Quantifying particle size and turbulent scale dependence of dust flux in the Sahara using aircraft measurements

Philip D. Rosenberg, Douglas J. Parker, Claire L. Ryder, John H. Marsham, Luis Garcia-Carreras, James R. Dorsey, Ian M. Brooks, Angela R. Dean, Jonathon Crosier, James B. McQuaid, Richard Washington

    Research output: Contribution to journalArticlepeer-review

    Abstract

    The first size-resolved airborne measurements of dust fluxes and the first dust flux measurements from the central Sahara are presented and compared with a parameterization by Kok (2011a). High-frequency measurements of dust size distribution were obtained from 0.16 to 300 μm diameter, and eddy covariance fluxes were derived. This is more than an order of magnitude larger size range than previous flux estimates. Links to surface emission are provided by analysis of particle drift velocities. Number flux is described by a -2 power law between 1 and 144 μm diameter, significantly larger than the 12 μm upper limit suggested by Kok (2011a). For small particles, the deviation from a power law varies with terrain type and the large size cutoff is correlated with atmospheric vertical turbulent kinetic energy, suggesting control by vertical transport rather than emission processes. The measured mass flux mode is in the range 30-100 μm. The turbulent scales important for dust flux are from 0.1 km to 1-10 km. The upper scale increases during the morning as boundary layer depth and eddy size increase. All locations where large dust fluxes were measured had large topographical variations. These features are often linked with highly erodible surface features, such as wadis or dunes. We also hypothesize that upslope flow and flow separation over such features enhance the dust flux by transporting large particles out of the saltation layer. The tendency to locate surface flux measurements in open, flat terrain means these favored dust sources have been neglected in previous studies. Key Points Aircraft based, size-resolved, Saharan dust fluxes are measured The eddy covariance method is used with particles up to 300 micrometers Links to terrain, topography and vertical turbulent kinetic energy are discussed

    Original languageEnglish
    Pages (from-to)7577-7598
    Number of pages22
    JournalJournal of Geophysical Research: Atmospheres
    Volume119
    Issue number12
    DOIs
    Publication statusPublished - 27 Jun 2014

    Keywords

    • aircraft measurements
    • eddy covariance flux
    • emission
    • mineral dust
    • subgrid parameterization
    • topography

    Fingerprint

    Dive into the research topics of 'Quantifying particle size and turbulent scale dependence of dust flux in the Sahara using aircraft measurements'. Together they form a unique fingerprint.

    Cite this