The production of temperature and salinity variance and covariance : implications for mixing

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2013Large-scale thermal forcing and freshwater fluxes play an essential role in setting temperature and salinity in the ocean. A number of recent estimates of the global oceanic freshwater balance as well as the global oceanic surface net heat flux are used to investigate the effects of heat- and freshwater forcing at the ocean surface. Such forcing induces changes in both density and density-compensated temperature and salinity changes (’spice’). The ratio of the relative contributions of haline and thermal forcing in the mixed layer is maintained by large-scale surface fluxes, leading to important consequences for mixing in the ocean interior. In a stratified ocean, mixing processes can be either along lines of constant density (isopycnal) or across those lines (diapycnal). The contribution of these processes to the total mixing rate in the ocean can be estimated from the large-scale forcing by evaluating the production of thermal variance, salinity variance and temperature-salinity covariance. Here, I use new estimates of surface fluxes to evaluate these terms and combine them to generate estimates of the production of density and spice variance under the assumption of a linear equation of state. As a consequence, it is possible to estimate the relative importance of isopycnal and diapycnal mixing in the ocean. While isopycnal and diapycnal processes occur on very different length scales, I find that the surface-driven production of density and spice variance requires an approximate equipartition between isopycnal and diapycnal mixing in the ocean interior. In addition, consideration of the full nonlinear equation of state reveals that surface fluxes require an apparent buoyancy gain (expansion) of the ocean, which allows an estimate of the amount of contraction on mixing due to cabbeling in the ocean interior.The author would like to acknowledge support from the National Aeronautics and Space Administration, grant #NNX12AF59G and the National Science Foundation, grant #OCE-0647949

Visualization of gas-liquid mass transfer and wake structure of rising bubbles using pH-sensitive PLIF

A planar laser-induced fluorescence (PLIF) technique for visualizing gas–liquid mass transfer and wake structure of rising gas bubbles is described. The method uses an aqueous solution of the pH-sensitive dye Naphthofluorescein and CO2 as a tracer gas. It features a high spatial resolution and frame rates of up to 500 Hz, providing the ability to capture cinematographic image sequences. By steering the laser beam with a set of two programmable scanning mirrors, sequences of three-dimensional LIF images can be recorded. The technique is applied to freely rising bubbles with diameters between 0.5 and 5 mm, which perform rectilinear, oscillatory or irregular motions. The resulting PLIF image sequences reveal the evolution of characteristic patterns in the near and far wake of the bubbles and prove the potential of the technique to provide new and detailed insights into the spatio-temporal dynamics of mass transfer of rising gas bubbles. The image sequences further allow the estimation of bubble size and rise velocity. The analysis of bubble rise velocities in the Naphthofluorescein solution indicates that surfactant-contaminated conditions are encountered

The global oceanic freshwater cycle : a state-of-the-art quantification

Author Posting. © Sears Foundation for Marine Research, 2010. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 68 (2010): 569-595, doi:10.1357/002224010794657164.The current capabilities of quantifying the oceanic freshwater cycle are shown based on new observations from satellite data and re-analysis models for evaporation and precipitation over the ocean. For this purpose, we analyze the homogeneity and internal consistency of eight evaporation and seven precipitation products. Discontinuities are found around 1987 for all datasets, attributable to the launch of a microwave imaging satellite. Based on a review of comparisons with independent data and these analyses, the Global Precipitation Climatology Project (GPCP) and the Objectively Analyzed Ocean-Atmosphere Fluxes (OAFlux) evaporation product are combined with a state-of-the-art river discharge dataset to produce a new estimate of the global oceanic freshwater cycle for 1987-2006. The annual mean precipitation into the ocean averaged over 19 years is estimated at 12.2±1.2 Sv, the evaporative loss at 13.0±1.3 Sv, and the total freshwater input from land at 1.25±0.1 Sv. The oceanic budget closes within the errors estimated for each data set with an imbalance of 0.5±1.8 Sv. Based on this quantification, the global patterns of oceanic freshwater fluxes are described and a global mean is integrated to provide estimates of freshwater fluxes between basins. We find the Atlantic to be less evaporative and the Pacific less precipitative than previous in-situ estimates.The authorswould like to acknowledge support from the National Science Foundation, grant #OCE-0647949

Urban-Rural Gradient Analysis of Amount and Distribution of Carbon and Nitrogen in Soils of Kumasi Region, Ghana

While urbanisation is a global phenomenon, cities in developing countries exhibit particularly high levels of growth in recent years. In Ghana, this phenomenon of rapid growth from 31% of the people living in urban areas in 1984 to 51% urban population in 2010 has created expansive urban forms, impacting natural resources. The aim of this study is to analyse some of the impacts on soils of this rapid urban development. A stratified random sampling design was used to sample soils from 70 maize fields on Acrisols within the area of Kumasi, which was urban already in 1986, and other areas that became urban later. Rural maize fields and forests were also sampled. Three replicates were taken at each site of maize mono-crop and/or mixed-crop subsistence farms to keep consistency. Topsoil samples (0-10 cm depth) were taken volumetrically in 250 cm3 steel cylinders. The samples are currently analysed for soil pH, and for C and N by use of a Leco TruSpec CHN analyser. An ANOVA will be calculated to analyse the differences in means between urban and non-urban areas. A variogram will then be fitted to characterise spatial correlations in the urban to rural continuum of C and N amounts, and consequently mapped out. We hypothesise that C and N contents of soils under maize in urbanised areas of Kumasi exceed those of comparable soils and land-use in adjacent rural areas as reported by Bellwood-Howard et al. 2015, for other West-African cities. Among other reasons, disposal of household waste including organic materials, which is generally practised in urban Ghana due to inadequate waste management, is expected to increase C and N contents. We suggest that urban farms, if well-coordinated into urban planning and management, can provide a viable source of food security to urban dwellers in developing countries. Although analyses of additional parameters are needed pH as well as C and N amounts already provide relevant information on the critical role urbanisation play in the sustainable development of cities in Ghana

Morphology and Oxygen Sensor Response of Luminescent Ir-Labeled Poly(dimethylsiloxane)/Polystyrene Polymer Blend Films

Polymer films consisting of a linear poly(dimethylsiloxane) end-functionalized with a luminescent Ir(III) complex (Ir−PDMS), blended with polystyrene (PS), function as optical oxygen sensors. The sensor response arises by quenching of the luminescence from the Ir(III) chromophore by oxygen that permeates into the polymer film. The morphology and luminescence oxygen sensor properties of blend films consisting of Ir−PDMS and PS have been characterized by fluorescence microscopy, atomic force microscopy, and scanning electron microscopy. The investigations demonstrate that microscale phase segregation occurs in the films. In blends that contain a relatively small amount of Ir−PDMS in PS (ca. 10 wt %), the Ir−PDMS exists as circular domains, with diameters ranging from 2 to 5 μm, surrounded by the majority PS phase. For larger weight fractions of Ir−PDMS in the blends, the film morphology becomes bicontinuous. A novel epifluorescence microscopy method is applied that allows the construction of Stern−Volmer quenching images that quantify the oxygen sensor response of the blend films with micrometer spatial resolution. These images provide a map of the oxygen permeability of the polymer blend films with a spatial resolution of ca. 1 μm. The results of this investigation show that the micrometer-sized Ir−PMDS domains display a 2−3-fold higher oxygen sensor response compared to the surrounding PS matrix. This result is consistent with the fact that PDMS is considerably more gas permeable compared to PS. The relationship of the microscale morphology of the blends to their performance as macroscale optical oxygen sensors is discussed

Impurity effects on the band structure of one-dimensional photonic crystals: Experiment and theory

We study the effects of single impurities on the transmission in microwave realizations of the photonic Kronig-Penney model, consisting of arrays of Teflon pieces alternating with air spacings in a microwave guide. As only the first propagating mode is considered, the system is essentially one dimensional obeying the Helmholtz equation. We derive analytical closed form expressions from which the band structure, frequency of defect modes, and band profiles can be determined. These agree very well with experimental data for all types of single defects considered (e.g. interstitial, substitutional) and shows that our experimental set-up serves to explore some of the phenomena occurring in more sophisticated experiments. Conversely, based on the understanding provided by our formulas, information about the unknown impurity can be determined by simply observing certain features in the experimental data for the transmission. Further, our results are directly applicable to the closely related quantum 1D Kronig-Penney model.Comment: 16 pages, 7 figure

The Calogero-Moser equation system and the ensemble average in the Gaussian ensembles

From random matrix theory it is known that for special values of the coupling constant the Calogero-Moser (CM) equation system is nothing but the radial part of a generalized harmonic oscillator Schroedinger equation. This allows an immediate construction of the solutions by means of a Rodriguez relation. The results are easily generalized to arbitrary values of the coupling constant. By this the CM equations become nearly trivial. As an application an expansion for in terms of eigenfunctions of the CM equation system is obtained, where X and Y are matrices taken from one of the Gaussian ensembles, and the brackets denote an average over the angular variables.Comment: accepted by J. Phys.

Pressure-sensitive paint measurements in a shock tube

Abstract Surface pressures were measured in the shortduration, transient flow environment of a small-scale, low pressure-ratio shock tube using thin-film pressure-sensitive paint (PSP). Issues regarding coating formulation, measurement uncertainty, optical system design, and temperature and illumination compensation are discussed. The pressure measurements were acquired during steady flow conditions following the passage of normal shocks and expansion regions along a flat sidewall and a wedge sidewall. The PSP characteristic response time was 3 to 6 ms. Overall pressure uncertainty for the shock tube measurements ranged up to 5% over one atmosphere and compared well with theoretical estimates of uncertainty

Geometry-dependent scattering through quantum billiards: Experiment and theory

We present experimental studies of the geometry-specific quantum scattering in microwave billiards of a given shape. We perform full quantum mechanical scattering calculations and find an excellent agreement with the experimental results. We also carry out the semiclassical calculations where the conductance is given as a sum of all classical trajectories between the leads, each of them carrying the quantum-mechanical phase. We unambiguously demonstrate that the characteristic frequencies of the oscillations in the transmission and reflection amplitudes are related to the length distribution of the classical trajectories between the leads, whereas the frequencies of the probabilities can be understood in terms of the length difference distribution in the pairs of classical trajectories. We also discuss the effect of non-classical "ghost" trajectories that include classically forbidden reflection off the lead mouths.Comment: 4 pages, 4 figure