Supercritical Flow Interaction within the Cape Blanco–Cape Mendocino Orographic Complex

Haack, Tracy; Burk, Stephen D.; Dorman, Clive E.; Rogers, David P.

doi:10.1175/1520-0493(2001)129<0688:sfiwtc>2.0.co;2

Cited by 58 publications

(64 citation statements)

References 23 publications

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“…It is the ratio of the flow speed to the fastest possible gravity wave in the layer, which is proportional to MBL height and strength of the inversion. Typically, if the wind is strong within a shallow MBL, local variation along the coast is often attributed to mechanical forcing (e.g., Edwards et al 2001;Haack et al 2001). Strictly speaking in the ideal case, Fr of unity is transcritical.…”

Section: Introductionsupporting

confidence: 83%

Coastal Jet Adjustment near Point Conception, California, with Opposing Wind in the Bight

Rahn

Parish

Leon

2014

Monthly Weather Review

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Typical spring and summer conditions offshore of California consist of strong northerly low-level wind contained within the cool, well-mixed marine boundary layer (MBL) that is separated from the warm and dry free troposphere by a sharp temperature inversion. This system is often represented by two layers constrained by a lateral boundary. Aircraft measurements near Point Conception, California, on 3 June 2012 during the Precision Atmospheric MBL Experiment (PreAMBLE) captured small-scale features associated with northerly flow approaching the point with the added complexity of encountering opposing wind in the Santa Barbara Channel. An extremely sharp cloud edge extends south-southwest of Point Conception and the flight strategy consisted of a spoke pattern to map the features across the cloud edge. Lidar and in situ measurements reveal a nearly vertical jump in the MBL from 500 to 100 m close to the coast and a sharp edge at least 70 km away from the coast. In this case, it is hypothesized that it is not solely hydraulic features responsible for the jump, but the opposing flow in the Santa Barbara Channel is a major factor modifying the flow. Just southeast of Point Conception are three distinct layers: a shallow, cold layer near the surface with northwesterly winds associated with an abrupt decrease in MBL height from the north that thins eastward into the Santa Barbara Channel; a cool middle layer with easterly wind whose top slopes upward to the east; and the warm and dry free troposphere above.

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Section: Introductionsupporting

confidence: 83%

Coastal Jet Adjustment near Point Conception, California, with Opposing Wind in the Bight

Rahn

Parish

Leon

2014

Monthly Weather Review

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“…When the coast opens away from the oncoming supercritical flow, an expansion fan develops to smoothly turn the flow around the bend, accompanied by a decrease of the MABL height and by an increase of the wind speed due to a Bernoulli effect. For this reason, the CLLJ wind speed is usually higher and the SST lower in the lee of headlands (Haak et al, 2000;Tjernstro¨m and Grisogono, 2000). If the coast bends inward, the flow is decelerated and transits from super-to sub-critical in a shock wave (a ''hydraulic jump''), while the gravity waves farther downstream, which can propagate against the wind, accumulate and break at this point.…”

Section: Introductionmentioning

confidence: 74%

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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“…The monthly mean zonal wind stress and mean zonal gradient are also shown (side black line). Haack, et al, 2001;Koračin et al, 2004;Renault et al, 2015, among others), we now document the relationship between the relative importance of Ekman transport and pumping, and the coastal topography and shape of the coastline in the region. An along-coast orography index (H index ) is estimated from the average of the orographic height between the coastline and 100 km inland (as in Renault et al, 2015).…”

Section: Contributions Of Ekman Transport and Ekman Pumping To The Upmentioning

confidence: 99%

Seasonal variability of the Ekman transport and pumping in the upwelling system off central-northern Chile (∼  30° S) based on a high-resolution atmospheric regional model (WRF)

et al. 2016

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Abstract. Two physical mechanisms can contribute to coastal upwelling in eastern boundary current systems: offshore Ekman transport due to the predominant alongshore wind stress and Ekman pumping due to the cyclonic wind stress curl, mainly caused by the abrupt decrease in wind stress (drop-off) in a cross-shore band of 100 km. This wind drop-off is thought to be an ubiquitous feature in coastal upwelling systems and to regulate the relative contribution of both mechanisms. It has been poorly studied along the central-northern Chile region because of the lack in wind measurements along the shoreline and of the relatively low resolution of the available atmospheric reanalysis. Here, the seasonal variability in Ekman transport, Ekman pumping and their relative contribution to total upwelling along the central-northern Chile region ( ∼ 30 • S) is evaluated from a high-resolution atmospheric model simulation. As a first step, the simulation is validated from satellite observations, which indicates a realistic representation of the spatial and temporal variability of the wind along the coast by the model. The model outputs are then used to document the fine-scale structures in the wind stress and wind curl in relation to the topographic features along the coast (headlands and embayments). Both wind stress and wind curl had a clear seasonal variability with annual and semiannual components. Alongshore wind stress maximum peak occurred in spring, second increase was in fall and minimum in winter. When a threshold of −3 × 10 −5 s −1 for the across-shore gradient of alongshore wind was considered to define the region from which the winds decrease toward the coast, the wind dropoff length scale varied between 8 and 45 km. The relative contribution of the coastal divergence and Ekman pumping to the vertical transport along the coast, considering the estimated wind drop-off length, indicated meridional alternation between both mechanisms, modulated by orography and the intricate coastline. Roughly, coastal divergence predominated in areas with low orography and headlands. Ekman pumping was higher in regions with high orography and the presence of embayments along the coast. In the study region, the vertical transport induced by coastal divergence and Ekman pumping represented 60 and 40 % of the total upwelling transport, respectively. The potential role of Ekman pumping on the spatial structure of sea surface temperature is also discussed.

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Supercritical Flow Interaction within the Cape Blanco–Cape Mendocino Orographic Complex

Cited by 58 publications

References 23 publications

Coastal Jet Adjustment near Point Conception, California, with Opposing Wind in the Bight

Coastal Jet Adjustment near Point Conception, California, with Opposing Wind in the Bight

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

Seasonal variability of the Ekman transport and pumping in the upwelling system off central-northern Chile (∼  30° S) based on a high-resolution atmospheric regional model (WRF)

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Supercritical Flow Interaction within the Cape Blanco–Cape Mendocino Orographic Complex

Cited by 58 publications

References 23 publications

Coastal Jet Adjustment near Point Conception, California, with Opposing Wind in the Bight

Coastal Jet Adjustment near Point Conception, California, with Opposing Wind in the Bight

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

Seasonal variability of the Ekman transport and pumping in the upwelling system off central-northern Chile (∼ 30° S) based on a high-resolution atmospheric regional model (WRF)

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Product

Resources

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Seasonal variability of the Ekman transport and pumping in the upwelling system off central-northern Chile (∼  30° S) based on a high-resolution atmospheric regional model (WRF)