The Summertime Low-Level Jet and Marine Boundary Layer Structure along the California Coast

Burk, Stephen D.; Thompson, W. T.

doi:10.1175/1520-0493(1996)124<0668:tsllja>2.0.co;2

Cited by 173 publications

(154 citation statements)

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“…During the summer months, stronger winds associated with a nocturnal low-level jet (LLJ) occur at or below 500 m, soon after the collapse of the boundary layer (0300-1100 UTC or 1900-0300 LT). This is in accordance with previous studies (Burk and Thompson 1996;Bao et al 2008). The LLJ begins in March-April and continues through the summer until September-October, with the height of the jet maximum near 400 m a.g.l., with little hourly variation in the jet height during the night, or from month to month.…”

Section: Cbl Depth (Km)supporting

confidence: 94%

Diurnal Evolution and Annual Variability of Boundary-Layer Height and Its Correlation to Other Meteorological Variables in California’s Central Valley

Bianco

Djalalova

King

et al. 2011

Boundary-Layer Meteorol

109

111

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One year of observations from a network of five 915-MHz boundary-layer radar wind profilers equipped with radio acoustic sounding systems located in California's Central Valley are used to investigate the annual variability of convective boundary-layer depth and its correlation to meteorological parameters and conditions. Results from the analysis show that at four of the sites, the boundary-layer height reaches its maximum in the late-spring months then surprisingly decreases during the summer months, with mean July depths almost identical to those for December. The temporal decrease in boundary-layer depth, as well as its spatial variation, is found to be consistent with the nocturnal low-level lapse rate observed at each site. Multiple forcing mechanisms that could explain the unexpected seasonal behaviour of boundary-layer depth are investigated, including solar radiation, precipitation, boundary-layer mesoscale convergence, low-level cold-air advection, local surface characteristics and irrigation patterns and synoptic-scale subsidence. Variations in solar radiation, precipitation and synoptic-scale subsidence do not explain the shallow summertime convective boundary-layer depths observed. Topographically forced cold-air advection and local land-use characteristics can help explain the shallow CBL depths at the four sites, while topographically forced low-level convergence helps maintain larger CBL depths at the fifth site near the southern end of the valley.

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Section: Cbl Depth (Km)supporting

confidence: 94%

Diurnal Evolution and Annual Variability of Boundary-Layer Height and Its Correlation to Other Meteorological Variables in California’s Central Valley

Bianco

Djalalova

King

et al. 2011

Boundary-Layer Meteorol

109

111

View full text Add to dashboard Cite

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“…These mesoscale intensifications of the surface wind speed along the coast in the EBCCS area, on the north-west African coast, occur due to the sharpening of the pressure gradient there through a positive feedback process triggered by upwelling and by the low SST at the coast [64][65][66][67]. The low SST decreases the air temperature within the MABL at the coast, and a sharp inversion develops due to warm subsiding air above [68,69]. The decreasing MABL air temperature towards the coast causes the capping inversion to slope gently from west to east, leading to the channeling of the flow at the coast that, due to a Bernoulli effect, leads to a wind-speed increase [46].…”

Section: Wind Sea and Swell Wave Heights And Periodsmentioning

confidence: 99%

“…This feature is sometimes accompanied with the occurrence of coastal jets in summer, with the wind speed increasing in altitude, with maxima around the MABL height, at altitudes of the order of 400-600 m [39,40,53,54,[70][71][72]. The presence of headlands as well as the orientation of the coast line can also result in additional local enhancement of the wind speed at the coast [41,68,73], as well as in changes in the flow direction. When the flow interacts with points and capes protruding off the coast, gravity waves are exited.…”

Section: Wind Sea and Swell Wave Heights And Periodsmentioning

confidence: 99%

Seasonal Variability of Wind Sea and Swell Waves Climate along the Canary Current: The Local Wind Effect

Semedo

2018

JMSE

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A climatology of wind sea and swell waves along the Canary eastern boundary current area, from west Iberia to Mauritania, is presented. The study is based on the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis ERA-Interim. The wind regime along the Canary Current, along west Iberia and north-west Africa, varies significantly from winter to summer. High summer wind speeds generate high wind sea waves, particularly along the coasts of Morocco and Western Sahara. Lower winter wind speeds, along with stronger extratropical storms crossing the North Atlantic sub-basin up north lead to a predominance of swell waves in the area during from December to February. In summer, the coast parallel wind interacts with the coastal headlands, increasing the wind speed and the locally generated waves. The spatial patterns of the wind sea or swell regional wave fields are shown to be different from the open ocean, due to coastal geometry, fetch dimensions, and island sheltering.

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“…Considering the influence of topography and the geometry of the coastline to describe the spatial variability of the wind stress (e.g., Winant et al, 1988;Burk and Thompson, 1996;Figure 6. Hovmöller diagrams of alongshore wind stress seasonal cycle (top panels) and the zonal gradient of alongshore wind (lower panels) for the regions at 28.5 (a, d), 30.5 (b, e) and 32.5 • S (c, f).…”

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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The Summertime Low-Level Jet and Marine Boundary Layer Structure along the California Coast

Cited by 173 publications

References 0 publications

Diurnal Evolution and Annual Variability of Boundary-Layer Height and Its Correlation to Other Meteorological Variables in California’s Central Valley

Diurnal Evolution and Annual Variability of Boundary-Layer Height and Its Correlation to Other Meteorological Variables in California’s Central Valley

Seasonal Variability of Wind Sea and Swell Waves Climate along the Canary Current: The Local Wind Effect

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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The Summertime Low-Level Jet and Marine Boundary Layer Structure along the California Coast

Cited by 173 publications

References 0 publications

Diurnal Evolution and Annual Variability of Boundary-Layer Height and Its Correlation to Other Meteorological Variables in California’s Central Valley

Diurnal Evolution and Annual Variability of Boundary-Layer Height and Its Correlation to Other Meteorological Variables in California’s Central Valley

Seasonal Variability of Wind Sea and Swell Waves Climate along the Canary Current: The Local Wind Effect

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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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)