Boundary Layer Meteorology

Turbulent Structure functions in Geophysical Flows

by Jose M. Redondo

TURBULENT STRUCTURE FUNCTIONS IN GEOPHYSICAL FLOWS
O. Ben Mahjoub*, J. M. Redondo and R. Alami
Dept. Fisica Aplicada, (*Estadistica) Universitat Politècnica de Catalunya. Campus Nord B5, 08034 Barcelona, Spain

In geophysical flows, there are many instances, where turbulence is originated locally. such as in surface wave... more In geophysical flows, there are many instances, where turbulence is originated locally. such as in surface wave breaking at the surfzone or
by internai wave breaking in the lee of a mountain. The use of velocity structure functions and their moments may give an indication of
the spatial and time delay from the source of turbulence. The variation of the structure functions and the scaling exponents in decaying
non-homogeneous turbulence flows produced by a grid is investigated by means of sonic velocimeter SONTEK3-D. In the analysis we
invoke the concept of the Extended Self Similarity (ESS) and find that there are changes in the structure functions related to the
intermittency.
Keywords:JTurbulence

Turbulence structure of the atmospheric boundary layer in stable conditions

by Jose M. Redondo

TURBULENCE STRUCTURE OF THE ATMOSPHERIC
BOUNDARY LAYER IN STABLE CONDITIONS
J. M. Redondo (1), I. R. Cantalapiedra (1), O.B. Mahjoub (1),
Vindel (2) and C. Yagüe (2).
(1) Univ. Politecnica de Cataluña, Barcelona, Spain.
(2) Univ. Complutense de Madrid, Spain.


Conference proceedings

A partir de las mediciones de velocidad del aire, temperatura y humedad realizadas en la atmósfera en horario nocturno, se ha analizado la influencia de la estabilidad atmosférica en los flujos de momento y temperatura.
978-84-9747-185-5
http://hdl.handle.net/2117/1418

Data from SABLES98 experimental campaign have been used in order to study the
influence of stability (from weak... more Data from SABLES98 experimental campaign have been used in order to study the
influence of stability (from weak to strong stratification) on the flux-profile
relationships for momentum and heat: fm and fh. Standard instrumentation, 14
thermocouples and 3 sonic anemometers at three levels (5.8, 13.5 and 32 m) were
available from 10 to 28 September 1998 and calculations are done in order to extract
structure functions and intermittency. The results show increasing values of fm and fh
with increasing stability parameter and then values remain constant. As a consequence
of these constant, but different values of fm and fh for strong stability, when linear
similarity functions (Businger et al., 1971) are used to calculate surface fluxes of
momentum and heat an important underestimation of the turbulent mixing is produced.
The differences in structure and higher order moments between stable and neutral
turbulence is studied in terms of turbulent intermittent mixing and velocity PDF’s

Meteorological Database Algorithm for Studying Boundary Layer Effects

by Thomas Yesufu

Arctic inversion strength in climate models

by Brian Medeiros

Medeiros, B., C. Deser, R. A. Tomas, J. E. Kay, 2011: Arctic inversion strength in climate models. Journal of Climate, 24(17), pp. 4733-4740 doi: 10.1175/2011JCLI3968.1

Recent work indicates that climate models have a positive bias in the strength of the winter- time low-level... more Recent work indicates that climate models have a positive bias in the strength of the winter- time low-level temperature inversion over the high-latitude northern hemisphere. It has been argued this bias leads to underestimates of the Arctic’s surface temperature response to an- thropogenic forcing. Here the bias in inversion strength is revisited. The spatial distribution of low-level stability is found to be bimodal in climate models and observational reanalysis products, with low-level inversions represented by a stable primary mode over the interior Arctic Ocean and adjacent continents, and a secondary unstable mode over the Atlantic Ocean. Averaging over these differing conditions is detrimental to understanding the origins of the inversion strength bias. While nearly all of the 21 models examined overestimate the area-average inversion strength, conditionally sampling the two modes shows about half the models are biased because of the relative partitioning of the modes and half because of biases within the stable mode.

1993 Dependence of Chance of Snow Depth on Snowfalls at Brzegi Dolne

by Marek Nowosad

Evaporation, Water Balance & Deposition, Proceedings of the International Symposium on Precipitation and Evaporation, A. Becker, B. Sevruk, M. Lapin (eds.), Vol. 3, Bratislava, 329-334.

The daily snow depth and daily solid precipitations during 25 winters at the meteorological station Brzegi Dolne (SE... more The daily snow depth and daily solid precipitations during 25 winters at the meteorological station Brzegi Dolne (SE parth of Poland) was analyzed.
The results (only for days with snow falls):
- in about half of the cases snow depth increases;
- in 13% of the cases snow cover occurs without any changes of its depth;
- in 24% of the cases snow depth decreases;
- in 13% of cases in not snow cover in both morning meteorological observations.

The snow falls which give the increase of snow depth for more than 10 cm (15 cm) from day to day, appear on the average 2.8 (1.1) times a year.

Large-eddy simulation of small-scale surface effects on the convective boundary-layer structure

by Monique Leclerc

Forward-in-time and Backward-in-time Dispersion in the Convective Boundary Layer: the Concentration Footprint

by Monique Leclerc

How large must surface inhomogeneities be before they influence the convective boundary layer structure? A case study

by Monique Leclerc

A spatially-analytical scheme for surface temperatures and conductive heat fluxes in urban canopy models

by Zhihua Wang

Boundary-Layer Meteorology, 138(2): 171-193, 2011

In the urban environment, surface temperatures and conductive heat fluxes through solid media (roofs, walls, roads and... more In the urban environment, surface temperatures and conductive heat fluxes through solid media (roofs, walls, roads and vegetated surfaces) are of paramount importance for the comfort of residents (indoors) and for microclimatic conditions (outdoors). Fully discrete numerical methods are currently used to model heat transfer in these solid media in parameterizations of built surfaces commonly used in weather prediction models. These discrete methods usually use finite difference schemes in both space and time. In this paper, we propose a spatially-analytical scheme, where the temperature field and conductive heat fluxes are solved analytically in space. Spurious numerical oscillations due to temperature discontinuities at the sublayer interfaces can be avoided since the method does not involve spatial discretization. The proposed method is compared to the fully discrete method for a test case of one-dimensional heat conduction with sinusoidal forcing. Subsequently, the analytical scheme is incorporated into the offline version of the current urban canopy model (UCM) used in WRF and the new UCM is validated against field measurements using a wireless sensor network and other supporting measurements over a suburban area under real-world conditions. Results of comparison clearly show the advantage of the proposed scheme over the fully discrete model, particularly for more complicated cases.

Analyzing the sensitivity of WRF’s single-layer urban canopy model to parameter uncertainty using advanced Monte Carlo simulation

by Zhihua Wang

Journal of Applied Meteorology and Climatology, 50(9): 1795-1814, 2011

Single-layer physically-based urban canopy models (UCM) have gained popularity for modeling urban-atmosphere... more Single-layer physically-based urban canopy models (UCM) have gained popularity for modeling urban-atmosphere interactions, especially the energy transport component. For an urban canopy model to capture the physics of conductive, radiative, and turbulent advective transport of energy, it is important to provide it with an accurate parameter space, including both mesoscale meteorological forcing and microscale surface inputs. While field measurement of all input parameters of an urban canopy model is rarely possible, understanding the model sensitivity to individual parameters is essential to determine the relative importance of parameter uncertainty for model performance. In this paper, we use an advanced Monte Carlo approach, namely Subset Simulation, to quantify the impact of the uncertainty of surface input parameters on the output of an offline modified version of WRF-UCM. Based on the conditional sampling technique, the importance of surface parameters is determined in terms of their impact on critical model responses. It is found that model outputs (both critical energy fluxes and surface temperatures) are highly sensitive to uncertainties in urban geometry, while variations in emissivities and building interior temperatures are relatively insignificant. In addition, the sensitivity of the model to input surface parameters is also shown to be very weakly dependent on meteorological parameters. The statistical quantification of the model’s sensitivity to input parameters has practical implications, such as surface parameter calibrations in UCM and guidance for urban heat island mitigation strategies.

An Open Channel Flow Experimental and Theoretical Study of Resistance and Turbulent Characterization over Flexible Vegetated Linings

by Jose M. Redondo

DAVID VELASCO1, ALLEN BATEMAN1, JOSE M. REDONDO2 and
VICENTE DEMEDINA1
1Hydraulic and Hydrological Section, 2Applied Physics Department, Polytechnic University of
Catalonia UPC, E-80340 Barcelona, Spain

Journal of Flow, Turbulence and Combustion 70: 69–88, 2003.

Hydraulic engineers and scientists working on river restoration recognize the need for
a deeper understanding of... more Hydraulic engineers and scientists working on river restoration recognize the need for
a deeper understanding of natural streams as a complex and dynamic system, which involves not
only abiotic elements (flow, sediments) but also biotic or biological components. From this point of
view, the role played by riverine vegetation in river dynamics and flow conditions becomes essential.
Hydro-mechanic interaction between flow and flexible plants covering a river bed is studied in this
paper and some previous works are discussed. Experimental tests and measurements of turbulence
on the flow in an open channel were performed using plastic plants seeded in a gravel bed. Characterization
of flow resistance (friction factors) due to vegetation flexible roughness for different plant
densities was attained; furthermore, measuring detailed turbulent velocity profiles within and above
submerged and flexed stems allowed us to distinguish different turbulent regimes. Some interesting
relationships were obtained between the velocity field and the deflected height of the plants, such as
a linear fit between the non-dimensional flexural parameter and the relative deflection of the plants.
Turbulent stresses were measured showing two different regions: above and inside the vegetation
domain. The spectral interaction between the plant oscillations, their wakes and the turbulence
at different heights, forces strongly anisotropic Reynolds tensors and in order to clarify turbulent
processes and their complex structure, theoretical concepts (Taylor, Kolmogorov’s K41) and several
data analysis (autocorrelation functions, integral scales) were applied.
Key words: canopy flows, plant turbulence

The Shear Layer above and in Urban Canopies

by Jose M. Redondo

co-authors: P-Huq,A.Carrillo, L.A.White, S. Dharmavaran and S.R. Hanna

JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY,  46, 368-376. 2006.

The nature and role of the shear layer, which occurs at the level of the average building height in urbanmore The nature and role of the shear layer, which occurs at the level of the average building height in urban
canopies, are poorly understood. Velocity data are analyzed to determine the characteristics of the shear
layer of the urban canopy, defined as the broad, linear segment of the mean velocity profile in a region of
high shear. Particle image velocimetry measurements in a water tunnel were undertaken to resolve velocity
profiles for urban canopies of two geometries typical of Los Angeles, California, and New York City, New
York, for which the aspect ratios (average building height-to-width ratio) H/wb are 1 and 3, respectively.
The shear layers evolve with distance differently: For H/wb  1 the urban canopy shear layer extends
quickly from above the building height to ground level, whereas for H/wb  3 the urban canopy shear layer
remains elevated at the vicinity of the building height, only reaching to a depth of z/H 0.5 far downstream.
Profiles of the mean velocity gradient also differ from each other for urban canopies associated with H/wb
of 1 or 3. Values of shear dU/dz increase toward ground level for an urban canopy associated with H/wb 
1. For an urban canopy associated with H/wb  3, localized peaks of shear dU/dz exist at the building height
and at ground level, with values of shear decreasing to zero at building midheight and far above the building
height. A consequence of the different forms of the shear layers of the two urban canopies is that the
ground-level dispersion coefficient is likely to be greater for urban canopies associated with H/wb  1 than
for those associated with H/wb  3 because of an increased ventilation and exchange mechanism for cities
such as Los Angeles relative to cities such as New York City that possess urban canyons