The Indian Ocean Experiment (INDOEX) had as a primary objective determining the radiative forcing due to anthropogenic aerosols over climatologically significant space and time scales: the Indian Ocean during the winter monsoon, January-March. During the winter monsoon, polluted, low-level air from the Asian subcontinent blows over the Arabian Sea and Indian Ocean. As part of INDOEX, aerosol optical depths were derived from Advanced Very High Resolution Radiometer (AVHRR) data for the cloud-free ocean regions. The AVHRR radiances were first calibrated using the interior zone of the Antarctic and Greenland ice sheets, which proved to be radiometrically stable calibration targets. Optical depths were derived by matching the observed radiances to radiances calculated for a wide range of optical depths and viewing geometry. Optical depths derived with the AVHRR were compared with those derived with NASA's Aerosol Robotic Network (AERONET) CIMEL instrument at the Center for Clouds, Chemistry, and Climate's Kaashidhoo Observatory, as well as with other surface and shipboard observations taken in the INDOEX region. The retrieved and surface-based optical depths agreed best for a new 2-channel, 2- aerosol model scheme in which the AVHRR observations at O·64 and O·84 microns were used to determine relative amounts of marine and polluted continental aerosol and then the resulting aerosol mixture was used to derive the optical depths. Broadband radiative transfer calculations for the mixture of marine and polluted continental aerosols were combined with the 0·64 and 0·84-micron AVHRR radiances to determine the radiative forcing due to aerosols in the INDOEX region. Monthly composites of aerosol optical depth and top of the atmosphere, surface, and atmospheric radiative forcing were derived from calibrated AVHRR radiances for January-March 1996-2000. An inter-annual variability in the magnitude and spatial extent of high value regions is noted for derived optical depths and radiative forcing, with highest values reached in 1999, particularly in the Bay of Bengal which during the IFP was covered by plumes from Indochina. Frequency distributions of the optical depth for 1⁰ x 1⁰ latitude-longitude regions are well represented by gamma distribution functions. The day-to-day and year-to-year variability of the optical depth for such regions is correlated with the long term average optical depth. Interannual variability of the monthly mean optical depths for such regions is found to be as large as the day to day. / Graduation date: 2001

In this study we investigate the flow of a Boussinesq fluid contained in a rotating, differentially heated spherical shell. Previous work, on the spherical shell of Boussinesq fluid, differentially heated the shell by prescribing temperature on the inner boundary of the shell, setting the temperature deviation from the reference temperature to vary proportionally with -cos 20, from the equator to the pole. We change the model to include an energy balance equation at the earth's surface, which incorporates latitudinal solar radiation distribution and ice-albedo feedback mechanism with moving ice boundary. For the fluid velocity, on the inner boundary, two conditions are considered: stress-free and no-slip. However, the model under consideration contains only simple representations of a small number of climate variables and thus is not a climate model per se but rather a tool to aid in understanding how changes in these variables may affect our planet's climate. The solution of the model is followed as the differential heating is changed, using the pseudo arc-length continuation method, which is a reliable method that can successfully follow a solution curve even at a turning point. Our main result is in regards to hysteresis phenomenon that is associated with transition from one to multiple convective cells, in a dfferentially heated, co-rotating spherical shell. In particular, we find that hysteresis can be observed without transition from one to multiple convective cells. Another important observation is that the transition to multiple convective cells is significantly suppressed altogether, in the case of stress-free boundary conditions on the fluid velocity. Also, the results of this study will be related to our present-day climate. / UOIT

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.

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.

Aerosols are important atmospheric constituents that impact the Earth's radiative balance and climate. The detailed knowledge of the aerosol optical properties is required for a comprehensive analysis of the impacts of aerosols on climate. Mie theory is often used in satellite and ground-based retrieval algorithms to account for atmospheric mineral dust. However, the approximations used in Mie theory are often not appropriate for mineral dust and can lead to errors in the optical properties modeling. Analytic models based on Rayleigh theory that account for particle shapes can offer significant advantages when used to model infrared (IR) extinction of mineral dust. Here, the IR optical properties of some components of mineral dust, authentic dust samples and minerals processed with organic acids were investigated. Detailed characterization of the particles through online and offline methods of analysis that include IR extinction spectroscopy, micro-Raman spectroscopy and scanning electron microscopy was performed. Analysis of the IR extinction spectra and spectral simulations showed that the positions of the peaks and the shapes of the bands of the IR characteristic features are not well simulated by Mie theory in any of the samples studied. The resonance peaks were consistently shifted relative to the experimental spectrum in the Mie simulation. Rayleigh model solutions derived for different particle shapes better predicted the peak positions and band shapes of experimental spectra. To fill the gaps in the refractive index data for atmospherically relevant organic compounds in the IR region optical properties of atmospherically relevant carboxylic acids and humic-like substances using the IR extinction spectra and size distributions measured in the laboratory were determined. In addition to properties of mineral dust this dissertation focuses on properties of sea spray aerosol. Chemical and elemental composition of individual sea spray aerosol particles were studies using micro-Raman spectroscopy, mass-spectrometry and X-ray spectroscopy to provide insights into the biochemical processes that give rise to classes of organic molecules that make up these aerosol particles. The results suggested that degradation of biota (bacteria and diatoms) present in sea water led to lipopolysaccharides and extracellular polymeric substances that further degraded down to carbohydrates and fatty acids. Solubility of the resulting organic species seemed to play a role in their transfer to the aerosol phase. Furthermore, water uptake and hygroscopic growth of multi-component particles were studied. Understanding the interactions of water with atmospheric aerosols is crucial for determining their size, physical state, reactivity, and therefore for aerosol interactions with electromagnetic radiation and clouds. It was determined that particles composed of ammonium sulfate with succinic acid and of mixture of chlorides typical for marine environment show size dependent hygroscopic behavior. Microscopic analysis of the distribution of components within the aerosol particles showed that the observed size dependence is due to the differences in the mixing state. The composition and water uptake properties of sea spray aerosol particles were also measured during a phytoplankton bloom. The results showed that water uptake properties were directly related to the chemical composition of the particles and hygroscopicity decreased with increase in the fraction of water insoluble organic matter emitted during phytoplankton bloom. Finally, multiple methods of particle size, phase and shape analysis were compared and the results showed that the techniques that operate under ambient conditions provide the most relevant and robust measurement of particle size. Additionally, several storage methods for substrate deposited aerosol particles were evaluated and it was determined that storing samples at low relative humidity led to irreversible changes due to sample dehydration while sample freezing and thawing leads to irreversible changes due to phase changes and water condensation. Therefore it is suggested that samples used for single-particles analysis should be stored at ambient laboratory conditions, or near conditions which they were collected, in order to preserve the sample phase and hydration state. The results presented in this dissertation provide insight into physicochemical properties of atmospheric aerosols and help us better understand the role of aerosol particles in the Earth's atmosphere.

The Arctic climate has changed significantly in the last decades, experiencing a dramatic loss of sea ice and stronger than global warming. The Arctic surface temperature and the growth or melt of sea ice is determined by the local surface energy budget. In this context, clouds are of essential importance as they strongly interact with the radiative fluxes and modulate the surface energy budget depending on their properties, the surface types, and atmospheric thermodynamics. For the quantification of changes in the radiative energy budget (REB) associated with the presence or absence of clouds, the concept of cloud radiative forcing (CRF) is commonly used. This concept is defined as the differences between the REB in cloudy and cloud-free conditions, two atmospheric states which can not be observed at the same location and time. Consequently, either radiative transfer simulations or observations in both states have to be related, both of which complicate the derivation of CRF. A review of available studies and their approaches to derive the CRF reveals conceptual differences as well as deficiencies in the handling of radiative processes related to the surface albedo. These findings call into question the current state of CRF assessment in the Arctic based on the few available studies, but also their comparability. By combining atmospheric radiative transfer simulations with a snow albedo model, two processes that control the surface albedo during the transition from cloud-free to cloudy conditions and their role in the derivation of CRF are discussed. The broadband surface albedo of snow surfaces typically increases in the presence of clouds due to a spectral weighting of downward irradiance toward shorter wavelengths. For more absorbing surface types such as white ice and melt ponds, which are common in summer, there is a strong shift between the albedo of direct and diffuse illuminated surface, which diminishes the surface albedo depending on the cloud optical thickness and solar zenith angle. In this thesis, a hypothesis on the impact of those surface-albedo--cloud interactions on the annual cycle of shortwave CRF is discussed, but an application to inner Arctic conditions remains an open issue. An improved method to derive the shortwave CRF is proposed and an application to two airborne campaigns in the marginal sea ice zone northwest of Svalbard (Norway) illustrates the role of surface-albedo--cloud interactions in the Arctic in spring and early summer. For the longwave CRF, conceptual differences and the general interpretation of the different CRF estimates are discussed and illustrated for a case study. Radiative transfer simulations of a rarely observed annual cycle of thermodynamic profiles in the inner Arctic are used to study both longwave CRF approaches and the impact of thermodynamic profiles on the longwave CRF. Making use of airborne low-level flights in the MIZ and other available datasets, common seasonal radiative states on sea ice and case studies of warm air intrusions and cold air outbreaks are illustrated. The CRF is analyzed as a function of the observed cloud/surface regime, which is extended by radiative transfer simulations characterizing the conditions in this region and seasons.

Aerosol–cloud interactions (ACIs) are considered to be the most uncertain driver of present-day radiative forcing due to human activities. The nonlinearity of cloud-state changes to aerosol perturbations make it challenging to attribute causality in observed relationships of aerosol radiative forcing. Using correlations to infer causality can be challenging when meteorological variability also drives both aerosol and cloud changes independently. Natural and anthropogenic aerosol perturbations from well-defined sources provide “opportunistic experiments” (also known as natural experiments) to investigate ACI in cases where causality may be more confidently inferred. These perturbations cover a wide range of locations and spatiotemporal scales, including point sources such as volcanic eruptions or industrial sources, plumes from biomass burning or forest fires, and tracks from individual ships or shipping corridors. We review the different experimental conditions and conduct a synthesis of the available satellite datasets and field campaigns to place these opportunistic experiments on a common footing, facilitating new insights and a clearer understanding of key uncertainties in aerosol radiative forcing. Cloud albedo perturbations are strongly sensitive to background meteorological conditions. Strong liquid water path increases due to aerosol perturbations are largely ruled out by averaging across experiments. Opportunistic experiments have significantly improved process-level understanding of ACI, but it remains unclear how reliably the relationships found can be scaled to the global level, thus demonstrating a need for deeper investigation in order to improve assessments of aerosol radiative forcing and climate change.

The Arctic large-scale circulation is governed by a wide range of factor. In order to investigate the sensitivity of the Arctic large-scale circulation to the regional radiative forcing over Europe, we conducted sensitivity experiments using a state-of-the-art atmosphere-land-ocean coupled model. Using advanced Deep Learning (DL) algorithms, we analyzed the Arctic circulation regimes response to negative radiative forcing anomalies over Europe. We examined different architectures for our DL algorithm to find the most suitable one for our analysis. We simultaneously layer Thickness (300-700-T) and their spatiotemporal patterns with the DL algorithm. The DL algorithm showed good skills in capturing the general structure of the large-scale circulation. The radiative forcing over Europe doesn't seem to induce the occurrence frequency of preferred circulation regimes. / Die arktische großräumige Zirkulation wird von einer Vielzahl von Faktoren bestimmt. Um die Sensitivität der arktischen großräumigen Zirkulation auf den regionalen Strahlungsantrieb über Europa zu untersuchen, haben wir Sensitivitätsexperimente mit einem hochmodernen gekoppelten Atmosphäre-Land-Ozean-Modell untersucht. Unter Verwendung neuer Deep-Learning-Algorithmen (DL) analysierten wir die Reaktion der arktischen Zirkulationsregime auf negativen Strahlungsantriebsanomalien über Europa. Wir haben verhsciedene Architekturen für unseren DL-Algorithmus untersucht, um die am besten geeignete für unsere Analyse zu finden. Wir haben die Felder des mittleren Drucks auf Meeresspiegelniveau und der Schichtdicke von 700 bis 300 hPa und ihre raumzeitlichen Muster mit dem DL-Algorithmus analysiert. Die DL-Algorithmen zeigten gute Ergebnisse bei der Erfassung der allgmeinen Struktur der großräumigen Zirkulation. Der Strahlungsantrieb über Europa scheint der großräumigen Zirkulation keine neuen raumzeitlichen Muster zuzufügen, veränderte aber die Häufigkeit des Auftretens bevorzugter Zirkulationsmuster.