Supercritical channel flow in the coastal atmospheric boundary layer: Idealized numerical simulations

Söderberg, Stefan; Tjernström, Michael

doi:10.1029/2001jd900195

Cited by 12 publications

(11 citation statements)

References 34 publications

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“…This effect in the wind direction is nevertheless, in the present case-study, noticeable south of Cabo de S. Vicente. The same kind of flow over-running over low terrain during CLLJ events, near Cape Mendocino in California, was also described by So¨derberg and Tjernstro¨m (2001). The analysis of this case-study showed that the algorithm developed by Ranjha et al (2013), applied to the downscaled data set seems to be appropriate to filter CLLJ occurrences off the coasts of the Iberian Peninsula.…”

Section: Coastal Low-level Jet Climatologymentioning

confidence: 85%

Climatology of the Iberia coastal low-level wind jet: weather research forecasting model high-resolution results

Soares

Cardoso²,

Semedo

et al. 2014

Tellus A: Dynamic Meteorology and Oceanography

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A B S T R A C T Coastal low-level jets (CLLJ) are a low-tropospheric wind feature driven by the pressure gradient produced by a sharp contrast between high temperatures over land and lower temperatures over the sea. This contrast between the cold ocean and the warm land in the summer is intensified by the impact of the coastal parallel winds on the ocean generating upwelling currents, sharpening the temperature gradient close to the coast and giving rise to strong baroclinic structures at the coast. During summertime, the Iberian Peninsula is often under the effect of the Azores High and of a thermal low pressure system inland, leading to a seasonal wind, in the west coast, called the Nortada (northerly wind). This study presents a regional climatology of the CLLJ off the west coast of the Iberian Peninsula, based on a 9 km resolution downscaling dataset, produced using the Weather Research and Forecasting (WRF) mesoscale model, forced by 19 years of ERA-Interim reanalysis (1989Á2007). The simulation results show that the jet hourly frequency of occurrence in the summer is above 30% and decreases to about 10% during spring and autumn. The monthly frequencies of occurrence can reach higher values, around 40% in summer months, and reveal large inter-annual variability in all three seasons. In the summer, at a daily base, the CLLJ is present in almost 70% of the days. The CLLJ wind direction is mostly from north-northeasterly and occurs more persistently in three areas where the interaction of the jet flow with local capes and headlands is more pronounced. The coastal jets in this area occur at heights between 300 and 400 m, and its speed has a mean around 15 m/s, reaching maximum speeds of 25 m/s.

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Section: Coastal Low-level Jet Climatologymentioning

confidence: 85%

Climatology of the Iberia coastal low-level wind jet: weather research forecasting model high-resolution results

Soares

Cardoso²,

Semedo

et al. 2014

Tellus A: Dynamic Meteorology and Oceanography

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“…The model is well documented and has been used in a variety of applications including orographic flows (Enger et al, 1993;Grisogono 1995;Enger and Grisogono, 1998) and coastal flows Grisogono and Tjernström, 1996;Sundararajan and Tjernström, 2000). It has been used in a number of studies based on the CW96 experiment (Tjernström, 1999;Tjernström and Grisogono, 2000;and Söderberg and Tjernström, 2001) as well as more general studies of US West Coast flow (Cui et al, 1998;Söderberg and Tjernström, 2002).…”

Section: Model Discussionmentioning

confidence: 99%

“…Eleven research flights were made by the National Centre for Atmospheric Research C-130 Hercules during June and early July 1996. An overview is given by Rogers et al (1998) and results have been presented in an extensive series of publications (Burk et al, 1999;Tjernström, 1999, Ström, 1999Dorman et al, 1999;Dorman and Winant, 2000;Tjernström and Grisogono, 2000;Edwards et al, 2001;Haack et al, 2001;Brooks, 2001;Söderberg and Tjernström, 2001). To date the analysis of aircraft data from CW96 and associated modelling studies have focused on the mesoscale dynamics and variability.…”

Section: Introductionmentioning

confidence: 99%

The Turbulence Structure of the Stable Atmospheric Boundary Layer Around a Coastal Headland: Aircraft Observations and Modelling Results

Brooks

Söderberg

Tjernström

2003

Boundary-Layer Meteorology

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The turbulence structure of a stable marine atmospheric boundary layer in the vicinity of a coastal headland is examined using aircraft observations and numerical simulation.Measurements are drawn from a flight by the NCAR C-130 around Cape Mendocino on the coast of Northern California on June 7 1996 during the Coastal Waves 96 field program.Local similarity scaling of the velocity variances is found to apply successfully within the continuously turbulent layer; the empirical scaling function is similar to that found by several previous studies. Excellent agreement is found between the modelled and observed scaling results. No significant change in scaling behaviour is observed for the region within the expansion fan that forms downstream of the cape, suggesting that the scaling can be applied to horizontally heterogeneous conditions; however, the precise form of the function relating scaled velocities and stability is observed to change close to the surface. This result, differences between the scaling functions found here and in other studies, and the departure of these functions from the constant value predicted by the original theory leads us to question the nature of the similarity functions observed. We hypothesize that the form of the functions is controlled by non-local contributions to the velocity variance budgets, and that differences in the non-local terms between studies explain the differences in the observed scaling functions.2

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“…The identification of BL depth from the location of the maximum in W f (a, b) works well where background gradients are negligible and the transition zone sharp and well defined, but these conditions are frequently not met. Under stable conditions, where mixing is poor, vertical gradients are common both within and above the BL, and the inversion layer may be a significant fraction of the depth of the BL as a whole (Söderberg and Tjernström 2001); here the problem of identifying the BL depth in an automated manner becomes more complicated. It should also be noted that under some conditions the boundary layer may be so ill-defined that a absolute top cannot sensibly be defined.…”

Section: The Wavelet Covariance Transformmentioning

confidence: 99%

Finding Boundary Layer Top: Application of a Wavelet Covariance Transform to Lidar Backscatter Profiles

Brooks

2003

J. Atmos. Oceanic Technol.

330

260

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Several recent studies have utilized a Haar wavelet covariance transform to provide automated detection of the boundary layer top from lidar backscatter profiles by locating the maximum in the covariance profiles. This approach is effective where the vertical gradient in the backscatter is small within and above the boundary layer, and where the inversion is sharp and well defined. These near-ideal conditions are often not met, particularly under stable stratification where the inversion may be deep and is sometimes ill defined, and vertical gradients are common. Here the effects of vertical gradients and inversion depth on the covariance transform are examined. It is found that a significant dilation-dependent bias in the determination of the boundary layer top may result when using the published method. An alternative approach is developed utilizing multiple wavelet dilations, and is capable of identifying both the upper and lower limits of the backscatter transition zone associated with the inversion while remaining insensitive to mean vertical gradients in the background signal. This approach enables more detailed information on the small-scale structure of the inversion and entrainment zone to be retrieved than is possible using existing techniques.

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Supercritical channel flow in the coastal atmospheric boundary layer: Idealized numerical simulations

Cited by 12 publications

References 34 publications

Climatology of the Iberia coastal low-level wind jet: weather research forecasting model high-resolution results

Climatology of the Iberia coastal low-level wind jet: weather research forecasting model high-resolution results

The Turbulence Structure of the Stable Atmospheric Boundary Layer Around a Coastal Headland: Aircraft Observations and Modelling Results

Finding Boundary Layer Top: Application of a Wavelet Covariance Transform to Lidar Backscatter Profiles

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