Browsing by Subject "Tropical"
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Item Characterization of hurricane gust factors using observed and analytical data(Texas Tech University, 2009-05) Edwards, Rebecca Paulsen; Schroeder, John L.; Gilliam, Kathleen; Smith, Douglas A.The nature of turbulence in the hurricane boundary layer has been the subject of much discussion. Two questions in particular continue to be the source for debate and ongoing research. The first question is whether or not hurricane GFs exhibit the same behavior as GFs from winds generated by extratropical systems (thunderstorms excluded). The second question is whether the structure of the wind, and the resulting gust factors, change at high wind speeds. This study seeks to address those two questions using a variety of data sources and analysis techniques. Observational data were collected from both landfalling tropical cyclones and synoptically generated extratropical wind. Analytical data at a variety of wind speeds were created using an inverse fast Fourier Transform of the universal spectrum for wind in the perturbed terrain. Gust factors and other parameters were computed for both types of data and the results assimilated in a data base. Analysis of these data yielded interesting results. A strong dependence on surface roughness was noted for gust factors from both observed and analytical data. However, once efforts were made to control for this dependency by stratifying the data into roughness regimes using the roughness length, slight differences between the tropical and extratropical gust factor data remained. Analysis of the artificial data, suggest spectral differences between the tropical and extratropical regimes due to the presence of additional low-frequency energy in the tropical regime. A slight decrease of the gust factor with increasing wind speed was noted in the high-speed analytical data. A similar decrease was suggested in the tropical data. It was concluded that the low-frequency spectral differences between the two regimes have less of an effect on the resulting gust factors as the wind speed increases, resulting in better agreement between the two distributions.Item Realizability of tropical lines in the fan tropical plane(2013-08) Haque, Mohammad Moinul; Helm, David, doctor of mathematicsIn this thesis we construct an analogue in tropical geometry for a class of Schubert varieties from classical geometry. In particular, we look at the collection of tropical lines contained in the fan tropical plane. We call these tropical spaces "tropical Schubert prevarieties", and develop them after creating a tropical analogue for flag varieties that we call the "flag Dressian". Having constructed this tropical analogue of Schubert varieties we then determine that the 2-skeleton of these tropical Schubert prevarieties is realizable. In fact, as long as the lift of the fan tropical plane is in general position, only the 2-skeleton of the tropical Schubert prevariety is realizable.Item The response of bats to landscape structure in amazonian forest: an analysis at multiple scales(2007-05) Klingbeil, Brian T.; Willig, Michael R.; Salazar-Bravo, Jorge; McIntyre, Nancy E.Habitat loss and fragmentation are currently the most serious threats to conserving biodiversity. This is especially the case in the Amazon Basin where species richness and diversity are at their peak, and deforestation is increasing at an alarming rate. Bats achieve their highest functional and taxonomic diversity in the Neotropics, and provide a suite of ecosystem services critical to maintaining tropical forests. However, very little is known regarding the response of populations and assemblages to spatially explicit aspects of landscape structure. The responses of 24 phyllostomid species and 4 assemblage characteristics to landscape structure were analyzed at each of 3 focal scales at 14 sites. Satellite imagery was classified into two land-cover types (i.e., forest and non-forest) and processed with FRAGSTATS to quantify characteristics of landscape composition and configuration. Assemblage, trophic guild, and population responses to landscape characteristics were scale dependent. Frugivores responded more to landscape composition, whereas gleaning animalivores and assemblage characteristics responded only to landscape configuration. In general, the abundances and richness of species were higher in moderately fragmented forest than in continuous forest. This is likely due to the dominance of frugivores in assemblages and the abundance of fruits provided by successional plant species, suggesting that bats may be important in promoting secondary succession. Although frugivorous bats may increase when deforestation and fragmentation is small compared to the size of the regional landscape, changes in land use, specifically conversion of forest habitat, likely enhance the vulnerability of bats with specialized ecological requirements. Consequently, even moderate amounts of fragmentation can affect local populations and may thereby alter the structure of assemblages.Item Tropical precipitation simulated by the NCAR Community Climate Model (CCM3): an evaluation based on TRMM satellite measurements(Texas A&M University, 2005-11-01) Collier, Jonathan CraigThis study evaluates the simulation of tropical precipitation by the Community Climate Model, Version 3, developed at the National Center for Atmospheric Research. For an evaluation of the annual cycle of precipitation, monthly-mean precipitation rates from an ensemble of CCM3 simulations are compared to those computed from observations of the TRMM satellite over a 44-month period. On regional and sub-regional scales, the comparison fares well over much of the Eastern Hemisphere south of 10◦S and over South America. However, model - satellite differences are large in portions of Central America and the Caribbean, the southern tropical Atlantic, the northern Indian Ocean, and the western equatorial and southern tropical Pacific. Since precipitation in the Tropics is the primary source of latent energy to the general circulation, such large model - satellite differences imply large differences in the amount of latent energy released. Differences are seasonally-dependent north of 10◦N, where model wet biases occur in realistic wet seasons or model-generated artificial wet seasons. South of 10◦N, the model wet biases exist throughout the year or have no recognizable pattern. For an evaluation of the diurnal cycle of precipitation, hourly-averaged precipitation rates from the same ensemble of simulations and for the same 44-month period are compared to observations from the Tropical Rainfall Measuring Mission (TRMM) satellite. Comparisons are made for 15◦ longitude ?? 10◦ latitude boxes and for larger geographical areas within the Tropics. The temporally- and spatially-averaged hourly precipitation rates from CCM3 and from TRMM are fit to the diurnal harmonic by the method of linear leastsquares regression, and the phases and the amplitudes of the diurnal cycles are compared. The model??s diurnal cycle is too strong over major land masses, particularly over South America (by a factor of 3), and is too weak over many oceans, particularly the northwestern Tropical Pacific (by a factor of 2). The model-satellite phase differences tend to be more homogeneous. The peak in the daily precipitation in the model consistently precedes the observations nearly everywhere. Phase differences are large over Australia, Papua New Guinea, and Saharan Africa, where CCM3 leads TRMM by 4 hours, 5 to 6 hours, and 9 to 11 hours respectively. A model sensitivity experiment shows that increasing the convective adjustment time scale in the model??s deep convective parameterization reduces its positive amplitude bias over land regions but has no effect on the phase of the diurnal cycle.Item Tropical theta functions and log Calabi-Yau surfaces(2014-05) Mandel, Travis Glenn; Keel, SeánWe describe combinatorial techniques for studying log Calabi-Yau surfaces. These can be viewed as generalizing the techniques for studying toric varieties in terms of their character and cocharacter lattices. These lattices are replaced by certain integral linear manifolds described in [GHK11], and monomials on toric varieties are replaced with the canonical theta functions defined in [GHK11] using ideas from mirror symmetry. We classify deformation classes of log Calabi-Yau surfaces in terms of the geometry of these integral linear manifolds. We then describe the tropicalizations of theta functions and use them to generalize the dual pairing between the character and cocharacter lattices. We use this to describe generalizations of dual cones, Newton and polar polytopes, Minkowski sums, and finite Fourier series expansions. We hope that these techniques will generalize to higher rank cluster varieties.