Browsing by Subject "Cyclones -- Tropics"
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Item A WSR-88D data analysis of cyclic tornadic mesocyclones associated with tropical cyclones(Texas Tech University, 2000-08) Grams, Dan JosephOnly recently has the problem of forecasting tomadic activity associated with tropical cyclones been thoroughly addressed. The deployment of the WSR-88D (Weather Surveillance Radar-1988 Doppler) has allowed meteorologists to fiirther investigate the storm-scale characteristics of tomadic mesocyclones produced within a tropical cyclone environment. Radar-derived physical parameters along with algorithm-derived products have provided some very detailed information about the behavior of these storms. This thesis is an investigation of two cyclic tomadic mesocyclones associated with tropical cyclones using WSR-88D data. A tomadic mesocyclone that occurred on 2 September 1998 in association with Hurricane Earl and another on 4 November 1998 in association with Tropical Storm Mitch. Level II radar tapes recorded from the Tampa Bay (KTBW) National Weather Service Office during Hurricane Earl's approach and from the Miami (KAMX) office during Tropical Storm Mitch were processed and thoroughly analyzed. Common storm-scale characteristics for both mesocyclones during the times of tornadoes were found. A decreasing diameter of the low-altitude mesocyclone was found to occur before a tornado touchdown. Base reflectivity images displayed hook appendages and inflow regions during tornado events typically associated with tomadic storms of the Great Plains. Analysis of algorithm-derived trends displayed these fluctuating rotational diameters corresponding to the mesocyclones strength indicating that the mesocyclones were cyclic in nature. Additional data from area soundings provided a synoptic view for each event that displayed an atmosphere lacking the necessary thermodynamics needed for tomadogenesis. Very strong low-level wind fields seemed to be the only major meteorological contributor.Item Coastal boundary layer transition within tropical cyclones at landfall(Texas Tech University, 2004-05) Howard, James RobertHurricanes pose a great risk to life and property with their high winds, excessive rainfall, wave action, and storm surge. Predicting changes within hurricanes at and near the time of landfall requires an understanding of the dynamics that drive the boundary layer flow. Forecasters predict the timing, duration, and effects of the intense winds associated with a hurricane when it comes ashore, while emergency management officials call for public evacuations based upon these forecasts. One region where understanding the magnitude and structure of the wind is critical is within the surface layer just downstream of the coastline in the onshore flow. Within this region the flow begins to adjust to changes in surface triggered by its passage from the shallow coastal waters to the less homogeneous and rougher land. This adjustment may include a slowing of the mean wind with an increase in turbulence, both resulting from the increased friction of the man-made and natural terrain. Hurricane observing programs consisting of portable and mobile equipment and regional coastal mesoscale observing networks are leading to a better understanding of the processes involved with these flow modifications. The Texas Tech University Wind Engineering Mobile Instrumented Tower Experiment (WEMITE) continues to play a leading role in the observation and analysis of the boundary layer of tropical cyclones at landfall. In order to gain further insight into the characteristics of this coastal transition zone, experiments were planned utilizing portable in-situ and remote measuring devices to be placed within the onshore flow at landfall. Experiment plan designs along with results from these experiments ate discussed, including the analysis of a dataset collected by multiple institutions during the landfall of Hurricane Lili (2002) along the south-central Louisiana coast Investigation reveals the existence of frictionally-induced changes in the boundary layer downwind of the coastline within the right semicircle with respect to Lili's forward motion. In the outer reaches of Lili, these transitions appear similar to internal boundary layers produced by flow moving over an abrupt change in surface. The impact on the magnitude of the wind within this near-shore region is a reduction of 4-10% per 10 km distance from the coast up to 50 km inland for open terrain. Results of the study show this reduction to be an exponential function of distance from the coast which is dependent upon surface roughness. This rate of wind decay slows with farther progression inland and appears to be much faster than the rate found in soma modeling studies. In contrast near Lili's circulation center, little or no decrease in the magnitude of the mean wind was found for distances of up to 20 km inland.