Supplementary material to "Measurement report: Vertical distribution of biogenic and anthropogenic secondary organic aerosols in the urban boundary layer over Beijing during late summer"
Hong RenWei HuLianfang WeiSiyao YueJian ZhaoLinjie LiLibin WuWanyu ZhaoLujie RenMingjie KangQiaorong XieSihui SuXiaole PanZifa WangYele SunKimitaka KawamuraPingqing Fu
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Urban climatology
Sensitivity of mesoscale model urban boundary layer meteorology to the scale of urban representation
Abstract. Mesoscale modeling of the urban boundary layer requires careful parameterization of the surface due to its heterogeneous morphology. Model estimated meteorological quantities, including the surface energy budget and canopy layer variables, will respond accordingly to the scale of representation. This study examines the sensitivity of the surface energy balance, canopy layer and boundary layer meteorology to the scale of urban surface representation in a real urban area (Detroit-Windsor (USA-Canada)) during several dry, cloud-free summer periods. The model used is the Weather Research and Forecasting (WRF) model with its coupled single-layer urban canopy model. Some model verification is presented using measurements from the Border Air Quality and Meteorology Study (BAQS-Met) 2007 field campaign and additional sources. Case studies span from "neighborhood" (10 s ~308 m) to very coarse (120 s ~3.7 km) resolution. Small changes in scale can affect the classification of the surface, affecting both the local and grid-average meteorology. Results indicate high sensitivity in turbulent latent heat flux from the natural surface and sensible heat flux from the urban canopy. Small scale change is also shown to delay timing of a lake-breeze front passage and can affect the timing of local transition in static stability.
Urban climatology
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In contrast to the classical homogeneous atmospheric boundary layer, the urban boundary layer is more complex due to several specific features and processes caused by the buildings which introduce a large amount of vertical surfaces, high roughness elements, and artificial materials. The most well-known result is the urban heat island, but urban areas also influence the wind field, precipitation, atmospheric stability, and the mixing height.
Urban climatology
Atmospheric instability
Urban Heat Island
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Urban climatology
Convective Boundary Layer
Thermal wind
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The Helsinki Urban Boundary-Layer Atmosphere Network (UrBAN: http://urban.fmi.fi) is a dedicated research-grade observational network where the physical processes in the atmosphere above the city are studied. Helsinki UrBAN is the most poleward intensive urban research observation network in the world and thus will allow studying some unique features such as strong seasonality. The network's key purpose is for the understanding of the physical processes in the urban boundary layer and associated fluxes of heat, momentum, moisture, and other gases. A further purpose is to secure a research-grade database, which can be used internationally to validate and develop numerical models of air quality and weather prediction. Scintillometers, a scanning Doppler lidar, ceilometers, a sodar, eddy-covariance stations, and radiometers are used. This equipment is supplemented by auxiliary measurements, which were primarily set up for general weather and/or air-quality mandatory purposes, such as vertical soundings and the operational Doppler radar network. Examples are presented as a testimony to the potential of the network for urban studies, such as (i) evidence of a stable boundary layer possibly coupled to an urban surface, (ii) the comparison of scintillometer data with sonic anemometry above an urban surface, (iii) the application of scanning lidar over a city, and (iv) combination of sodar and lidar to give a fuller range of sampling heights for boundary layer profiling.
SODAR
Urban climatology
Ceilometer
Urban Heat Island
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Abstract. The urban boundary layer (UBL), in comparison with "rural" homogeneous atmospheric boundary layers, is characterised by greatly enhanced mixing, resulting from both the large surface roughness and increased surface heating, and by horizontal heterogeneity of the mixing height (MH) and other meteorological fields due to variations in surface roughness and heating from rural to central city areas. So, the UBL is considered as a specific case of the atmospheric boundary layer (ABL) over a non-homogeneous terrain. Therefore it is important to study how much the MH characteristics differ in urban and rural, marine or other more homogeneous areas. Most of the parameterisations of MH were developed for the conditions of a homogeneous terrain, so their applicability for urban conditions should be verified. Just a few authors suggested specific methods for MH determination in urban areas. In this paper the MH over urban, semi-urban, rural and marine areas of the Copenhagen metropolitan area is considered. Proceeding from the data from the Jægersborg radiosounding station measurement and analysis of different methods of the MH estimation, the peculiarities of the UBL and intercomparison of different MH estimation methods for urban and rural conditions are discussed. It is shown that the urban MH is considerably bigger for stably stratified (nocturnal) boundary layer cases in comparison with the "non-urban" MH. Daytime (usually the convective boundary layer) MH does not differ significatly in urban and "non-urban" sectors.
Urban climatology
Convective Boundary Layer
Urban Heat Island
Urban area
Mixing ratio
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Abstract. Mesoscale modeling of the urban boundary layer requires careful parameterization of the surface due to its heterogeneous morphology. Model estimated meteorological quantities, including the surface energy budget and canopy layer variables, will respond accordingly to the scale of representation. This study examines the sensitivity of the surface energy balance, canopy layer and boundary layer meteorology to the scale of urban surface representation in a real urban area (Detroit-Windsor (USA-Canada)) during several dry, cloud-free summer periods. The model used is the Weather Research and Forecasting (WRF) model with its coupled single-layer urban canopy model. Some model verification is presented using measurements from the Border Air Quality and Meteorology Study (BAQS-Met) 2007 field campaign and additional sources. Case studies span from "neighborhood" (10 s ~ 30 m) to very coarse (120 s ~ 3.7 km) resolution. Small changes in scale can affect the classification of the surface, affecting both the local and grid-average meteorology. Results indicate high sensitivity in turbulent latent heat flux from the natural surface and sensible heat flux from the urban canopy. Small scale change is also shown to delay timing of a lake-breeze front passage and can affect the timing of local transition in static stability.
Urban climatology
Energy budget
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Abstract A modified version of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) was applied to the arid Phoenix, Arizona, metropolitan region. The ability of the model to simulate characteristics of the summertime urban planetary boundary layer (PBL) was tested by comparing model results with observations from two field campaigns conducted in May/June 1998 and June 2001. The modified MM5 included a refined land use/cover classification and updated land use data for Phoenix and bulk approaches of characteristics of the urban surface energy balance. PBL processes were simulated by a version of MM5’s Medium-Range Forecast Model (MRF) scheme that was enhanced by new surface flux and nonlocal mixing approaches. Simulated potential temperature profiles were tested against radiosonde data, indicating that the modified MRF scheme was able to simulate vertical mixing and the evolution and height of the PBL with good accuracy and better than the original MRF scheme except in the late afternoon. During both simulation periods, it is demonstrated that the modified MM5 simulated near-surface air temperatures and wind speeds in the urban area consistently and considerably better than the standard MM5 and that wind direction simulations were improved slightly.
MM5
Urban climatology
Phoenix
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Theoretical descriptions of the atmospheric boundary layer have not changed substantially during the past four years. The Monin‐Obukhov theory remains the most complete description of the surface layer. Rather idealized models of the deeper convective boundary layer are also reasonably accurate. The stable boundary layer is still poorly understood, and the controversy persists in several attempts to relate boundary layer motions to deeper tropospheric flow.
Convective Boundary Layer
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Low-speed wind-tunnel studies have been conducted that examined mean velocity profiles and longitudinal turbulence quantities including the energy spectra for a zero-pressure-gradient turbulent boundary layer flow over a rough-to-smooth change in surface roughness. The flow examined modeled the lower 30 to 50 m of the urban atmospheric boundary layer. The wind-tunnel flow was developed over a 12 m long flow conditioning section where roughness elements occupied the lower 10 to 13% of a 70 cm thick boundary layer with the freestream velocity of approximately 3.0 m/s. The present results provided unique information concerning the wind tunnel simulation of the urban atmospheric boundary layer in the following areas: (1) the presence and growth of an ''inner boundary layer'' downstream of a step transition in surface roughness; (2) the enhancement of boundary layer thickness ad turbulence characteristics using vortex generators or spires; and (3) determination of the appropriate modeling length scales. 56 figs., 4 tabs.
Freestream
Roughness length
Pressure gradient
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Based on a pseudo-spectral large eddy simulation (LES) model, an LES model with an anisotropy turbulent kinetic energy (TKE) closure model and an explicit multi-stage third-order Runge-Kutta scheme is established. The modeling and analysis show that the LES model can simulate the planetary boundary layer (PBL) with a uniform underlying surface under various stratifications very well. Then, similar to the description of a forest canopy, the drag term on momentum and the production term of TKE by subgrid city buildings are introduced into the LES equations to account for the area-averaged effect of the subgrid urban canopy elements and to simulate the meteorological fields of the urban boundary layer (UBL). Numerical experiments and comparison analysis show that: (1) the result from the LES of the UBL with a proposed formula for the drag coefficient is consistent and comparable with that from wind tunnel experiments and an urban subdomain scale model; (2) due to the effect of urban buildings, the wind velocity near the canopy is decreased, turbulence is intensified, TKE, variance, and momentum flux are increased, the momentum and heat flux at the top of the PBL are increased, and the development of the PBL is quickened; (3) the height of the roughness sublayer (RS) of the actual city buildings is the maximum building height (1.5-3 times the mean building height), and a constant flux layer (CFL) exists in the lower part of the UBL.
Urban climatology
Large-Eddy Simulation
Momentum (technical analysis)
Roughness length
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