Spatial variations of surface stress over the coastal shoaling zone are studied offshore of Duck, North Carolina, by the LongEZ research aircraft, equipped to measure both atmospheric turbulence and oceanic waves. We find that the spatial variation of the friction velocity with offshore distance is much larger with offshore flow...
Both the form of functional relationships applied for soil water properties and the natural field-scale variability of such properties can significantly impact simulation of the soil-plant-atmosphere system on a diurnal timescale. Various input parameters for soil water properties including effective saturation, residual water content, anerobiosis point, field capacity, and permanent...
Lake-induced atmospheric circulations over three lakes ranging from 3 to 10 km width are analyzed using data from three aircraft during the 1994 Boreal Ecosystem-Atmosphere Study (BOREAS). A well-defined divergent lake breeze circulation is observed over all three lakes during the day. Under light wind conditions, the lake breeze is...
Toward the goal of predicting area-averaged evapotranspiration, the evaporative fraction is modelled in terms of surface radiation temperature, air temperature, solar zenith angle, Normalized Difference of the Vegetation Index and albedo. Previous relationships break down when applied simultaneously to a variety of surfaces. The zenith angle is required to account...
Eddy‐correlation fluxes are compared to air‐sea fluxes predicted by a widely used bulk flux formulation without wave‐state effects. Systematic discrepancies are found. For example, the model approximately equates the roughness lengths for heat and moisture; however, the observed roughness length for heat (zoh) exceeds that for moisture (zoq) by an...
Aircraft data collected at approximately 15 m above the sea surface in the coastal zone are analyzed to examine the spatial distribution of surface stress. Advection of stronger turbulence from land dominates the near-surface turbulence for the first few kilometers offshore. With offshore flow of warm air over cold water,...
This study evaluates the prediction of heat and moisture fluxes from a new land surface scheme with eddy correlation data collected at the old aspen site during the Boreal Ecosystem-Atmosphere Study (BOREAS) in 1994. The model used in this study couples a multilayer vegetation model with a soil model. Inclusion...
This study examines the spatial variability of ozone fluxes over flat heterogeneous terrain consisting of a patchwork of irrigated and nonirrigated surfaces. Fluxes of ozone and other quantities are computed from eight sequential flight legs of the Canadian Twin Otter research aircraft over the same track at 33 m above...
The correlation between dimensionless shear ϕₘ and dimensionless height z/L, where L is the Obukhov length, for stable conditions is strongly influenced by self‐correlation for the present datasets. This effect is quite large for stronger stability but still significant for near‐neutral conditions. A conditional analysis of nocturnal stable boundary‐layer data,...
Whole ecosystem carbon dioxide (CO₂) exchange estimated with the eddy covariance (EC) technique has been central to studies on the responses of terrestrial ecosystems to disturbance and intra‐annual and interannual variations in climate, but challenges exist in understanding and reducing the uncertainty in estimates of net ecosystem exchange (NEE) of...
The value of the effective exchange coefficient for area-averaged fluxes can depend significantly on the averaging scale. This dependence implies that the exchange coefficient in numerical models should depend on grid size. The main goal of this study is the assessment of the importance of such scale-dependence. When the large-scale...
Vertical profiles of the time-averaged wind stress, wind speed and buoyancy flux from the off-shore tower site in the Risø Air Sea Experiment are used to evaluate similarity theory in the coastal zone. The observed dependence of the non-dimensional wind shear on stability is compared to the traditional parametrization. Relationships...
In this article, we examine the stochastic characteristics of non-turbulent motions in the stable boundary layer. The behaviour of mesoscale motions in the atmospheric stable boundary layer is poorly understood beyond case studies of unusually well-defined events or monotonic waves. Eight networks of wind observations are analysed in order to...
The light-wind, clear-sky, very stable boundary layer (vSBL) is characterized by large values of bulk
Richardson number. The light winds produce weak shear, turbulence, and mixing, and resulting strong
temperature gradients near the surface. Here five nights with weak-wind, very stable boundary layers during
the Cooperative Atmosphere–Surface Exchange Study (CASES-99)...
This study examines the spatial variation of the wind field observed in the coastal zone of southeast Korea with its complex terrain, using measurements from a regional network 75 km across and centered about Busan. Results are compared with observations from an inland regional network centered around Daegu, Korea, with...
The Office of Naval Research's Coupled Boundary Layers and Air–Sea Transfer (CBLAST) program is being conducted to investigate the processes that couple the marine boundary layers and govern the exchange of heat, mass, and momentum across the air–sea interface. CBLAST-LOW was designed to investigate these processes at the low-wind extreme...
Numerical weather prediction models often perform poorly for weakly forced, highly variable winds in nocturnal stable boundary layers (SBLs). When used as input to air-quality and dispersion models, these wind errors can lead to large errors in subsequent plume forecasts. Finer grid resolution and improved model numerics and physics can...
This study addresses the relationship between thermal microfronts and coherent vortex structures in homogeneous turbulence. The turbulence is created by mean shear in a weakly stratified flow. The data set is generated by direct numerical simulation providing highly resolved instantaneous three‐dimensional fields of fluctuating velocity and temperature (1603 data points...
From almost 7000 near-surface eddy-covariance flux measurements over the sea, the authors deduce a new air–sea drag relation for aerodynamically rough flow: u* = 0.0583Uₙ₁₀ 2 0.243. Here u* is the measured friction velocity, and Uₙ₁₀ is the neutral-stability wind speed at a reference height of 10 m. This relation...
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...
The 10-m neutral drag coefficient (C[subscript DN10]) over the sea is calculated using a large observational dataset consisting of 5800 estimates of the mean flow and the fluxes from aircraft eddy-covariance measurements. The dataset includes observations from 11 different experiments with four different research aircraft. One of the goals is...
Turbulence measurements for very stable conditions near the surface are contrasted
among three sites: a high altitude basin during winter with grass or snow-covered
grass, a broad valley with complex agricultural land use, and a more narrow valley that is
influenced by a valley cold pool and cold air drainage....
This study investigates the exchange of momentum between the atmosphere and ocean using data collected from four oceanic field experiments. Direct covariance estimates of momentum fluxes were collected in all four experiments and wind profiles were collected during three of them. The objective of the investigation is to improve parameterizations...
The Bowen ratio, the ratio of the turbulent surface fluxes of sensible (Hₛ) and latent (Hₗ) heat, Bo ≡ Hₛ/Hₗ, occurs throughout micrometeorology. It finds application in the Bowen ratio and energy budget method, where it provides both turbulent heat fluxes when only the available energy at the surface is...
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...
Over 5000 aircraft eddy-covariance measurements from four different aircraft in nine different experiments are used to develop a simple model for the friction velocity over the sea. Unlike the widely used Coupled Ocean–Atmosphere Response Experiment (COARE) bulk flux scheme, the simple model (i) does not use Monin–Obukhov similarity theory (MOST)...
The authors investigate atmospheric internal gravity waves (IGWs): their generation and induction of global intermittent turbulence in the nocturnal stable atmospheric boundary layer based on the new concept of turbulence generation discussed in a prior paper by Sun et al. The IGWs are generated by air lifted by convergence forced...
Turbulence measurements for very stable conditions near the surface are contrasted
among three sites: a high altitude basin during winter with grass or snow-covered
grass, a broad valley with complex agricultural land use, and a more narrow valley that is
influenced by a valley cold pool and cold air drainage....
Turbulence measurements for very stable conditions near the surface are contrasted
among three sites: a high altitude basin during winter with grass or snow-covered
grass, a broad valley with complex agricultural land use, and a more narrow valley that is
influenced by a valley cold pool and cold air drainage....
This study investigates the exchange of momentum between the atmosphere and ocean using data collected from four oceanic field experiments. Direct covariance estimates of momentum fluxes were collected in all four experiments and wind profiles were collected during three of them. The objective of the investigation is to improve parameterizations...
This study investigates the exchange of momentum between the atmosphere and ocean using data collected from four oceanic field experiments. Direct covariance estimates of momentum fluxes were collected in all four experiments and wind profiles were collected during three of them. The objective of the investigation is to improve parameterizations...
Using eddy correlation data collected by the LongEZ research aircraft, the adjustment of atmospheric flow downstream from a coastline is examined. Along-shore variation of the turbulence over the water is generated by the varying width of the upstream land strip between the sea and inland water. Over the coastal zone,...
The flux-gradient relationship of water vapor Fq was obtained from the Cooperative Atmosphere-Surface Exchange Study-1999 (CASES-99) field experiment, which was conducted on a flat and grassy field in the southeastern part of Kansas, USA, during October 1999. The CASES-99 data include turbulence measurements of wind, temperature, and vapor density along...
This study surveys and evaluates similarity theory for estimating the sea-surface drag coefficient with the bulk aerodynamic method. The most commonly used formulations of the aerodynamic roughness length, required by similarity theory, are examined using data sets from four different field programs. These relationships include the Charnock formulation and the...
The stable nocturnal boundary layer is commonly viewed or modelled as a balance between the temperature tendency (cooling) and vertical heat-flux divergence. Sometimes the radiative-flux divergence is also included. This perspective has dictated the design of field experiments for investigating stable nocturnal boundary layers. Tower-based micrometeorological data from three field...
This study examines the dependence of the computed drag coefficient on wind speed, stability, fetch, flux sampling problems, and method of calculation of the drag coefficient. The analysis is applied to data collected at a tower 2 km off the coast of Denmark during the Risø Air Sea Experiment (RASEX)....
The sublimation of snow and evaporation of melted snow is contrasted between brush, grass and bare ground sites using eddy-correlation data. Averaged over the entire winter season, the evaporation/sublimation is about 20% greater over the brush site than the bare ground site, apparently due to greater supply of snow. Blowing...
The aerodynamic temperature is required for prediction of the surface heat flux using Monin-Obukhov similarity. This "fictitious" temperature is not systematically equal to the actual air temperature near the surface and is not directly available from observations or in numerical models. The aerodynamic temperature is normally replaced with either the...
This study investigates atmospheric factors influencing the quality and the postprocessing (e.g., tilt correction) of fast-response measurements of turbulent fluxes for difficult open-sea measurements over an offshore platform. The data were collected at the Ieodo Ocean Research Station over the Yellow Sea during the period from 5 November 2007 to...