scholarly journals Convective Boundary Layer Depth Estimation from Wind Profilers: Statistical Comparison between an Automated Algorithm and Expert Estimations

2008 ◽  
Vol 25 (8) ◽  
pp. 1397-1413 ◽  
Author(s):  
Laura Bianco ◽  
James M. Wilczak ◽  
Allen B. White
Keyword(s):  
Boundary Layer ◽  
Fuzzy Logic ◽  
Vertical Velocity ◽  
Convective Boundary Layer ◽  
Index Structure ◽  
Small Scale ◽  
Vertical Profiles ◽  
Improved Method ◽  
Layer Depth ◽  
Convective Boundary

Abstract A previous study showed success in determining the convective boundary layer depth with radar wind-profiling radars using fuzzy logic methods, and improvements to the earlier work are discussed. The improved method uses the Vaisala multipeak picking (MPP) procedure to identify the atmospheric signal in radar spectra in place of a fuzzy logic peak picking procedure that was previously used. The method then applies fuzzy logic techniques to calculate the depth of the convective boundary layer. The planetary boundary layer depth algorithm is improved with respect to the one used in the previous study in that it adds information obtained from the small-scale turbulence (vertical profiles of the spectral width of the vertical velocity), while also still using vertical profiles of the radar-derived refractive index structure parameter C2n and the variance of vertical velocity. Modifications to the fuzzy logic rules (especially to those using vertical velocity data) that improve the algorithm’s accuracy in cloudy boundary layers are incorporated. In addition, a reliability threshold value to the fuzzy logic–derived score is applied to eliminate PBL depth data values with low score values. These low score values correspond to periods when the PBL structure does not match the conceptual model of the convective PBL built into the algorithm. Also, as a final step, an optional temporal continuity test on boundary layer depth has been developed that helps improve the algorithm’s skill. A comparison with independent boundary layer depth estimations made “by eye” by meteorologists at two radar wind-profiler sites, significantly different in their characteristics, shows that the new improved method gives significantly more accurate estimates of the boundary layer depth than does the previous method, and also much better estimates than the simpler “standard” method of selecting the peak of C2n. The new method produces an absolute error of the mixing-depth estimates comparable to the vertical range resolution of the profilers.

Marginal Stability of the Convective Boundary Layer

2020 ◽  
Vol 77 (2) ◽  
pp. 435-442
Author(s):  
John Thuburn ◽  
Georgios A. Efstathiou
Keyword(s):  
Boundary Layer ◽  
Stability Analysis ◽  
Linear Stability Analysis ◽  
Convective Boundary Layer ◽  
Eddy Viscosity ◽  
Potential Temperature ◽  
Marginal Stability ◽  
Layer Depth ◽  
Convective Boundary ◽  
Layer Potential

Abstract We hypothesize that the convective atmospheric boundary layer is marginally stable when the damping effects of turbulence are taken into account. If the effects of turbulence are modeled as an eddy viscosity and diffusivity, then an idealized analysis based on the hypothesis predicts a well-known scaling for the magnitude of the eddy viscosity and diffusivity. It also predicts that the marginally stable modes should have vertical and horizontal scales comparable to the boundary layer depth. A more quantitative numerical linear stability analysis is presented for a realistic convective boundary layer potential temperature profile and is found to support the hypothesis.

scholarly journals Vertical velocity and turbulence aspects during Mistral events as observed by UHF wind profilers

2004 ◽  
Vol 22 (11) ◽  
pp. 3927-3936 ◽  
Author(s):  
J.-L. Caccia ◽  
V. Guénard ◽  
B. Benech ◽  
B. Campistron ◽  
P. Drobinski
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Vertical Velocity ◽  
Convective Boundary Layer ◽  
Dissipation Rate ◽  
Convective Boundary ◽  
Turbulent Dissipation ◽  
The Alps ◽  
Rhone Valley ◽  
Wind Profilers

Abstract. The general purpose of this paper is to experimentally study mesoscale dynamical aspects of the Mistral in the coastal area located at the exit of the Rhône-valley. The Mistral is a northerly low-level flow blowing in southern France along the Rhône-valley axis, located between the French Alps and the Massif Central, towards the Mediterranean Sea. The experimental data are obtained by UHF wind profilers deployed during two major field campaigns, MAP (Mesoscale Alpine Program) in autumn 1999, and ESCOMPTE (Expérience sur Site pour COntraindre les Modèles de Pollution atmosphériques et de Transports d'Emission) in summer 2001. Thanks to the use of the time evolution of the vertical profile of the horizontal wind vector, recent works have shown that the dynamics of the Mistral is highly dependent on the season because of the occurrence of specific synoptic patterns. In addition, during summer, thermal forcing leads to a combination of sea breeze with Mistral and weaker Mistral due to the enhanced friction while, during autumn, absence of convective turbulence leads to substantial acceleration as low-level jets are generated in the stably stratified planetary boundary layer. At the exit of the Rhône valley, the gap flow dynamics dominates, whereas at the lee of the Alps, the dynamics is driven by the relative contribution of "flow around" and "flow over" mechanisms, upstream of the Alps. This paper analyses vertical velocity and turbulence, i.e. turbulent dissipation rate, with data obtained by the same UHF wind profilers during the same Mistral events. In autumn, the motions are found to be globally and significantly subsident, which is coherent for a dry, cold and stable flow approaching the sea, and the turbulence is found to be of pure dynamical origin (wind shears and mountain/lee wave breaking), which is coherent with non-convective situations. In summer, due to the ground heating and to the interactions with thermal circulation, the vertical motions are less pronounced and no longer have systematic subsident charateristics. In addition, those vertical motions are found to be much less developed during the nighttimes because of the stabilization of the nocturnal planetary boundary layer due to a ground cooling. The enhanced turbulent dissipation-rate values found at lower levels during the afternoons of weak Mistral cases are consistent with the installation of the summer convective boundary layer and show that, as expected in weaker Mistral events, the convection is the preponderant factor for the turbulence generation. On the other hand, for stronger cases, such a convective boundary layer installation is perturbed by the Mistral.

scholarly journals Comparison of Convective Boundary Layer Velocity Spectra Retrieved from Large- Eddy-Simulation and Weather Research and Forecasting Model Data

2014 ◽  
Vol 53 (2) ◽  
pp. 377-394 ◽  
Author(s):  
Jeremy A. Gibbs ◽  
Evgeni Fedorovich
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Wrf Model ◽  
Velocity Fields ◽  
Weather Research And Forecasting ◽  
Small Scale ◽  
Convective Boundary ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Velocity Spectra

AbstractAs computing capabilities expand, operational and research environments are moving toward the use of finescale atmospheric numerical models. These models are attractive for users who seek an accurate description of small-scale turbulent motions. One such numerical tool is the Weather Research and Forecasting (WRF) model, which has been extensively used in synoptic-scale and mesoscale studies. As finer-resolution simulations become more desirable, it remains a question whether the model features originally designed for the simulation of larger-scale atmospheric flows will translate to adequate reproductions of small-scale motions. In this study, turbulent flow in the dry atmospheric convective boundary layer (CBL) is simulated using a conventional large-eddy-simulation (LES) code and the WRF model applied in an LES mode. The two simulation configurations use almost identical numerical grids and are initialized with the same idealized vertical profiles of wind velocity, temperature, and moisture. The respective CBL forcings are set equal and held constant. The effects of the CBL wind shear and of the varying grid spacings are investigated. Horizontal slices of velocity fields are analyzed to enable a comparison of CBL flow patterns obtained with each simulation method. Two-dimensional velocity spectra are used to characterize the planar turbulence structure. One-dimensional velocity spectra are also calculated. Results show that the WRF model tends to attribute slightly more energy to larger-scale flow structures as compared with the CBL structures reproduced by the conventional LES. Consequently, the WRF model reproduces relatively less spatial variability of the velocity fields. Spectra from the WRF model also feature narrower inertial spectral subranges and indicate enhanced damping of turbulence on small scales.

scholarly journals Derivation of third–order vertical velocity turbulence moment in the convective boundary layer from large eddy simulation data: an application to the dispersion modeling

2013 ◽  
Vol 4 (2) ◽  
pp. 191-198 ◽  
Author(s):  
Silvana Maldaner ◽  
Gervasio Annes Degrazia ◽  
Umberto Rizza ◽  
Virnei Silva Moreira ◽  
Franciano Scremin Puhales ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Vertical Velocity ◽  
Convective Boundary Layer ◽  
Dispersion Modeling ◽  
Third Order ◽  
Simulation Data ◽  
Convective Boundary ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Velocity Turbulence

scholarly journals Convective Boundary Layer Depth Estimation from S-Band Dual-Polarization Radar

2018 ◽  
Vol 35 (8) ◽  
pp. 1723-1733 ◽  
Author(s):  
John R. Banghoff ◽  
David J. Stensrud ◽  
Matthew R. Kumjian
Keyword(s):  
Boundary Layer ◽  
New York ◽  
Convective Boundary Layer ◽  
Depth Estimation ◽  
Dual Polarization ◽  
Layer Depth ◽  
Reasonable Estimate ◽  
Convective Boundary ◽  
Using Data ◽  
Differential Reflectivity

AbstractThis study investigates Bragg scatter signatures in dual-polarization radar observations, which are defined by low differential reflectivity values, as a proxy for convective boundary layer (CBL) depth. Using data from the WSR-88D in Twin Lakes, Oklahoma (KTLX), local minima in quasi-vertical profiles of are found to provide a reasonable estimate of CBL depth when compared with depth estimates from upper-air soundings from Norman, Oklahoma (KOUN), during 2014. The 243 Bragg scatter and upper-air sounding CBL depth estimates have a correlation of 0.90 and an RMSE of 254 m. Using Bragg scatter as a proxy for CBL depth was expanded to other seasons and locations—performing well in Wilmington, Ohio; Fairbanks, Alaska; Tucson, Arizona; Minneapolis, Minnesota; Albany, New York; Portland, Oregon; and Tampa, Florida—showing its potential usefulness in monitoring CBL depth throughout the year in a variety of geographic locations and meteorological conditions.

Analysis of small-scale patterns of atmospheric motion in a sheared, convective boundary layer

1996 ◽  
Vol 101 (D5) ◽  
pp. 9391-9411 ◽  
Author(s):  
F. L. Ludwig ◽  
R. L. Street ◽  
J. M. Schneider ◽  
K. R. Costigan
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Small Scale ◽  
Convective Boundary ◽  
Atmospheric Motion ◽  
Sheared Convective Boundary Layer
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