Abstract
The distribution of mineral dust around topographical obstacles is examined, employing the dimensionless Froude number that describes different flow regimes in a fluid. Flow around a peak with a near-circular shape in a dusty environment like the Sahara and the Sahel was examined in order to investigate the distribution of the dust around the obstacle. The Total Ozone Mapping Spectrometer Aerosol Index (TOMS-AI) daily Aerosol Index, the u and v wind components and the temperature, were used for the period 1979-1992, i.e. 14 years. It is found by the AI data that the shape of the dust distribution around the circular peak is in good agreement with the shape of the peak itself. Additionally good correlation exists between the vertical distribution of the dust above the peak and the Froude Number in its vicinity. This method allows for the first time the investigation of the flow above and around topographical obstacles in different flow conditions in the open space employing dust as the flow tracer.
Highlights
Introduction and Scientific BackgroundExtensive research exists about the hydrodynamics of boundary layer flow over complex terrain
It was found that when the Froude number is low, i.e. less than one, the flow regimes are characterized by splitting of the upwind flow (Reisner and Smolarkiewitz, 1994 [4])
The Total Ozone Mapping Spectrometer Aerosol Index (TOMS-AI) daily data were used in order to estimate an index for the total atmospheric column dust amount (Herman et al, 1997 [10])
Summary
Extensive research exists about the hydrodynamics of boundary layer flow over complex terrain. (Dubovik et al, 2008 [6]; Chin et al, 2004 [7]; Jaenicke., 1990 [8]) The purpose of this preliminary study is to examine the distribution of mineral dust around topographical obstacles in order to identify consistent features that may serve as indicators to the effects of various mountainous obstacles as well as the atmospheric stability on the flow dynamics in their vicinity. In this paper we first present the methodology of our research for a near-circular mountain shape, examine the location of the dust minimum around the peak vicinity and its relation to the Fr number. As mentioned above, this is a preliminary study aimed to examine a relatively simple topographic obstacle with a close to a circular shape
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