Author
James D. Iversen
Bio: James D. Iversen is an academic researcher from Iowa State University. The author has contributed to research in topics: Wind tunnel & Saltation (geology). The author has an hindex of 28, co-authored 66 publications receiving 3495 citations.
Papers published on a yearly basis
Papers
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01 Jan 1995
TL;DR: In this paper, the authors derived z 0 values for a wide variety of surfaces in the southwestern United States and obtained radar data for these sites in P-band, L-band and C-band (wavelength = 5.6 cm).
Abstract: The transport of windblown sand is controlled by many factors, including wind regime and sediment supply. Surface roughness at the sub-meter scale is also important because it influences both the threshold conditions for particle entrainment and the flux of sand once it is set into motion. In general, increases in surface roughness result in higher threshold speeds for particle movement and decreases in sand fluxes. Aerodynamic roughness (z 0) is the aeolian parameter related to surface roughness and is defined as the height above some mean level at which average wind speed is zero. Values of z 0 are derived from wind measurements through the boundary layer, but few z 0 values have been obtained over natural surfaces because of the expense and limitations of making such measurements. Rather, remote sensing using radar systems has the potential for addressing this problem. In this investigation, we derived z 0 values for a wide variety of surfaces in the southwestern United States and obtained radar data for these sites in P-band (wavelength = 68 cm), L-band (wavelength = 24 cm) and C-band (wavelength = 5.6 cm). We show that there are good correlations among z 0, the RMS height of the surface, and the radar backscatter coefficient, σ0, with the best correlation for L-band HV polarized radar data. This study shows the potential for mapping large regions with radar in order to derive aerodynamic roughness values, which in turn can be used in predictive models of sand transport.
21 citations
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TL;DR: In this article, the merger of two vortices was studied with a laser velocimeter designed to measure the two cross-stream components of velocity, which provided well difined contours of cross-flow velocity, stream function and vorticity.
Abstract: The merger of two vortices was studied with a laser velocimeter designed to measure the two cross-stream components of velocity. Measurements were made at several downstream distances in the vortex wake shed by two semispan wings mounted on the wind tunnel walls. The velocity data provided well difined contours of cross-flow velocity, stream function and vorticity. Downstream of the merger point the vorticity was shown to be independent of the downstream distance for small radii, and at larger radii was dependent on the distance from the wing rather than from the merger point. Upstream of the merger point a multicell vorticity pattern was shown.
17 citations
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TL;DR: In this paper, the authors derived a correlation parameter for analysis of experimental Magnus force data, which is a function of angle of attack, the fineness ratio, and the Reynolds number for finless slender spinning circular cylinders.
Abstract: Time-dependent results of numerical finite-difference solution for the two-dimensional spinning circular cylinder are used to derive a correlation parameter for analysis of experimental Magnus force data. The correlation parameter, which is a function of angle of attack, the fineness ratio, and the Reynolds number, is derived on the basis of the impulse or cross-flow analogy. The correlation parameter, derived for finless slender spinning circular cylinders is shown to successfully correlate experimental data for fineness ratios from 6 to 24, for subsonic through supersonic freestream speeds, and for cross-flow Mach numbers up to 0.4 at transonic and supersonic speeds. Cy = Cyp = d = k = / = M p p t t/oo Uc V x 7 a v p Nomenclature two-dimensional lift coefficient, lift per unit span/(l/2)p Uc2 d local side-force coefficient, side-force per unit span/(l/2)p Uc2 d = Magnus force coefficient, 87/pl/^2 nd2p = body diameter = constant of proportionality = body length = freestream Mach number = spin rate = dimensionless spin rate, pd/211^ = time = freestream speed = component of freestream speed normal to body axis = tangential surface speed due to spin = distance along body axis from nose = Magnus force = angle of attack = kinematic viscosity = air density
14 citations
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13 citations
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TL;DR: In this article, the global distribution of dust aerosol is simulated with the Georgia Tech/Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model.
Abstract: The global distribution of dust aerosol is simulated with the Georgia Tech/Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model. In this model all topographic lows with bare ground surface are assumed to have accumulated sediments which are potential dust sources. The uplifting of dust particles is expressed as a function of surface wind speed and wetness. The GOCART model is driven by the assimilated meteorological fields from the Goddard Earth Observing System Data Assimilation System (GEOS DAS) which facilitates direct comparison with observations. The model includes seven size classes of mineral dust ranging from 0.1–6 μm radius. The total annual emission is estimated to be between 1604 and 1960 Tg yr−1 in a 5-year simulation. The model has been evaluated by comparing simulation results with ground-based measurements and satellite data. The evaluation has been performed by comparing surface concentrations, vertical distributions, deposition rates, optical thickness, and size distributions. The comparisons show that the model results generally agree with the observations without the necessity of invoking any contribution from anthropogenic disturbances to soils. However, the model overpredicts the transport of dust from the Asian sources to the North Pacific. This discrepancy is attributed to an overestimate of small particle emission from the Asian sources.
1,767 citations
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TL;DR: In this article, a soil-derived dust emission scheme was designed to provide an explicit representation of the desert dust sources for the atmospheric transport models dealing with the simulation of the dust cycle.
Abstract: A soil-derived dust emission scheme has been designed to provide an explicit representation of the desert dust sources for the atmospheric transport models dealing with the simulation of the desert dust cycle. Two major factors characterizing the erodible surface are considered: (1) the size distribution of the erodible loose particles of the soil which controls the erosion threshold and the emission strength and (2) the surface roughness which imposes the efficient wind friction velocity acting on the erodible surface. These two parameters are included in a formulation of the threshold wind friction velocity by adapting a size-dependent parameterization proposed by Iversen and White (1982) and by applying to the rough erodible surfaces a drag partition scheme derived from Arya (1975). This parameterization of the threshold friction velocity has been included in an horizontal flux equation proposed by White (1979). This allows to attribute a specific production rate to each soil size range for each type of surface. The dust flux F is then considered as a fraction of the total horizontal flux G, the value of the ratio F/G being imposed, at this time, by the soil clay content. In summary, the computed mass fluxes depend on the soil size distribution, the roughness lengths, and the wind friction velocity. The different steps of this scheme have been independently validated by comparison with relevant experimental data. Globally, the agreement is satisfying, so that the dust fluxes could be retrieved with less uncertainties than those observed in previous simulations of the desert dust cycle.
1,244 citations
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TL;DR: The physics of aeolian saltation, the formation and development of sand dunes and ripples, the physics of dust aerosol emission, the weather phenomena that trigger dust storms, and the lifting of dust by dust devils and other small-scale vortices are reviewed.
Abstract: The transport of sand and dust by wind is a potent erosional force, creates sand dunes and ripples, and loads the atmosphere with suspended dust aerosols This article presents an extensive review of the physics of wind-blown sand and dust on Earth and Mars Specifically, we review the physics of aeolian saltation, the formation and development of sand dunes and ripples, the physics of dust aerosol emission, the weather phenomena that trigger dust storms, and the lifting of dust by dust devils and other small-scale vortices We also discuss the physics of wind-blown sand and dune formation on Venus and Titan
1,175 citations
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TL;DR: The Context Camera (CTX) on the Mars Reconnaissance Orbiter (MRO) is a Facility Instrument (i.e., government-furnished equipment operated by a science team not responsible for design and fabrication) designed, built, and operated by Malin Space Science Systems and the MRO Mars Color Imager team (MARCI) as mentioned in this paper.
Abstract: [1] The Context Camera (CTX) on the Mars Reconnaissance Orbiter (MRO) is a Facility Instrument (i.e., government-furnished equipment operated by a science team not responsible for design and fabrication) designed, built, and operated by Malin Space Science Systems and the MRO Mars Color Imager team (MARCI). CTX will (1) provide context images for data acquired by other MRO instruments, (2) observe features of interest to NASA's Mars Exploration Program (e.g., candidate landing sites), and (3) conduct a scientific investigation, led by the MARCI team, of geologic, geomorphic, and meteorological processes on Mars. CTX consists of a digital electronics assembly; a 350 mm f/3.25 Schmidt-type telescope of catadioptric optical design with a 5.7° field of view, providing a ∼30-km-wide swath from ∼290 km altitude; and a 5000-element CCD with a band pass of 500–700 nm and 7 μm pixels, giving ∼6 m/pixel spatial resolution from MRO's nearly circular, nearly polar mapping orbit. Raw data are transferred to the MRO spacecraft flight computer for processing (e.g., data compression) before transmission to Earth. The ground data system and operations are based on 9 years of Mars Global Surveyor Mars Orbiter Camera on-orbit experience. CTX has been allocated 12% of the total MRO data return, or about ≥3 terabits for the nominal mission. This data volume would cover ∼9% of Mars at 6 m/pixel, but overlapping images (for stereo, mosaics, and observation of changes and meteorological events) will reduce this area. CTX acquired its first (instrument checkout) images of Mars on 24 March 2006.
1,111 citations
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TL;DR: In this article, an extensive review of the physics of wind-blown sand and dust on Earth and Mars is presented, including a review of aeolian saltation, the formation and development of sand dunes and ripples, dust aerosol emission, weather phenomena that trigger dust storms, and the lifting of dust by dust devils and other small-scale vortices.
Abstract: The transport of sand and dust by wind is a potent erosional force, creates sand dunes and ripples, and loads the atmosphere with suspended dust aerosols. This paper presents an extensive review of the physics of wind-blown sand and dust on Earth and Mars. Specifically, we review the physics of aeolian saltation, the formation and development of sand dunes and ripples, the physics of dust aerosol emission, the weather phenomena that trigger dust storms, and the lifting of dust by dust devils and other small-scale vortices. We also discuss the physics of wind-blown sand and dune formation on Venus and Titan.
1,069 citations