Dragan Zajic

The MATERHORN: Unraveling the Intricacies of Mountain Weather

AbstractEmerging application areas such as air pollution in megacities, wind energy, urban security, and operation of unmanned aerial vehicles have intensified scientific and societal interest in mountain meteorology. To address scientific needs and help improve the prediction of mountain weather, the U.S. Department of Defense has funded a research effort—the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program—that draws the expertise of a multidisciplinary, multi-institutional, and multinational group of researchers. The program has four principal thrusts, encompassing modeling, experimental, technology, and parameterization components, directed at diagnosing model deficiencies and critical knowledge gaps, conducting experimental studies, and developing tools for model improvements. The access to the Granite Mountain Atmospheric Sciences Testbed of the U.S. Army Dugway Proving Ground, as well as to a suite of conventional and novel high-end airborne and surface measurement platfor...

Flow and Turbulence in an Urban Canyon

Abstract A better understanding of the interaction between the built environment and the atmosphere is required to more effectively manage urban airsheds. This paper reports an analysis of data from an atmospheric measurement campaign in Oklahoma City, Oklahoma, during the summer of 2003 that shows wind flow patterns, turbulence, and thermal effects in the downtown area. Experimental measurements within a street canyon yielded airflow patterns, stability conditions, and turbulence properties as a function of the incoming wind direction and time of the day. Air and surface temperatures at two different sites, one within the downtown urban canyon and the other in a nearby park, were measured. A study of the stability conditions within the urban canyon during the campaign indicates that dynamically stable conditions did not occur within the canyon. This provides evidence that the built environment can strongly influence the thermal characteristics in cities. Mean flow patterns close to the street level are a...

On flows in simulated urban canopies

Flow and turbulence within building canopies continue to be a topic of profound interest in the context of pedestrian comfort, wind loading, contaminant dispersion and energy usage in populated urban areas. Many experimental studies have been reported on this topic, but they either deal with wind/water tunnel measurements (at low Reynolds numbers) or complex urban building clusters (where the results are site dependent and difficult to interpret). To avert such problems, an instrumented mock building cluster made of a regular array of man-sized objects (shipping containers) placed in the atmospheric boundary layer was used to investigate spatial flow adjustment, flow patterns (as a function of approach angle) and turbulence within the building canopy. A new scaling is proposed for the characteristic canopy velocity based on the approach flow and canopy morphology, which was found to perform well when evaluated against experimental data. The flow adjustment at the leading and trailing edges of the canopy was found to be in good agreement with the formulation of Belcher et al. (J Fluid Mech 488:369–398, 2003). The results have applications to developing simple and fast contaminant transport and dispersion models that can be used in conjunction with emergency response.