scholarly journals Wind-induced upwelling in the Kerguelen Plateau region

2014 ◽  
Vol 11 (22) ◽  
pp. 6389-6400 ◽  
Author(s):  
S. T. Gille ◽  
M. M. Carranza ◽  
R. Cambra ◽  
R. Morrow
Keyword(s):  
Wind Stress ◽  
Vertical Mixing ◽  
Euphotic Zone ◽  
Ekman Pumping ◽  
Kerguelen Plateau ◽  
Wind Stress Curl ◽  
Chl A ◽  
The North ◽  
The Impact ◽  
Ekman Upwelling

Abstract. In contrast to most of the Southern Ocean, the Kerguelen Plateau supports an unusually strong spring chlorophyll (Chl a) bloom, likely because the euphotic zone in the region is supplied with higher iron concentrations. This study uses satellite wind, sea surface temperature (SST), and ocean color data to explore the impact of wind-driven processes on upwelling of cold (presumably iron-rich) water to the euphotic zone. Results show that, in the Kerguelen region, cold SSTs correlate with high wind speeds, implying that wind-mixing leads to enhanced vertical mixing. Cold SSTs also correlate with negative wind-stress curl, implying that Ekman pumping can further enhance upwelling. In the moderate to high eddy kinetic energy (EKE) regions surrounding Kerguelen, we find evidence of coupling between winds and SST gradients associated with mesoscale eddies, which can locally modulate the wind-stress curl. This coupling introduces persistent wind-stress curl patterns and Ekman pumping around these long-lived eddies, which may modulate the evolution of Chl a in the downstream plume far offshore. Close to the plateau, this eddy coupling breaks down. Kerguelen has a significant wind shadow on its downwind side, which changes position depending on the prevailing wind and which generates a wind-stress curl dipole that shifts location depending on wind direction. This leads to locally enhanced Ekman pumping for a few hundred kilometers downstream from the Kerguelen Plateau; Chl a values tend to be more elevated in places where wind-stress curl induces Ekman upwelling than in locations of downwelling, although the estimated upwelling rates are too small for this relationship to derive from direct effects on upward iron supply, and thus other processes, which remain to be determined, must also be involved in the establishment of these correlations. During the October and November (2011) KErguelen Ocean and Plateau compared Study (KEOPS-2) field program, wind conditions were fairly typical for the region, with enhanced Ekman upwelling expected to the north of the Kerguelen Islands.

scholarly journals Wind-induced upwelling in the Kerguelen Plateau Region

2014 ◽  
Vol 11 (6) ◽  
pp. 8373-8397 ◽  
Author(s):  
S. T. Gille ◽  
M. M. Carranza ◽  
R. Cambra ◽  
R. Morrow
Keyword(s):  
Wind Stress ◽  
Vertical Mixing ◽  
Euphotic Zone ◽  
Sea Surface ◽  
Ekman Pumping ◽  
Kerguelen Plateau ◽  
Wind Stress Curl ◽  
Chl A ◽  
Wind Speeds ◽  
The Impact

Abstract. In contrast to most of the Southern Ocean, the Kerguelen Plateau supports an unusually strong spring chlorophyll (Chl a) bloom, likely because the euphotic zone in the region is supplied with higher iron concentrations. This study uses satellite wind, sea surface temperature (SST), and ocean color data to explore the impact of wind-driven processes on upwelling of cold (presumably iron-rich) water to the euphotic zone. High wind speeds typically correlate with cold sea surface temperatures, implying that wind-mixing leads to enhanced vertical mixing. Negative wind-stress curl also correlates with cold SSTs, implying that Ekman pumping can further enhance upwelling, and coupling between winds and SSTs associated with mesoscale eddies can locally modulate the wind-stress curl. Kerguelen has a significant wind shadow on its downwind side, which generates a wind-stress curl dipole that shifts location depending on wind direction. This leads to locally enhanced Ekman pumping on the downstream side of the Kerguelen Plateau, where Chl a blooms are observed most years.

scholarly journals Seasonal variability of SST fronts and winds on the southeastern continental shelf of Brazil

2019 ◽  
Vol 69 (11-12) ◽  
pp. 1387-1399 ◽  
Author(s):  
Huan-Huan Chen ◽  
Yiquan Qi ◽  
Yuntao Wang ◽  
Fei Chai
Keyword(s):  
Continental Shelf ◽  
Wind Stress ◽  
Seasonal Variability ◽  
Detection Algorithm ◽  
Coupling Coefficients ◽  
Seafloor Topography ◽  
Wind Stress Curl ◽  
Large Coupling ◽  
The Impact ◽  
Sst Fronts

Abstract Fourteen years (September 2002 to August 2016) of high-resolution satellite observations of sea surface temperature (SST) data are used to describe the frontal pattern and frontogenesis on the southeastern continental shelf of Brazil. The daily SST fronts are obtained using an edge-detection algorithm, and the monthly frontal probability (FP) is subsequently calculated. High SST FPs are mainly distributed along the coast and decrease with distance from the coastline. The results from empirical orthogonal function (EOF) decompositions reveal strong seasonal variability of the coastal SST FP with maximum (minimum) in the astral summer (winter). Wind plays an important role in driving the frontal activities, and high FPs are accompanied by strong alongshore wind stress and wind stress curl. This is particularly true during the summer, when the total transport induced by the alongshore component of upwelling-favorable winds and the wind stress curl reaches the annual maximum. The fronts are influenced by multiple factors other than wind forcing, such as the orientation of the coastline, the seafloor topography, and the meandering of the Brazil Current. As a result, there is a slight difference between the seasonality of the SST fronts and the wind, and their relationship was varying with spatial locations. The impact of the air-sea interaction is further investigated in the frontal zone, and large coupling coefficients are found between the crosswind (downwind) SST gradients and the wind stress curl (divergence). The analysis of the SST fronts and wind leads to a better understanding of the dynamics and frontogenesis off the southeastern continental shelf of Brazil, and the results can be used to further understand the air-sea coupling process at regional level.

scholarly journals Effects of Tropical Cyclones on Sea Surface Salinity in the Bay of Bengal Based on SMAP and Argo Data

Water ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 2975
Author(s):  
Huabing Xu ◽  
Rongzhen Yu ◽  
Danling Tang ◽  
Yupeng Liu ◽  
Sufen Wang ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
Bay Of Bengal ◽  
Vertical Mixing ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Ekman Pumping ◽  
Surface Salinity ◽  
Argo Data ◽  
Before And After ◽  
The Impact

This paper uses the Argo sea surface salinity (SSSArgo) before and after the passage of 25 tropical cyclones (TCs) in the Bay of Bengal from 2015 to 2019 to evaluate the sea surface salinity (SSS) of the Soil Moisture Active Passive (SMAP) remote sensing satellite (SSSSMAP). First, SSSArgo data were used to evaluate the accuracy of the 8-day SMAP SSS data, and the correlations and biases between SSSSMAP and SSSArgo were calculated. The results show good correlations between SSSSMAP and SSSArgo before and after TCs (before: SSSSMAP = 1.09SSSArgo−3.08 (R2 = 0.69); after: SSSSMAP = 1.11SSSArgo−3.61 (R2 = 0.65)). A stronger negative bias (−0.23) and larger root-mean-square error (RMSE, 0.95) between the SSSSMAP and SSSArgo were observed before the passage of 25 TCs, which were compared to the bias (−0.13) and RMSE (0.75) after the passage of 25 TCs. Then, two specific TCs were selected from 25 TCs to analyze the impact of TCs on the SSS. The results show the significant SSS increase up to the maximum 5.92 psu after TC Kyant (2016), which was mainly owing to vertical mixing and strong Ekman pumping caused by TC and high-salinity waters in the deep layer that were transported to the sea surface. The SSSSMAP agreed well with SSSArgo in both coastal and offshore waters before and after TC Roanu (2016) and TC Kyant (2016) in the Bay of Bengal.

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.

scholarly journals Sensitivity of phytoplankton distributions to vertical mixing along a North Atlantic transect

2014 ◽  
Vol 11 (2) ◽  
pp. 839-893
Author(s):  
L. Hahn-Woernle ◽  
H. A. Dijkstra ◽  
H. J. Van der Woerd
Keyword(s):  
North Atlantic ◽  
Light Attenuation ◽  
Vertical Mixing ◽  
Clear Correlation ◽  
Optical Parameters ◽  
Chl A ◽  
Phytoplankton Concentration ◽  
In Situ Data ◽  
The North ◽  
Using Data

Abstract. Using in situ data of upper ocean vertical mixing profiles along a transect in the North Atlantic and an idealised phytoplankton growth model (PGM), we study the sensitivity of the surface phytoplankton concentration to vertical mixing distributions. Optical parameters in the PGM are calibrated with observations of light attenuation. The calibration of the biological parameters in the PGM is carried out at three different referent stations with observed vertical profiles of chlorophyll a (Chl a) and nutrient concentration. Vertical mixing profiles at all other stations are next used at the reference stations to study the sensitivity of modelled phytoplankton distributions to vertical mixing. We find that shifts in vertical mixing are able to induce a transition from an upper chlorophyll maximum to a deep one and vice-versa. Furthermore, a clear correlation between the surface phytoplankton concentration and the mixing induced nutrient flux is found in nutrient limited regions. This may open up the possibility to extract characteristics of vertical mixing from satellite ocean colour data using data-assimilation methods.

On the Influence of Random Wind Stress Errors on the Four-Dimensional, Midlatitude Ocean Inverse Problem

2009 ◽  
Vol 137 (6) ◽  
pp. 1844-1862
Author(s):  
Tsuyoshi Wakamatsu ◽  
Michael G. G. Foreman ◽  
Patrick F. Cummins ◽  
Josef Y. Cherniawsky
Keyword(s):  
Inverse Problem ◽  
Wind Stress ◽  
A Priori ◽  
Ocean Dynamics ◽  
Wind Stress Curl ◽  
Error Covariance ◽  
Model State ◽  
The Impact ◽  
Stress Error ◽  
State Error

Abstract The effects of the parameterized wind stress error covariance function on the a priori error covariance of an ocean general circulation model (OGCM) are examined. These effects are diagnosed by computing the projection of the a priori model state error covariance matrix to sea surface height (SSH). The sensitivities of the a priori error covariance to the wind stress curl error are inferred from the a priori SSH error covariance and are shown to differ between the subpolar and subtropical gyres because of different contributions from barotropic and baroclinic ocean dynamics. The spatial structure of the SSH error covariance due to the wind stress error indicates that the a priori model state error is determined indirectly by the wind stress curl error. The impact of this sensitivity on the solution of a four-dimensional inverse problem is inferred.

scholarly journals The Wintertime Wind Stress Curl Field in the North Atlantic and Its Relation to Atmospheric Teleconnection Patterns

2010 ◽  
Vol 67 (5) ◽  
pp. 1687-1694 ◽  
Author(s):  
Shusaku Sugimoto ◽  
Kimio Hanawa
Keyword(s):  
Wind Stress ◽  
North Atlantic ◽  
Wind Stress Curl ◽  
Atlantic Sector ◽  
Atmospheric Teleconnection ◽  
Maximum Covariance Analysis ◽  
Teleconnection Patterns ◽  
The North ◽  
The North Atlantic ◽  
Atmospheric Teleconnection Patterns

Abstract Adopting a rotated empirical orthogonal function (REOF) analysis and a maximum covariance analysis (MCA), characteristics of the wintertime wind stress curl (WSC) anomaly field in the North Atlantic are investigated. In terms of both temporal variation and spatial distribution, the first four leading modes of WSC show a one-to-one relation with four atmospheric teleconnection patterns over the North Atlantic sector: the North Atlantic Oscillation (NAO) and the east Atlantic (EA), tropical–Northern Hemisphere (TNH), and Pacific–North American (PNA) patterns. These four patterns characterize the WSC variations over the different regions in the North Atlantic: NAO and EA over the eastern side of the basin, TNH over the central part of the basin, and PNA over the western side of the basin.

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