<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.

At the International Comparison of Turbulence Measuring Instruments, 1970, velocity components and momentum flux measurements were compared using propeller-type Fluxatrons (Hicks, 1970) and sonic anemometers from Kaijo-Denki, Japan and the Institute of Atmospheric Physics, U.S.S.R. There were distinct differences found in the measurements of the vertical velocity from the propeller sensors. The propeller's momentum flux measurements computed from its velocity components were also different. The U¹ propeller was found to be linear for lower frequencies with an associated distance constant of about 7 metre. Measurement of the variance of U¹ for f < 0.16 hz. showed the U¹ propeller in excess of both sonics by 20%. However, with the propeller's high frequency loss beyond f = 0.2 hz. the discrepancy was reduced to only an 8% excess for .00055 hz. < f < 10.8 hz. The W¹ propeller response was non-linear and had an upper cut-off frequency of 1hz. Because of its non-linear response and stalling characteristics at low wind speeds and also its high frequency cut-off the W¹ propeller was observed to measure only about 50% of the total fluctuating W¹ energy available. Analysis of the sonic cospectra of momentum showed that significant contributions to the momentum flux were to be found in the frequency domain 0.001 hz. < f < 5.0 hz. The combined response effects of the propeller were enough to reduce the Fluxatron’s estimate of this momentum flux by 32.5%. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The objective of this study was to investigate the turbulent transfer mechanisms near the surface. Direct measurements of the turbulent fluxes of momentum, heat, and moisture were made in the atmospheric surface layer: principally, 2 m above a grass surface at Ladner, Canada, and for comparison 8 m above the Atlantic Ocean near Barbados. The spectral correlation coefficients were considered to be a measure of the transfer efficiency as a function of scale size. For momentum transfer the efficiency decreased at all scales as instability increased. It was postulated that this was due to greater amounts of momentum being transferred in bursts of short duration, thus making the spectral correlation coefficient, averaged over sufficient time, smaller. The Ladner results for heat transfer showed that its transfer efficiency increased at all scales when instability increased. The ratios of the transfer efficiency of heat to that of momentum were greater than 1 for most scales, even for near neutral stratifications, and increased to between 2 and 3 for more unstable conditions. The efficiency of moisture transfer, when moisture is a passive scalar, was usually smaller than that for heat transfer and was found to depend on the correlation between moisture fluctuations and those of temperature, which is the active scalar. The results from Barbados pointed out two main differences between the subtropics and mid-latitudes: that the temperature spectrum is much narrower in bandwidth and that the humidity fluctuations make an equally important contribution to buoyancy. These features are reflected in the transfer mechanisms. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Current and temperature data were acquired in the source region of the Somali Current, jointly by the Universities of Kiel and Miami, as part of the INDEX pilot studies. The data were acquired over a six-month period (January-July, 1976) which spans the springtime Monsoon reversal. The experiment and the data are described in Düing and Schott (1978). This thesis describes the results of the spectrum analysis of fluctuations found in data from the experiment's two southernmost sensor locations. It is found that, once the annual cycle is removed, most of the variance in these current and temperature records resides in subinertial fluctuations. The most prominent spectral feature is a 40- to 50-day peak. This 40- to 50-day period is coincident with that of the global-scale circulation cells found in the tropical atmosphere by Madden and Julian (1971 and 1972). The analysis of wind stress and wind stress curl data for the years 1976 and 1979 presented in this thesis indicate that the 40-to 50-day oscillation was present over the Western Indian Ocean during these years. It is suggested here that wind-forcing excites a long coastally trapped wave. To test this idea, a wind-forced quasi-geostrophic, three-layer model and a reduced-gravity model incorporating lateral mean current shear are applied to the Somali Current regime. Model results suggest that the wind forcing is strong enough to excite the observed current and temperature fluctuations. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Two systems for remote measurements of the air-sea fluxes of momentum, sensible heat and moisture during moderate to strong winds are described. One employs the dissipation method and the other the Reynolds flux or eddy correlation method. A modified Gill propeller-vane anemometer is the velocity sensor and a method of resolving the vertical velocity component, that accounts for the propeller's non-cosine behavior and avoids its non-linear operating region, is derived. The dynamic responses of the sensors are found from measurements in the actual turbulent conditions of the flux measurements. The results of an experiment on the Bedford tower, a stable platform moored in 59m of water 10 km offshore, are presented. Spectra, cospectra, turbulence statistics and transfer coefficients are calculated from the Reynolds flux velocity and temperature data and found to be comparable to previously reported values. Simultaneous dissipation and Reynolds flux estimates of both the momentum and sensible heat fluxes in up to 20 m/s winds are shown to be in excellent agreement. Also presented are the results of a second experiment where the systems were deployed on the weathership CCGS Quadra. A comparison of ship and tower drag coefficients from the dissipation system, demonstrates that the Bedford tower is essentially an open ocean site. The neutral drag coefficient, CDN, is found, on average, to be nearly constant at 1.14x10⁻³ for winds between 4 and 10 m/s and to increase almost linearly to about 2.18x10⁻³ at 26 m/s. No variation with either fetch (greater than 10 km) or stability is observed. Dissipation estimates of the sensible heat flux from a wide range of conditions are presented. The neutral transfer coefficient, CTN, is found, on average, to vary from about 0.69x10⁻³ in stable stratification to 1.08x10⁻³ in the unstable case. An increase in CTN with increasing wind speed is suggested by only some of the data. Time series of the fluxes are used to investigate additional sources of variation in the transfer coefficients. Their statistical variability about a running mean is seen to be about 10%. Evidence is presented that indicates that persistent departures from average values are related to sea surface conditions. CDN is observed to be significantly smaller, on average, during rising winds than during falling winds or after a change in wind direction. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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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A hurricane is a threat to socio-economic activities in coastal communities bordering the South Atlantic Ocean (SAO). Hurricanes rarely form over this region and as such these communities are not prepared for them. Previous studies have suggested that anthropogenic warming may lead to more frequent hurricanes over the region and have demonstrated the capability of the Weather Research and Forecasting model (WRF) in capturing the impacts of the warming on hurricanes. However, none of the studies have investigated how the model's horizontal resolution and boundary forcing could alter the characteristics of simulated hurricanes. The present study used WRF to perform a series of experiments to simulate two hurricanes (Hurricane Catarina and Hurricane Anita) over the SAO at three horizontal resolutions (3.3 km, 10 km, and 30 km), using two reanalysis datasets (ERA-Interim (hereafter ERAINT) and NCEP CFSR (hereafter CFSR)) as the boundary forcing data. The performances of the reanalysis and WRF are compared with observational data from the International Best Track and Archive for Climate Stewardship. The results show that both reanalyses datasets give a good representation of the two hurricanes, but they grossly underestimate the intensity thereof. CFSR gives a better representation than that of ERAINT. However, both reanalyses also suggest that the South Atlantic Convergence Zone may be the moisture belt for hurricane formation over the SAO. WRF gives a credible simulation of the hurricanes. In simulating Hurricane Catarina, WRF performs best at a 10-km resolution; but in reproducing Hurricane Anita, the model performs best at a 3.3 km resolution. For both cases, the model performs better when forced with ERAINT than with CFSR. Hence, the study shows that increasing the resolution of the model may not necessarily improve the simulated hurricane over the SAO, and that, the quality of the simulated hurricane depends on the dataset that provides the boundary forcing. The results of the study have improved the understanding of hurricane characteristics in the SAO, and have shown the potentials of WRF to forecast and project future events as well as for downscaling the potential impacts of future climate change on hurricanes over the SAO.