scholarly journals Development of a Nationwide, Low-Level Wind Shear Mosaic in France

2013 ◽  
Vol 28 (5) ◽  
pp. 1241-1260 ◽  
Author(s):  
Clotilde Augros ◽  
Pierre Tabary ◽  
Adrien Anquez ◽  
Jean-Marc Moisselin ◽  
Pascal Brovelli ◽  
...  
Keyword(s):  
Wind Shear ◽  
Propagation Speed ◽  
Horizontal Wind ◽  
Small Scale ◽  
Wind Gust ◽  
Density Currents ◽  
Use Of Data ◽  
Low Levels ◽  
Cell Propagation ◽  
Convective Cells

Abstract An algorithm for the detection of horizontal wind shear at low levels was developed. The algorithm makes use of data collected by all radars from the Application Radar à la Météorologie Infra-Synoptique (ARAMIS) operational network, in order to build a complete mosaic of wind shear over metropolitan France. The product provides an estimation of the maximum horizontal wind shear detected in the low levels, between 0 and 2 km AGL. Examination of the wind shear mosaic for different cases shows that the product is able to retrieve small-scale wind shear signatures that can be linked to either convergence lines ahead of convective cells, which are indicative of gust fronts, or strong convergence areas inside intense cells. A statistical evaluation of the wind shear mosaic was performed, by comparing horizontal wind shear observed inside the area defined by convective objects with wind gusts recorded along their trajectory by weather stations. A link between those different observations was clearly established. Therefore, the use of wind shear for wind gust prediction was tested in combination with other parameters: an estimation of the energetic potential of density currents, the cell surface with reflectivity over 51 dBZ, relative helicity, and cell propagation speed. Different wind gust warning rules were tested on 468 convection nowcasting objects (CONOs). The results clearly highlighted the benefits of using wind shear for wind gust estimation, and also demonstrated the improvement in forecasting skill when combining different parameters. The wind shear mosaic will be produced operationally before the end of 2013 and will be used to improve wind gust warnings provided to end users.

scholarly journals Extreme Low-Level Updrafts and Wind Speeds Measured by Dropsondes in Tropical Cyclones

2016 ◽  
Vol 144 (6) ◽  
pp. 2177-2204 ◽  
Author(s):  
Daniel P. Stern ◽  
George H. Bryan ◽  
Sim D. Aberson
Keyword(s):  
Tropical Cyclones ◽  
Close Association ◽  
Vertical Wind Shear ◽  
Horizontal Wind ◽  
Small Scale ◽  
Vertical Acceleration ◽  
Low Level ◽  
Wind Speeds ◽  
Primary Mechanism ◽  
Low Levels

Abstract Previous studies have found surprisingly strong vertical motions in low levels of some tropical cyclones. In this study, all available dropsondes (12 000) within tropical cyclones during 1997–2013 are examined, in order to create a dataset of the most extreme updrafts (10 m s−1; 169 sondes) and wind speeds (90 m s−1; 64 sondes). It is shown that extreme low-level (0–3 km) updrafts are ubiquitous within intense (category 4 and 5) tropical cyclones, and that few such updrafts have been observed within weaker storms. These extreme updrafts, which are almost exclusively found within the eyewall just inward of the radius of maximum winds, sometimes occur in close association with extreme horizontal wind speeds. Consistent with previous studies, it is suggested that both the extremes in vertical velocity and wind speed are associated with small-scale (1 km) vortices that exist along the eye–eyewall interface. As a substantial number of updrafts are found within a kilometer of the surface, it can be shown that it is implausible for buoyancy to be the primary mechanism for vertical acceleration. Additionally, the azimuthal distribution of both the extreme updrafts and wind speeds is strongly associated with the orientation of the environmental vertical wind shear.

scholarly journals Wind shear over the Nice Côte d'Azur airport: case studies

2013 ◽  
Vol 13 (9) ◽  
pp. 2223-2238 ◽  
Author(s):  
A. Boilley ◽  
J.-F. Mahfouf
Keyword(s):  
Numerical Simulation ◽  
Numerical Model ◽  
Numerical Simulations ◽  
Wind Shear ◽  
Horizontal Wind ◽  
Wind Profiler ◽  
Measurement Campaign ◽  
Wind Lidar ◽  
Real Time Applications ◽  
Wind Shears

Abstract. The Nice Côte d'Azur international airport is subject to horizontal low-level wind shears. Detecting and predicting these hazards is a major concern for aircraft security. A measurement campaign took place over the Nice airport in 2009 including 4 anemometers, 1 wind lidar and 1 wind profiler. Two wind shear events were observed during this measurement campaign. Numerical simulations were carried out with Meso-NH in a configuration compatible with near-real time applications to determine the ability of the numerical model to predict these events and to study the meteorological situations generating an horizontal wind shear. A comparison between numerical simulation and the observation dataset is conducted in this paper.

Observations of Small-Scale Turbulence and Energy Dissipation Rates in the Cloudy Boundary Layer

2006 ◽  
Vol 63 (5) ◽  
pp. 1451-1466 ◽  
Author(s):  
Holger Siebert ◽  
Katrin Lehmann ◽  
Manfred Wendisch
Keyword(s):  
Boundary Layer ◽  
Energy Dissipation ◽  
Wind Velocity ◽  
Turbulence Theory ◽  
Horizontal Wind ◽  
Inertial Subrange ◽  
Intermittent Flow ◽  
Small Scale ◽  
Dissipation Rates ◽  
Wide Range

Abstract Tethered balloon–borne measurements with a resolution in the order of 10 cm in a cloudy boundary layer are presented. Two examples sampled under different conditions concerning the clouds' stage of life are discussed. The hypothesis tested here is that basic ideas of classical turbulence theory in boundary layer clouds are valid even to the decimeter scale. Power spectral densities S( f ) of air temperature, liquid water content, and wind velocity components show an inertial subrange behavior down to ≈20 cm. The mean energy dissipation rates are ∼10−3 m2 s−3 for both datasets. Estimated Taylor Reynolds numbers (Reλ) are ∼104, which indicates the turbulence is fully developed. The ratios between longitudinal and transversal S( f ) converge to a value close to 4/3, which is predicted by classical turbulence theory for local isotropic conditions. Probability density functions (PDFs) of wind velocity increments Δu are derived. The PDFs show significant deviations from a Gaussian distribution with longer tails typical for an intermittent flow. Local energy dissipation rates ɛτ are derived from subsequences with a duration of τ = 1 s. With a mean horizontal wind velocity of 8 m s−1, τ corresponds to a spatial scale of 8 m. The PDFs of ɛτ can be well approximated with a lognormal distribution that agrees with classical theory. Maximum values of ɛτ ≈ 10−1 m2 s−3 are found in the analyzed clouds. The consequences of this wide range of ɛτ values for particle–turbulence interaction are discussed.

scholarly journals Low-Level Wind Shear Identification along the Glide Path at BCIA by the Pulsed Coherent Doppler Lidar

Atmosphere ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 50
Author(s):  
Hongwei Zhang ◽  
Xiaoying Liu ◽  
Qichao Wang ◽  
Jianjun Zhang ◽  
Zhiqiang He ◽  
...  
Keyword(s):  
Wind Shear ◽  
Vertical Direction ◽  
Small Scale ◽  
Observation Data ◽  
Doppler Lidar ◽  
Low Level ◽  
Glide Path ◽  
Coherent Doppler Lidar ◽  
Scanning Strategies ◽  
Meteorological Phenomenon

Low-level wind shear is usually to be a rapidly changing meteorological phenomenon that cannot be ignored in aviation security service by affecting the air speed of landing and take-off aircrafts. The lidar team in Ocean University of China (OUC) carried out the long term particular researches on the low-level wind shear identification and regional wind shear inducement search at Beijing Capital International Airport (BCIA) from 2015 to 2020 by operating several pulsed coherent Doppler lidar (PCDL) systems. On account of the improved glide path scanning strategy and virtual multiple wind anemometers based on the rang height indicator (RHI) modes, the small-scale meteorological phenomenon along the glide path and/or runway center line direction can be captured. In this paper, the device configuration, scanning strategies, and results of the observation data are proposed. The algorithms to identify the low-level wind shear based on the reconstructed headwind profiles data have been tested and proved based on the lidar data obtained from December 2018 to January 2019. High spatial resolution observation data at vertical direction are utilized to study the regional wind shear inducement at the 36L end of BCIA under strong northwest wind conditions.

scholarly journals Resonance in Optimal Perturbation Evolution. Part II: Effects of a Nonzero Mean PV Gradient

2007 ◽  
Vol 64 (3) ◽  
pp. 695-710 ◽  
Author(s):  
H. de Vries ◽  
J. D. Opsteegh
Keyword(s):  
Potential Vorticity ◽  
Propagation Speed ◽  
Building Blocks ◽  
Joint Effect ◽  
Optimal Perturbation ◽  
Orr Mechanism ◽  
Nonzero Mean ◽  
Low Levels ◽  
Pv Gradient

Abstract Optimal perturbations are constructed for a two-layer β-plane extension of the Eady model. The surface and interior dynamics is interpreted using the concept of potential vorticity building blocks (PVBs), which are zonally wavelike, vertically confined sheets of quasigeostrophic potential vorticity. The results are compared with the Charney model and with the two-layer Eady model without β. The authors focus particularly on the role of the different growth mechanisms in the optimal perturbation evolution. The optimal perturbations are constructed allowing only one PVB, three PVBs, and finally a discrete equivalent of a continuum of PVBs to be present initially. On the f plane only the PVB at the surface and at the tropopause can be amplified. In the presence of β, however, PVBs influence each other’s growth and propagation at all levels. Compared to the two-layer f-plane model, the inclusion of β slightly reduces the surface growth and propagation speed of all optimal perturbations. Responsible for the reduction are the interior PVBs, which are excited by the initial PVB after initialization. Their joint effect is almost as strong as the effect from the excited tropopause PVB, which is also negative at the surface. If the optimal perturbation is composed of more than one PVB, the Orr mechanism dominates the initial amplification in the entire troposphere. At low levels, the interaction between the surface PVB and the interior tropospheric PVBs (in particular those near the critical level) takes over after about half a day, whereas the interaction between the tropopause PVB and the interior PVBs is responsible for the main amplification in the upper troposphere. In all cases in which more than one PVB is used, the growing normal mode configuration is not reached at optimization time.

scholarly journals Characteristics of Large-Scale Orographic Precipitation in a Linear Perspective

2011 ◽  
Vol 12 (1) ◽  
pp. 27-44 ◽  
Author(s):  
Michael Kunz
Keyword(s):  
Time Scales ◽  
Characteristic Time ◽  
Large Scale ◽  
Linear Perspective ◽  
Horizontal Wind ◽  
Small Scale ◽  
Orographic Precipitation ◽  
Observation Data ◽  
Horizontal Wind Speed ◽  
Precipitation Patterns

Abstract Simulations of orographic precipitation over the low mountain ranges of southwestern Germany and eastern France with two different physics-based linear precipitation models are presented. Both models are based on 3D airflow dynamics from linear theory and consider advection of condensed water and leeside drying. Sensitivity studies for idealized conditions and a real case study show that the amount and spatial distribution of orographic precipitation is strongly controlled by characteristic time scales for cloud and hydrometeor advection and background precipitation due to large-scale lifting. These parameters are estimated by adjusting the model results on a 2.5-km grid to observed precipitation patterns for a sample of 40 representative orography-dominated stratiform events (24 h) during a calibration period (1971–80). In general, the best results in terms of lowest rmse and bias are obtained for characteristic time scales of 1600 s and background precipitation of 0.4 mm h−1. Model simulations of a sample of 84 events during an application period (1981–2000) with fixed parameters demonstrate that both models are able to reproduce quantitatively precipitation patterns obtained from observations and reanalyses from a numerical model [Consortium for Small-scale Modeling (COSMO)]. Combining model results with observation data shows that heavy precipitations over mountains are restricted to situations with strong atmospheric forcings in terms of synoptic-scale lifting, horizontal wind speed, and moisture content.

scholarly journals Modeling and simulating the spatial spread of an epidemic through multiscale kinetic transport equations

2021 ◽  
pp. 1-39
Author(s):  
Walter Boscheri ◽  
Giacomo Dimarco ◽  
Lorenzo Pareschi
Keyword(s):  
Large Scale ◽  
Scaling Limit ◽  
Propagation Speed ◽  
Multiscale Model ◽  
Transport Equations ◽  
Small Scale ◽  
Spatial Spread ◽  
Model Interpretation ◽  
Mass Migration ◽  
Migration Dynamics

In this paper, we propose a novel space-dependent multiscale model for the spread of infectious diseases in a two-dimensional spatial context on realistic geographical scenarios. The model couples a system of kinetic transport equations describing a population of commuters moving on a large scale (extra-urban) with a system of diffusion equations characterizing the non-commuting population acting over a small scale (urban). The modeling approach permits to avoid unrealistic effects of traditional diffusion models in epidemiology, like infinite propagation speed on large scales and mass migration dynamics. A construction based on the transport formalism of kinetic theory allows to give a clear model interpretation to the interactions between infected and susceptible in compartmental space-dependent models. In addition, in a suitable scaling limit, our approach permits to couple the two populations through a consistent diffusion model acting at the urban scale. A discretization of the system based on finite volumes on unstructured grids, combined with an asymptotic preserving method in time, shows that the model is able to describe correctly the main features of the spatial expansion of an epidemic. An application to the initial spread of COVID-19 is finally presented.

scholarly journals Gravity wave amplitudes and momentum fluxes inferred from OH airglow intensities and meteor radar winds during SpreadFEx

2009 ◽  
Vol 27 (6) ◽  
pp. 2361-2369 ◽  
Author(s):  
F. Vargas ◽  
D. Gobbi ◽  
H. Takahashi ◽  
L. M. Lima
Keyword(s):  
Gravity Waves ◽  
Horizontal Wind ◽  
Small Scale ◽  
Meteor Radar ◽  
Plasma Bubble ◽  
Spatial And Temporal Scales ◽  
Analysis Technique ◽  
Momentum Fluxes ◽  
Different Types ◽  
Wave Directionality

Abstract. We show in this report the momentum flux content input in the mesosphere due to relatively fast and small scale gravity waves (GWs) observed through OH airglow images. The acquisition of OH NIR images was carried out in Brazil at Brasilia (14.8° S, 47.6° W) and Cariri (7.4° S, 36.5° W) from September 2005 to November 2005 during the SpreadFEx Campaign. Horizontal wind information from meteor radar was available in Cariri only. Our findings showed strong wave activity in both sites, mainly in Cariri. High wave directionality was also observed in both sites during SpreadFEx, which have been observed by other investigators using different analysis' techniques and different types of data during the campaign. We discuss also the possibility of plasma bubble seeding by gravity waves presenting spatial and temporal scales estimated with our novel analysis technique during the SpreadFEx campaign.

scholarly journals Preliminary results from the FARCE 2015 campaign: multidisciplinary study of the forest–gas–aerosol–cloud system on the tropical island of La Réunion

2019 ◽  
Vol 19 (16) ◽  
pp. 10591-10618 ◽  
Author(s):  
Valentin Duflot ◽  
Pierre Tulet ◽  
Olivier Flores ◽  
Christelle Barthe ◽  
Aurélie Colomb ◽  
...  
Keyword(s):  
Wind Shear ◽  
Forest Cover ◽  
Horizontal Resolution ◽  
Cloud System ◽  
Horizontal Wind ◽  
La Réunion ◽  
Aerosol Formation ◽  
Mountain Slope ◽  
Tropical Island ◽  
Aerosol Cloud

Abstract. The Forests gAses aeRosols Clouds Exploratory (FARCE) campaign was conducted in March–April 2015 on the tropical island of La Réunion. For the first time, several scientific teams from different disciplines collaborated to provide reference measurements and characterization of La Réunion vegetation, volatile organic compounds (VOCs), biogenic VOCs (BVOCs), (bio)aerosols and composition of clouds, with a strong focus on the Maïdo mountain slope area. The main observations obtained during this 2-month intensive field campaign are summarized. They include characterizations of forest structure, concentrations of VOCs and precursors emitted by forests, aerosol loading and optical properties in the planetary boundary layer (PBL), formation of new particles by nucleation of gas-phase precursors, ice-nucleating particles concentrations, and biological loading in both cloud-free and cloudy conditions. Simulations and measurements confirm that the Maïdo Observatory lies within the PBL from late morning to late evening and that, when in the PBL, the main primary sources impacting the Maïdo Observatory are of marine origin via the Indian Ocean and of biogenic origin through the dense forest cover. They also show that (i) the marine source prevails less and less while reaching the observatory; (ii) when in the PBL, depending on the localization of a horizontal wind shear, the Maïdo Observatory can be affected by air masses coming directly from the ocean and passing over the Maïdo mountain slope, or coming from inland; (iii) bio-aerosols can be observed in both cloud-free and cloudy conditions at the Maïdo Observatory; (iv) BVOC emissions by the forest covering the Maïdo mountain slope can be transported upslope within clouds and are a potential cause of secondary organic aerosol formation in the aqueous phase at the Maïdo Observatory; and (v) the simulation of dynamics parameters, emitted BVOCs and cloud life cycle in the Meso-NH model are realistic, and more advanced Meso-NH simulations should use an increased horizontal resolution (100 m) to better take into account the orography and improve the simulation of the wind shear front zone within which lies the Maïdo Observatory. Using various observations and simulations, this work draws up an inventory of the in situ studies that could be performed in La Réunion and at the Maïdo Observatory. It also aims to develop scientific collaborations and to support future scientific projects in order to better understand the forest–gas–aerosol–cloud system in an insular tropical environment.

Distribution Patterns of Escherichia coli O157:H7 in Ground Beef Produced by a Laboratory-Scale Grinder†

2002 ◽  
Vol 65 (12) ◽  
pp. 1894-1902 ◽  
Author(s):  
ROLANDO A. FLORES ◽  
MARK L. TAMPLIN
Keyword(s):  
Escherichia Coli ◽  
Ground Beef ◽  
Distribution Patterns ◽  
Small Scale ◽  
Escherichia Coli O157 ◽  
Inoculum Level ◽  
E Coli ◽  
Specific Distribution ◽  
Low Levels ◽  
G Prior

This study determined the distribution patterns of Escherichia coli O157:H7 in ground beef when a contaminated beef trim was introduced into a batch of uncontaminated beef trims prior to grinding in a small-scale laboratory grinder. A beef trim (15.3 ± 2 g) was inoculated with a rifampicin-resistant strain of E. coli O157:H7 (E. coli O157:H7rif) and introduced into a stream of noncontaminated beef (322 ± 33 g) prior to grinding. Seven inoculum levels (6, 5, and 4 total log CFU [high]; and 3, 2, 1, and 0 total log CFU [low]) were studied in triplicate. E. coli O157:H7rif was not detected in 3.1 to 43% of the ground beef inoculated with the high levels or in 3.4 to 96.9% of the ground beef inoculated with the low levels. For all inoculum levels studied, the five ground beef fractions (each 7.8 ± 0.6 g) with the highest pathogen levels accounted for 59 to 100% of the total pathogens detected. For all inoculum levels, there was a linear relationship between the quantity of ground beef containing E. coli O157:H7rif and the inoculum level. The quantity of E. coli O157:H7rif in the beef remaining in the grinder was proportional to the inoculum level and was related to the location in the grinder. Different components of the grinder accumulated E. coli O157:H7rif in different quantities, with the most significant accumulation being in the nut (collar) that attaches the die to the blade. This study determined specific distribution patterns of E. coli O157:H7rif after the grinding of a contaminated beef trim along with uncontaminated trims, and the results indicate that the grinding operation should be regarded as a means of distribution of microbial contamination in risk analyses of ground beef operations.

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