An Explanation for the Warmwater Intrusion off the British Columbia Coast

1972 ◽  
Vol 29 (1) ◽  
pp. 103-107 ◽  
Author(s):  
Richard E. Thomson
Keyword(s):  
British Columbia ◽  
Characteristic Feature ◽  
Direct Effect ◽  
Wind Stress ◽  
Stress Component ◽  
Meridional Wind ◽  
Warm Water ◽  
Ekman Transport ◽  
Temperature Variations ◽  
Annual Variations

An explanation is given for the well-known annual variations in the northward penetration of relatively warm water off the British Columbia coast. At the top of the permanent halocline, a characteristic feature of the region, both the onshore Ekman transport, resulting from a northward meridional wind-stress component, and the relative warmth of the upper oceanic layer in winter are suggested as being responsible for these variations. At the bottom of the halocline, which lies below the depth of direct surface influence, comparison of the northward meridional wind-stress component with the temperature variations suggests that other processes besides the direct effect of Ekman transport are important in determining the variations at that level.

scholarly journals Trends in coastal upwelling intensity during the late 20th century

Ocean Science ◽  
2010 ◽  
Vol 6 (3) ◽  
pp. 815-823 ◽  
Author(s):  
N. Narayan ◽  
A. Paul ◽  
S. Mulitza ◽  
M. Schulz
Keyword(s):  
20Th Century ◽  
Wind Stress ◽  
Coastal Upwelling ◽  
Meridional Wind ◽  
Steady Increase ◽  
Late 20Th Century ◽  
North West ◽  
Basin Scale ◽  
Upwelling Intensity ◽  
Instrumental Records

Abstract. This study presents linear trends of coastal upwelling intensity in the later part of the 20th century (1960–2001) employing various indices of upwelling, derived from meridional wind stress and sea surface temperature. The analysis was conducted in the four major coastal upwelling regions in the world, which are off North-West Africa, Lüderitz, California and Peru. The trends in meridional wind stress showed a steady increase of intensity from 1960–2001, which was also reflected in the SST index calculated for the same time period. The steady cooling observed in the instrumental records of SST off California substantiated this observation further. It was also noted that the trends in meridional wind stress obtained from different datasets differ substantially from each other. Correlation analysis showed that basin-scale oscillations like the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO) could not be directly linked to the observed increase of upwelling intensity off NW Africa and California respectively. The relationship of the North Atlantic Oscillation (NAO) with coastal upwelling off NW Africa turned out to be ambiguous due to a negative correlation between the NAO index and the meridional wind stress and a lack of correlation with the SST index. Our results give additional support to the hypothesis that the coastal upwelling intensity increases globally because of raising greenhouse gas concentrations in the atmosphere and an associated increase of the land-sea pressure gradient and meridional wind stress.

scholarly journals SEASONAL PATTERN OF WIND INDUCED UPWELLING OVER JAVA-BALI SEA WATERS AND SURROUNDING AREA

2010 ◽  
Vol 5 (1) ◽  
Author(s):  
Siswanto ◽  
Suratno
Keyword(s):  
Wind Stress ◽  
Coastal Upwelling ◽  
Sea Water ◽  
Mixed Layer Depth ◽  
Surface Wind ◽  
Ekman Transport ◽  
Monsoon Circulation ◽  
Wide Field ◽  
Surrounding Area ◽  
Noaa Avhrr

The influence of monsoonal wind to coastal upwelling mechanism which is generated by Ekman transport was studied here by analyzing wind stress curl (WSC) distribution over Java-Bali Sea waters and its surrounding area. Surface wind data were used as input data to calculate curl of wind stress in barotropic model. Confirmation with Corioli effect in the Southern Hemisphere, it could be known that negative curl value has relation with vertical motion of sea water as resulted by Ekman transport. Result of analysis showed that negative curl near coast over Java Sea which is stretching to Lombok Sea occurred in December to April when westerly wind of the North West Monsoon actives. It can be guidance and related with season of coastal upwelling in the region. Reversal condition, the occurrance of coastal upwelling in the south coast of JAva island related with the negative value of WSC that occurs since easterlies wind take place in May to August as a part of South East Monsoon episode. Generally, upwelling occurrance in the field of study is a response to the Monsoon circulation. This study with related data such as sea surface temperature, chlorophyll concetration and mixed layer depth that derived from satellite imaging data National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer (NOAA-AVHRR), Aqua/Modis and sea viewing Wide Field-of-view Sensor(Sea WiFS) shows as magnificent confirmation pattern. So applying WSC to recoqnize upwelling zone is alternatively way as climatic approach to maps potential fertilizing of sea water in maritime-continent Indonesia. Key words: coastal upwelling, Ekman transport, Java-Bali Sea, Monsoon circulation, upwelling.

scholarly journals 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)

Ocean Science ◽  
2016 ◽  
Vol 12 (5) ◽  
pp. 1049-1065 ◽  
Author(s):  
Luis Bravo ◽  
Marcel Ramos ◽  
Orlando Astudillo ◽  
Boris Dewitte ◽  
Katerina Goubanova
Keyword(s):  
High Resolution ◽  
Wind Stress ◽  
Seasonal Variability ◽  
Coastal Upwelling ◽  
Ekman Transport ◽  
Northern Chile ◽  
Ekman Pumping ◽  
Relative Contribution ◽  
Alongshore Wind Stress ◽  
Alongshore Wind

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 drop-off 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.

scholarly journals First Records of Long-beaked Common Dolphins, Delphinus capensis, in Canadian Waters

2005 ◽  
Vol 119 (1) ◽  
pp. 110 ◽  
Author(s):  
John K. B. Ford
Keyword(s):  
British Columbia ◽  
Warm Water ◽  
Common Dolphin ◽  
Central California ◽  
Far North ◽  
Common Dolphins ◽  
Delphinus Capensis

The genus Delphinus has recently been determined to be comprised of two species, the Short-beaked Common Dolphin, D. delphis, and the Long-beaked Common Dolphin, D. capensis. D. delphis is regularly observed in eastern Canadian waters, but is known only from a single stranding in British Columbia. Two specimen records and a series of sightings of D. capensis in British Columbian waters during 1993-2003, detailed here, are the first for this species in Canada. D. capensis normally ranges only as far north as central California, and its abundance in those waters increases in association with warm-water oceanographic events. Although the species appears to be rare in British Columbia, future sightings during warm-water periods might be anticipated.

The Role of the NECC in a Strong El Niño.

2020 ◽  
Author(s):  
David Webb
Keyword(s):  
Ocean Model ◽  
Warm Water ◽  
Ekman Transport ◽  
Global Ocean ◽  
Instability Waves ◽  
Tropical Instability Waves ◽  
The North ◽  
Ocean Science ◽  
The Pacific ◽  
North Equatorial Counter Current

<p>An analysis of archived data from the NEMO 1/12th degree global ocean model shows the importance of the North Equatorial Counter Current (NECC) in the development of the strong 1982–1983 and 1997–1998 El Niños.  The model results indicate that in a normal year the coreof warm water in the NECC is diluted by the surface Ekman transport, by geostrophic inflow and by tropical instability waves. During the development of the 1982–1983 and 1997–1998 El Niños, these processes had reduced effect at the longitudes of warmest equatorial temperatures. During the autumns of 1982 and 1997, the speed of the NECC was also increased by a stronger-than-normal annual Rossby wave and other changes in sea level in the western Pacific.  The resulting increased transport of warm water by the NECC resulted in water with temperatures above 28C reaching the eastern Pacific.  This appears to have been a major factor in moving the centre of deep atmospheric convection eastwards across the Pacific.</p><p>Note:  This is based on the paper published in Ocean Science.  An oral presentation is possible.</p>

Nonlinear stratified spin-up

2002 ◽  
Vol 473 ◽  
pp. 211-244 ◽  
Author(s):  
LEIF N. THOMAS ◽  
PETER B. RHINES
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Wind Stress ◽  
Thermal Boundary Layer ◽  
Ekman Layer ◽  
Ekman Transport ◽  
Ekman Pumping ◽  
Vertical Diffusion ◽  
Vertical Vorticity ◽  
Horizontal Advection

Both a weakly nonlinear analytic theory and direct numerical simulation are used to document processes involved during the spin-up of a rotating stratified fluid driven by wind-stress forcing for time periods less than a homogeneous spin-up time. The strength of the wind forcing, characterized by the Rossby number ε, is small enough (i.e. ε[Lt ]1) that a regular perturbation expansion in ε can be performed yet large enough (more specifically, ε∝E1/2, where E is the Ekman number) that higher-order effects of vertical diffusion and horizontal advection of momentum/density are comparable in magnitude. Cases of strong stratification, where the Burger number S is equal to one, with zero heat flux at the upper boundary are considered. The Ekman transport calculated to O(ε) decreases with increasing absolute vorticity. In contrast to nonlinear barotropic spin-up, vortex stretching in the interior is predominantly linear, as vertical advection negates stretching of interior relative vorticity, yet is driven by Ekman pumping modified by nonlinearity. As vertical vorticity is generated during the spin-up of the fluid, the vertical vorticity feeds back on the Ekman pumping/suction, enhancing pumping and vortex squashing while reducing suction and vortex stretching. This feedback mechanism causes anticyclonic vorticity to grow more rapidly than cyclonic vorticity. Strict application of the zero-heat-flux boundary condition leads to the growth of a diffusive thermal boundary layer E−1/4 times thicker than the Ekman layer embedded within it. In the Ekman layer, vertical diffusion of heat balances horizontal advection of temperature by extracting heat from the thermal boundary layer beneath. The flux of heat extracted from the top of the thermal boundary layer by this mechanism is proportional to the product of the Ekman transport and the horizontal gradient of the temperature at the surface. The cooling caused by this heat flux generates density inversions and intensifies lateral density gradients where the wind-stress curl is negative. These thermal gradients make the potential vorticity strongly negative, conditioning the fluid for ensuing symmetric instability which greatly modifies the spin-up process.

The Response of Buoyant Coastal Plumes to Upwelling-Favorable Winds*

2004 ◽  
Vol 34 (11) ◽  
pp. 2458-2469 ◽  
Author(s):  
Steven Lentz
Keyword(s):  
Wind Stress ◽  
Vertical Mixing ◽  
Wind Forcing ◽  
Ekman Transport ◽  
Entrainment Rate ◽  
Buoyant Plume ◽  
Cross Sectional ◽  
Buoyancy Forcing ◽  
Density Anomaly ◽  
Variable Wind

Abstract To better understand the response of a buoyant coastal plume to wind-induced upwelling, a two-dimensional theory is developed that includes entrainment. The primary assumption is that competition between wind-driven vertical mixing and lateral buoyancy forcing in the region where the isopycnals slope upward to intersect the surface results in continual entrainment at the offshore edge of the plume. The theory provides estimates of the buoyant plume characteristics and offshore displacement as a function of time t, given the wind stress, the characteristics of the buoyant plume prior to the onset of the wind forcing, and a critical value for the bulk Richardson number (Ric). The theory predicts that, for t̂ ≡ t/ts, the plume density anomaly decreases as (1 + t̂)−1, the thickness increases as (1 + t̂)1/3, the width increases as (1 + t̂)2/3, and the plume average entrainment rate decreases as (1 + t̂)−2/3. Here ts = 2Ao/(RicUE) is the time for entrainment to double the cross-sectional area of the plume Ao at the onset of the wind forcing, where UE is the Ekman transport. The theory reproduces results from 20 numerical model runs by Fong and Geyer, including their estimates of the plume-average entrainment rate (correlations greater than 0.98 and regression coefficients approximately 1 for plume characteristics and 1.7 for the entrainment rate). The theory, modified to allow for time-variable wind stress, also reproduces the observed response of the buoyant coastal plume from Chesapeake Bay during an 11-day period of upwelling winds in August 1994.

scholarly journals Trends in coastal upwelling intensity during the late 20th century

2010 ◽  
Vol 7 (1) ◽  
pp. 335-360 ◽  
Author(s):  
N. Narayan ◽  
A. Paul ◽  
S. Mulitza ◽  
M. Schulz
Keyword(s):  
20Th Century ◽  
Wind Stress ◽  
Coastal Upwelling ◽  
Meridional Wind ◽  
Steady Increase ◽  
Late 20Th Century ◽  
North West ◽  
Basin Scale ◽  
Upwelling Intensity ◽  
Instrumental Records

Abstract. This study presents linear trends of coastal upwelling intensity in the later part of the 20th century (1960–2001) employing various indices of upwelling, derived from meridional wind stress and sea surface temperature. The analysis was conducted in the four major coastal upwelling regions in the world, which are off North-West Africa, Lüderitz, California and Peru respectively. The trends in meridional wind stress showed a steady increase of intensity from 1960–2001, which was also reflected in the SST index calculated for the same time period. The steady cooling observed in the instrumental records of SST off California substantiated this observation further. Correlation analysis showed that basin-scale oscillations like the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO) could not be directly linked to the observed increase of upwelling intensity off NW Africa and California respectively. The relationship of the North Atlantic Oscillation (NAO) with coastal upwelling off NW Africa turned out to be ambiguous due to a negative correlation between the NAO index and the meridional wind stress and a lack of correlation with the SST index. Our results give additional support to the hypothesis that the coastal upwelling intensity increases globally because of raising greenhouse gas concentrations in the atmosphere and an associated increase of the land-sea pressure gradient and meridional wind stress.

scholarly journals The wind-driven overturning circulation of the World Ocean

2005 ◽  
Vol 2 (5) ◽  
pp. 473-505 ◽  
Author(s):  
K. Döös
Keyword(s):  
Boundary Layer ◽  
Wind Stress ◽  
World Ocean ◽  
Conveyor Belt ◽  
Meridional Overturning Circulation ◽  
Ekman Transport ◽  
Western Boundary ◽  
Overturning Circulation ◽  
The World ◽  
Meridional Overturning

Abstract. The wind driven aspects of the meridional overturning circulation of the world ocean and the Conveyor Belt is studied making use of a simple analytical model. The model consists of three reduced gravity layers with an inviscid Sverdrupian interior and a western boundary layer. The net north-south exchange is made possible by setting appropriate western boundary conditions, so that most of the transport is confined to the western boundary layer, while the interior is the Sverdrupian solution to the wind stress. The flow across the equator is made possible by the change of potential vorticity by the Rayleigh friction in the western boundary layer, which is sufficient to permit water and the Conveyor Belt to cross the equator. The cross-equatorial flow is driven by a weak meridional pressure gradient in opposite direction in the two layers on the equator at the western boundary. The model is applied to the World Ocean with a realistic wind stress. The amplitude of the Conveyor Belt is set by the northward Ekman transport in the Southern Ocean and the outcropping latitude of the NADW. It is in this way possible to set the amount of NADW that is pumped up from the deep ocean and driven northward by the wind and converted in the surface layer into less dense water by choosing the outcropping latitude and the depth of the layers at the western boundary. The model has proved to be able to simulate many of the key features of the Conveyor Belt and the meridional overturning cells of the World Ocean. This despite that there is no deep ocan mixing and that the water mass conversions in the this model are made at the surface.

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