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Northern Asia (northern + asia)

Distribution by Scientific Domains
Earth and Environmental Science100%

Selected Abstracts

Evaluation of a wind erosion model in a desert area of northern Asia by eddy covariance

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2009
Gerardo Fratini
Abstract For the first time, vertical fluxes of mineral dust measured by Eddy Covariance in two desert sites of Northern Asia have been used to test the performances of a wind erosion model in the field. Soil parameters required by the model were obtained through field and laboratory determinations. Model predictions and direct measurements have been compared. The main finding was that the direction of the horizontal wind relative to the orientation of nebkhas played a crucial role in determining the emission of particles in one of the investigated sites. Being unable to simulate such interaction, the model generally overestimated the actual emission. It provided, instead, reliable predictions (r2 = 0·87) when the wind direction was suitable in detaching loose erodible elements placed on nebkhas thanks to their normal orientation. Copyright © 2009 John Wiley & Sons, Ltd. [source]

The lowermost mantle beneath northern Asia,II.

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2002
Evidence for lower-mantle anisotropy
Summary We have analysed prediffracted S -waves with turning points beneath northern Siberia in a study of anisotropy in the lowermost mantle. Deep-focus earthquakes beneath the Marianas, Izu Bonin and the Sea of Japan recorded at stations in western Europe are used. A correction for upper-mantle anisotropy is applied to the data. Comparisons of the data with synthetic data for models with and without a high velocity D, layer suggest that there is a velocity discontinuity at the top of the D, region and that the style of anisotropy is transversely isotropic in this region. Time separations between S -waves on the radial and transverse component show a weak trend where the separation increases with epicentral distance. A normalization of this separation with the travel distance within D, (300 km thick in this region) suggests that the anisotropy is uniformly distributed within this layer and has an average value of 0.5 per cent. A combination of different studies which investigate the structure of the lowermost mantle beneath Europe and northern Siberia reveals a complicated picture. Tomographic models from this area and evidence of D, anisotropy, lower mantle scatterers, reflections from a D, discontinuity and ultra-low-velocity zones suggest two distinct regions. One exhibits high velocities, D, anisotropy, a D, discontinuity and no evidence of scatterers or ultra-low-velocity zones. These features are likely associated with the palaeosubduction of the Izanagi plate well into the lowermost mantle. The other region has a lower overall velocity and shows evidence of scatterers and ultra-low-velocity zones, perhaps suggesting the presence of partial melt. These results suggest dramatic lateral variations in the nature of the lowermost mantle beneath northern Asia over a length scale of roughly 30 degrees. [source]