Browsing by Subject "geosciences, multidisciplinary"
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Item Open Access From divots to swales: Hillslope sediment transport across divers length scales(2010) Furbish, David Jon; Haff, Peter KIn soil-mantled steeplands, soil motions associated with creep, ravel, rain splash, soil slips, tree throw, and rodent activity are patchy and intermittent and involve widely varying travel distances. To describe the collective effect of these motions, we formulate a nonlocal expression for the soil flux. This probabilistic formulation involves upslope and downslope convolutions of land surface geometry to characterize motions in both directions, notably accommodating the bidirectional dispersal of material on gentle slopes as well as mostly downslope dispersal on steeper slopes, and it distinguishes between the mobilization of soil material and the effect of surface slope in giving a downslope bias to the dispersal of mobilized material. The formulation separates dispersal associated with intermittent surface motions from the slower bulk behavior associated with small-scale bioturbation and similar dilational processes operating mostly within the soil column. With a uniform rate of mobilization of soil material, the nearly parabolic form of a hillslope profile at steady state resembles a diffusive behavior. With a slope-dependent rate of mobilization, the steady state hillslope profile takes on a nonparabolic form where land surface elevation varies with downslope distance x as x(a) with a similar to 3/2, consistent with field observations and where the flux increases nonlinearly with increasing slope. The convolution description of the soil flux, when substituted into a suitable expression of conservation, yields a nonlinear Fokker-Planck equation and can be mapped to discrete particle models of hillslope behavior and descriptions of soil-grain transport by rain splash as a stochastic advection-dispersion process.Item Open Access Statistical collapse of stratiform and convective drop diameter distributions at the ground(2010) Ignaccolo, M; De Michele, CThe probability density function of the drop diameter at the ground is investigated during stratiform and convective precipitation intervals at Darwin, Australia. We show how, after a renormalization procedure of the drop diameter, the empirical probability density functions of both types of precipitation collapse in a single curve, indicating the possible existence of an invariant distribution of the drop diameter at the ground. Citation: Ignaccolo, M., and C. De Michele (2010), Statistical collapse of stratiform and convective drop diameter distributions at the ground, Geophys. Res. Lett., 37, L24402, doi:10.1029/2010GL045454.Item Open Access Three-dimensional seismic velocity tomography of Montserrat from the SEA-CALIPSO offshore/onshore experiment(2010) Shalev, E; Kenedi, CL; Malin, P; Voight, V; Miller, V; Hidayat, D; Sparks, RSJ; Minshull, T; Paulatto, M; Brown, L; Mattioli, GThe SEA-CALIPSO experiment in December 2007 incorporated a sea-based airgun source, and seismic recorders both on Montserrat and on the adjacent sea floor. A high quality subset of the data was used for a first arrival P-wave velocity tomographic study. A total of more than 115,000 traveltime data from 4413 airgun shots, and 58 recording stations, were used in this high resolution tomographic inversion. The experiment geometry limited the depth of well resolved structures to about 5 km. The most striking features of the tomography are three relatively high velocity zones below each of the main volcanic centers on Montserrat, and three low velocity zones flanking Centre Hills. We suggest that the high velocity zones represent the solid andesitic cores of the volcano complexes, characterized by wave speeds faster than adjacent volcaniclastic material. The low velocity zones may reflect porous volcaniclastic material and/or alteration by formerly active hydrothermal systems. Citation: Shalev, E., et al. (2010), Three-dimensional seismic velocity tomography of Montserrat from the SEA-CALIPSO offshore/onshore experiment, Geophys. Res. Lett., 37, L00E17, doi: 10.1029/2010GL042498.