Lightning detection over Houston, Texas is possible with the Lightning Detection and Ranging (LDAR-II) network and the National Lightning Detection Network (NLDN). A comparison of the two datasets in conjunction with 37 isolated, ordinary thunderstorms reveals a time separation of 3.1 minutes between the first detected Very High Frequency (VHF) source (i.e. first intracloud discharge) and the first cloud-toground (CG) lightning flash. This CG warning time is increased to 16.1 minutes when using the radar-defined criterion of when the 30-dBZ contour first reaches the -10°C isotherm level. Several attempts were made to establish a similar characteristic that could be used to forewarn the occurrence of the final CG in this storm type. Based on the average radar characteristics during the last CG flash in each thunderstorm case, CG activity comes to an end when the 45-dBZ echo falls below the -10°C isotherm. Detection efficiencies that remain slightly less than perfect for each network may have allowed for some error when analyzing VHF sources and ground flashes for each convective case. Exhibiting this possible error, four cases actually recorded a greater number of CG flashes than intracloud flashes, which is contrary to typical lightning characteristics. Future studies hope to increase the number of thunderstorm cases to analyze as the LDAR network continues to observe more lightning events. Also, similar approaches could be implemented in differing geographic regions of the country to observe if these lightning characteristics vary depending on latitude, longitude, or climate.

Modifying a high occupancy vehicle (HOV) lane into a high occupancy/toll (HOT) lane generally involves allowing single occupant vehicles (SOVs) to travel on the free-flow HOV lane for a toll. This may entice some former transit riders to pay the toll to obtain the benefits of traveling in their own vehicle on the HOV lane. Thus, the introduction of a HOT lane has the potential to impact transit ridership, dramatically lowering the average vehicle occupancy of the lane. In 2003, surveys were distributed to park-and-ride bus passengers on the Katy Freeway and Northwest Freeway corridors in Houston. Passengers’ responses to questions regarding their trip characteristics, their socioeconomic characteristics, and stated preference scenarios were used to develop a mode choice model. To determine how transit passengers might react to a proposed HOT lane, HOT lane scenarios with varying tolls and travel time savings were simulated using this model. For all scenarios, only a small percentage of transit passengers were estimated to switch to driving alone on the HOV lane. Fewer people would switch during the peak period than during the off-peak period. Transit passengers shifting to SOV on the HOV lane would reduce the average vehicle occupancy (AVO) only about 1 percent to 2 percent. SOV drivers shifting from the general purpose lanes to the HOV lanes are likely to affect AVO much more. However, as long as free-flow conditions are maintained, this analysis shows that the HOV lane can be successfully adapted to a HOT lane and move more people, even if a few transit passengers choose to drive alone.

An increase in the amount of lightning and rainfall over the Houston area, compared to the surrounding rural areas, has been well documented in previous studies. The placement of a Shared Mobile Atmospheric Research and Teaching Radar (SMART-R) in the Houston area during the summer season of 2005 presented a unique opportunity to investigate the role of boundary-layer convergence in modulating convective frequency and intensity and, thereby, likely causing the rainfall and lightning anomalies. The role of the urban heat island (UHI) and the sea-breeze, as a source of low-level convergence leading to enhanced convection over Houston, was examined. Hourly average dual-Doppler wind and convergence maps were created on 1 X 1 km grids for an eleven-week period. By using these images along with average lightning, rainfall, and reflectivity for a large Houston-centered domain, it was possible to discern a correlation between low-level convergence and convection. Also, past findings of enhancement in lightning and rainfall over Houston and downwind of Houston were validated. High convergence levels for the Houston area in the mid-morning were followed closely by a peak in convection in the early afternoon. The enhancement of rainfall and lightning over and downwind of downtown was found to be primarily from a large increase in frequency of deep convective events when compared to the surrounding domain. Also, it was found that UHI, rather than sea-breeze, was likely the primary causative mechanism in the development of convection over the Houston area because of the lack of deep convection in areas equally affected by the sea-breeze and the timing of the convection compared to time of peak sea-breeze. An area of weaker enhancement south of Houston, not discussed in previous studies, was found to be present, possibly from the interactions between the bay-breeze off of the Galveston Bay and the seabreeze.

Based on Thesis (M.A.)--University of Houston. / Bibliography: p. 67-69.

A flux measurement setup was established at a communications tower north of downtown Houston, Texas, to measure energy and trace gas fluxes from a variety of emission sources in the urban surface layer. The first part of this study details the development of a correction for latent heat and carbon dioxide (CO2) fluxes due to a low-pass filtering of the true water vapor and CO2 atmospheric signals. A method of spectral analysis was used to develop a correction scheme for this flux underestimation through the observation that the low-pass filtering is a strong function of atmospheric relative humidity and wind speeds. The determined flux corrections for latent heat fluxes (average correction of 34%) were significantly larger than CO2 fluxes (3-4%), suggesting the low-pass filtering had a more dominant effect on the water vapor signal. For the second part of this study, we describe a quadrant analysis technique for separating measured net fluxes into their biogenic (c’ < 0 and q’ > 0 signals) and anthropogenic (c’ > 0 and T’ > 0 signals) components, and quantify these fluxes through the use of a refined relaxed eddy accumulation model. A method of minimizing a defined net – (biogenic + anthropogenic) residual was used to determine an accurate “hole” around the origin to exclude points in the desired quadrants that appear there randomly. The magnitude of the biogenic flux contribution showed expected relationships with temperature and irradiance. The anthropogenic flux contribution showed a strong correlation with measured traffic counts collected on local thoroughfares. Due to a presumed small bias in the flux calculation methodology, neither flux contribution truly measured zero, so anthropogenic and biogenic “background” fluxes were calculated (0.01 µmol mo^-1 m s^-1 and 0.01 – 0.02 µmol mol^-1 m s^-1 respectively). Future work involves perfecting the model, with the goal being widespread use of the theory at urban flux sites. The accurate separation of the net flux gives a more complete picture of the carbon cycle and allows for more accurate analysis of the effects of increased temperature and CO2 concentration on urban vegetation as compared to non-urban vegetation.

Based on Thesis (M.A.)--University of Houston. / Bibliography: p. 67-69.

Treatise (D.M.A.)--University of Texas at Austin, 2004. / Supervisors: Michael Tusa and Rose Taylor. Vita. Includes bibliographical references. Also available from UMI.

Not available / text

Not available / text

Thesis (M.S.)--University of Hawaii at Manoa, 2007. / Includes bibliographical references (leaves 94-97). / ix, 97 leaves, bound ill., maps 29 cm