Surface Layer Turbulence Measurements during a Frontal Passage

Piper, Mark; Lundquist, Julie K.

doi:10.1175/1520-0469(2004)061<1768:sltmda>2.0.co;2

Cited by 53 publications

(71 citation statements)

References 53 publications

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“…For example, an along-front temperature advection modifies the propagation of fronts (Gidel, 1978). Also, effects of turbulence are profound within surface fronts (Piper and Lundquist, 2004) and a strong cross-frontal air exchange leads to 7 a frontal retardation. In addition, ageostrophic mechanisms and gravity waves induce secondary circulations (Egger and Hoinka, 1992) and probably cause the greatest inaccuracies of v f in the vicinity of mountains.…”

Section: Frontal Motion and Typesupporting

confidence: 82%

Detection and climatology of fronts in a high‐resolution model reanalysis over the Alps

Jenkner

Sprenger

Schwenk

et al. 2009

Meteorological Applications

103

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The identification of low-level thermal fronts is particularly challenging in high-resolution model fields over complex terrain. Firstly, direct model output often contains numerical noise which spuriously influences the highfrequency variability of thermal parameters. Secondly, the boundary layer interferes via convection and consequently leaves its thermal marks on low levels. Here, an automated objective method for the detection of frontal lines is introduced which is designed to be insusceptible to consequences of small grid spacings. To this end, existing algorithms are readopted and combined in a novel way. The overall technique subdivides into a basic detection of fronts and a supplemental division into local fronts and synoptic fronts. The fundamental parts of the detection are: (1) a smoothing of the initial fields, (2) a definition of the frontal strength, and, (3) a localisation with the thermal front parameter. The local fronts are identified by means of a classification of open and closed thermal contours. The resulting data comprise the spatial outline of the frontal structures in a binary field as well as their type and movement. The novel methodology is applied to a 3 year high-resolution reanalysis over central Europe computed with the COSMO model using a grid spacing of 7 km. Grid-point based climatologies are derived for the Alpine region. Frequencies of occurrence and characteristics of motion are analysed for different frontal types. The novel climatology also provides quantitative evidence of dynamical properties such as the retardation of cold fronts ahead of mountains and the dissolution of warm fronts over mountains.

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Section: Frontal Motion and Typesupporting

confidence: 82%

Detection and climatology of fronts in a high‐resolution model reanalysis over the Alps

Jenkner

Sprenger

Schwenk

et al. 2009

Meteorological Applications

103

View full text Add to dashboard Cite

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“…This suggests that an inertial subrange may exist within the frequency limits measured by the sonic anemometer 13 m above the ground. Piper and Lundquist (2004) found similar result in their data (shown in their Fig. 1).…”

Section: Analysis Of the Strongest Bora Intervalmentioning

confidence: 99%

“…The Kolmogorov constant α=0.53 (e.g. Champagne, 1978;Oncley et al, 1996;Piper and Lundquist, 2004) is used in Eq. (2).…”

Section: Analysis Of the Strongest Bora Intervalmentioning

confidence: 99%

Characteristics of the near-surface turbulence during a bora event

Večenaj¹,

Belušić

Grisogono

2010

Ann. Geophys.

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Abstract. During a bora event, the turbulence is strongly developed in the lee of the Dinaric Alps at the eastern Adriatic coast. In order to study its properties, a 3-D ultrasonic anemometer operating at 4 Hz sampling frequency was placed in the town of Senj at 13 m above ground. The strong bora case that occurred on 7 January and lasted till 11 January 2006 is analyzed here. This data set is used for evaluation of the turbulent kinetic energy, TKE, and its dissipation rate, ε. The computation of ε is performed using the inertial dissipation method. The empirical length scale parameter for this event is estimated with respect to ε and TKE. Some considerations about defining turbulent perturbations of the bora wind velocity are also pointed out.

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“…For momentum and heat flux calculations, the mean of each time series over 30-minutes is removed. Measurements of turbulent kinetic energy (TKE) dissipation rate are also obtained from these data, using the inertial estimation method as described in Piper and Lundquist (2004).…”

Section: The Joint Urban 2003 Field Studymentioning

confidence: 99%

Consequences of Urban Stability Conditions for Computational Fluid Dynamics Simulations of Urban Dispersion

Lundquist

Chan

2007

Journal of Applied Meteorology and Climatology

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Abstract.The validity of omitting stability considerations when simulating transport and dispersion in the urban environment is explored using observations from the Joint URBAN 2003 field experiment and computational fluid dynamics simulations of that experiment. Four releases of sulfur hexafluoride, during two daytime and two nighttime intensive observing periods, are simulated using the building-resolving computational fluid dynamics model, FEM3MP to solve the Reynolds Averaged Navier-Stokes equations with two options of turbulence parameterizations. One option omits stability effects but has a superior turbulence parameterization using a non-linear eddy viscosity (NEV) approach, while the other considers To further explore this assumption of a neutrally-stable atmosphere within the urban area, TKE budget profiles slightly downwind of the urban wake region in the "urban shadow" are examined. Dissipation and shear production are the largest terms which may be calculated directly. The advection of TKE is calculated as a residual; as would be expected downwind of an urban area, the advection of TKE produced within the urban area is a very large term. Buoyancy effects may be neglected in favor of advection, shear production, and dissipation. For three of the IOPs, buoyancy production may be neglected entirely, and for one IOP, buoyancy production 4 contributes approximately 25% of the total TKE at this location. For both nighttime releases, the contribution of buoyancy to the total TKE budget is always negligible though positive.Results from the simulations provide estimates of the average TKE values in the upwind, downtown, downtown shadow, and urban wake zones of the computational domain. These values suggest that building-induced turbulence can cause the average turbulence intensity in the urban area to increase by as much as much as seven times average "upwind" values, explaining the minimal role of buoyant forcing in the downtown region. The downtown shadow exhibits an exponential decay in average TKE, while the distant downwind wake region approaches the average upwind values. For long-duration releases in downtown and downtown shadow areas, the assumption of neutral stability is valid because building-induced turbulence dominates the budget. However, further downwind in the urban wake region, which we find to be approximately 1500 m beyond the perimeter of downtown Oklahoma City, the levels of building-induced turbulence greatly subside, and therefore the assumption of neutral stability is less valid.

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Surface Layer Turbulence Measurements during a Frontal Passage

Cited by 53 publications

References 53 publications

Detection and climatology of fronts in a high‐resolution model reanalysis over the Alps

Detection and climatology of fronts in a high‐resolution model reanalysis over the Alps

Characteristics of the near-surface turbulence during a bora event

Consequences of Urban Stability Conditions for Computational Fluid Dynamics Simulations of Urban Dispersion

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