Estimating the diffusive heat flux across a stable interface forced by convective motions

Original article can be found at: http://www.nonlin-processes-geophys.net/volumes_and_issues.html Copyright Author(s) 2010. This work is distributed under the Creative Commons Attribution 3.0 License.Entrainment at the top of the convectively-driven boundary layer (CBL) is revisited using data from a high-resolution large-eddy simulation (LES). In the range of values of the bulk Richardson number RiB studied here (about 15–25), the entrainment process is mainly driven by the scouring of the interfacial layer (IL) by convective cells. We estimate the length and time scales associated with these convective cells by computing one-dimensional wavenumber and frequency kinetic energy spectra. Using a Taylor assumption, based upon transport by the convective cells, we show that the frequency and wavenumber spectra follow the Kolmogorov law in the inertial range, with the multiplicative constant being in good agreement with previous measurements in the atmosphere. We next focus on the heat flux at the top of the CBL, , which is parameterized in classical closure models for the entrainment rate we at the interface. We show that can be computed exactly using the method proposed by Winters et al. (1995), from which the values of a turbulent diffusivity across the IL can be inferred. These values are recovered by tracking particles within the IL using a Lagrangian stochastic model coupled with the LES. The relative difference between the Eulerian and Lagrangian values of is found to be lower than 10%. A simple expression of we as a function of is also proposed. Our results are finally used to assess the validity of the classical "first-order'' model for we. We find that, when RiB is varied, the values for we derived from the "first-order'' model with the exact computation of agree to better than 10% with those computed directly from the LES (using its definition). The simple expression we propose appears to provide a reliable estimate of we for the largest values of RiB only.Peer reviewe

Drivers of severe air pollution events in a deep valley during wintertime: a case study from the Arve river valley, France

© 2020 Elsevier Ltd. All rights reserved. This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence (http://creativecommons.org/licenses/by-nc-nd/4.0/).The Arve river valley airshed in the French Alps experiences particularly severe air pollution during wintertime stable atmospheric conditions associated with persistent cold-air pools. PM10 data recorded in the region indicate that the urbanised area of the central basin-shape section of the valley is generally the most polluted, with a harmful impact on the health of inhabitants. In the present work, we examine the air pollution transport potential of the Arve river valley airshed using results from high-resolution numerical simulations of a cold-air pool documented as part of the Passy-2015 field campaign. Passive tracers were used to model PM10 with emissions provided by a detailed inventory developed by the local air-quality agency. The observed differential in PM10 levels between valley sections was well captured by the numerical model and could not be explained solely by the differential in emissions. The stagnation, recirculation and ventilation potential of the airshed was evaluated spatially and temporally using integral quantities. The analysis indicated that the central basin-shape section of the valley is poorly ventilated and hence air pollution there would originate mostly from local emission sources. This stagnation zone appears to be almost decoupled from the rest of the airshed. The airshed was decomposed in separate valley sections so as to quantify the fate of the pollutants emitted within each section. Air pollution apportioned according to the contribution of emissions from the different valley sections shows that indeed the central basin-shape section is dominated by local sources. The situation was found more complex in the valley sections further downstream, where the contribution from the sum of the non-local sources can be as large as that from local sources. This study allows to identify the origin of the strong pollution in the Arve river valley, through the link between the local topography, emission sources and pollutant transport.Peer reviewedFinal Accepted Versio

The baroclinic secondary instability of the two-dimensional shear layer

The focus of this study is on the numerical investigation of two-dimensional, isovolume, high Reynolds and Froude numbers, variable-density mixing layers. Lagrangian simulations, of both the temporal and the spatial models, are performed. They reveal the breaking-up of the strained vorticity and density-gradient braids, connecting two neighboring primary structures. The secondary instability arises where the vorticity has been intensified by the baroclinic torque. A simplified model of the braid of the variable-density mixing layer, consisting of a strained vorticity and density-gradient filament, is analyzed. It is concluded that the physical mechanism responsible for the secondary instability is the forcing of the vorticity field by the baroclinic torque, itself sensitive to perturbations. This mechanism suggests a rapid route to turbulence for the variable-density mixing layer

Mixing efficiency and entrainment at an atmospheric inversion layer

The context is that of the convectively-driven atmospheric boundary layer capped by an inversion layer (i.e. a stably-stratified interface) and we focus on the regime of equilibrium entrainment, i.e. when the boundary-layer evolution is in a quasi steady state. The parameterization of the entrainment process across the interfacial layer is usually based on the entrainment ratio, namely the ratio of the negative of the heat flux at the interface to the heat flux at the ground surface. Hence the issue is to relate the entrainment ratio to measurable parameters. In this study, we rely on a formulation of convective entrainment in terms of mixing efficiency, which can be computed directly for instance from high-resolution vertical profiles of virtual potential temperature. We discuss the applicability of this parameterization for an explicit treatment of the entrainment process in classical boundary-layer parameterization schemes implemented in meso-scale models

Extended Round Robin Testing program of COST Action TU1404 – lessons learned from the initial experimental phase

The extended round robin testing program (RRT + ) is used in the Working Group 1 of the COST Action TU1404 as a fundamental mechanism: i) to validate advanced, non- standardised experimental techniques for testing cement-based materials and structures, ii) to benchmark different sustainable variations of concrete mixes prepared with mineral admixtures, recycled materials and/or by-products, and iii) to obtain input data for a range of concrete properties which could serve designers and engineers to better predict lifespan, durability, and serviceability of concrete struct ures. With a total of 45 laboratories from Europe, Japan and Canada, performing over 50 test methods on the same concrete mix, it presents one of the most extensive initiatives for joint testing of cement-based materials. The RRT + is divided into two phases: the initial and main experimental phases. During the initial phase, an ordinary concrete mix is prepared using the same constituting materials and following identical preconditioning, preparation, conditioning and test procedures. Even though the framework is identical and potential external causes of deviations are limited, concrete is prepared in different laboratories and some scatter in results can be expected. This paper describes the observations during the initial experimental phase and discusses methods including statistical analysis performed to understand the scatter and results obtainedEDF, France, CEVA Logistics, Austria and Germany, OeBB Infra, Austria, Staten Vegvesen, Norway and Schleibinger Gerate, German

A Double‐Blind Comparison of Orally Administered Ciramadol and Codeine for Relief of Postoperative Pain

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97154/1/j.1552-4604.1985.tb02882.x.pd

Caractérisation des mouvements oscillants dans l'atmosphère stable d'une vallée encaissée

In a valley sheltered from strong synoptic effects, the dynamics of the valley atmosphere at night are dominated by katabatic winds. In a stably stratified atmosphere, these winds undergo temporal oscillations, whose frequency is given by Nsinθ for an infinitely long slope of constant slope angle θ, N being the buoyancy frequency. Such an unsteady flow in a stably stratified atmosphere may also generate internal gravity waves (IGWs)

Comparative Studies on Naturally Occurring Antikeratin Antibodies in Human Sera

Comparative studies on the specificity of the so-called antiepidermal antibodies (Abs) found in human sera were performed by immunoblotting, enzyme-linked immunosorbent assay (ELISA), and immunoelectron microscopy (LEM). After a screening test by indirect immunofluorescence (IF), sera obtained from patients with various diseases and controls could be classified in 5 different groups according to the IF patterns on the epidermis: sera reactive with: (1) the stratum corneum (SC); (2) the upper layer (U-Cyt); (3) the whole epidermis (G-Cyt); (4) basal cells (B-Cyt); and (5) negative ones. By immunoblotting, all the 23 IF-positive sera were found to bind to one or more keratin bands, and did not show any reactivity with epidermal Nonidet P-40 soluble proteins. SC-Abs were mainly directed against a 67 kD Keratin band, whereas U-Cyt- and G-Cyt-Abs bound to both 58-56 kD and 67-63 kD keratins. B-Cyt-Abs reacted strongly with 63 kD keratins and slightly with a 50 kD band. Antikeratin Abs were detected by immunoblotting even in the IF-negative sera. The ELISA study showed that sera with high IF titers contained high levels of antikeratin Abs. In the IEM study using sera containing U-Cyt- or B-Cyt-Abs, 2 distinct reaction patterns were demonstrated: U-Cyt-Abs stained tonofilaments of suprabasal keratinocytes, while B-Cyt- Abs characteristically reacted with those of basal cells. Moreover, SC-, U-Cyt-, and G-Cyt-Abs were absorbed out by insoluble epidermal proteins, and B-Cyt-Abs were decreased in titer after the absorption test. The present study provides strong evidence that most, though not all, human antiepidermal Abs are directed against different keratin polypeptides, and that antikeratin Abs commonly occur in almost all human sera