scholarly journals A wavelet analysis of low-wind-speed submeso motions in a nocturnal boundary layer

2016 ◽  
Vol 143 (703) ◽  
pp. 661-669 ◽  
Author(s):  
D. Cava ◽  
L. Mortarini ◽  
U. Giostra ◽  
R. Richiardone ◽  
D. Anfossi
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Wavelet Analysis ◽  
Nocturnal Boundary Layer ◽  
Low Wind Speed ◽  
Submeso Motions

scholarly journals Stable Atmospheric Boundary Layers and Diurnal Cycles: Challenges for Weather and Climate Models

2013 ◽  
Vol 94 (11) ◽  
pp. 1691-1706 ◽  
Author(s):  
A. A. M. Holtslag ◽  
G. Svensson ◽  
P. Baas ◽  
S. Basu ◽  
B. Beare ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Atmospheric Boundary Layer ◽  
Climate Models ◽  
Model Performance ◽  
Weather Forecast ◽  
The Arctic ◽  
Diurnal Cycles ◽  
Low Wind Speed ◽  
Weather And Climate

The representation of the atmospheric boundary layer is an important part of weather and climate models and impacts many applications such as air quality and wind energy. Over the years, the performance in modeling 2-m temperature and 10-m wind speed has improved but errors are still significant. This is in particular the case under clear skies and low wind speed conditions at night as well as during winter in stably stratified conditions over land and ice. In this paper, the authors review these issues and provide an overview of the current understanding and model performance. Results from weather forecast and climate models are used to illustrate the state of the art as well as findings and recommendations from three intercomparison studies held within the Global Energy and Water Exchanges (GEWEX) Atmospheric Boundary Layer Study (GABLS). Within GABLS, the focus has been on the examination of the representation of the stable boundary layer and the diurnal cycle over land in clear-sky conditions. For this purpose, single-column versions of weather and climate models have been compared with observations, research models, and large-eddy simulations. The intercomparison cases are based on observations taken in the Arctic, Kansas, and Cabauw in the Netherlands. From these studies, we find that even for the noncloudy boundary layer important parameterization challenges remain.

scholarly journals Connecting Turbulence and Meandering Parameterization to Describe Passive Scalars Dispersion in Low Wind Speed Conditions

2013 ◽  
Vol 2013 ◽  
pp. 1-8
Author(s):  
V. S. Moreira ◽  
G. Degrazia ◽  
A. U. Timm ◽  
D. R. Roberti ◽  
S. Maldaner
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Planetary Boundary Layer ◽  
Mathematical Formulation ◽  
Field Measurements ◽  
Horizontal Wind ◽  
Passive Scalars ◽  
Turbulence Parameterization ◽  
Low Wind Speed ◽  
Mean Time

The following study deals with meandering of the horizontal mean wind. The main motivation for such investigation came from the difficulty in describing contaminant dispersion in meandering conditions. Observational field measurements point out that the autocorrelation function of the horizontal wind components, obtained for the meandering cases, displays an oscillating behavior with the presence of large negative lobes. Such negative lobes are described by an equation containing functions that represent patterns of movement associated to meandering and turbulence. As a consequence, this mathematical formulation connects the turbulence and meandering phenomenon establishing the employment of hybrid parameters in models that describe the meandering dispersion. Therefore, considering this dualistic aspect between meandering and turbulence manifestations, a new set of relations for the turbulence parameterization joined with the meandering of the wind have been developed and are available. This new turbulence parameterization for a stable shear forcing planetary boundary layer, united with a meandering mean time scale is able to describe contaminant meandering enhanced spread in a low wind speed stable planetary boundary layer.

Impact of wind speeds on turbulent transport of carbon dioxide (CO2) fluxes at a tropical location in Ile - Ife, southwest Nigeria

2020 ◽  
Author(s):  
Theodora Bello ◽  
Adewale Ajao ◽  
Oluwagbemiga Jegede
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Land Surface ◽  
Stable Boundary Layer ◽  
Turbulent Transport ◽  
Strong Wind ◽  
Stable Boundary ◽  
Wind Speeds ◽  
Low Wind Speed ◽  
Tropical Area

<p>The study investigates impact of wind speeds on the turbulent transport of CO<sub>2 </sub>fluxes for a land-surface atmosphere interface in a low-wind tropical area between May 28<sup>th</sup> and June 14<sup>th</sup>, 2010; and May 24<sup>th</sup> and June 15<sup>th</sup>, 2015. Eddy covariance technique was used to acquire turbulent mass fluxes of CO<sub>2</sub> and wind speed at the study site located inside the main campus of Obafemi Awolowo University, Ile – Ife, Nigeria. The results showed high levels of CO<sub>2 </sub>fluxes at nighttime attributed to stable boundary layer conditions and low wind speed. Large transport and distribution of CO<sub>2 </sub>fluxes were observed in the early mornings due to strong wind speeds recorded at the study location. In addition, negative CO<sub>2 </sub>fluxes were observed during the daytime attributed to prominent convective and photosynthetic activities. The study concludes there was an inverse relationship between turbulent transport of CO<sub>2 </sub>fluxes and wind speed for daytime period while nighttime CO<sub>2</sub> fluxes showed no significant correlation.</p><p><strong>Keywords</strong>: CO<sub>2 </sub>fluxes, Wind speed, Turbulent transport, Low-wind tropical area, Stable boundary layer</p>

scholarly journals The Minimum Wind Speed for Sustainable Turbulence in the Nocturnal Boundary Layer

2012 ◽  
Vol 69 (11) ◽  
pp. 3116-3127 ◽  
Author(s):  
B. J. H. Van de Wiel ◽  
A. F. Moene ◽  
H. J. J. Jonker ◽  
P. Baas ◽  
S. Basu ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Heat Transport ◽  
Radiative Forcing ◽  
Geostrophic Wind ◽  
Nocturnal Boundary Layer ◽  
Feedback Mechanism ◽  
Turbulent Heat ◽  
Radiative Loss ◽  
Surface Cooling

Abstract The collapse of turbulence in the nocturnal boundary layer is studied by means of a simple bulk model that describes the basic physical interactions in the surface energy balance. It is shown that for a given mechanical forcing, the amount of turbulent heat that can be transported downward is limited to a certain maximum. In the case of weak winds and clear skies, this maximum can be significantly smaller than the net radiative loss minus soil heat transport. In the case when the surface has low heat capacity, this imbalance generates rapid surface cooling that further suppresses the turbulent heat transport, so that eventually turbulence largely ceases (positive feedback mechanism). The model predicts the minimum wind speed for sustainable turbulence for the so-called crossing level. At this level, some decameters above the surface, the wind is relatively stationary compared to lower and higher levels. The critical speed is predicted in the range of about 5–7 m s−1, depending on radiative forcing and surface properties, and is in agreement with observations at Cabauw. The critical value appears not very sensitive to model details or to the exact values of the input parameters. Finally, results are interpreted in terms of external forcings, such as geostrophic wind. As it is generally larger than the speed at crossing height, a 5 m s−1 geostrophic wind may be considered as the typical limit below which sustainable, continuous turbulence under clear-sky conditions is unlikely to exist. Below this threshold emergence of the very stable nocturnal boundary layer is anticipated.

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.

Two mechanisms for accelerated diffusion of COVID-19 outbreaks in regions with high intensity of population and polluting industrialization: the air pollution-to-human and human-to-human transmission dynamics (Preprint)

2020 ◽  
Author(s):  
Mario Coccia
Keyword(s):  
Air Pollution ◽  
Wind Speed ◽  
Critical Role ◽  
Meteorological Condition ◽  
Meteorological Conditions ◽  
Lessons Learned ◽  
Transmission Dynamics ◽  
Critical Threshold ◽  
Viral Infectivity ◽  
Low Wind Speed

BACKGROUND Coronavirus disease 2019 (COVID-19) is viral infection that generates a severe acute respiratory syndrome with serious pneumonia that may result in progressive respiratory failure and death. OBJECTIVE This study has two goals. The first is to explain the main factors determining the diffusion of COVID-19 that is generating a high level of deaths. The second is to suggest a strategy to cope with future epidemic threats with of accelerated viral infectivity in society. METHODS Correlation and regression analyses on on data of N=55 Italian province capitals, and data of infected individuals at as of April 2020. RESULTS The main results are: o The accelerate and vast diffusion of COVID-19 in North Italy has a high association with air pollution. o Hinterland cities have average days of exceeding the limits set for PM10 (particulate matter 10 micrometers or less in diameter) equal to 80 days, and an average number of infected more than 2,000 individuals as of April 1st, 2020, coastal cities have days of exceeding the limits set for PM10 equal to 60 days and have about 700 infected in average. o Cities that average number of 125 days exceeding the limits set for PM10, last year, they have an average number of infected individual higher than 3,200 units, whereas cities having less than 100 days (average number of 48 days) exceeding the limits set for PM10, they have an average number of about 900 infected individuals. o The results reveal that accelerated transmission dynamics of COVID-19 in specific environments is due to two mechanisms given by: air pollution-to-human transmission and human-to-human transmission; in particular, the mechanisms of air pollution-to-human transmission play a critical role rather than human-to-human transmission. o The finding here suggests that to minimize future epidemic similar to COVID-19, the max number of days per year in which cities can exceed the limits set for PM10 or for ozone, considering their meteorological condition, is less than 50 days. After this critical threshold, the analytical output here suggests that environmental inconsistencies because of the combination between air pollution and meteorological conditions (with high moisture%, low wind speed and fog) trigger a take-off of viral infectivity (accelerated epidemic diffusion) with damages for health of population, economy and society. CONCLUSIONS Considering the complex interaction between air pollution, meteorological conditions and biological characteristics of viral infectivity, lessons learned for COVID-19 have to be applied for a proactive socioeconomic strategy to cope with future epidemics, especially an environmental policy based on reduction of air pollution mainly in hinterland zones of countries, having low wind speed, high percentage of moisture and fog that create an environment that can damage immune system of people and foster a fast transmission of viral infectivity similar to the COVID-19. CLINICALTRIAL not applicable

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