Katherine McCaffrey | University of Colorado, Boulder (original) (raw)

No longer an academic researcher, I am now a Research Analyst for S&P Global Market Intelligence. See my LinkedIn profile for up-to-date professional activities: LinkedIn.com/in/Katherine-McCaffrey

I received my PhD in Atmospheric and Ocean Sciences at CU-Boulder, and completed an NRC RAP postdoctoral fellowship at the National Oceanic and Atmospheric Administration's Earth Systems Research Laboratory (NOAA-ESRL), Physical Sciences Division. I then worked as a Research Scientist at the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder and NOAA-ESRL.

During my time at CU, I was a Teaching Assistant for the ATOC Weather Lab for two semesters before beginning research with the Fox-Kemper Group. I conducted my research under the CIRES and NOAA-ESRL Graduate Student Fellowship, from Fall 2010-Spring 2014.

For my first research project, I computed the second-order temperature structure function from data collected by Argo profiling floats (http://www.argo.ucsd.edu/). Though many theories predict the structure function slope, which is closely related to the kinetic energy spectral slope, few observations at depth have been made to indicate which turbulent scheme exists in the oceans below the thermocline. I compared the structure functions and their dependence on latitude, depth, and strength of eddy kinetic energy (eddy-rich vs eddy-poor regions). Though I am not setting out to explain why the theories are right or wrong, the data analysis that I performed is the first to reveal what is happening down to 2,000 meters.

My second project was in characterizing turbulence in potential tidal energy sites. First, I used acoustic Doppler velocimeter observations from the Puget Sound, WA to parameterize the anisotropy, intermittency, and coherence in the tidal flow. Next, I am comparing the turbulence statistics from the National Renewable Energy Laboratory's stochastic tidal turbulence simulator (HydroTurbSim) and a Large Eddy Simulation model to the observations from the Puget Sound.

In August 2014, I began a postdoctoral research project with Dr Jim Wilczak at NOAA-ESRL in Boulder, CO. There, I analyzed wind profiling radar (WPR) observations to characterize atmospheric turbulence and improve wind forecast models.

My postdoctoral research has extended in my CIRES position as I compare observations to NWP data as a part of the second Wind Forecast Improvement Project, a DOE- and NOAA-funded project. My research includes model verification, meteorological analysis of large forecast error events, and meteorological characterization of events that impact wind energy generation in a region of complex terrain.
Supervisors: Jim Wilczak and Baylor Fox-Kemper
Phone: 303-497-5096
Address: David Skaggs Research Center, Rm 3B704

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Papers by Katherine McCaffrey

Observations of turbulence in the planetary boundary layer are critical for developing and evalua... more Observations of turbulence in the planetary boundary layer are critical for developing and evaluating boundary layer parameterizations in mesoscale numerical weather prediction models. These observations, however, are expensive and rarely profile the entire boundary layer. Using optimized configurations for 449 and 915 MHz wind profiling radars during the eXperimental Planetary boundary layer Instrumentation Assessment (XPIA), improvements have been made to the historical methods of measuring vertical velocity variance through the time series of vertical velocity, as well as the Doppler spectral width. Using six heights of sonic anemometers mounted on a 300 m tower, correlations of up to R2 = 0.74 are seen in measurements of the large- scale variances from the radar time series and R2 = 0.79 in measurements of small-scale variance from radar spectral widths. The total variance, measured as the sum of the small and large scales, agrees well with sonic anemometers, with R2 = 0.79. Correlation is higher in daytime convective boundary layers than nighttime stable conditions when turbulence levels are smaller. With the good agreement with the in situ measurements, highly resolved profiles up to 2 km can be accurately observed from the 449MHz radar and 1km from the 915 MHz radar. This optimized configuration will provide unique observations for the verification and improvement to boundary layer parameterizations in mesoscale models.

The eXperimental Planetary boundary layer Instrumentation Assessment (XPIA) field campaign took p... more The eXperimental Planetary boundary layer Instrumentation Assessment (XPIA) field campaign took place in March through May 2015 at the Boulder Atmospheric Observatory, utilizing its 300 m meteorological tower, instrumented with two sonic anemometers mounted on opposite sides of the tower at six heights. This allowed for at least one sonic anemometer at each level to be upstream of the tower at all times and for identification of the times when a sonic anemometer is in the wake of the tower frame. Other instrumentation, including profiling and scanning lidars aided in the identification of the tower wake. Here we compare pairs of sonic anemometers at the same heights to identify the range of directions that are affected by the tower for each of the opposing booms. The mean velocity and turbulent kinetic energy are used to quantify the wake impact on these first- and second-order wind measurements, showing up to a 50 % reduction in wind speed and an order of magnitude increase in turbulent kinetic energy. Comparisons of wind speeds from profiling and scanning lidars confirmed the extent of the tower wake, with the same reduction in wind speed observed in the tower wake, and a speed-up effect around the wake boundaries. Wind direction differences between pairs of sonic anemometers and between sonic anemometers and lidars can also be significant, as the flow is deflected by the tower structure. Comparisons of lengths of averaging intervals showed a decrease in wind speed deficit with longer averages, but the flow deflection remains constant over longer averages. Furthermore, asymmetry exists in the tower effects due to the geometry and placement of the booms on the triangular tower. An analysis of the percentage of observations in the wake that must be removed from 2 min mean wind speed and 20 min turbulent values showed that removing even small portions of the time interval due to wakes impacts these two quantities. However, a vast majority of intervals have no observations in the tower wake, so removing the full 2 or 20 min intervals does not diminish the XPIA dataset.

Observations of turbulence in the planetary boundary layer are crucial for validation of paramete... more Observations of turbulence in the planetary boundary layer are crucial for validation of parameterizations in numerical weather prediction models. However, these observations are sparse. For this reason, demonstrating the ability of commonly-used wind profiling radars (WPRs) to measure turbulence dissipation rates would be greatly beneficial. During the XPIA field campaign at the Boulder Atmospheric Observatory, two WPRs operated in an optimized configuration, using high spectral resolution for increased accuracy of Doppler spectral width, specifically chosen to measure turbulence from a vertically-pointing beam only. Multiple post-processing techniques, including different numbers of spectral averages and peak-processing algorithms for calculating spectral moments, were analyzed to determine the most accurate procedures for measuring turbulence dissipation rates using the information contained in the Doppler spectral width, and compared to sonic anemometers mounted on a 300-meter tower. The optimal settings were determined, producing a constant low bias, which was later corrected. Resulting measurements of turbulence dissipation rates correlated well (R2 = 0.57) with sonic anemometers, and profiles up to 2 km from the 449-MHz WPR and 1 km from the 915-MHz WPR were observed.

To assess current capabilities for measuring flow within the atmospheric boundary layer, includin... more To assess current capabilities for measuring flow within the atmospheric boundary layer, including within wind farms, the U.S. Dept. of Energy sponsored the eXperimental Planetary boundary layer Instrumentation Assessment (XPIA) campaign at the Boulder Atmospheric Observatory (BAO) in spring 2015. Herein, we summarize the XPIA field experiment, highlight novel measurement approaches, and quantify uncertainties associated with these measurement methods. Line-of-sight velocities measured by scanning lidars and radars exhibit close agreement with tower measurements, despite differences in measurement volumes. Virtual towers of wind measurements, from multiple lidars or radars, also agree well with tower and profiling lidar measurements. Estimates of winds over volumes from scanning lidars and radars are in close agreement, enabling assessment of spatial variability. Strengths of the radar systems used here include high scan rates, large domain coverage, and availability during most precipitation events, but they struggle at times to provide data during periods with limited atmospheric scatterers. In contrast, for the deployment geometry tested here, the lidars have slower scan rates and less range, but provide more data during non-precipitating atmospheric conditions. Microwave radiometers provide temperature profiles with approximately the same uncertainty as Radio-Acoustic Sounding Systems (RASS). Using a motion platform, we assess motion-compensation algorithms for lidars to be mounted on offshore platforms. Finally, we highlight cases for validation of mesoscale or large-eddy simulations, providing information on accessing the archived dataset. We conclude that modern remote sensing systems provide a generational improvement in observational capabilities, enabling resolution of fine-scale processes critical to understanding inhomogeneous boundary-layer flows.

ASME 2010 Summer Bioengineering Conference, Parts A and B, 2010

Page 1. CRYOSURGERY AS AN ALTERNATIVE TREATMENT FOR MENORRHAGIA AND UTERINE FIBROIDS Katherine L.... more Page 1. CRYOSURGERY AS AN ALTERNATIVE TREATMENT FOR MENORRHAGIA AND UTERINE FIBROIDS Katherine L. McCaffrey1, Karen M. Rose1, John P. Abraham2 1Department of Mathematics University of Saint Thomas Saint Paul, MN 55105 ...

2010 14th International Heat Transfer Conference, Volume 1, 2010

ABSTRACT Nearly 80% of all women may suffer from menorrhagia caused by uterine fibroids (leiomyom... more ABSTRACT Nearly 80% of all women may suffer from menorrhagia caused by uterine fibroids (leiomyomas) which are benign tumors made up of muscle and fibrous tissue that grow from the muscular wall of the uterus. The vast majority of women whose symptoms are strong enough to require treatment obtain a hysterectomy. Other treatment options which are less invasive than hysterectomy include thermal therapies such as thermal ablation or cryosurgical removal of tissue. This project numerically evaluates the efficacy of a liquid-nitrogen-based cryotherapy for the treatment of uterine fibroids. A bioheat transfer model was utilized which includes both the effects of blood perfusion and the impacts of liquid-to-solid phase change. Changes in all physical properties including thermal conductivity, heat capacity, and perfusion rate were taken into account as the tissue passed through a range of temperatures where it would be transitioning from unfrozen to fully frozen. The numerical model was based on a one-dimensional unsteady bioheat equation. The results show that even for the direct-contact cooling, it is unlikely that intracellular ice would form during the procedure. On the other hand, based on data obtained from previous cell-survival studies, it was found that necrosis would occur when the cooling rates exceeded 30°/min. According to the present numerical results, necrosis would occur within the tissue up to a depth of approximately 5.8 mm, thereby ensuring that sufficient tissue would be cryosurgically destroyed to result in effective treatment.

Figure 2 shows the structure function in the Atlantic Ocean at 30-35N at several depths. It was e... more Figure 2 shows the structure function in the Atlantic Ocean at 30-35N at several depths. It was expected that the overall strength of the structure function would be lower at depth, since there is more turbulence in the mixed layer, but the structure function is approximately the same at all depths. Theory predicted that the spectral slope would be 2 at the surface, and this is clearly not the case. The structure function slope of 0 is equivalent to a spectral slope of-1, as was achieved by Batchelor's theory of tracer spectra. A forcing scale below ...

Journal of Marine Research, 2012

ABSTRACT The restratification of the cold wakes of Tropical Cyclones Fanapi, Frances, Igor and Ka... more ABSTRACT The restratification of the cold wakes of Tropical Cyclones Fanapi, Frances, Igor and Katrina are examined based on derived scalings for processes that can restore the hurricane wake toward the precyclone conditions. The different restoration processes depend on the parameters of the wake: depth, width, buoyancy anomaly and wind stress. The parameters needed are derived for each wake from satellite and climatological data. The scalings are based on model results and existing parameterizations, including air-sea heat fluxes (one-dimensional) Ekman buoyancy fluxes (two-dimensional) and mixed layer eddies (three-dimensional). The dominant surface restoration occurs by a combination of surface fluxes and Ekman buoyancy fluxes, while the submesoscale mixed layer eddy bolus fluxes are the dominant subsurface effect.

The Argo profiling float network has repeatedly sampled much of the world’s ocean. This study use... more The Argo profiling float network has repeatedly sampled much of the world’s ocean. This study uses Argo temperature and salinity data to form the tracer structure function of ocean variability at the macro-scale (10 − 1000 km, mesoscale and above). Here, second- order temperature and salinity structure functions over horizontal separations are calculated along either pressure or potential density surfaces, which allows analysis of both active and passive tracer structure functions. Using Argo data, a map of global variance is created from the climatological average and each datum. When turbulence is homogeneous, the structure function slope from Argo can be related to the wavenumber spectrum slope in ocean temperature or salinity variability. This first application of structure function techniques to Argo data gives physically meaningful results based on bootstrapped confidence intervals, showing geographical dependence of the structure functions with slopes near 2/3 on average, independent of depth.

Renewable Energy, Apr 2015

As interest in marine renewable energy increases, observations are crucial for understanding the ... more As interest in marine renewable energy increases, observations are crucial for understanding the environments that prospective turbines will encounter. Data from an acoustic Doppler velocimeter in Puget Sound, WA are used to perform a detailed characterization of the turbulent flow encountered by a turbine in a tidal strait. Metrics such as turbulence intensity, structure functions, probability density functions, intermittency, coherent turbulence kinetic energy, anisotropy invariants, and a new scalar measure of anisotropy are used to characterize the turbulence. The results indicate that the scalar anisotropy magnitude can be used to identify and parameterize coherent, turbulent events in the flow. An analysis of the anisotropy characteristics leads to a physical description of turbulent stresses as being primarily one- or two-dimensional, in contrast to isotropic, three-dimensional turbulence. A new measure of the anisotropy magnitude is introduced to quantify the level of anisotropic, coherent turbulence in a coordinate-independent way. These diagnostics and results will be useful for improved realism in modeling the performance and loading of turbines in realistic ocean environments.

Journal of Marine Research

The restratification of the cold wakes of Tropical Cyclones Fanapi, Frances, Igor, and Katrina ar... more The restratification of the cold wakes of Tropical Cyclones Fanapi, Frances, Igor, and Katrina are examined based on derived scalings for processes that can restore the hurricane wake toward the pre-cyclone conditions. The different restoration processes depend on the parameters of the wake: depth, width, buoyancy anomaly, and wind stress. The parameters needed are derived for each wake from satellite and climatological data. The scalings are based on model results and existing parameterizations, including air-sea heat fluxes (1d), Ekman buoyancy fluxes (2d), and mixed layer eddies (3d). The dominant surface restoration occurs by a combination of surface fluxes and Ekman buoyancy fluxes, while the submesoscale mixed layer eddy bolus fluxes are the dominant subsurface effect.

Talks by Katherine McCaffrey

Thesis Chapters by Katherine McCaffrey

Turbulence is inherently chaotic and unsteady, so observing it and modeling it are no easy tasks.... more Turbulence is inherently chaotic and unsteady, so observing it and modeling it are no easy tasks. The ocean’s sheer size makes it even more difficult to observe, and its unpredictable and ever-changing forcings introduce additional complexities. Turbulence in the oceans ranges from basin scale to the scale of the molecular viscosity. The method of energy transfer between scales is, however, an area of active research, so observations of the ocean at all scales are crucial to understanding the basic dynamics of its motions. In this collection of work, I use a variety of datasets to characterize a wide range of scales of turbulence, including observations from multiple instruments and from models with different governing equations.
I analyzed the largest scales of the turbulent range using the global salinity data of the Argo profiling float network. Taking advantage of the scattered and discontinuous nature of this dataset, the second-order structure function was calculated down to 2000m depth, and shown to be useful for predicting spectral slopes. Results showed structure function slopes of 2 at small scales, and 0 at large scales, which corresponds with spectral slopes of -5/3 at small scales, and −1 at large scales. Using acoustic Doppler velocity measurements, I characterized the meter- to kilometer-scale turbulence at a potential tidal energy site in the Puget Sound, WA. Acoustic Doppler current profiler (ADCP) and acoustic Doppler velocimeter (ADV) observations provided the data for an analysis that includes coherence, anisotropy, and intermittency. In order to more simply describe these features, a parameterization was done with four turbulence metrics, and the anisotropy magnitude, introduced here, was shown to most closely capture the coherent events. Then, using both the NREL TurbSim stochastic turbulence generator and the NCAR large-eddy simulation (LES) model, I calculated turbulence statistics to validate the accuracy of these methods in reproducing the tidal channel. TurbSim models statistics at the height of a turbine hub (5m) well, but do not model coherent events, while the LES does create these events, but not realistically in this configuration, based on comparisons with observations.
Each of the datasets have disadvantages when it comes to observing turbulence. The Argo network is sparse in space, and few measurements are taken simultaneously in time. Therefore spatial and temporal averaging is needed, which requires the turbulence to be homogeneous and stationary if it is to be generalized. Though the acoustic Doppler current profiler provides a vertical profile of velocities, the fluctuations are dominated by instrument noise and beam spread, preventing it from being used for most turbulence metrics. ADV measurements have much less noise, and no beam spread, but the observations are made at one point in space, limiting us to temporal statistics or an assumption of “frozen turbulence” to infer spatial scales. As for the models, TurbSim does not have any real-world forcing, and uses parameterized spectra, and coherence functions and randomizes phase information, while LES models must make assumptions about sub-grid scales, which may be inaccurate. Additionally, all models are set up with idealizations of the forcing and domain, which may make the results unlike observations in a particular location and time. Despite these difficulties in observing and characterizing turbulence, I present several quantities that use the imperfect, yet still valuable observations, to attain a better description of the turbulence in the oceans.

Observations of turbulence in the planetary boundary layer are critical for developing and evalua... more Observations of turbulence in the planetary boundary layer are critical for developing and evaluating boundary layer parameterizations in mesoscale numerical weather prediction models. These observations, however, are expensive and rarely profile the entire boundary layer. Using optimized configurations for 449 and 915 MHz wind profiling radars during the eXperimental Planetary boundary layer Instrumentation Assessment (XPIA), improvements have been made to the historical methods of measuring vertical velocity variance through the time series of vertical velocity, as well as the Doppler spectral width. Using six heights of sonic anemometers mounted on a 300 m tower, correlations of up to R2 = 0.74 are seen in measurements of the large- scale variances from the radar time series and R2 = 0.79 in measurements of small-scale variance from radar spectral widths. The total variance, measured as the sum of the small and large scales, agrees well with sonic anemometers, with R2 = 0.79. Correlation is higher in daytime convective boundary layers than nighttime stable conditions when turbulence levels are smaller. With the good agreement with the in situ measurements, highly resolved profiles up to 2 km can be accurately observed from the 449MHz radar and 1km from the 915 MHz radar. This optimized configuration will provide unique observations for the verification and improvement to boundary layer parameterizations in mesoscale models.

The eXperimental Planetary boundary layer Instrumentation Assessment (XPIA) field campaign took p... more The eXperimental Planetary boundary layer Instrumentation Assessment (XPIA) field campaign took place in March through May 2015 at the Boulder Atmospheric Observatory, utilizing its 300 m meteorological tower, instrumented with two sonic anemometers mounted on opposite sides of the tower at six heights. This allowed for at least one sonic anemometer at each level to be upstream of the tower at all times and for identification of the times when a sonic anemometer is in the wake of the tower frame. Other instrumentation, including profiling and scanning lidars aided in the identification of the tower wake. Here we compare pairs of sonic anemometers at the same heights to identify the range of directions that are affected by the tower for each of the opposing booms. The mean velocity and turbulent kinetic energy are used to quantify the wake impact on these first- and second-order wind measurements, showing up to a 50 % reduction in wind speed and an order of magnitude increase in turbulent kinetic energy. Comparisons of wind speeds from profiling and scanning lidars confirmed the extent of the tower wake, with the same reduction in wind speed observed in the tower wake, and a speed-up effect around the wake boundaries. Wind direction differences between pairs of sonic anemometers and between sonic anemometers and lidars can also be significant, as the flow is deflected by the tower structure. Comparisons of lengths of averaging intervals showed a decrease in wind speed deficit with longer averages, but the flow deflection remains constant over longer averages. Furthermore, asymmetry exists in the tower effects due to the geometry and placement of the booms on the triangular tower. An analysis of the percentage of observations in the wake that must be removed from 2 min mean wind speed and 20 min turbulent values showed that removing even small portions of the time interval due to wakes impacts these two quantities. However, a vast majority of intervals have no observations in the tower wake, so removing the full 2 or 20 min intervals does not diminish the XPIA dataset.

Observations of turbulence in the planetary boundary layer are crucial for validation of paramete... more Observations of turbulence in the planetary boundary layer are crucial for validation of parameterizations in numerical weather prediction models. However, these observations are sparse. For this reason, demonstrating the ability of commonly-used wind profiling radars (WPRs) to measure turbulence dissipation rates would be greatly beneficial. During the XPIA field campaign at the Boulder Atmospheric Observatory, two WPRs operated in an optimized configuration, using high spectral resolution for increased accuracy of Doppler spectral width, specifically chosen to measure turbulence from a vertically-pointing beam only. Multiple post-processing techniques, including different numbers of spectral averages and peak-processing algorithms for calculating spectral moments, were analyzed to determine the most accurate procedures for measuring turbulence dissipation rates using the information contained in the Doppler spectral width, and compared to sonic anemometers mounted on a 300-meter tower. The optimal settings were determined, producing a constant low bias, which was later corrected. Resulting measurements of turbulence dissipation rates correlated well (R2 = 0.57) with sonic anemometers, and profiles up to 2 km from the 449-MHz WPR and 1 km from the 915-MHz WPR were observed.

To assess current capabilities for measuring flow within the atmospheric boundary layer, includin... more To assess current capabilities for measuring flow within the atmospheric boundary layer, including within wind farms, the U.S. Dept. of Energy sponsored the eXperimental Planetary boundary layer Instrumentation Assessment (XPIA) campaign at the Boulder Atmospheric Observatory (BAO) in spring 2015. Herein, we summarize the XPIA field experiment, highlight novel measurement approaches, and quantify uncertainties associated with these measurement methods. Line-of-sight velocities measured by scanning lidars and radars exhibit close agreement with tower measurements, despite differences in measurement volumes. Virtual towers of wind measurements, from multiple lidars or radars, also agree well with tower and profiling lidar measurements. Estimates of winds over volumes from scanning lidars and radars are in close agreement, enabling assessment of spatial variability. Strengths of the radar systems used here include high scan rates, large domain coverage, and availability during most precipitation events, but they struggle at times to provide data during periods with limited atmospheric scatterers. In contrast, for the deployment geometry tested here, the lidars have slower scan rates and less range, but provide more data during non-precipitating atmospheric conditions. Microwave radiometers provide temperature profiles with approximately the same uncertainty as Radio-Acoustic Sounding Systems (RASS). Using a motion platform, we assess motion-compensation algorithms for lidars to be mounted on offshore platforms. Finally, we highlight cases for validation of mesoscale or large-eddy simulations, providing information on accessing the archived dataset. We conclude that modern remote sensing systems provide a generational improvement in observational capabilities, enabling resolution of fine-scale processes critical to understanding inhomogeneous boundary-layer flows.

ASME 2010 Summer Bioengineering Conference, Parts A and B, 2010

Page 1. CRYOSURGERY AS AN ALTERNATIVE TREATMENT FOR MENORRHAGIA AND UTERINE FIBROIDS Katherine L.... more Page 1. CRYOSURGERY AS AN ALTERNATIVE TREATMENT FOR MENORRHAGIA AND UTERINE FIBROIDS Katherine L. McCaffrey1, Karen M. Rose1, John P. Abraham2 1Department of Mathematics University of Saint Thomas Saint Paul, MN 55105 ...

2010 14th International Heat Transfer Conference, Volume 1, 2010

ABSTRACT Nearly 80% of all women may suffer from menorrhagia caused by uterine fibroids (leiomyom... more ABSTRACT Nearly 80% of all women may suffer from menorrhagia caused by uterine fibroids (leiomyomas) which are benign tumors made up of muscle and fibrous tissue that grow from the muscular wall of the uterus. The vast majority of women whose symptoms are strong enough to require treatment obtain a hysterectomy. Other treatment options which are less invasive than hysterectomy include thermal therapies such as thermal ablation or cryosurgical removal of tissue. This project numerically evaluates the efficacy of a liquid-nitrogen-based cryotherapy for the treatment of uterine fibroids. A bioheat transfer model was utilized which includes both the effects of blood perfusion and the impacts of liquid-to-solid phase change. Changes in all physical properties including thermal conductivity, heat capacity, and perfusion rate were taken into account as the tissue passed through a range of temperatures where it would be transitioning from unfrozen to fully frozen. The numerical model was based on a one-dimensional unsteady bioheat equation. The results show that even for the direct-contact cooling, it is unlikely that intracellular ice would form during the procedure. On the other hand, based on data obtained from previous cell-survival studies, it was found that necrosis would occur when the cooling rates exceeded 30°/min. According to the present numerical results, necrosis would occur within the tissue up to a depth of approximately 5.8 mm, thereby ensuring that sufficient tissue would be cryosurgically destroyed to result in effective treatment.

Figure 2 shows the structure function in the Atlantic Ocean at 30-35N at several depths. It was e... more Figure 2 shows the structure function in the Atlantic Ocean at 30-35N at several depths. It was expected that the overall strength of the structure function would be lower at depth, since there is more turbulence in the mixed layer, but the structure function is approximately the same at all depths. Theory predicted that the spectral slope would be 2 at the surface, and this is clearly not the case. The structure function slope of 0 is equivalent to a spectral slope of-1, as was achieved by Batchelor's theory of tracer spectra. A forcing scale below ...

Journal of Marine Research, 2012

ABSTRACT The restratification of the cold wakes of Tropical Cyclones Fanapi, Frances, Igor and Ka... more ABSTRACT The restratification of the cold wakes of Tropical Cyclones Fanapi, Frances, Igor and Katrina are examined based on derived scalings for processes that can restore the hurricane wake toward the precyclone conditions. The different restoration processes depend on the parameters of the wake: depth, width, buoyancy anomaly and wind stress. The parameters needed are derived for each wake from satellite and climatological data. The scalings are based on model results and existing parameterizations, including air-sea heat fluxes (one-dimensional) Ekman buoyancy fluxes (two-dimensional) and mixed layer eddies (three-dimensional). The dominant surface restoration occurs by a combination of surface fluxes and Ekman buoyancy fluxes, while the submesoscale mixed layer eddy bolus fluxes are the dominant subsurface effect.

The Argo profiling float network has repeatedly sampled much of the world’s ocean. This study use... more The Argo profiling float network has repeatedly sampled much of the world’s ocean. This study uses Argo temperature and salinity data to form the tracer structure function of ocean variability at the macro-scale (10 − 1000 km, mesoscale and above). Here, second- order temperature and salinity structure functions over horizontal separations are calculated along either pressure or potential density surfaces, which allows analysis of both active and passive tracer structure functions. Using Argo data, a map of global variance is created from the climatological average and each datum. When turbulence is homogeneous, the structure function slope from Argo can be related to the wavenumber spectrum slope in ocean temperature or salinity variability. This first application of structure function techniques to Argo data gives physically meaningful results based on bootstrapped confidence intervals, showing geographical dependence of the structure functions with slopes near 2/3 on average, independent of depth.

Renewable Energy, Apr 2015

As interest in marine renewable energy increases, observations are crucial for understanding the ... more As interest in marine renewable energy increases, observations are crucial for understanding the environments that prospective turbines will encounter. Data from an acoustic Doppler velocimeter in Puget Sound, WA are used to perform a detailed characterization of the turbulent flow encountered by a turbine in a tidal strait. Metrics such as turbulence intensity, structure functions, probability density functions, intermittency, coherent turbulence kinetic energy, anisotropy invariants, and a new scalar measure of anisotropy are used to characterize the turbulence. The results indicate that the scalar anisotropy magnitude can be used to identify and parameterize coherent, turbulent events in the flow. An analysis of the anisotropy characteristics leads to a physical description of turbulent stresses as being primarily one- or two-dimensional, in contrast to isotropic, three-dimensional turbulence. A new measure of the anisotropy magnitude is introduced to quantify the level of anisotropic, coherent turbulence in a coordinate-independent way. These diagnostics and results will be useful for improved realism in modeling the performance and loading of turbines in realistic ocean environments.

Journal of Marine Research

The restratification of the cold wakes of Tropical Cyclones Fanapi, Frances, Igor, and Katrina ar... more The restratification of the cold wakes of Tropical Cyclones Fanapi, Frances, Igor, and Katrina are examined based on derived scalings for processes that can restore the hurricane wake toward the pre-cyclone conditions. The different restoration processes depend on the parameters of the wake: depth, width, buoyancy anomaly, and wind stress. The parameters needed are derived for each wake from satellite and climatological data. The scalings are based on model results and existing parameterizations, including air-sea heat fluxes (1d), Ekman buoyancy fluxes (2d), and mixed layer eddies (3d). The dominant surface restoration occurs by a combination of surface fluxes and Ekman buoyancy fluxes, while the submesoscale mixed layer eddy bolus fluxes are the dominant subsurface effect.

Turbulence is inherently chaotic and unsteady, so observing it and modeling it are no easy tasks.... more Turbulence is inherently chaotic and unsteady, so observing it and modeling it are no easy tasks. The ocean’s sheer size makes it even more difficult to observe, and its unpredictable and ever-changing forcings introduce additional complexities. Turbulence in the oceans ranges from basin scale to the scale of the molecular viscosity. The method of energy transfer between scales is, however, an area of active research, so observations of the ocean at all scales are crucial to understanding the basic dynamics of its motions. In this collection of work, I use a variety of datasets to characterize a wide range of scales of turbulence, including observations from multiple instruments and from models with different governing equations.
I analyzed the largest scales of the turbulent range using the global salinity data of the Argo profiling float network. Taking advantage of the scattered and discontinuous nature of this dataset, the second-order structure function was calculated down to 2000m depth, and shown to be useful for predicting spectral slopes. Results showed structure function slopes of 2 at small scales, and 0 at large scales, which corresponds with spectral slopes of -5/3 at small scales, and −1 at large scales. Using acoustic Doppler velocity measurements, I characterized the meter- to kilometer-scale turbulence at a potential tidal energy site in the Puget Sound, WA. Acoustic Doppler current profiler (ADCP) and acoustic Doppler velocimeter (ADV) observations provided the data for an analysis that includes coherence, anisotropy, and intermittency. In order to more simply describe these features, a parameterization was done with four turbulence metrics, and the anisotropy magnitude, introduced here, was shown to most closely capture the coherent events. Then, using both the NREL TurbSim stochastic turbulence generator and the NCAR large-eddy simulation (LES) model, I calculated turbulence statistics to validate the accuracy of these methods in reproducing the tidal channel. TurbSim models statistics at the height of a turbine hub (5m) well, but do not model coherent events, while the LES does create these events, but not realistically in this configuration, based on comparisons with observations.
Each of the datasets have disadvantages when it comes to observing turbulence. The Argo network is sparse in space, and few measurements are taken simultaneously in time. Therefore spatial and temporal averaging is needed, which requires the turbulence to be homogeneous and stationary if it is to be generalized. Though the acoustic Doppler current profiler provides a vertical profile of velocities, the fluctuations are dominated by instrument noise and beam spread, preventing it from being used for most turbulence metrics. ADV measurements have much less noise, and no beam spread, but the observations are made at one point in space, limiting us to temporal statistics or an assumption of “frozen turbulence” to infer spatial scales. As for the models, TurbSim does not have any real-world forcing, and uses parameterized spectra, and coherence functions and randomizes phase information, while LES models must make assumptions about sub-grid scales, which may be inaccurate. Additionally, all models are set up with idealizations of the forcing and domain, which may make the results unlike observations in a particular location and time. Despite these difficulties in observing and characterizing turbulence, I present several quantities that use the imperfect, yet still valuable observations, to attain a better description of the turbulence in the oceans.