Vertical Scale Research Articles

Species turnover in ant assemblages is greater horizontally than vertically in the world's tallest tropical forest.

Abiotic and biotic factors structure species assembly in ecosystems both horizontally and vertically. However, the way community composition changes along comparable horizontal and vertical distances in complex three‐dimensional habitats, and the factors driving these patterns, remains poorly understood. By sampling ant assemblages at comparable vertical and horizontal spatial scales in a tropical rainforest, we tested hypotheses that predicted differences in vertical and horizontal turnover explained by different drivers in vertical and horizontal space. These drivers included environmental filtering, such as microclimate (temperature, humidity, and photosynthetic photon flux density) and microhabitat connectivity (leaf area), which are structured differently across vertical and horizontal space. We found that both ant abundance and richness decreased significantly with increasing vertical height. Although the dissimilarity between ant assemblages increased with vertical distance, indicating a clear distance‐decay pattern, the dissimilarity was higher horizontally where it appeared independent of distance. The pronounced horizontal and vertical structuring of ant assemblages across short distances is likely explained by a combination of microclimate and microhabitat connectivity. Our results demonstrate the importance of considering three‐dimensional spatial variation in local assemblages and reveal how highly diverse communities can be supported by complex habitats.

Evaluation of basal melting parameterisations using in situ ocean and melting observations from the Amery Ice Shelf, East Antarctica

Abstract. Ocean-driven melting of Antarctic ice shelves is causing accelerating loss of grounded ice from the Antarctic continent. However, the ocean processes governing ice shelf melting are not well understood, contributing to uncertainty in projections of Antarctica's contribution to sea level. Here, we analyse oceanographic data and in situ measurements of ice shelf melt collected from an instrumented mooring beneath the centre of the Amery Ice Shelf, East Antarctica. This is the first direct measurement of basal melting from the Amery Ice Shelf and was made through the novel application of an upward-facing acoustic Doppler current profiler (ADCP). ADCP data were also used to map a region of the ice base, revealing a steep topographic feature or “scarp” in the ice with vertical and horizontal scales of ∼ 20 and ∼ 40 m, respectively. The annually averaged ADCP-derived melt rate of 0.51 ± 0.18 m yr−1 is consistent with previous modelling results and glaciological estimates. There is significant seasonal variation around the mean melt rate, with a 40 % increase in melting in May and a 60 % decrease in September. Melting is driven by temperatures ∼ 0.2 ∘C above the local freezing point and background and tidal currents, which have typical speeds of 3.0 and 10.0 cm s−1, respectively. We use the coincident measurements of ice shelf melt and oceanographic forcing to evaluate parameterisations of ice–ocean interactions and find that parameterisations in which there is an explicit dependence of the melt rate on current speed beneath the ice tend to overestimate the local melt rate at AM06 by between 200 % and 400 %, depending on the choice of drag coefficient. A convective parameterisation in which melting is a function of the slope of the ice base is also evaluated and is shown to underpredict melting by 20 % at this site. By combining these new estimates with available observations from other ice shelves, we show that the commonly used current speed-dependent parameterisation overestimates melting at all but the coldest and most energetic cavity conditions.

Genetic Relationships of Puccinia striiformis f. sp. tritici in Southwestern and Northwestern China.

ABSTRACTWheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a crucial disease for wheat worldwide and constantly threatens wheat production in southwestern and northwestern China, where the environment is a good fit for Pst oversummering and overwintering. However, the underlying genetic dynamics of spring epidemic Pst populations across large areas of continuous planting in the southwestern and northwestern regions are poorly understood. A total of 2,103 Pst isolates were sampled in the spring of 2019 from the two agroecosystems and grouped into three horizontal spatial scales (countywide, provincial, and regional subpopulations) and two vertical spatial scales that consisted of elevational and geomorphic subpopulations. A total of 776 multilocus genotypes were identified, with the highest genetic diversity found in the northern and Sichuan populations, particularly in the Ningxia and Sichuan Basins, while the lowest genetic diversity was found in the Yunnan and Guizhou populations. Multivariate discriminant analysis of principal components (DAPC) and STRUCTURE (STRUCTURE 2.3.4) analyses revealed variation in the genotypic compositions of the molecular groups on horizontal and vertical dimensions from north to south or vice versa and from low to high or vice versa, respectively. The regional neighbor-joining tree revealed three large spatial structures consisting of the southwestern, the northwestern, and the Xinjiang regions, while the Tibetan population connected the southwestern and northwestern regions. The isolates of the Sichuan Basin were scattered over the four quartiles by principal coordinate analysis, which indicated frequent genotype interchange with others. Greater genetic differentiation was observed between the southwestern and northwestern regions. Linkage equilibrium (P ≥ 0.05) was detected on different spatial scales, suggesting that Pst populations are using sexual reproduction or mixed reproduction (sexual and clonal reproduction) in southwestern and northwestern China.IMPORTANCE Understanding the epidemiology and population genetics of plant pathogens is crucial to formulate efficient predictions of disease outbreaks and achieve sustainable integrated disease management, especially for pathogens with migratory capability. Here, this study covers the genetic homogeneity and heterogeneity of different geographical Pst populations on broad to fine spatial scales from the key epidemic regions of the two agroecosystems in China, where wheat stripe rust occurs annually. We provide knowledge of the population genetics of Pst and reveal that, for instance, there is greater genetic diversity in northwestern China, there are close genetic relationships between Yunnan and Guizhou and between Gansu-Ningxia and Qinghai, and there are effects of altitude on genetic compositions, etc. All of these findings clarify the genetic relationships and expand the insights into the population dynamics and evolutionary mechanisms of Pst in southwestern and northwestern China, providing a theoretical basis for achieving sustainable control of wheat stripe rust in key epidemic regions.

On the Hydrostatic Approximation of Compressible Anisotropic Navier–Stokes Equations–Rigorous Justification

In this work, we derive the hydrostatic approximation by taking the small aspect ratio limit to the Navier–Stokes equations. The aspect ratio (the ratio of the depth to horizontal width) is a geometrical constraint in the general large scale geophysical motions meaning that the vertical scale is significantly smaller than horizontal. We derive the versatile relative entropy inequality. Applying the versatile relative entropy inequality we gave the rigorous derivation of the limit from the compressible Navier–Stokes equations to the compressible Primitive Equations. This is the first work where the relative entropy inequality was used for proving hydrostatic approximation - the compressible Primitive Equations.

Seabed Observations at the New England Mud Patch: Reflection and Scattering Measurements and Direct Geoacoustic Information

Seabed reflection and scattering measurements were conducted at the New England Mud Patch to better understand the acoustic properties of fine-grained (muddy) sediments. The measurement philosophy and the measurements themselves are summarized. In addition, geoacoustic information accessed directly from the data in the time and frequency domains is presented. The main result is the existence of an angle of intromission. This observation proves that the mud sound speed is less than that of the water and yields a sediment sound speed ratio 0.9865 with outer bounds {0.985 0.989}. Another result is the observation of strong scattered arrivals from within the mud volume at/near normal incidence but not at low grazing angles. These are likely due to anisotropic sediment heterogeneities with a large horizontal to vertical scale. Evidence is also presented for a highly heterogeneous mud–sand horizon with lateral variability down to scales of order meters. Finally, the reflection measurements successfully capture Bragg interference patterns. Their importance is their substantial geoacoustic information content, which can be accessed by several inversion methods.

Asymptotic Standard Errors of IRT Linking Coefficients for the Bifactor Extension of the 3PL Model

The bifactor extension of the three-parameter logistic (B3PL) model has been used in applications of multidimensional item response theory (IRT) such as test equating and vertical scaling. Developing a common multidimensional IRT scale (that is, multidimensional coordinate system) is critical in those applications. Three common-item scale linking methods, the direct least squares (DLS), mean/least squares (MLS), and item response function (IRF) methods, for the B3PL model have been found to be effective in developing a common multidimensional IRT ability scale between two test forms to be linked. In this paper, the asymptotic standard errors (SEs) of IRT linking coefficients estimated by the DLS, MLS, and IRF methods are derived assuming that the B3PL model holds and the asymptotic variance-covariance matrix of item parameter estimates from separate calibrations is available. The delta method is used for the derivations. Computer simulations which investigate the accuracy of the derivations under various conditions are given, showing that the derivations are reasonably accurate when sufficiently large samples are used and that in general the SEs of the IRF method are smaller than those of the DLS and MLS methods. The simulation results also suggest that the SEs of linking coefficient estimates are, approximately, inversely proportional to the square root of the sample size when two test forms are administered to the same number of examinees.

Vertical Scales, Deceleration, and Empirical Benchmarks for Growth

Empirical growth benchmarks, as introduced by Hill, Bloom, Black, and Lipsey (2008), are a well-known way to contextualize effect sizes in education research. Past work on these benchmarks, both positive and negative, has largely avoided confronting the role of vertical scales, yet technical issues with vertical scales trouble the use of such benchmarks. This article introduces vertical scales and outlines their role in the creation of empirical benchmarks for growth. I then outline three strands of recent vertical scale research that call into question the grounds for relying on these benchmarks. I conclude with recommendations for researchers looking to contextualize observed effects of educational interventions without confounding their effects with vertical scaling artifacts.

Spatial-temporal heterogeneity of environmental factors and ecosystem functions in farmland shelterbelt systems in desert oasis ecotones

Farmland shelterbelt system (FSS) in oasis desert ecotones can effectively improve ecosystem services, especially in fragile agricultural areas. However, the spatial-temporal heterogeneity of its ecological effects still needs further clarity, because the interactions are complex and multiple. Understanding this allows us to know the key practical significance of ecological construction and agricultural management. In this study, four typical patterns of FSS (i.e. two lines pattern, TWLP; four lines pattern, FOLP; five lines pattern, FILP; eight lines pattern, EILP) were selected in a desert oasis ecotone in northern China to assess the distributions at vertical (0–100 cm), horizontal (0–3 H) and temporal (May- October) scales of soil properties, vegetation attributes, microclimates and variations of soil moisture storage (SMS) and soil salt contents (C) during the three growing seasons. The results showed that the major difference in soil properties and vegetation attributes of FSSs are the soil particle composition and canopy size, respectively. In FOLP and EILP, the silt contents were 51.6% and 41.5% respectively. The canopy size ranked from the highest to lowest values as follows: FOLP (8.70 m2) > EILP (6.91 m2) > TWLP (4.64 m2) > FILP (4.47 m2). Compared to the control, all patterns of FSSs registered significant effects on microclimate improvement. The FOLP and FILP achieved the same effects as well as EILP, with less spatial costs. Moreover, the variations of SMS and C were mainly different at the vertical scale. As indicated by the Redundancy (RDA) and variation partitioning (VP) analyses, soil properties played a more important role in reserving soil water and controlling soil salinity than vegetation attributes and microclimates, which the independent influence can explain 48.5% of total influence among all factors. Our results provide an efficient theoretical basis for FSS construction and agricultural water management practices.

Towards a Science of Scaling for Urban Climate Action and Governance

AbstractThe scaling of urban climate action and its governance is rapidly becoming a central focus in the urban climate governance literature and policy debates. Building on the broader scaling literature and inspired by related initiatives in other fields, this article calls for the development of a systematic “science of scaling” for urban climate governance. Such a science of scaling may help to give a better understanding of how well-performing urban climate action and its governance can be multiplied, accelerated and broadened (ie horizontal and vertical scaling and scaling out, up and down), and it may help to uncover scaling trajectories towards systemic change in cities (ie deep scaling).

Multiscale physical–chemical analysis of the impact of fracture networks on weathering: Application to nickel redistribution in the formation of Ni-laterite ores, New Caledonia

Supergene processes related to downward water migration and dissolution of primary minerals in the New Caledonian peridotites result in Ni enrichment at the bottom of the lateritic profile near bedrock. However, the combined effects of relief, lateral fluid flow, and complex inherited discontinuity networks filled by serpentine generate a more complex Ni distribution than a simple flat horizon. In surficial environments, fluid flow and mass transfer are not limited to the vertical scale; they can also be related to lateral fluid circulation and local drainage along damage zones in the vicinity of faults. In this study, we present new structural, petrophysical and geochemical data for core samples to shed light on the impact of a fracture network on the alteration and progression of the Ni-enrichment front during weathering. The analysis of element redistribution by XRF mapping coupled with fracture extraction from computed tomography (CT) establishes that the serpentine fracture network comprises sets of sub-orthogonal fractures whose orientations are potentially determined by pre-existing magmatic foliation. The progression of the olivine dissolution front leads to the redistribution and concentration of Ni into the serpentine fracture network as secondary Mg-Ni talc-like phases. The increase in porosity from < 1 % in the bedrock to > 10 % in the saprock is mainly driven by the formation of nanopores. Nanoporosity may control the development of the weathering front and the redistribution of Ni by small-scale diffusion. Structural and geochemical characteristics identified at the sample scale are analogous to those observed on the larger scale of the outcrop and deposit. Scale invariance in the structural organization and geochemical evolution indicates the potential upscaling of the processes involved in the redistribution of Ni.

Способ повышения качества оцифровки графических данных

This paper considers the actual problem of graphical information converting back into raw data format that was used to represent it. This is due to the great scientifi achievements contained in editions from the Soviet period, as well as the intention global publishers from "unfriendly" countries to close access for Russian and Belarusian organisations to scientific publications and technical information databases. As a result, Russian scientists can only have graphical materials in formats similar to PDF documents. This paper considers a fairly simple way of solving this problem when digitising graphs in printed or electronic publications with low resolution and a large picture scale, which does not allow to detail its separate fragments. The procedure for pre-processing the original image in bitmap format is described. In order to improve the numerical data resulting accuracy from the subsequent digitising, a number of features are recommended, which are available in the well-known and most common graphical editors. These functions include changing the color mode of the image, color inversion, sharpening and contrast, linear scaling (vertical and horizontal scaling), and graph line spline approximation. The above operations are accessible to users with the minimum familiarity of graphical editors Microsoft Power Point and Adobe Photoshop. As an developed procedure use example, the results of FRB 160317 signal digitising (a so-called Fast Radio Burst), are presented. The digitising of its graphical image has provided more accurate additional information on signal characteristics not given by publication authors. A visual evaluation of the digitised FRB 160317 signal accuracy by matching it with the original graphical image is presented, which showed a satisfactory match to the original. The numerical data array obtained by digitising the raw graphical material using a pre-processing procedure is becomes available for further analysis. The described way can be used by university teachers both at the initial stages of students teaching to work with images and carry out data analysis, and when preparing teaching materials when organising the educational process using distance learning technologies. The results are applicable at the starting stages of scientifi research in the initial data set formation for dependency analysis in various subject areas, where there are no initial samples refl the results of observation.

A STUDY TO ASSESS ANTHROPOMETRIC PARAMETERS AND SERUM LIPID VARIATIONS IN HIV PATIENTS RECEIVING HAART

Background:- There is evidence that ART is associated with lipodystrophy syndrome, a disturbance of lipid metabolism characterised by insulin resistance, dyslipidaemia and fat maldistribution, usually presenting as visceral abdominal obesity and cervical fat pad accumulation (buffalo hump)1,metabolic bone disease (osteopenia and/or osteoporosis) and lactic acidosis. ART- associated dyslipidaemia is characterized by elevated serum concentrations of total cholesterol, triglycerides, low density lipoprotein 2(LDL-c), very low-density lipoprotein (VLDL), Apo lipoprotein B (apoB) and low levels of high density lipoprotein (HDL-c) constituting an atherogenic lipid profile2. Materials And Methods:- In this study 100 young patients who were attending the Antiretroviral Therapy Plus Centre &amp; Medicine Wards, ACSR GMC, NELLORE were included randomly. Anthropometric Measurement :- Body weights were measured (to the nearest 0.5 kilogram) with the subject standing on a weighing scale after it was adjusted to zero kg. Heights were measured (to the nearest 1.0 centimeter) with the subject standing in an erect position against a vertical scale of portable standiometer and a L-square placed on the head and the head positioned to a level with the inferior margin of the bony orbit. The waist measurements were taken from the middle point between the iliac crest and the last rib as recommended by the WHO. Hip circumference was measured as the maximal circumference over the buttocks. BMIs were then calculated as weight in kilograms divided by the height in meter squared. Results:- The results of the study showed that the Anthropometric parameters on analysis showed a normal range BMI in 59% of patients. Waist-to-hip ratio which have been shown to be better reflector of body fat distribution and is significantly elevated in the HIV-infected patients on HAART. Waist-Hip ratio value analysis showed normal in 18.19% and abnormal in 81.81% of cases. The mean value in males is 0.9578 and in females is 0.9204. This showed a significant correlation to Waist/ hip ratio and the gender. Conclusions:- Significant metabolic and morphological alterations occur in HIV infected patients especially in patients on HAART. The patients on HAART had an elevated Castelli Index I, indicating an increased risk for atherosclerotic cardiovascular disease in this population. Waist-to-hip ratio which are the key indices for assessing body fat distribution were significantly raised in HAART-experienced patients in this study implying that HAART could result to lipodystrophy.

Linking and Comparability across Conditions of Measurement: Established Frameworks and Proposed Updates

AbstractOne result of recent changes in testing is that previously established linking frameworks may not adequately address challenges in current linking situations. Test linking through equating, concordance, vertical scaling or battery scaling may not represent linkings for the scores of tests developed to measure constructs differently for different examinees, or tests that are administered in different modes and data collection designs. This article considers how previously proposed linking frameworks might be updated to address more recent testing situations. The first section summarizes the definitions and frameworks described in previous test linking discussions. Additional sections consider some sources of more disparate approaches to test development and administrations, as well as the implications of these for test linking. Possibilities for reflecting these features in an expanded test linking framework are proposed that encourage limited comparability, such as comparability that is restricted to subgroups or to the conditions of a linking study when a linking is produced, or within, but not across tests or test forms when an empirical linking based on examinee data is not produced. The implications of an updated framework of previously established linking approaches are further described in a final discussion.

Reliability Analysis of Serviceability Limit State for Braced Excavation Considering Multiple Failure Modes in Spatially Variable Soil

High uncertainty is an inherent behavior of geotechnical materials. Nowadays, random field theory is an advanced method to quantify the effect of high uncertainty on geotechnical engineering. This study investigates the effect of spatial variable soil layers on deformations of deep excavation via the random finite element method. A procedure based on PLAXIS 2D software was developed to generate two-dimension random finite element models including multiple variables. Via the K-S test and S-W test, the excavation deformations basically followed lognormal distribution. With the growth of standard deviation of soil properties parameters, the distribution of excavation deformations becomes wider, and the failure probability increases. When the vertical scale of fluctuation ranges from 1 m to 25 m, the distribution of excavation deformations becomes wider. To analyze system reliability, this study proposed a fitted multiple lognormal distribution methods, which was a method with higher efficiency. The results indicated that system reliability was lower than single failure probability and sensitive to design level. The system failure probability will be over-evaluated or under-evaluated if the correlation between excavation responses is ignored. This study provided a novel method to quantify the effect of high uncertainty of soil layer on excavation responses and proposed an efficient method for system reliability analysis, which is meaningful for excavation reliability design.

Reliability Analysis of Safety Assessment of Buildings above Twin Shield Tunnels Based on Random Field Theory

Aiming at the problem of deformation of adjacent masonry structures caused by the surrounding soil disturbance in the construction of twin shield tunnels, taking the spatial variability of soil parameters as the breakthrough point and the surface deformation mode as the basis, a program is compiled to search the position of characteristic points of the settlement curve, and a safety assessment method of masonry buildings above twin tunnels based on the random field theory is obtained. According to the reliability theory, the concept of the potential damage zone is defined. The probability that the maximum tensile strain of the building exceeds the allowable ultimate tensile strain is not less than 5% in the potential damage zone. The assessment method mentioned above, together with the Monte Carlo simulation, is used to evaluate the safety of buildings and the range of potential damage zones induced by twin tunneling with different relative locations and different construction sequences, taking into account configurations and construction sequences of twin tunnels, the scales of fluctuation of elastic modulus of the soil, and the size of the building. The research results show that, in the parallel and overlapping twin tunnels, the randomness of the surface deformation mode caused by construction increases with the decrease of the transverse scales of fluctuation or the increase of the vertical scales of fluctuation. In overlapping and shoulder-mounted twin tunnels, the effect of the construction sequence on the safety of buildings is the opposite. When the overlying tunnel is excavated first in shoulder-mounted condition, the safety of buildings is more excellent. Considering the effect of the spatial variability of parameters, the probability of higher damage levels in the buildings is significantly increased. The greater the scales of fluctuation, the greater the damage probability. The potential damage zones of the buildings will be expanded, and the safety distance of the buildings will be wider than the deterministic analysis result by 1.5∼2.5 m.

Environmental selection dominates over dispersal limitation in shaping bacterial biogeographical patterns across different soil horizons of the Qinghai-Tibet Plateau

Soil microbial biogeographical patterns have been widely explored from horizontal to vertical scales. However, studies of microbial vertical distributions were still limited (e.g., how soil genetic horizons influence microbial distributions). To shed light on this question, we investigated soil bacterial communities across three soil horizons (topsoil: horizon A; midsoil: horizon B; subsoil: horizon C) of 60 soil profiles along a 3500 km transect in the Qinghai-Tibet Plateau. We found that bacterial diversity was highest in the topsoil and lowest in the subsoil, and community composition significantly differed across soil horizons. The network complexity decreased from topsoil to subsoil. There were significant geographical/environmental distance-decay relationships (DDR) in three soil horizons, with a lower slope from topsoil to subsoil due to the decreased environmental heterogeneity. Variation partitioning analysis (VPA) showed that bacterial community variations were explained more by environmental than spatial factors. Although environmental selection processes played a dominant role, null model analysis revealed that deterministic processes (mainly variable selection) decreased with deeper soil horizons, while stochastic processes (mainly dispersal limitation) increased from topsoil to subsoil. These results suggested that microbial biogeographical patterns and community assembly processes were soil horizon dependent. Our study provides new insights into the microbial vertical distributions in large-scale alpine regions and highlights the vital role of soil genetic horizons in affecting microbial community assembly, which has implications for understanding the pedogenetic process and microbial responses to extreme environment under climate change.

Seasonal variability of the potential vorticity in the Lofoten vortex

The anticyclonic quasi-permanent Lofoten vortex is a strong dynamic formation in the center of the Lofoten Basin in the Norwegian Sea. We used the oceanic reanalysis data GLORYS12V1. We analyzed a seasonal distribution of the relative and potential vorticity, as well as the orbital velocities and the potential density in the Lofoten vortex. The main points of the potential vorticity calculating are considered. The values of the Lofoten vortex volume, the horizontal dimension (the diameter) as well as the vertical scale for the period from 2000 to 2019 are obtained, as well as the method for estimates of these characteristics is described in detail. It was shown that the intensification of the vortex occurs in the summer, and its relaxation -- in the winter.

Shear Instability and Turbulent Mixing in the Stratified Shear Flow Behind a Topographic Ridge at High Reynolds Number

Observations on the lee of a topographic ridge show that the turbulence kinetic energy (TKE) dissipation rate due to shear instabilities is three orders of magnitude higher than the typical value in the open ocean. Laboratory-scale studies at low Reynolds number suggest that high turbulent dissipation occurs primarily within the core region of shear instabilities. However, field-scale studies indicate that high turbulence is mainly populated along the braids of shear instabilities. In this study, a high-resolution, resolving the Ozmidov-scale, non-hydrostatic model with Large Eddy Simulation (LES) turbulent closure is applied to investigate dominant mechanisms that control the spatial and temporal scales of shear instabilities and resulting mixing in stratified shear flow at high Reynolds number. The simulated density variance dissipation rate is elevated in the cusp-like bands of shear instabilities with a specific period, consistent with the acoustic backscatter taken by shipboard echo sounder. The vertical length scale of each cusp-like band is nearly half of the vertical length scale of the internal lee wave. However, it is consistent with instabilities originating from a shear layer based on linear stability theory. The model results indicate that the length scale and/or the period of shear instabilities are the key parameters to the mixing enhancement that increases with lateral Froude number FrL, i.e. stronger shear and/or steeper ridge.

Effect of Device Scaling on Electron Mobility in Nanoscale GaN HEMTs with Polarization Charge Modulation.

We have experimentally investigated the impact of vertical and lateral scaling on low-field electron mobility (µ) in InAlN/GaN high-electron-mobility transistors (HEMTs). It is found that µ reduces as InAlN barrier (TB) and gate length (LG) scale down but increases with the scaled source–drain distance (LSD). Polarization Coulomb Field (PCF) scattering is believed to account for the scaling-dependent electron mobility characteristic. The polarization charge distribution is modulated with the vertical and lateral scaling, resulting in the changes in µ limited by PCF scattering. The mobility characteristic shows that PCF scattering should be considered when devices scale down, which is significant for the device design and performance improvement for RF applications.

Vertical propagation of submeso and coherent structure in a tall and dense amazon forest in different stability conditions. PART II: Coherent structures analysis

Observations of the vertical structure of the turbulent flow in different stability regimes above and within the Amazon Forest at the Amazon Tall Tower Observatory (ATTO) site have been presented in Part I. Here, the influence of stability on the inception and development of coherent structures is investigated. According to the mixing-layer analogy the coherent vortices that dominate the turbulent flows at the canopy-atmosphere interface are generated by hydrodynamical instabilities triggered by an inflection in the vertical profile of the mean wind speed at or near the canopy top. The coherent motions time, Tpeak and separation length scale, Λ, depend on the shear length scale, Ls, close to the canopy top. The present analysis studies the characteristics of Ls, Tpeak and Λ in the five stability regimes defined in Part I.The behaviour of Ls with stability is evaluated and parameterized. Ls increases with decreasing stability, presenting two asymptotes for large unstable and stable stratification and a linear behaviour close to neutral stratification. Coherent structures and their timescale are detected with an original method based on the autocorrelation functions of 5-min subsets of turbulent quantities. The vertical time scale is larger in neutral conditions and decreases for both increasing and decreasing stability. At the canopy top the separation length scale presents a linear dependence on Ls, whose slope is maximum in neutral conditions and decreases departing from neutrality. An original parameterization of the dependence of this slope on h/L, where h is the canopy height and L is the Obukhov length, is shown. Combining the parameterizations, the dependence of the separation length scale is finally presented. Λ has a maximum for slightly unstable conditions, linearly decreases towards neutral and weakly stable stratifications and then it tends to zero for very intense unstable and stable stratifications.