2024
Trends of Sediment Resuspension and Budget in Southern Lake Michigan under Changing Wave Climate and Hydrodynamic EnvironmentLonghuan Zhu, Pengfei Xue, Guy A. Meadows, Chenfu Huang, Jianzhong Ge, Cary D. Troy, Chin H. Wu
Journal of Geophysical Research - Oceans
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2023
Beach rebuilding period buffers Indiana beach erosion in Lake MichiganNelson-Mercer, B., H. Tomkins, T. Ahsan, and C.D. Troy
Accepted, Journal of Great Lakes Research
A Machine Learning Framework for Extending Wave Height Time Series Using Historical Wind RecordsAbdelhady, H.U., and C.D. Troy
In review, Applied Ocean Research
(submitted)
Modeling Lake Michigan Shoreline Changes in Response to Rapid Water Level FluctuationsAbdelhady, H., and C.D. Troy
Proceedings of The Coastal Sediments Conference 2023
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AbstractThe focus of this paper is on the development and application of a reduced-complexity shoreline model that explicitly accounts for the enhanced shoreline changes that occur due to water level changes. Contrary to previous shoreline models, this model accounts for wave and water level disequilibrium as well as passive flooding, which makes it suitable for simulating shorelines with large water level fluctuations. The model was applied to four segments of Lake Michigan shoreline. Shoreline time series were extracted from high resolution multispectral satellite images and used for calibrating and testing the model. The model was able to accurately simulate the observed shoreline changes at the four sites and reproduce the seasonal and interannual shoreline changes. The simulation results highlight the relative importance of the water level disequilibrium and waves disequilibrium for each site. Additionally, the results highlight the potential importance of accounting for other coastal processes in the proposed model.
U.S. community perspectives on coastal floodingElko, N., Briggs, T. R., Marsooli, R., Barrineau, P., Hapke, C., McKenna, K., ... & Troy, C.
Shore and Beach
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AbstractCoastal flooding, from both extreme events and sea level rise, is one of the top management challenges facing U.S. coastal stakeholders today. The intensity of coastal flooding is expected to increase with global sea level rise. This paper focuses on f looding challenges from the perspective of coastal communities.
2022
A reduced-complexity shoreline model for coastal areas with large water level fluctuationsAbdelhady, H., and C.D. Troy
Coastal Engineering
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AbstractIn this paper, we debut a new reduced-complexity shoreline model that can be used to simulate shoreline position changes in response to not only wave (which people have done) but water level fluctuations. This "Great Lakes Shoreline Model" (GLSM) is tested on two Lake Michigan beaches and shows a great ability to simulate shoreline changes that are strongly linked to water level fluctuations.
A simple, fully-automated shoreline detection algorithm for high-resolution, multi-spectral imageryAbdelhady, H., C.D. Troy, A. Habib, and R. Manish
Remote Sensing
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2021
Rapid Lake Michigan shoreline changes revealed by UAV LiDAR surveysTroy, C.D., Y.-T. Cheng, Y.-C. Lin, and A. Habib.
Coastal Engineering
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Emergency responder and public health considerations for plastic sewer lining chemical waste exposures in indoor environmentsNoh, Y., B.E. Boor, J.H. Shannahan, C.D. Troy, C.T. Jafvert, and A.J. Whelton.
Journal of Hazardous Materials
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Characterizing the seasonal variability of hypolimnetic mixing in a large, deep lakeCannon, D.J., C.D. Troy, H. Bootsma, Q. Liao, and R.-A. Maclellan-Hurd.
Journal of Geophysical Research
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Seasonality modulates wind-driven mixing pathways in a large lakeCastro, B.F., D. Bouffard, C.D. Troy, H.N. Ulloa, S. Piccolroaz, O.S. Steiner, H.E. Chmiel, L.S. Moncadas, S. Lavanchy, and A. Wüest
Communications Earth & Environment
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2020
Lateral dispersion of dye and drifters in the center of a very large lakeChoi, J.M., C.D. Troy, N. Hawley, M. McCormick, and M.G. Wells
Limnology and Oceanography
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AbstractTo better understand lateral dispersion of buoyant and nonbuoyant pollutants within the surface waters of large lakes, two lateral dispersion experiments were carried out in Lake Michigan during the stratified period: (1) a dye tracking experiment lasting 1 d; and (2) a drifter tracking experiment lasting 24 d. Both the dye patch and drifters were surface-released at the center of Lake Michigan's southern basin. Near-surface shear induced by near-inertial Poincaré waves partially explains elevated dye dispersion rates (1.5–4.2 m2 s−1). During the largely windless first 5 d of the drifter release, the drifters exhibited nearly scale-independent dispersion ( K ∼ L0.2), with an average dispersion coefficient of 0.14 m2 s−1. Scale-dependent drifter dispersion ensued after 5 d, with K ∼ L1.09 and corresponding dispersion coefficients of 0.3–2.0 m2 s−1 for length scales L = 1500–8000 m. The largest drifter dispersion rates were found to be associated with lateral shear-induced spreading along a thermal front. Comparisons with other systems show a wide range of spreading rates for large lakes, and larger rates in both the ocean and the Gulf of Mexico, which may be caused by the relative absence of submesoscale processes in offshore Lake Michigan.
2019
Evaluation of UAV LiDAR for mapping coastal EnvironmentsLin, Y.-C., Cheng, Y.-T., Zhou, T., Ravi, R., Hasheminasab, S.M., Flatt, J.E., Troy, C., Habib, A.
Remote Sens. 2019 11, 2893
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AbstractUnmanned Aerial Vehicle (UAV)-based remote sensing techniques have demonstrated great potential for monitoring rapid shoreline changes. With image-based approaches utilizing Structure from Motion (SfM), high-resolution Digital Surface Models (DSM), and orthophotos can be generated efficiently using UAV imagery. However, image-based mapping yields relatively poor results in low textured areas as compared to those from LiDAR. This study demonstrates the applicability of UAV LiDAR for mapping coastal environments. A custom-built UAV-based mobile mapping system is used to simultaneously collect LiDAR and imagery data. The quality of LiDAR, as well as image-based point clouds, are investigated and compared over different geomorphic environments in terms of their point density, relative and absolute accuracy, and area coverage. The results suggest that both UAV LiDAR and image-based techniques provide high-resolution and high-quality topographic data, and the point clouds generated by both techniques are compatible within a 5 to 10 cm range. UAV LiDAR has a clear advantage in terms of large and uniform ground coverage over different geomorphic environments, higher point density, and ability to penetrate through vegetation to capture points below the canopy. Furthermore, UAV LiDAR-based data acquisitions are assessed for their applicability in monitoring shoreline changes over two actively eroding sandy beaches along southern Lake Michigan, Dune Acres, and Beverly Shores, through repeated field surveys. The results indicate a considerable volume loss and ridge point retreat over an extended period of one year (May 2018 to May 2019) as well as a short storm-induced period of one month (November 2018 to December 2018). The foredune ridge recession ranges from 0 m to 9 m. The average volume loss at Dune Acres is 18.2 cubic meters per meter and 12.2 cubic meters per meter within the one-year period and storm-induced period, respectively, highlighting the importance of episodic events in coastline changes. The average volume loss at Beverly Shores is 2.8 cubic meters per meter and 2.6 cubic meters per meter within the survey period and storm-induced period, respectively.
Ice-free radiative convection drives spring mixing in a large lakeCannon, D.J., C.D. Troy, Q. Liao, and H. Bootsma.
Geophysical Research Letters, 46(12), 6811-6820
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AbstractIn this work we highlight the importance of radiative convection as a mixing mechanism in a large, ice-free lake (Lake Michigan, USA), where solar heating of waters below the temperature of maximum density drives vertical convection during the vernal turnover. Measurements taken over a 2-week period at a 55-m deep site demonstrate the ability of radiative convection to mix the entire water column. Observations show a diurnal cycle in which solar heating drives a steady deepening of the convective mixed layer throughout the day (dHCML/dt = 12.8 m/hr), followed by surface-cooling-induced restratification during the night. Radiative convection is linked to a dramatic enhancement in turbulence characteristics, including both turbulent kinetic energy dissipation (ϵ: 10−9–10−7 W/kg) and turbulent scalar diffusivity (Kz: 10−3–10−1 m2/s), suggesting that radiative convection plays a major role in driving vertical mixing throughout the water column during the isothermal spring.
2018
Observations of turbulence and mean flow in the low‐energy hypolimnetic boundary layer of a large lakeCannon, D. J., & Troy, C. D.
Limnology and Oceanography, 63(6), 2762-2776
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AbstractNear-bed measurements are reported for both mean flow and turbulence structure in the deep hypolimnetic waters of Lake Michigan (55 m depth) during stratified and unstratified periods to determine validity and restrictions of the expected law-of-the-wall (LOW) behavior. Near-bed currents were weak (U50 = 3, 16 cm s−1 for mean, maximum currents respectively at 50 cm elevation), dominated by subinertial energy across all seasons, and showed little seasonal variation in spite of the strong seasonality to wind forcing. Velocity structure for wave-free conditions showed strong log-linear trends within 1 mab, with over 98% of the 2152 velocity profiles producing significant log-linear fits within the bottom meter and a strictly logarithmic velocity profile extending to only 66 cmab on average (Cd 50 = 0.0052; zo = 0.0015 m). Stratification was dynamically unimportant to mean flow and turbulence, but fitted log-linear length scales suggest that deviations from strictly logarithmic velocity structure may be explained by flow unsteadiness. Turbulent quantities measured within 1 m of the bed including dissipation, turbulent kinetic energy, and turbulent length scales followed LOW expectations in the mean, but individual estimates deviated by several orders of magnitude. The observed deviations from LOW turbulent structure were found to be correlated with the log-linear length scales fit to mean velocity profiles and were consistent with the effects of flow unsteadiness.
Assessment and characterization of writing exercises and core engineering textbooksEssig, R.R., C.D. Troy, B.K. Jesiek, N.T. Buswell, and J.E. Boyd
Journal of Professional Issues in Engineering Education and Practice, 144(4): 04018007. DOI: 10.1061/(ASCE)EI.1943-5541.0000378
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AbstractWriting has been identified as a critical skill and element of the engineering profession, yet it is rarely included in sophomore-level and junior-level courses. Textbooks often influence how courses are structured, and reading assignments and homework problems are frequently assigned directly from textbooks. In this project, textbooks are systematically searched for writing-based problems in four core engineering courses: fluid mechanics, thermodynamics, statics, and circuits. The authors focused efforts on identifying learning activities that could potentially allow students to practice writing, learn through writing, and use writing to relate course content to broader applications and contexts. Results included the total number of end-of-chapter questions with writing components and the classification of types of writing prompts. Analysis showed a limited availability of questions with writing components in textbooks and a missed opportunity to incorporate important writing education within the context of technical engineering concepts.
Engineering instructors on writing: Perceptions, practices, and needsBuswell, N.T., B.K. Jesiek, C.D. Troy, R.R. Essig, and J. Boyd
IEEE Transactions on Professional Communication. DOI 10.1109/TPC.2019.2893392
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AbstractBackground- With communication skills deemed increasingly important for engineering graduates, we wanted to understand how writing is currently included in engineering classes, what challenges are caused by including writing in such classes, and what resources would be most useful to help engineering instructors more easily include writing in engineering classes. Literature review- Writing is a necessary skill for engineering graduates and has received increased attention in engineering classes. However, despite many instructors' beliefs that writing is an important skill for engineers, it is not typically taught in a systematic and comprehensive way across the engineering curriculum. Research questions- 1. What perceptions of writing, and specifically writing in engineering, do engineering instructors hold? 2. To what extent do engineering instructors report incorporation of writing activities and assignments in their classes? 3. What barriers do engineering instructors perceive as inhibiting the inclusion of more writing in engineering courses? 4. What resources do engineering instructors desire to expand and improve the inclusion of writing in engineering courses? Research methods: A survey was completed by engineering instructional staff (n = 190 respondents, 10.7% response rate) from seven institutions as well as by some members of the Big10+ Engineering Deans Mailing List. Instructors were asked about their general perceptions about writing in engineering and were also asked to consider the most recent engineering course that they taught and reflect on how they included (or did not include) writing in their course. Findings and conclusions- As expected, we found that most engineering instructional staff agree that writing skills are very important in engineering. Yet, we found that constraints on time and resources kept instructors from including more writing in their courses. This paper concludes with a discussion of our efforts to develop resources, such as rubrics, graded writing examples, and strategies for developing writing prompts, to help instructors include more writing in their engineering courses.
Regulation of plankton and nutrient dynamics by profundal quagga mussels in Lake Michigan: a one-dimensional modelShen, C., Q. Liao, H.A. Bootsma, C.D. Troy, and D. Cannon
Hydrobiologia, 1-17
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AbstractInvasive dreissenid mussels have altered plankton abundance and nutrient cycling in the Great Lakes. In this study, a 1-D hydrodynamic-biogeochemical coupled model is developed to investigate their effects at a mid-depth offshore site in Lake Michigan. Model simulation shows that water surface temperature and vertical thermal structure can be well reproduced. Driven by the simulated vertical mixing, the biological model solves the transport and transformation of nutrients, plankton and detritus in the water column. Mussel grazing and excretion are added at the bottom boundary. The biological model predicts a notable decline of phytoplankton biomass and considerable increase of dissolved phosphorus (DP) in the entire water column at the end of spring. However, the reduction of phytoplankton and the increase of DP are limited to the bottom 20 m in summer as a result of the strong stratification. Model results also show that mussels can maximize particle delivery to the benthos, as the modeled benthic diffusive flux of particulate phosphorus exceeds the passive settling rate by 4.2× on average. Model simulation over a 10-month period indicates that profundal mussels have the potential to significantly change the distribution of energy and nutrients in the water column, even in a deep and stratified environment.
Physicochemical characteristics of a southern Lake Michigan river plumeJameel, Y., S. Stein, E.F. Grimm, C. Roswell, A.E. Wilson, C.D. Troy, T. Höök, and G.J. Bowen
Journal of Great Lakes Research 44(2), 209-218
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AbstractRiverine inputs are a major source of nutrients to the Laurentian Great Lakes and have important effects on nearshore biological processes, where mixing between river and lake water leads to formation of heterogeneous
river plumes. We examined the physical and chemical characteristics of the St. Joseph River plume in southern Lake Michigan between May and October 2011, and in October 2012, June 2013 and April 2014. Specific electric conductivity and
stable isotopes of water were used to quantify the fraction of river water (FRW) at sampling sites in Lake Michigan. Both tracers predicted similar patterns of FRW among sites; however, there was a systematic offset between the two methods, and specific electric conductivity method under-predicted the FRW by ~5%. We observed a distinct, seasonally varying river plume, with plume size correlated with flow rate of St. Joseph River. Within the plume, sediments and nutrients were non-conservative and exhibited significant and seasonally varying losses that we attribute to settling of particle-bound nutrients and/or nutrients in particulate phase below the plume. The characteristics and the spatiotemporal heterogeneity of the river plume documented here may have important implications for the nearshore
biogeochemistry of the Great Lakes and for understanding the roles of these features in ecological processes in nearshore areas.
2017
Asynchrony in the inter-annual recruitment of lake whitefish Coregonus clupeaformis in the Great Lakes regionZischke, M., D.B. Bunnell, C.D. Troy, E.K. Berglund, D.C. Caroffino, M.P. Ebener, J.X. He, S.P. Sitar, and T.O. Höök
Journal of Great Lakes Research, in press and available online
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AbstractSpatially separated fish populations may display synchrony in annual recruitment if the factors that drive recruitment success, particularly abiotic factors such as temperature, are synchronised across broad spatial scales. We examined inter-annual variation in recruitment among lake whitefish (Coregonus clupeaformis) populations in lakes Huron, Michigan and Superior using fishery-dependent and -independent data from 1971 to 2014. Relative year-class strength (RYCS) was calculated from catch-curve residuals for each year class across multiple sampling years. Pairwise comparison of RYCS among datasets revealed no significant associations either within or between lakes, suggesting that recruitment of lake whitefish is spatially asynchronous. There was no consistent correlation between pairwise agreement and the distance between datasets, and models to estimate the spatial scale of recruitment synchrony did not fit well to these data. This suggests that inter-annual recruitment variation of lake whitefish is asynchronous across broad spatial scales in the Great Lakes. While our method primarily evaluated year-to-year recruitment variation, it is plausible that recruitment of lake whitefish varies at coarser temporal scales (e.g. decadal). Nonetheless, our findings differ from research on some other Coregonus species and suggest that local biotic or density-dependent factors may contribute strongly to lake whitefish recruitment rather than inter-annual variability in broad-scale abiotic factors.
2016
Recruitment dynchrony of Yellow Perch (Perca flavescens, Percidae) in the Great Lakes Region, 1966-2008Honsey, A.E., D.B. Bunnell, C.D. Troy, D.G. Fielder, M.V. Thomas, C.T. Knight, S.C. Chong, and T.O. Höök
Fisheries Research, 181, 214-221
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AbstractPopulation-level reproductive success (recruitment) of many fish populations is characterized by high inter-annual variation and related to annual variation in key environmental factors (e.g., climate). When such environmental factors are annually correlated across broad spatial scales, spatially separated populations may display recruitment synchrony (i.e., the Moran effect). We investigated inter-annual (1966–2008) variation in yellow perch (Perca flavescens, Percidae) recruitment using 16 datasets describing populations located in four of the five Laurentian Great Lakes (Erie, Huron, Michigan, and Ontario) and Lake St. Clair. We indexed relative year class strength using catch-curve residuals for each year-class across 2–4 years and compared relative year-class strength among sampling locations. Results indicate that perch recruitment is positively synchronized across the region. In addition, the spatial scale of this synchrony appears to be broader than previous estimates for both yellow perch and freshwater fish in general. To investigate potential factors influencing relative year-class strength, we related year-class strength to regional indices of annual climatic conditions (spring-summer air temperature, winter air temperature, and spring precipitation) using data from 14 weather stations across the Great Lakes region. We found that mean spring-summer temperature is significantly positively related to recruitment success among Great Lakes yellow perch populations.
Why this flip wasn’t a flop: What the numbers don’t tell you about flipped classesFedesco, H.N., and C.D. Troy
In Proceedings of the 2016 ASEE Annual Conference and Exposition, New Orleans, LA, June 26-29, 2016
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AbstractThis paper details the conversion of a large, required Civil Engineering fluid mechanics course into a more student-centered, active learning-oriented course through the flipping of one lecture per week. In the flipped class, students collaboratively solve homework problems in groups while receiving “expert” feedback from instructors and TAs. To offset the lost lectures, some course material that has been delivered in traditional lectures has been placed online in the form of short videos and textbook readings, with low-stakes quizzes for assessment.
Student learning gains were quantitatively assessed by comparing quiz and final exam scores for three semesters (1 pre-flip and 2 post-flip). To maintain some element of consistency across the course transformation, a comprehensive, multiple-choice final exam has served to provide quantitative metrics on which the course improvement can be gaged. In addition, quiz questions remained relatively similar across semesters. One-way ANOVAs revealed a statically significant difference on quiz performance, with post-flip students performing better than those in pre-flip semesters. In addition, students in the final iteration of the course transformation significantly outperformed previous students on final exams by about 7%.
Taken together, the numbers suggest that the process of flipping a large fluid mechanics course is associated with small but positive improvements to quiz and final exam performance. However, it is best to rely on other indicators beyond course performance in order to more accurately depict the impact of a course transformation. To supplement the results of the quantitative analyses, student comments about the course and instructor observations of the transformation implementation were assessed. Students found the work sessions to be very effective, enjoyed collaborating with peers and the instructor, and thought the online videos were helpful. The instructor indicated that the benefits of the flipped class include the following: heightened student engagement during class periods; greatly increased instructor awareness of student perceptions, challenges, personal issues, and conceptual bottlenecks; eventual reduction in instructor preparation time; improved instructor-student relationships; and a better focus on more important course objectives.
Challenges and opportunities for recruiting students to undergraduate civil engineering programsTroy, C.D., J. Bruntz, R.S. Govindaraju, G. Haikal, J.D. Horn, M.M. Kelly, M.G. Schroeder, J. See, and J.C. Tompkins
In Proceedings of the 2016 ASEE Annual Conference and Exposition, New Orleans, LA, June 26-29, 2016
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AbstractSociety needs more civil engineers, with the projected near-term need for civil engineers greater than any other engineering discipline. Ailing national infrastructure and projected retirement rates have led to job projections suggesting that the near-term need for civil engineering graduates is almost double that of any other engineering discipline. This need, combined with other attractive attributes of civil engineering, should make civil engineering a top engineering major at many undergraduate universities. In spite of the career opportunities readily available to graduating civil engineers, and in spite of the general increasing trend in the number of total undergraduate engineering students, undergraduate civil engineering programs, taken as a whole, have struggled to maintain and grow their numbers. Individually, many undergraduate programs struggle to recruit students to civil engineering, and this poses a major problem not only to individual programs but to the profession itself.
We analyzed a set of civil engineering student surveys to determine the factors, attitudes, and experiences that typically lead students to select careers in civil engineering and found several common responses, many of which can be leveraged to promote the discipline. The data suggest that about one half of our students pre-select civil engineering prior to beginning as first-year engineering students, and that the top reasons for their selection of civil engineering include: a passion for building things; a desire to make a difference; flexible career options; and a love for math and science (which presumably is shared by young engineers of all disciplines).
We present data from another survey carried out with undergraduate students in other engineering majors, as to why students select other disciplines and how civil engineering is perceived. This survey highlights several perceptions about civil engineering among first year engineers. These include the misperception of civil engineering as a narrow field focused only around bridges, buildings, and roads, as well as the perception of civil engineers earning low salaries.
These student perceptions pose challenges to civil engineering recruiters, but also afford opportunities for clarification and improved recruitment, especially for programs that allow students to select their engineering discipline during their first year of college. We conclude this paper with a set of talking points we have deployed at our own university that directly address the above challenges and opportunities.
Engineering faculty on writing: What they think and what they wantTrellinger, N.M., B.K. Jesiek, C.D. Troy, J. Boyd, and R.R. Essig
In Proceedings of the 2016 ASEE Annual Conference and Exposition, New Orleans, LA, June 26-29, 2016
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AbstractWriting has been identified as an important skill for engineers, and while faculty generally agree that writing should be included in the engineering classroom, there are many barriers that may discourage faculty to do so. This survey explored how faculty are including writing in their classes, what barriers they face, and also asks faculty what resources they would like so that the inclusion of writing could be more realistic and feasible.
In terms of their approaches to incorporating writing in their courses, a majority of respondents reported sometimes or frequently assigning writing in the following types of assignments: project documentation, written explanations of homework, and short-answer questions on tests and quizzes. A majority of respondents also reported frequent use of grading rubrics for writing, as well as specifying the audiences for whom students should target their writing.
Respondents identified their top challenges to including writing in their courses, including large enrollments, lack of time, and lack of teaching assistants competent to assess writing. To address these challenges, the most favored suggestion was having teaching assistants trained to assess writing, followed by expanding the availability of writing resources for faculty and students. Additionally, the issue of student preparation was brought up on numerous occasions; faculty stated that previous negative experiences with student writing hindered faculty from including writing assignments in their courses.
In a perfect world, all faculty would have teaching assistants that were trained in teaching engineering writing. However, other more realistic resources include providing rubrics and sample work on an accessible and easy to use website. This paper reports on the faculty survey about writing and also how it relates the larger project that includes providing these important resources to faculty.
Writing to learn engineering: Identifying effective techniques for the integration of written communication into engineering classes and curricula (NSF RIGEE project)Troy, C.D., B.K. Jesiek, N.M. Trellinger, and R.R. Essig
In Proceedings of the 2016 ASEE Annual Conference and Exposition, New Orleans, LA, June 26-29, 2016
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AbstractThe inclusion of writing-based exercises in technical courses has multiple learning benefits to students. Writing exercises not only serve to improve students’ written communication skills (i.e., “learn to write”), but can also be leveraged to develop critical thinking skills and promote deeper understanding of technical concepts (i.e., “write to learn”). Nevertheless, while writing-intensive assignments are relatively common in upper-level technical courses, especially in the form of laboratory and project reports, writing is often absent in the larger, required core courses that are taken by large numbers of engineering students. This is a missed opportunity to both enhance student learning of technical content as well as missed chance for students to have more writing practice. This NSF RIGEE project aims to investigate, support, and promote the inclusion of writing in technical courses, particularly introductory and core courses. Analysis of an engineering instructor survey carried out as part of the project revealed concerns about assessment and feedback on students’ written work. Additionally, writing instructors were interested in the creation of guides designed to aid instructors in the creation and tailoring of writing prompts for use in their existing technical courses. This paper introduces preliminary resources we have created in response to these stated needs, in order to help instructors develop, implement, and assess writing assignments in their courses. Current resources include a decision tree to help instructors create writing assignments within their classrooms and assessment rubrics that can easily be adapted to specific writing assignment needs. Resources will continue to be developed during the remainder of the project, culminating in a writing website geared towards instructors.
Testing for synchrony in recruitment among four Lake Michigan fish speciesBunnell, D. B., Höök, T. O., Troy, C. D., Liu, W., Madenjian, C. P., & Adams, J. V.
Canadian Journal of Fisheries and Aquatic Sciences, 999(1-10)
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AbstractIn the Great Lakes region, multiple fish species display intraspecific spatial synchrony in recruitment success, with interannual climate variation hypothesized as the most likely driver. In Lake Michigan, we evaluated whether climatic or other physical variables could also induce spatial synchrony across multiple species, including bloater (Coregonus hoyi), rainbow smelt (Osmerus mordax), yellow perch (Perca flavescens), and alewife (Alosa pseudoharengus). The residuals from stock–recruitment relationships revealed yellow perch recruitment to be correlated with recruitment of both rainbow smelt (r = 0.37) and alewife (r = 0.36). Across all four species, higher than expected recruitment occurred in 5 years between 1978 and 1987 and then switched to lower than expected recruitment in 5 years between 1996 and 2004. Generalized additive models revealed warmer spring and summer water temperatures and lower wind speeds corresponded to higher than expected recruitment for the nearshore-spawning species, and overall variance explained ranged from 14% (yellow perch) to 61% (alewife). For all species but rainbow smelt, higher recruitment also occurred in extremely high or low years of the North Atlantic Oscillation index. Future development of indices that describe the physical Great Lakes environment could improve understanding of how climate can synchronize fish populations within and across species.
Logarithmic velocity structure in the deep hypolimnetic waters of Lake MichiganTroy, C.D., D. Cannon, Q. Liao, and H. Bootsma
Journal of Geophysical Research: Oceans, 121(1), 949-965
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AbstractThe characteristics of the bottom boundary layer are reported from a Lake Michigan field study carried out in deep hypolimnetic waters (55 m depth) during the stratified period (June–September 2012). The sandy substrate at the measurement site was densely covered with invasive quagga mussels (mean size: 1.6 cm; mean density: 10,000 mussels m−2). The measurements reveal a sluggish, compact bottom boundary layer, with flow speeds at 1 mab less than 5 cm s−1 for most of the period, and a dominance of subinertial energy. A downwelling event caused the largest currents observed during the deployment (10 cm s−1 at 1 mab) and a logarithmic layer thickness of 15 m. In spite of the weak flow, logarithmic profile fitting carried out on high-resolution, near-bed velocity profiles show consistent logarithmic structure (90% of profiles). Flow was dominated by subinertial energy but strong modified by near-inertial waves. Fitted drag coefficients and roughness values are Cd1m = 0.004 and Z0 = 0.12 cm, respectively. These values increase with decreasing flow speed, but approach canonical values for 1 mab flow speeds exceeding 4 cm s−1. The estimated vertical extent of the logarithmic region was compact, with a mean value of 1.2 m and temporal variation that is reasonably described by Ekman scaling, 0.07 u*/f, and the estimated overall Ekman layer thickness was generally less than 10 m. Near-bed dissipation rates inferred from the law of the wall were 10−8−10−7 W kg−1 and turbulent diffusivities were 10−4−10−3 m2s−1.
Water quality estimation of river plumes in southern Lake Michigan using hyperionTan, J., K.A. Cherkauer, I. Chaubey, C.D. Troy, and R. Essig
Journal of Great Lakes Research, 42(3), 524-535
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AbstractThis study focuses on the calibration of an existing bio-geo-optical model for studying the spatial variability of water quality parameters including chlorophyll (CHL), non-algal particles (NAP), and colored dissolved organic matter (CDOM) in episodic
river plumes. The geographic focus is the St. Joseph River plume in southern Lake Michigan. One set of EO-1
Hyperion imagery and one set of boat-based
spectrometer measurements were successfully acquired to capture episodic plume events. Coincident water quality measurements were also collected during these plume events. In this study, a database of inherent
optical properties (IOPs) measurements and
spectral signatures was generated and used to calibrate the bio-geo-optical model. Field measured concentrations of NAP and CDOM at 67% of the sampled sites fall within one standard deviation of the retrieved means using the spectrometer measurements. The percentage of sites, 88%, is higher for the estimation of CHL concentrations. Despite the dynamic nature of the observed plume and the
time lag during field sampling, 77% of the sampled sites show field measured CHL and NAP concentrations falling within one standard deviation of the Hyperion derived values. The spatial maps of water quality parameters generated from the Hyperion image provided a synoptic view of water quality conditions. Results show that concentrations of NAP, CHL, and CDOM were more than three times higher in conjunction with river outflow, and inside the river plumes, than in ambient water. It is concluded that the storm-initiated plume is a significant source of sediments, carbon and chlorophyll to Lake Michigan.
2015
Shear dispersion from near‐inertial internal Poincaré waves in large lakesChoi, J. M., Troy, C. D., & Hawley, N.
Limnology and Oceanography, , 60(6), 2222-2235
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AbstractIn this work, we study mixed layer lateral dispersion that is enhanced by near-inertial internal Poincaré waves in the offshore region of a large stratified lake, Lake Michigan. We examine the hypothesis that the vertical shear created by near-inertial internal Poincaré waves is not only an energy source for vertical mixing in the thermocline and mixed layer, but also enhances horizontal dispersion via an unsteady shear flow dispersion mechanism. Complex empirical orthogonal function analysis reveals that the dominant shear structure is observed to mirror the thermal structure, with the location of maximum shear gradually lowered as the mixed layer deepens. This changing structure of shear and vertical mixing produces different characteristics in shear flow dispersion between the early and later stratified periods. The estimated depth-averaged surface layer vertical turbulent diffusivity grows from 10-5 m2s-1 to 10-3 m2s-1 over the stratified period, and the associated lateral dispersion coefficients are estimated as 0.1 - 40 m2s-1. The Poincaré waves are found to enhance greatly lateral dispersion for times less than the inertial period following release. In contrast, sub-inertial shear is the dominant mechanism responsible for shear dispersion for times greater than the inertial period. A simple approximation of the dispersion coefficient for lateral dispersion is developed, which scales as the product of surface current velocity (or wind friction velocity) and mixed layer depth. The calculated dispersion coefficients agree well with Okubo's diffusion diagram for times up to a week, which suggests that unsteady shear dispersion is a plausible mechanism to explain observed dispersion rates in the mixed layer for early times after release.
Something to write home(work) about: An analysis of writing exercises in fluid mechanics textbooksTrellinger, N.M., R.R. Essig, C.D. Troy, B.K. Jesiek, J. Boyd
In Proceedings of the 2015 ASEE Annual Conference and Exposition, Seattle, WA, June 14-17, 2015
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AbstractSomething to Write Home(work) About: An Analysis of Writing Exercises in Fluid Mechanics TextbooksAs assessments of learning outcomes are increasingly emphasized through accreditationrequirements (e.g., via ABET) and other quality assurance initiatives, written communication isone area that engineering instructors often find challenging to incorporate and assess. This isparticularly true in large core courses at the sophomore and junior levels. In this project, ananalysis of writing-based problems in fluid mechanics textbooks attempts to locate theavailability of activities that would allow students to practice writing, to learn through writing,and to use writing to relate course content to broader applications and contexts.This study is part of a larger ongoing project to understand and expand the incorporation ofwriting in large-lecture engineering courses, including investigation of faculty perspectives andtextbook assignments and assessments. This snapshot of writing-across-engineering will theninform efforts to create a range of writing activities (and assessment methods), mapped to ABETlearning outcomes, that instructors can incorporate in large engineering classes. Our objective isto examine widely-used textbooks in thermodynamics, materials, circuits, statics, and dynamics.In the preliminary analysis reported in this paper, we study problem sets from five popular fluidmechanics textbooks to find problems requiring more than merely numerical or calculatedanswers. As these writing-based problems are identified, we will categorize them in terms of thetype of prompt they represent, such as asking for explanation of a solution, application of aconcept to real-world examples, or problem-solving that requires description of processes.Once the number and types of writing problems in these textbooks has been analyzed andorganized, we will further explore how well the texts support actually using these exercises inclass. While writing-based prompts might be present, for example, instructors might not havethe resources, expertise, and/or support needed to incorporate them in their classes. Morespecifically, examination of solution sets and instructor’s guides will reveal how much thetextbooks equip instructors to assign and then assess the writing prompts that do exist. Finally,the extant writing assignments will be mapped to ABET learning outcomes to see how promptscan potentially be used to address key learning outcomes, e.g., in relation to the studentoutcomes in ABET Criterion 3.The result of this analysis will be an understanding of how well popular fluid mechanicstextbook assignments guide students in writing, and how well the textbooks equip instructors tomake use of those assignments. We will use this data to identify areas in which more writingassignments and assessment training would be useful for the teaching of engineering. This paperwill likely be of particular interest to faculty and staff interested in using writing to support avariety of technical, professional, and global learning outcomes in core engineering courses.
Species‐specific effects of subdaily temperature fluctuations on consumption, growth and stress responses in two physiologically similar fish species.Coulter, D. P., Sepúlveda, M. S., Troy, C. D., & Höök, T. O.
Ecology of Freshwater Fish.
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AbstractFluctuations in water temperature can have important physiological consequences for fishes. Effects of daily thermal cycles are well studied and can be beneficial, increasing prey consumption and growth rates when mean and maximum temperatures of the fluctuations are at or below the species’ optimum temperature. While less studied, subdaily temperature fluctuations are also common in many aquatic habitats and can be caused by both natural and anthropogenic processes. We performed laboratory experiments to examine how two fish species (yellow perch, Perca flavescens, and walleye, Sander vitreus) with similar thermal preferences respond to chronic exposure to subdaily temperature variability. We selected temperature treatments that reflected observed thermal variation after examining water temperature data from multiple aquatic systems. We then separately exposed yellow perch and walleye to a stable 23 °C treatment and 12-h cycles of 23 ± 2 °C or 23 ± 4 °C for 45 days. Adult yellow perch exposed to fluctuations of 23 ± 4 °C over 12 h expressed higher consumption, growth and food conversion efficiency than fish experiencing stable 23 °C. Temperature fluctuations, though, resulted in mortalities and the development of skin ulcers in yellow perch that did not occur under stable temperatures. In contrast, the same 12-h temperature fluctuations did not result in mortalities or stress responses in juvenile walleye. Moreover, unlike yellow perch, growth rates of walleye were lower under 12-h temperature fluctuations compared with the stable 23 °C treatment. Our results indicate that species with similar thermal preferences can respond differently to the same subdaily temperature fluctuations.
Diets and growth potential of early stage larval yellow perch and alewife in a nearshore region of southeastern Lake MichiganWithers, J.L., T.M. Sesterhenn, C.J. Foley, C.D. Troy, and T.O. Höök
Journal of Great Lakes Research Volume 41, Supplement 3, Pages 197-209
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AbstractTransition from endogenous to exogenous feeding is thought to be a critical period for many fish larvae, when
prey availability (type, size, and density) and ambient physical conditions (e.g., temperature, water clarity) can strongly influence survival. In Lake Michigan, two important fish species, yellow perch (
Perca flavescens) and alewife (
Alosa pseudoharengus), hatch and, presumably, begin exogenously feeding in the nearshore zone, an area characterized by short-term variation in environmental conditions. During 2010-2011, we examined environmental conditions and spatial and
temporal distributions of larval yellow perch, larval alewife, and their potential prey in a nearshore region of southeastern Lake Michigan. To consider implications of environmental conditions on larval fish habitat quality, we quantified diet contents of young larval yellow perch and alewife and modeled bioenergetic growth rate potential (an index of habitat quality) under observed and predicted prey consumption scenarios. As expected, in this dynamic nearshore zone temperatures, light levels, zooplankton prey availability, and resulting growth rate potential were highly variable. Many larval fish digestive tracts were empty, suggesting that starvation may affect cohort survival. Among early-feeding larval fish, relatively small diet items were common, with larval alewives consuming diatoms and larval yellow perch consuming veligers of invasive dreissenid mussels. Though the mechanisms underlying such prey consumption and the consequences of ingesting these prey items remain largely unexplored, our results suggest dreissenid mussel veligers present early-feeding larvae with a relatively abundant prey source that may partially offset the apparent low consumption of other prey sources within Lake Michigan’s nearshore region.
2014
Thermal habitat quality of aquatic organisms near power plant discharges: potential exacerbating effects of climate warmingCoulter, D. and M.S. Sepúlveda, C.D. Troy, T.O. Höök
Fisheries Ecology and Management, 21: 196-210
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AbstractWater temperature strongly affects aquatic ectotherms, as even slight temperature changes can have dramatic effects on physiological rates. Water bodies receiving industrial thermal discharges can undergo dramatic spatial and temporal changes in water temperature. To quantify effects on aquatic ectotherms, thermal habitat quality (bioenergetic growth rate potential; GRP) for zebra mussel, Dreissena polymorpha (Pallas), rusty crayfish, Orconectes rusticus (Girard), walleye, Sander vitreus (Mitchill) and smallmouth bass, Micropterus dolomieu (Lacepède) was estimated near two power plant thermal discharges on the Ohio River, USA, from 2010 to 2012 using bioenergetics models. These results were then compared with GRP under increased base temperatures representing climate warming. Growth rate potential for all species was low near the discharges during summer and highest in winter, with increasing prey consumption minimising the negative effects of increased temperatures. In their immediate vicinity, thermal discharges had a more adverse effect on GRP than plausible climate warming but primarily affected GRP over a small spatial area, particularly within 400 m downstream from the power plants. Examining thermal habitat suitability will become increasingly important as rising energy demand and climate change collectively affect aquatic organisms and their habitats.
Adventures in paragraph writing: The development and refinement of scalable and effective writing exercises for large-enrollment engineering coursesEssig, R., C. Troy, B.K. Jesiek, J. Boyd, and N.M. Trellinger
In Proceedings of the 2014 ASEE Annual Conference and Exposition, Indianapolis, IN, June 15-18, 2014
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AbstractAdventures in paragraph writing: the development and refinement of scalable and effective writing exercises for large enrollment engineering coursesThe ability to communicate effectively is a highly desirable attribute for today’s graduatingengineers. Additionally, the inclusion of communication components in technical courses hasbeen shown to enhance learning of technical content and can be leveraged to satisfy non-technical learning outcomes. However, the incorporation of such components in undergraduateengineering curricula remains challenging due to resource limitations, credit hour crunches, andother issues. This paper presents the design considerations and preliminary results from ourongoing work to create an effective, transferrable, low-overhead approach to paragraph writingexercises suitable for inclusion in any large engineering course. Key considerations in thedevelopment of these exercises include: identification of the motivations and learning outcomesfor each exercise; development and tailoring of writing prompts (questions) appropriate for theseoutcomes; and the development and implementation of an assessment and feedback strategy,including resource-efficient grading rubrics and techniques.Results are reported from the application of the paragraph writing exercise in a large civilengineering undergraduate fluid mechanics course (120 students; approximately 15assignments). A primary focus of this first application centered on two key components thatmust be refined in order for the exercise to be effective and transferrable: (1) the selection ofwriting prompts, and (2) assessment and feedback. Analysis of student paragraphs highlights theimportance of the writing prompts in the success of the exercise, indicating that specific wordchoice, question focus, and supplemental instruction greatly affected the level of writing studentssubmitted. Some writing prompts were selected to address and enhance technical content in thecourse, while other writing prompts were developed to broaden student awareness of engineeringin societal, environmental, and global contexts. In addition to developing productive writingprompts, the assessment and feedback strategies were evaluated using student surveys andfeedback. While minimal marking and holistic rubric assessment methods proved effective froma grading resource standpoint, students were frustrated by the lack of feedback associated withthese techniques and uncomfortable with the holistic grading rubric. Data from student surveyspoint to the importance of giving meaningful feedback to students, and providing them withopportunities to revise their written submissions. Student surveys also highlighted an unforeseenobstacle to the exercise: student resistance to writing in technical courses. We provide severalsuggestions for overcoming student resistance, as well as improved assessment and feedbackstrategies that better meet student needs while still not over-burdening instructors and teachingassistants.
Writing to learn engineering: Identifying effective fechniques for the integration of written communication into engineering classes and curricula (NSF RIGEE project)Troy, C.D., R.R. Essig, B.K. Jesiek, J. Boyd, N.M. Trellinger
In Proceedings of the 2014 ASEE Annual Conference and Exposition, Indianapolis, IN, June 15-18, 2014
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AbstractThe inclusion of writing-based exercises in technical courses has multiple learning benefits to students. Writing exercises not only serve to improve students’ written communication skills (i.e., “learn to write”), but can also be leveraged to develop critical thinking skills and promote deeper understanding of technical concepts (i.e., “write to learn”). Nevertheless, while writing-intensive assignments are relatively common in upper-level technical courses, especially in the form of laboratory and project reports, writing is often absent in the larger, required core courses that are taken by large numbers of engineering students. This is a missed opportunity to both enhance student learning of technical content as well as missed chance for students to have more writing practice. This NSF RIGEE project aims to investigate, support, and promote the inclusion of writing in technical courses, particularly introductory and core courses. Analysis of an engineering instructor survey carried out as part of the project revealed concerns about assessment and feedback on students’ written work. Additionally, writing instructors were interested in the creation of guides designed to aid instructors in the creation and tailoring of writing prompts for use in their existing technical courses. This paper introduces preliminary resources we have created in response to these stated needs, in order to help instructors develop, implement, and assess writing assignments in their courses. Current resources include a decision tree to help instructors create writing assignments within their classrooms and assessment rubrics that can easily be adapted to specific writing assignment needs. Resources will continue to be developed during the remainder of the project, culminating in a writing website geared towards instructors.
Spatial structure of internal Poincaré waves in Lake MichiganAhmed, S., C.D. Troy, and N. Hawley
Environmental Fluid Mechanics, , 14:1229
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AbstractIn this paper we examine the characteristics of near-inertial internal Poincaré waves in Lake Michigan (USA) as discerned from field experiments and hydrodynamic simulations. The focus is on the determination of the lateral and vertical structure of the waves. Observations of near-inertial internal wave properties are presented from two field experiments in southern Lake Michigan conducted during the years 2009 and 2010 at Michigan City (IN, USA) and Muskegon (MI, USA), respectively. Spectra of thermocline displacements and baroclinic velocities show that kinetic and potential baroclinic energy is dominated by near-inertial internal Poincaré waves. Vertical structure discerned from empirical orthogonal function analysis shows that this energy is predominantly vertical mode 1. Idealized hydrodynamic simulations using stratifications from early summer (June), mid-summer (July) and fall (September) identify the basin-scale internal Poincaré wave structure as a combination of single- and two-basin cells, similar to those identified in Lake Erie by Schwab, with near-surface velocities largest in the center of the northern and southern basins. Near-inertial bottom kinetic energy is seen to have roughly constant magnitude over large swathes across the basin, with higher magnitude in the shallower areas like the Mid-lake Plateau, as compared with the deep northern and southern basins. The near-bottom near-inertial kinetic energy when mapped appears similar to the bottom topography map. The wave-induced vertical shear across thermocline is concentrated along the longitudinal axis of the lake basin, and both near-bottom velocities and thermocline shear are reasonably explained by a simple conceptual model of the expected transverse variability.
2012
A Year of Internal Poincaré Waves in Southern Lake MichiganChoi, J. M., C. D. Troy, T.-C. Hsieh, N. Hawley, and M. J. McCormick
Journal of Geophysical Research
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AbstractA unique set of full year, deep water observations from the middle of Lake Michigan's southern basin are analyzed to quantify the seasonal variability of the dominant near-inertial internal Poincaré wave. At this mid-lake location, the Poincaré wave is seen to describe more than 80% of the observed surface current variability for much of the year, with characteristic near-inertial frequency and clockwise-rotating velocities. The dominance of the near-inertial seiche on the flow decreases with depth. The wave persists during the “stratified period,” roughly May through late December, and is supported by as few as 1–2 degrees of thermal stratification over 150 m; only after complete water column mixing does the wave go dormant for January through April. The strongest Poincaré wave activity is seen to correspond to the period of strongest summer thermal stratification (August), in spite of the relatively weak winds at this time. A simple inertial slab model optimized with linear friction is shown to capture the seasonal variability of the near-inertial energy at this location reasonably well. The vertical structure of the wave shows good agreement with that calculated with a standard normal modes formulation, which is in turn used to characterize the potential shear and mixing caused by the wave. Late-spring and summer events of elevated Poincaré wave activity are shown to generate sufficiently strong shear with persistent periods of sub-1 Richardson numbers within the thermocline, suggesting that the near-inertial seiche is likely generating thermocline instabilities in the lake's interior.
Cross-shelf thermal structure in Lake Michigan during the stratified periodsTroy, C.D., Ahmed, S., Hawley, N., and A. Goodwell
Journal of Geophysical Research, VOL. 117, C02028, 16 PP., 2012
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AbstractResults from a field experiment in southern Lake Michigan are used to quantify the cross-shelf nearshore variability in Great Lakes temperatures during the stratified season. The experiment was conducted along the Indiana coast of southern Lake Michigan, with temperature and velocity moorings arranged in a cross-shelf transect that extended to approximately 20 km from shore (40 m depth). The field site is noteworthy because of its location at the end of a major axis of an elliptical Great Lake, the relatively mild bathymetric slope, and local shoreline orientation that is perpendicular relative to the dominant summer winds. Measurements demonstrate that the location of the thermocline-bottom intersection is highly variable, causing a wide zone of extreme thermal variability in the nearshore region with time scales of variability ranging from hours to months. Near-inertial internal Poincaré waves are shown to cause large thermocline excursions but primarily only during periods of elevated activity. Several full upwelling events were observed, but in general, they were brief, lasting only 1–2 days, and had very limited spatial extent (2.5 km or less). Nonetheless, the offshore extent of the upwelling front was shown to be reasonably estimated with a simple estimate of the cross-shelf transport caused by alongshore wind events. A persistent feature that determined the zone of elevated thermal variability (the thermocline-shelf intersection point) was the strongly tilted thermocline, which resulted in the thermocline being located very close to shore. No evidence was found to support the hypothesis that internal Kelvin waves affect thermal variability at the study location.
2011
The mixing efficiency of interfacial waves breaking at a ridge. Part I: Overall mixing efficiencyHult, E.L., C.D. Troy, and J.R. Koseff
Journal of Geophysical Research, VOL. 116, C02003
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AbstractThe overall mixing efficiency of periodic, interfacial waves breaking at a Gaussian ridge is investigated through laboratory experiments. Cumulative measurements are used to investigate the fraction of the wave energy lost in the breaking event that contributes to irreversible mixing of the background density gradient. Using the tank as a control volume, the distribution of energy into reflected waves, transmitted waves, and dissipation and irreversible mixing from the breaking event is determined. The overall fraction of wave energy lost in the breaking event that is converted irreversibly to mixing is found to be 3–8%, which is low compared with typical values of around 20% for steady, parallel, stratified shear instabilities. Spatial variability in the mixing event may contribute to the relatively low overall efficiency of the event.
The mixing efficiency of interfacial waves breaking at a ridge. Part II: Local EnergeticsHult, E.L., C.D. Troy, and J.R. Koseff
Journal of Geophysical Research, VOL. 116, C02004
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AbstractThe efficiency with which internal wave energy is converted irreversibly to diapycnal mixing in bathymetry-induced mixing events is of great importance to larger-scale ocean modeling efforts. High-resolution laboratory measurements are used to investigate the spatial and temporal variability of interfacial wave breaking events at a submerged bathymetric ridge. From high spatial resolution measurements, it appears the local efficiency can vary significantly. Parameterizations based on the turbulent Reynolds number and Froude number suggest that the local mixing efficiency within the overturning patch at the interface is 10–17% but the local efficiency is near zero within the relatively homogenous layers. When the local mixing efficiency is integrated over the entire event, the resulting overall efficiency is consistent with the result from Part 1 that the overall event efficiency is 3–8%. This spatial variation in the mixing efficiency reinforces the importance of dynamic mixing efficiency parameterizations based on local stratified turbulence parameters.
2009
The breaking of interfacial waves at a submerged bathymetric ridgeHult, E.L., C.D. Troy, and J.R. Koseff
Journal of Fluid Mechanics, 637, 45-71
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AbstractThe breaking of periodic progressive two-layer interfacial waves at a Gaussian ridge is investigated through laboratory experiments. Length scales of the incident wave and topography are used to parameterize when and how breaking occurs. Qualitative observations suggest both shear and convection play a role in the instability of waves breaking at the ridge. Simultaneous particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) measurements are used to calculate high resolution, two-dimensional velocity and density fields from which the local gradient Richardson number Rig is calculated. The transition to breaking occurred when 0.2 ≤ Rig ≤ 0.4. In these wave-ridge breaking events, the destabilizing effects of waves steepening in shallow layers may be responsible for breaking at higher Rig than for similar waves breaking through shear instability in deep water (Troy & Koseff, J. Fluid Mech., vol. 543, 2005b, p. 107). Due to the effects of unsteadiness, nonlinear shoaling and flow separation, the canonical Rig > 0.25 is not sufficient to predict the stability of interfacial waves. A simple model is developed to estimate Rig in waves between finite depth layers using scales of the incident wave scale and topography. The observed breaking transition corresponds with a constant estimated value of Rig from the model, suggesting that interfacial shear plays an important role in initial wave instability. For wave amplitudes above the initial breaking transition, convective breaking events are also observed.
2006
The viscous decay of progressive interfacial wavesTroy, C.D., and J.R. Koseff
Physics of Fluids, 18, 026602
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AbstractThe viscous damping of progressive, two-layer interfacial waves is examined theoretically and experimentally. Traditional water wave theory is modified to derive the damping rates associated with interfacial wave propagation in a rectangular channel. The individual wave damping contributions are considered from the bottom, side, and interfacial boundary layers, as well as the damping associated with the wave-induced velocities within the homogenous fluid layers. These results show that for most laboratory-scale experiments, sidewall friction plays the dominant role in wave damping. Laboratory experiments are conducted to verify the damping rates for progressive two-layer internal waves in a rectangular channel. Experiments are conducted on both monochromatic and polychromatic wave trains. The results of these experiments are in good agreement with the derived damping rates, but show poorer agreement for large-amplitude waves when the sidewall boundary layers become turbulent. More work is necessary to quantify the damping associated with nonlinear internal waves in order to allow for accurate interpretation of the results from laboratory experiments.
2005
The instability and breaking of long internal wavesTroy, C.D., and J.R. Koseff
Journal of Fluid Mechanics, 543, 107-136
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AbstractLaboratory experiments are carried out to determine the nature of internal wave breaking and the limiting wave steepness for progressive, periodic, lowest-mode internal waves in a two-layer, miscible density stratification. Shoaling effects are not considered. The waves investigated here are long relative to the thickness of the density interface separating the two fluid layers. Planar laser-induced fluoresence (PLIF) flow visualization shows that wave breaking most closely resembles a Kelvin–Helmholtz shear instability originating in the high-shear wave crest and trough regions. However, this instability is strongly temporally and spatially modified by the oscillations of the driving wave shear. Unlike a steady stratified shear layer, the wave instability discussed here is not governed by the canonical $it Ri{=}1/4$ stability limit. Instead, the wave time scale (the time scale of the destabilizing shear) imposes an additional constraint on instability, lowering the critical Richardson number below 1/4. Experiments were carried out to quantify this instability threshold, and show that, for the range of wavenumbers considered in this study, the critical wave steepness at which the wave breaking occurs is wavenumber-dependent (unlike surface waves). The corresponding critical wave Richardson numbers at incipient wave breaking are well below 1/4, in consonance with a modified instability analysis based on results from stratified shear flow instability theory.
The generation and quantitative visualization of breaking internal wavesTroy, C. D., & Koseff, J. R.
Experiments in fluids, 38(5), 549-562
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AbstractNew techniques for the generation and quantitative visualization of breaking progressive internal waves are presented. Laboratory techniques applicable to general stratified flow experiments are also demonstrated. The planar laser-induced fluorescence (PLIF) technique is used to produce calibrated images of the wave breaking process, and the details of the PLIF measurements are described in terms of the necessary corrections and considerations for the application of PLIF to stratified flows. Results of the flow visualization and wave generation techniques are presented, which show that the nature of internal wave breaking is strongly dependent on the type of breaking internal wave considered.