A parameterization is presented for turbulence dissipation due to baroclinic tide impacting on abrupt shelf topography that is supercritical with respect to the tide. The parameterization requires knowledge of the topography, stratification, and the remote forcing velocity. Upon impact, the tide cascades to higher vertical modes. Vertical internal modes that are arrested at the crest of the topography in the form of lee waves are assumed to dissipate, while faster modes are assumed to propagate away. The energy flux in each mode is predicted with topography that allows linear numer- ical solutions. The parameterization is tested using high-resolution two-dimensional numerical models of baroclinic tides impinging on an isolated shelf of various heights approximated as a step-function. The recipe is seen to work well compared to numeri- cal simulations of isolated shelves, although it consistently underestimates model flux divergence. Despite low forcing velocities having a more accurate numerical linear solution, the recipe does poorly because it does not accurately predict the modes that become trapped and dissipate. Maximum dissipation occurs when flow is on-shelf and lee waves form, indicating lee waves are the mechanism by which dissipation occurs. / Graduate / 0415

A parameterization is presented for turbulence dissipation due to baroclinic tide impacting on abrupt shelf topography that is supercritical with respect to the tide. The parameterization requires knowledge of the topography, stratification, and the remote forcing velocity. Upon impact, the tide cascades to higher vertical modes. Vertical internal modes that are arrested at the crest of the topography in the form of lee waves are assumed to dissipate, while faster modes are assumed to propagate away. The energy flux in each mode is predicted with topography that allows linear numer- ical solutions. The parameterization is tested using high-resolution two-dimensional numerical models of baroclinic tides impinging on an isolated shelf of various heights approximated as a step-function. The recipe is seen to work well compared to numeri- cal simulations of isolated shelves, although it consistently underestimates model flux divergence. Despite low forcing velocities having a more accurate numerical linear solution, the recipe does poorly because it does not accurately predict the modes that become trapped and dissipate. Maximum dissipation occurs when flow is on-shelf and lee waves form, indicating lee waves are the mechanism by which dissipation occurs. / Graduate / 0415

We have coupled a 3-dimensional physical planetary geostrophic ocean general circulation model to different biological models to investigate the interaction between physical and biological processes. A 1-dimensional particle cycle model with two particle size classes has been developed and coupled to the physical model as well. / The ocean model (Zhang et al., 1992) is based on the planetary geostrophic equations in spherical coordinates. The model equations include the full prognostic temperature and salinity equations. The momentum equations are diagnostic and include geostrophic balance, and a linear friction term in order to provide a western boundary current. The wind stress is applied at the top level of the model. The temperature and salinity distributions used in the surface boundary restoring condition are taken from climatological data. The model domain consists of a flat-bottomed box of 60$ sp circ$ longitude extending between 5$ sp circ$N and 65$ sp circ$N. The horizontal resolution is 2.3$ sp circ$ in both latitude and longitude with 14 levels in the vertical. / The physical model is first coupled to a biological model where new production is given by a restoring condition of surface nitrate towards its observed concentration. The coupled model is used to examine Martin et al.'s (1987) hypothesis that lateral transport and decomposition of slow or non-sinking organic matter can cause a non-local balance between the remineralization rate and the overlying new production rate in open ocean regions. The role of the Gulf Stream in nutrient transport is examined. The model results agree well with the North Atlantic nutrient transport calculated from observed nutrients and hydrographic data. The model results suggest that the thermohaline overturning circulation and the Gulf Stream horizontal recirculation play an important role in the North Atlantic nutrient distribution. / The physical model is then tested in the seasonal mode, and coupled with a biological model which is based on nitrate limiting the rate of new production. The model simulated seasonal oxygen cycle agrees well with the results of observational studies and 1-dimensional model simulations. The oxygen utilization rate below the euphotic zone provides a useful estimate of new production. / A 1-dimensional time dependent particle cycling model with two particle size classes based on Clegg and Whitfield (1990) is then developed. The simulated total organic carbon concentration and large particle flux are consistent with observations and other 1-dimensional model simulations. The downward transport of organic carbon is mainly accomplished by the fast sinking large particles, which comprise a small fraction of the total particulate mass. The steady state version of the particle model is also coupled with the 3-dimensional physical model. The magnitudes of simulated organic carbon flux and total organic matter concentration are comparable with observations.

A thermodynamic-dynamic sea ice model based on the granular material rheology of Tremblay and Mysak is used to study the interannual variability of the Arctic sea ice cover during the 41-year period 1958--1998. The sea ice model is coupled to both a mixed layer ocean model and a one-layer thermodynamic atmospheric model. The model is first run with monthly climatology for most of the thermodynamic and dynamic forcing components to obtain a stable periodic seasonal cycle. For the 41-year run, the monthly wind stress forcing is derived from analyzed sea level pressures from the National Centers for Environmental Prediction (NCEP Reanalysis) data. The atmospheric thermodynamic forcings are based on monthly climatology. / In this thesis we explore the high-latitude sea ice circulation and thickness changes due to year-to-year variations in the wind field. We focus our study on the interannual variability of the sea ice. volume in the Arctic Basin, and the subsequent changes in the export of sea ice from the Arctic Basin into the northern North Atlantic via Fram Strait. (Abstract shortened by UMI.)

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6586. Adviser: Chris R. Rehmann. Includes bibliographical references (leaves 251-261) Available on microfilm from Pro Quest Information and Learning.

<p> Airborne hydrographic surveys are routinely used to create and update nautical charts around the world. This research is intended to assist in maximizing the utility of the data products made available from those surveys in accordance with the current survey&mdash;once, use&ndash;many&mdash;times initiatives. Specifically, this project evaluates the feasibility of using the data available airborne hydrographic systems that utilize bathymetric lasers and hyperspectral sensors to estimate the concentration of suspended particulate matter (SPM). SPM is sometimes also called suspended sediment. The ability to chart spatial distributions of SPM utilizing hydrographic survey systems already in operation will assist researchers, managers, and stakeholders of the areas thus surveyed. </p><p> Ship-based <i>in situ</i> measurements of multiple IOPs at up to twelve wavelengths were gathered in the northern Gulf of Mexico during five cruises between 2009 and 2010. One hundred sixty-nine IOP based SPM models using all available quality-checked data were developed and evaluated for performance. This large number of algorithms allowed for a comparison of the effectiveness of the IOPs that may be derived from airborne hydrographic surveys with other IOPs that may or may not be so readily available. The results were varied. </p><p> The apparent optical property remote sensing reflectance (R_rs) is a data product of hyperspectral sensors that are often part of airborne survey systems. A method to predict suspended particulate matter concentration using the wavelength of maximum intensity for R_rs is presented. This represents a new way to estimate suspended particulate matter concentration from an airborne platform. </p><p> Due to the methods used for gathering the in-situ data, it was necessary to consider the validity of the assumption that consecutive water column profiling events from a ship represent the same sampling environment. Though this research demonstrates that this assumption is false, it does indicate that consecutive profiling events do sample the same water properties in many instances and that with a little care, datasets gathered this way may be used in research efforts similar to this one. Finally, the distribution and selected properties of SPM concentrations in the northern Gulf of Mexico were examined.</p><p>

<p> In this dissertation, Large Eddy Simulations (LES) are used to model the coupled turbulence-reactive tracer dynamics within the upper mixed layer of the ocean. Prior work has shown that LES works well over the spatial and time scales relevant to both turbulence and reactive biogeochemistry. Additionally, the code intended for use is able to carry an arbitrary number of tracer equations, allowing for easy expansion of the species reactions. Research in this dissertation includes a study of 15 idealized non-reactive tracers within an evolving large-scale temperature front in order determine and understand the fundamental dynamics underlying turbulence-tracer interaction in the absence of reactions. The focus of this study, in particular, was on understanding the evolution of biogeochemically-relevant, non-reactive tracers in the presence of both large (~5 km) submesoscale eddies and smallscale (~100 m) wave-driven Langmuir turbulence. The 15 tracers studied have different initial, boundary, and source conditions and significant differences are seen in their distributions depending on these conditions. Differences are also seen between regions where submesoscale eddies and small-scale Langmuir turbulence are both present, and in regions with only Langmuir turbulence. A second study focuses on the examination of Langmuir turbulence effects on upper ocean carbonate chemistry. Langmuir mixing time scales are similar to those of chemical reactions, resulting in potentially strong tracer-flow coupling effects. The strength of the Langmuir turbulence is varied, from no wave-driven turbulence (i.e., only shear-driven turbulence), to Langmuir turbulence that is much stronger than that found in typical upper ocean conditions. Three different carbonate chemistry models are also used in this study: time-dependent chemistry, equilibrium chemistry, and no-chemistry (i.e., non-reactive tracers). The third and final study described in this dissertation details the development of a reduced-order biogeochemical model with 17 state equations that can accurately reproduce the Bermuda Atlantic Time-series Study (BATS) ecosystem behavior, but that can also be integrated within high-resolution LES.</p><p>

For most of the 20th century, multiyear landfast sea ice (MLSI) existed in semi-permanent plugs across Nansen Sound and Sverdrup Channel and formed an incipient ice shelf in Yelverton Bay, Ellesmere Island in the northern CAA. Both plugs broke in 1962 and 1998, and several breakups within the last decade indicate that the plugs are becoming temporary seasonal features. The history of the plugs is reviewed using Canadian Ice Service ice charts, satellite imagery and a literature review. The weather systems associated with plug breakup events are related to a sequence of synoptic patterns, with most breakups occurring when low pressure centers over the Asian side of the Arctic Ocean and a warm pressure ridge develops over the QEI, creating warm temperatures, clear skies, and frequent wind reversals. The 2005 simultaneous breakup of the plugs was accompanied by the removal of 690 km2 of 55-60 year old MLSI from Yelverton Bay. Ground Penetrating Radar (GPR) and ice cores taken in June 2009 provide the first detailed assessment of the remaining MLSI in Yelverton Inlet, which in turn provides ground-truthing of satellite scenes and air photos used to chart historical changes in the MLSI. The last of the Yelverton Bay MLSI was removed in August 2010. The removal of these MLSI features in recent years aligns with the larger trend of reductions in age and thickness of sea ice in the Canadian Arctic Archipelago.

Coupled climate and sea ice variability in the Arctic was investigated using a combination of modern, historical and proxy observations. In the Canadian Arctic, operational sea ice charts were homogenized into a spatially and temporally consistent gridded dataset. A complete climatic analysis of this dataset revealed the presence of dominant modes of sea ice variability related to driving climate patterns and atmospheric circulation indices such as the North Atlantic Oscillation (NAO) and El Nino Southern Oscillation (ENSO). On a hemispheric scale, the late-summer ice cover extent is decreasing at a much faster rate than the maximum winter ice cover. The disappearing perennial ice is partly replaced by seasonal ice, the areal extent of which has increased steadily over the last century. The enhanced seasonal sea ice freeze-thaw cycle is predicted to increase the salinity of surface waters over continental shelves, thereby enhancing haline convection and ventilation of the deeper Arctic Ocean. Coupled sea ice and climate proxies for the North Baffin Bay region were developed from an existing ice core from Devon Ice Cap and a new ice core from the Prince-of-Wales (POW) Icefield on Ellesmere Island. A sea-salt concentration record from the Devon ice core was found to relate with sea ice concentration in nearby Baffin Bay. The record was used to study past sea ice conditions in Baffin Bay over the last 200 years in relation with temperature proxies (melt %, delta18O). Sea ice extent variations in northern Baffin Bay appear to be mostly dynamically driven, with sea ice decreasing when Nares Strait becomes congested with ice from the Arctic Ocean, and northerly winds advect ice from Baffin Bay southward. A new high-resolution melt record was developed using digital image analysis of the POW ice core. The record was used to show that melting affects the solid conductivity signal of the core, which compromises dating by seasonal layer counting, and hinders the identification of acidic volcanic horizons. The POW melt record, a proxy for summer warmth, was shown to be site-specific, which may be explained by the close presence of the North Open Water polynya and the peculiar position of the ice cap which rests on the shifting boundary between the maritime climate of Baffin Bay and the drier, colder climate of the high Arctic. The long-term, natural variability of late-summer Arctic sea ice was reconstructed from a network of 68 climate proxies from the circum-Arctic region. The proxy network contains both a temperature and a sea ice signal. Past sea ice extent was reconstructed using multivariate statistical calibration of the network against historical sea ice observations over the last century. The record shows that the decline in sea ice extent of the last two decades is anomalous in the context of the last 900 years. Non-linear processes are responsible for much of the variability in ice extent over the past millennium, and the same processes may be enhancing the greenhouse gas-induced decrease in ice extent currently observed.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1982. / Microfiche copy available in Archives and Science / Bibliography: leaves 40-41. / by Eduardo Pantig Olaguer. / M.S.