We used extensive measurements made by the Jicamarca Unattended Long-Term Investigations of the Ionosphere and Atmosphere (JULIA) and Incoherent Scatter Radar (ISR) systems at Jicamarca, Peru during geomagnetic quiet conditions to determine the climatologies of lunar tidal effects on equatorial vertical plasma drifts. We use, for the first time, the expectation maximization (EM) algorithm to derive the amplitudes and phases of the semimonthly and monthly lunar tidal perturbations. Our results indicate, as expected, lunar tidal effects can significantly modulate the equatorial plasma drifts. The local time and seasonal dependent phase progression has been studied in much more detail than previously and has shown to have significant variations from the average value. The semimonthly drift amplitudes are largest during December solstice and smallest during June solstice during the day, and almost season independent at night. The monthly lunar tidal amplitudes are season independent during the day, while nighttime monthly amplitudes are largest and smallest in December solstice and autumnal equinox, respectively. The monthly and semimonthly amplitudes decrease from early morning to afternoon and evening to morning with moderate to large increases near dusk and dawn. We also examined these perturbation drifts during periods of sudden stratospheric warmings (SSWs). Our results show, for the first time, the enhancements of the lunar semimonthly tidal effects associated with SSWs to occur at night, as well as during the day. Our results also indicate during SSWs, monthly tidal effects are not enhanced as strongly as the semimonthly effects.

Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Meteorology. / Bibliography: leaves 70-72. / M.S.

Thesis: S.M., Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 97-103). / The presence of superimposed bedforms, where smaller bedforms exist on larger bedforms, is ubiquitous to energetic tidal environments. Due to their wide range in scale, it is difficult to simultaneously observe these features over tidal timescales. This thesis examines the morphological response of superimposed bedforms to a tidally reversing flow using novel instrumentation and platform systems. A method is outlined in chapter 2 to expand the functionality of low-mounted sidescan sonars by utilizing sonar shadows to estimate bedform height and asymmetry. Empirical models are generated to account for realistic variability in the seabed and the method is validated with bathymetric observations of wave-orbital ripples and tidally reversing megaripples. Given the high temporal and spatial resolution of seafloor frame mounted rotary sidescan sonars, the dynamics and evolution of the bedforms over an approximately 40 m x 40 m area can be resolved. In chapter 3 the method is applied to data of superimposed bedforms at Wasque Shoals, an ebb delta off the southeast corner of Martha's Vineyard, MA. These data reveal the small, superimposed bedforms reversing their asymmetry with the flow while the larger bedforms on which they reside remain oriented in the direction of the dominant flow. Similar bedform dynamics are observed at Nauset Inlet, a dynamic inlet system, on Cape Cod, MA using an autonomous jet-powered kayak, the Jetyak, equipped with a bathymetric swath sonar. The time needed for bedform asymmetry to reverse in the presence of a tidal flow was estimated with a geometric bedform model that incorporates an empirical sediment transport rate. The morphological lag time from the observations agree well with the geometric model with larger bedforms and slower flows resulting in a longer lag time. Finally, the migration of these superimposed bedforms is considered in chapter 4. Data from the rotary sidescan sonar at Wasque Shoals capture the interaction of smaller bedforms, or megaripples, with a dune. The net convergence of megaripples on the tidally dominate lee face of the dune suggests that the smaller bedforms serve as an intermediate step between grain-scale transport processes and larger scale dune migration. / by Katie Renae Jones. / S.M.

In der mittleren und oberen Atmosphäre spielen atmosphärische solare Gezeiten eine wichtige Rolle für die Dynamik und den Vertikaltransport von Energie und Impuls aus der Stratosphäre. Angeregt werden sie primär durch Absorption solarer Strahlung in der Troposphäre und Stratosphäre. Dabei entsprechen die Perioden der solaren Gezeiten den harmonischen Anteilen der täglichen Variation solarer Strahlung. Mittlerweile sind die täglichen, halbtägigen und dritteltägigen Gezeiten relativ gut erforscht, was bei der vierteltägigen Gezeit nicht der Fall ist. Die Informationen über diese Gezeit sind bislang rudimentär vor allem bzgl. einer globalen Klimatologie als auch der Details über möglichen Anregungsmechanismen und Wechselwirkungen. Dies ist darauf zurückzuführen, dass die Amplituden sehr klein sind und eine hohe zeitliche Auflösung für die Analyse benötigt wird. Die vierteltägige Gezeit wurde bislang von bodengebundenen Instrumenten und mit Fernerkundungsgsmethoden beobachtet, welche bislang lediglich einen räumlich und zeitlich begrenzten Überblick über die vierteltägige Gezeit boten. Da es nicht möglich ist die Beiträge der einzelnen Anregungen zu messen, muss sich numerischer Modelle als mächtiges Werkzeug bedient werden. Mit numerischen Modellen ist es möglich die verschiedenen Anregungsmechanismen zu separieren und ihre Beiträge für die vierteltägige Gezeit zu analysieren. Modellstudien lieferten bislang kein umfassendes Bild der QDT und berücksichtigten auch keine vierteltägige Schwerwellenanregungen. Diese Arbeit soll das Wissen zu diesem Thema erweitern, indem ein nichtlineares, mechanistisches, globales Zirkulationsmodell genutzt wird. Es wird eine umfassende numerische Studie durchgeführt, um die Wichtigkeit und das Zusammenspiel der drei vierteltägigen Anregungsmechanismen zu untersuchen, das sind die direkte solare Anregung, nichtlineare Wechselwirkung zwischen Gezeiten und Schwerewellen-Gezeiten-Wechselwirkungen. Erstmalig werden Anregungsterme, die über die Erwärmungsraten hinausgehen, selbst analysiert und quantifiziert und die Wechselwirkungen der vierteltägigen Gezeiten aus den unterschiedlichen Quellen untersucht. Darüber hinaus werden verschiedene Gezeitenmoden untersucht, um Interaktionen der vierteltätigen Gezeit aus den unterschiedlichen Anregungsmechanismen zu identifizieren. Darüber hinaus werden mit Hilfe der theoretischen Hough-Moden diejenigen Moden der vierteltägigen Gezeit abgeleitet, die in den Modellsimulationen maßgeblich für die meridionale Struktur verantwortlich sind. Diese aufwändige und umfassende Modellstudie analysiert die Anregungsmechanismen und deren Interaktion der vierteltägigen Gezeit. Die Arbeit hilft somit das Verständnis über die Wellenausbreitung der mittleren Atmosphäre auf ein neues Niveau zu heben.:1. Tides in the Middle Atmosphere - An Introduction 2. Quarterdiurnal Solar Tides 2.1. Forcing of Quarterdiurnal Tides 2.1.1. Overview of the different Forcing Mechanisms 2.1.2. Theoretical Consideration of the Nonlinear Forcing Mechanism 2.2. Observations and Model Study of the QDT 2.3. Summary and Outlook 3. The Middle and Upper Atmosphere Model (MUAM) 3.1. Introduction 3.2. Numerical Properties 3.3. Model Physics 3.4. Parameterizations 3.5. Background Climatology 4. Mathematical and Numerical Methods 4.1. Fast Fourier Transform 4.2. Harmonic Analysis 5. MUAM: Sensitivity Studies 5.1. Influence of Horizontal Resolution on the Background Climatology and QDT amplitudes 5.2. Influence of the Initial Conditions on the Background Climatology and QDT amplitudes 5.3. Influence of temporal resolution on the Background Climatology and QDT amplitudes 6. MUAM: Climatology of the Quarterdiurnal Tide 6.1. Amplitudes 6.2. Phases and Vertical Wavelengths 6.3. QDT reconstruction with Hough modes 7. MUAM: The Quarterdiurnal Tide Forcing Mechanisms 7.1. The Quarterdiurnal Forcing Terms 7.2. Model Experiments and Single Forcing Mechanisms 7.2.1. The Solar Forcing 7.2.2. The Gravity Wave Forcing 7.2.3. The Nonlinear Forcing 7.2.4. No Gravity Wave Forcing 7.2.5. No Nonlinear Forcing 7.3. Hough modes in Model experiments 7.3.1. SOL Hough modes 7.3.2. GW Hough modes 7.3.3. NLIN Hough modes 7.3.4. Hough modes: Seasonal cycle 7.4. Nonlinear Tidal Interactions 7.4.1. Model run without SDT/SDT interaction 7.4.2. Model run without DT/TDT interaction 7.4.3. Model run without tide-tide interaction 7.5. Solar Tidal Interactions 7.6. Interactions of Different Forcing Mechanisms 7.6.1. Interaction between Nonlinear and Solar Forcing 7.6.2. Interaction between Gravity wave and Solar Forcing 7.7. Influence of Enhanced Forcing Mechanisms 7.7.1. Influence of Enhanced Solar Forcing Mechanisms 7.7.2. Influence of Enhanced Gravity Wave Forcing Mechanisms 7.7.3. Influence of Enhanced Nonlinear Forcing Mechanisms 8. Summary and Conclusion 9. Outlook / In the middle and upper atmosphere atmospheric solar tides play an important role in the dynamics and vertical transport of energy and momentum from the stratosphere. They are primarily excited by absorption of solar radiation in the troposphere and stratosphere. The periods of the solar tides correspond to the harmonic components of the daily variation of solar radiation. Meanwhile, the diurnal, semidiurnal and terdiurnal tides have been relatively well studied, which is not the case with the quarterdiurnal tide. The knowledge about this tide is so far rudimentary, especially with regard to global climatology and details of possible excitation mechanisms and interactions. This is due to the fact that the amplitudes are very small and a high temporal resolution is required for the analysis. The quarterdiurnal tide has been observed by ground-based instruments and remote sensing methods, which until now have only provided a spatially and temporally limited overview of the quarterdiurnal tide. Since it is not possible to measure the contributions of the individual excitations, numerical models must be used as a powerful tool. With the numerical models it is possible to separate the different excitation mechanisms and to analyse their contributions for the quarterdiurnal tide. Model studies so far did not provide a comprehensive picture of QDT and did not consider QDT gravity wave excitation. This work is intended to extend the knowledge on this topic by using a nonlinear, mechanistic, global circulation model. A comprehensive numerical study will be carried out to investigate the importance and the interaction of the three quarterdiurnal excitation mechanisms, i.e. direct solar excitation, nonlinear tidal interactions and gravity wave tidal interactions. For the first time, excitation terms beyond the heating rates will be analyzed and quantified and the interactions of the quarterdiurnal tides from different sources will be investigated. Furthermore, different tidal modes will be investigated to identify quarterdiurnal tide interactions from the different excitation mechanisms. Furthermore, the theoretical Hough modes are used to derive those quarterdiurnal modes that are significantly responsible for the meridional structure in the model simulations. This elaborate and comprehensive model study analyses the excitation mechanisms and their interaction of the quarter-day tide. The work thus helps to raise the understanding of wave propagation in the middle atmosphere to a new level.:1. Tides in the Middle Atmosphere - An Introduction 2. Quarterdiurnal Solar Tides 2.1. Forcing of Quarterdiurnal Tides 2.1.1. Overview of the different Forcing Mechanisms 2.1.2. Theoretical Consideration of the Nonlinear Forcing Mechanism 2.2. Observations and Model Study of the QDT 2.3. Summary and Outlook 3. The Middle and Upper Atmosphere Model (MUAM) 3.1. Introduction 3.2. Numerical Properties 3.3. Model Physics 3.4. Parameterizations 3.5. Background Climatology 4. Mathematical and Numerical Methods 4.1. Fast Fourier Transform 4.2. Harmonic Analysis 5. MUAM: Sensitivity Studies 5.1. Influence of Horizontal Resolution on the Background Climatology and QDT amplitudes 5.2. Influence of the Initial Conditions on the Background Climatology and QDT amplitudes 5.3. Influence of temporal resolution on the Background Climatology and QDT amplitudes 6. MUAM: Climatology of the Quarterdiurnal Tide 6.1. Amplitudes 6.2. Phases and Vertical Wavelengths 6.3. QDT reconstruction with Hough modes 7. MUAM: The Quarterdiurnal Tide Forcing Mechanisms 7.1. The Quarterdiurnal Forcing Terms 7.2. Model Experiments and Single Forcing Mechanisms 7.2.1. The Solar Forcing 7.2.2. The Gravity Wave Forcing 7.2.3. The Nonlinear Forcing 7.2.4. No Gravity Wave Forcing 7.2.5. No Nonlinear Forcing 7.3. Hough modes in Model experiments 7.3.1. SOL Hough modes 7.3.2. GW Hough modes 7.3.3. NLIN Hough modes 7.3.4. Hough modes: Seasonal cycle 7.4. Nonlinear Tidal Interactions 7.4.1. Model run without SDT/SDT interaction 7.4.2. Model run without DT/TDT interaction 7.4.3. Model run without tide-tide interaction 7.5. Solar Tidal Interactions 7.6. Interactions of Different Forcing Mechanisms 7.6.1. Interaction between Nonlinear and Solar Forcing 7.6.2. Interaction between Gravity wave and Solar Forcing 7.7. Influence of Enhanced Forcing Mechanisms 7.7.1. Influence of Enhanced Solar Forcing Mechanisms 7.7.2. Influence of Enhanced Gravity Wave Forcing Mechanisms 7.7.3. Influence of Enhanced Nonlinear Forcing Mechanisms 8. Summary and Conclusion 9. Outlook

No description available.

Submarine canyons incising the continental shelf and slope are hot spots for topography-internal wave interactions, with elevated dissipation and mixing contributing to regional transport and biological productivity. At two Barkley Canyon sites (the continental slope below the shelf-break, and deep within the canyon), four overlapping years of horizontal velocity time-series data are used to examine the effects of irregular topography on the internal wave field. Mean currents are topographically guided at both sites, and in the canyon there is an inter-annually consistent, periodic (about a week) up-canyon flow (-700 to -900 m) above a near-bottom down-canyon layer. There is elevation of internal wave energy near topography, up to a factor of 10, 130 m above the slope, and up to a factor of 100, 230 m above the canyon bottom. All bands display weak inter-annual variability, but significant seasonality. Sub-diurnal and diurnal flows are presumably sub-inertially trapped along topography, and the diurnal band appears to be forced locally (barotropically). Both sites have high near-inertial energy. At the slope site, near-inertial energy is attenuated with depth, while in the canyon it is amplified near the bottom. Both sites show intermittent near-inertial forcing associated with wind events, downward propagation of high-mode internal waves, and the seasonal mixed-layer depth, though fewer events are observed in the canyon. Free semidiurnal internal tides are focused and reflected near critical shelf-break and canyon floor topography, and appear to experience both local and remote (baroclinic) forcing. The high-frequency internal wave continuum has enhanced energy near bottom at both sites (up to 7 times the open-ocean Garrett-Munk spectrum), and inferred dissipation rates increasing from a background of less than 10^-9 W kg^-1 and reaching 10^-7 W kg^-1 near topography. Dissipation is most strongly correlated with the semidiurnal (M2) constituent at both sites, with secondary contributions from the sub-diurnal (Sub_K1) band on the slope, and the near-inertial (NI) band in the canyon. Power laws for these dependencies are dissipation ~ M2^0.83 + Sub_K1^0.59 at the slope, and dissipation ~ M2^1.47 + NI^0.24 in the canyon. There is evidence in spectra of a near-buoyancy frequency build-up of energy correlated with high-frequency continuum variability, with a power law fit of 'shoulder' power ~ dissipation^0.34 that is independent of site topography. Though some general results are expected from observations at other slope and canyon sites, the greater temporal extent of these data provide a uniquely long-term evaluation of such processes. / Graduate

Recent cooperative efforts between the University of Central Florida, the Florida Department of Environmental Protection, and the South Florida Water Management District explore the development of a two-dimensional, depth-integrated tidal model for the Loxahatchee River estuary (Southeastern Florida). Employing a large-domain approach (i.e., the Western North Atlantic Tidal model domain), two-dimensional tidal flows within the Loxahatchee River estuary are reproduced to provide: 1) recommendations for the domain extent of an integrated, surface/groundwater, three-dimensional model; 2) nearshore, harmonically decomposed, tidal elevation boundary conditions. Tidal simulations are performed using a two-dimensional, depth-integrated, finite element-based code for coastal and ocean circulation, ADCIRC-2DDI. Multiple variations of an unstructured, finite element mesh are applied to encompass the Loxahatchee River estuary and different spatial extents of the Atlantic Intracoastal Waterway (AIW). Phase and amplitude errors between model output and historical data are quantified at five locations within the Loxahatchee River estuary to emphasize the importance of including the AIW in the computational domain. In addition, velocity residuals are computed globally to reveal significantly different net circulation patterns within the Loxahatchee River estuary, as depending on the spatial coverage of the AIW.

This thesis focuses on the simulation of astronomic tides of the Pascagoula River. The work is comprised of five steps: 1) Production of a digital elevation model describing the entire Pascagoula River system; 2) Development of an inlet-based, unstructured mesh for inbank flow to better understand the basis of the hydrodynamics within the Pascagoula riverine system. In order to assist in the mesh development, a toolbox was constructed to implement one-dimensional river cross sections into the two-dimensional model; 3) Implementation of a sensitivity analysis of the Pascagoula River two inlet system to examine the inlet effects on tidal propagation; 4) Improvement of the inlet-based model by performing a preliminary assessment of a spatially varied bottom friction; 5) Implementation of an advection analysis to reveal its influence on the flow velocity and water elevation within the domain. The hydrodynamic model employed for calculating tides is ADCIRC-2DDI (ADvanced CIRCulation Model for Shelves, Coasts and Estuaries, Two-Dimensional Depth Integrated). This finite element based model solves the shallow water equations in their full nonlinear form. Boundary conditions including water surface elevation at the off-shore boundary and tidal potential terms allow the full simulation of astronomic tides. The improved astronomic tide model showed strong agreement with the historical data at seven water level monitoring gauge stations. The main conclusions of this research are: 1) The western inlet of the Pascagoula River is more dominant than the eastern inlet; however, it is necessary to include both inlets in the model. 2) Although advection plays a significant role in velocity simulation, water elevations are insensitive to advection. 3) The astronomic model is sensitive to bottom friction (both global and spatial variations); therefore, a spatially varied bottom friction coefficient is suggested. As a result of this successful effort to produce an astronomic tide model of the Pascagoula River, a comprehensive storm surge model can be developed. With the addition of inundation areas the surge model can be expected to accurately predict storm tides generated by hurricanes along the Gulf Coast.

A high-resolution, finite element-based, shallow water equation model is developed to simulate the tides in the South Atlantic Bight. The model is constructed to include all of the estuarine features along the southeastern United States seaboard: coastal inlets, rivers and tidal creeks, sounds and lagoons, intertidal zones including salt marshes and mangrove swamps, and the Atlantic Intracoastal Waterway. The estuaries are represented in the finite element mesh using triangular elements with side lengths on the order of tens of meters. Also incorporated into the model is a spatially distributed bottom friction parameterization, based on the various landcover and benthic characteristics in the domain. The motivation to use this comprehensive representation of the system was inspired by a desire to capably account for the full estuarine tidal physics. In this approach, no calibration is performed and the model is used as a tool to assess the physical processes it describes. Upon its development, the model is first validated by accurately simulating tidal hydrodynamics in the South Atlantic Bight including the described estuaries. Variants of the model are then constructed by selectively removing estuarine features from the domain. All model representations are subsequently applied in nearly identical simulations: the only differing factor between the simulations being the inland extent of the estuaries described. The solutions are compared with respect to including versus excluding the estuarine features of the domain. Where water surface elevations are shown to be unaffected by the estuarine features of the South Atlantic Bight, tidal velocities exhibit far more sensitivity. This effect is pronounced locally, with regional effects extending offshore. Further analysis is performed on cross-sectional flows recomposed locally and on tidal energetics diagnosed throughout the domain. It is discovered that the high frictional environment of the vast estuarine surface area plays a role in local and regional tidal circulation in the South Atlantic Bight.

The focus of this thesis is the forcing mechanisms incorporated with salinity transport for the Lower St. Johns River. There are two primary analyses performed: a historical data analysis of primary forcing mechanisms to determine the importance of each individual influence, and a tidal hydrodynamics analysis for the Lower St. Johns River to determine the required tidal constituents for an accurate resynthesis. This thesis is a preliminary effort in understanding salinity transport for the Lower St. Johns River for engineering projects such as the dredging of navigation canals and freshwater withdrawal from the river. The analysis of the physical forcing mechanisms is performed by examining the impact of precipitation, tides, and wind advection on historical salinity measurements. Three 30-day periods were selected for the analysis, to correspond with representative peak, most-variable, and low-salinity periods for 1999. The analysis displays that wind advection is the dominant forcing mechanism for the movement of salinity over a 30 day duration; however all mechanisms have an impact at some level. The dominant forcing mechanism is also dependent on the period of record examined where tidal influence is vital for durations of hours to a day, while freshwater inflow has more significance over a longer period due to climatological variation. A two-dimensional finite difference numerical model is utilized to generate a one month tidal elevations and velocities simulations that incorporates geometry, nonlinear advection and quadratic bottom friction. Several combinations of tidal constituents are extracted from this modeled tidal signal to investigate which combination of tidal constituents produces an accurate tidal resynthesis for the Lower St. Johns River. The analysis displays the need for 39 total tidal harmonic constituents to accurately resynthesize the original tidal signal. Additionally, due to the nonlinear nature of shallow water, the influence of the overtides for upstream or downstream locations in the Lower St. Johns River is shown to be spatially variable for different frequencies depending on the geometry. The combination of the constituent analysis and the historical analysis provides the basis information needed for the development of an accurate salinity transport model for the Lower St. Johns River.