scholarly journals Modeling Turbulent Flow in an Urban Central Business District

2007 ◽  
Vol 46 (12) ◽  
pp. 2147-2164 ◽  
Author(s):  
Donald A. Burrows ◽  
Eric A. Hendricks ◽  
Steve R. Diehl ◽  
Robert Keith
Keyword(s):  
Wind Speed ◽  
Central Business District ◽  
Oklahoma City ◽  
Dynamics Model ◽  
Near Surface ◽  
Computational Fluid Dynamics Model ◽  
Sonic Anemometers ◽  
Turbulent Airflow ◽  
Joint Urban 2003 Experiment ◽  
Business District

Abstract The Realistic Urban Spread and Transport of Intrusive Contaminants (RUSTIC) model has been developed as a simplified computational fluid dynamics model with a k–ω turbulence model to be used to provide moderately fast simulations of turbulent airflow in an urban environment. RUSTIC simulations were compared with wind tunnel measurements to refine and “calibrate” the parameters for the k–ω model. RUSTIC simulations were then run and compared with data from five different periods during the Joint Urban 2003 experiment. Predictions from RUSTIC were compared with data from 33 near-surface sonic anemometers as well as 8 sonic anemometers on a 90-m tower and a sodar wind profiler located in the Oklahoma City, Oklahoma, central business district. The data were subdivided into daytime and nighttime datasets and then the daytime data were further subdivided into exposed and sheltered sonic anemometers. While there was little difference between day and night for wind speed and direction comparisons, there was considerable difference for the turbulence kinetic energy (TKE) comparisons. In the nighttime cases, RUSTIC overpredicted the TKE but without any correlation between model and observations. On the other hand, for the daytime cases, RUSTIC underpredicted the TKE values and correlated well with the observations. RUSTIC predicted both winds and TKE much better for the exposed sonic anemometers than for the sheltered ones. For the 90-m tower location downwind of the central business district, RUSTIC predicted the vertical profile of wind speed and direction very closely but underestimated the TKE.

scholarly journals Analysis of Urban Effects in Oklahoma City using a Dense Surface Observing Network

2016 ◽  
Vol 55 (3) ◽  
pp. 723-741 ◽  
Author(s):  
Xiao-Ming Hu ◽  
Ming Xue ◽  
Petra M. Klein ◽  
Bradley G. Illston ◽  
Sheng Chen
Keyword(s):  
Metropolitan Area ◽  
Land Surface ◽  
Critical Role ◽  
Central Business District ◽  
Temperature Inversion ◽  
Oklahoma City ◽  
Near Surface ◽  
Open Questions ◽  
The Stability ◽  
Business District

AbstractMany studies have investigated urban heat island (UHI) intensity for cities around the world, which is normally quantified as the temperature difference between urban location(s) and rural location(s). A few open questions still remain regarding the UHI, such as the spatial distribution of UHI intensity, temporal (including diurnal and seasonal) variation of UHI intensity, and the UHI formation mechanism. A dense network of atmospheric monitoring sites, known as the Oklahoma City (OKC) Micronet (OKCNET), was deployed in 2008 across the OKC metropolitan area. This study analyzes data from OKCNET in 2009 and 2010 to investigate OKC UHI at a subcity spatial scale for the first time. The UHI intensity exhibited large spatial variations over OKC. During both daytime and nighttime, the strongest UHI intensity is mostly confined around the central business district where land surface roughness is the highest in the OKC metropolitan area. These results do not support the roughness warming theory to explain the air temperature UHI in OKC. The UHI intensity of OKC increased prominently around the early evening transition (EET) and stayed at a fairly constant level throughout the night. The physical processes during the EET play a critical role in determining the nocturnal UHI intensity. The near-surface rural temperature inversion strength was a good indicator for nocturnal UHI intensity. As a consequence of the relatively weak near-surface rural inversion, the strongest nocturnal UHI in OKC was less likely to occur in summer. Other meteorological factors (e.g., wind speed and cloud) can affect the stability/depth of the nighttime boundary layer and can thus modulate nocturnal UHI intensity.

scholarly journals Influence of Soil Moisture on Urban Microclimate and Surface-Layer Meteorology in Oklahoma City

2014 ◽  
Vol 53 (1) ◽  
pp. 83-98 ◽  
Author(s):  
Syed Zahid Husain ◽  
Stéphane Bélair ◽  
Sylvie Leroyer
Keyword(s):  
Surface Layer ◽  
Soil Moisture ◽  
Wind Speed ◽  
Urban Soil ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Oklahoma City ◽  
Near Surface ◽  
Model Simulations ◽  
Urban Surface Layer

AbstractThe influence of soil moisture on the surface-layer atmosphere is examined in this paper by analyzing the outputs of model simulations for different initial soil moisture configurations, with particular emphasis on urban microclimate. In addition to a control case, four different soil moisture distributions within the urban and surrounding rural areas are considered in this study. Outputs from the Global Environmental Multiscale atmospheric model simulations are compared with observations from the Joint Urban 2003 experiment held in Oklahoma City, Oklahoma, and the relevant conclusions drawn in this paper are therefore valid for similar medium-size cities. In general, high soil moisture is found to be associated with colder near-surface temperature and lower near-surface wind speed, whereas drier soil resulted in warmer temperatures and enhanced low-level wind. Relative to urban soil moisture content, rural soil conditions are predicted to have larger impacts on both rural and urban surface-layer meteorological conditions. Dry rural and wet urban soil configurations are shown to have a strong influence on the urban–rural temperature contrast and resulted in city-induced secondary circulations that considerably affect the near-surface wind speed. Dry rural soil in particular is found to intensify the nocturnal low-level jet and significantly affect the thermal stability of nocturnal near-neutral urban surface layer by altering both thermal and mechanical generation of turbulence.

scholarly journals The relative importance of wind-driven and chimney effect cave ventilation: Observations in Postojna Cave (Slovenia)

2021 ◽  
Vol 50 (3) ◽  
pp. 275-288
Author(s):  
Lovel Kukuljan ◽  
Franci Gabrovsek ◽  
Matthew Covington
Keyword(s):  
Wind Speed ◽  
Pressure Field ◽  
Wind Pressure ◽  
Relative Importance ◽  
Dynamics Model ◽  
Near Surface ◽  
Cave System ◽  
Irregular Topography ◽  
Theoretical Considerations ◽  
Chimney Effect

Density-driven chimney effect airflow is the most common form of cave ventilation, allowing gas exchange between the outside and the karst subsurface. However, cave ventilation can also be driven by other mechanisms, such as barometric changes or pressure differences induced by the outside winds. We discuss the mechanism and dynamics of wind-driven ventilation using observations in Postojna Cave, Slovenia. We show how seasonal airflow patterns driven by the chimney effect are substantially modified by outside winds. Wind flow over irregular topography forms near-surface air pressure variations and thus pressure differences between cave entrances at different locations. These pressure differences depend on wind speed and direction and their relationship to surface topography and the location of cave entrances. Winds can act in the same or opposite direction as the chimney effect and can either enhance, diminish or even reverse the direction of the density-driven airflows. To examine the possibility of wind-driven flow, we used a computational fluid dynamics model to calculate the wind pressure field over Postojna Cave and the pressure differences between selected points for different configurations of wind speed and direction. We compared these values with those obtained from airflow measurements in the cave and from simple theoretical considerations. Despite the simplicity of the approach and the complexity of the cave system, the comparisons showed satisfactory agreement. This allowed a more general assessment of the relative importance of wind pressure for subsurface ventilation. We are certain that this example is not unique and that the wind-driven effect needs to be considered elsewhere to provide better insights into the dynamics of cave climate, air composition or dripwater geochemistry.

scholarly journals The relative importance of wind-driven and chimney effect cave ventilation: Observations in Postojna Cave (Slovenia)

2021 ◽  
Author(s):  
Lovel Kukuljan ◽  
Franci Gabrovšek ◽  
Matthew Covington
Keyword(s):  
Wind Speed ◽  
Pressure Field ◽  
Wind Pressure ◽  
Relative Importance ◽  
Dynamics Model ◽  
Near Surface ◽  
Cave System ◽  
Irregular Topography ◽  
Theoretical Considerations ◽  
Chimney Effect

Density-driven chimney effect airflow is the most common form of cave ventilation, allowing gas exchange between the outside and the karst subsurface. However, cave ventilation can also be driven by other mechanisms, namely winds. We discuss the mechanism and dynamics of wind-driven ventilation using observations in Postojna Cave, Slovenia. We show how seasonal airflow patterns driven by the chimney effect are substantially modified by outside winds. Wind flow over irregular topography forms near-surface air pressure variations and thus pressure differences between cave entrances at different locations. These pressure differences depend on wind speed and direction and their relationship to surface topography and the location of cave entrances. Winds can act in the same or opposite direction as the chimney effect and can either enhance, diminish or even reverse the direction of the density-driven airflows. To examine the possibility of wind-driven flow, we used a computational fluid dynamics model to calculate the wind pressure field over Postojna Cave and the pressure differences between selected points for different configurations of wind speed and direction. We compared these values with those obtained from airflow measurements in the cave and from simple theoretical considerations. Despite the simplicity of the approach and the complexity of the cave system, the comparisons showed satisfactory agreement. This allowed a more general assessment of the relative importance of wind pressure for the subsurface ventilation. We are certain that this example is not unique and that the wind-driven effect needs to be considered elsewhere to provide better insights into the dynamics of cave climate, air composition or dripwater geochemistry.

scholarly journals Trends in Mean Annual Minimum and Maximum Near Surface Temperature in Nairobi City, Kenya

2010 ◽  
Vol 2010 ◽  
pp. 1-6 ◽  
Author(s):  
George Lukoye Makokha ◽  
Chris A. Shisanya
Keyword(s):  
Urban Planning ◽  
Surface Temperature ◽  
Minimum Temperature ◽  
Central Business District ◽  
Maximum Temperature ◽  
Rank Test ◽  
Homogeneity Test ◽  
Near Surface ◽  
Business District ◽  
The City

This paper examines the long-term urban modification of mean annual conditions of near surface temperature in Nairobi City. Data from four weather stations situated in Nairobi were collected from the Kenya Meteorological Department for the period from 1966 to 1999 inclusive. The data included mean annual maximum and minimum temperatures, and was first subjected to homogeneity test before analysis. Both linear regression and Mann-Kendall rank test were used to discern the mean annual trends. Results show that the change of temperature over the thirty-four years study period is higher for minimum temperature than maximum temperature. The warming trends began earlier and are more significant at the urban stations than is the case at the sub-urban stations, an indication of the spread of urbanisation from the built-up Central Business District (CBD) to the suburbs. The established significant warming trends in minimum temperature, which are likely to reach higher proportions in future, pose serious challenges on climate and urban planning of the city. In particular the effect of increased minimum temperature on human physiological comfort, building and urban design, wind circulation and air pollution needs to be incorporated in future urban planning programmes of the city.

scholarly journals Profiles of Wind Speed Variances within Nocturnal Low-Level Jets Observed with a Sodar

2013 ◽  
Vol 30 (9) ◽  
pp. 1970-1977 ◽  
Author(s):  
Margarita A. Kallistratova ◽  
Rostislav D. Kouznetsov ◽  
Valerii F. Kramar ◽  
Dmitrii D. Kuznetsov
Keyword(s):  
Wind Speed ◽  
Wind Shear ◽  
Periodic Structures ◽  
Microwave Radiometer ◽  
Wind Component ◽  
Mean Velocity ◽  
Near Surface ◽  
Low Level ◽  
Sonic Anemometers ◽  
Low Level Jets

Abstract Continuous sodar measurements of wind profiles have been carried out at the Zvenigorod Scientific Station of the Obukhov Institute of Atmospheric Physics since 2008. The station is located in a slightly inhomogeneous rural area about 45 km west of Moscow, Russia. The data were used to determine the parameters of wind and turbulence within low-level jets in the stable atmospheric boundary layer (ABL). Along with the mean velocity profiles, the profiles of variances of wind speed components from the sodar and the profiles of temperature from a microwave radiometer have been used to quantify turbulence and thermal stratification. Data from two sonic anemometers were used to get the near-surface parameters. The typical standard deviation of the vertical wind component σw within the low-level jet is about 5% of the maximum wind speed in the jet. No noticeable vertical variation of σw across the jets was detected in several earlier sodar campaigns, and it was not found in the present study. An increase in horizontal variances was detected in zones of substantial wind shear, which agrees with earlier published lidar data. Quasi-periodic structures in the sodar return signal, which appear in sodar echograms as braid-shaped patterns, were found to emerge preferably when a substantial increase of wind shear occurs at the top of the stable ABL. The braid patterns in the sodar echograms were not accompanied by any noticeable increase of observed σw, which disagrees with earlier data and indicates that such patterns may originate from various phenomena.

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