This project bridges the gap between modern research practices and student education in an area of growing national interest - urban meteorology. The main objectives are (i) to fully utilize modern observation techniques in boundary-layer research, (ii) to gain new knowledge of boundary-layer dynamics and turbulence structure over terrain with large roughness elements, (iii) to advance urban surface-layer parameterization schemes and (iv) to create synergistic and integrated learning experiences to better educate future scientists and professionals about urban environmental impacts.
The novelty of the Laboratory for Research and Education in Urban Meteorology (ILREUM) originates from the integrated design of a laboratory that fully utilizes new technologies in meteorological studies. In-situ and remote-sensing instrumentation, as well as fieldwork and wind tunnel simulations are combined in an innovative and complementary way. Three observational sites representative for different land use types are being designed to obtain high-resolution and long-term data of flow and turbulence within the lowest hundreds of meters of the urban boundary layer. These data, in combination with data available from a number of recent urban field and laboratory campaigns, will provide new insights into (i) boundary-layer development from rural through sub-urban to urban terrain, (ii) the interaction between thermally and mechanically produced turbulence in urban areas, (iii) the properties of flow and turbulence inside the urban roughness sublayer, and (iv) the exchange of momentum, heat, and pollutants between the urban canopy layer and the above roof level flow. All these questions are still not fully understood and of crucial importance for the development and improvement of modeling systems that serve as tools to solve current and future environmental challenges of cities Because of the ongoing trend of urbanization, atmospheric processes in urban areas are of great concern and directly affect the majority of the world's population. ILREUM aims at a broader knowledge in urban meteorology and improvement of parameterization schemes for atmospheric models.
Broader impacts: The expected results are of great relevance for a wide range of applications including (i) weather prediction and climate models for urban and regional scales, (ii) modeling systems for urban air quality management, and (iii) emergency response tools in the event of unexpected releases of air toxics in an urban environment. As part of ILREUM, interactive and hands-on teaching modules will be developed and disseminated through digital libraries, which will assist in closing the gap between research and education and promote lasting knowledge of scientific principles in this challenging field beyond the OU campus. The International Association of Urban Climatology (IAUC) has recognized the need for improved teaching resources in urban meteorology: the ILREUM materials will be announced in the IAUC newsletter in response to this call. The education plan includes also an international exchange program, which will further assure that future graduates are better prepared for challenges and opportunities arising from ongoing urbanization and the related global, regional and local environmental problems. Research and travel fellowships will be awarded to undergraduate students participating in the exchange programs and special efforts will be undertaken to attract underrepresented groups in these fellowships. In collaboration with existing outreach programs of the Oklahoma Climatological Survey, the obtained data and results will also be prepared in a format targeting K-12 education and training of first responders.
The surfaces of urban landscapes are typically much rougher and drier than the ones of rural landscapes. The high building density in cities further alters the radiative transfer with the atmosphere and urban materials have different thermal properties than soils. All these effects influence weather and climate in cities. To better understand the magnitude of urban effects and to identify key processes, the NSF Career award ILREUM focused on the integrated design of a laboratory that utilizes new observation and simulation technologies. In total, three measurement campaigns were conducted in suburban and urban terrain to provide new insights about flow and turbulent processes in cities. Two suburban campaigns had the primary objective to evaluate the performance of a scintillometer, a laser based instrument. Its remotely-sensed, spatially-averaged heat and momentum fluxes, were compared against in-situ measurements with sonic anemometers. The studies identified a number of uncertainties in the scintillometer measurements, which limited the use of this type of instrument in the urban studies. The urban campaign included year-long measurements on the campus of the University of Oklahoma (Fig. 1), which provide information about seasonal influences and upwind-roughness effects on street-canyon flow and turbulence. Previous findings that flow and turbulence characteristics in street canyons vary strongly with wind direction were confirmed. For most wind directions, flow channeling along the canyon dominates. Only for narrow sectors with wind directions perpendicular to buildings, recirculation patterns develop inside the street canyon that are characterized by low horizontal wind speeds, pronounced vertical motions along the walls, and reverse flow at the bottom of the canyon (Fig 2). Turbulent motions peak under such conditions. New insights were gained about the flow and turbulence properties within the roughness sublayer and the exchange between the urban canopy layer and the above- roof level flow. If recirculation patterns prevail within the urban canopy layer, turbulence is actively transported from the region above the buildings into the canopy layer. Since upwind terrain and larger-scale atmospheric stability influence turbulence levels in the above-roof level flow, canopy-layer turbulence properties also depend on these parameters, while local stability effects due to differential heating of buildings walls were not observed. The extended analysis of data sets collected during the Join Urban 2003 experiment in Oklahoma City further demonstrated how urban climate and air quality is affected by the structure of the rural boundary layer. The nocturnal low-level jet, a prominent feature in the US Southern Great Plains, plays an important role in moderating the urban heat island intensity and also affects ozone concentrations in the Oklahoma City area. During nights with strong low-level jets, vertical mixing within the atmospheric boundary layer persists, which supports the transport of momentum and heat from higher elevations to the surface. Compared to nights without strong low-level jets, wind speeds and air temperatures remain higher near the surface and atmospheric stability is thus rather weak. Under such conditions, the contrasts between urban rural and temperatures, also called the urban heat island intensity, decrease. A negative correlation between urban heat island intensity and low-level jet strength was observed (Fig. 3). Urban ozone concentrations are also strongly affected by nocturnal mixing and thus also by the strength and evolution of the low-level jet. Within shallow, stable surface layers, which develop when low-level jets are weak or absent, urban ozone concentrations near the surface rapidly decrease after sunset due to reactions with nitrogen oxides. For situations with strong low-level jets that promote strong vertical mixing, ozone is transported from higher elevations to the surface where nighttime concentrations then remain higher than in a shallow stable layer. These findings have important implications for modeling of urban areas and for future urban planning. ILREUM also actively supported the international collaboration of the PI and students, including the participation in a measurement campaign in France. Leveraging of ILREUM funds further allowed to conduct studies at an experimental green roof (Fig. 4) and to acquire a Doppler Wind Lidar, which significantly enhances our capabilities to study wind and turbulence in the lower atmosphere. ILREUM supported two PhD students and a total of eight undergraduate students. An important aspect of ILREUM was also the integration of hands-on training of students in meteorological data collection, storage and analysis. In average, 50 students were involved every year in taking measurements at various sites and analyzing the collected data. The student projects included both training in the lab (Fig. 5) and outdoor campaigns (Fig. 6). They focused on various topics including urban heat islands, impacts of green roofs on local weather and microclimates in rural areas.
