44 research outputs found

    Estimating aerodynamic roughness over complex surface terrain

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    Surface roughness plays a key role in determining aerodynamic roughness length (zo) and shear velocity, both of which are fundamental for determining wind erosion threshold and potential. While zo can be quantified from wind measurements, large proportions of wind erosion prone surfaces remain too remote for this to be a viable approach. Alternative approaches therefore seek to relate zo to morphological roughness metrics. However, dust-emitting landscapes typically consist of complex small-scale surface roughness patterns and few metrics exist for these surfaces which can be used to predict zo for modeling wind erosion potential. In this study terrestrial laser scanning was used to characterize the roughness of typical dust-emitting surfaces (playa and sandar) where element protrusion heights ranged from 1 to 199 mm, over which vertical wind velocity profiles were collected to enable estimation of zo. Our data suggest that, although a reasonable relationship (R2 > 0.79) is apparent between 3-D roughness density and zo, the spacing of morphological elements is far less powerful in explaining variations in zo than metrics based on surface roughness height (R2 > 0.92). This finding is in juxtaposition to wind erosion models that assume the spacing of larger-scale isolated roughness elements is most important in determining zo. Rather, our data show that any metric based on element protrusion height has a higher likelihood of successfully predicting zo. This finding has important implications for the development of wind erosion and dust emission models that seek to predict the efficiency of aeolian processes in remote terrestrial and planetary environments

    A vertical profile of PM10 dust concentrations measured during a regional dust event identified by MODIS Terra, western Queensland, Australia

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    Accurate determination of the spatiotemporal properties of dust plumes and their dust concentrations is essential for calibration of satellite products and the initialization and validation of numerical models that simulate the physical properties and affects of dust events. In this paper, we present a 500 m vertical profile of PM10 dust concentrations measured during a regional dust event in western Queensland, Australia. PM10 dust concentrations within the haze were found to be >20 times background ambient values and decreased with height following an exponential function. We apply an over-land algorithm to MODIS Terra satellite images of the dust haze to enhance its visual appearance against the bright land surface and define its size. In conjunction with the measured attenuation of dust concentrations with height we calculate the PM10 dust load of the plume to be ∌60% of that which would have been calculated assuming a constant dust concentration up to the dust ceiling height. Results extend previous findings from tower-based studies made close to the surface and confirm that atmospheric dust concentrations decrease rapidly with increasing height, thereby enabling more accurate calculation of atmospheric dust loads during synoptic-scale dust outbreaks

    Integrated Spatiotemporal Characterization of Dust Sources and Outbreaks in Central and East Asia

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    The potential of atmospheric dust aerosols to modify the Earth's environment and climate has been recognized for some time. However, predicting the diverse impact of dust has several significant challenges. One is to quantify the complex spatial and temporal variability of dust burden in the atmosphere. Another is to quantify the fraction of dust originating from human-made sources. This thesis focuses on the spatiotemporal characterization of sources and dust outbreaks in Central and East Asia by integrating ground-based data, satellite multi-sensor observations, and modeling. A new regional dust modeling system capable of operating over a span of scales was developed. The modeling system consists of a dust module DuMo, which incorporates several dust emission schemes of different complexity, and the PSU/NCAR mesoscale model MM5, which offers a variety of physical parameterizations and flexible nesting capability. The modeling system was used to perform for the first time a comprehensive study of the timing, duration, and intensity of individual dust events in Central and East Asia. Determining the uncertainties caused by the choice of model physics, especially the boundary layer parameterization, and the dust production scheme was the focus of our study. Implications to assessments of the anthropogenic dust fraction in these regions were also addressed. Focusing on Spring 2001, an analysis of routine surface meteorological observations and satellite multi-sensor data was carried out in conjunction with modeling to determine the extent to which to this integrated data set can be used to characterize the spatiotemporal distribution of dust plumes at a range of temporal scales, addressing the active dust sources in China and Mongolia, mid-range transport and trans-Pacific, long-range transport of dust outbreaks on a case-by-case basis. This work demonstrates that adequate and consistent characterization of individual dust events is central to establishing a reliable climatology, ultimately leading to improved assessments of dust impacts on the environment and climate. This will also help to identify the appropriate temporal and spatial scales for adequate intercomparison between model results and observational data as well as for developing an integrated analysis methodology for dust studies.Ph.D.Committee Chair: Irina Sokolik; Committee Member: Derek Cunnold; Committee Member: Irina Petropavlovskikh; Committee Member: Judith Curry; Committee Member: Robert Dickinso

    Development of a physically based dust emission module within the Weather Research and Forecasting (WRF) model: Assessment of dust emission parameterizations and input parameters for source regions in Central and East Asia

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    International audience[1] Significant problems with modeling dust emission are highlighted. Not only do dust emission schemes rely on various assumptions, but also their implementation within a regional or global model presents challenges. This paper provides an in-depth comparative analysis of two different physically based schemes that were originally developed by Marticorena and Bergametti (1995) and Shao et al. (1996) with some recent improvements. Both schemes were implemented in a dust module (DuMo) and coupled with the Weather Research and Forecasting (WRF) model. Here we examine the physical parameterizations employed by these schemes, identify the key input parameters, and establish linkages between them by developing a new data set for dust sources in Central and East Asia. The relative importance of the input parameters is assessed through partial derivatives. The major issues involved in implementing the physically based schemes within a regional model are also discussed. Consistent implementation of two state-of-the-art dust schemes within the same regional model enables us to bracket inherent uncertainties in simulated dust emission. The results of a case study based on WRF-DuMo simulations are presented to demonstrate associated biases in the magnitude and spatial patterns of emitted dust vertical fluxes. Also, recommendations on the selection of input parameters, including land and meteorological variables, to achieve an improved modeling of dust emission in Central and East Asia are provided

    Drought-sensitivity of fine dust in the U.S. Southwest: Implications for air quality and public health under future climate change

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    We investigate the present-day sensitivity of fine dust levels in the U.S. Southwest to regional drought conditions and use the observed relationships to assess future changes in fine dust levels and associated health impacts under climate change. Empirical Orthogonal Function analysis reveals that the most dominant mode of fine dust interannual variability for each season consists of a pattern of large-scale co-variability across the Southwest. This mode is strongly correlated to the Standardized Precipitation-Evapotranspiration Index (SPEI) accumulated over 1-6 months in local and surrounding regions spanning the major North American deserts. Across the seasons, a unit decrease in 2-month SPEI averaged over the U.S. Southwest and northern Mexico is significantly associated with increases in Southwest fine dust of 0.22-0.43 ÎŒg m-3. We apply these sensitivities to statistically downscaled meteorological output from 22 climate models following two Representative Concentration Pathways (RCPs), and project future increases in seasonal mean fine dust of 0.04-0.10 ÎŒg m-3 (5-8%) under RCP2.6 and 0.15-0.55 ÎŒg m-3 (26-46%) under RCP8.5 relative to the present-day (2076-2095 vs. 1996-2015). Combined with the same projections of future population and baseline incidence rates, annual premature mortality attributable to fine dust exposure could increase by 140 (24%) deaths under RCP2.6 and 750 (130%) deaths under RCP8.5 for adults aged ≄30 years, and annual hospitalizations due to cardiovascular and respiratory illnesses could increase by 170 (59%) admissions under RCP2.6 and 860 (300%) admissions under RCP8.5 for adults aged ≄65 years in the Southwest relative to the present-day. Our results highlight a climate penalty that has important socioeconomic and policy implications for the U.S. Southwest but is not yet widely recognized
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