Urban modification of thermal conditions in the planetary boundary layer has been well documented in both humid and arid regions of North America. Among the manifestations of these modifications is the urban heat island. Urban modification of processes modulating convection in and around urban areas also has been established in humid regions like the southeastern U.S. The relationship between urbanization and changes in regional convective parameters is less well understood in arid regions. This collaborative research project will examine modification of parameters related to convection in the arid Las Vegas Valley of Nevada. The Las Vegas Valley has been rapidly urbanizing over the past three decades and produces an extensive urban heat island during the summer season. The investigators initially will analyze the intensity and extent of the urban heat island for the period from 1990 to 2006 following procedures established in arid regions, such as those developed in Phoenix, Arizona. The objective of the project then will shift to collecting, formatting, and integrating surface, upper-air, and remotely sensed meteorological data sets. The data-integration procedure will pair data sets based on temporal and spatial resolution and develop appropriate interpolation procedures for point data sets so that these data can be interpreted within a common grid structure. Sources of data to be integrated include the Clark County Regional Flood Control District surface meso-network observations (temperature, wind speed/direction, and rainfall), NEXRAD volume scans (composite reflectivity, storm-relative velocity, and rainfall rate), National Lightning Detection Network (NLDN) point data (cloud-to-ground lightning flashes), Geostationary Operational Environmental Satellite (GOES) imagery (visible and thermal infrared), and regional radiosonde observation (RAOB) network soundings (thermodynamic parameters). Following the data-integration phase, the investigators will test a number of methodologies to identify the most efficient techniques for extracting information related to the intensity, duration, and location of the Las Vegas Convergence Zone (LVCZ) and the intensity, duration, and extent of the North American Monsoon (NAM) circulation. The integrated data set developed in the prior research phase will be used in sensitivity studies to test the feasibility of detecting a urban heat island impact signal on convection in the presence of strong/weak LVCZ scenarios and during strong and weak NAM circulations. A primary objective of this proof-of-concept study will be the compilation of a number of case-studies that illustrate the spatial and temporal interactions of multi-scale atmospheric processes during summer season convection episodes in the Las Vegas Valley. The case studies will include parameters describing convective cloud development, CG lightning flashes, and convective rainfall in the valley.
This project will design experiments and conduct case studies to assess the feasibility of identifying a measurable urban heat island influence on summer season convection in an urban region in the arid southwestern U.S. The project will analyze meso-scale and synoptic scale circulations like as the Las Vegas Convergence Zone (LVCZ) and the North American Monsoon (NAM), how those circulations can produce a complicated and interrelated convective environment in the Las Vegas Valley. It also will yield case studies illustrating variability in both processes. Parameters describing regional development of convective clouds, cloud-to-ground lightning flashes, and rainfall patterns will be include in case studies for weak and strong NAM circulations and for weak and strong LVCZ development. The research will be carried out with the assistance of graduate students from the University of Nevada and with high school senior interns from Monogue High School in Reno, Nevada as part of a previously established student internship program. The case studies produced by the research will be made available to the Geographic Alliance in Nevada, for distribution to science teachers statewide as part of a curriculum enhancement project. This project will advance fundamental scientific understanding in urban climatology in arid regions. It will provide new insights regarding North American Monsoon influence on meso-scale processes, and the use of cloud-to-ground lightning flash data in the study of convection. The project also will provide the planning community in the Las Vegas Valley with data sets and case-studies that provide context for decisions related to flood control, public safety, and residential development.
