Cooperative Atmosphere Surface Exchange Study Research Articles

External controls on the transition between stable boundary‐layer turbulence regimes

AbstractThe mean wind speed at which the stable boundary layer (SBL) experiences a turbulence regime transition (Vr) depends on other flow characteristics, such as its thermal stability. Here, Vr variability is examined both at a single site and across sites using three multiple‐level datasets: Santa Maria, Cooperative Atmosphere–Surface Exchange Study–1999 (CASES‐99), and Fluxes over Snow Surfaces (FLOSS II). A method to determine Vr is introduced and validated. It is taken as the mean wind speed at which the vertical gradient of the turbulence velocity scale switches sign. Emphasis is given to the control exerted on Vr by quantities that are external to the SBL, such as radiation, roughness, and soil properties. In each of the experiments, Vr increases with net radiative loss at the surface (Rn) at a rate that is site‐dependent. It also increases for smaller roughness lengths, as indicated by its wind direction dependence. No conclusive relationship has been found between Vr and downward longwave radiation observed at the surface. The across‐site comparison indicates that soil heat capacity influences the rate at which Vr increases with Rn.

The Role of Radiation in Heating the Clear-Air Convective Boundary Layer: Revisiting CASES-97

Using data for 3 days in the Cooperative Atmosphere-Surface Exchange Study 1997 field experiment that are analyzed in LeMone et al. (Boundary-Layer Meteorol 104:1–52, 2002, hereafter L2002), it is shown that direct radiative heating can have a significant role in warming the nearly cloudless fair-weather convective boundary layer (CBL). Radiative heating becomes especially important in the presence of aerosols in the CBL, with a moist layer above the CBL also contributing. Not only does inclusion of radiative heating help “close” their potential-temperature budgets, but it affects entrainment estimates. Combined, radiative heating rates are of the order of 0.2 K h−1, based on calculations using the Rapid-Radiative Transfer Model for general circulation models (RRTMG) code in a single-column version of the Advanced Research Weather Research and Forecasting model and estimates of aerosol heating published in L2002. Our current estimates of clear-air direct radiative heating differ from the estimates in L2002 because the surface skin temperature was not included in the earlier calculations. Upwelling and downwelling longwave radiation computed using the RRTMG code agrees with aircraft measurements within 10–15 W m−2.

Scaling Behavior of a Turbulent Kinetic Energy Closure Scheme for the Stably Stratified Atmosphere: A Steady-State Analysis

Abstract We present a turbulent kinetic energy (TKE) closure scheme for the stably stratified atmosphere in which the mixing lengths for momentum and heat are not parameterized in the same manner. The key difference is that, while the mixing length for heat tends toward the stability independent mixing length for momentum in neutrally stratified conditions, it tends toward one based on the Brunt–Väisälä time scale and square root of the TKE in the limit of large stability. This enables a unique steady-state solution for TKE to be obtained, which we demonstrate would otherwise be impossible if the mixing lengths were the same. Despite the model’s relative simplicity, it is shown to perform reasonably well with observational data from the 1999 Cooperative Atmosphere–Surface Exchange Study (CASES-99) using commonly employed model constants. Analyzing the scaling behavior of the nondimensional velocity and potential temperature gradients, or of the stability (correction) functions, reveals that for large stability the present model scales in the same manner as the first-order operational scheme of Viterbo et al. Alternatively, it appears as a blend of two cases of the TKE closure scheme of Baas et al. Critically, because a unique steady-state TKE can be obtained, the present model avoids the nonphysical behavior identified in one of the cases of Baas et al.

Non-Gaussian Lagrangian Stochastic Model for Wind Field Simulation in the Surface Layer

Wind field simulation in the surface layer is often used to manage natural resources in terms of air quality, gene flow (through pollen drift), and plant disease transmission (spore dispersion). Although Lagrangian stochastic (LS) models describe stochastic wind behaviors, such models assume that wind velocities follow Gaussian distributions. However, measured surface-layer wind velocities show a strong skewness and kurtosis. This paper presents an improved model, a non-Gaussian LS model, which incorporates controllable non-Gaussian random variables to simulate the targeted non-Gaussian velocity distribution with more accurate skewness and kurtosis. Wind velocity statistics generated by the non-Gaussian model are evaluated by using the field data from the Cooperative Atmospheric Surface Exchange Study, October 1999 experimental dataset and comparing the data with statistics from the original Gaussian model. Results show that the non-Gaussian model improves the wind trajectory simulation by stably producing precise skewness and kurtosis in simulated wind velocities without sacrificing other features of the traditional Gaussian LS model, such as the accuracy in the mean and variance of simulated velocities. This improvement also leads to better accuracy in friction velocity (i.e., a coupling of three-dimensional velocities). The model can also accommodate various non-Gaussian wind fields and a wide range of skewness–kurtosis combinations. Moreover, improved skewness and kurtosis in the simulated velocity will result in a significantly different dispersion for wind/particle simulations. Thus, the non-Gaussian model is worth applying to wind field simulation in the surface layer.

Nocturnal boundary layer turbulence regimes analysis during the BLLAST campaign

Abstract. A night-time turbulence regime classification, the so-called “HOckey-Stick Transition ” (HOST) theory, proposed by Sun et al. (2012) from the Cooperative Atmosphere–Surface Exchange Study-1999 (CASES-99) is explored using data from the Boundary-Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign which took place during summer 2011 in the central French Pyrenean foothills. Results show that the HOST turbulence relationships for the BLLAST field campaign data are strongly dependent on both the meteorological and orographic features. The HOST pattern only appears for nights when a stably stratified boundary layer can be developed, corresponding to fair-weather and clear-sky nights, when the flow is generated by the nearby orography, from the south and the south-east. Those flows strongly influenced by the orography may generate intermittent or enhanced turbulence. When considering the whole nocturnal dataset for these flow directions, several enhanced turbulence points are found to be associated with sudden wind speed and directional shear transitions. In contrast, flows from other directions do not reproduce the HOST relationships and the turbulence relationship is almost linear, independent of vertical temperature gradients, corresponding to flows driven by synoptic scales. In addition we identify examples of gravity waves and top-down turbulent events that lead to transitions between the turbulence regimes.

Wind farm density and harvested power in very large wind farms: A low-order model

In this work we create new understanding of wind turbine wakes recovery process as a function of wind farm density using large-eddy simulations of an atmospheric boundary layer diurnal cycle. Simulations are forced with a constant geostrophic wind and a time varying surface temperature extracted from a selected period of the Cooperative Atmospheric Surface Exchange Study field experiment. Wind turbines are represented using the actuator disk model with rotation and yaw alignment. A control volume analysis around each turbine has been used to evaluate wind turbine wake recovery and corresponding harvested power. Results confirm the existence of two dominant recovery mechanisms, advection and flux of mean kinetic energy, which are modulated by the background thermal stratification. For the low-density arrangements advection dominates, while for the highly loaded wind farms the mean kinetic energy recovers through fluxes of mean kinetic energy. For those cases in between, a smooth balance of bothmechanisms exists. From the results, a low-order model for the wind farms' harvested power as a function of thermal stratification and wind farm density has been developed, which has the potential to be used as an order-of-magnitude assessment tool.

Characteristics of the Heat Flux in the Unstable Atmospheric Surface Layer

AbstractThe behavior of the heat flux H with respect to the stability parameter (=z/L, where z is the height above the ground, and L is the Obukhov length) in the unstable atmospheric surface layer is analyzed within the framework of Monin–Obukhov similarity (MOS) theory. Using MOS equations, H is expressed as a function of and vertical surface-layer potential temperature gradient . A mathematical analysis is carried out to analyze the theoretical nature of heat flux with the stability parameter by considering the vertical potential temperature gradient as (i) a constant and (ii) a power-law function of heat flux. For a given value of H, two values of associated with different stability regimes are found to occur in both the conditions, suggesting the nonuniqueness of MOS equations.Turbulent data over three different sites—(i) Ranchi, India; (ii) the Met Office’s Cardington, United Kingdom, monitoring facility; and (iii) 1999 Cooperative Atmosphere–Surface Exchange Study (CASES-99; United States—are analyzed to compare the observed nature of H with that predicted by MOS. The analysis of observational data over these three sites reveals that the observed variation of H with is consistent with that obtained theoretically from MOS equations when considering the vertical temperature gradient as a power-law function of heat flux having the exponent larger than 2/3. The existence of two different values of the stability parameter for a given value of heat flux suggests that the application of heat flux as a boundary condition involves some intricacies, and it should be applied with caution in convective conditions.

Air–Sea Interactions in Light of New Understanding of Air–Land Interactions

Abstract Air–sea interactions are investigated using the data from the Coupled Boundary Layers Air–Sea Transfer experiment under low wind (CBLAST-Low) and the Surface Wave Dynamics Experiment (SWADE) over sea and compared with measurements from the 1999 Cooperative Atmosphere–Surface Exchange Study (CASES-99) over land. Based on the concept of the hockey-stick transition (HOST) hypothesis, which emphasizes contributions of large coherent eddies in atmospheric turbulent mixing that are not fully captured by Monin–Obukhov similarity theory, relationships between the atmospheric momentum transfer and the sea surface roughness, and the role of the sea surface temperature (SST) and oceanic waves in the turbulent transfer of atmospheric momentum, heat, and moisture, and variations of drag coefficient Cd(z) over sea and land with wind speed V are studied. In general, the atmospheric turbulence transfers over sea and land are similar except under weak winds and near the sea surface when wave-induced winds and oceanic currents are relevant to wind shear in generating atmospheric turbulence. The transition of the atmospheric momentum transfer between the stable and the near-neutral regimes is different over land and sea owing to the different strength and formation of atmospheric stable stratification. The relationship between the air–sea temperature difference and the turbulent heat transfer over sea is dominated by large air temperature variations compared to the slowly varying SST. Physically, Cd(z) consists of the surface skin drag and the turbulence drag between z and the surface; the increase of the latter with decreasing V leads to the minimum Cd(z), which is observed, but not limited to, over sea.

Exploring Vertical Turbulence Structure in Neutrally and Stably Stratified Flows Using the Weather Research and Forecasting–Large-Eddy Simulation (WRF–LES) Model

Following Sun et al. (J Atmos Sci 69(1):338–351, 2012), vertical variations of turbulent mixing in stably stratified and neutral environments as functions of wind speed are investigated using the large-eddy simulation capability in the Weather Research and Forecasting model. The simulations with a surface cooling rate for the stable boundary layer (SBL) and a range of geostrophic winds for both stable and neutral boundary layers are compared with observations from the Cooperative Atmosphere–Surface Exchange Study 1999 (CASES-99). To avoid the uncertainty of the subgrid scheme, the investigation focuses on the vertical domain when the ratio between the subgrid and the resolved turbulence is small. The results qualitatively capture the observed dependence of turbulence intensity on wind speed under neutral conditions; however, its vertical variation is affected by the damping layer used in absorbing undesirable numerical waves at the top of the domain as a result of relatively large neutral turbulent eddies. The simulated SBL fails to capture the observed temperature variance with wind speed and the observed transition from the SBL to the near-neutral atmosphere with increasing wind speed, although the vertical temperature profile of the simulated SBL resembles the observed profile. The study suggests that molecular thermal conduction responsible for the thermal coupling between the surface and atmosphere cannot be parameterized through the Monin–Obukhov bulk relation for turbulent heat transfer by applying the surface radiation temperature, as is common practice when modelling air–surface interactions.

The Role of Large-Coherent-Eddy Transport in the Atmospheric Surface Layer Based on CASES-99 Observations

The analysis of momentum and heat fluxes from the Cooperative Atmosphere-Surface Exchange Study 1999 (CASES-99) field experiment is extended throughout the diurnal cycle following the investigation of nighttime turbulence by Sun et al. (J Atmos Sci 69:338–351, 2012). Based on the observations, limitations of Monin–Obukhov similarity theory (MOST) are examined in detail. The analysis suggests that strong turbulent mixing is dominated by relatively large coherent eddies that are not related to local vertical gradients as assumed in MOST. The HOckey-Stick Transition (HOST) hypothesis is developed to explain the generation of observed large coherent eddies over a finite depth and the contribution of these eddies to vertical variations of turbulence intensity and atmospheric stratification throughout the diurnal cycle. The HOST hypothesis emphasizes the connection between dominant turbulent eddies and turbulence generation scales, and the coupling between the turbulence kinetic energy and the turbulence potential energy within the turbulence generation layer in determining turbulence intensity. For turbulence generation directly influenced by the surface, the HOST hypothesis recognizes the role of the surface both in the vertical variation of momentum and heat fluxes and its boundary effect on the size of the dominant turbulence eddies.

A Shear-Based Parameterization of Turbulent Mixing in the Stable Atmospheric Boundary Layer

AbstractIn this study, shear-based parameterizations of turbulent mixing in the stable atmospheric boundary layer (SABL) are proposed. A relevant length-scale estimate for the mixing length of the turbulent momentum field is constructed from the turbulent kinetic energy and the mean shear rate S as . Using observational data from two field campaigns—the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment and the 1999 Cooperative Atmosphere–Surface Exchange Study (CASES-99)— is shown to have a strong correlation with . The relationship between and corresponds to the ratio of the magnitude of the tangential components of the turbulent momentum flux tensor to , known as stress intensity ratio, . The field data clearly show that is linked to stability. The stress intensity ratio also depends on the flow energetics that can be assessed using a shear-production Reynolds number, , where P is shear production of turbulent kinetic energy and is the kinematic viscosity. This analysis shows that high mixing rates can indeed persist at strong stability. On this basis, shear-based parameterizations are proposed for the eddy diffusivity for momentum, , and eddy diffusivity for heat, , showing remarkable agreement with the exact quantities. Furthermore, a broader assessment of the proposed parameterizations is given through an a priori evaluation of large-eddy simulation (LES) data from the first GEWEX Atmospheric Boundary Layer Study (GABLS). The shear-based parameterizations outperform many existing models in predicting turbulent mixing in the SABL. The results of this study provide a framework for improved representation of the SABL in operational models.

Objectively Determined Fair-Weather NBL Features in ARW-WRF and Their Comparison to CASES-97 Observations

AbstractHeights of nocturnal boundary layer (NBL) features are determined using vertical profiles from the Advanced Research Weather Research and Forecasting Model (ARW-WRF), and then compared to data for three moderately windy fair-weather nights during the April–May 1997 Kansas-based Cooperative Atmosphere–Surface Exchange Study (CASES-97) to evaluate the success of four PBL schemes in replicating observations. The schemes are Bougeault–LaCarrere (BouLac), Mellor–Yamada–Janjić (MYJ), quasi-normal scale elimination (QNSE), and Yonsei University (YSU) versions 3.2 and 3.4.1. This study’s chosen objectively determined model NBL height h estimate uses a turbulence kinetic energy (TKE) threshold equal to 5% , where TKE′ is relative to its background (free atmosphere) value. The YSU- and MYJ-determined h could not be improved upon. Observed heights of the virtual temperature maximum hTvmax and wind speed maximum hSmax, and the heights h1wsonde and h2wsonde, between which the radiosonde slows from ~5 to ~3 m s−1 as it rises from turbulent to nonturbulent air, and thus brackets h, were used for comparison to model results. The observations revealed a general pattern: hTvmax increased through the night, and hTvmax and hSmax converged with time, and the two mostly lay between h1wsonde and h2wsonde after several hours. Clear failure to adhere to this pattern and large excursions from observations or other PBL schemes revealed excess mixing for BouLac and YSU version 3.2 (but not version 3.4.1) and excess thermal mixing for QNSE under windy conditions. Observed friction velocity was much smaller than model values, with differences consistent with the observations reflecting local skin drag and the model reflecting regional form drag + skin drag.

Nested Large-Eddy Simulations of the Intermittently Turbulent Stable Atmospheric Boundary Layer over Real Terrain

AbstractThe nighttime stable atmospheric boundary layer over real terrain is modeled with nested high-resolution large-eddy simulations (LESs). The field site is located near Leon, Kansas, where the 1999 Cooperative Atmosphere–Surface Exchange Study took place. The terrain is mostly flat with an average slope of 0.5°. The main topographic feature is a shallow valley oriented in the east–west direction. The night of 5 October is selected to study intermittent turbulence under prevailing quiescent conditions. Brief turbulent periods triggered by shear-instability waves are modeled with good magnitude and temporal precision with a dynamic reconstruction turbulence closure. In comparison, conventional closures fail to excite turbulent motions and predict a false laminar flow. A plausible new intermittency mechanism, previously unknown owing to limited spatial coverage of field instruments at this site, is unveiled with the LESs. Turbulence can be generated through gravity wave breaking over a stagnant cold-air bubble in the valley upwind of the main tower. The bubble is preceded by the formation of a valley cold-air pool due to down-valley drainage flows during the evening transition. The bubble grows in depth by entraining cold down-valley and downslope flows from below and is eroded by shear-induced wave breaking on the top. The cyclic process of formation and erosion is repeated during the night, leading to sporadic turbulent bursting.

The Relationships among Wind, Horizontal Pressure Gradient, and Turbulent Momentum Transport during CASES-99

Abstract Relationships among the horizontal pressure gradient, the Coriolis force, and the vertical momentum transport by turbulent fluxes are investigated using data collected from the 1999 Cooperative Atmosphere–Surface Exchange Study (CASES-99). Wind toward higher pressure (WTHP) adjacent to the ground occurred about 50% of the time. For wind speed at 5 m above the ground stronger than 5 m s−1, WTHP occurred about 20% of the time. Focusing on these moderate to strong wind cases only, relationships among horizontal pressure gradients, Coriolis force, and vertical turbulent transport in the momentum balance are investigated. The magnitude of the downward turbulent momentum flux consistently increases with height under moderate to strong winds, which results in the vertical convergence of the momentum flux and thus provides a momentum source and allows WTHP. In the along-wind direction, the horizontal pressure gradient is observed to be well correlated with the quadratic wind speed, which is demonstrated to be an approximate balance between the horizontal pressure gradient and the vertical convergence of the turbulent momentum flux. That is, antitriptic balance occurs in the along-wind direction when the wind is toward higher pressure. In the crosswind direction, the pressure gradient varies approximately linearly with wind speed and opposes the Coriolis force, suggesting the importance of the Coriolis force and approximate geotriptic balance of the airflow. A simple one-dimensional planetary boundary layer eddy diffusivity model demonstrates the possibility of wind directed toward higher pressure for a baroclinic boundary layer and the contribution of the vertical turbulent momentum flux to this phenomenon.

Sunset decay of the convective turbulence with Large-Eddy Simulation under realistic conditions

Large-Eddy Simulation is performed for a single day from the Cooperative Atmosphere-Surface Exchange Study (CASES-99) field program. This study investigates an observed case of evening transition boundary layer over land. Parameters of the ambient atmosphere in the LES-decay studies conducted so far were typically prescribed in an idealized form. To provide suitable data under the wide range of the PBL weather conditions, the LES should be able to adequately reproduce the PBL turbulence dynamics including–if possible–baroclinicity, radiation, large scale advection and not only be related to a decreasing surface heating. In addition LES-decay studies usually assume that the sensible heat flux decreases instantaneously or with a very short time scale. The main purpose of this investigation is to study the decay of boundary-layer average turbulent kinetic energy at sunset with Large-Eddy Simulation that is forced with realistic environment conditions. This allows investigating the Turbulent Kinetic Energy decay over the realistic time scale that is observed in the atmosphere. During the intermediate and last stage of decay of the boundary-layer average Turbulent Kinetic Energy the exponents of the decay power law t−n go from 2 to 6, as evidenced by experimental results and recent analytical modeling in the surface layer.

Objectively Determined Fair-Weather CBL Depths in the ARW-WRF Model and Their Comparison to CASES-97 Observations

Abstract High-resolution 24-h runs of the Advanced Research version of the Weather Research and Forecasting Model are used to test eight objective methods for estimating convective boundary layer (CBL) depth h, using four planetary boundary layer schemes: Yonsei University (YSU), Mellor–Yamada–Janjic (MYJ), Bougeault–LaCarrere (BouLac), and quasi-normal scale elimination (QNSE). The methods use thresholds of virtual potential temperature Θυ, turbulence kinetic energy (TKE), Θυ,z, or Richardson number. Those that identify h consistent with values found subjectively from modeled Θυ profiles are used for comparisons to fair-weather observations from the 1997 Cooperative Atmosphere–Surface Exchange Study (CASES-97). The best method defines h as the lowest level at which Θυ,z = 2 K km−1, working for all four schemes, with little sensitivity to horizontal grid spacing. For BouLac, MYJ, and QNSE, TKE thresholds did poorly for runs with 1- and 3-km grid spacing, producing irregular h growth not consistent with Θυ-profile evolution. This resulted from the vertical velocity W associated with resolved CBL eddies: for W > 0, TKE profiles were deeper and Θυ profiles more unstable than for W < 0. For the 1-km runs, 25-point spatial averaging was needed for reliable TKE-based h estimates, but thresholds greater than free-atmosphere values were sensitive to horizontal grid spacing. Matching Θυ(h) to Θυ(0.05h) or Θυ at the first model level were often successful, but the absence of eddies for 9-km grids led to more unstable Θυ profiles and often deeper h. Values of h for BouLac, MYJ, and QNSE, are mostly smaller than observed, with YSU values close to slightly high, consistent with earlier results.

An Analysis for the Applicability of Monin–Obukhov Similarity Theory in Stable Conditions

Abstract An analysis in a plane of the stability parameters ζ = z/L (where z is a height above the ground surface and L is the Obukhov length) and bulk Richardson number RiB is proposed to examine the applicability of Monin–Obukhov similarity (MOS) theory in stable conditions. In this analysis, the data available from two different experimental datasets [(i) Cooperative Atmosphere–Surface Exchange Study-1999 (CASES-99) and (ii) Cardington] are divided into four quadrants. An unexpected behavior of decreasing ζ with increasing RiB was observed with both datasets in quadrant II characterized by ζ < 1 and RiB > 0.2 and in quadrant IV with ζ > 1 and RiB < 0.2. This is in contrast to a commonly expected monotonically increasing behavior between ζ and RiB. It is shown that the MOS theory is consistent for computing the surface fluxes corresponding to the data points lying in quadrants I (with ζ > 1 and RiB > 0.2) and III (with ζ < 1 and RiB < 0.2), whereas it may not be applicable for the points in quadrants II and IV. Thus, a breakdown of the relationship between observed ζ and RiB with growing stability in these quadrants may limit the applicability of MOS theory in stable conditions. Since quadrant IV has very few data points, the applicability of MOS theory needs to be substantiated further with the availability of sufficient data points in this regime.

Turbulence Regimes and Turbulence Intermittency in the Stable Boundary Layer during CASES-99

Abstract An investigation of nocturnal intermittent turbulence during the Cooperative Atmosphere–Surface Exchange Study in 1999 (CASES-99) revealed three turbulence regimes at each observation height: 1) regime 1, a weak turbulence regime when the wind speed is less than a threshold value; 2) regime 2, a strong turbulence regime when the wind speed exceeds the threshold value; and 3) regime 3, a moderate turbulence regime when top-down turbulence sporadically bursts into the otherwise weak turbulence regime. For regime 1, the strength of small turbulence eddies is correlated with local shear and weakly related to local stratification. For regime 2, the turbulence strength increases systematically with wind speed as a result of turbulence generation by the bulk shear, which scales with the observation height. The threshold wind speed marks the transition above which the boundary layer approaches near-neutral conditions, where the turbulent mixing substantially reduces the stratification and temperature fluctuations. The preference of the turbulence regimes during CASES-99 is closely related to the existence and the strength of low-level jets. Because of the different roles of the bulk and local shear with regard to turbulence generation under different wind conditions, the relationship between turbulence strength and the local gradient Richardson number varies for the different turbulence regimes. Turbulence intermittency at any observation height was categorized in three ways: turbulence magnitude oscillations between regimes 1 and 2 as wind speed varies back and forth across its threshold value, episodic turbulence enhancements within regime 1 as a result of local instability, and downbursts of turbulence in regime 3.

Vertical cross-spectral phases in neutral atmospheric flow

The cross-spectral phases between velocity components at two heights are analyzed from observations at the Høvsøre test site and from the field experiments under the Cooperative Atmosphere-Surface Exchange Study in 1999. These phases represent the degree to which turbulence sensed at one height leads (or lags) in time the turbulence sensed at the other height. The phase angle of the cross-wind component is observed to be significantly greater than the phase for the along-wind component, which in turn is greater than the phase for the vertical component. The cross-wind and along-wind phases increase with stream-wise wavenumber and vertical separation distance, but there is no significant change in the phase angle of vertical velocity, which remains close to zero. The phases are also calculated using a rapid distortion theory model and large-eddy simulation. The results from the models show similar order in phasing, but the slopes of the phase curves are slightly different from the observations, especially for low wavenumbers.

A Study of the Stable Boundary Layer Based on a Single-Column K-Theory Model

We document numerical experiments with a single-column, high-resolution model of the stable boundary layer. The model resolves the logarithmic layer, and does not require inverting the Monin–Obukhov similarity functions in order to calculate the surface fluxes. The turbulence closure is based on the K-theory approach, with a new form of stability functions of the Richardson number, evaluated by using the Surface Heat Budget of the Arctic Ocean (SHEBA) and the Cooperative Atmosphere-Surface Exchange Study (CASES-99) data. A comparison with two, high-resolution large-eddy simulation models shows very good agreement. The reported numerical experiments test the effects of shear, surface cooling, the Coriolis parameter, subsidence, and baroclinicity. The time evolution of the drag coefficient, the heat-transfer coefficient, and the cross-isobar angle is also evaluated.