Unstable Atmospheric Surface Layer Research Articles

A Novel Similarity Approach for Describing the Bulk Shear in the Atmospheric Surface Layer

The Monin–Obukhov Similarity Theory (MOST) is a cornerstone of boundary layer meteorology and the basis of most parameterizations of the atmospheric surface layer. Due to its significance for observations and modelling, we generalize the dimensional analysis of MOST by considering the bulk gradient directly, enabling the study of any sublayer of the atmospheric surface layer. This results in a family of similarity relations describing all gradients from the local gradient to the full-layer bulk gradient. By applying the profiles derived from the law-of-the-wall and MOST, we are able to derive analytic expressions for this family of similarity relations. Under stable conditions, we discover that the log-linear profile of Businger–Dyer generalizes from the local to the bulk shear where the slope is dependent on the choice of the layer. The simplicity of the general log-linear relation allows for estimating the influence of stability on the non-dimensional gradients. It is shown that bulk gradients are less sensitive to stability than the local gradient. By correctly filtering cases where the full-layer bulk gradient is influenced by stability, we demonstrate that MOST is compatible with the Hockey-Stick Transition. For unstable conditions, the Kader and Yaglom (J Fluid Mech 212(151):637-662, 1990) model represents the local gradient well but was not successful in representing the bulk gradient, demonstrating the need for further analysis of scaling relations for the unstable atmospheric surface layer.

Scalar Flux Profiles in the Unstable Atmospheric Surface Layer Under the Influence of Large Eddies: Implications for Eddy Covariance Flux Measurements and the Non‐Closure Problem

AbstractHow convective boundary‐layer (CBL) processes modify fluxes of sensible (SH) and latent (LH) heat and CO2 (Fc) in the atmospheric surface layer (ASL) remains a recalcitrant problem. Here, large eddy simulations for the CBL show that while SH in the ASL decreases linearly with height regardless of soil moisture conditions, LH and Fc decrease linearly with height over wet soils but increase with height over dry soils. This varying flux divergence/convergence is regulated by changes in asymmetric flux transport between top‐down and bottom‐up processes. Such flux divergence and convergence indicate that turbulent fluxes measured in the ASL underestimate and overestimate the “true” surface interfacial fluxes, respectively. While the non‐closure of the surface energy balance persists across all soil moisture states, it improves over drier soils due to overestimated LH. The non‐closure does not imply that Fc is always underestimated; Fc can be overestimated over dry soils despite the non‐closure issue.

Applicability of Taylor's frozen hypothesis and elliptic model in the atmospheric surface layer

Based on the synchronous multi-point temperature data measured at different streamwise positions with the application of distributed temperature sensing, a field investigation on the applicability of Taylor's frozen hypothesis and elliptic model was performed in the atmospheric surface layer (ASL). In this work, several important spatial statistical functions of temperature field, such as longitudinal space–time correlation [CTT(r, t)], space correlation [RTT(r)], normalized second-order structure function [⟨ΔT+2(r)⟩], and wavenumber spectrum [ΦTT(k)] of temperature fluctuations, were directly measured in the ASL. By comparing the directly measured spatial statistical functions with the predicted results, our study indicates that both Taylor's frozen hypothesis and elliptic model are applicable in the near-neutral and stable ASLs when the turbulence level is low. However, only the elliptic model is substantially accurate in the unstable ASL when the turbulence level is high. The elliptic model can relate CTT(r, t) to RTT(rE), where rE = [(r−Ueτ)2+(Veτ)2]1/2, Ue is the convection velocity, and Ve is the sweeping velocity. With the application of Ue and Ve, RTT(r) and ⟨ΔT+2(r)⟩ can be estimated by the elliptic model in the near-neutral, unstable, and stable ASLs.

Revisiting the role of intermittent heat transport towards Reynolds stress anisotropy in convective turbulence

Abstract

On the Role of Large-Scale Updrafts and Downdrafts in Deviations From Monin\u2013Obukhov Similarity Theory in Free Convection

We investigate by means of direct numerical simulation how large-scale circulations produce deviations from Monin–Obukhov similarity theory (MOST) in the limit of free convection, disentangling the role of large-scale downdrafts from updrafts using conditional analysis. We compare the convective boundary layer to two other free-convective flows: Rayleigh–Bénard convection with an adiabatic top lid and classical Rayleigh–Bénard convection. This serves a dual purpose: firstly, to ascertain how changes in the upper boundary conditions and thereby in the large-scale circulations modify the near-surface behaviour and secondly, to assess to what extent we can extrapolate results from idealized systems to the unstable atmospheric surface layer. Using a low-pass filter to define the large scales we find that, whilst deviations from MOST occur within large-scale downdraft regions, strong deviations also occur within large-scale updraft regions. The deviations within updrafts are independent of the filter length scale used to define the large-scale circulations, independent of whether updrafts are defined as ascending air, or as air that is both ascending and positively buoyant, and are not due to changes with height of the updraft area fraction. This suggests that even updraft properties are not just determined locally, but also by outer scales. Cold, strong downdrafts in classical Rayleigh–Bénard convection notably modify the near-surface behaviour compared to the other two systems. For the moderate Reynolds numbers considered, Rayleigh–Bénard convection with an adiabatic top lid thus seems more appropriate than classical Rayleigh–Bénard convection for studying the unstable atmospheric surface layer in the limit of free convection.

An evaluation of the dissimilarity in heat and momentum transport through quadrant analysis for an unstable atmospheric surface layer flow

To elucidate the role of each fluid motion in the transport of momentum and heat fluxes in an unstable atmospheric surface layer (ASL) flow from single point measurements on a micrometeorological tower, we develop a novel method based on quadrant analysis where the contour maps of the turbulent statistics (fluxes, temperature variances and triple order moments between vertical velocity and temperature) are plotted on the quadrant planes between streamwise (u)–vertical (w) velocities, and vertical velocity (w)–temperature (T). We find that the dissimilarities in the heat and momentum transport with atmospheric stability are closely linked to the non-Gaussian nature of the joint probability density function (JPDF) between w and T. To highlight the changes in the fluid motions which cause this dissimilarity, we plot the contour maps of the third order moments between w and T on the u − w quadrant plane, and also of the streamwise momentum flux conditioned on every quadrant of u − w plane onto the T − w plane, referred to as octant analysis. The results indicate that in a highly-convective ASL, the cold downdrafts interspersed with strong ejections of hot fluid, carry a significant amount of both down-gradient and counter-gradient momentum flux, thus making the momentum transport inefficient. However, in a near-neutral ASL, the heat and momentum both are carried by the ejection and sweep quadrants of u − w quadrant plane, which indicates the temperature fluctuations are highly correlated with the high-speed and low-speed streaks commonly found in pure shear flows in the laboratory experiments.

Intrinsic Constraints on Asymmetric Turbulent Transport of Scalars Within the Constant Flux Layer of the Lower Atmosphere

AbstractA widely used assumption in boundary layer meteorology is the z independence of turbulent scalar fluxes Fs throughout the atmospheric surface layer, where z is the distance from the boundary. This assumption is necessary for the usage of Monin‐Obukhov Similarity Theory and for the interpretation of eddy covariance measurements of Fs when using them to represent emissions or uptake from the surface. It is demonstrated here that the constant flux assumption offers intrinsic constraints on the third‐order turbulent transport of Fs in the unstable atmospheric surface layer. When enforcing z independence of Fs on multilevel Fs measurements collected above different surface cover types, it is shown that increasing instability leads to a novel and universal description of (i) the imbalance between ejecting and sweeping eddy contributions to Fs and (ii) the ratio formed by a dimensionless turbulent transport of Fs and a dimensionless turbulent transport of scalar variance. When combined with structural models for the turbulent transport of Fs, these two findings offer a new perspective on “closing” triple moments beyond conventional gradient diffusion schemes. A practical outcome is a diagnostic of the constant flux assumption from single‐level Fs measurements.

Experimental investigation of turbulent transport of momentum and heat in the atmospheric surface layer

In our study, turbulent transport of momentum and heat is investigated in the neutral and unstable atmospheric surface layer (ASL) over the edge of a desert. Our results reveal that with the increase of wind speed the transport efficiencies for momentum and heat increased, furthermore, transport efficiency of momentum increases faster than that of heat. In addition, the method of quadrant analysis and turbulent events were used to analyze the moment flux and heat flux. Experimental results show that the influence of wind speed on moment flux and heat flux can be quite different, which maybe has a great impact on the turbulent transport of momentum and heat in ASL.

Role of large eddies in the breakdown of the Reynolds analogy in an idealized mildly unstable atmospheric surface layer

While the breakdown in similarity between turbulent transport of heat and momentum (or Reynolds analogy) is not disputed in the atmospheric surface layer (ASL) under unstably stratified conditions, the causes of this breakdown are still debated. One reason for the breakdown is differences between how coherent structures transport heat and momentum, and their differing responses to increasing instability. Monin—Obukhov Similarity Theory (MOST), which hypothesizes that only local length‐scales play a role in ASL turbulent transport, implicitly assumes that large‐scale structures are inactive, despite their large energy content. Widely adopted mixing‐length models also rest on this assumption in the ASL. The difficulty of characterizing low‐wavenumber turbulent motions with field measurements motivates the use of high‐resolution Direct Numerical Simulation (DNS), which is free from subgrid‐scale parametrizations and adhoc assumptions near the boundary. Despite the low Reynolds number and idealized geometry of the DNS, DNS‐estimated MOST functions are consistent with ASL field experiments, as are low‐frequency features of the spectra. Parsimonious spectral models for MO stability correction functions for momentum (φm) and heat (φh) are derived, based on idealized vertical velocity variance and buoyancy variance spectra fit to the corresponding DNS spectra. For φm, a spectral model, based only on local length‐scales, matches DNS and field measurements well. In contrast, for φh, the model is substantially biased unless contributions from larger length‐scales are also included. These results are supported by sensitivity analyses based on field measurements that are independent of the DNS. They show that ASL heat transport is not MO‐similar, even under mild stratification, and in the absence of entrainment, non‐stationarity and canopy effects. It further suggests that the breakdown of the Reynolds analogy is at least partially caused by the influence of large eddies on turbulent heat transport.

Characteristics of the Heat Flux in the Unstable Atmospheric Surface Layer

Abstract The 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.

Large eddies modulating flux convergence and divergence in a disturbed unstable atmospheric surface layer

AbstractThe effects of large eddies on turbulence structures and flux transport were studied using data collected over a flat cotton field during the Energy Balance Experiment 2000 in the San Joaquin Valley of California in August 2000. Flux convergence (FC; larger fluxes at 8.7 m than 2.7 m) and divergence (FD) in latent heat flux (LE) were observed in a disturbed, unstable atmospheric surface layer, and their magnitudes largely departed from the prediction of Monin‐Obukhov similarity theory. From our wavelet analysis, it was identified that large eddies affected turbulence structures, scalar distribution, and flux transport differently at 8.7 m and 2.7 m under the FC and FD conditions. Using the ensemble empirical mode decomposition, time series data were decomposed into large eddies and small‐scale background turbulence, the time‐domain characteristics of large eddies were examined, and the flux contribution by large eddies was also determined quantitatively. The results suggest that large eddies over the frequency range of 0.002 Hz < f < 0.02 Hz (predominantly 300–400 m) enhanced the vertical velocity spectra more significantly at 8.7 m than 2.7 m, leading to an increased magnitude of the cospectra and thus LE at 8.7 m. In the FD case, however, these large eddies were not present and even suppressed in the vertical velocity spectra at 8.7 m. Consequently, the cospectra divergence over the low‐frequency ranges primarily caused the LE divergence. This work implies that large eddies may either improve or degrade the surface energy balance closure by increasing or decreasing turbulent fluxes, respectively.

Air humidity thresholds trigger active moss spore release to extend dispersal in space and time

Summary Understanding the complete dispersal process is important for making realistic predictions of species distributions, but mechanisms for diaspore release in wind‐dispersed species are often unknown. However, diaspore release under conditions that increase the probability of longer dispersal distances and mechanisms that extend dispersal events in time may have evolutionary advantages. We quantified air humidity thresholds regulating spore release in the moss Brachythecium rutabulum. We also investigated the prevailing micrometeorological conditions when these thresholds occur in nature and how they affect dispersal distances up to 100 m, using a mechanistic dispersal model. We show that moss spores were mainly released when the peristome teeth were opening, as relative air humidity (RH) decreased from high values to relatively low (mainly between 90% and 75% RH). This most often occurred in the morning, when wind speeds were relatively low. Surprisingly, the model predicted that an equally high proportion of the spores would travel distances beyond 100 m (horizontally) when released in the wind conditions prevailing during events of RH decrease in the morning, that lead to peristome opening, as in the highest wind speeds. Moreover, a higher proportion of the spores reached high altitudes when released at the lower wind speeds during the morning compared to the higher speeds later in the day, indicating a possibility for extended dispersal distances when released in the morning. Dispersal in the morning is enhanced by a combination of a more unstable atmospheric surface layer that promotes vertical dispersal, and a lower wind speed that decreases the spore deposition probability onto the ground, compared to later in the day. Our study demonstrates an active spore release mechanism in response to diurnally changing air humidity. The mechanism may promote longer dispersal distances, because of enhanced vertical dispersal and because spores being released in the morning have more time to travel before the wind calms down at night. The mechanism also leads to a prolonged dispersal period over the season, which may be viewed as a risk spreading in time that ultimately also leads to a higher diversity of establishment conditions, dispersal distances and directions.

A review of the remote sensing of lower tropospheric thermodynamic profiles and its indispensable role for the understanding and the simulation of water and energy cycles

AbstractA review of remote sensing technology for lower tropospheric thermodynamic (TD) profiling is presented with focus on high accuracy and high temporal‐vertical resolution. The contributions of these instruments to the understanding of the Earth system are assessed with respect to radiative transfer, land surface‐atmosphere feedback, convection initiation, and data assimilation. We demonstrate that for progress in weather and climate research, TD profilers are essential. These observational systems must resolve gradients of humidity and temperature in the stable or unstable atmospheric surface layer close to the ground, in the mixed layer, in the interfacial layer—usually characterized by an inversion—and the lower troposphere. A thorough analysis of the current observing systems is performed revealing significant gaps that must be addressed to fulfill existing needs. We analyze whether current and future passive and active remote sensing systems can close these gaps. A methodological analysis and demonstration of measurement capabilities with respect to bias and precision is executed both for passive and active remote sensing including passive infrared and microwave spectroscopy, the global navigation satellite system, as well as water vapor and temperature Raman lidar and water vapor differential absorption lidar. Whereas passive remote sensing systems are already mature with respect to operational applications, active remote sensing systems require further engineering to become operational in networks. However, active remote sensing systems provide a smaller bias as well as higher temporal and vertical resolutions. For a suitable mesoscale network design, TD profiler system developments should be intensified and dedicated observing system simulation experiments should be performed.

Similarity Relations for $$C_{T}^2 $$ C T 2 in the Unstable Atmospheric Surface Layer: Dependence on Regression Approach, Observation Height and Stability Range

A great variety of similarity functions for the structure parameter of temperature ( $$C_{T}^2$$ ) have been proposed in the literature. They differ in the way they were derived from the data and in the characteristics of the dataset used for their derivation (surface type, observation level, stability range). In this study, we use one single dataset (CASES-99 experiment) and investigate the impact on the similarity functions of applying various regression approaches, and measuring at different heights and within different stability ranges. We limit ourselves to similarity functions under unstable conditions, and evaluate only the most common shape that describes the relation with two coefficients ( $$f\left( z/L\right) =c_{1} \left( 1-c_{2} {z}/{L}\right) ^{-2/3}$$ , where $$z$$ is the height, and $$L$$ is the Obukhov length and a measure of the stability, and $$c_{1}$$ and $$c_{2}$$ are the regression coefficients). The results show that applying various regression approaches has an impact on the regression coefficients $$c_{1}$$ and $$c_{2}$$ . Thus studies should always specify the regression approach when presenting similarity relations. We suggest use of an orthogonal distance regression method such that uncertainties in $$-z/L$$ are also taken into account, to apply this to the logarithmic transformation of both dimensionless groups, and to use a weighted dataset such that unreliable data points have a smaller influence on the fit. Dividing the dataset into eight height ( $$z$$ ) and eight stability ( $$-{1/L}$$ classes) classes, we show that the observation height and the stability range has an impact on the coefficients too. This implies that variations in $$c_{1}$$ and $$c_{2}$$ found in the literature may result from variations in the height and stability ranges among the datasets. Furthermore, application of the coefficients on a dataset obtained at a different height or within a different stability range has to be made with care. Finally, the variation in the coefficients between the classes indicates that the Monin–Obukhov similarity function for $$C_{T}^2$$ is not sufficiently described by the two-coefficient function used here.

Coherent structures detected in the unstable atmospheric surface layer above the Amazon forest

Some characteristics of the turbulence structure above primary forest localized in the south-western Amazon are analyzed. The data was collected in 60m height meteorological tower erected in Rebio-Jarú Reserve, Brazil. The Morlet’s wavelet is used to detect coherent structures (CS) “ramp” time scales from turbulent virtual temperature data measured above forest, under day-time conditions. It is shown that there is a close relationship between time scale of the coherent structure (TCS) and the height to the inflection point in the mean wind speed profile (IP). A time scale associated with the IP is used to provide useful information on inside canopy penetration flow in order to be compared with the CS time-scale. The results show a very robust correlation between these two time scales (for 144 half-hourly data sets, a correlation coefficient value of 0.9 have been obtained). Such results provide new insights regarding shear instability and turbulent eddy characteristics above tall vegetation, in the surface roughness sub-layer (SRS).

Environmental Controls on the Surface Energy Budget over a Large Southern Inland Water in the United States: An Analysis of One-Year Eddy Covariance Flux Data

Abstract The authors analyzed the surface energy fluxes that were measured by an eddy covariance system over the Ross Barnett Reservoir in Mississippi for a 1-yr period in 2008. On a monthly basis over the course of the year, positive vertical temperature and vapor pressure differences were observed, though negative vertical temperature differences occurred occasionally during some short periods when overwater air masses were warmer than the water surface. Consequently, the unstable atmospheric surface layer (ASL) and sufficient mechanical mixing led to positive sensible H and latent λE heat fluxes. The quantities H and λE were distinctively out of phase with the net radiation Rn. The H and λE from the water to the ASL was still substantial on nights with a negative Rn and in winter when Rn was very small. From February to August, approximately 60%–91% of the Rn was used for H and λE, with the remainder being stored in the water. Fueled by the previously stored heat in the water, H and λE exceeded Rn by almost 3 times from September to January. Nighttime evaporation represented a large loss of water (i.e., λE = 82.8 W m−2 at night versus 91.4 W m−2 during the daytime). Intraseasonal and seasonal variations in H and λE were strongly affected by frequent passages of large-scale air masses that were brought in by different synoptic weather systems (e.g., cyclones or anticyclones). The authors’ analysis suggested that this southern reservoir responded to atmospheric forcings on both diurnal and seasonal scales in the same ways as northern lakes of comparable sizes and depths.

Probability density functions of turbulent velocity and temperature fluctuations in the unstable atmospheric surface layer

[1] The behavior of probability density functions (pdfs) of the velocity and temperature fluctuations in the unstable surface layer is systematically studied within the framework of similarity theory. The pdfs of horizontal velocity fluctuations are nearly Gaussian for a wide range of atmospheric stability conditions. Thus, the standard deviations of horizontal velocity fluctuations are sufficient to predict the pdfs. Using mixed-layer similarity, these standard deviations can be estimated from mean meteorological conditions. The pdfs of vertical velocity fluctuations are non-Gaussian. We introduce the truncated stable distributions and find that they can be better for fitting the tails of measured pdfs than other non-Gaussian pdfs commonly used in the airborne dispersion models. This implies that the truncated stable distributions can be better for describing the small probability but high-impact events. Similar to the pdfs of the horizontal velocity fluctuations, the standard deviations of vertical velocity fluctuations are also sufficient to predict the pdfs. Using Monin-Obukhov similarity, their standard deviations can also be estimated from mean meteorological conditions. The pdfs of temperature fluctuations are much more complicated than those of velocity fluctuations. We show that the left tails of the temperature pdfs are likely to be power law and the right tails of temperature pdfs are Gaussian. Although complicated for pdfs, the Monin-Obukhov similarity is also valid to the standard deviations of temperature fluctuations.

Coherent Structures and the Dissimilarity of Turbulent Transport of Momentum and Scalars in the Unstable Atmospheric Surface Layer

Atmospheric stability effects on the dissimilarity between the turbulent transport of momentum and scalars (water vapour and temperature) are investigated in the neutral and unstable atmospheric surface layers over a lake and a vineyard. A decorrelation of the momentum and scalar fluxes is observed with increasing instability. Moreover, different measures of transport efficiency (correlation coefficients, efficiencies based on quadrant analysis and bulk transfer coefficients) indicate that, under close to neutral conditions, momentum and scalars are transported similarly whereas, as the instability of the atmosphere increases, scalars are transported increasingly more efficiently than momentum. This dissimilarity between the turbulent transport of momentum and scalars under unstable conditions concurs with, and is likely caused by, a change in the topology of turbulent coherent structures. Previous laboratory and field studies report that under neutral conditions hairpin vortices and hairpin packets are present and dominate the vertical fluxes, while under free-convection conditions thermal plumes are expected. Our results (cross-stream vorticity variation, quadrant analysis and time series analysis) are in very good agreement with this picture and confirm a change in the structure of the coherent turbulent motions under increasing instability, although the exact structure of these motions and how they are modified by stability requires further investigation based on three-dimensional flow data.

Turbulence Spectra and Cospectra Under the Influence of Large Eddies in the Energy Balance EXperiment (EBEX)

During the Energy Balance EXperiment, the patch-by-patch, flood irrigation in a flat cotton field created an underlying surface with heterogeneous soil moisture, leading to a dry (warm)-to-wet (cool) transition within the cotton field under northerly winds. Moreover, the existence of an extremely dry, large bare soil area upstream beyond the cotton field created an even larger step transition from the bare soil region to the cotton field. We investigated the turbulence spectra and cospectra in the atmospheric surface layer (ASL) that was disturbed by large eddies generated over regions upstream and also influenced by horizontal advection. In the morning, the ASL was unstable while in the afternoon a stable internal boundary layer was observed at the site. Therefore, the turbulence data at 2.7 and 8.7 m are interpreted and compared in terms of interactions between large eddies and locally generated turbulence under two atmospheric conditions: the unstable ASL beneath the convective boundary layer (CBL) (hereafter the unstable condition) and the stable ASL beneath the CBL (hereafter the stable condition). We identified the influences of multiple sizes of large eddies on ASL turbulence under both stratifications; these large eddies with multiple sizes were produced over the dry patches and dry, large bare soil areas upstream. As a consequence of the disturbance of large eddies, the broadening, erratic variability, and deviation of spectra and cospectra, relative to those described by Monin–Obukhov similarity theory, are evident in the low- to mid-frequencies. Transfer of momentum, heat, and water vapour by large eddies is distinctly observed from the turbulence cospectra and leads to significant run-to-run variations of residuals of the surface energy balance closure. Our results indicate that these large eddies have greater influences on turbulence at higher levels compared to lower levels, and in the unstable ASL compared to the stable ASL.

Coherent structures and flux contribution over an inhomogeneously irrigated cotton field

The turbulence data measured at two levels (i.e., 8.7 and 2.7 m) in the Energy Balance Experiment (EBEX), which was conducted in San Joaquin Valley in California during the period from July 20 to August 24, 2000, are used to study the characteristics of coherent structures over an irrigated cotton field. Patch-to-patch irrigation in the field generated the dry-to-wet horizontal advection and the oasis effects, leading to the development of a stably internal boundary layer (SIBL) in the late mornings or the early afternoons. The SIBL persisted in the rest of the afternoons. Under this circumstance, a near-neutral atmospheric surface layer (ASL) developed during the period with a stratification transition from the unstable to stable conditions during the daytime. Therefore, EBEX provides us with unique datasets to investigate the features of coherent structures that were generated over the patches upstream and passed by our site in the unstable ASL, the near-neutral ASL, and the SIBL. We use an objective detection technique and the conditional average method that is developed based on the wavelet analysis. Our data reveal some consistencies and inconsistencies in the characteristics of coherent structures as compared with previous studies. Ramp-like structures and sweep–ejection cycles under the daytime SIBL have similar patterns to those under the nocturnal stable ASL. However, some features (i.e., intermittence) are different from those under the nocturnal stable ASL. Under the three stratifications, thermal and mechanical factors in the ASL perform differently in affecting the ramp intensity for different quantities (i.e., velocity components, temperature, and specific humidity), leading to coherent structures that modulate turbulence flow and alter turbulent transfer differently. It is also found that coherent structures contribute about 10–20% to the total fluxes in our case with different flux contributions under three stratifications and with higher transporting efficiency in sensible heat flux than latent heat and momentum fluxes.