-associated enterococci is the transport of bacteria introduced into the beach environment. Here, plastic microspheres are used as a proxy to examine the wave-induced movement of bacterial-like particles through sand on an ocean beach. Laboratory tests suggest microspheres and bacteria move similarly through sand columns, and have qualitatively similar short-term adsorption-to-sand behavior. Microspheres buried ~0.05 m below the sand surface on an ocean beach moved rapidly [O(10-3) m/s] away from their initial location, both vertically into the ground water below the sand and horizontally seaward within the sediment matrix in response to waves running up the beach face and percolating through the sand.

Enhancement of Feedback Efficiency by Active Galactic Nucleus Outflows via the Magnetic Tension Force in the Inhomogeneous Interstellar Medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Asahina, Yuta; Ohsuga, Ken; Nomura, Mariko, E-mail: asahina@cfca.jp

By performing three-dimensional magnetohydrodynamics simulations of subrelativistic jets and disk winds propagating into the magnetized inhomogeneous interstellar medium (ISM), we investigate the magnetic effects on the active galactic nucleus feedback. Our simulations reveal that the magnetic tension force promotes the acceleration of the dense gas clouds, since the magnetic field lines, which are initially straight, bend around the gas clouds. In the jet models, the velocity dispersion of the clouds increases with an increase in the initial magnetic fields. The increment of the kinetic energy of the clouds is proportional to the initial magnetic fields, implying that the magnetic tensionmore » force increases the energy conversion efficiency from the jet to the gas clouds. Through simulations of the mildly collimated disk wind and the funnel-shaped disk wind, we confirm that such an enhancement of the energy conversion efficiency via the magnetic fields appears even if the energy is injected via the disk winds. The enhancement of the acceleration of the dense part of the magnetized ISM via the magnetic tension force will occur wherever the magnetized inhomogeneous matter is blown away.« less

Sedimentation Waves on the Martian North Polar Cap: Analogy with Megadunes in Antarctica

NASA Astrophysics Data System (ADS)

Herny, C.; Masse, M.; Bourgeois, O.; Carpy, S.; Le Mouelic, S.; Appéré, T.; Smith, I. B.; Spiga, A.; Perret, L.; Rodriguez, S.; Piquet, T.; Gaudin, D.; Le Menn, E.

2014-12-01

Complex feedbacks between katabatic winds and the cryosphere may lead to the development of sedimentation waves at the surface of ice sheets. These have been first described and named megadunes in Antarctica. Here we use topographic data, optical images, spectroscopic data and radar soundings, acquired by Mars orbiters, to show that the surface of the Martian North Polar Cap displays two superimposed sets of sedimentation waves with differing wavelengths. These sedimentation waves grow and migrate upwind in response to the development of periodic accumulation/ablation patterns controlled by katabatic winds. They have similarities with Antarctic megadunes regarding their surface morphology, texture, grain size, and internal stratigraphic architecture. Based on this analogy, we are currently developing a model of ice/wind interaction at the surface of ice sheets. In Antarctica the accumulation processes on megadunes fields is generally attributed to the wind-blown snow transport while on sedimentation waves of the North Polar Cap of Mars the accumulation seems to be dominated by sublimation/condensation processes at the surface. The model is designed to explore the implication of the water vapor mass transfer and heat transfer on the development of sedimentation waves both on Mars and Earth.

Sand pulses and sand patches on the Colorado River in Grand Canyon

USGS Publications Warehouse

Grams, Paul E.; Buscombe, Daniel; Topping, David; Mueller, Erich R.

2017-01-01

Alluvial sandbars occur in lateral recirculation zones (eddies) along the Colorado River in Grand Canyon National Park (Schmidt, 1990). Resource managers periodically release controlled floods from the upstream Glen Canyon Dam to rebuild these bars (Grams et al., 2015), which erode during fluctuating dam releases, and by hillslope runoff and wind deflation (Hazel et al., 2010). Because the dam blocks upstream sediment, episodic floods from tributaries provide the only supply to replace eroded sand; and much of this sand originates from a single tributary (Topping et al., 2000). Here, we present new evidence for the downstream translation of the sand component of these sediment inputs as discontinuous sand pulses. Improved understanding of the behaviour of these sand pulses may be used to adjust the timing, magnitude, and duration of controlled floods to maximize potential for deposition on sandbars in different segments of the 450 km-long Grand Canyon.

Evaluation of solid oxide fuel cell systems for electricity generation

NASA Technical Reports Server (NTRS)

Somers, E. V.; Vidt, E. J.; Grimble, R. E.

1982-01-01

Air blown (low BTU) gasification with atmospheric pressure Solid Electrolyte Fuel Cells (SOFC) and Rankine bottoming cycle, oxygen blown (medium BTU) gasification with atmospheric pressure SOFC and Rankine bottoming cycle, air blown gasification with pressurized SOFC and combined Brayton/Rankine bottoming cycle, oxygen blown gasification with pressurized SOFC and combined Brayton/Rankine bottoming cycle were evaluated.

Surface features on Mars: Ground-based albedo and radar compared with Mariner 9 topography

NASA Technical Reports Server (NTRS)

Frey, H.

1973-01-01

Earth-based albedo maps of Mars were compared with Mariner 9 television data and ground-based radar profiles to investigate the nature of the bright and dark albedo features. Little correlation was found except at the boundaries of classical albedo features, where some topographic control is indicated. Wind-blown dust models for seasonal and secular albedo variations are supported, but it is not clear whether the fines are derived from bright or dark parent rock. Mars, like the Earth and Moon, has probably generated two distinct types of crustal material.

Desert landforms of southwest Egypt: A basis for comparison with Mars

NASA Technical Reports Server (NTRS)

El-Baz, F. (Editor); Maxwell, T. A. (Editor)

1982-01-01

Geologic interpretations of The Gilf Kebir-Uweinat of Apollo-Soyuz photographs were verified. The photographs and LANDSAT images showed features reminiscent of those depicted by Mariner and Viking missions to Mars. These features were to better understand their morphologic analogs on Mars. It is indicated that climate change played a significant role in the formation of the eastern Sahara. It is also revealed that correlations between the eolian features in southwestern Egypt and the wind blown patterns on the surface of Mars result in a better understanding of eolian activity on both planets.

Ring Around the Black Hole

NASA Technical Reports Server (NTRS)

Wanjek, Christopher

2003-01-01

Regardless of size, black holes easily acquire accretion disks. Supermassive black holes can feast on the bountiful interstellar gas in galactic nuclei. Small black holes formed from collapsing stars often belong to binary systems in which a bulging companion star can spill some of its gas into the black hole s reach. In the chaotic mess of the accretion disk, atoms collide with one another. Swirling plasma reaches speeds upward of 10% that of light and glows brightly in many wavebands, particularly in X-rays. Gas gets blown back by a wind of radiation from the inner disk. New material enters the disks from different directions.

Rock Abrasion as Seen by the MSL Curiosity Rover: Insights on Physical Weathering on Mars

NASA Astrophysics Data System (ADS)

Bridges, N.; Day, M. D.; Le Mouelic, S.; Martin-Torres, F. J.; Newsom, H. E.; Sullivan, R. J., Jr.; Ullan, A.; Wiens, R. C.; Zorzano, M. P.

2014-12-01

Mars is a dry planet, with actively blowing sand in many regions. In the absence of stable liquid water and an active hydrosphere, rates of chemical weathering are slow, such that aeolian abrasion is a dominant agent of landscape modification where sand is present and winds above threshold occur at sufficient frequency. Reflecting this activity, ventifacts, rocks that have been abraded by windborne particles, and wind-eroded outcrops, are common. They provide invaluable markers of the Martian wind record and insight into climate and landscape modification. Ventifacts are distributed along the traverse of the Mars Science Laboratory Curiosity rover. They contain one or more diagnostic features and textures: Facets, keels, basal sills, elongated pits, scallops/flutes, grooves, rock tails, and lineations. Keels at the junction of facets are sharp enough to pose a hazard MSL's wheels in some areas. Geomorphic and textural patterns on outcrops indicate retreat of windward faces. Moonlight Valley and other depressions are demarcated by undercut walls and scree boulders, with the valley interiors containing fewer rocks, most of which show evidence for significant abrasion. Together, this suggests widening and undercutting of the valley walls, and erosion of interior rocks, by windblown sand. HiRISE images do not show any dark sand dunes in the traverse so far, in contrast to the large dune field to the south that is migrating up to 2 m per year. In addition, ChemCam shows that the rock Bathurst has a rind rich in mobile elements that would be removed in an abrading environment. This indicates that rock abrasion was likely more dominant in the past, a hypothesis consistent with rapid scarp retreat as suggested by the cosmogenic noble gases in Yellowknife Bay. Ventifacts and evidence for bedrock abrasion have also been found at the Pathfinder, Spirit, and Opportunity sites, areas, like the Curiosity traverse so far, that lack evidence for current high sand fluxes. Yardangs are also common on the planet, regardless of whether local sand is mobile. This suggest that abrasion on Mars is an episodic process driven by the passage of sand in which rock retreat rates, based on fluxes of current active dunes, may reach 10s of microns per year. Such a process has acted, over long time scales, to imprint upon the surface a record of sand activity.

Joint by Design: The Western Desert Campaign

DTIC Science & Technology

2015-05-21

levels, he knew he would be unable to hold his tenuous position indefinitely. Under a full moon that glinted off the desert sand on the night of...treacherous minefields and loose sand under heavy fire from coalition aircraft and artillery. The slow movement further depleted his precious fuel...shifting sands .2 One Allied commander wrote, “Not only was Rommel’s bid for Egypt ended, but he was totally and finally defeated. He would never

A Workshop on Desert Processes, September 24-28, 1984- Report on the Conference,

DTIC Science & Technology

1987-01-01

W12 *j2 ll .. m11116’ w 1.25 *IM.4 1. 6 MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF SIANOAROS-1963-A , / i9 Z- - ;im... ... i U.S. GEOLOGICAL...Winds Department of Agriculture (USDA) Wind Erosion Laboratory, and D.A. Gillette, National J.F. McCauley, C.S. Breed, P.J. Helm. Oceanic and...protected area on of wind as a geologic agent. public land west of White Sands National Measurements of wind speeds (including peak Monument, New

ARC-2005-ACD05-0022-017

NASA Image and Video Library

2005-02-04

Ames Mars Wind Tunnel Facility N-245: NASA is simulating small martian 'dust devils' and wind in a laboraotry to determine how they may affect the landscape and environment of the red planet. Dust Devils on Mars are often a great deal biggger than those on Earth and can at times cover the whole planet. Martian winds & dust devils, big and little, collectively are a great force that is constantly changing the planet's environment. shown here: Silica Sand (Oklahoma 90) particles used in vortex generatory and Mars Wind Tunnel

Recent advances in research on the aeolian geomorphology of China's Kumtagh Sand Sea

NASA Astrophysics Data System (ADS)

Dong, Z.; Lv, P.

2014-02-01

The Kumtagh Sand Sea in the hyper-arid region of northwestern China remained largely unexplored until the last decade. It deserves study due to its significance in understanding the evolution of the arid environments in northwestern China, and even central Asia. Aeolian geomorphology in the sand sea has received unprecedented study in the last decade. Encouraging advances have been made in types of aeolian landforms, geological outlines, wind systems, the formation of aeolian landforms, several unique aeolian landforms, aeolian geomorphic regionalization, aeolian geomorphological heritages and tourism development, and aeolian sand hazards and their control. These advances expand our knowledge of aeolian geomorphology.

Dunes on Saturn’s moon Titan as revealed by the Cassini Mission

NASA Astrophysics Data System (ADS)

Radebaugh, Jani

2013-12-01

Dunes on Titan, a dominant landform comprising at least 15% of the surface, represent the end product of many physical processes acting in alien conditions. Winds in a nitrogen-rich atmosphere with Earth-like pressure transport sand that is likely to have been derived from complex organics produced in the atmosphere. These sands then accumulate into large, planet-encircling sand seas concentrated near the equator. Dunes on Titan are predominantly linear and similar in size and form to the large linear dunes of the Namib, Arabian and Saharan sand seas. They likely formed from wide bimodal winds and appear to undergo average sand transport to the east. Their singular form across the satellite indicates Titan’s dunes may be highly mature, and may reside in a condition of stability that permitted their growth and evolution over long time scales. The dunes are among the youngest surface features, as even river channels do not cut through them. However, reorganization time scales of large linear dunes on Titan are likely tens of thousands of years. Thus, Titan’s dune forms may be long-lived and yet be actively undergoing sand transport. This work is a summary of research on dunes on Titan after the Cassini Prime and Equinox Missions (2004-2010) and now during the Solstice Mission (to end in 2017). It discusses results of Cassini data analysis and modeling of conditions on Titan and it draws comparisons with observations and models of linear dune formation and evolution on Earth.

Community airborne particulate matter from mining for sand used as hydraulic fracturing proppant.

PubMed

Peters, Thomas M; O'Shaughnessy, Patrick T; Grant, Ryan; Altmaier, Ralph; Swanton, Elizabeth; Falk, Jeffrey; Osterberg, David; Parker, Edith; Wyland, Nancy G; Sousan, Sinan; Stark, Aimee Liz; Thorne, Peter S

2017-12-31

Field and laboratory studies were conducted to evaluate the impact of proppant sand mining and processing activities on community particulate matter (PM) concentrations. In field studies outside 17 homes within 800m of sand mining activities (mining, processing, and transport), respirable (PM 4 ) crystalline silica concentrations were low (<0.4μg/m 3 ) with crystalline silica detected on 7 samples (2% to 4% of mass). In long-term monitoring at 6 homes within 800m of sand mining activities, the highest daily mean PM concentrations observed were 14.5μg/m 3 for PM 2.5 and 37.3μg/m 3 for PM 10 , although infrequent (<3% of time), short-term elevated PM concentrations occurred when wind blew over the facility. In laboratory studies, aerosolized sand was shown to produce respirable-sized particles, containing 6% to 19% crystalline silica. Dispersion modeling of a mine and processing facility indicated that PM 10 can exceed standards short distances (<40m) beyond property lines. Lastly, fence-line PM and crystalline silica concentrations reported to state agencies were substantially below regulatory or guideline values, although several excursions were observed for PM 10 when winds blew over the facility. Taken together, community exposures to airborne particulate matter from proppant sand mining activities at sites similar to these appear to be unlikely to cause chronic adverse health conditions. Copyright © 2017 Elsevier B.V. All rights reserved.

Holocene record of eolian activity from Genggahai Lake, northeastern Qinghai-Tibetan Plateau, China

NASA Astrophysics Data System (ADS)

Qiang, Mingrui; Liu, Yingying; Jin, Yanxiang; Song, Lei; Huang, Xiangtong; Chen, Fahu

2014-01-01

The history of dust emission and eolian activity in dust source areas remains unclear due to the scarcity of geological archives. Grain-size data from Genggahai Lake on the northeastern Qinghai-Tibetan Plateau show that sand-sized particles in the lake sediments were transported primarily by strong winds to the lake and therefore can be used as a proxy for eolian activity. Eolian activity was weak from 10.3 to 6.3 ka, which may be a response to increased vegetation cover due to the strengthened Asian summer monsoon. In contrast, eolian activity occurred episodically when the summer monsoon weakened. The abrupt, intense sand deposition events are likely to have resulted from strong wind regimes, in turn linked to cooling events in the North Atlantic. Our results suggest that changes in atmospheric circulation patterns may have strongly affected the moisture balance and wind strength in the dust source area and hence dust emissions.

Atmospheric pressure, density, temperature and wind variations between 50 and 200 km

NASA Technical Reports Server (NTRS)

Justus, C. G.; Woodrum, A.

1972-01-01

Data on atmospheric pressure, density, temperature and winds between 50 and 200 km were collected from sources including Meteorological Rocket Network data, ROBIN falling sphere data, grenade release and pitot tube data, meteor winds, chemical release winds, satellite data, and others. These data were analyzed by a daily difference method and results on the distribution statistics, magnitude, and spatial structure of the irregular atmospheric variations are presented. Time structures of the irregular variations were determined by the analysis of residuals from harmonic analysis of time series data. The observed height variations of irregular winds and densities are found to be in accord with a theoretical relation between these two quantities. The latitude variations (at 50 - 60 km height) show an increasing trend with latitude. A possible explanation of the unusually large irregular wind magnitudes of the White Sands MRN data is given in terms of mountain wave generation by the Sierra Nevada range about 1000 km west of White Sands. An analytical method is developed which, based on an analogy of the irregular motion field with axisymmetric turbulence, allows measured or model correlation or structure functions to be used to evaluate the effective frequency spectra of scalar and vector quantities of a spacecraft moving at any speed and at any trajectory elevation angle.

Arabian Sea as seen from STS-62

NASA Technical Reports Server (NTRS)

1994-01-01

The photo depicts many of the types of ocean features seen when illuminated by sunglint. These features include a shear line, bilge dump, currents, and ship wakes. Winds, currents and oils effect the smoothness of the surface of the water. The oils smooth the water which reflect the sun more than the rougher surrounding water. This is seen in the bright curved line which is a bilge dump of oily water from a ship. The oils then start to take the form of the currents and in this case are also being blown by the surface winds. The shear line is approximately 240 miles west of Bombay, India. This shear line appears to be a result of two water masses, moving at slightly different speeds, having converged. Ship wakes, such as those in the photo, which cross a shear line, often give us an indication of the relative strength of a shear.

Earth observations taken from shuttle orbiter Discovery on STS-70 mission

NASA Image and Video Library

1995-07-21

STS070-717-011 (13-22 JULY 1995) --- Volcanic landscapes with a thin dusting of snow appear in this near-vertical view of the dry, high spine of the Andes Mountains at around 28 degrees south latitude. Strong westerly winds (from left) have blown the snow off the highest volcanic peaks (center and bottom): many of these peaks rise higher than 20,000 feet. A small, dry lake appears top right, the white color derived from salts. The border between Argentina and Chile winds from volcano to volcano and passes just left of the small blue lake (left center). Black lava flows can be detected bottom right. The larger area of brown-pink rocks (bottom rock) is also an area of volcanic rocks, of a type known as ash flow tuffs which are violently extruded, often in volumes measured in cubic kilometers.

Windblown Dunes and Ripples

NASA Technical Reports Server (NTRS)

2003-01-01

MGS MOC Release No. MOC2-411, 4 July 2003

July 4, 2003, is the 6th anniversary of the Mars Pathfinder landing. One of the elements carried to the red planet by Pathfinder was the Wind Sock Experiment. This project was designed to measure wind activity by taking pictures of three aluminum 'wind socks.' While the winds at the Mars Pathfinder site did not blow particularly strong during the course of that mission, dust storms seen from orbit and Earth-based telescopes attest to the fact that wind is a major force of change on the dry, desert surface of Mars today. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) narrow angle image shows dark sand dunes and lighter-toned ripples trapped among the mountainous central peak of an old impact crater in Terra Tyrrhena near 13.9oS, 246.7oW. The dune slip faces--the steepest slope on the larger dunes--indicate sand transport is from the top/upper left toward the bottom/lower right. North is toward the top/upper right; the picture is 3 km (1.9 mi) across. Sunlight illuminates the scene from the upper left. This picture was obtained in April 2003.

Geologic and paleoecologic studies of the Nebraska Sand Hills

USGS Publications Warehouse

Ahlbrandt, Thomas S.; Fryberger, S.G.; Hanley, John H.; Bradbury, J. Platt

1980-01-01

PART A: The Nebraska Sand Hills are an inactive, late Quaternary, most probably Holocene, dune field (covering 57,000 km 2 ) that have been eroded along streams and in blowouts, resulting in excellent lateral and vertical exposures of the stratification of dune and interdune sediments. This paper presents new data on the geometry, primary sedimentary structures, modification of sedimentary structures, direction of sand movement, and petrography of these eolian deposits. Eolian deposits of the Sand Hills occur as relatively thin (9-24 m) 'blanket' sands, composed of a complex of dune and discontinuous, diachronous interdune deposits unconformably overlying fluviolacustrine sediments. The internal stratification of large dunes in the Sand Hills (as high as 100 m), is similar to the internal stratification of smaller dunes of the same type in the Sand Hills, differing only in scale. Studies of laminae orientation in the Sand Hills indicate that transverse, barchan, and blowout dunes can be differentiated in rocks of eolian origin using both the mean dip angle of laminae and the mean angular deviation of dip direction. A variety of secondary structures modify or replace primary eolian stratification in the Sand Hills, the more common of which are dissipation structures and bioturbation. Dissipation structures in the Sand Hills may develop when infiltrating water deposits clay adjacent to less permeable layers in the sand, or along the upper margins of frozen layers that form in the sands during winter. Cross-bed measurements from dunes of the Nebraska Sand Hills necessitate a new interpretation of the past sand transport directions. The data from these measurements indicate a general northwest-to-southeast drift of sand, with a more southerly drift in the southeast part of the Sand Hills. A large area of small dunes < 100 m high) described by Smith (1965) as linear or seif in the central part of the Sand Hills was interpreted by him on the basis of morphology only. We interpret these as transverse-ridge dunes that were generally moving to the south. Further, our measurements indicate that dunes in the western part of the Sand Hills did not develop in response to present-day effective wind regimes. The presence of 'transverse' and en echelon barchan dunes in the Sand Hills corresponds to a developmental sequence of barchan to linear dunes proposed by Tsoar (1978). Dune and interdune deposits of the Sand Hills are subfeldsarenites to feldsarenites. Sand grains are commonly coated with montmorillonitic clay, which may be the local source of the clay concentrated in the dissipation structures. Textures of sand samples taken from adjacent layers within a dune were as dissimilar as textures of samples taken from widely separated dunes. This common occurrence indicates that textural data must be used carefully and in combination with other data to recognize ancient rocks of eolian origin. Organic material derived from a variety of flora and fauna that inhabit the interdunes (chapters B and C) generated both oil and gas upon heating. Thus, interdune sediments may be an indigenous hydrocarbon source if buried in eolianites. The twofold stratigraphy of loess and correlative dune deposits in the Sand Hills proposed by Reed and Dreeszen (1965) could not be confirmed by the present study. Rather, available data indicate that the dunes represent a single formation as suggested by Lugn (1935). PART B: Three assemblages of nonmarine Mollusca from paleointerdune deposits in the Nebraska Sand Hills inhabited shallow, quiet, vegetated, subpermanent or temporary, freshwater interdune ponds and adjacent terrestrial habitats. Analysis of factors affecting the taxonomic composition, diversity, and abundance of species in living assemblages of mollusks support this interpretation. The mollusks have long biostratigraphic ranges and broad biogeographic distributions. They fail to establish precise age relations of the faunas othe

Earth Observations taken by the Expedition 35 Crew

NASA Image and Video Library

2013-03-25

ISS035-E-009454 (25 March 2013 ) --- One of the Expedition 35 crew members aboard the Earth-orbiting International Space Station used a 400 millimeter lens to photograph this view of the Great Sandy Desert, northwestern Australia on March 25. It bears evidence that much of Australia is arid. In northwest Australia the Great Sandy Desert holds great geological interest as a zone of active sand dune movement; strings of narrow lakes that represent very ancient rivers are also present. While a variety of dune forms can be seen in the region, this photograph features numerous linear dunes (approximately 25 meters high) separated in a roughly regular fashion (0.5?1.5 kilometers), and aligned closely to the winds that generated them?that is, winds blowing from east to west. Where linear dunes converge, dune confluences point downwind. One of the main visual impressions flying over such tropical dune fields ? both from an airplane or from the orbital station outpost?apart from the dune patterns are fire scars where thin vegetation has been burned off the dunes. The result is dunes that appear red from the underlying sand (image top left and top right), and darker areas where the vegetation remains (image lower left and lower right). The white feature visible down the center of the image is Lake Auld, the white color being the result of a cemented combination of fine clayey sediment and salts from evaporation of flood waters that occasionally fill the lake. Wider views of the area show that this lake is part of what is now known to have been a major, ancient river system in northwest Australia, draining northwest to the Indian Ocean. Such sinuous lakes are also known in Australia as ?river lakes.? Scientists point out that the river system is remarkably well preserved considering that the rivers were probably active in the Paleocene Epoch more than 55 million years ago. Australia then lay much further south in a wetter climatic zone. Today?s desert climate results in almost all rivers in the Great Sandy Desert being dry. Linear dunes can be seen entering Lake Auld on the east side. During flooding events, the sand of the dune noses is dispersed, becoming incorporated into the lake floor sediments together with muds and salts. During the long intervening dry periods, sand can blow across the lake floor to build thinner, smaller dunes visible as linear accumulations on the west side of the lake.

Meroe Patera

NASA Image and Video Library

2002-11-26

This image is located in Meroe Patera (longitude: 292W/68E, latitude: 7.01), which is a small region within Syrtis Major Planitia. Syrtis Major is a low-relief shield volcano whose lava flows make up a plateau more than 1000 km across. These flows are of Hesperian age (Martian activity of intermediate age) and are believed to have originated from a series of volcanic depressions, called calderas. The caldera complex lies on extensions of the ring faults associated with the Isidis impact basin toward the northeast - thus Syrtis Major volcanism may be associated with post-impact adjustments of the Martian crust. The most striking feature in this image is the light streaks across the image that lead to dunes in the lower left region. Wind streaks are albedo markings interpreted to be formed by aeolian action on surface materials. Most are elongate and allow an interpretation of effective wind directions. Many streaks are time variable and thus provide information on seasonal or long-term changes in surface wind directions and strengths. The wind streaks in this image are lighter than their surroundings and are the most common type of wind streak found on Mars. These streaks are formed downwind from crater rims (as in this example), mesas, knobs, and other positive topographic features. The dune field in this image is a mixture of barchan dunes and transverse dunes. Dunes are among the most distinctive aeolian feature on Mars, and are similar in form to barchan and transverse dunes on Earth. This similarity is the best evidence to indicate that martian dunes are composed of sand-sized material, although the source and composition of the sand remain controversial. Both the observations of dunes and wind streaks indicate that this location has a windy environment - and these winds are persistent enough to product dunes, as sand-sized material accumulates in this region. These features also indicate that the winds in this region are originating from the right side of the image, and moving towards the left. http://photojournal.jpl.nasa.gov/catalog/PIA04012

Nutrient and dust enrichment in Danish wind erosion sediments for different tillage directions

NASA Astrophysics Data System (ADS)

Mohammadian Behbahani, Ali; Fister, Wolfgang; Heckrath, Goswin; Kuhn, Nikolaus J.

2015-04-01

More than 80% of the soil types in Denmark have a sandy texture. Denmark is also subject to strong offshore and onshore winds, therefore, Danish soils are considered especially vulnerable to wind erosion. Where conventional tillage operations are applied on poorly aggregated soils, tillage ridges are more or less the only roughness element that can be used to protect soils against wind erosion until crop plants are large enough to provide sufficient breaks. Since wind erosion is a selective process, it can be assumed that increasing erosion rates are associated with increasing loss of dust sized particles and nutrients. However, selective erosion is strongly affected by the orientation and respective trapping efficiency of tillage ridges and furrows. The main objective of this study, therefore, was to determine the effect of tillage direction on nutrient mobilization by wind erosion from agricultural land in Denmark. In order to assess the relationship between the enrichment ratio of specific particle sizes and the amount of eroded nutrients, three soils with loamy sand texture, but varying amounts of sand-sized particles, were selected. In addition, a soil with slightly less sand, but much higher organic matter content was chosen. The soils were tested with three different soil surface scenarios (flat surface, parallel tillage, perpendicular tillage) in a wind tunnel simulation. The parallel tillage operation experienced the greatest erosion rates, independent of soil type. Particles with D50 between 100-155 µm showed the greatest risk of erosion. However, due to a greater loss of dust sized particles from perpendicularly tilled surfaces, this wind-surface arrangement showed a significant increase in nutrient enrichment ratio compared to parallel tillage and flat surfaces. The main reason for this phenomenon is most probably the trapping of larger particles in the perpendicular furrows. This indicates that the highest rate of soil protection does not necessarily coincide with lowest soil nutrient losses and dust emissions. For the evaluation of protection measures on these soil types in Denmark it is, therefore, important to differentiate between their effectivity to reduce total soil erosion amount, dust emission, and nutrient loss.

Movement of tagged dredged sand at thalweg disposal sites in the Upper Mississippi River. Volume 2. Savanna Bay and Duck Creek sites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paddock, R.A.; McCown, D.L.

Experiments were conducted on the Upper Mississippi River at two sites, Savanna Bay and Duck Creek, to investigate the movement of dredged sand after disposal in the thalweg. These experiments are part of a larger study, which includes similar experiments conducted earlier at two other sites on the Upper Mississippi River. At the Savanna Bay site, hydraulically dredged sand was tagged with sand coated with fluorescent dye before being deposited as a pile in the thalweg. Bathymetric surveys and surficial bottom sampling were conducted on five occasions over a nine-month period following disposal to identify changes in the topography ofmore » the pile and to detect the presence of dyed sand. At the Duck Creek site, only bathymetric surveys were conducted. The general behavior of the disposal piles at these two new sites was similar to that of the piles at the first two sites. Topographic evidence of the piles disappeared, and bottom conditions similar to the predisposal conditions were reestablished following the first period of high river flows after disposal. At Savanna Bay, as had happened at the first two sites, the tagged sand remained in the main river channel as it moved downstream in response to flood currents and did not migrate into nearby border areas, backwaters, or sloughs. 6 references, 89 figures, 2 tables.« less

Pin stripe lamination: A distinctive feature of modern and ancient eolian sediments

USGS Publications Warehouse

Fryberger, S.G.; Schenk, C.J.

1988-01-01

Pin stripe laminations are a distinctive feature of modern and ancient eolian sediments. In sets of eolian ripple (or translatent) strata they represent deposition of silt and very fine sand in the troughs of the advancing wind ripples. In sets of avalanche strata they probably result from the downward settling of fine sand and silt within the moving avalanche to the interface of moving and unmoving sands. Wind tunnel experiments suggest that pin stripe laminations can also form in grainfall deposits. The textural segregation associated with deposition of the fine layers in most cases leads to early cementation along and near the finest sand and silt comprising the pin stripe lamination. The pin stripe effect seen in outcrops is usually due to resistance to weathering along such cemented zones. The cementation of the pin stripe laminations can occur early in the history of diagenesis and thus may provide clues to the post-depositional history of the rock. Pin stripe laminations in many instances represent the sequestering of the small population of ultrafine sediment present in most eolian depositional systems. They may prove useful in the recognition of ancient eolian sediments. ?? 1988.

Role of Automobile Exhaust on the Photoreductive Solubilization of Atmospheric Iron

NASA Astrophysics Data System (ADS)

Haynes, J.; Majestic, B. J.; Cutler, E.

2016-12-01

Atmospheric iron (Fe) plays an essential role in the carbon cycle, affecting the Earth's energy balance and human health. Fe catalyzes oxidations of organic carbon species and serves as a limiting nutrient for phytoplankton in about half of the world's oceans. Wind-blown dust is the major source of atmospheric insoluble Fe while urban areas are correlated with relatively high percentages of soluble Fe. The occurrence of elevated levels of soluble Fe near urban and industrial regions suggests a correlation between Fe solubilization and organic combustion products, including polycyclic aromatic hydrocarbons (PAH). Fossil fuel consumption for internal combustion engines produce atmospheric PAH as a major component of automobile exhaust. Under light, PAH transform into oxidized components such as ketones and carboxylic acids. For example, phthalic acid (formed from naphthalene) inhibits Fe oxidation reactions and therefore may contribute to Fe reduction and increased solubility. The wind-blown dust and PAH-containing combustion products undergo long-range atmospheric transport leading to mixing and metal-organic interactions. The current study focuses on how a saturated PAH suspension affects the production of soluble Fe. Reactions of soil-based Fe and saturated solutions of PAH are performed under controlled conditions simulating natural sunlight. Samples are analyzed by ICPMS for soluble Fe before and after solar exposure reactions; soluble Fe is separated from total Fe by filtration and total Fe by acid-assisted microwave digestion. Data indicate an increase in Fe solubility (1.2% to 4.2%) in the presence of PAH, as compared to soil in water alone, and an even greater increase in Fe solubility (4.2% to 8.4%) when exposed to solar radiation. Research is ongoing to determine the dependence of oxidized PAH on kinetic and overall Fe solubility.

Two Regimes of Interaction of a Hot Jupiter’s Escaping Atmosphere with the Stellar Wind and Generation of Energized Atomic Hydrogen Corona

NASA Astrophysics Data System (ADS)

Shaikhislamov, I. F.; Khodachenko, M. L.; Lammer, H.; Kislyakova, K. G.; Fossati, L.; Johnstone, C. P.; Prokopov, P. A.; Berezutsky, A. G.; Zakharov, Yu. P.; Posukh, V. G.

2016-12-01

The interaction of escaping the upper atmosphere of a hydrogen-rich non-magnetized analog of HD 209458b with a stellar wind (SW) of its host G-type star at different orbital distances is simulated with a 2D axisymmetric multi-fluid hydrodynamic (HD) model. A realistic Sun-like spectrum of X-ray and ultraviolet radiation, which ionizes and heats the planetary atmosphere, together with hydrogen photochemistry, as well as stellar-planetary tidal interaction are taken into account to generate self-consistently an atmospheric HD outflow. Two different regimes of the planetary and SW interaction have been modeled. These are: (1) the “captured by the star” regime, when the tidal force and pressure gradient drive the planetary material beyond the Roche lobe toward the star, and (2) the “blown by the wind” regime, when sufficiently strong SW confines the escaping planetary atmosphere and channels it into the tail. The model simulates in detail the HD interaction between the planetary atoms, protons and the SW, as well as the production of energetic neutral atoms (ENAs) around the planet due to charge exchange between planetary atoms and stellar protons. The revealed location and shape of the ENA cloud, either as a paraboloid shell between the ionopause and bowshock (for the “blown by the wind” regime), or a turbulent layer at the contact boundary between the planetary stream and SW (for the “captured by the star” regime) are of importance for the interpretation of Lyα absorption features in exoplanetary transit spectra and characterization of the plasma environments.

Possible Signs of Ancient Drying in Martian Rock

NASA Image and Video Library

2017-01-17

A grid of small polygons on the Martian rock surface near the right edge of this view may have originated as cracks in drying mud more than 3 billion years ago. Multiple images from the Mast Camera (Mastcam) on NASA's Curiosity Mars rover were combined for this mosaic of a block called "Squid Cove" and its immediate surroundings. The location is within an exposure of Murray formation mudstone on lower Mount Sharp inside Gale Crater. Mastcam's right-eye camera, which has a telephoto lens, took the component images of this view on Dec. 20, 2016, during the 1,555th Martian day, or sol, of Curiosity's work on Mars. The rover drove farther uphill on Gale Crater before the possible mud cracks were detected in the Mastcam images. This possible evidence about the area's ancient environment prompted the rover mission to backtrack for closer inspection of Squid Cove and nearby target rocks. This scene is presented with a color adjustment that approximates white balancing, to resemble how the rocks and sand would appear under daytime lighting conditions on Earth. The polygons are about half an inch to 1 inch (about 1 to 2 centimeters) across. Figure 1 includes a scale bar of 30 centimeters (12 inches). The polygons are outlined by ridges. This could result from a three-step process after cracks form due to drying: Wind-blown sediments accumulate in the open cracks. Later, these sediments and the dried mud become rock under the pressure of multiple younger layers that accumulate on top of them. Most recently, after the overlying layers were eroded away by wind, the vein-filling material resists erosion better than the once-muddy material, so the pattern that began as cracks appears as ridges. Mud cracks would be evidence of a drying interval between wetter periods that supported lakes in the area. Curiosity has found evidence of ancient lakes in older, lower-lying rock layers and also in younger mudstone that is above Squid Cove. http://photojournal.jpl.nasa.gov/catalog/PIA21263

Likely effects of construction of Scroby Sands offshore wind farm on a mixed population of harbour Phoca vitulina and grey Halichoerus grypus seals.

PubMed

Skeate, Eleanor R; Perrow, Martin R; Gilroy, James J

2012-04-01

Scroby Sands offshore wind farm was built close to a haul-out and breeding site for harbour seal, a species of conservation concern. An aerial survey programme conducted during a five-year period spanning wind farm construction, revealed a significant post-construction decline in haul-out counts. Multivariate model selection suggested that the decline was not related to the environmental factors considered, nor did it mirror wider population trends. Although cause and effect could not be unequivocally established, the theoretical basis of hearing in pinnipeds and previous studies suggested that extreme noise (to 257 dB re 1 μ Pa(pp) @ 1m) generated by pile-driving of turbine bases led to displacement of seals. A lack of full recovery of harbour seal during the study was also linked to their sensitivity to vessel activity and/or rapid colonisation of competing grey seal. Any impact of offshore wind farm development upon pinnipeds would be much reduced without pile-driving. Copyright © 2012 Elsevier Ltd. All rights reserved.

SAND FLUX IN THE NORTHERN CHIHUAHUAN DESERT, NEW MEXICO, USA, AND THE INFLUENCE OF MESQUITE-DOMINATED LANDSCAPES

EPA Science Inventory

This study was designed to test two hypotheses: (1) that land dominated by mesquite (Prosopis glandulosa) is the most important area for active sand movement at the Jornada Experimental Range, located in the northern part of the Chihuahuan desert, and (2) that the most active san...

Turbulence measurements over immobile gravel with additions of sand from supply limited to capacity transport conditions

USDA-ARS?s Scientific Manuscript database

Measurement of the turbulence that drives sand transport over and through immobile gravels is relevant to efforts to model sediment movement downstream of dams, where fine sediments are eroded from coarse substrates and are not replaced due to the presence of the upstream dam. The relative elevatio...

Desert winds: Monitoring wind-related surface processes in Arizona, New Mexico, and California

USGS Publications Warehouse

Breed, Carol S.; Reheis, Marith C.

1999-01-01

The 18-year Desert Winds Project established instrumented field sites in the five major regions of the North American Desert to obtain meteorological, geological, and vegetation data for natural desert sites affected by wind erosion. The eight chapters in this volume describe the settings and operation of the stations and summarize eolian-related research to date around the stations. The report includes studies of the sand-moving effectiveness of storm winds, wind-erosion susceptibility of different ground-surface types, relations of dust storms to meteorological conditions, mediation of wind erosion by vegetation, remote sensing to detect vegetation changes related to climate change, and comparison of regional dust deposition to that near Owens (dry) Lake.

Wind tunnel simulation of Martian sand storms

NASA Technical Reports Server (NTRS)

Greeley, R.

1980-01-01

The physics and geological relationships of particles driven by the wind under near Martian conditions were examined in the Martian Surface Wind Tunnel. Emphasis was placed on aeolian activity as a planetary process. Threshold speeds, rates of erosion, trajectories of windblown particles, and flow fields over various landforms were among the factors considered. Results of experiments on particles thresholds, rates of erosion, and the effects of electrostatics on particles in the aeolian environment are presented.

HUBBLE PROBES THE COMPLEX HISTORY OF A DYING STAR

NASA Technical Reports Server (NTRS)

2002-01-01

This NASA Hubble Space Telescope image shows one of the most complex planetary nebulae ever seen, NGC 6543, nicknamed the 'Cat's Eye Nebula.' Hubble reveals surprisingly intricate structures including concentric gas shells, jets of high-speed gas and unusual shock-induced knots of gas. Estimated to be 1,000 years old, the nebula is a visual 'fossil record' of the dynamics and late evolution of a dying star. A preliminary interpretation suggests that the star might be a double-star system. The dynamical effects of two stars orbiting one another most easily explains the intricate structures, which are much more complicated than features seen in most planetary nebulae. (The two stars are too close together to be individually resolved by Hubble, and instead, appear as a single point of light at the center of the nebula.) According to this model, a fast 'stellar wind' of gas blown off the central star created the elongated shell of dense, glowing gas. This structure is embedded inside two larger lobes of gas blown off the star at an earlier phase. These lobes are 'pinched' by a ring of denser gas, presumably ejected along the orbital plane of the binary companion. The suspected companion star also might be responsible for a pair of high-speed jets of gas that lie at right angles to this equatorial ring. If the companion were pulling in material from a neighboring star, jets escaping along the companion's rotation axis could be produced. These jets would explain several puzzling features along the periphery of the gas lobes. Like a stream of water hitting a sand pile, the jets compress gas ahead of them, creating the 'curlicue' features and bright arcs near the outer edge of the lobes. The twin jets are now pointing in different directions than these features. This suggests the jets are wobbling, or precessing, and turning on and off episodically. The image was taken with the Wide Field Planetary Camera-2 on September 18, 1994. NGC 6543 is 3,000 light-years away in the northern constellation Draco. The term planetary nebula is a misnomer; dying stars create these cocoons when they lose outer layers of gas. The process has nothing to do with planet formation, which is predicted to happen early in a star's life. This material was presented at the 185th meeting of the American Astronomical Society in Tucson, AZ on January 11, 1995. Credit: J.P. Harrington and K.J. Borkowski (University of Maryland), and NASA

Field measurements of mean and turbulent airflow over a barchan sand dune

NASA Astrophysics Data System (ADS)

Weaver, Corinne M.; Wiggs, Giles F. S.

2011-05-01

Advances in our knowledge of the aeolian processes governing sand dune dynamics have been restricted by a reliance on measures of time-averaged airflow, such as shear velocity ( u*). It has become clear that such measures are incapable of explaining the complete dynamics of sediment transport across dune surfaces. Past evidence from wind tunnel and modelling studies has suggested that in some regions on a dune's surface the sediment transport might be better explained through investigations of the turbulent nature of the airflow. However, to date there have been no field studies providing data on the turbulent characteristics of the airflow around dunes with which to support or refute such hypotheses. The field investigation presented here provides mean and turbulent airflow measurements across the centre-line of a barchan sand dune in Namibia. Data were collected using arrays of sonic anemometers and were compared with sand flux data measured using wedge-shaped traps. Results support previously published data derived from wind tunnels and numerical models. The decline in mean wind velocity at the upwind toe of the dune is shown to coincide with a rise in turbulence, whilst mean velocity acceleration on the upper slope corresponds with a general decline in measured turbulence. Analysis of the components of Reynold shear stress ( -u'¯w'¯) and normal stresses ( u¯ and w2 ¯) supports the notion that the development of flow turbulence along the dune centre-line is likely to be associated with the interplay between streamline curvature and mean flow deceleration/acceleration. It is suggested that, due to the nature of its calculation, turbulence intensity is a measure of less practical use than direct assessments of the individual components of Reynolds stress, particularly the instantaneous horizontal streamwise component ( u2 ¯) and shear stress ( -uw¯). Whilst, increases in Reynolds shear stress and the horizontal streamwise component of stress in the toe region of the dune may effectively explain the maintenance of sand flux in a region of declining mean velocity, they have much less explanatory power for sand flux on the upper windward slope and in the crestal region of the dune. Here, it is suggested that mean flow acceleration is likely to provide the most significant driving force on sand flux, possibly augmented by a rise in the horizontal streamwise component of Reynolds stress ( u2 ¯) in the crest/brink region. Therefore, although wind turbulence is considered to be of fundamental importance in explaining the sediment transport dynamics across the dune's surface it is recognised that the interaction between mean flow deceleration/acceleration, streamline curvature and individual components of Reynolds stress is complex and the identification of a single element of flow that offers a panacea for accounting for sand flux and dune dynamics is difficult to find.

Investigating Mars: Olympia Undae

NASA Image and Video Library

2018-03-15

This VIS image highlights the dune form/dune density aspects of Olypmia Undae. In the center there is a brighter, diagonal region of few dunes. These dunes are the arc or crescent shape of barchan dunes. As more sand becomes available the barchan dunes begin to merge into transverse dunes. The region of dunes surrounding the bright swath still have the underlying surface visible, and the transverse dunes have a lace-like layout. In the regions with a significant abundance of sand have developed the tightly packed transverse dunes with the wave-like distribution. Olympia Undae is a vast dune field in the north polar region of Mars. It consists of a broad sand sea or erg that partly rings the north polar cap from about 120° to 240°E longitude and 78° to 83°N latitude. The dune field covers an area of approximately 470,000 km2 (bigger than California, smaller than Texas). Olympia Undae is the largest continuous dune field on Mars. Olympia Undae is not the only dune field near the north polar cap, several other smaller fields exist in the same latitude, but in other ranges of longitude, e.g. Abolos and Siton Undae. Barchan and transverse dune forms are the most common. In regions with limited available sand individual barchan dunes will form, the surface beneath and between the dunes is visible. In regions with large sand supplies, the sand sheet covers the underlying surface, and dune forms are found modifying the surface of the sand sheet. In this case transverse dunes are more common. Barchan dunes "point" down wind, transverse dunes are more linear and form parallel to the wind direction. The "square" shaped transverse dunes in Olympia Undae are due to two prevailing wind directions. The density of dunes and the alignments of the dune crests varies with location, controlled by the amount of available sand and the predominant winds over time. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 13238 Latitude: 80.7247 Longitude: 173.91 Instrument: VIS Captured: 2004-12-08 09:25 https://photojournal.jpl.nasa.gov/catalog/PIA22296

Winds of Change

NASA Image and Video Library

2010-03-05

Observation Date: 1 pointing on Dec 4, 2000 and 9 pointings between Nov 18 and Dec 5, 2008. Distance Estimate: About 50 million light years away. This is a composite image of NGC 1068, one of the nearest and brightest galaxies containing a rapidly growing supermassive black hole. The X-ray images and spectra obtained using Chandra's High Energy Transmission Grating Spectrometer show that a strong wind is being driven away from the center of NGC 1068 at a rate of about a million miles per hour. This wind is likely generated as surrounding gas is accelerated and heated as it swirls toward the black hole. A portion of the gas is pulled into the black hole, but some of it is blown away. High energy X-rays produced by the gas near the black hole heat the ouflowing gas, causing it to glow at lower X-ray energies. X-ray data from the Chandra X-ray Observatory are shown in red, optical data from the Hubble Space Telescope in green and radio data from the Very Large Array in blue. The spiral structure of NGC 1068 is shown by the X-ray and optical data, and a jet powered by the central supermassive black hole is shown by the radio data. This Chandra study is much deeper than previous X-ray observations. Using this data, researchers believe that each year several times the mass of our sun is being deposited out to large distances, about 3,000 light years from the black hole. The wind likely carries enough energy to heat the surrounding gas and suppress extra star formation. These results help explain how a supermassive black hole can alter the evolution of its host galaxy. It has long been suspected that material blown away from a black hole can affect its environment, but a key question has been whether such "black hole blowback" typically delivers enough power to have a significant impact. NGC 1068 is located about 50 million light years from Earth and contains a supermassive black hole about twice as massive as the one in the middle of the Milky Way Galaxy. Image Credit: X-ray (NASA/CXC/ MIT/C.Canizares, D.Evans et al), Optical (NASA/STScI), Radio (NSF/ NRAO/VLA)

Impact of erosion and accretion on the distribution of enterococci in beach sands.

PubMed

Gast, Rebecca J; Gorrell, Levi; Raubenheimer, Britt; Elgar, Steve

2011-09-15

Bacterial pathogens in coastal sediments may pose a health risk to users of beaches. Although recent work shows that beach sands harbor both indicator bacteria and potential pathogens, it is not known how deep within beach sands the organisms may persist nor if they may be exposed during natural physical processes. In this study, sand cores of approximately 1 m depth were collected at three sites across the beach face in Kitty Hawk, North Carolina before, during and after large waves from an offshore hurricane. The presence of DNA from the fecal indicator bacterium Enterococci was detected in subsamples at different depths within the cores by PCR amplification. Erosion and accretion of beach sand at the three sites also was determined for each sampling day. The results indicate that ocean beach sands with persisting enterococci signals could be exposed and redistributed when wind, waves, and currents cause beach erosion or accretion.

Investigating Mars: Olympia Undae

NASA Image and Video Library

2018-03-09

This VIS image of Olympia Undae was collected during north polar spring. The crests of the dunes and other surfaces are light colored, indicative of a frost covering. The density of dunes and the alignments of the dune crests varies with location, controlled by the amount of available sand and the predominant winds over time. As the season changes into summertime, the dune crests will lose the frost and reveal the darker sand beneath. Olympia Undae is a vast dune field in the north polar region of Mars. It consists of a broad sand sea or erg that partly rings the north polar cap from about 120° to 240°E longitude and 78° to 83°N latitude. The dune field covers an area of approximately 470,000 km2 (bigger than California, smaller than Texas). Olympia Undae is the largest continuous dune field on Mars. Olympia Undae is not the only dune field near the north polar cap, several other smaller fields exist in the same latitude, but in other ranges of longitude, e.g. Abolos and Siton Undae. Barchan and transverse dune forms are the most common. In regions with limited available sand individual barchan dunes will form, the surface beneath and between the dunes is visible. In regions with large sand supplies, the sand sheet covers the underlying surface, and dune forms are found modifying the surface of the sand sheet. In this case transverse dunes are more common. Barchan dunes "point" down wind, transverse dunes are more linear and form parallel to the wind direction. The "square" shaped transverse dunes in Olympia Undae are due to two prevailing wind directions. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 27402 Latitude: 81.2035 Longitude: 183.317 Instrument: VIS Captured: 2008-02-17 13:59 https://photojournal.jpl.nasa.gov/catalog/PIA22292

Investigating Mars: Olympia Undae

NASA Image and Video Library

2018-03-07

This VIS image of Olympia Undae was collected early in north polar spring. The crests of the dunes are light colored, indicative of a frost covering. As the season changes into summertime, the dune crests will lose the frost and reveal the darker sand beneath. The linear nature of transverse dunes can be seen at the bottom of the image. The density of dunes and the alignments of the dune crests varies with location, controlled by the amount of available sand and the predominant winds over time. Olympia Undae is a vast dune field in the north polar region of Mars. It consists of a broad sand sea or erg that partly rings the north polar cap from about 120° to 240°E longitude and 78° to 83°N latitude. The dune field covers an area of approximately 470,000 km2 (bigger than California, smaller than Texas). Olympia Undae is the largest continuous dune field on Mars. Olympia Undae is not the only dune field near the north polar cap, several other smaller fields exist in the same latitude, but in other ranges of longitude, e.g. Abolos and Siton Undae. Barchan and transverse dune forms are the most common. In regions with limited available sand individual barchan dunes will form, the surface beneath and between the dunes is visible. In regions with large sand supplies, the sand sheet covers the underlying surface, and dune forms are found modifying the surface of the sand sheet. In this case transverse dunes are more common. Barchan dunes "point" down wind, transverse dunes are more linear and form parallel to the wind direction. The "square" shaped transverse dunes in Olympia Undae are due to two prevailing wind directions. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 10380 Latitude: 79.7273 Longitude: 176.363 Instrument: VIS Captured: 2004-04-17 02:00 https://photojournal.jpl.nasa.gov/catalog/PIA22290

Evidences of Neotectonic Movements Recorded in Fluvial and Lacustrine Deposits of the Niger River in Bamako, Mali

NASA Astrophysics Data System (ADS)

Dembele, N. D. J.

2015-12-01

Two alluvial profiles showing evidences of tectonic movements were discovered along the right bank of the Niger River at Bamako. The first profile of 25 meters thick is composed of a laminated silt layer of about 22 meters, of a gray sand layer of 25 cm and a pebble layer of 2 meters. A layer of 80 cm wide, an intrusive body, crosscuts the silt layers. The Grain size and heavy minerals analysis showed that this vertical layer is different in structure, texture and composition from the other layers. The second profile of about 20 meters is composed of interbedded fluvial gravel and sand deposits. The tectonic evidences found on those layers are of three types: faults and fractures, folds and the intrusion between silts deposits of the sand layers previously presented. The faults and fractures are located mainly on the fluvial gravel and sand deposits, whereas the silts deposits are folded and show some microfaults. The intrusion of a sand layer between the silt layer is a geological process that is not yet well understood but it is believed that this phenomena occurs during earthquakes as the sand layer during such event behave as a liquid. The discovery of such layer testifies that earthquakes used to happen in the area. As they concern only the alluvial deposits, their age should be no more than the Quaternary period. The presence of such tectonic evidences is surprising as Bamako like all the Republic of Mali is located on the west African craton that is supposed to be tectonically stable and their occurrence on Quaternary unconsolidated sediments shows that tectonic movements used to occur on that area during the last 2 millions years or may be less whereas people continue to build houses and other social infrastructures on them without any caution.

Lineage diversification of fringe-toed lizards (Phrynosomatidae: Uma notata complex) in the Colorado Desert: Delimiting species in the presence of gene flow

USGS Publications Warehouse

Gottscho, Andrew D.; Wood, Dustin A.; Vandergast, Amy; Lemos Espinal, Julio A.; Gatesy, John; Reeder, Tod

2017-01-01

Multi-locus nuclear DNA data were used to delimit species of fringe-toed lizards of theUma notata complex, which are specialized for living in wind-blown sand habitats in the deserts of southwestern North America, and to infer whether Quaternary glacial cycles or Tertiary geological events were important in shaping the historical biogeography of this group. We analyzed ten nuclear loci collected using Sanger sequencing and genome-wide sequence and single-nucleotide polymorphism (SNP) data collected using restriction-associated DNA (RAD) sequencing. A combination of species discovery methods (concatenated phylogenies, parametric and non-parametric clustering algorithms) and species validation approaches (coalescent-based species tree/isolation-with-migration models) were used to delimit species, infer phylogenetic relationships, and to estimate effective population sizes, migration rates, and speciation times. Uma notata, U. inornata, U. cowlesi, and an undescribed species from Mohawk Dunes, Arizona (U. sp.) were supported as distinct in the concatenated analyses and by clustering algorithms, and all operational taxonomic units were decisively supported as distinct species by ranking hierarchical nested speciation models with Bayes factors based on coalescent-based species tree methods. However, significant unidirectional gene flow (2NM >1) from U. cowlesi and U. notata into U. rufopunctata was detected under the isolation-with-migration model. Therefore, we conservatively delimit four species-level lineages within this complex (U. inornata, U. notata, U. cowlesi, and U. sp.), treating U. rufopunctata as a hybrid population (U. notata x cowlesi). Both concatenated and coalescent-based estimates of speciation times support the hypotheses that speciation within the complex occurred during the late Pleistocene, and that the geological evolution of the Colorado River delta during this period was an important process shaping the observed phylogeographic patterns.

Sedimentary processes of the Bagnold Dunes: Implications for the eolian rock record of Mars.

PubMed

Ewing, R C; Lapotre, M G A; Lewis, K W; Day, M; Stein, N; Rubin, D M; Sullivan, R; Banham, S; Lamb, M P; Bridges, N T; Gupta, S; Fischer, W W

2017-12-01

The Mars Science Laboratory rover Curiosity visited two active wind-blown sand dunes within Gale crater, Mars, which provided the first ground-based opportunity to compare Martian and terrestrial eolian dune sedimentary processes and study a modern analog for the Martian eolian rock record. Orbital and rover images of these dunes reveal terrestrial-like and uniquely Martian processes. The presence of grainfall, grainflow, and impact ripples resembled terrestrial dunes. Impact ripples were present on all dune slopes and had a size and shape similar to their terrestrial counterpart. Grainfall and grainflow occurred on dune and large-ripple lee slopes. Lee slopes were ~29° where grainflows were present and ~33° where grainfall was present. These slopes are interpreted as the dynamic and static angles of repose, respectively. Grain size measured on an undisturbed impact ripple ranges between 50 μm and 350 μm with an intermediate axis mean size of 113 μm (median: 103 μm). Dissimilar to dune eolian processes on Earth, large, meter-scale ripples were present on all dune slopes. Large ripples had nearly symmetric to strongly asymmetric topographic profiles and heights ranging between 12 cm and 28 cm. The composite observations of the modern sedimentary processes highlight that the Martian eolian rock record is likely different from its terrestrial counterpart because of the large ripples, which are expected to engender a unique scale of cross stratification. More broadly, however, in the Bagnold Dune Field as on Earth, dune-field pattern dynamics and basin-scale boundary conditions will dictate the style and distribution of sedimentary processes.

Factors controlling the size and shape of stream channels in coarse noncohesive sands

USGS Publications Warehouse

Wolman, M. Gordon; Brush, Lucien M.

1961-01-01

The size and shape of equilibrium channels in uniform, noncohesive sands, 0.67 mm and 2.0 mm in diameter, were studied experimentally in a laboratory flume 52 feet long in which discharge, slope, sediment load, and bed and bank material could be varied independently. For each run a straight trapezoidal channel was molded in the sand and the flume set at a predetermined slope. Introduction of the discharge was accompanied by widening and aggradation until a stable channel was established. By definition a stable equilibrium existed when channel width, water surface slope, and rate of transport became constant. The duration of individual runs ranged from 2 to 52 hours depending upon the time required for establishing equilibrium. Stability of the banks determined channel shape. In the 2.0 mm sand at a given slope and discharge, only one depth was stable. At this depth the flow was just competent to move particles along the bed of the channel. An increase in discharge produced a wider channel of the same depth and thus transport per unit width remained at a minimum. Channels in the 0.67 mm sand were somewhat more stable and permitted a 1.5 fold increase in depth above that required to start movement of the bed material. An increased transport was associated with the increase in depth. The rate of transport is adequately described in terms of the total shear or in terms of the difference between the total shear and the critical shear required to begin movement. In these experiments the finer, or 0.67 mm, sand, began to move along the bed of the channel at a constant shear stress. Incipient movement of the coarser, or 2.0 mm, sand, varied with the shear stress as well as the mean velocity. At the initiation of movement a lower shear was associated with a higher velocity and vice versa. Anabranches of braided rivers and some natural river channels formed in relatively noncohesive materials resemble the essential characteristics of the flume channels. For a given slope and size of bed material the discharge per unit width in the laboratory channels was similar to that computed for anabranches and river channels measured in the field. Unlike most natural channels, despite impressive bank erosion, the channels in the laboratory only meandered at supercritical flows associated with very steep slopes. These conditions involving shallow depths, high velocity, and steep slopes are uncommon in most natural rivers.

Late Pleistocene dune activity in the central Great Plains, USA

USGS Publications Warehouse

Mason, J.A.; Swinehart, J.B.; Hanson, P.R.; Loope, D.B.; Goble, R.J.; Miao, X.; Schmeisser, R.L.

2011-01-01

Stabilized dunes of the central Great Plains, especially the megabarchans and large barchanoid ridges of the Nebraska Sand Hills, provide dramatic evidence of late Quaternary environmental change. Episodic Holocene dune activity in this region is now well-documented, but Late Pleistocene dune mobility has remained poorly documented, despite early interpretations of the Sand Hills dunes as Pleistocene relicts. New optically stimulated luminescence (OSL) ages from drill cores and outcrops provide evidence of Late Pleistocene dune activity at sites distributed across the central Great Plains. In addition, Late Pleistocene eolian sands deposited at 20-25 ka are interbedded with loess south of the Sand Hills. Several of the large dunes sampled in the Sand Hills clearly contain a substantial core of Late Pleistocene sand; thus, they had developed by the Late Pleistocene and were fully mobile at that time, although substantial sand deposition and extensive longitudinal dune construction occurred during the Holocene. Many of the Late Pleistocene OSL ages fall between 17 and 14 ka, but it is likely that these ages represent only the later part of a longer period of dune construction and migration. At several sites, significant Late Pleistocene or Holocene large-dune migration also probably occurred after the time represented by the Pleistocene OSL ages. Sedimentary structures in Late Pleistocene eolian sand and the forms of large dunes potentially constructed in the Late Pleistocene both indicate sand transport dominated by northerly to westerly winds, consistent with Late Pleistocene loess transport directions. Numerical modeling of the climate of the Last Glacial Maximum has often yielded mean monthly surface winds southwest of the Laurentide Ice Sheet that are consistent with this geologic evidence, despite strengthened anticyclonic circulation over the ice sheet. Mobility of large dunes during the Late Pleistocene on the central Great Plains may have been the result of cold, short growing seasons with relatively low precipitation and low atmospheric CO2 that increased plant moisture stress, limiting the ability of vegetation to stabilize active dune sand. The apparent coexistence of large mobile dunes with boreal forest taxa suggests a Late Pleistocene environment with few modern analogs. ?? 2011 Elsevier Ltd.

Martian Dune Ripples as Indicators of Recent Surface Wind Patterns

NASA Astrophysics Data System (ADS)

Johnson, M.; Zimbelman, J. R.

2015-12-01

Sand dunes have been shown to preserve the most recent wind patterns in their ripple formations. This investigation continues the manual documentation of ripples on Martian dunes in order to assess surface wind flow. Study sites investigated must have clear HiRISE frames and be able to represent diverse locations across the surface, decided primarily by their spread of latitude and longitude values. Additionally, frames with stereo pairs are preferred because of their ability to create digital terrain models. This will assist in efforts to relate dune slopes and obstacles to ripple patterns. The search and analysis period resulted in 40 study sites with mapped ripples. Lines were drawn perpendicular to ripple crests across three adjacent ripples in order to document both ripple wavelength from line length and inferred wind direction from azimuth. It is not possible to infer a unique wind direction from ripple orientation alone and therefore these inferred directions have a 180 degree ambiguity. Initial results from all study sites support previous observations that the Martian surface has many dune types in areas with adequate sand supply. The complexity of ripple patterns varies greatly across sites as well as within individual sites. Some areas of uniform directionality for hundreds of kilometers suggest a unimodal wind regime while overlapping patterns suggest multiple dominant winds or seasonally varying winds. In most areas, form flow related to dune shape seems to have a large effect on orientation and must be considered along with the dune type. As long as the few steep slip faces on these small dunes are avoided, form flow can be considered the dominant cause of deviation from the regional wind direction. Regional results, wind roses, and comparisons to previous work will be presented for individual sites.

Solar Wind Ablation of Terrestrial Planet Atmospheres

NASA Technical Reports Server (NTRS)

Moore, Thomas Earle; Fok, Mei-Ching H.; Delcourt, Dominique C.

2009-01-01

Internal plasma sources usually arise in planetary magnetospheres as a product of stellar ablation processes. With the ignition of a new star and the onset of its ultraviolet and stellar wind emissions, much of the volatiles in the stellar system undergo a phase transition from gas to plasma. Condensation and accretion into a disk is replaced by radiation and stellar wind ablation of volatile materials from the system- Planets or smaller bodies that harbor intrinsic magnetic fields develop an apparent shield against direct stellar wind impact, but UV radiation still ionizes their gas phases, and the resulting internal plasmas serve to conduct currents to and from the central body along reconnected magnetic field linkages. Photoionization and thermalization of electrons warms the ionospheric topside, enhancing Jeans' escape of super-thermal particles, with ambipolar diffusion and acceleration. Moreover, observations and simulations of auroral processes at Earth indicate that solar wind energy dissipation is concentrated by the geomagnetic field by a factor of 10-100, enhancing heavy species plasma and gas escape from gravity, and providing more current carrying capacity. Thus internal plasmas enable coupling with the plasma, neutral gas and by extension, the entire body. The stellar wind is locally loaded and slowed to develop the required power. The internal source plasma is accelerated and heated, inflating the magnetosphere as it seeks escape, and is ultimately blown away in the stellar wind. Bodies with little sensible atmosphere may still produce an exosphere of sputtered matter when exposed to direct solar wind impact. Bodies with a magnetosphere and internal sources of plasma interact more strongly with the stellar wind owing to the magnetic linkage between the two created by reconnection.

Body size and substrate type modulate movement by the western Pacific crown-of-thorns starfish, Acanthaster solaris.

PubMed

Pratchett, Morgan S; Cowan, Zara-Louise; Nadler, Lauren E; Caballes, Ciemon F; Hoey, Andrew S; Messmer, Vanessa; Fletcher, Cameron S; Westcott, David A; Ling, Scott D

2017-01-01

The movement capacity of the crown-of-thorns starfishes (Acanthaster spp.) is a primary determinant of both their distribution and impact on coral assemblages. We quantified individual movement rates for the Pacific crown-of-thorns starfish (Acanthaster solaris) ranging in size from 75-480 mm total diameter, across three different substrates (sand, flat consolidated pavement, and coral rubble) on the northern Great Barrier Reef. The mean (±SE) rate of movement for smaller (<150 mm total diameter) A. solaris was 23.99 ± 1.02 cm/ min and 33.41 ± 1.49 cm/ min for individuals >350 mm total diameter. Mean (±SE) rates of movement varied with substrate type, being much higher on sand (36.53 ± 1.31 cm/ min) compared to consolidated pavement (28.04 ± 1.15 cm/ min) and slowest across coral rubble (17.25 ± 0.63 cm/ min). If average rates of movement measured here can be sustained, in combination with strong directionality, displacement distances of adult A. solaris could range from 250-520 m/ day, depending on the prevailing substrate. Sustained movement of A. solaris is, however, likely to be highly constrained by habitat heterogeneity, energetic constraints, resource availability, and diurnal patterns of activity, thereby limiting their capacity to move between reefs or habitats.

Parabolic dune development modes according to shape at the southern fringes of the Hobq Desert, Inner Mongolia, China

NASA Astrophysics Data System (ADS)

Guan, Chao; Hasi, Eerdun; Zhang, Ping; Tao, Binbin; Liu, Dan; Zhou, Yanguang

2017-10-01

Since the 1970s, parabolic dunes at the southern fringe of the Hobq Desert, Inner Mongolia, China have exhibited many different shapes (V-shaped, U-shaped, and palmate) each with a unique mode of development. In the study area, parabolic dunes are mainly distributed in Regions A, B, and C with an intermittent river running from the south to the north. We used high-resolution remote-sensing images from 1970 to 2014 and RTK-GPS measurements to study the development modes of different dune shapes; the modes are characterized by the relationship between the intermittent river and dunes, formation of the incipient dune patterns, the predominant source supply of dunes, and the primary formation of different shapes (V-shaped, U-shaped, and palmate). Most parabolic dunes in Region A are V-shaped and closer to the bank of the river. The original barchans in this region exhibit "disconnected arms" behavior. With the sand blown out of the riverbed through gullies, the nebkhas on the disconnected arms acquire the external sand source through the "fertile island effect", thereby developing into triangular sand patches and further developing into V-shaped parabolic dunes. Most parabolic dunes in Regions B and C are palmate. The residual dunes cut by the re-channelization of river from transverse dune fields on the west bank are the main sand source of Region B. The parabolic dunes in Region C are the original barchans having then been transformed. The stoss slopes of V-shaped parabolic dunes along the riverbank are gradual and the dunes are flat in shape. The dune crest of V-shaped parabolic dune is the deposition area, which forms the "arc-shaped sand ridge". Their two arms are non-parallel; the lateral airflow of the arms jointly transport sand to the middle part of dunes, resulting in a narrower triangle that gradually becomes V-shaped. Palmate parabolic dunes have a steeper stoss slope and height. The dune crest of the palmate parabolic dune is the erosion area, which forms a long and narrow trough between nebkhas by the "funnelling effect". This process forces sand towards lee slopes, which transform from concave (original barchans) into convex, ultimately resulting in the formation of palmate parabolic dunes.

Can a sand storm in Arabia cause a dip in the yield of your photovoltaic plant?

NASA Astrophysics Data System (ADS)

Ravindra, B.

2018-05-01

Solar power generation has accelerated worldwide during the last decade. Often the regions of high intensity of solar radiation are in the desert areas which are prone to Haboobs (Arabic word meaning "wind"). Haboobs are sandstorms caused by strong horizontal winds. They occur regularly in arid regions throughout the world. Impact of these events has been examined from various angles such as health, aviation, transportation, agriculture as they affect a billion people around the world. Here it is shown that these events can decrease the yield of a solar photovoltaic plant significantly. Analysis of measured solar radiation during a sand storm is carried out to assess its impact on solar power generation.

Design and optimize of 3-axis filament winding machine

NASA Astrophysics Data System (ADS)

Quanjin, Ma; Rejab, M. R. M.; Idris, M. S.; Bachtiar, B.; Siregar, J. P.; Harith, M. N.

2017-10-01

Filament winding technique is developed as the primary process for composite cylindrical structures fabrication at low cost. Fibres are wound on a rotating mandrel by a filament winding machine where resin impregnated fibres pass through a pay-out eye. This paper aims to develop and optimize a 3-axis, lightweight, practical, efficient, portable filament winding machine to satisfy the customer demand, which can fabricate pipes and round shape cylinders with resins. There are 3 main units on the 3-axis filament winding machine, which are the rotary unit, the delivery unit and control system unit. Comparison with previous existing filament winding machines in the factory, it has 3 degrees of freedom and can fabricate more complex shape specimens based on the mandrel shape and particular control system. The machine has been designed and fabricated on 3 axes movements with control system. The x-axis is for movement of the carriage, the y-axis is the rotation of mandrel and the z-axis is the movement of the pay-out eye. Cylindrical specimens with different dimensions and winding angles were produced. 3-axis automated filament winding machine has been successfully designed with simple control system.

LARGE-SCALE NATURAL GRADIENT TRACER TEST IN SAND AND GRAVEL, CAPE COD, MASSACHUSETTS - 1. EXPERIMENTAL DESIGN AND OBSERVED TRACER MOVEMENT

EPA Science Inventory

A large-scale natural gradient tracer experiment was conducted on Cape Cod, Massachusetts, to examine the transport and dispersion of solutes in a sand and gravel aquifer. The nonreactive tracer, bromide, and the reactive tracers, lithium and molybdate, were injected as a pulse i...

Dust and nutrient enrichment by wind erosion from Danish soils in dependence of tillage direction

NASA Astrophysics Data System (ADS)

Mohammadian Behbahani, Ali; Fister, Wolfgang; Heckrath, Goswin; Kuhn, Nikolaus J.

2016-04-01

Wind erosion is a selective process, which promotes erosion of fine particles. Therefore, it can be assumed that increasing erosion rates are generally associated with increasing loss of dust sized particles and nutrients. However, this selective process is strongly affected by the orientation and respective trapping efficiency of tillage ridges and furrows. Since tillage ridges are often the only protection measure available on poorly aggregated soils in absence of a protective vegetation cover, it is very important to know which orientation respective to the dominant wind direction provides best protection. This knowledge could be very helpful for planning erosion protection measures on fields with high wind erosion susceptibility. The main objective of this study, therefore, was to determine the effect of tillage direction on dust and nutrient mobilization by wind, using wind tunnel simulations. In order to assess the relationship between the enrichment ratio of specific particle sizes and the amount of eroded nutrients, three soils with loamy sand texture, but varying amounts of sand-sized particles, were selected. In addition, a soil with slightly less sand, but much higher organic matter content was chosen. The soils were tested with three different soil surface scenarios - flat surface, parallel tillage, perpendicular tillage. The parallel tillage operation experienced the greatest erosion rates, independent of soil type. Particles with D50 between 100-155 μm showed the greatest risk of erosion. However, due to a greater loss of dust sized particles from perpendicularly tilled surfaces, this wind-surface arrangement showed a significant increase in nutrient enrichment ratio compared to parallel tillage and flat surfaces. The main reason for this phenomenon is most probably the trapping of larger particles in the perpendicular furrows. This indicates that the highest rate of soil protection does not necessarily coincide with lowest soil nutrient losses and dust emissions. For the evaluation of protection measures on these soil types in Denmark it is, therefore, important to differentiate between their effectivity to reduce total soil erosion amount, dust emission, and nutrient loss.

Dust over Japan

NASA Image and Video Library

2017-12-08

March 24, 2010 - Dust over Japan This image of gray/brown dust being blown over Japan was captured on March 21, 2010 by the MODIS on the Terra satellite. On the left is the Korean peninsula. Japan stretches diagonally across the image, up to the top right corner. The dust is likely from the sandstorm that swept across the China the previous day. The sand and dust originated from the south and east of Inner Mongolia. In this image from March 20, the dust is nearly obscuring the Bohai Sea, which is just west of the Korean peninsula. Here is a handy map. For more information related to this image go to: modis.gsfc.nasa.gov/gallery/individual.php?db_date=2010-0... For more information about Goddard Space Flight Center go here: www.nasa.gov/centers/goddard/home/index.html

GRB 011121: A Collimated Outflow into Wind-Blown Surroundings

NASA Technical Reports Server (NTRS)

Greiner, J.; Klose, S.; Salvato, M.; Zeh, A.; Schwarz, R.; Hartmann, D. H.; Masetti, N.; Stecklum, B.; Lamer, G.; Lodieu, N.;

Shape and evolution of wind-blown bubbles of massive stars: on the effect of the interstellar magnetic field

NASA Astrophysics Data System (ADS)

van Marle, A. J.; Meliani, Z.; Marcowith, A.

2015-12-01

Context. The winds of massive stars create large (>10 pc) bubbles around their progenitors. As these bubbles expand they encounter the interstellar coherent magnetic field which, depending on its strength, can influence the shape of the bubble. Aims: We wish to investigate if, and how much, the interstellar magnetic field can contribute to the shape of an expanding circumstellar bubble around a massive star. Methods: We use the MPI-AMRVAC code to make magneto-hydrodynamical simulations of bubbles, using a single star model, combined with several different field strengths: B = 5, 10, and 20 μG for the interstellar magnetic field. This covers the typical field strengths of the interstellar magnetic fields found in the galactic disk and bulge. Furthermore, we present two simulations that include both a 5 μG interstellar magnetic field and a warm (10 000 K) interstellar medium (ISM) and two different ISM densities to demonstrate how the magnetic field can combine with other external factors to influence the morphology of the circumstellar bubbles. Results: Our results show that low magnetic fields, as found in the galactic disk, inhibit the growth of the circumstellar bubbles in the direction perpendicular to the field. As a result, the bubbles become ovoid, rather than spherical. Strong interstellar fields, such as observed for the galactic bulge, can completely stop the expansion of the bubble in the direction perpendicular to the field, leading to the formation of a tube-like bubble. When combined with an ISM that is both warm and high density the bubble is greatly reduced in size, causing a dramatic change in the evolution of temporary features inside the bubble such as Wolf-Rayet ring nebulae. Conclusions: The magnetic field of the interstellar medium can affect the shape of circumstellar bubbles. This effect may have consequences for the shape and evolution of circumstellar nebulae and supernova remnants, which are formed within the main wind-blown bubble. Appendices and movies associated to Figs. A.1-A.12 are available in electronic form at http://www.aanda.org

Concentrations and Distribution of Slag-Related Trace Elements and Mercury in Fine-Grained Beach and Bed Sediments of Lake Roosevelt, Washington, April-May 2001

USGS Publications Warehouse

Majewski, Michael S.; Kahle, Sue C.; Ebbert, James C.; Josberger, Edward G.

2003-01-01

A series of studies have documented elevated concentrations of trace elements such as arsenic, cadmium, copper, lead, mercury, and zinc in the water, bed sediment, or fish of Lake Roosevelt and the upstream reach of the Columbia River. Elevated concentrations of some trace elements in this region are largely attributable to the transport of slag and metallurgical waste discharged into the Columbia River from a smelter in Canada. Although most recent studies have focused on contamination levels in water, bed sediment, and fish, there is growing concern in the region over the potential threat of airborne contaminants to human health. In response to these concerns, the U.S. Geological Survey conducted an assessment of trace-element concentrations in the relatively shallow fine-grained sediment along the shore of Lake Roosevelt that is exposed annually during periods of reservoir drawdown. During each winter and spring, the water level of Lake Roosevelt is lowered as much as about 80 feet to provide space to capture high river flows from spring runoff, exposing vast expanses of lake-bottom sediment for a period of several months. Upon drying, these exposed areas provide an extremely large source for wind-blown dust. This study concluded that trace elements associated with slag and metallurgical waste are present in the fine-grained fraction (less than 63 micrometers) of bed sediments along the length of Lake Roosevelt, and as such, could be components of the airborne dust resulting from exposure, drying, and wind mobilization of the sediments exposed during the annual drawdowns of the reservoir. Trace-element concentrations in the surficial bed sediment varied, but the major components in slag?arsenic, cadmium, copper, lead, and zinc?showed generally pronounced gradients of decreasing concentrations from near the International Border to the Grand Coulee Dam. The results of this study provide base-line information needed to plan and conduct air monitoring of trace elements in wind-blown dust along Lake Roosevelt.

The dynamics of İzmir Bay under the effects of wind and thermohaline forces

NASA Astrophysics Data System (ADS)

Sayın, Erdem; Eronat, Canan

2018-04-01

The dominant circulation pattern of İzmir Bay on the Aegean Sea coast of Turkey is studied taking into consideration the influence of wind and thermohaline forces. İzmir Bay is discussed by subdividing the bay into outer, middle and inner areas. Wind is the most important driving force in the İzmir coastal area. There are also thermohaline forces due to the existence of water types of different physical properties in the bay. In contrast to the two-layer stratification during summer, a homogeneous water column exists in winter. The free surface version of the Princeton model (Killworth's 3-D general circulation model) is applied, with the input data obtained through the measurements made by the research vessel K. Piri Reis. As a result of the simulations with artificial wind, the strong consistent wind generates circulation patterns independent of the seasonal stratification in the bay. Wind-driven circulation causes cyclonic or anticyclonic movements in the middle bay where the distinct İzmir Bay Water (IBW) forms. Cyclonic movement takes place under the influence of southerly and westerly winds. On the other hand, northerly and easterly winds cause an anticyclonic movement in the middle bay. The outer and inner bay also have the wind-driven recirculation patterns expected.

Quantifying postfire aeolian sediment transport using rare earth element tracers

USGS Publications Warehouse

Dukes, David; Gonzales, Howell B.; Ravi, Sujith; Grandstaff, David E.; Van Pelt, R. Scott; Li, Junran; Wang, Guan; Sankey, Joel B.

2018-01-01

Grasslands, which provide fundamental ecosystem services in many arid and semiarid regions of the world, are undergoing rapid increases in fire activity and are highly susceptible to postfire-accelerated soil erosion by wind. A quantitative assessment of physical processes that integrates fire-wind erosion feedbacks is therefore needed relative to vegetation change, soil biogeochemical cycling, air quality, and landscape evolution. We investigated the applicability of a novel tracer technique—the use of multiple rare earth elements (REE)—to quantify soil transport by wind and to identify sources and sinks of wind-blown sediments in both burned and unburned shrub-grass transition zone in the Chihuahuan Desert, NM, USA. Results indicate that the horizontal mass flux of wind-borne sediment increased approximately threefold following the fire. The REE tracer analysis of wind-borne sediments shows that the source of the horizontal mass flux in the unburned site was derived from bare microsites (88.5%), while in the burned site it was primarily sourced from shrub (42.3%) and bare (39.1%) microsites. Vegetated microsites which were predominantly sinks of aeolian sediments in the unburned areas became sediment sources following the fire. The burned areas showed a spatial homogenization of sediment tracers, highlighting a potential negative feedback on landscape heterogeneity induced by shrub encroachment into grasslands. Though fires are known to increase aeolian sediment transport, accompanying changes in the sources and sinks of wind-borne sediments may influence biogeochemical cycling and land degradation dynamics. Furthermore, our experiment demonstrated that REEs can be used as reliable tracers for field-scale aeolian studies.

Parasites reveal movement of bats between the New and Old Worlds.

PubMed

Hamilton, Patrick B; Cruickshank, Catriona; Stevens, Jamie R; Teixeira, Marta M G; Mathews, Fiona

2012-05-01

The global distribution of bat taxa indicates that the Atlantic and Pacific Oceans are effective barriers to movement between the Old and New Worlds. For instance, one of the major suborders, Yinpterochiroptera, has an exclusively Old World distribution, and within the other, Yangochiroptera, no species and only five genera are common to both. However, as bats are sometimes blown out to sea, and have colonised isolated islands, occasional natural movement between the New and Old Worlds does appear to be possible. Here we identify new genotypes of a blood parasite, Trypanosoma dionisii, in Old World bats that are closely related to South American strains. Using highly conservative calibration points, divergence of Old and New World strains is estimated to have occurred 3.2-5.0 million years ago (MYA), depending on the method used (upper 95% CL for maximum time 11.4MYA). The true date of divergence is likely to be considerably more recent. These results demonstrate that taxon-specific parasites can indicate historical movements of their hosts, even where their hosts may have left no lasting phylogenetic footprint. Copyright © 2012 Elsevier Inc. All rights reserved.

Geomorphology context and characterization of dunefields developed by the southern westerlies at drying Colhué Huapi shallow lake, Patagonia Argentina

NASA Astrophysics Data System (ADS)

Montes, Alejandro; Rodríguez, Silvana Soledad; Domínguez, Carlos Eduardo

2017-10-01

Patagonia is the only continental territory exposed to the southern westerlies. The speed and frequency of these westerly winds generate a landscape strongly influenced by aeolian processes. This research shows a characterization of depositional and erosive aeolian landforms developed in dunefields associated to Lake Colhué Huapi, in the Extra-Andean Patagonia. Dunefields are located at 45°-46°S and moved in west-east direction due to the southern westerlies. We identified two big groups of active dunefields, one migrating through the dry lakebed of Colhué Huapi and the other migrating eastwards from the lakeshore. The dunefields mainly consist of transverse dunes, barchans, sand shadows and sand sheets. Yardangs, desert pavements, exhumed roots and decapitated soils were recognized in interdune areas. Longitudinal sand ridges, parallel to the prevailing wind direction, often remain preserved after the dunefields have passed. This allows to recognize the path of the dunes in the past. Sand ridges are recognized up to 28 km east from the present coast of the lake and evidenced former dunefields development. We describe the geomorphology context, landforms and sediments supply of dunefields related to the lake dynamics subject to clear tendency to desiccation.

Impact Crater with Peak

NASA Technical Reports Server (NTRS)

2002-01-01

(Released 14 June 2002) The Science This THEMIS visible image shows a classic example of a martian impact crater with a central peak. Central peaks are common in large, fresh craters on both Mars and the Moon. This peak formed during the extremely high-energy impact cratering event. In many martian craters the central peak has been either eroded or buried by later sedimentary processes, so the presence of a peak in this crater indicates that the crater is relatively young and has experienced little degradation. Observations of large craters on the Earth and the Moon, as well as computer modeling of the impact process, show that the central peak contains material brought from deep beneath the surface. The material exposed in these peaks will provide an excellent opportunity to study the composition of the martian interior using THEMIS multi-spectral infrared observations. The ejecta material around the crater can is well preserved, again indicating relatively little modification of this landform since its initial creation. The inner walls of this approximately 18 km diameter crater show complex slumping that likely occurred during the impact event. Since that time there has been some downslope movement of material to form the small chutes and gullies that can be seen on the inner crater wall. Small (50-100 m) mega-ripples composed of mobile material can be seen on the floor of the crater. Much of this material may have come from the walls of the crater itself, or may have been blown into the crater by the wind. The Story When a meteor smacked into the surface of Mars with extremely high energy, pow! Not only did it punch an 11-mile-wide crater in the smoother terrain, it created a central peak in the middle of the crater. This peak forms kind of on the 'rebound.' You can see this same effect if you drop a single drop of milk into a glass of milk. With craters, in the heat and fury of the impact, some of the land material can even liquefy. Central peaks like the one above are common in large, fresh craters on both Mars and the Moon. In many older Martian craters, however, the central peak has either been eroded or was buried by later deposits of sand, dust, and 'dirt' on the terrain. With the pronounced, non-eroded peak in this crater, you can tell that it hasn't been around for a long time. Its youth is also apparent because of the ejected material around the crater that spreads out from it in an almost flame-or petal-like pattern with little evidence of erosion. Observations of large craters on the Earth and the Moon, as well as computer modeling of the impact process, show that central peaks contain material brought from deep beneath the surface. The material exposed in these peaks will provide an excellent opportunity to study what the interior of Mars is made of. In addition to providing images of Mars like the one above, the THEMIS camera system has the capability to analyze the mineral composition of the surface. That means it will be able to look at this area and 'see' both the composition of the top surface, as well as the exposed interior that is uplifted in the central peak. Stay tuned for more news later from this crater! Until then, take a closer look at the walls of this crater. Particularly on the western side, you can see how whole portions of the wall have slid or 'slumped' downward, probably sometime during the impact event. Since then, smaller amounts of material have slid downslope as well, forming small chutes and gullies that streak down the inner crater wall. On the floor of the crater, you can also see small, mobile mega-ripples that extend up to a football field in length. (Look for the tiny, bright, white ripples especially to the north of the crater floor.) These ripples were probably created from material coming down from the wall of the crater or alternatively from dust and 'dirt' that was blown into the crater by the wind.

Mars Global Digital Dune Database (MGD3): Global dune distribution and wind pattern observations

USGS Publications Warehouse

Hayward, Rosalyn K.; Fenton, Lori; Titus, Timothy N.

2014-01-01

The Mars Global Digital Dune Database (MGD3) is complete and now extends from 90°N to 90°S latitude. The recently released south pole (SP) portion (MC-30) of MGD3 adds ∼60,000 km2 of medium to large-size dark dune fields and ∼15,000 km2 of sand deposits and smaller dune fields to the previously released equatorial (EQ, ∼70,000 km2), and north pole (NP, ∼845,000 km2) portions of the database, bringing the global total to ∼975,000 km2. Nearly all NP dunes are part of large sand seas, while the majority of EQ and SP dune fields are individual dune fields located in craters. Despite the differences between Mars and Earth, their dune and dune field morphologies are strikingly similar. Bullseye dune fields, named for their concentric ring pattern, are the exception, possibly owing their distinctive appearance to winds that are unique to the crater environment. Ground-based wind directions are derived from slipface (SF) orientation and dune centroid azimuth (DCA), a measure of the relative location of a dune field inside a crater. SF and DCA often preserve evidence of different wind directions, suggesting the importance of local, topographically influenced winds. In general however, ground-based wind directions are broadly consistent with expected global patterns, such as polar easterlies. Intriguingly, between 40°S and 80°S latitude both SF and DCA preserve their strongest, though different, dominant wind direction, with transport toward the west and east for SF-derived winds and toward the north and west for DCA-derived winds.

Earth Observations taken by the Expedition 15 Crew

NASA Image and Video Library

2007-05-12

ISS015-E-07771 (12 May 2007) --- Isla Blanquilla, Venezuela is featured in this image photographed by an Expedition 15 crewmember on the International Space Station. The small island of Blanquilla is so named for its white sand beaches, visible in this image as a bright border along the northeastern -- eastern shoreline. Located approximately 292 kilometers (182 miles) northeast of Caracas, this Caribbean island is a popular destination for divers and tourists arriving by boat or airplane (the airstrip is visible at left center). Surface currents extending from the western coastline of the island (right center) are caused by easterly trade winds. According to scientists, this dominant wind has also caused movement of beach sand to form white "fingers" extending inland along the east coast (bottom center). The flora and fauna of Isla Blanquilla are an interesting mixture of arid (cacti, iguanas) and introduced species (wild donkeys and goats), but it is particularly notable for the presence of black coral. Black coral (order Antipatharia) is something of a misnomer, as it refers to the skeleton of the coral rather than the living organism (which is typically brightly colored). Black corals around the world are harvested for use in jewelry and other craftwork, so much so that the species has been listed for protection under the Convention on International Trade in Endangered Species of Wild Fauna and Flora. The island is the southernmost subaerial (above water) exposure of the Aves Ridge, a seafloor topography feature of the southernmost Caribbean ocean. The western third of the island is comprised of Cretaceous to Paleocene granitic rock (brown to tan), while the remainder consists of three limestone terraces of Pleistocene age deposited on the older granitic basement rock. The terraces decrease in age outwards from the western third of the island. The terraces record fluctuating sea levels, thought to be related to glacial advances and retreats during the Pleistocene together with tectonic uplift of the island.

Comparison of aerodynamically and model-derived roughness lengths (zo) over diverse surfaces, central Mojave Desert, California, USA

USGS Publications Warehouse

MacKinnon, D.J.; Clow, G.D.; Tigges, R.K.; Reynolds, R.L.; Chavez, P.S.

2004-01-01

The vulnerability of dryland surfaces to wind erosion depends importantly on the absence or the presence and character of surface roughness elements, such as plants, clasts, and topographic irregularities that diminish wind speed near the surface. A model for the friction velocity ratio has been developed to account for wind sheltering by many different types of co-existing roughness elements. Such conditions typify a monitored area in the central Mojave Desert, California, that experiences frequent sand movement and dust emission. Two additional models are used to convert the friction velocity ratio to the surface roughness length (zo) for momentum. To calculate roughness lengths from these models, measurements were made at 11 sites within the monitored area to characterize the surface roughness element. Measurements included (1) the number of roughness species (e.g., plants, small-scale topography, clasts), and their associated heights and widths, (2) spacing among species, and (3) vegetation porosity (a measurement of the spatial distribution of woody elements of a plant). Documented or estimated values of drag coefficients for different species were included in the modeling. At these sites, wind-speed profiles were measured during periods of neutral atmospheric stability using three 9-m towers with three or four calibrated anemometers on each. Modeled roughness lengths show a close correspondence (correlation coefficient, 0.84-0.86) to the aerodynamically determined values at the field sites. The geometric properties of the roughness elements in the model are amenable to measurement at much higher temporal and spatial resolutions using remote-sensing techniques than can be accomplished through laborious ground-based methods. A remote-sensing approach to acquire values of the modeled roughness length is particularly important for the development of linked surface/atmosphere wind-erosion models sensitive to climate variability and land-use changes in areas such as the southwestern United States, where surface roughness has large spatial and temporal variations. ?? 2004 Elsevier B.V. All rights reserved.

Sand/dust storm processes in Northeast Asia and associated large-scale circulations

NASA Astrophysics Data System (ADS)

Yang, Y. Q.; Hou, Q.; Zhou, C. H.; Liu, H. L.; Wang, Y. Q.; Niu, T.

2008-01-01

This paper introduces a definition of sand/dust storm process as a new standard and idea of sand/dust storm (SDS) groups a number of SDS-events in Northeast Asia. Based on the meteorological data from WMO/GOS network, 2456 Chinese surface stations and NCEP-NCAR reanalysis, the sand/dust storm processes in Northeast Asia in spring 2000-2006 are investigated. And the evolutions of anomalies of general circulation in the troposphere are analyzed by comparing the spring having most and least occurrences of SDS in year 2006 and 2003. Associated with the noticeably increased occurrence of SDS processes in spring 2006, the anomalies in 3-D structure of general circulation especially in the mid-and high latitudes of the Northen Hemisphere (NH) are revealed. The transition period from the winter of 2005 to spring 2006 has witnessed a fast-developed high center over the circumpolar vortex area in the upper troposphere, which pushes the polar vortex more southwards to mid-latitudes with a more extensive area over the east NH. In spring 2006, there are the significant circulation anomalies in the middle troposphere from the Baikal Lake to northern China with a stronger southward wind anomaly over Northeast Asia. Compared with a normal year, stronger meridional wind with a southward wind anomaly also in the lower troposphere prevail over the arid and semiarid regions in Mongolia and northern China during spring 2006. The positive anomalies of surface high pressure registered an abnormal high of 4-10 hPa in the Tamil Peninsular make a stronger cold air source for the repeated cold air outbreak across the desert areas in spring 2006 resulting in the most frequent SDS seasons in the last 10 years in Northeast Asia.

Unsteady Gas Dynamics Problems Related to Flight Vehicles

DTIC Science & Technology

1979-05-01

vertical-axis wind turbines typified by the Darrieus machine (see Cha’. !. Ref. R9 and R10). When cUL.figured in the zero-bending- moment Tropeq.-!n...Performance Data for the Darrieus Wind Turbine with NASA 0012 Blades," Sandia Labs Energy Report, SAND 76-0130, May 1976. R11. Steele, C.R., "Application of...aspect!ratio wings proved often to be unfavorable. Improved steady and unsteady theories were published for the loading of vertical-axis wind turbines

Dust deposits on Mars: The 'parna' analog

NASA Technical Reports Server (NTRS)

Greeley, Ronald; Williams, Steven H.

1994-01-01

Parna is an Autralian aboriginal word meaning 'sandy dust'. It has been applied to deposits of clay, silt, and sand which were initially transported by the wind as aggregates, or pellets, of sand size. Parna is distinguished by its silt and clay content, which in some cases exceeds 85% of the total volume of the deposit. Much of the fine-grained playa silt and clay is incorporated into the parna as sand-sized aggregates, which greatly facilitate their transportation and reworking by the wind. Rain following aggregate emplacement can cause their disintegration, rendering the parna immobile by the wind, yet some pellets can survive several wetting/drying episodes. Parna deposits on Earth occur both as dune forms and as sheet deposits which mantle older terrains. In both cases the deposits are typically derived from lacustrine (lake) beds, such as playas. There is substantial evidence to suggest that bodies of water existed on Mars in the past. Thus, the potential is high for lacustrine deposits and the formation of parna on Mars. Although no parna dunes have been identified, it is suggested that the deposits derived from White Rock (-8 deg, 335 deg W), near Mamers Valles (34 deg, 343 deg W), and elsewhere on Mars may represent sheet parna. Data obtained from Mars-94/96 missions and potential landed spacecraft may provide additional evidence for the existence of parna on Mars.

Security Applications Of Computer Motion Detection

NASA Astrophysics Data System (ADS)

Bernat, Andrew P.; Nelan, Joseph; Riter, Stephen; Frankel, Harry

1987-05-01

An important area of application of computer vision is the detection of human motion in security systems. This paper describes the development of a computer vision system which can detect and track human movement across the international border between the United States and Mexico. Because of the wide range of environmental conditions, this application represents a stringent test of computer vision algorithms for motion detection and object identification. The desired output of this vision system is accurate, real-time locations for individual aliens and accurate statistical data as to the frequency of illegal border crossings. Because most detection and tracking routines assume rigid body motion, which is not characteristic of humans, new algorithms capable of reliable operation in our application are required. Furthermore, most current detection and tracking algorithms assume a uniform background against which motion is viewed - the urban environment along the US-Mexican border is anything but uniform. The system works in three stages: motion detection, object tracking and object identi-fication. We have implemented motion detection using simple frame differencing, maximum likelihood estimation, mean and median tests and are evaluating them for accuracy and computational efficiency. Due to the complex nature of the urban environment (background and foreground objects consisting of buildings, vegetation, vehicles, wind-blown debris, animals, etc.), motion detection alone is not sufficiently accurate. Object tracking and identification are handled by an expert system which takes shape, location and trajectory information as input and determines if the moving object is indeed representative of an illegal border crossing.