University of Maryland, Baltimore County

About: University of Maryland, Baltimore County is a education organization based out in Baltimore, Maryland, United States. It is known for research contribution in the topics: Population & Aerosol. The organization has 8749 authors who have published 20843 publications receiving 795706 citations. The organization is also known as: UMBC.

Spatial heterogeneity in aeolian erodibility: Uniform, topographic, geomorphic, and hydrologic hypotheses

Abstract: [1] Soil aeolian erodibility is the efficiency with which soil produces dust for a given meteorological forcing. Quantifying soil erodibility is crucial for forecasting dust events and the climatological distribution and forcing of dust. We use long-term station observations and satellite indices of mineral dust to ascertain the role of regional topography, geomorphology, and hydrology in controlling sediment availability and erodibility. Our null hypothesis is that soil erodibility is globally uniform, so that emissions are determined by instantaneous local meteorology, vegetation, and soil moisture. We describe and quantify three competing hypotheses on regional processes which may affect local soil erodibility: (1) Erodibility is characterized by the relative elevation of source regions in surrounding basins. (2) Erodibility is characterized by the upstream area from which sediments may have accumulated locally through all climate regimes. (3) Erodibility is characterized by the local present-day surface runoff. These hypotheses are tested in 3-year simulations of the global Dust Entrainment and Deposition (DEAD) model. All three spatially varying erodibility hypotheses produce significantly better agreement with station and satellite data than the null (Uniform) hypothesis. The Uniform hypothesis explains none of the spatial structure of emissions in Australia. Heterogeneous erodibility may explain up to 15–20%, 15–20%, and 50% more of the spatial structure of dust emissions than Uniform erodibility in the Sahara+Arabian Peninsula, East Asia, and Australia, respectively. The Geomorphic erodibility hypothesis performs best overall, but results vary by region and by metric. These results support the hypothesis that dust emission ‘‘hot spots’’ exist in regions where alluvial sediments have accumulated and may be disturbed. Our physically based erodibility hypotheses help explain dust observations in some regions, particularly East Asia, and can be used to help discriminate between natural and anthropogenic soil emissions. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 1625 Global Change: Geomorphology and weathering (1824, 1886); 1815 Hydrology: Erosion and sedimentation; 1824 Hydrology: Geomorphology (1625); KEYWORDS: mineral dust aerosol, arid geomorphology, aeolian processes, hydrologic routing, landscape erodibility

GRB 080503: implications of a naked short gamma-ray burst dominated by extended emission

Abstract: We report on observations of GRB 080503, a short gamma-ray burst (GRB) with very bright extended emission (about 30 times the gamma-ray fluence of the initial spike) in conjunction with a thorough comparison to other short Swift events. In spite of the prompt-emission brightness, however, the optical counterpart is extraordinarily faint, never exceeding 25 mag in deep observations starting at ~1 hr after the Burst Alert Telescope (BAT) trigger. The optical brightness peaks at ~1 day and then falls sharply in a manner similar to the predictions of Li & Paczynski (1998) for supernova-like emission following compact binary mergers. However, a shallow spectral index and similar evolution in X-rays inferred from Chandra observations are more consistent with an afterglow interpretation. The extreme faintness of this probable afterglow relative to the bright gamma-ray emission argues for a very low density medium surrounding the burst (a naked GRB), consistent with the lack of a coincident host galaxy down to 28.5 mag in deep Hubble Space Telescope imaging. The late optical and X-ray peak could be explained by a slightly off-axis jet or by a refreshed shock. Our observations reinforce the notion that short GRBs generally occur outside regions of active star formation, but demonstrate that in some cases the luminosity of the extended prompt emission can greatly exceed that of the short spike, which may constrain theoretical interpretation of this class of events. This extended emission is not the onset of an afterglow, and its relative brightness is probably either a viewing-angle effect or intrinsic to the central engine itself. Because most previous BAT short bursts without observed extended emission are too faint for this signature to have been detectable even if it were present at typical level, conclusions based solely on the observed presence or absence of extended emission in the existing Swift sample are premature.

High aerosol optical depth biomass burning events: A comparison of optical properties for different source regions

Abstract: Received 29 May 2003; revised 8 September 2003; accepted 17 September 2003; published 21 October 2003. [1] The optical properties of aerosols such as smoke from biomass burning vary due to aging processes and these particles reach larger sizes at high concentrations. We compare the spectra of aerosol optical depth (ta), columnintegrated volume size distributions, refractive indices, and single scattering albedo retrieved from AERONET observations for four selected events of very high smoke optical depth (ta � 2 at 500 nm). Two case studies are from tropical biomass burning regions (Brazil and Zambia) and two are cases of boreal forest and peat fire smoke transported long distances to sites in the US and Moldova. Smoke properties for these extreme events can be significantly different from those reported in more typical plumes. In particular, large differences in smoke fine mode particle radius (� 0.17 to 0.25 mm) and single scattering albedo (� 0.88 to 0.99 at 440 nm) were observed as a result of differences in fuels burned, combustion phase, and aging. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation. Citation: Eck, T. F., B. N. Holben, J. S. Reid, N. T. O’Neill, J. S. Schafer, O. Dubovik, A. Smirnov, M. A. Yamasoe, and P. Artaxo, High aerosol optical depth biomass burning events: A comparison of optical properties for different source regions, Geophys. Res. Lett., 30(20), 2035, doi:10.1029/ 2003GL017861, 2003.

“Just give me a number!” Practical values for the social discount rate

Abstract: A major reason the quality of cost-benefit analysis (CBA) varies widely is inconsistent use of the social discount rate (SDR). This article offers guidance about the choice of the SDR. Namely, we recommend the following procedures: If the project is intragenerational (does not have effects beyond 50 years) and there is no crowding out of private investment, then discount all flows at 3.5 percent; if the project is intragenerational and there is some crowding out of investment, then weight investment flows by the shadow price of capital of 1.1 and then discount at 3.5 percent; if the project is intergenerational and there is no crowding out of investment, then use a time-declining scale of discount rates; if the project is intergenerational and investment is crowded out, then convert investment flows during the first 50 years to consumption equivalents using a shadow price of 1.1, and then discount all of these flows at 3.5 percent, and discount all flows after the 50th year using time-declining rates. We then compare current discounting practices of U.S. federal agencies with our estimates. Consistent use of the recommended rates would eliminate arbitrary choices of discount rates and would lead to better public sector decision-making. © 2004 by the Association for Public Policy Analysis and Management.