scholarly journals Measurements of Boundary Layer Profiles with In Situ Sensors and Doppler Lidar

2008 ◽  
Vol 25 (8) ◽  
pp. 1328-1340 ◽  
Author(s):  
Rod Frehlich ◽  
Yannick Meillier ◽  
Michael L. Jensen
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Energy Dissipation Rate ◽  
High Rate ◽  
Doppler Lidar ◽  
Stratified Turbulence ◽  
In Situ Sensors ◽  
The Impact ◽  
Turbulence Parameters

Abstract A new in situ measurement system and lidar processing algorithms were developed for improved measurements of boundary layer profiles. The first comparisons of simultaneous Doppler lidar–derived profiles of the key turbulence statistics of the two orthogonal horizontal velocity components (longitudinal and transverse) are presented. The instrument requirements for accurate observations of stably stratified turbulence were determined. A region of stably stratified low turbulence with constant gradients of temperature and velocity was observed above the nocturnal boundary layer using high-rate sensors. The important turbulence parameters were estimated, and turbulence spectra were consistent with new theoretical descriptions of stratified turbulence. The impact of removing the larger-scale velocity features in Doppler lidar estimates of turbulent velocity variance and length scales was investigated. The Doppler lidar–derived estimates of energy dissipation rate ε were found to be insensitive to spatial filtering of the large-scale atmospheric processes. The in situ and lidar-derived profiles were compared for the stable boundary layer in a suburban environment.

scholarly journals Measurements of Boundary Layer Profiles in an Urban Environment

2006 ◽  
Vol 45 (6) ◽  
pp. 821-837 ◽  
Author(s):  
Rod Frehlich ◽  
Yannick Meillier ◽  
Michael L. Jensen ◽  
Ben Balsley ◽  
Robert Sharman
Keyword(s):  
Boundary Layer ◽  
Urban Environment ◽  
Small Scale ◽  
Doppler Lidar ◽  
Stable Boundary Layers ◽  
Low Wind Speed ◽  
Velocity Statistics ◽  
In Situ Sensors ◽  
Scale Turbulence

Abstract Boundary layer profiles of mean temperature, velocity, and small-scale turbulence from in situ sensors, Doppler lidar, sodar, and rawinsondes are intercompared for an urban environment. A new Doppler lidar algorithm is presented to produce high-resolution profiles of small-scale velocity statistics. The lidar-derived profiles are robust and accurate even for challenging conditions such as stable boundary layers with a low-level jet, low turbulence, and low wind speed. Similar results are expected for other locations and convective conditions.

Study on Deformation and Damage of Rock Mass Subject to High In Situ Stress by Using a Elastoplastic Damage Model and Considering the Impact of Weak Planes

2013 ◽  
Vol 838-841 ◽  
pp. 705-709
Author(s):  
Yun Hao Yang ◽  
Ren Kun Wang
Keyword(s):  
Rock Mass ◽  
Large Scale ◽  
Damage Model ◽  
Back Analysis ◽  
In Situ Stress ◽  
Surrounding Rock ◽  
High In Situ Stress ◽  
Underground Caverns ◽  
The Impact

Large scale underground caverns are under construction in high in-situ stress field at Houziyan hydropower station. To investigate deformation and damage of surrounding rock mass, a elastoplastic orthotropic damage model capable of describing induced orthotropic damage and post-peak behavior of hard rock is used, together with a effective approach accounting for the presence of weak planes. Then a displacement based back analysis was conducted by using the measured deformation data from extensometers. The computed displacements are in good agreement with the measured ones at most of measurement points, which confirm the validities of constitutive model and numerical simulation model. The result of simulation shows that damage of surrounding rock mass is mainly dominated by the high in-situ stress rather than the weak planes and heavy damage occur at the cavern shoulders and side walls.

scholarly journals Observations of Turbulence in Free Atmosphere by Balloon-Borne Sensors

Sensors ◽  
2018 ◽  
Vol 18 (10) ◽  
pp. 3273
Author(s):  
Lesong Zhou ◽  
Zheng Sheng ◽  
Qixiang Liao
Keyword(s):  
Large Scale ◽  
Turbulent Energy ◽  
Energy Dissipation Rate ◽  
Sensor Data ◽  
Free Atmosphere ◽  
Height Range ◽  
High Latitude Region ◽  
Thorpe Scale ◽  
Scale Turbulence ◽  
Turbulence Parameters

In recent years, Thorpe analysis has been used to retrieve the characteristics of turbulence in free atmosphere from balloon-borne sensor data. However, previous studies have mainly focused on the mid-high latitude region, and this method is still rarely applied at heights above 30 km, especially above 35 km. Therefore, seven sets of upper air (>35 km) sounding data from the Changsha Sounding Station (28°12′ N, 113°05′ E), China are analyzed with Thorpe analysis in this article. It is noted that, in the troposphere, Thorpe analysis can better retrieve the turbulence distribution and the corresponding turbulence parameters. Also, because of the thicker troposphere at low latitudes, the values of the Thorpe scale L T and turbulent energy dissipation rate ε remain greater in a larger height range. In the stratosphere below the height of 35 km, the obtained ε is higher, and Thorpe analysis can only be used to analyze the characteristics of large-scale turbulence. In the stratosphere at a height of 35–40 km, because of the interference of sensor noise, Thorpe analysis can only help to retrieve the rough distribution position of large-scale turbulence, while it can hardly help with the calculation of the turbulence parameters.

Dynamics of Aeolian Sand Streamers and Airflow Turbulence over a Beach Surface

2021 ◽  
Author(s):  
Andreas Baas
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Temporal Variability ◽  
Large Scale ◽  
Sonic Anemometer ◽  
Dynamic Structure ◽  
Sand Transport ◽  
Video Imagery ◽  
Spatio Temporal ◽  
The Impact

<p>Sand transport by wind over granular beds displays dynamic structure and organisation in the form of streamers (aka ‘sand snakes’) that appear, meander and intertwine, and then dissipate as they are advected downwind. These patterns of saltating grain populations are thought to be initiated and controlled by coherent flow structures in the turbulent boundary layer wind that scrape over the bed surface raking up sand into entrainment. Streamer behaviour is thus fundamental to understanding sand transport dynamics, in particular its strong spatio-temporal variability, and is equally relevant to granular transport in other geophysical flows (fluvial, submarine).</p><p>This paper presents findings on streamer dynamics and associated wind turbulence observed in a field experiment on a beach, with measurements from 30Hz video-imagery using Large-Scale Particle Image Velocimetry (LS-PIV), combined with 50Hz wind measurements from 3D sonic anemometry and co-located sand transport rate monitoring using an array of laser particle counters (‘Wenglors’), all taking place over an area of ~10 m<sup>2</sup> and over periods of several minutes. The video imagery was used to identify when and where streamers advected past the sonic anemometer and laser sensors so that relationships could be detected between the passage of turbulence structures in the airflow and the length- and time-scales, propagation speeds, and sand transport intensities of associated streamers. The findings form the basis for a phenomenological model of streamer dynamics under turbulent boundary layer flows that predicts the impact of spatio-temporal variability on local measurement of sand transport.</p>

scholarly journals What Is the Impact of Additional Tropical Observations on a Modern Data Assimilation System?

2019 ◽  
Vol 147 (7) ◽  
pp. 2433-2449
Author(s):  
Laura C. Slivinski ◽  
Gilbert P. Compo ◽  
Jeffrey S. Whitaker ◽  
Prashant D. Sardeshmukh ◽  
Jih-Wang A. Wang ◽  
...  
Keyword(s):  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Mean Square ◽  
Observational Network ◽  
In Situ Observations ◽  
The Mean ◽  
The Impact ◽  
Assimilation System

Abstract Given the network of satellite and aircraft observations around the globe, do additional in situ observations impact analyses within a global forecast system? Despite the dense observational network at many levels in the tropical troposphere, assimilating additional sounding observations taken in the eastern tropical Pacific Ocean during the 2016 El Niño Rapid Response (ENRR) locally improves wind, temperature, and humidity 6-h forecasts using a modern assimilation system. Fields from a 50-km reanalysis that assimilates all available observations, including those taken during the ENRR, are compared with those from an otherwise-identical reanalysis that denies all ENRR observations. These observations reveal a bias in the 200-hPa divergence of the assimilating model during a strong El Niño. While the existing observational network partially corrects this bias, the ENRR observations provide a stronger mean correction in the analysis. Significant improvements in the mean-square fit of the first-guess fields to the assimilated ENRR observations demonstrate that they are valuable within the existing network. The effects of the ENRR observations are pronounced in levels of the troposphere that are sparsely observed, particularly 500–800 hPa. Assimilating ENRR observations has mixed effects on the mean-square difference with nearby non-ENRR observations. Using a similar system but with a higher-resolution forecast model yields comparable results to the lower-resolution system. These findings imply a limited improvement in large-scale forecast variability from additional in situ observations, but significant improvements in local 6-h forecasts.

scholarly journals In Situ Observation of Stress Accumulation during Sub-Merged Arc Welding

2014 ◽  
Vol 996 ◽  
pp. 417-423 ◽  
Author(s):  
Arne Kromm ◽  
Thomas Kannengiesser
Keyword(s):  
Arc Welding ◽  
Large Scale ◽  
X Ray Diffraction ◽  
X Ray ◽  
Residual Stress State ◽  
Testing Facility ◽  
Large Scale Testing ◽  
The Impact ◽  
Stress Accumulation

Results obtained from laboratory tests mostly need to be verified under fabrication conditions in order to incorporate design specifics (joint configuration and restraint), which effect the residual stress state considerably. For this purpose, multi-pass sub merged arc welding was performed in a special large-scale testing facility. The impact of varying interpass temperatures could be proven in-situ by means of a pronounced stress accumulation during welding and subsequent heat treatment accompanied by stress determination using X-ray diffraction.

scholarly journals Characterization of a boreal convective boundary layer and its impact on atmospheric chemistry during HUMPPA-COPEC-2010

2012 ◽  
Vol 12 (19) ◽  
pp. 9335-9353 ◽  
Author(s):  
H. G. Ouwersloot ◽  
J. Vilà-Guerau de Arellano ◽  
A. C. Nölscher ◽  
M. C. Krol ◽  
L. N. Ganzeveld ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
Convective Boundary Layer ◽  
Large Scale ◽  
Spatial Scales ◽  
Potential Temperature ◽  
Chemical Species ◽  
Convective Boundary ◽  
The Impact

Abstract. We studied the atmospheric boundary layer (ABL) dynamics and the impact on atmospheric chemistry during the HUMPPA-COPEC-2010 campaign. We used vertical profiles of potential temperature and specific moisture, obtained from 132 radio soundings, to determine the main boundary layer characteristics during the campaign. We propose a classification according to several main ABL prototypes. Further, we performed a case study of a single day, focusing on the convective boundary layer, to analyse the influence of the dynamics on the chemical evolution of the ABL. We used a mixed layer model, initialized and constrained by observations. In particular, we investigated the role of large scale atmospheric dynamics (subsidence and advection) on the ABL development and the evolution of chemical species concentrations. We find that, if the large scale forcings are taken into account, the ABL dynamics are represented satisfactorily. Subsequently, we studied the impact of mixing with a residual layer aloft during the morning transition on atmospheric chemistry. The time evolution of NOx and O3 concentrations, including morning peaks, can be explained and accurately simulated by incorporating the transition of the ABL dynamics from night to day. We demonstrate the importance of the ABL height evolution for the representation of atmospheric chemistry. Our findings underscore the need to couple the dynamics and chemistry at different spatial scales (from turbulence to mesoscale) in chemistry-transport models and in the interpretation of observational data.

scholarly journals Observed Evolution of Northward-Propagating Intraseasonal Variation over the Western Pacific: A Case Study in Boreal Early Summer

2013 ◽  
Vol 141 (2) ◽  
pp. 690-706 ◽  
Author(s):  
Masaki Katsumata ◽  
Hiroyuki Yamada ◽  
Hisayuki Kubota ◽  
Qoosaku Moteki ◽  
Ryuichi Shirooka
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Lower Troposphere ◽  
Western Pacific ◽  
Boreal Summer ◽  
Intraseasonal Variation ◽  
Middle Troposphere ◽  
Inactive Period ◽  
The Western Pacific

Abstract This report describes the in situ observed evolution of the atmospheric profile during an event of the boreal summer intraseasonal variation (BSISV) in the tropical western Pacific Ocean. The convectively active region of the BSISV proceeded northward over the sounding and radar network. Over the array, the situation changed from a convectively inactive period to an active period. Inspection of the sounding data revealed the gradual moistening of the lower troposphere during the convectively inactive period. The sounding-derived heat and moisture budget analyses indicated that both the convective- and large-scale processes caused moistening of the lower and middle troposphere where the radar echo tops were observed most frequently. This study is the first to identify such a “preconditioning” process for the BSISV in the western Pacific using detailed in situ observational data. During the preconditioning, an increase in CAPE was observed, as in previous studies of the MJO. An increase of moisture in the boundary layer was responsible for the increase of CAPE. The large-scale horizontal convergence in the boundary layer may be a key factor to moisten the boundary layer through the convective-scale processes, as well as through the large-scale processes to moisten the lower and middle troposphere.

Small-scale characteristics of a turbulent boundary layer over a rough wall

1997 ◽  
Vol 342 ◽  
pp. 263-293 ◽  
Author(s):  
H. S. SHAFI ◽  
R. A. ANTONIA
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Outer Layer ◽  
Large Scale ◽  
Energy Dissipation Rate ◽  
Wall Layer ◽  
Rough Wall ◽  
Small Scale ◽  
Smooth Wall ◽  
Velocity Derivative

Measurements of the spanwise and wall-normal components of vorticity and their constituent velocity derivative fluctuations have been made in a turbulent boundary layer over a mesh-screen rough wall using a four-hot-wire vorticity probe. The measured spectra and variances of vorticity and velocity derivatives have been corrected for the effect of spatial resolution. The high-wavenumber behaviour of the spectra conforms closely with isotropy. Over most of the outer layer, the normalized magnitudes of the velocity derivative variances differ significantly from those over a smooth wall layer. The differences are such that the variances are much more nearly isotropic over the rough wall than on the smooth wall. This behaviour is consistent with earlier observations that the large-scale structure in this rough wall layer is more isotropic than that in a smooth wall layer. Isotropy-based approximations for the mean energy dissipation rate and mean enstrophy are consequently more reliable in this rough wall layer than in a smooth wall layer. In the outer layer, the vorticity variances are slightly larger than those over a smooth wall; reflecting structural differences between the two flows.

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