The purpose of following project is to study the effect of dust aerosols on the radiative forcing which is directly related to the surface temperature. A single column radiative convective model is used for simulation purpose. A series of simulations have been performed by varying the amount of dust aerosols present in the atmosphere to study the trends in ground temperature, heating rate and radiative forcing for both its longwave and shortwave components. A case study for dust storm is also performed as dust storms are common in Arabian Peninsula. A sensitivity analyses is also performed to study the relationship of surface temperature minimum and maximum against aerosol concentration, single scattering albedo and asymmetry factor. These analyses are performed to get more insight into the role of dust aerosols on radiative forcing.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (p. 295-332).

Yes / This paper re-examines the long-run relationship between radiative forcing (including emissions of carbon dioxide, sulphur oxides, methane, and solar radiation) and temperatures from a structural time series modeling perspective. We assess whether forcing measures are cointegrated with global temperatures using the structural time series approach.

Measurements of the key aerosol properties including light scattering and backscattering coefficients (σsp and σbsp), light absorption coefficient (σap), and particle concentration were made at Summit, Greenland, in the summer of 2011. From these quantities, the single scattering albedo (ω) and angstrom scattering and absorption exponents (åsp, åap) were calculated. In conjunction with these measurements, aerosol optical depth (AOD or τ) and the spectral surface albedo, Rs, were measured. Additionally, the aerosol chemical composition was characterized through snow and air filter analyses. A radiative transfer model was used to estimate the direct aerosol radiative forcing and radiative forcing efficiency using the measurements as inputs. Taken as a whole, this project allowed for the first ever measurement-based characterization of aerosol radiative forcing over central Greenland.

This thesis explores the factors controlling the distribution of black carbon (BC) in the atmosphere/troposphere and its implications for climate forcing. BC is of great climate interest because of its warming potential. Estimates of BC climate forcing have large uncertainty, in part due to poor knowledge of the distribution of BC in the atmosphere. This dissertation first examines the factors controlling the sources of BC in the Arctic in winter and spring using a global chemical transport model (GEOS-Chem). Emission inventories of BC and wet scavenging of aerosols in the model are updated to reproduce observed atmospheric concentrations of BC as well as observed snow BC content in the Arctic in winter-spring. The simulation shows a dominant contribution of fuel (fossil fuel and biofuel) combustion to BC in Arctic spring. Arctic snow BC content is dominated by fuel combustion sources in winter, but has equal contributions from open fires and fuel combustion in spring. The estimated decrease in Arctic snow albedo due to BC deposition in spring is 0.6%, resulting in a regional surface radiative forcing of 1.2 W m-2. The dissertation then extends the evaluation of the BC simulation to the global scale using aircraft observations over source regions, continental outflow and remote regions and ground-based measurements. The observed low BC concentrations over the remote oceans imply more efficient BC removal than is currently implemented in models. The simulation that has total BC emissions of 6.5 Tg C a-1 and a mean tropospheric lifetime of 4.2 days for 2009 (vs. 6.8 &plusmn 1.8 days for the AeroCom models) captures the principal features of observed BC. The simulation estimates a global mean BC absorbing aerosol optical depth of 0.0017 and a top-of-atmosphere direct radiative forcing (DRF) of 0.19 W m-2, with a range of 0.17-0.31 W m-2 based on uncertainties in the BC atmospheric distribution. The DRF is lower than previous estimates, which could be biased high because of excessive BC concentrations over the oceans and in the free troposphere. / Engineering and Applied Sciences

A change in the atmospheric inventory of a greenhouse gas produces a radiative forcing on the atmosphere which results in climatic change. Thus to understand climate change resulting from perturbations to atmospheric greenhouse gas concentrations it is necessary to quantify the radiative forcing. Here, radiative forcings are presented for large changes in atmospheric CO2, CH4, and N2O in the modern atmosphere and large changes in atmospheric CO2, CH4 and 18 other gases for the Archean atmosphere. For the modern Earth, I present new calculations of radiative forcing at very high concentrations of CO2, CH4, and N2O, relevant to extreme anthropogenic climate change and paleoclimate studies. CO2 forcing is calculated over the range 100 ppmv to 50,000 ppmv. CH4, and N2O forcings are calculated over the range 100 ppbv to 100 ppmv. The sensitivity of these calculations to spatial averaging and tropopause definition are examined. I compare our results with the ``simplified expressions'' reported by IPCC, and find significant differences at high greenhouse gas concentrations. I provide new simplified expressions which agree much better with the calculated forcings, and suggest that these expressions be used in place of the IPCC expressions. Additionally, I provide meridionally resolved forcings which may be used to force simple and intermediate complexity climate models. For the Archean Earth, I present new calculations of radiative forcing for CO2 (10^-6 - 1 bar), CH4 (500 ppbv - 10,000 ppmv) and 18 other gases (10 ppbv - 10 ppmv). I aim to provide a set of radiative forcing and overlap calculations which can be used as a standard for comparisons. Radiative forcings are calculated for atmospheres with various N2 inventories (0.5, 1, and 2 bar). The effect of overlap and atmospheric pressure on radiative forcing are examined. The CO2 radiative forcings are consistent with previous work, however, I find significantly more shortwave absorption by CH4 than previously reported which may limit warming above 100 ppmv. For the 18 other gases, I find that significant radiative forcings result from low concentrations (<1 ppmv). These forcings are compared to those given in the literature. / Graduate / 0756 / 0608 / 0725 / bbyrne@uvic.ca

A change in the atmospheric inventory of a greenhouse gas produces a radiative forcing on the atmosphere which results in climatic change. Thus to understand climate change resulting from perturbations to atmospheric greenhouse gas concentrations it is necessary to quantify the radiative forcing. Here, radiative forcings are presented for large changes in atmospheric CO2, CH4, and N2O in the modern atmosphere and large changes in atmospheric CO2, CH4 and 18 other gases for the Archean atmosphere. For the modern Earth, I present new calculations of radiative forcing at very high concentrations of CO2, CH4, and N2O, relevant to extreme anthropogenic climate change and paleoclimate studies. CO2 forcing is calculated over the range 100 ppmv to 50,000 ppmv. CH4, and N2O forcings are calculated over the range 100 ppbv to 100 ppmv. The sensitivity of these calculations to spatial averaging and tropopause definition are examined. I compare our results with the ``simplified expressions'' reported by IPCC, and find significant differences at high greenhouse gas concentrations. I provide new simplified expressions which agree much better with the calculated forcings, and suggest that these expressions be used in place of the IPCC expressions. Additionally, I provide meridionally resolved forcings which may be used to force simple and intermediate complexity climate models. For the Archean Earth, I present new calculations of radiative forcing for CO2 (10^-6 - 1 bar), CH4 (500 ppbv - 10,000 ppmv) and 18 other gases (10 ppbv - 10 ppmv). I aim to provide a set of radiative forcing and overlap calculations which can be used as a standard for comparisons. Radiative forcings are calculated for atmospheres with various N2 inventories (0.5, 1, and 2 bar). The effect of overlap and atmospheric pressure on radiative forcing are examined. The CO2 radiative forcings are consistent with previous work, however, I find significantly more shortwave absorption by CH4 than previously reported which may limit warming above 100 ppmv. For the 18 other gases, I find that significant radiative forcings result from low concentrations (<1 ppmv). These forcings are compared to those given in the literature. / Graduate / 0756 / 0608 / 0725 / bbyrne@uvic.ca

No description available.

Humans have extensively altered terrestrial surfaces through land-use and land-cover change. This change has resulted in increased food, fiber, fuel, and wood that is provisioned by ecosystems to support the human population. Unfortunately, the change has also altered climate through carbon emissions and changes in the surface energy balance. Consequently, maximizing both the provisioning and climate regulation services provided by terrestrial ecosystems is a grand challenge facing a growing global population living in a changing climate. The planting of pine forests for timber and carbon storage and switchgrass fields for bioenergy are two land-cover types that can potentially be used for climate mitigation. Importantly, both are highly productive systems representing contrasts in albedo (grass are brighter than pines) and vegetation height (pines are taller than the grass) along with unknown differences in carbon and water balance that influence local to global climate. Here I use eddy-covariance data to investigate how a transition from a perennial bioenergy crop (switchgrass) to a planted pine plantation alters the local surface temperature, global carbon dioxide concentrations, and global energy balance. First, I found that switchgrass and pine ecosystems have very similar local surface temperatures, especially during the grass growing season. After the switchgrass is harvested, surface temperature in the pine forest is much lower than switchgrass because no vegetation is present to facilitate the evaporation of water. The surface temperature in a bare-ground system (a recent clear-cut) was also high relative to the pine and pre-harvest switchgrass ecosystems. This illustrates the importance of maintaining vegetation cover to reduce local surface temperature. Second, I found that the 30-year mean change in global energy balance (i.e., radiative forcing) from planting a pine ecosystem rather than a switchgrass field was positive (pine warms climate) when considering changes in albedo and carbon measured using eddy-covariance systems. When including harvested carbon, pine and switchgrass can have similar global radiative forcing if all harvested pine carbon is stored, but harvested switchgrass carbon is burned. However, no scenarios I explored resulted in a strong negative radiative forcing by the pine ecosystem relative to the switchgrass field. These results show that afforestation or reforestation in the eastern United States may not result in any climate benefit over planting a switchgrass field. However, the presence of vegetation in both ecosystem types offers a clear benefit by cooling local surface temperatures. / Doctor of Philosophy / Humans are changing the Earth's climate by using oil and gas as fuel that emits greenhouse gases, mainly carbon dioxide, into the atmosphere. Planting trees to reestablish forests is a natural solution for climate change because forests absorb carbon dioxide from the air, but reforestation also changes the Earth's climate in other ways. For example, forests are generally darker than crops and grasses and absorb more sunlight, which traps energy in the atmosphere that can warm global temperature. These non-carbon effects can potentially offset the climate benefit from absorbed carbon dioxide. An alternative natural climate solution is to replace oil and gas with fuels derived from plants, known as bioenergy. Here I compared the local and global climate influence of a tree plantation (loblolly pine) to a bioenergy crop (switchgrass). I found that the local temperature of pine and switchgrass were similar in the summer when the grass was growing, and both were cooler than bare-ground, which was unable to evaporate and transpire water to the atmosphere. Over 30 years, I found that pine and switchgrass absorb similar amounts of carbon. The pine forest absorbs more carbon than switchgrass when it is fully grown but releases carbon during the first five years of growth. As a switchgrass field is brighter than a pine forest, planting a pine forest instead of a switchgrass field warms the Earth's climate. However, assuming no carbon from the harvested trees is released to the atmosphere, the pine and switchgrass have the same influence on global climate. My findings show that a pine plantation and a bioenergy crop can have similar climate benefits when carbon is stored in forests.

Mineral dust aerosol plays an important role in determining the physical and chemical equilibrium of the atmosphere. The radiative balance of the Earth's atmosphere can be affected by mineral dust through both direct and indirect means. Mineral dust can directly scatter or absorb incoming visible solar radiation and outgoing terrestrial IR radiation. Dust particles can also serve as cloud condensation nuclei, thereby increasing albedo, or provide sites for heterogeneous reactions with trace gas species, which are indirect effects. Unfortunately, many of these processes are poorly understood due to incomplete knowledge of the physical and chemical characteristics of the particles including dust concentration and global distribution, as well as aerosol composition, mixing state, and size and shape distributions. Much of the information about mineral dust aerosol loading and spatial distribution is obtained from remote sensing measurements which often rely on measuring the scattering or absorption of light from these particles and are thus subject to errors arising from an incomplete understanding of the scattering processes. The light scattering properties of several key mineral components of atmospheric dust have been measured at three different wavelengths in the visible. In addition, measurements of the scattering were performed for several authentic mineral dust aerosols, including Saharan sand, diatomaceous earth, Iowa loess soil, and palagonite. These samples include particles that are highly irregular in shape. Using known optical constants along with measured size distributions, simulations of the light scattering process were performed using both Mie and T-Matrix theories. Particle shapes were approximated as a distribution of spheroids for the T-Matrix calculations. It was found that the theoretical model simulations differed markedly from experimental measurements of the light scattering, particularly near the mid-range and near backscattering angles. In many cases, in the near backward direction, theoretical models predicted scattering intensities for near spherical particles that were up to 3 times higher than the experimentally measured values. It was found that better agreement between simulations and experiments could be obtained for the visible scattering by using a much wider range of more eccentric particle shapes.