scholarly journals The Influence of Swell on the Atmospheric Boundary Layer under Nonneutral Conditions

2018 ◽  
Vol 48 (4) ◽  
pp. 925-936 ◽  
Author(s):  
Zhongshui Zou ◽  
Dongliang Zhao ◽  
Jun A. Zhang ◽  
Shuiqing Li ◽  
Yinhe Cheng ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Similarity Theory ◽  
Complex Problem ◽  
Wind Speeds ◽  
Stable Conditions ◽  
Turbulent Closure ◽  
Low Wind Speeds ◽  
Wind Profiles ◽  
Neutral Conditions ◽  
Wave Boundary

AbstractThe anomalous phenomena induced by the prevailing swell at low wind speeds prevent a complete understanding of air–sea interaction processes. Many studies have considered this complex problem, but most have focused on near-neutral conditions. In this study, the influence of the swell on the atmospheric boundary under nonneutral conditions was addressed by extending the turbulent closure models of Makin and Kudryavtsev and the Monin–Obukhov similarity theory (MOST; Monin and Yaglom) to the existence of swell and nonneutral conditions. It was shown that wind profiles derived from these models were consistent with each other and both departed from the traditional MOST. At low wind speeds, a supergeostrophic jet appeared on the upper edge of the wave boundary layer, which was also reported in earlier studies. Under nonneutral conditions, the influence of buoyancy was significant. The slope of the wind profile increased under stable conditions and became smoother under unstable conditions. Considering the effects of buoyancy and swell, the wind stress derived from the model agreed quantitatively with the observations.

Evaluation of Boundary Layer Similarity Theory for Stable Conditions in CASES-99

2007 ◽  
Vol 135 (10) ◽  
pp. 3474-3483 ◽  
Author(s):  
Kyung-Ja Ha ◽  
Yu-Kyung Hyun ◽  
Hyun-Mi Oh ◽  
Kyung-Eak Kim ◽  
Larry Mahrt
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Similarity Theory ◽  
Unknown Origin ◽  
Strong Stability ◽  
Surface Exchange ◽  
Stability Functions ◽  
Stable Conditions ◽  
Mean Wind Speed ◽  
Strong Winds

Abstract The Monin–Obukhov similarity theory and a generalized formulation of the mixing length for the stable boundary layer are evaluated using the Cooperative Atmosphere–Surface Exchange Study-1999 (CASES-99) data. The large-scale wind forcing is classified into weak, intermediate, and strong winds. Although the stability parameter, z/L, is inversely dependent on the mean wind speed, the speed of the large-scale flow includes independent influences on the flux–gradient relationship. The dimensionless mean wind shear is found to obey existing stability functions when z/L is less than unity, particularly for the strong and intermediate wind classes. For weak mean winds and/or strong stability (z/L > 1), this similarity theory breaks down. Deviations from similarity theory are examined in terms of intermittency. A case study of a weak-wind night indicates important modulation of the turbulence flux by mesoscale motions of unknown origin.

scholarly journals Finescale Clusterization Intermittency of Turbulence in the Atmospheric Boundary Layer

2020 ◽  
Vol 77 (7) ◽  
pp. 2375-2392
Author(s):  
Lei Liu ◽  
Fei Hu
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Return Time ◽  
Statistical Simulation ◽  
Convective Boundary ◽  
Wind Speeds ◽  
Stable Conditions ◽  
Telegraphic Approximation ◽  
Better Than

AbstractThe intermittency of atmospheric turbulence plays an important role in the understanding of particle dispersal in the atmospheric boundary layer and in the statistical simulation of high-frequency wind speed in various applications. There are two kinds of intermittency, namely, the magnitude intermittency (MI) related to non-Gaussianity and the less studied clusterization intermittency (CI) related to long-term correlation. In this paper, we use a 20 Hz ultrasonic dataset lasting for 1 month to study CI of turbulent velocity fluctuations at different scales. Basing on the analysis of return-time distribution of telegraphic approximation series, we propose to use the shape parameter of the Weibull distribution to measure CI. Observations of this parameter show that contrary to MI, CI tends to weaken as the scale increases. Besides, significant diurnal variations, showing that CI tends to strengthen during the daytime (under unstable conditions) and weaken during the nighttime (under stable conditions), are found at different observation heights. In the convective boundary layer, the mixed-layer similarity is found to scale the CI exponent better than the Monin–Obukhov similarity. At night, CI is found to vary less with height in the regime with large mean wind speeds than in the regime with small mean wind speeds, according to the hockey-stick theory.

scholarly journals Winds near the Surface of Waves: Observations and Modeling

2018 ◽  
Vol 48 (5) ◽  
pp. 1079-1088 ◽  
Author(s):  
Alexander V. Babanin ◽  
Jason McConochie ◽  
Dmitry Chalikov
Keyword(s):  
Boundary Layer ◽  
Wind Wave ◽  
Wave Boundary Layer ◽  
Wind Speeds ◽  
Vertical Profiling ◽  
The Mean ◽  
Flux Layer ◽  
Logarithmic Layer ◽  
Wave Boundary ◽  
Lake George

AbstractThe concept of a constant-flux layer is usually employed for vertical profiling of the wind measured at some elevation near the ocean surface. The surface waves, however, modify the balance of turbulent stresses very near the surface, and therefore such extrapolations can introduce significant biases. This is particularly true for buoy measurements in extreme conditions, when the anemometer mast is within the wave boundary layer (WBL) or even below the wave crests. In this paper, field data and a WBL model are used to investigate such biases. It is shown that near the surface the turbulent stresses are less than those obtained by extrapolation using the logarithmic-layer assumption, and the mean wind speeds very near the surface, based on Lake George field observations, are up to 5% larger. The behavior is then simulated by means of a WBL model coupled with nonlinear waves, which confirmed the observations and revealed further details of complex behaviors at the wind-wave boundary layer.

Impact of Surface Waves on Wind Stress under Low to Moderate Wind Conditions

2020 ◽  
Author(s):  
Sheng Chen ◽  
Fangli Qiao ◽  
Wenzheng Jiang ◽  
Jingsong Guo ◽  
Dejun Dai
Keyword(s):  
Surface Waves ◽  
Wind Stress ◽  
Climate Models ◽  
Similarity Theory ◽  
Ocean Surface Waves ◽  
China Sea ◽  
Wind Speeds ◽  
Mean Sea Surface ◽  
Wind Profiles ◽  
The Impact

<p>The impact of ocean surface waves on wind stress at the air–sea interface under low to moderate wind<br>conditions was systematically investigated based on a simple constant flux model and flux measurements<br>obtained from two coastal towers in the East China Sea and South China Sea. It is first revealed that the<br>swell-induced perturbations can reach a height of nearly 30m above the mean sea surface, and these perturbations<br>disturb the overlying airflow under low wind and strong swell conditions. The wind profiles severely<br>depart from the classical logarithmic profiles, and the deviations increase with the peak wave phase speeds. At<br>wind speeds of less than 4 m/s, an upward momentumtransfer from the wave to the atmosphere is predicted,<br>which is consistent with previous studies. A comparison between the observations and model indicates that<br>the wind stress calculated by the model is largely consistent with the observational wind stress when considering<br>the effects of surface waves, which provides a solution for accurately calculating wind stress in ocean<br>and climate models. Furthermore, the surface waves at the air–sea interface invalidate the traditional<br>Monin–Obukhov similarity theory (MOST), and this invalidity decreases as observational height increases.</p>

scholarly journals Turbulent Velocity-Variance Profiles in the Stable Boundary Layer Generated by a Nocturnal Low-Level Jet

2006 ◽  
Vol 63 (11) ◽  
pp. 2700-2719 ◽  
Author(s):  
Robert M. Banta ◽  
Yelena L. Pichugina ◽  
W. Alan Brewer
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Strong Wind ◽  
Surface Exchange ◽  
Stable Boundary ◽  
Low Level ◽  
Stable Conditions ◽  
Velocity Scale ◽  
Low Level Jet ◽  
Wind Profiles

Abstract Profiles of mean winds and turbulence were measured by the High Resolution Doppler lidar in the strong-wind stable boundary layer (SBL) with continuous turbulence. The turbulence quantity measured was the variance of the streamwise wind velocity component σ2u. This variance is a component of the turbulence kinetic energy (TKE), and it is shown to be numerically approximately equal to TKE for stable conditions—profiles of σ2u are therefore equivalent to profiles of TKE. Mean-wind profiles showed low-level jet (LLJ) structure for most of the profiles, which represented 10-min averages of mean and fluctuating quantities throughout each of the six nights studied. Heights were normalized by the height of the first LLJ maximum above the surface ZX, and the velocity scale used was the speed of the jet UX, which is shown to be superior to the friction velocity u* as a velocity scale. The major results were 1) the ratio of the maximum value of the streamwise standard deviation to the LLJ speed σu/UX was found to be 0.05, and 2) the three most common σ2u profile shapes were determined by stability (or Richardson number Ri). The least stable profile shapes had the maximum σ2u at the surface decreasing to a minimum at the height of the LLJ; profiles that were somewhat more stable had constant σ2u through a portion of the subjet layer; and the most stable of the profiles had a maximum of σ2u aloft, although it is important to note that the Ri for even the most stable of the three profile categories averaged less than 0.20. The datasets used in this study were two nights from the Cooperative Atmosphere–Surface Exchange Study 1999 campaign (CASES-99) and four nights from the Lamar Low-Level Jet Project, a wind-energy experiment in southeast Colorado, during September 2003.

scholarly journals Measurement of wind profiles by motion-stabilised ship-borne Doppler lidar

2015 ◽  
Vol 8 (9) ◽  
pp. 9339-9372 ◽  
Author(s):  
P. Achtert ◽  
I. M. Brooks ◽  
B. J. Brooks ◽  
B. I. Moat ◽  
J. Prytherch ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Open Water ◽  
The Arctic ◽  
Doppler Lidar ◽  
Arctic Boundary Layer ◽  
Wind Speeds ◽  
Custom Made ◽  
Wind Measurements ◽  
Wind Profiles

Abstract. Three months of Doppler lidar wind measurements were obtained during the Arctic Cloud Summer Experiment on the icebreaker Oden during the summer of 2014. Such ship-borne measurements require active stabilisation to remove the effects of ship motion. We demonstrate that the combination of a commercial Doppler lidar with a custom-made motion-stabilisation platform enables the retrieval of wind profiles in the Arctic boundary layer during both cruising and ice-breaking with statistical uncertainties comparable to land-based measurements. This holds particularly within the planetary boundary layer even though the overall aerosol load was very low. Motion stabilisation was successful for high wind speeds in open water and the resulting wave conditions. It allows for the retrieval of winds with a random error below 0.2 m s−1, comparable to the measurement error of standard radiosondes. The combination of a motion-stabilised platform with a low-maintenance autonomous Doppler lidar has the potential to enable continuous long-term high-resolution ship-based wind profile measurements over the oceans.

scholarly journals Analysis of Turbulence Profiles from Three Tall Towers: Departure from Similarity Theory in Near-Neutral and Stable Conditions

2008 ◽  
Vol 2 (1) ◽  
pp. 106-116 ◽  
Author(s):  
Brent M. Bowen
Keyword(s):  
Similarity Theory ◽  
National Laboratory ◽  
Los Alamos National Laboratory ◽  
Rocky Flats ◽  
Vertical Diffusivity ◽  
Stable Conditions ◽  
Multi Level ◽  
Neutral Conditions ◽  
Good Agreement

Long-term wind and turbulence profiles were analyzed for all stability conditions at three tall, multi-level towers located at the Los Alamos National Laboratory (LANL), Rocky Flats Environmental Plant (RF), and the Boulder Atmospheric Observatory (BAO). The LANL and RF sites are located in complex terrain and the BAO is located over relatively simple terrain, but within 3 to 5 km of an abrupt 20 to 30 m increase in terrain. Results indicate that normalized turbulence parameter profiles at all three sites agree well with widely used empirical relationships during unstable conditions. During near neutral conditions, σu parameter profiles are also well behaved at all three sites while σw increases with height for complex fetch (BAO downwind of bluff, LANL, and RF) while σw remains nearly constant up to 200 m AGL at BAO with simple fetch. The σw /u* values at 10-m AGL are close to one at all sites and they increase by an order of 50% in the lowest 60 to 200 m for complex fetch and remain approximately constant in the lowest 200 m with simple fetch. During very stable conditions, typical values of σu and σ v range between 0.4 to 0.6 ms-1 and increase slightly with height while median σw values nearly double from about 0.1 to 0.2 ms-1 between the 10- and 100 to 200-m levels. A comparison of predicted with measured u* values at two of the sites shows generally good agreement over 6 stability categories. It is suggested that M-O similarity theory will usually greatly underestimate vertical diffusivity and dispersion during very stable conditions, especially at larger heights, based on idealized Kz profiles calculated from measured σw values. Finally, rules of thumb are formulated to describe departure from similarity theory during near-neutral and stable conditions.

Wind-turning over the atmospheric boundary layer in observations and models

2020 ◽  
Author(s):  
Gunilla Svensson ◽  
Jenny Lindvall ◽  
Joakim Pyykkö
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Climate Models ◽  
Similarity Theory ◽  
Rossby Number ◽  
Surface Drag ◽  
Turning Angle ◽  
Wind Speeds ◽  
The Vertical Distribution ◽  
Clear Increase

<p>As an attempt to find a way of evaluating the surface drag in global models, we have derived a climatology of the boundary-layer wind-turning angle over land (Lindvall and Svensson, 2019). It is based on radiosonde observations from 800 stations in the Integrated Global Radiosonde Archive (IGRA). The climatology and how the wind turning depend on a suite of parameters is analyzed. Results from previous studies indicating the importance of the planetary boundary layer (PBL) stratification for the angle of wind turning are confirmed. A clear increase in the wind-turning angle with wind speed, particularly for stratified conditions, is also evident. According to Rossby number similarity theory, the crossisobaric angle for a neutral and barotropic boundary layer decreases with the surface Rossby number, Ro. The IGRA observations indicate that this dependence on Ro might partly be linked to the dependence of the stratification on the wind speed, a dependence that seems to prevail even for the high wind speeds, a criterium that traditionally is used to approximate a neutral PBL. The vertical distribution of the turning of the wind is analyzed using the high resolution Stratospheric Processes And their Role in Climate (SPARC) data. For unstable cases, there is a maximum in the directional wind shear around the PBL top, whereas for the most stable class of cases there is a maximum near the surface. The midlatitude cross-isobaric mass transport is estimated using the IGRA data. The wind-turning angles from reanalysis fields and climate models are also presented, they generally underestimate the turning angle.</p>

Speed and Direction Shear in the Stable Nocturnal Boundary Layer

2009 ◽  
Vol 131 (1) ◽  
Author(s):  
Kevin Walter ◽  
Christopher C. Weiss ◽  
Andrew H. P. Swift ◽  
Jamie Chapman ◽  
Neil D. Kelley
Keyword(s):  
Boundary Layer ◽  
Atmospheric Stability ◽  
Turbine Rotor ◽  
Vertical Shear ◽  
Inertial Oscillation ◽  
Power Performance ◽  
Simulation Code ◽  
Meteorological Forcing ◽  
Wind Speeds ◽  
Stable Conditions

Numerous previous works have shown that vertical shear in wind speed and wind direction exist in the atmospheric boundary layer. In this work, meteorological forcing mechanisms, such as the Ekman spiral, thermal wind, and inertial oscillation, are discussed as likely drivers of such shears in the statically stable environment. Since the inertial oscillation, the Ekman spiral, and statically stable conditions are independent of geography, potentially significant magnitudes of speed and direction shear are hypothesized to occur to some extent at any inland site in the world. The frequency of occurrence of non-trivial magnitudes of speed and direction shear are analyzed from observation platforms in Lubbock, Texas and Goodland, Indiana. On average, the correlation between speed and direction shear magnitudes and static atmospheric stability are found to be very high. Moreover, large magnitude speed and direction shears are observed in conditions with relatively high hub-height wind speeds. The effects of speed and direction shear on wind turbine power performance are tested by incorporating a simple steady direction shear profile into the fatigue analysis structures and turbulence simulation code from the National Renewable Energy Laboratory. In general, the effect on turbine power production varies with the magnitude of speed and direction shear across the turbine rotor, with the majority of simulated conditions exhibiting power loss relative to a zero shear baseline. When coupled with observational data, the observed power gain is calculated to be as great as 0.5% and depletion as great as 3% relative to a no shear baseline. The average annual power change at Lubbock is estimated to be −0.5%.

Vertical Variations of Mixing Lengths under Neutral and Stable Conditions during CASES-99

2011 ◽  
Vol 50 (10) ◽  
pp. 2030-2041 ◽  
Author(s):  
Jielun Sun
Keyword(s):  
Similarity Theory ◽  
Mixing Length ◽  
Vertical Layer ◽  
Surface Exchange ◽  
Exchange Study ◽  
Von Karman ◽  
Stable Conditions ◽  
Vertical Variations ◽  
Von Kármán ◽  
Neutral Conditions

AbstractAn investigation on vertical variations of the mixing lengths for momentum and heat under neutral and stable conditions was conducted using the data collected from the Cooperative Atmosphere–Surface Exchange Study in 1999 (CASES-99). By comparing κz with the mixing lengths under neutral conditions calculated using the observations from CASES-99, the vertical layer where the Monin–Obukhov similarity theory (MOST) is valid was identified. Here κ is the von Kármán constant and z is the height above the ground. On average, MOST is approximately valid between 0.5 and 10 m. Above the layer, the observed mixing lengths under neutral conditions are smaller than the MOST κz and can be approximately described by Blackadar’s mixing length, κz/[1 + (κz/l∞)], with l∞ = 15 m for up to z ~ 20 m for the mixing length for momentum and up to the highest observation height for the mixing length for heat. Above ~20 m, the mixing length for momentum approaches a constant. Both MOST κz and Blackadar’s formula systematically overestimate the mixing length for momentum above ~20 m, leading to overestimates of turbulence.

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