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 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)

2015 ◽  
Vol 12 (6) ◽  
pp. 3003-3041 ◽  
Author(s):  
L. Bravo ◽  
M. Ramos ◽  
O. Astudillo ◽  
B. Dewitte ◽  
K. Goubanova
Keyword(s):  
High Resolution ◽  
Wind Stress ◽  
Seasonal Variability ◽  
Coastal Upwelling ◽  
Vertical Transport ◽  
Ekman Transport ◽  
Northern Chile ◽  
Ekman Pumping ◽  
Study Region ◽  
Relative Contribution

Abstract. Two physical mechanisms can contribute to coastal upwelling, offshore Ekman transport 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 proper 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 with the topographic features along the coast (headlands and embayments). Both wind stress and wind curl had a clear seasonal variability with a marked semiannual component. Alongshore wind stress maximum peak occurred in spring, second increase was in fall and minimum in winter. When a threshold of −3 x 10−5 s−1 for the across-shore wind curl was considered to define the region from which the winds decrease on-shoreward, the wind drop-off length scale varied between 8 and 45 km. The relative contribution of Ekman transport 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 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.

A close look at the middle Adriatic upwelling: schematized ROMS model simulations

2021 ◽  
Author(s):  
Gordana Beg Paklar ◽  
Zoran Pasaric ◽  
Mirko Orlic ◽  
Antonio Stanesic
Keyword(s):  
Wind Stress ◽  
Coastal Upwelling ◽  
Cold Water ◽  
Model Simulation ◽  
Initial Density ◽  
Wind Component ◽  
Ekman Pumping ◽  
Flat Bottom ◽  
Roms Model ◽  
Adcp Measurements

<p>Strong upwelling driven by the NNW winds was detected off the eastern middle Adriatic coast in May 2017. High resolution CTD data revealed thermocline doming by about 20 m at approximately 20 km from the coast. Main characteristics of the upwelling event are reproduced in the realistic ROMS model simulation. Adriatic scale ROMS model having 2.5 km horizontal resolution, forced by the air-sea fluxes calculated using surface fields from operational weather forecast model ALADIN-HR (Tudor et al., 2013; Termonia et al., 2018), river discharges, tides and water mass exchange through the Strait of Otranto, reproduces cold water dome and two-layer offshore flow in accordance with CTD and shipborne ADCP measurements. Significant improvement in the upwelling simulations is obtained using increased drag coefficient. The location of upwelling is correctly modelled, although with somewhat lower upper layer temperatures if compared with measurements. Moreover, the surface cyclonic circulation indicated by ADCP measurements along the cross-Adriatic transect is also evident in the model results. In order to improve understanding of the upwelling mechanism, several schematized numerical experiments are conducted. Wind fields from dynamical adaptation (Zagar and Rakovec, 1999; Ivatek-Sahdan and Tudor, 2004) of ALADIN-HR8 (8 km horizontal grid spacing) wind forecast to 2 km grid, are decomposed by the Natural Helmholtz-Hodge Decomposition (HHD) into divergence-free (incompressible), rotation-free (irrotational), and harmonic (translational) component (Bhatia et al., 2014). The components thus obtained and their combinations are used for calculation of the wind stress instead of the total wind field. Simulations with decomposed wind stress are conducted in the Adriatic domains with both flat bottom and realistic topography. Schematized simulations reveal that the positive rotational wind component is responsible for the rising of thermocline through Ekman pumping and it is more pronounced in the flat bottom basin. In the simulations with divergent wind component, the thermocline doming disappears and only coastal upwelling is reproduced. Additional idealised simulations with homogeneous NW wind stress are performed assuming both two-layer and uniform initial density field.</p>

scholarly journals The Seasonal Variability of the Arctic Ocean Ekman Transport and Its Role in the Mixed Layer Heat and Salt Fluxes

2006 ◽  
Vol 19 (20) ◽  
pp. 5366-5387 ◽  
Author(s):  
Jiayan Yang
Keyword(s):  
Arctic Ocean ◽  
Mixed Layer ◽  
Seasonal Variability ◽  
Surface Wind ◽  
Beaufort Sea ◽  
Ekman Transport ◽  
The Arctic ◽  
Ekman Pumping ◽  
Basin Scale ◽  
The Arctic Ocean

Abstract The oceanic Ekman transport and pumping are among the most important parameters in studying the ocean general circulation and its variability. Upwelling due to the Ekman transport divergence has been identified as a leading mechanism for the seasonal to interannual variability of the upper-ocean heat content in many parts of the World Ocean, especially along coasts and the equator. Meanwhile, the Ekman pumping is the primary mechanism that drives basin-scale circulations in subtropical and subpolar oceans. In those ice-free oceans, the Ekman transport and pumping rate are calculated using the surface wind stress. In the ice-covered Arctic Ocean, the surface momentum flux comes from both air–water and ice–water stresses. The data required to compute these stresses are now available from satellite and buoy observations. But no basin-scale calculation of the Ekman transport in the Arctic Ocean has been done to date. In this study, a suite of satellite and buoy observations of ice motion, ice concentration, surface wind, etc., will be used to calculate the daily Ekman transport over the whole Arctic Ocean from 1978 to 2003 on a 25-km resolution. The seasonal variability and its relationship to the surface forcing fields will be examined. Meanwhile, the contribution of the Ekman transport to the seasonal fluxes of heat and salt to the Arctic Ocean mixed layer will be discussed. It was found that the greatest seasonal variations of Ekman transports of heat and salt occur in the southern Beaufort Sea in the fall and early winter when a strong anticyclonic wind and ice motion are present. The Ekman pumping velocity in the interior Beaufort Sea reaches as high as 10 cm day−1 in November while coastal upwelling is even stronger. The contributions of the Ekman transport to the heat and salt flux in the mixed layer are also considerable in the region.

scholarly journals From monsoon to marine productivity in the Arabian Sea: insights from glacial and interglacial climates

2017 ◽  
Vol 13 (7) ◽  
pp. 759-778 ◽  
Author(s):  
Priscilla Le Mézo ◽  
Luc Beaufort ◽  
Laurent Bopp ◽  
Pascale Braconnot ◽  
Masa Kageyama
Keyword(s):  
Stress Intensity ◽  
Summer Monsoon ◽  
Wind Stress ◽  
Arabian Sea ◽  
Coastal Upwelling ◽  
Boreal Summer ◽  
Tropospheric Temperature ◽  
Ekman Pumping ◽  
Wind Stress Curl ◽  
Jet Axis

Abstract. The current-climate Indian monsoon is known to boost biological productivity in the Arabian Sea. This paradigm has been extensively used to reconstruct past monsoon variability from palaeo-proxies indicative of changes in surface productivity. Here, we test this paradigm by simulating changes in marine primary productivity for eight contrasted climates from the last glacial–interglacial cycle. We show that there is no straightforward correlation between boreal summer productivity of the Arabian Sea and summer monsoon strength across the different simulated climates. Locally, productivity is fuelled by nutrient supply driven by Ekman dynamics. Upward transport of nutrients is modulated by a combination of alongshore wind stress intensity, which drives coastal upwelling, and by a positive wind stress curl to the west of the jet axis resulting in upward Ekman pumping. To the east of the jet axis there is however a strong downward Ekman pumping due to a negative wind stress curl. Consequently, changes in coastal alongshore stress and/or curl depend on both the jet intensity and position. The jet position is constrained by the Indian summer monsoon pattern, which in turn is influenced by the astronomical parameters and the ice sheet cover. The astronomical parameters are indeed shown to impact wind stress intensity in the Arabian Sea through large-scale changes in the meridional gradient of upper-tropospheric temperature. However, both the astronomical parameters and the ice sheets affect the pattern of wind stress curl through the position of the sea level depression barycentre over the monsoon region (20–150° W, 30° S–60° N). The combined changes in monsoon intensity and pattern lead to some higher glacial productivity during the summer season, in agreement with some palaeo-productivity reconstructions.

Seasonal to interannual variations of wind forcing in the Peruvian upwelling system

2020 ◽  
Author(s):  
Sadegh Yari ◽  
Volker Mohrholz
Keyword(s):  
Wind Stress ◽  
Coastal Upwelling ◽  
Temporal Variations ◽  
Wind Forcing ◽  
Enso Cycle ◽  
Spatial And Temporal Variability ◽  
Ekman Pumping ◽  
North West ◽  
Upwelling System ◽  
Peruvian Coast

<p>The Humboldt (Peruvian) Upwelling System (HUS) is the most productive among the main Eastern Boundary Upwelling Systems (EBUS), namely California, North West Africa, Benguela and itself. In spite of comparable upwelling intensity its fisheries production exceeds that of the other upwelling systems considerably (Chavez and Messie 2009). Wind is the major driving force of the coastal and curl driven upwelling, that controlls the nutrient supply from the deep water pool to the euphotic surface layer. Strength, spatial and temporal variability of the wind forcing are subjected to seasonal and interannual changes. The core of this study is describe the wind driven upwelling cells in the Peruvian coastal area in detail using long-term data which is not well understood. A better understanding of the state and dynamics of HUS seems essential for fututre regional climate predictions. ASCAT wind stress data for the period of 11 years (2008-2018) is analyzed to assess the spatio-temporal variations of the wind stress field, coastal upwelling and Ekman pumping along the Peruvian coast. The meridional component of wind stress off the peruvian coast, which is the main driver of offshore transport, has been marginally inensified over the entire priod. However, a high level of interannual variability is evident. The El-Niño years show anomalously high wind stress and associated Ekman transoprt. Our results indicate that the southern sector is more influenced by ENSO cycle than the northern sector. Additionally, a strong seasonality in the wind stress is observed. During the austral summer (December-February) the wind stress show the minimum value while the high values are observed in July-September.</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.

Wind-induced upwelling along the west coast of North America, 1899–1988

1995 ◽  
Vol 52 (2) ◽  
pp. 325-334 ◽  
Author(s):  
William W. Hsieh ◽  
Daniel M. Ware ◽  
Richard E. Thomson
Keyword(s):  
British Columbia ◽  
Baja California ◽  
Coastal Upwelling ◽  
Function Analysis ◽  
Geostrophic Wind ◽  
Second Mode ◽  
Coastal Sea ◽  
Coastal Downwelling ◽  
Alongshore Wind Stress ◽  
Alongshore Wind

Alongshore geostrophic wind stresses (AWS) were used as an "index" of wind-induced coastal upwelling/downwelling for eight coastal stations from Baja California to Alaska for 1899–1988. For winters since around 1940, downwelling has intensified along Alaska and northern British Columbia, while upwelling has increased along Baja California. El Niño events induced strong winter coastal downwelling poleward of 40°N. During summer, upwelling has increased since around 1940 along southern British Columbia to Baja California, while from 1899 to 1940, upwelling declined along southern California to Baja California. Empirical orthogonal function analysis of the AWS showed that the first mode consisted of the AWS at the eight stations all varying in-phase, while the second mode had the northern four stations out-of-phase with the southern four stations. Off southern British Columbia, correlations between coastal sea level and AWS and between sea surface temperature and AWS were both strong during winter but insignificant during summer. In contrast, correlation between salinity and alongshore wind stress was insignificant during fall and winter, but strong during spring and moderate during summer. Summer AWS was positively correlated with both the fatness of sardine and the condition factor of herring off British Columbia.

scholarly journals Upwelling di Laut Banda dan Pesisir Selatan Jawa serta Hubungannya dengan ENSO dan IOD

Omni-Akuatika ◽  
2016 ◽  
Vol 12 (3) ◽  
Author(s):  
Herlina Ika Ratnawati ◽  
Rahmat Hidayat ◽  
Ahmad Bey ◽  
Tania June
Keyword(s):  
Chlorophyll A ◽  
Partial Correlation ◽  
Coastal Upwelling ◽  
Ekman Transport ◽  
Ekman Pumping ◽  
Southern Coast ◽  
Partial Correlation Analysis ◽  
June July August ◽  
June July ◽  
Equal Contribution

Upwelling events analysis in southern coast of Java and Banda sea were conducted. The events were identified by using satellite data i.e. wind surface, Sea Surface Temperature (SST) and ocean color during period of 14 years (2002-2016) which calculated by Ekman pumping and Ekman transport. It’s found that Ekman pumping velocity in Banda Sea reached a maximum in June-July-August (JJA) by approximately 3,65x10 -6 . Comparing with Ekman transport, Ekman pumping makes an even greater contribution to the local upwelling in Banda Sea. Ekman pumping velocity in southern coast of Java reached a maximum in June-July-August (JJA) by approximately 4,9x10 -1 ms . Ekman pumping and Ekman transport makes an equal contribution to coastal upwelling in southern coast of Java. That’s related to highest clorophyll-a concentration apperars in JJA periode. Partial correlation analysis then was applied to identify a correlation between chlorophyll-a concentration and interannual climate variabilities such as ENSO and IOD. Partial Correlation between chlorophyll-a and Nino 3.4 and DMI-Dipole Mode Index (controlled) in Banda Sea is 0.18, and 0.05 in southercoast of Java. It’s represent ENSO (Elnino Southern Oscilation) has higher influences to Banda Sea than southern coast of Java. Partial correlation between chlorophyll-a and DMI and Nino 3.4 (controlled) is 0.55 in southern coast of Java, and 0.25 in Banda Sea. Its represent IOD (Indian Ocean Dipole) has higher influences to southern coast of Java than Banda Sea. Upwelling in Banda sea and along southern coast of Java dominantly occurs in southeast monsoon as a responds to regional wind driven motion associated with the monsoon climate. Various condition of chlorophyll-a booming also occured according to combination of ENSO and IOD events. -6 -1 msKeywords: upwelling, Banda sea, southern coast of Java, Ekman transport, Ekman pumping, IOD, ENSO 

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