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.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000JD000053

Sources and distributions of dust aerosols simulated with the GOCART model

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.

/pdf/modeling-the-atmospheric-dust-cycle-1-design-of-a-soil-2ibugqq5c6.pdf

Modeling the atmospheric dust cycle: 1. Design of a soil-derived dust emission scheme

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

/pdf/the-physics-of-wind-blown-sand-and-dust-4kx7jekt62.pdf

The physics of wind-blown sand and dust

[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.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2006JE002808

Context Camera Investigation on board the Mars Reconnaissance Orbiter

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.

/pdf/the-physics-of-wind-blown-sand-and-dust-4ggy9vm6xy.pdf

New formulations valid for wide ranges of particle diameter and density and gas density are presented for prediction of saltation threshold speed for small particles. A low-air-density wind tunnel was used to extend the range of previous investigations and to separate the effects of Reynolds number and interparticle forces of cohesion. The new formulations are used to predict saltation threshold for atmospheric conditions on the surface of the Earth, Mars, and Venus.

Saltation threshold on Earth, Mars and Venus

This book gives an account of geological aspects of windblown material. Aeolian processes play an important role in modifying the surface of the Earth, and they are also active on Mars. Additionally, they are thought to occur on Venus and possibly Titan as well. The authors describe the following aspects: wind as a geological process, the aeolian environment, physics of particle motion, aeolian abrasion and erosion; aeolian sand deposits and bedforms, interaction of wind and topography and windblown dust. A particular strength of the book is that it deals with aeolian processes in a planetary context, rather than as a purely terrestrial phenomenon. In so doing, the authors ably demonstrate how we can gain better understanding of the Earth through comparative planetology. This paperback reissue will enable the book to be used as a text for advanced students in planetary science. Special terms are defined when they are first used. There is a glossary and an exhaustive bibliography.

Wind as a Geological Process: On Earth, Mars, Venus and Titan

Wind friction threshold speeds for particle movement were determined in a wind tunnel operating at martian surface pressure with a 95 percent CO2 and 5 percent air atmosphere. The relationship between friction speed and free-stream velocity is extended to the critical case for Mars of momentum thickness Reynolds numbers between 425 and 2000. It is determined that the dynamic pressure required to initiate saltation is nearly constant for pressures between 1 bar and 4 mb for atmospheres of both air and CO2.

James D. Iversen

Papers

Saltation threshold on Earth, Mars and Venus

Wind as a Geological Process: On Earth, Mars, Venus and Titan

Threshold windspeeds for sand on Mars: Wind tunnel simulations

Saltation threshold on Mars: The effect of interparticle force, surface roughness, and low atmospheric density

Saltation threshold on Mars - The effect of interparticle force, surface roughness, and low atmospheric density. [from wind-tunnel experiments