Effects of Wind Stress and Wind Stress Curl Variability on Coastal Upwelling

Enriquez, Amelito G; Friehe, Carl A.

doi:10.1175/1520-0485(1995)025<1651:eowsaw>2.0.co;2

Cited by 134 publications

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“…Despite that the length scale of the wind drop-off in front of central-northern Chile (∼ 45 km) is on average less than that estimated in the California Current system (Enriquez and Friehe, 1996;Renault et al, 2015), the wind-stress curl from this zonal gradient of the wind generates an Ekman pumping with a marked seasonality (Fig. 5) and positive vertical velocities (upward) that reach 4 m d −1 , similar values to that obtained by Pickett and Paduan (2003) in front of the region of the California Current system.…”

Section: Annual Variability Of the Wind Stress And Ekman Pumpingmentioning

confidence: 73%

“…This negative wind curl is mainly due to the onshore decay of the wind (wind drop-off), which presented length scales (L d ) between 8 and 45 km with a significant latitudinal variability. The wind drop-off scale is in (Enriquez and Friehe., 1996;Renault et al, 2015), we find that it is smaller in our study region. For instance L d ranges from 10 and 80 km between 35 and 45 • N (Renault et al, 2015).…”

Section: Discussionmentioning

confidence: 99%

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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)

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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Section: Annual Variability Of the Wind Stress And Ekman Pumpingmentioning

confidence: 73%

Section: Discussionmentioning

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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“…This spatial structure in wind stress results in the upwelling of waters not only at the coast due to the adjustment of cross-shelf Ekman transport to the presence of the coast, but also away from the coast where positive curl in the wind stress produces areas of divergent Ekman transport (Enriquez and Friehe 1995;Koračin et al 2004).…”

Section: Spatial Structure In Wind Forcing and Ocean Responsementioning

confidence: 99%

WEST: A northern California study of the role of wind-driven transport in the productivity of coastal plankton communities

Largier

Lawrence

Roughan

et al. 2006

Deep Sea Research Part II: Topical Studies in Oceanography

104

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The "Wind Events and Shelf Transport" (WEST) program was an interdisciplinary study of coastal upwelling off northern California in 2000 was comprised of modeling and field observations. The primary goal of WEST was to better describe and understand the competing influences of wind forcing on planktonic productivity in coastal waters. While increased upwelling favorable winds lead to increased nutrient supply, they also result in reduced light exposure due to deeper surface mixed layers and increased advective loss of plankton from coastal waters. The key to understanding high levels of productivity, amidst these competing responses to wind forcing, is the temporal and spatial structure of upwelling. Temporal fluctuations and spatial patterns allow strong upwelling that favors nutrient delivery to be juxtaposed with less energetic conditions that favor stratification and plankton blooms.

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“…[4] Disruptions to coastal upwelling are linked to changes in wind speed and direction [Hawkins and Stuart, 1980;Enriquez and Friehe, 1995]. In the western Caribbean, equatorward atmospheric departures originating at the mid 1 northern latitudes can abruptly change the normal wind pattern, bringing cold surges lasting less than a week as far south as the Isthmus of Panama [Shultz et al, 1998].…”

Section: Introductionmentioning

confidence: 99%

Atmospheric events disrupting coastal upwelling in the southwestern Caribbean

2010

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[1] Year-round coastal upwelling is a prevalent phenomenon in the southwestern Caribbean region, driven by northeast trade winds. This pattern can be disrupted during the boreal winter-to-spring transition by event-scale departures in the pressure systems, characterized by a change in wind direction to northward, with the accompanying relaxation of coastal upwelling. To study these poorly understood events, regional atmospheric and data-assimilative ocean modeling experiments were carried out for the period 4 March to 9 April 2003 and compared to shipboard observations This combined ocean-atmosphere approach allowed us to study the evolution of a 3-day atmospheric disturbance affecting ocean currents and collapsing the upwelling pattern against the Colombian coast along the Guajira Peninsula near 12°N. The southward extension of the coastal upwelling, which normally reaches 10.5°N, was blocked by the warmer and slightly lower salinity waters of the cyclonic Panama-Colombia gyre. Under typical conditions, the ocean model and shipboard observations of temperature and salinity profiles were in good agreement with each other, both at coastal and oceanic stations. The presence of a low-level westward wind jet was manifested in the atmospheric model simulation, confirming that it promotes the Guajira upwelling system; however, the jet vanishes under disturbed atmospheric conditions.

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Effects of Wind Stress and Wind Stress Curl Variability on Coastal Upwelling

Cited by 134 publications

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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)

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)

WEST: A northern California study of the role of wind-driven transport in the productivity of coastal plankton communities

Atmospheric events disrupting coastal upwelling in the southwestern Caribbean

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Effects of Wind Stress and Wind Stress Curl Variability on Coastal Upwelling

Cited by 134 publications

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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)

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)

WEST: A northern California study of the role of wind-driven transport in the productivity of coastal plankton communities

Atmospheric events disrupting coastal upwelling in the southwestern Caribbean

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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)

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)