The aim of this research is to study the formation mechanism of Barrier Layers (BL) in the western tropical Atlantic and their influence on the tropical Atlantic climate at both short and long timescales. Many Coupled General Circulation Models (CGCMs) tend to overestimate the salinity in the Atlantic warm pool or the Northwestern Tropical Atlantic (NWTA) and underestimate the surface salinity in the subtropical salinity maxima region. Most of these models also suffer from a seasurface temperature (SST) bias in the NWTA region, leading to suggestions that the upper ocean salinity stratification may need to be improved in order to improve the BL simulations and thus the SST through BL-SST-Intertropical Convergence Zone (ITCZ) feedbacks. We used a CGCM to perform a set of idealized numerical experiments to understand the sensitivity of the BL and consequently SST in the NWTA region to freshwater flux and hence the upper ocean salinity strati cation. We find that the BL of the western tropical Atlantic is quite sensitive to upper ocean salinity changes in the Amazon River discharge region and the subtropical salinity maxima region. The BL phenomenon is further manifested by the formation of winter temperature inversions in our model simulations. However, in the region of improved BL simulation, the SST response is not statistically significant. SST response to Tropical Cyclones (TCs) is studied for the Atlantic region using a high-resolution coupled regional climate model (CRCM) and observational data sets. The presence of a BL, defined as the layer below the mixed layer that separates the base of the isothermal layer from the base of the isohaline layer, is found to modulate the SST response. The amplitude of TC-induced surface cooling is reduced by more than 35 percent in the presence of a BL, as a consequence of the weak thermal stratification. Furthermore, in locations when the BL exhibits a temperature inversion, TC-induced mixing can result in weak surface warming. BLs considerably reduce the rightward bias for tropical storms, but the effect is less conspicuous for TCs. The enthalpy flux into the atmosphere at the air-sea interface is enhanced by 16 percent and the increase in upper ocean potential energy due to TC-induced mixing is reduced by 25 percent in the presence of BLs. The results from the coupled model are supported by an observational analysis performed using re-analysis data sets, as well as data from Argo floats and TRMM satellite. As previous modeling and observational studies have indicated that the surface cooling caused by TC-induced mixing acts as a negative feedback for its intensity, results from our study suggest that BLs may have potential implications for TC intensity prediction.

Annually, tropical cyclones do tremendous damage and are agents of long-term coastal change. To test this idea of different tropical cyclones delivering consistent coastal change, a landform with such evolution is needed. One such landform is a spit. What contributions do tropical cyclones give toward the evolution of a spit, and do tropical cyclones give the same kinds of impacts? To determine if tropical cyclones have similar impacts, shoreline and volumetric change from four storms impacting Bolivar Peninsula are considered. Being a southwest-trended spit at a length of 33.5 kilometers, storm impacts are measured in the form of one dimensional shoreline and two dimensional volumetric change. These impacts are abstracted into shoreline change and volumetric change patterns. These patterns are identified and compared for differences between each storm and similarity among all storms. Results indicate that shoreline accretionary zones vary alongshore. Results from Hurricane Ike indicate an accretionary zone ten kilometers from the distal end. Shoreline change patterns for Hurricane Rita show an unstable accretionary zone at four kilometers from the distal end. Results for Tropical Storm Fay indicate an unstable accretionary zone that begins at the distal end and continues to the middle of the spit. In terms of similarity for shoreline change, all patterns from storms demonstrated erosion near Rollover Fish Pass. One dimensional volumetric change patterns were entirely erosive for Hurricanes Rita and Ike, and Tropical Storm Fay had by small zones of accretion near the distal portion of the spit. Tropical Storm Josephine demonstrated an accretion zone between the middle and distal portion of the spit. Results from two dimensional volumetric change patterns suggest a threshold for inland penetration. Tropical Storm Fay showed a ten to twenty meter wide pattern of erosion around five kilometers from the distal end and near the proximal end of the spit, and Hurricane Rita demonstrated a twenty meter wide pattern of erosion near the distal end. Hurricane Ike had erosive penetration of up to 200 meters around fifteen kilometers from the distal end. Results suggest that certain storms reinforce the standard spit growth model, and others work against it.

Bulls of various breedtypes including Angus (Bos taurus), Bonsmara (Sanga X Bos taurus), Brahman (Bos indicus), Romosinuano (Criollo), Tuli (Sanga) and Wagyu (Japanese Bos taurus) were utilized to evaluate the influence of tropical adaptation on adrenal and testicular function. The objectives were to determine if tropical adaptation influenced: a) response to management stressors, b) organ and gland weights, adrenal and testis StAR and P450 content and total adrenal, medullary and cortical areas, c) basal and hCG-induced testosterone and d) testis and epididymal sperm concentrations. Blood samples were obtained within 5 min before and after transportation and during restraint every 15 min for 6 h to evaluate cortical response. Angus, Brahman and Romosinuano bulls were slaughtered following sexual maturity. Cortical responses to transportation and restraint were not influenced by tropical adaptation. Response to these stressors could be categorized into high responders (Angus, Brahman), intermediate responders (Romosinuano, Tuli) and low responders (Wagyu, Bonsmara). Tropically-adapted breedtypes were not categorized into a single group; therefore, cortical responses to management stressors were influenced by breedtype, but not by tropical adaptation. Most organ and gland weights (actual weight and weight corrected for BW) and the steroid precursors, StAR and P450, were not influenced by tropical adaptation, but were by breedtype. Paired adrenal gland weight, total adrenal area, medullary and cortical areas were influenced by tropical adaptation. Tropically-adapted breedtypes had lighter glands and smaller areas than the temperate Bos taurus breedtypes. All breedtypes except Wagyu had similar basal concentrations of plasma testosterone prior to hCG administration; therefore, basal testosterone was not influenced by tropical adaptation, but only by breedtype. Wagyu had greater basal concentrations of testosterone than other breedtypes. Testosterone concentrations following hCG administration was similar between adaptation groups and breedtypes. As expected, testis and epididymal sperm concentrations were influenced by tropical adaptation. Tropically-adapted breedtypes had greater testicular and epididymal sperm concentrations than the temperate Bos taurus breedtypes during the summer months. In summary, adrenal weight and area and testicular and epididymal sperm concentrations were influenced by tropical adaptation. Cortical response to management stressors, basal testosterone and StAR and P450 content were influenced by breedtype, not tropical adaptation.

Thesis (M.S.)--Naval Postgraduate School, 2002. / Thesis advisor(s): Russell L. Elsberry, Patrick A. Harr. Includes bibliographical references (p. 69). Also available online.

The interplay between convective processes and the stabilizing effects of largescale systems remains debated, especially for warmer climates. We study sets of simulations of past and present climates in which carbon dioxide (CO2) concentrations vary over a wide range: from pre-industrial era levels of 280 ppm to an exceedingly high value of 8960 ppm. This allows us to assess the importance of convective processes relative to middle latitude thermal stratification and changes to the general circulation in progressively warmer climate states. As a tool to assess the stability of the atmosphere, we calculate a thermodynamic variable called saturation potential vorticity (P*), which has the property of being identically zero wherever lapse rates are neutral with respect to moist convection, and large where lapse rates are stable. Using P* allows us to examine convective motions arising from both gravitational accelerations as well as symmetric instabilities. We assess the ability of current models (of varying spectral resolutions) in resolving conditions unstable to slantwise convection. We show that the coarse resolution reanalysis data captures instances of observed slantwise convection. Our results show examples of vertically stable lapse rates, while being conditionally unstable along slanted angular momentum surfaces. This suggests the need for model parameterizations of convection to include instabilities arising from symmetric displacements. Tropical regions are neutral with respect to moist convection while higher latitudes most often have stable lapse rates, especially during the winter months. In the warmer climate simulations, the frequency of convectively neutral air masses increases in both middle latitude and polar regions, especially during the summer months. These simulations also show expansion of the Hadley cell and shifting of middle latitude storm tracks. Using Maximum Potential Intensity (MPI) as a tool to assess the upper bound of hurricane strength, we show sustainment of intense tropical cyclones in regions they cannot in our present climate.

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Thesis (M.S. in Meteorology)--Naval Postgraduate School, March 2005. / Thesis Advisor(s): Russell L. Elsberry. Includes bibliographical references (p. 103-105). Also available online.