Thesis (Ph.D.)--University of Washington, 2007. / (UMI)AAI3293489. Source: Dissertation Abstracts International, Volume: 68-12, Section: B, page: 7871. Adviser: Stephen G. Warren.

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3651. Adviser: Donald J. Wuebbles. Includes bibliographical references (leaves 130-148). Available on microfilm from Pro Quest Information and Learning.

<p> This dissertation explores the interactions between the atmosphere and wind turbines from numerous perspectives. The work presented here outlines three subjects: the characterization of wind-turbine wakes in the evening, the evaluation of simulated wind-power productions in a numerical weather prediction model, and the attempt to systematically quantify wind-speed (WS) variability over decades. </p><p> After introducing the background of wind-energy meteorology, the first part of this dissertation discusses the evolution of wind-turbine wakes during the evening transition. In observations as well as simulations from the Weather Research and Forecasting (WRF) model, turbine wakes, namely the in downwind WS reduction and turbulence enhancement, become more prominent in the evening. Hence, the power generations of downwind turbines decrease when the atmosphere changes from unstable to stable. </p><p> The second section of this dissertation focuses on validating the power-production predictions of the wind farm parameterization (WFP) scheme in the WRF model. Using the WFP with fine (&sim;12 m) vertical grid resolution leads to the most accurate power simulations. Compared to the actual power generations, the WFP tends to underestimate power in stable conditions with high winds and low turbulence. Overall, the accuracy of the WRF model in WS prediction dictates the skill of the WFP in simulating wind power. </p><p> The third topic of this dissertation explores optimal methods to assess the variability of WS and energy production. Among the 27 methods tested, the Robust Coefficient of Variation (RCoV), as a normalized, statistically robust and resistant spread metric, yields the strongest correlation in connecting the variations between monthly mean WS and monthly net energy generation. By comparison to a long data record from a reanalysis product, the RCoV also requires 6 years of WS data to effectively quantify the long-term variability of a location. </p><p> Finally, this dissertation ends with a remark on the importance of correctly using the WRF WFP and statistics. Future work includes improving the power curve and applying the variability metrics in evaluating financial risk.</p><p>

<p> The development of offshore wind energy is moving forward as one of several options for carbon-free energy generation along the populous US east coast. Accurate assessments of the wind resource are essential and can significantly lower financing costs that have been a barrier to development. Wind resource assessment in the Mid-Atlantic region is challenging since there are no long-term measurements of winds across the rotor span. Features of the coastal and inland terrain, such as such as the Appalachian mountains and the Chesapeake Bay, are known to lead to complex mesoscale wind regimes onshore, including low-level jets (LLJs), downslope winds and sea breezes. Little is known, however, about whether or how the inland physiography impacts the winds offshore. This research is based on the first comprehensive set of offshore wind observations in the Maryland Wind Energy Area gathered during a UMBC measurement campaign. The presentation will include a case study of a strong nocturnal LLJ that persisted for several hours before undergoing a rapid breakdown and loss of energy to smaller scales. Measurements from an onshore wind profiler and radiosondes, together with North American Regional Analysis (NARR) and a high resolution Weather Research and Forecast (WRF) model simulation, are used to untangle the forcing mechanisms on synoptic, regional and local scales that led to the jet and its collapse. The results suggest that the evolution of LLJs were impacted by a downslope wind from the Appalachians that propagated offshore riding atop a shallow near-surface boundary layer across the coastal plain. Baroclinic forcing from low sea surface temperatures (SSTs) due to coastal upwelling is also discussed. Smaller scale details of the LLJ breakdown are analyzed using a wave/mean flow/turbulence interaction approach. The case study illustrates several characteristics of low-level winds offshore that are important for wind energy, including LLJs, strong wind shear, turbulence and rapid changes in the wind, so-called "ramp events&rdquo;. A 3-year survey based on NARR analyses is used to estimate the likelihood that similar events could occur under the same meteorological conditions.</p><p>

Temperature variability and change over land and ocean exhibit characteristic spatial and temporal structures. Understanding the physical mechanisms underlying these structures provides information about the movement and storage of heat in the climate system. In this thesis, I first analyze, and present an energy balance model for, seasonal temperature variability in the extratropics, which supports the idea that the advection of heat between land and ocean by the mean atmospheric circulation can explain the regional characteristics of seasonal variability over both land and ocean. The model is subsequently combined with a large, representative ensemble of Lagrangian atmospheric trajectories to provide a realistic model of the seasonal cycle in the Northern Hemisphere mid-latitudes. Second, based on the Lagrangian trajectories, a new spatially-resolved metric, termed Relative Land Influence, is developed. The metric quantifies the role of land as compared to ocean in influencing the temperature variability at a given location. In addition to explaining the majority of the spatial pattern of seasonal variability, Relative Land Influence is a significant predictor of the observed temperature change over both land and ocean independently since 1950, suggesting that similar physical processes influence temperature variability on seasonal and decadal timescales. Finally, I explore the tails of temperature distributions in the context of identifying the causes of anomalously hot days in the Eastern United States during peak summer. A coupled ocean-atmosphere mode in the central mid-latitude Pacific is identified, which evolves on a characteristic timescale and ultimately leads to the amplification of a mid-latitude wave train that includes a blocking high over the Eastern United States. The early identification of the sea surface temperature precursors to this mode allows for skillful prediction of heat events at lead times greater than 40 days. The identification of physical processes underlying temperature variability on a range of timescales can inform predictions of how temperature variability may change in the future. / Earth and Planetary Sciences

<p> The proliferation of reanalysis models for the atmosphere in recent decades has allowed researchers to study Earth&rsquo;s past climate in great detail. While much work has gone into understanding key climate indicators such as surface temperature and precipitation trends, there have been few studies dealing with heat stress. As climate change grows increasingly exigent, it is becoming vitally important to understand the thermal impacts on biological systems. </p><p> This study analyzed data from five reanalysis models (20CRv2, NARR, NNRA 1, NCEP DOE 2, and ERA-I) and found agreement in average surface temperature increases of 0.2&ndash;0.6&deg;C per decade across the U.S. west coast and east coast since 1979. These trends were consistent with previous studies. Less agreement was found for the central U.S. The Temperature Humidity Index and the Heat Index were found to generally follow the temperature trends. An analysis of the role of moisture indicated that the effect of specific humidity on heat stress is dependent on climatology. Trends of heat stress over arid regions such as the desert southwest were found to be much more influenced by temperature trends than by moisture trends. In contrast, moisture seemed to play a stronger role in the more humid southeast. There appeared to be a more equal effect of temperature and moisture on heat stress in the northeast and Great Lake states. </p><p> Perhaps equally as important, the study provides a framework to reduce computational time but allows for more rigorous statistical methods that are not available in the typical suite of software and programming languages to analyze climate data. Functionality was developed to infer daily extrema from six-hourly reanalysis data. A shapefile was used to aggregate the data according to prescribed geographic boundaries and reduce the load of data for statistical analysis. Time series decomposition was performed on the aggregated daily data to determine linear trends which were then mapped out to visualize their spatial features.</p><p>

Engineering construction in cold regions is greatly effected by the environment. The type of structure, its design, its erection and its operation and maintenance are all influenced by the surrounding meteorological conditions. Another consideration is of course the site on which the construction is to be erected. Before construction one has to determine, above others, how deep the soil below the surface is frozen and this requires heat transfer analysis on that particular site. In this thesis heat flux for thirty-two sites are considered. These sites are chosen since their n-factors and soil properties are known experimentally. With weather data like air-temperature, dew-point temperature, cloud cover and wind speed supplied by the United States National Oceanic and Atmospheric Administration (NOAA), it is possible to calculate the net shortwave and longwave radiation, and the convective heat flux at the surface. For two of the sites; Fairbanks, Alaska and Boston, Massachussetts, data on radiation are available and they can be used to check the accuracy of the results obtained using the existing equations. For these two sites empirical relationships on the effect of cloud cover on shortwave and longwave radiation can also be obtained. With the calculation of seasonal heat fluxes and the known soil properties it is possible to calculate the air and surface indexes, the n-factor, and finally by using appropriate parameters, obtain an empirical relationship between the surface and the air indexes. It will also be seen how close the calculated results agree with the theory.

Tropical atmospheric waves play a major role in the variability and change of weather and climate in the tropics as well as in the globe. They also interact with other tropical systems such as tropical cyclones (TCs) and El Niño-Southern Oscillation (ENSO). The improved understanding of the tropical waves, such as their origins, their spatiotemporal structures, and their life cycles, can lead to better prediction of weather and climate change in the tropics as well as over many other areas of the globe. Most of the previous diagnoses of observed tropical waves came from two categories: (1) case studies in which individual waves of particular types are examined, leading to scattered information of the spatiotemporal characteristics of these waves; and (2) climatological studies using wavenumber-frequency domain analysis which is not able to identify spatiotemporal inhomogeneity of tropical waves. To fill the gap between these two approaches, we use a recently developed spatiotemporally local analysis method, the multi-dimensional ensemble empirical mode decomposition (MEEMD) method, and known spatial wind structures of different types of waves to systematically extract the evolution information of tropical waves over large temporal and spatial domains. Through further analysis of the extracted wave events, the spatiotemporal inhomogeneity of tropical waves is characterized. In this study, as the very first step toward a comprehensive study, our focus is placed on mixed Rossby-gravity (MRG) waves. The propagation characteristics, period, and horizontal (zonal and meridional) scale of MRG events detected in this study can match with both the theoretical results and observational studies. There are 23 MRG events detected from the 3rd MEEMD component in the year 2002, among which most events occurred over the western Pacific Ocean and fewest MRG events over the Indian Ocean. The phase velocity and meridional scale are largest over the Atlantic Ocean while smallest in the Indian Ocean. The locations and propagation characteristics of MRG events show great spatiotemporal inhomogeneity. After the evolution of MRG events are obtained, they can be connected with TCs. A new hypothesis, which better matches the observation, is proposed that the swelling and westward propagation of MRG wave pattern help the TCs moving westward and toward higher latitudes, which is necessary for TCs to develop at early stage. / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester, 2014. / October 9, 2014. / Ensemble Empirical Mode Decomposition, Mixed Rossby-Gravity Waves, MRG evolution, Tropical Depressions / Includes bibliographical references. / Zhaohua Wu, Professor Directing Thesis; Mark Bourassa, Committee Member; Vasu Misra, Committee Member.

The scopes of this thesis research are two folds: the first one is to the construct the intensity-based composite radial-vertical profiles of tropical cyclones (TC) using GPS-based dropsonde observations and the second one is to identify the major deficiencies of Mathur vortices against the dropsonde composites of TCs. The intensity-based dropsonde composites of TCs advances our understanding of the dynamic and thermal structure of TCs of different intensity along the radial direction in and above the boundary layer where lies the devastating high wind that causes property damages and storm surges. The identification of the major deficiencies of Mathur vortices in representing the radial-vertical profiles of TC of different intensity helps to improve numerical predictions of TCs since most operational TC forecast models need to utilize bogus vortices, such as Mathur vortices, to initialize TC forecasts and simulations. We first screen all available GPS dropsonde data within and round 35 named TCs over the tropical Atlantic basin from 1996 to 2010 and pair them with TC parameters derived from the best-track data provided by the National Hurricane Center (NHC) and select 1149 dropsondes that have continuous coverage in the lower troposphere. The composite radial-vertical profiles of tangential wind speed, temperature, mixing ratio and humidity are based for each TC category ranging from "Tropical Storm" (TS) to "Hurricane Category 1" (H1) through "Hurricane Category 5" (H5). The key findings of the dropsonde composites are: (i) all TCs have the maximum tangential wind within 1 km above the ground and a distance of 1-2 times of the radius of maximum wind (RMW) at the surface; (ii) all TCs have a cold ring surrounding the warm core near the boundary layer at a distance of 1-3 times of the RMW and the cold ring structure gradually diminishes at a higher elevation where the warm core structure prevails along the radial direction; (iii) the existence of such shallow cold ring outside the RMW explains why the maximum tangential wind is within 1 km above the ground and is outside the RMW, as required by the hydrostatic and gradient wind balance relations; (iv) one of the main differences among TCs of different intensity, besides the speed of the maximum tangential wind, is the vertical extent of near-saturated moisture air layer inside the core. A weaker TC tends to have a deep layer of the near-saturated moisture air layer whereas a stronger TC has a shallow one; (v) another main difference in the thermal structure among TCs of different intensity is the intensity and vertical extent of the warm core extending from the upper layer to the lower layer. In general, a stronger TC has a stronger warm core extending downward further into lower layer and vice versa. The features (iv) and (v) are consistent with the fact that a stronger TC tends to have stronger descending motion inside the core. The main deficiencies of Mathur vortices in representing the radial-vertical profiles of TC of different intensity are (i) Mathur vortices of all categories have the maximum wind at the surface; (ii) none of Mathur vortices have a cold ring outside the warm core near the boundary layer; (iii) Mathur vortices tend to overestimate warm core structure in reference to the horizontal mean temperature profile; (iv) Mathur vortices tend to overestimate the vertical depth of the near-saturated air layer near the boundary layer. / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester, 2014. / October 8, 2014. / Includes bibliographical references. / Ming Cai, Professor Directing Thesis; Vasu Misra, Committee Member; Philip Sura, Committee Member.

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