scholarly journals Characteristics of Cμ2 derived from ultrasonic anemometer in an urban boundary layer

2019 ◽  
Vol 28 (1) ◽  
pp. 14-24
Author(s):  
Monim Al-Jiboori ◽  
Sundus Jaber
Keyword(s):  
Refractive Index ◽  
Atmospheric Stability ◽  
Ground Level ◽  
Fast Response ◽  
Turbulent Medium ◽  
Optical Wave ◽  
Index Function ◽  
Function Coefficient ◽  
Stable Conditions ◽  
Ultrasonic Anemometer

Fast-response observations of three components of wind and air temperature have been applied to calculate the refractive index function coefficient (Cμ2 ), which is needed to describe optical wave propagation in a turbulent medium. These were measured by 3D ultrasonic anemometer installed on the roof of the building of Atmospheric Science Department which is 19 m above ground level. Refractive index function coeffi cient was calculated for various periods of three seasons: winter, spring and summer.Diurnal variations of (Cμ2) have been made at the surface layer for these seasons. The results show that high values ofmean (Cμ2) occurred during the day time more than at night, also they occurred more in summer than in winter and spring. The results of (Cμ2) found to change with atmospheric stability, whereas they inversely decrease under unstable conditions, approximately constant at neutral cases, and increase under stable conditions. Values of (Cμ2) on average appears to be lower during the rainy and foggy weather cases compared to those of clear sky.

Evolution of Ground Level Scalar Concentrations Through a Compact Cylinder Array Embedded in the Atmospheric Surface Layer

2002 ◽  
Author(s):  
Heidi E. Miner ◽  
Adam Rasmussen
Keyword(s):  
Surface Layer ◽  
Atmospheric Surface Layer ◽  
Field Experiments ◽  
Initial Conditions ◽  
Atmospheric Stability ◽  
Ground Level ◽  
Stability Conditions ◽  
Plume Dispersion ◽  
Gas Dispersion ◽  
Stable Conditions

Experiments for this study were designed to understand gas dispersion in the presence of surface mounted obstacles. To this end, model field experiments were conducted in a compact barrel array employing a spatial distribution of concentration sensors. Specific aims were to explore the effects of atmospheric stability and plume source initial conditions on the plume dispersion through the barrel array. The present results indicate a relaxation towards Gaussian behavior along the plume centerline. The rate of this Gaussian-like behavior is dependent upon atmospheric stability conditions. Plume dispersion through the array appears to be independent of source initial conditions under neutrally stable conditions.

scholarly journals A 3D study on the amplification of regional haze and particle growth by local emissions

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Wei Du ◽  
Lubna Dada ◽  
Jian Zhao ◽  
Xueshun Chen ◽  
Kaspar R. Daellenbach ◽  
...  
Keyword(s):  
Atmospheric Stability ◽  
Ground Level ◽  
Particle Growth ◽  
Chemical Compositions ◽  
Size Distributions ◽  
Aerosol Composition ◽  
Regional Haze ◽  
Haze Formation ◽  
Beijing China

AbstractThe role of new particle formation (NPF) events and their contribution to haze formation through subsequent growth in polluted megacities is still controversial. To improve the understanding of the sources, meteorological conditions, and chemistry behind air pollution, we performed simultaneous measurements of aerosol composition and particle number size distributions at ground level and at 260 m in central Beijing, China, during a total of 4 months in 2015–2017. Our measurements show a pronounced decoupling of gas-to-particle conversion between the two heights, leading to different haze processes in terms of particle size distributions and chemical compositions. The development of haze was initiated by the growth of freshly formed particles at both heights, whereas the more severe haze at ground level was connected directly to local primary particles and gaseous precursors leading to higher particle growth rates. The particle growth creates a feedback loop, in which a further development of haze increases the atmospheric stability, which in turn strengthens the persisting apparent decoupling between the two heights and increases the severity of haze at ground level. Moreover, we complemented our field observations with model analyses, which suggest that the growth of NPF-originated particles accounted up to ∼60% of the accumulation mode particles in the Beijing–Tianjin–Hebei area during haze conditions. The results suggest that a reduction in anthropogenic gaseous precursors, suppressing particle growth, is a critical step for alleviating haze although the number concentration of freshly formed particles (3–40 nm) via NPF does not reduce after emission controls.

scholarly journals Wind turbine power production and annual energy production depend on atmospheric stability and turbulence

2016 ◽  
Author(s):  
Clara M. St. Martin ◽  
Julie K. Lundquist ◽  
Andrew Clifton ◽  
Gregory S. Poulos ◽  
Scott J. Schreck
Keyword(s):  
Energy Production ◽  
Atmospheric Stability ◽  
Power Production ◽  
Department Of Energy ◽  
Power Performance ◽  
Stability Parameters ◽  
Wind Speeds ◽  
Stable Conditions ◽  
Wind Measurements ◽  
Power Curves

Abstract. Using detailed upwind and nacelle-based measurements from a General Electric [GE] 1.5 sle model with a 77 m rotor diameter, we calculated power curves and annual energy production (AEP) and explored their sensitivity to different atmospheric parameters. This work provides guidelines for the use of stability and turbulence filters in segregating power curves to gain a clearer picture of the power performance of a turbine. The wind measurements upwind of the turbine include anemometers mounted on a 135 m meteorological tower and lidar vertical profiles. We calculated power curves for different regimes based on turbulence parameters such as turbulence intensity (TI) and turbulence kinetic energy (TKE), as well as atmospheric stability parameters such as Bulk Richardson number (RB). AEP was also calculated with and without these atmospheric filters and differences between these calculations are highlighted in this article. The power curves for different TI and TKE regimes revealed that, at the U.S. Department of Energy (DOE) National Wind Technology Center (NWTC) at the National Renewable Energy Laboratory (NREL), increased TI and TKE undermined power production at wind speeds near rated, but increased power production at lower wind speeds. Similarly, power curves for different RB regimes revealed that periods of stable conditions produced more power at wind speeds near rated and periods of unstable conditions produced more power at lower wind speeds. AEP results suggest that calculations done without filtering for these atmospheric regimes may be overestimating the AEP. Because of statistically significant differences between power curves and AEP calculated with these turbulence and stability filters for this turbine at this site, we suggest implementing an additional step in analyzing power performance data to take atmospheric stability and turbulence across the rotor disk into account.

scholarly journals Identifying persistent temperature inversion events in a subalpine basin using radon-222

2019 ◽  
Vol 12 (8) ◽  
pp. 4455-4477 ◽  
Author(s):  
Dafina Kikaj ◽  
Janja Vaupotič ◽  
Scott D. Chambers
Keyword(s):  
Public Health ◽  
Air Quality ◽  
Atmospheric Stability ◽  
Poor Performance ◽  
Temperature Inversion ◽  
Relative Magnitude ◽  
World Health ◽  
Winter Period ◽  
Intermittent Turbulence ◽  
Stable Conditions

Abstract. One year of meteorological and atmospheric radon observations in a topographically complex subalpine basin are used to identify persistent temperature inversion (PTI) events. PTI events play a key role in public health due to the accumulation of urban pollutants that they cause. Two techniques are compared: a new radon-based method (RBM), based on single-height 222Rn measurements from a single centrally located station, and an existing pseudo-vertical temperature gradient method (TGM) based on observations from eight weather stations around the subalpine basin. The RBM identified six PTI events (four in winter, two in autumn), a subset of the 17 events identified by the TGM. The RBM was more consistent in its identification of PTI events for all seasons and more selective of persistent strongly stable conditions. The comparatively poor performance of the TGM was attributed to seasonal inconsistencies in the validity of the method's key assumptions (influenced by mesoscale processes, such as local drainage flows, nocturnal jets, and intermittent turbulence influence) and a lack of snow cover in the basin for the 2016–2017 winter period. Corresponding meteorological quantities for RBM PTI events (constituting 27 % of the autumn–winter cold season) were well characterized. PTI wind speeds in the basin were consistently low over the whole diurnal cycle (typically 0.2–0.6 m s−1). Suitability of the two techniques for air quality assessment was compared using hourly PM10 observations. Peak PM10 concentrations for winter (autumn) PTI events were underestimated by 13 µg m−3 (11 µg m−3) by the TGM compared with the RBM. Only the RBM indicated that nocturnal hourly mean PM10 values in winter PTI events can exceed 100 µg m−3, the upper threshold of low-level short-term PM10 exposure according to World Health Organization guidelines. The efficacy, simplicity, and cost effectiveness of the RBM for identifying PTI events has the potential to make it a powerful tool for urban air quality management in complex terrain regions, for which it adds an additional dimension to contemporary atmospheric stability classification tools. Furthermore, the long-term consistency of the radon source function will enable the RBM to be used in the same way in future studies, enabling the relative magnitude of PTI events to be gauged, which is expected to assist with the assessment of public health risks.

scholarly journals Determination of the Structural Characteristic of the Refractive Index of Optical Waves in the Atmospheric Boundary Layer with Remote Acoustic Sounding Facilities

Atmosphere ◽  
2019 ◽  
Vol 10 (11) ◽  
pp. 711 ◽  
Author(s):  
Odintsov ◽  
Gladkikh ◽  
Kamardin ◽  
Nevzorova
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Refractive Index ◽  
Atmospheric Boundary Layer ◽  
Structural Characteristic ◽  
Structural Characteristics ◽  
Acoustic Sounding ◽  
Optical Waves ◽  
Ultrasonic Anemometer

The structural characteristic of the refractive index of optical waves was calculated from experimental data on the microstructure of the temperature turbulence in the atmospheric boundary layer. The experimental data were obtained with an acoustic meteorological radar (sodar), ultrasonic anemometer–thermometer, and meteorological temperature profilometer. Estimates of the structural characteristics for different conditions in the atmospheric boundary layer are presented and were compared with model profiles.

Laser Absorption Techniques for the Measurementof Atmospheric Water Vapor Concentration

1977 ◽  
Vol 16 (10) ◽  
pp. 1072-1076 ◽  
Author(s):  
E. Brannen ◽  
Z. Kucerovsky
Keyword(s):  
Water Vapor ◽  
Laser Radiation ◽  
Response Time ◽  
Water Vapor Pressure ◽  
Ground Level ◽  
Fast Response ◽  
Vapor Concentration ◽  
Water Vapor Concentration ◽  
Laser Method ◽  
Laser Experiments

Abstract A sensitive laser method with fast response time has been developed which is suitable for measuringatmospheric water vapor concentration. The method utilizes the absorption of 33.02 and 27.972 pm radiationfrom a water vapor laser. Experiments were carried out in a 2 m controlled atmosphere absorption cell atconditions corresponding to ground-level to high-altitude atmospheric pressures. Typically, an absorptionof 1% was produced in a 1 m path length by a water vapor pressure of 1.1 Pa at ground level and 2.2 Paat 5 km using 33.02 pm laser radiation. With 27,972 pm laser radiation the absorption is about a factor 50less and can be used when higher concentrations of water vapor are encountered. The response time of thedetecting apparatus can be less than a second and still achieve these sensitivities. Possibilities of building anairborne instrument for measuring water vapor concentration are discussed.

scholarly journals Momentum and scalar transport within a vegetation canopy following atmospheric stability and seasonal canopy changes: the CHATS experiment

2012 ◽  
Vol 12 (13) ◽  
pp. 5913-5935 ◽  
Author(s):  
S. Dupont ◽  
E. G. Patton
Keyword(s):  
Water Vapor ◽  
Forced Convection ◽  
Atmospheric Stability ◽  
Vapor Transport ◽  
Scalar Transport ◽  
Water Vapor Transport ◽  
Heat Sources ◽  
Thermal Plumes ◽  
Vapor Transfer ◽  
Stable Conditions

Abstract. Momentum and scalar (heat and water vapor) transfer between a walnut canopy and the overlying atmosphere are investigated for two seasonal periods (before and after leaf-out), and for five thermal stability regimes (free and forced convection, near-neutral condition, transition to stable, and stable). Quadrant and octant analyses of momentum and scalar fluxes followed by space-time autocorrelations of observations from the Canopy Horizontal Array Turbulence Study's (CHATS) thirty meter tower help characterize the motions exchanging momentum, heat, and moisture between the canopy layers and aloft. During sufficiently windy conditions, i.e. in forced convection, near-neutral and transition to stable regimes, momentum and scalars are generally transported by sweep and ejection motions associated with the well-known canopy-top "shear-driven" coherent eddy structures. During extreme stability conditions (both unstable and stable), the role of these "shear-driven" structures in transporting scalars decreases, inducing notable dissimilarity between momentum and scalar transport. In unstable conditions, "shear-driven" coherent structures are progressively replaced by "buo-yantly-driven" structures, known as thermal plumes; which appear very efficient at transporting scalars, especially upward thermal plumes above the canopy. Within the canopy, downward thermal plumes become more efficient at transporting scalars than upward thermal plumes if scalar sources are located in the upper canopy. We explain these features by suggesting that: (i) downward plumes within the canopy correspond to large downward plumes coming from above, and (ii) upward plumes within the canopy are local small plumes induced by canopy heat sources where passive scalars are first injected if there sources are at the same location as heat sources. Above the canopy, these small upward thermal plumes aggregate to form larger scale upward thermal plumes. Furthermore, scalar quantities carried by downward plumes are not modified when penetrating the canopy and crossing upper scalar sources. Consequently, scalars appear to be preferentially injected into upward thermal plumes as opposed to in downward thermal plumes. In stable conditions, intermittent downward and upward motions probably related to elevated shear layers are responsible for canopy-top heat and water vapor transport through the initiation of turbulent instabilities, but this transport remains small. During the foliated period, lower-canopy heat and water vapor transport occurs through thermal plumes associated with a subcanopy unstable layer.

scholarly journals The aerodynamic drag of the earth’s surface and the value of von Karman’s constant in the lower atmosphere

1947 ◽  
Vol 188 (1013) ◽  
pp. 208-222 ◽  
Keyword(s):  
Velocity Profile ◽  
Aerodynamic Drag ◽  
Atmospheric Stability ◽  
Lower Atmosphere ◽  
Mixing Length ◽  
Horizontal Plate ◽  
Simultaneous Measurements ◽  
Atmospheric Stratification ◽  
Stable Conditions ◽  
Good Agreement

The drag which the earth’s surface exerts on the wind has been measured directly by observing the deflexion of a horizontal plate, floating in oil and under torsional control, and forming part of the earth’s surface. Simultaneous measurements of the velocity profile above the surface have enabled von Karman’s constant for the lower atmosphere to be deduced. The value obtained under moderately unstable atmospheric stratification is 0.46, which is considered to be in good agreement with Nikuradse’s value of 0.40, obtained from the flow of water through pipes under isothermal conditions. Evidence is also adduced for a considerable variation of von Karman’s constant with atmospheric stability. The observations of drag and velocity profile have also been used to determine the variation of mixing length with height. In unstable conditions the mixing length increases more rapidly than the height, while in stable conditions the increase is likely to be less rapid than the height.

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