Geologic records and climate model simulations suggest that changes in the meridional heat transport in the Atlantic Ocean were involved in the abrupt warming events – the so-called Dansgaard-Oeschger Interstadials (DOIs) – that punctuated an otherwise cold Greenland climate during the last glacial period. However, the role of Northern Hemisphere (NH) ice sheets in these events remains a subject of controversy. Here we report on the first attempt to combine quantitatively a paleo-temperature proxy with simplified ocean models, with the specific purpose of extracting information about the changes in mass balance of the NH ice sheets during the last glaciation. A Greenland paleotemperature record is combined with the climate models using Bayesian Stochastic Inversion (BSI) in order to estimate the changes that would be required to alter the Atlantic Ocean mass and heat transports between ~30 and 39 thousand years ago. The mean sea level changes implied by changes in NH ice sheet mass balance agree in amplitude and timing with reconstructions from the geologic record, which gives some support to the freshwater forcing hypothesis. Our results are unaffected by uncertainties in the representation of vertical buoyancy transport in the tropical ocean, in large part because the global adjustments to high latitude freshening bypass the tropics and affect sinking rate in the opposite pole. However, the solutions are sensitive to assumptions about physical processes at polar latitudes. We find that the inversion reproduces the gradual changes in sea level and Antarctic temperature inferred from the independent evidence provided by proxy records. The Greenland warm event lasting over 3000 years (DOI 8) can be explained by sustained growth of NH ice sheet and reduced supply of icebergs to the North Atlantic. Our results indicate a more involved role of the NH ice sheets than previously thought, in which both collapse and subsequent growth would be required to explain the full series of the long (> 3000 years) warm events recorded in Greenland ice. / text

No description available.

Mineral dust aerosols, the tiny soil particles in the atmosphere, play a key role in the atmospheric radiation budget through their radiative and cloud condensation nuclei effects. It is therefore important to evaluate the radiative forcing of mineral dust and subsequent changes in atmospheric dynamics. The Weather Research and Forecasting with Chemistry (WRF/Chem) regional model with the integrated dust modules and available observations have been used to investigate the three-dimensional distribution of mineral dust over Australia. Additionally, the WRF/Chem model was used to estimate the direct radiative forcing by mineral dust over Australia. Particular emphasize has been given to direct radiative feedback effect of mineral dust on boundary layer dynamics. Two dust emission schemes embedded within the WRF/Chem model have been utilized in this study: the dust transport (DUSTRAN) and the Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) schemes. The refractive index of mineral dust depends on the mineralogy, size and composition of dust over a given region. The refractive index of mineral dust for shortwave radiation was considered to be wavelength independent and set based on previous mineralogical studies over North Africa and Australia. However, the refractive index of mineral dust for longwave radiation was considered to be wavelength dependent and to vary for 16 longwave spectral bands. Model results were compared with observations to validate the performance of the model, including satellite datasets from the Moderate Resolution Imaging Spectroradiometer (MODIS), Multi-angle Imaging SpectroRadiometer (MISR) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), as well as ground-based measurements obtained from air quality monitoring sites over Australia. The major results can be summarized as follows: (1) Lake Eyre Basin is the most important source of dust in Australia, with a peak activity identified to be during austral spring and summer, and dust emission within the basin is often associated with the passage of dry cold fronts; (2) Mineral dust from Lake Eyre Basin can be transported long distances to southeastern Australia in association with eastward propagating frontal systems, reaching as far as New Zealand and beyond, and to northern tropical Australia by postfrontal southerly winds, and subsequently towards northwestern Australia and the Indian Ocean by southeasterly trade winds; (3) Australian dust plumes are mainly transported in the lower atmosphere, although variation of boundary layer depth during the passage of cold frontal systems, as well as ascending motion at the leading edge of these systems and descending motion where postfrontal anticyclonic circulation is dominant contribute to the vertical extent of mineral dust aerosols; (4) the shortwave direct radiative effect of mineral dust results in cooling of the atmosphere from the surface to near the boundary layer top, but warming of the boundary layer top and lower free atmosphere; (5) changes in the vertical profile of temperature result in an overall decrease of wind speed in the lower boundary layer and an increase within the upper boundary layer and lower free atmosphere; (6) the longwave warming effect of mineral dust partly offsets its shortwave cooling effect at the surface. This compensation is significantly larger over and immediately downwind of dust source regions where coarse particles are more abundant, as they have stronger interaction with longwave radiation emitted from the Earth’s surface; (7) both shortwave and longwave radiative forcing by mineral dust was found to have a diurnal variation in response to changes in solar zenith angle and in the intensity of longwave radiation, respectively; (8) the absorptive nature of dust was shown to be associated with the shortwave heating of the atmosphere; (9) on the other hand, longwave cooling of the atmosphere was identified because absorption of longwave radiation by dust is less than its emission to the surface and top of the atmosphere (TOA).

This dissertation deals with spectral measurements of solar radiation in the visible and near infrared wavelength range. The data were collected during a field campaign on the Cape Verde Islands in January / February 2008 within the DFG research group SAMUM 2 (Saharan Mineral Dust Experiment). During this campaign airborne measurements of upward radiances and irradiances were performed over aerosol layers. Since the Cape Verde Islands are in the advection area of air masses from the Sahara region northeast of the islands and from regions with bush fires from the southeast, the sampled aerosol mainly consists of mineral dust, biomass burning smoke or a mixture of both. These radiation measurements and airborne lidar measurements of aerosol extinction coefficients were used to calculate the dust radiative forcing at the top of atmosphere with an one-dimensional radiative transfer model. This required the spectral surface albedo and aerosol optical properties, determined by model retrievals. The dependence of the calculated dust radiative forcing on the aerosol optical thickness was used to distinguish between aerosol distributions with mineral dust only or mixed with biomass burning smoke. This mainly model-based method was compared with another mainly measurement-based method, which requires the net radiation at the flight altitude and its dependence on the aerosol optical thickness to distinguish between the different aerosol distributions. The mainly model-based method shows no differences between the calculated radiative forcings of aerosols mainly consisting of mineral dust and those mixed with biomass burning smoke due to high uncertainties. In contrast to the mainly model-based method, the mainly measurement-based method shows clear differences between aerosols with and without biomass burning smoke. Thus the mainly measurement-based method is the preferred method, because it omits the retrieval of the aerosol optical properties, which leads to high uncertainties, in contrast to the mainly model-based method.

The ocean emission and subsequent oxidation of dimethylsulfide (DMS) provides a source of sulfate in the atmosphere, potentially affecting the amount of solar radiation reaching the Earth's surface through both direct and indirect radiative effects of sulfate aerosols. DMS in the ocean can be quite variable with season and location, which in turn leads to high spatial and temporal variability of ocean DMS emissions. This study tested currently available observational and empirically-based climatologies of DMS concentration in the surface ocean. The exploration of the existing parameterizations mainly reveals the limitations of estimating DMS with an empirical model based on variables such as chlorophyll and mixed layer depth. The different algorithms show significant differences in spatial pattern, and none correlate strongly with observations. There is considerable uncertainty both in terms of the spatiotemporal distribution in DMS concentration and flux, as well as in the global total DMS flux. The present research investigates the influence of DMS on sulfate aerosols and radiative fluxes given different DMS climatologies in the fourth generation of the Canadian Global Atmospheric Climate Model (CanAM4.1). In general, the response in the radiative flux seems to follow the variation in the global mean flux of DMS linearly. Differences in the spatial and temporal structure of oceanic DMS have only a secondary effect on the radiative changes. The overall response of the atmosphere to the presence or absence of structure of DMS in space and time is distinctly smaller compared to the possible uncertainty of this response associated with the magnitude of the annually averaged global flux. / Graduate / 0425 / 0725 / 0416 / jetesdal@uvic.ca

Demand for intercity transportation has increased significantly in the past decades and is expected to continue to follow this trend in the future. In the meantime, concern about the environmental impact and potential climate change associated with this demand has grown, resulting in an increasing importance of climate impact considerations in the overarching issue of sustainability. This results in discussions on new regulations, policies and technologies to reduce transportation's climate impact. Policies may affect the demand for the different transportation modes through increased travel costs, increased market share of more fuel efficient vehicles, or even the introduction of new modes of transportation. However, the effect of policies and technologies on mobility, demand, fleet composition and the resulting climate impact remains highly uncertain due to the many interdependencies. This motivates the creation of a parametric modeling and simulation environment to explore a wide variety of policy and technology scenarios and assess the sustainability of transportation. In order to capture total transportation demand and the potential mode shifts, a multimodal approach is necessary. The complexity of the intercity transportation System-of-Systems calls for a hybrid Agent-Based Modeling and System Dynamics paradigm to better represent both micro-level and macro-level behaviors. Various techniques for combining these paradigms are explored and classified to serve as a hybrid modeling guide. A System Dynamics approach is developed, that integrates socio-economic factors, mode performance, aggregated demand and climate impact. It is used to explore different policy and technology scenarios, and better understand the dynamic behavior of the intercity transportation System-of-Systems. In order to generate the necessary data to create and validate the System Dynamics model, an Agent-Based model is used due to its capability to better capture the behavior of a collection of sentient entities. Equivalency of both models is ensured through a rigorous cross-calibration process. Through the use of fleet models, the fuel burn and life cycle emissions from different modes of transportation are quantified. The radiative forcing from the main gaseous and aerosol species is then obtained through radiative transfer calculations and regional variations are discussed. This new simulation environment called the environmental Ground and Air Mode Explorer (eGAME) is then used to explore different policy and technology scenarios and assess their effect on transportation demand, fleet efficiencies and the resulting climate impact. The results obtained with this integrated assessment tool aim to support a scenario-based decision making approach and provide insight into the future of the U.S. transportation system in a climate constrained environment.

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 70-74). Also available on the World Wide Web.

A presente dissertação é dedicada ao exame da terceira fase da Análise de Discurso, representada, predominantemente, como uma fase desconstrutiva e como indicadora de ainda incertos novos procedimentos de análise. Buscou-se, mediante o exame sistemático das teses apresentadas por Pêcheux em seus últimos escritos, definir tanto os termos mediante os quais se deu essa desconstrução quanto caracterizar positivamente as reordenações atinentes ao objeto, propósito e metodologia da AD neste período. / This thesis is devoted to the consideration of the third phase of the Discourse Analysis, represented predominantly as a deconstructive phase and as an indicator of still uncertain new analytical procedures. We sought, through systematic examination of the the views put forward by Pêcheux in his later writings, set up both the terms by which this deconstruction was made and positively characterize the reordering relating to the object, purpose and methodology of the AD.

A presente dissertação é dedicada ao exame da terceira fase da Análise de Discurso, representada, predominantemente, como uma fase desconstrutiva e como indicadora de ainda incertos novos procedimentos de análise. Buscou-se, mediante o exame sistemático das teses apresentadas por Pêcheux em seus últimos escritos, definir tanto os termos mediante os quais se deu essa desconstrução quanto caracterizar positivamente as reordenações atinentes ao objeto, propósito e metodologia da AD neste período. / This thesis is devoted to the consideration of the third phase of the Discourse Analysis, represented predominantly as a deconstructive phase and as an indicator of still uncertain new analytical procedures. We sought, through systematic examination of the the views put forward by Pêcheux in his later writings, set up both the terms by which this deconstruction was made and positively characterize the reordering relating to the object, purpose and methodology of the AD.

A presente dissertação é dedicada ao exame da terceira fase da Análise de Discurso, representada, predominantemente, como uma fase desconstrutiva e como indicadora de ainda incertos novos procedimentos de análise. Buscou-se, mediante o exame sistemático das teses apresentadas por Pêcheux em seus últimos escritos, definir tanto os termos mediante os quais se deu essa desconstrução quanto caracterizar positivamente as reordenações atinentes ao objeto, propósito e metodologia da AD neste período. / This thesis is devoted to the consideration of the third phase of the Discourse Analysis, represented predominantly as a deconstructive phase and as an indicator of still uncertain new analytical procedures. We sought, through systematic examination of the the views put forward by Pêcheux in his later writings, set up both the terms by which this deconstruction was made and positively characterize the reordering relating to the object, purpose and methodology of the AD.