Diurnal Variations In Flow Over A Succession of Ridges and Valleys

Mason, P. J.

doi:10.1002/qj.49711347804

Cited by 29 publications

(4 citation statements)

References 21 publications

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“…Several parameters are used to describe the relative importance of thermal and overlying flow (inertial) effects. Mason (1987) introduced F M = (2U 2 θ/ΔBh*) 1/2 to describe the effacing of valley stable stratification by overlying flow. Here ΔB is the buoyancy contrast between the valley and the overlying flow, h* is a vertical scale of buoyancy perturbations, and θ is the slope angle.…”

Section: May 2019mentioning

confidence: 99%

The Perdigão: Peering into Microscale Details of Mountain Winds

Fernando

Mann

Palma

et al. 2019

Bulletin of the American Meteorological Society

125

129

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A grand challenge from the wind energy industry is to provide reliable forecasts on mountain winds several hours in advance at microscale (∼100 m) resolution. This requires better microscale wind-energy physics included in forecasting tools, for which field observations are imperative. While mesoscale (∼1 km) measurements abound, microscale processes are not monitored in practice nor do plentiful measurements exist at this scale. After a decade of preparation, a group of European and U.S. collaborators conducted a field campaign during 1 May–15 June 2017 in Vale Cobrão in central Portugal to delve into microscale processes in complex terrain. This valley is nestled within a parallel double ridge near the town of Perdigão with dominant wind climatology normal to the ridges, offering a nominally simple yet natural setting for fundamental studies. The dense instrument ensemble deployed covered a ∼4 km × 4 km swath horizontally and ∼10 km vertically, with measurement resolutions of tens of meters and seconds. Meteorological data were collected continuously, capturing multiscale flow interactions from synoptic to microscales, diurnal variability, thermal circulation, turbine wake and acoustics, waves, and turbulence. Particularly noteworthy are the extensiveness of the instrument array, space–time scales covered, use of leading-edge multiple-lidar technology alongside conventional tower and remote sensors, fruitful cross-Atlantic partnership, and adaptive management of the campaign. Preliminary data analysis uncovered interesting new phenomena. All data are being archived for public use.

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Section: May 2019mentioning

confidence: 99%

The Perdigão: Peering into Microscale Details of Mountain Winds

Fernando

Mann

Palma

et al. 2019

Bulletin of the American Meteorological Society

125

129

View full text Add to dashboard Cite

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“…Remaining differences in parametrized surface stress between the IFS IFS-SSO and MetUM experiments are likely to be largely due to differences in orographic drag scheme parameter settings, differences in the implementation of the LM97 scheme, and indirectly via differences in GSO. For instance, as discussed in Elvidge (2019), in the MetUM there is a considerably larger LM97 scheme blocking coefficient, a different method for deriving the local Froude number used by the LM97 scheme (see appendix), and a different parameterization for turbulent orographic drag in the boundary layer (which employs a drag coefficient smaller by half than that recommended from a physical perspective by Mason, 1987). This results in elevated τ SSO and lower τ BL relative to the IFS, which uses the TOFD scheme for boundary layer drag, following Beljaars et al (2004).…”

Section: Impacts On Total Parameterized Surface Stress and Its Partitmentioning

confidence: 99%

Uncertainty in the Representation of Orography in Weather and Climate Models and Implications for Parameterized Drag

Elvidge

Sandu

Wedi

et al. 2019

J Adv Model Earth Syst

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The representation of orographic drag remains a major source of uncertainty for numerical weather prediction (NWP) and climate models. Its accuracy depends on contributions from both the model grid‐scale orography and the subgrid‐scale orography (SSO). Different models use different source orography data sets and different methodologies to derive these orography fields. This study presents the first comparison of orography fields across several operational global NWP models. It also investigates the sensitivity of an orographic drag parameterization to the intermodel spread in SSO fields and the resulting implications for representing the Northern Hemisphere winter circulation in a NWP model. The intermodel spread in both the grid‐scale orography and the SSO fields is found to be considerable. This is due to differences in the underlying source data set employed and in the manner in which this data set is processed (in particular how it is smoothed and interpolated) to generate the model fields. The sensitivity of parameterized orographic drag to the intermodel variability in SSO fields is shown to be considerable and dominated by the influence of two SSO fields: the standard deviation and the mean gradient of the SSO. NWP model sensitivity experiments demonstrate that the intermodel spread in these fields is of first‐order importance to the intermodel spread in parameterized surface stress, and to current known systematic model biases. The revealed importance of the SSO fields supports careful reconsideration of how these fields are generated, guiding future development of orographic drag parameterizations and reevaluation of the resolved impacts of orography on the flow.

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“…As indicated by Baines (1995), the occurrence of bluff-body flow separation in the lee of an obstacle depends on the speed of the approaching flow and on the stability. Mason (1987) observed flow separation or decoupling in a small, approximately 200-m deep valley under neutral and unstable conditions, while the flow remained attached under stable conditions with a Froude number < 2, and was able to reproduce that result with numerical simulations. Similar results based on tethersonde measurements were found by Holden et al (2000).…”

Section: Introductionmentioning

confidence: 78%

Flow Separation in the Lee of a Crater Rim

Lehner

Whiteman

Hoch

et al. 2019

Boundary-Layer Meteorol

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The nearly circular Meteor Crater, Arizona, is located on an extensive, slightly sloping plain, above which a south-westerly katabatic flow forms during undisturbed, clear-sky nights. For the katabatic flow over the upstream crater rim, the resulting flow regime in the lee depends on the upstream wind speed. For a shallow katabatic flow with a wind-speed maximum of about 5 m s −1 or less at a height of about 20 m above the ground, the flow decelerates as it approaches the crater. Cold-air intrusions form, that is, cold air spills over the crater rim and runs down the inner southwest sidewall. For a deep katabatic flow with a wind-speed maximum located above the 50-m high measurement tower and comparatively higher wind speeds, the flow accelerates towards the crater. The flow separates in the immediate lee of the crater rim, forming a wake over the southwest crater sidewall. The wake can either be small, affecting only the upper part of the sidewall, or large, affecting the entire crater sidewall or even the crater floor. When flow separation occurs, the wake region over the crater sidewall is characterized by low wind speeds and potentially a return circulation near the surface. Particularly for large wakes, stability in the crater atmosphere is reduced and relatively high wind speeds occur at the crater floor, which is otherwise submerged in a strong surface-based inversion. Turbulent kinetic energy at the crater sidewall is typically higher during cold-air intrusions than is the case during flow separation, but high values can occur at the floor when a large wake forms.

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Diurnal Variations In Flow Over A Succession of Ridges and Valleys

Cited by 29 publications

References 21 publications

The Perdigão: Peering into Microscale Details of Mountain Winds

The Perdigão: Peering into Microscale Details of Mountain Winds

Uncertainty in the Representation of Orography in Weather and Climate Models and Implications for Parameterized Drag

Flow Separation in the Lee of a Crater Rim

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