Full-scale wind speed spectra of 5 Year time series in urban boundary layer observed on a 325 m meteorological tower

2021 ◽  
Vol 218 ◽  
pp. 104791
Author(s):  
Bo Li ◽  
Chen Li ◽  
Qingshan Yang ◽  
Yuji Tian ◽  
Xinxin Zhang
Keyword(s):  
Boundary Layer ◽  
Time Series ◽  
Wind Speed ◽  
Urban Boundary Layer ◽  
Full Scale ◽  
Meteorological Tower

Prediction of Atmospheric Turbulence Characteristics for Surface Boundary Layer using Empirical Spectral Methods

2020 ◽  
Author(s):  
Yagya Dutta Dwivedi ◽  
Vasishta Bhargava Nukala ◽  
Satya Prasad Maddula ◽  
Kiran Nair
Keyword(s):  
Boundary Layer ◽  
Time Series ◽  
Surface Roughness ◽  
Wind Speed ◽  
Atmospheric Turbulence ◽  
Surface Boundary ◽  
Low Frequencies ◽  
Surface Boundary Layer ◽  
Power Spectral ◽  
Mean Wind Speed

Abstract Atmospheric turbulence is an unsteady phenomenon found in nature and plays significance role in predicting natural events and life prediction of structures. In this work, turbulence in surface boundary layer has been studied through empirical methods. Computer simulation of Von Karman, Kaimal methods were evaluated for different surface roughness and for low (1%), medium (10%) and high (50%) turbulence intensities. Instantaneous values of one minute time series for longitudinal turbulent wind at mean wind speed of 12 m/s using both spectra showed strong correlation in validation trends. Influence of integral length scales on turbulence kinetic energy production at different heights is illustrated. Time series for mean wind speed of 12 m/s with surface roughness value of 0.05 m have shown that variance for longitudinal, lateral and vertical velocity components were different and found to be anisotropic. Wind speed power spectral density from Davenport and Simiu profiles have also been calculated at surface roughness of 0.05 m and compared with k−1 and k−3 slopes for Kolmogorov k−5/3 law in inertial sub-range and k−7 in viscous dissipation range. At high frequencies, logarithmic slope of Kolmogorov −5/3rd law agreed well with Davenport, Harris, Simiu and Solari spectra than at low frequencies.

scholarly journals Venting of Heat and Carbon Dioxide from Urban Canyons at Night

2005 ◽  
Vol 44 (8) ◽  
pp. 1180-1194 ◽  
Author(s):  
J. A. Salmond ◽  
T. R. Oke ◽  
C. S. B. Grimmond ◽  
S. Roberts ◽  
B. Offerle
Keyword(s):  
Carbon Dioxide ◽  
Boundary Layer ◽  
Time Series ◽  
Wavelet Analysis ◽  
Air Temperature ◽  
Urban Boundary Layer ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Canopy Layer ◽  
Street Canyons

Abstract Turbulent fluxes of carbon dioxide and sensible heat were observed in the surface layer of the weakly convective nocturnal boundary layer over the center of the city of Marseille, France, during the Expérience sur Sites pour Contraindre les Modèles de Pollution Atmosphérique et de Transport d’Emission (ESCOMPTE) field experiment in the summer of 2001. The data reveal intermittent events or bursts in the time series of carbon dioxide (CO2) concentration and air temperature that are superimposed upon the background values. These features relate to intermittent structures in the fluxes of CO2 and sensible heat. In Marseille, CO2 is primarily emitted into the atmosphere at street level from vehicle exhausts. In a similar way, nocturnal sensible heat fluxes are most likely to originate in the deep street canyons that are warmer than adjacent roof surfaces. Wavelet analysis is used to examine the hypothesis that CO2 concentrations can be used as a tracer to identify characteristics of the venting of pollutants and heat from street canyons into the above-roof nocturnal urban boundary layer. Wavelet analysis is shown to be effective in the identification and analysis of significant events and coherent structures within the turbulent time series. Late in the evening, there is a strong correlation between the burst structures observed in the air temperature and CO2 time series. Evidence suggests that the localized increases of temperature and CO2 observed above roof level in the urban boundary layer (UBL) are related to intermittent venting of sensible heat from the warmer urban canopy layer (UCL). However, later in the night, local advection of CO2 in the UBL, combined with reduced traffic emissions in the UCL, limit the value of CO2 as a tracer of convective plumes in the UBL.

scholarly journals Meridional and vertical variations of the water vapour isotopic composition in the marine boundary layer over the Atlantic and Southern Ocean

2020 ◽  
Vol 20 (9) ◽  
pp. 5811-5835 ◽  
Author(s):  
Iris Thurnherr ◽  
Anna Kozachek ◽  
Pascal Graf ◽  
Yongbiao Weng ◽  
Dimitri Bolshiyanov ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Time Series ◽  
Wind Speed ◽  
Southern Ocean ◽  
Water Vapour ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Marine Boundary Layer ◽  
Sea Spray ◽  
Moisture Source

Abstract. Stable water isotopologues (SWIs) are useful tracers of moist diabatic processes in the atmospheric water cycle. They provide a framework to analyse moist processes on a range of timescales from large-scale moisture transport to cloud formation, precipitation and small-scale turbulent mixing. Laser spectrometric measurements on research vessels produce high-resolution time series of the variability of the water vapour isotopic composition in the marine boundary layer. In this study, we present a 5-month continuous time series of such ship-based measurements of δ2H and δ18O from the Antarctic Circumnavigation Expedition (ACE) in the Atlantic and the Southern Ocean in the time period from November 2016 to April 2017. We analyse the drivers of meridional SWI variations in the marine boundary layer across diverse climate zones in the Atlantic and Southern Ocean using Lagrangian moisture source diagnostics and relate vertical SWI differences to near-surface wind speed and ocean surface state. The median values of δ18O, δ2H and deuterium excess during ACE decrease continuously from low to high latitudes. These meridional SWI distributions reflect climatic conditions at the measurement and moisture source locations, such as air temperature, specific humidity and relative humidity with respect to sea surface temperature. The SWI variability at a given latitude is highest in the extratropics and polar regions with decreasing values equatorwards. This meridional distribution of SWI variability is explained by the variability in moisture source locations and its associated environmental conditions as well as transport processes. The westward-located moisture sources of water vapour in the extratropics are highly variable in extent and latitude due to the frequent passage of cyclones and thus widen the range of encountered SWI values in the marine boundary layer. Moisture loss during transport further contributes to the high SWI variability in the extratropics. In the subtropics and tropics, persistent anticyclones lead to well-confined narrow easterly moisture source regions, which is reflected in the weak SWI variability in these regions. Thus, the expected range of SWI signals at a given latitude strongly depends on the large-scale circulation. Furthermore, the ACE SWI time series recorded at 8.0 and 13.5 m above the ocean surface provide estimates of vertical SWI gradients in the lowermost marine boundary layer. On average, the vertical gradients with height found during ACE are -0.1‰m-1 for δ18O, -0.5‰m-1 for δ2H and 0.3 ‰ m−1 for deuterium excess. Careful calibration and post-processing of the SWI data and a detailed uncertainty analysis provide a solid basis for the presented gradients. Using sea spray concentrations and sea state conditions, we show that the vertical SWI gradients are particularly large during high wind speed conditions with increased contribution of sea spray evaporation or during low wind speed conditions due to weak vertical turbulent mixing. Although further SWI measurements at a higher vertical resolution are required to validate these findings, the simultaneous SWI measurements at several heights during ACE show the potential of SWIs as tracers for vertical mixing and sea spray evaporation in the lowermost marine boundary layer.

scholarly journals Interactions Between the Nocturnal Low-Level Jets and the Urban Boundary Layer: A Case Study over London

2022 ◽  
Author(s):  
Aristofanis Tsiringakis ◽  
Natalie E. Theeuwes ◽  
Janet F. Barlow ◽  
Gert-Jan Steeneveld
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Urban Areas ◽  
Prediction Models ◽  
Weather Prediction ◽  
Urban Boundary Layer ◽  
Limited Area ◽  
Low Level ◽  
Low Level Jets

AbstractUnderstanding the physical processes that affect the turbulent structure of the nocturnal urban boundary layer (UBL) is essential for improving forecasts of air quality and the air temperature in urban areas. Low-level jets (LLJs) have been shown to affect turbulence in the nocturnal UBL. We investigate the interaction of a mesoscale LLJ with the UBL during a 60-h case study. We use observations from two Doppler lidars and results from two high-resolution numerical-weather-prediction models (Weather Research and Forecasting model, and the Met Office Unified Model for limited-area forecasts for the U.K.) to study differences in the occurrence frequency, height, wind speed, and fall-off of LLJs between an urban (London, U.K.) and a rural (Chilbolton, U.K.) site. The LLJs are elevated ($$\approx $$ ≈ 70 m) over London, due to the deeper UBL, while the wind speed and fall-off are slightly reduced with respect to the rural LLJ. Utilizing two idealized experiments in the WRF model, we find that topography strongly affects LLJ characteristics, but there is still a substantial urban influence. Finally, we find that the increase in wind shear under the LLJ enhances the shear production of turbulent kinetic energy and helps to maintain the vertical mixing in the nocturnal UBL.

scholarly journals Meridional and vertical variations of the water vapour isotopic composition in the marine boundary layer over the Atlantic and Southern Ocean

2019 ◽  
Author(s):  
Iris Thurnherr ◽  
Anna Kozachek ◽  
Pascal Graf ◽  
Yongbiao Weng ◽  
Dimitri Bolshiyanov ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Time Series ◽  
Wind Speed ◽  
Southern Ocean ◽  
Water Vapour ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Marine Boundary Layer ◽  
Sea Spray ◽  
Moisture Source

Abstract. Stable water isotopologues (SWIs) are useful tracers of moist diabatic processes in the atmospheric water cycle. They provide a framework to analyse moist processes on a range of time scales from large-scale moisture transport to cloud formation, precipitation, and small-scale turbulent mixing. Laser spectrometric measurements on research vessels produce high-resolution time series of the variability of the water vapour isotopic composition in the marine boundary layer. In this study, we present a five-month continuous time series of such ship-based measurements of δ2H and δ18O from the Antarctic Circumnavigation Expedition (ACE) in the Atlantic and the Southern Ocean in the time period from November 2016 to April 2017. We analyse the drivers of meridional SWI variations in the marine boundary layer across diverse climate zones in the Atlantic and Southern Ocean using Lagrangian moisture source diagnostics and relate vertical SWI differences to near-surface wind speed and ocean surface state. The median values of δ18O, δ2H and d-excess during ACE decrease continuously from low to high latitudes. These meridional SWI distributions reflect climatic conditions at the measurement and moisture source sites, such as air temperature, specific humidity, and relative humidity with respect to sea surface temperature. The SWI variability at a given latitude is highest in the extratropics and polar regions with decreasing values equatorwards. This meridional distribution of SWI variability is explained by the variability in moisture source locations and its associated environmental conditions as well as transport processes. The westward located moisture sources of water vapour in the extratropics are highly variable in extent and latitude due to the frequent passage of cyclones and thus widen the range of encountered SWI values in the marine boundary layer. Moisture loss during transport further contributes to the high SWI variability in the extratropics. In the subtropics and tropics, persistent anticyclones lead to well-confined narrow easterly moisture source regions, which is reflected in the low SWI variability in these regions. Thus, the expected range of SWI signals at a given latitude strongly depends on the large-scale circulation. Furthermore, the ACE SWI time series recorded at different heights above the ocean surface provide estimates of vertical SWI gradients in the lowermost marine boundary layer. On average, the vertical gradients with height found during ACE are −0.1 ‰ m−1 for δ18O, −0.5 ‰ m−1 for δ2H and 0.3 ‰ m−1 for d-excess. Careful calibration and post-processing of the SWI data and a detailed uncertainty analysis provide a solid basis for the presented gradients. Using sea spray concentrations and sea state conditions, we show that the vertical SWI gradients are particularly large during high wind speed conditions with increased contribution of sea spray evaporation or during low wind speed conditions due to weak vertical turbulent mixing and dominating effects from non-equilibrium fractionation. Although further SWI measurements at a higher vertical resolution are required to validate these findings, the simultaneous SWI measurements at several heights during ACE show the potential of SWIs as tracers for vertical mixing and sea spray evaporation in the lowermost marine boundary layer.

scholarly journals Diurnal Evolution of the Wintertime Boundary Layer in Urban Beijing, China: Insights from Doppler Lidar and a 325-m Meteorological Tower

2020 ◽  
Vol 12 (23) ◽  
pp. 3935
Author(s):  
Yuanjian Yang ◽  
Sihui Fan ◽  
Linlin Wang ◽  
Zhiqiu Gao ◽  
Yuanjie Zhang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Diurnal Cycle ◽  
Wind Condition ◽  
Strong Wind ◽  
Doppler Lidar ◽  
Thermal Forcing ◽  
Meteorological Tower ◽  
Weak Wind ◽  
Pm2.5 Concentration

The diurnal evolution of the atmospheric boundary layer—the lowermost part of the atmosphere where the majority of human activity and meteorological phenomena take place—is described by its depth. Additionally, the boundary layer height (BLH) and the turbulence intensity strongly impact the pollutant diffusion, especially during transition periods. Based on integrated observations from a 325-m meteorological tower and a Doppler Wind lidar in the center of Beijing, the entire diurnal cycle of urban BLH in December 2016 was characterized. Results highlight that the Doppler lidar exhibited it is well suited for monitoring convective BLH while it trudges in monitoring stable BLH, while a 325-m meteorological tower provided an important supplement for Doppler lidar under nocturnal boundary layer and heavily polluted conditions. For the diurnal cycle, under light wind condition, the pattern of urban BLH was largely modulated by thermal forcing of solar radiation and may partly be affected by wind speed. While under strong wind condition, the pattern of urban BLH was largely modulated both by thermal forcing and dynamical forcing. The present work also presented evidence for several new features in the morning and afternoon transitions of the urban boundary layer, showing the duration of the morning transition varied between 1 and 5 h, with the largest value occurring under weak wind with high PM2.5 concentration; while the afternoon transition ranged from 3 to 6 h, which was positively (negatively) correlated to wind speed (PM2.5 concentration). Our work highlights that weak wind speed (weak dynamic motion) and heavy aerosol pollution (weak thermal forcing due to the effect of cooling) can dramatically affect the evolution of the boundary layer.

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