scholarly journals Modulation of the Agulhas Current Retroflection and Leakage by Oceanic Current Interaction with the Atmosphere in Coupled Simulations

2017 ◽  
Vol 47 (8) ◽  
pp. 2077-2100 ◽  
Author(s):  
Lionel Renault ◽  
James C. McWilliams ◽  
Pierrick Penven
Keyword(s):  
Energy Transfer ◽  
Marine Boundary Layer ◽  
Current System ◽  
Surface Current ◽  
Current Feedback ◽  
Agulhas Current ◽  
Benguela Upwelling ◽  
Oceanic Eddy ◽  
Ocean Surface Current ◽  
Mean Circulation

AbstractCoupled ocean–atmosphere simulations are carried out for the Mozambique Channel, the Agulhas Current system, and the Benguela upwelling system to assess the ocean surface current feedback to the atmosphere and its impact on the Agulhas Current (AC) retroflection and leakage. Consistent with previous studies, the authors show that the current feedback slows down the oceanic mean circulation and acts as an oceanic eddy killer by modulating the energy transfer between the atmosphere and the ocean, reducing by 25% the mesoscale energy and inducing a pathway of energy transfer from the ocean to the atmosphere. The current feedback, by dampening the eddy kinetic energy (EKE), shifts westward the distribution of the AC retroflection location, reducing the presence of eastern retroflections in the simulations and improving the realism of the AC simulation. By modulating the EKE, the AC retroflection and the Good Hope jet intensity, the current feedback allows a larger AC leakage (by 21%), altering the water masses of the Benguela system. Additionally, the eddy shedding is shifted northward and the Agulhas rings propagate less far north in the Atlantic. The current–wind coupling coefficient sw is not spatially constant: a deeper marine boundary layer induces a weaker sw. Finally the results indicate that the submesoscale currents may also be weakened by the current feedback.

scholarly journals Modulation of Wind Work by Oceanic Current Interaction with the Atmosphere

2016 ◽  
Vol 46 (6) ◽  
pp. 1685-1704 ◽  
Author(s):  
Lionel Renault ◽  
M. Jeroen Molemaker ◽  
James C. McWilliams ◽  
Alexander F. Shchepetkin ◽  
Florian Lemarié ◽  
...  
Keyword(s):  
Surface Stress ◽  
Coastal Region ◽  
Surface Current ◽  
Additional Energy ◽  
Current Feedback ◽  
Ocean Atmosphere ◽  
Wind Response ◽  
Oceanic Eddy ◽  
Ocean Surface Current ◽  
Work Done

AbstractIn this study, uncoupled and coupled ocean–atmosphere simulations are carried out for the California Upwelling System to assess the dynamic ocean–atmosphere interactions, namely, the ocean surface current feedback to the atmosphere. The authors show the current feedback, by modulating the energy transfer from the atmosphere to the ocean, controls the oceanic eddy kinetic energy (EKE). For the first time, it is demonstrated that the current feedback has an effect on the surface stress and a counteracting effect on the wind itself. The current feedback acts as an oceanic eddy killer, reducing by half the surface EKE, and by 27% the depth-integrated EKE. On one hand, it reduces the coastal generation of eddies by weakening the surface stress and hence the nearshore supply of positive wind work (i.e., the work done by the wind on the ocean). On the other hand, by inducing a surface stress curl opposite to the current vorticity, it deflects energy from the geostrophic current into the atmosphere and dampens eddies. The wind response counteracts the surface stress response. It partly reenergizes the ocean in the coastal region and decreases the offshore return of energy to the atmosphere. Eddy statistics confirm the current feedback dampens the eddies and reduces their lifetime, improving the realism of the simulation. Finally, the authors propose an additional energy element in the Lorenz diagram of energy conversion: namely, the current-induced transfer of energy from the ocean to the atmosphere at the eddy scale.

Oceanic eddy signature on SAR-derived sea ice drift and vorticity

2021 ◽  
Author(s):  
Angelina Cassianides ◽  
Camillie Lique ◽  
Anton Korosov
Keyword(s):  
Sea Ice ◽  
Surface Current ◽  
Satellite Observation ◽  
The Arctic ◽  
Global Ocean ◽  
Sar Images ◽  
Surface Ocean ◽  
Ice Drift ◽  
Sea Ice Drift ◽  
Oceanic Eddy

<p>In the global ocean, mesoscale eddies are routinely observed from satellite observation. In the Arctic Ocean, however, their observation is impeded by the presence of sea ice, although there is a growing recognition that eddy may be important for the evolution of the sea ice cover. In this talk, we will present a new method of surface ocean eddy detection based on their signature in sea ice vorticity retrieved from Synthetic Aperture Radar (SAR) images. A combination of Feature Tracking and Pattern Matching algorithm is used to compute the sea ice drift from pairs of SAR images. We will mostly focus on the case of one eddy in October 2017 in the marginal ice zone of the Canadian Basin, which was sampled by mooring observations, allowing a detailed description of its characteristics. Although the eddy could not be identified by visual inspection of the SAR images, its signature is revealed as a dipole anomaly in sea ice vorticity, which suggests that the eddy is a dipole composed of a cyclone and an anticyclone, with a horizontal scale of 80-100 km and persisted over a week. We will also discuss the relative contributions of the wind and the surface current to the sea ice vorticity. We anticipate that the robustness of our method will allow us to detect more eddies as more SAR observations become available in the future.</p>

Influence of coastal upwelling on the surface current in the Bay of Bengal using HF radar and satellite observations

2021 ◽  
Author(s):  
Shouvik Dey ◽  
Sourav Sil ◽  
Samiran Mandal
Keyword(s):  
Coastal Upwelling ◽  
Surface Current ◽  
Hf Radar ◽  
Second Phase ◽  
Biological Productivity ◽  
Maximum Peak ◽  
Current Observation ◽  
Ekman Layers ◽  
Ocean Surface Current ◽  
Upwelling Index

<p>Coastal Upwelling is a phenomenon in which cold and nutrient-enriched water from the Ekman layers reaches the surface enhancing the biological productivity of the upwelling region. In this work, an attempt is made to understand the influence of coastal upwelling on surface current variations during May 2018 to August 2018, when HF radar current observation (source: NIOT, India) is available. The wind-based Upwelling Index(UI<sub>wind</sub>) showed coastal upwelling throughout the study period. But the SST based upwelling index (UI<sub>sst</sub>) showed upwelling occurred only from May to the first week of June. Cross-shore components of HF radar-derived ocean surface current (CSSC)  showed strong similarity with UI<sub>sst</sub>. The first phase of upwelling from UI<sub>sst</sub> is observed to start on 5<sup>th</sup> May and lasts till 14<sup>th</sup> May with a maximum peak on around 10<sup>th</sup> May and having a horizontal extension of ~40 km. Then, there is a break period for about three days and after that, the second phase of upwelling starts on 17<sup>th</sup> May and lasts till 25<sup>th</sup> May with a maximum peak on around 20<sup>th</sup> May, but this time the horizontal extension is ~100 km which is much larger than during the first phase. A strong positive (from coast to offshore) CSSC is observed to start on around 5<sup>th</sup> May and lasts till 13<sup>th</sup> May with a maximum peak on around 10<sup>th</sup> May and having a horizontal extension of ~40 km, as observed from UIsst. A reversal of CSSC (towards coast) is noted on 14<sup>th</sup> May when the break of coastal upwelling is evident from UI<sub>sst</sub>. The CSSC then again started intensifying 15<sup>th</sup> May onwards and continued for ten days till 25<sup>th</sup> May, similar to UI<sub>sst</sub>.  The horizontal extension of the upwelling signature in the second phase of upwelling is ~70 km. Therefore, a 7-10 days of the coastal upwelling and its horizontal extension are identified in this study. This study suggests the use of high resolution (~6 km) HF radar current observation on the monitoring of coastal upwelling processes.</p>

scholarly journals The INALT family – a set of high-resolution nests for the Agulhas Current system within global NEMO ocean/sea-ice configurations

2019 ◽  
Vol 12 (7) ◽  
pp. 3329-3355 ◽  
Author(s):  
Franziska U. Schwarzkopf ◽  
Arne Biastoch ◽  
Claus W. Böning ◽  
Jérôme Chanut ◽  
Jonathan V. Durgadoo ◽  
...  
Keyword(s):  
High Resolution ◽  
Boundary Conditions ◽  
Current System ◽  
Western Boundary Current ◽  
Global Ocean ◽  
Western Boundary ◽  
Boundary Current ◽  
The South ◽  
Agulhas Current ◽  
Mesoscale Dynamics

Abstract. The Agulhas Current, the western boundary current of the South Indian Ocean, has been shown to play an important role in the connectivity between the Indian and Atlantic oceans. The greater Agulhas Current system is highly dominated by mesoscale dynamics. To investigate their influence on the regional and global circulations, a family of high-resolution ocean general circulation model configurations based on the NEMO code has been developed. Horizontal resolution refinement is achieved by embedding “nests” covering the South Atlantic and the western Indian oceans at 1/10∘ (INALT10) and 1/20∘ (INALT20) within global hosts with coarser resolutions. Nests and hosts are connected through two-way interaction, allowing the nests not only to receive boundary conditions from their respective host but also to feed back the impact of regional dynamics onto the global ocean. A double-nested configuration at 1/60∘ resolution (INALT60) has been developed to gain insights into submesoscale processes within the Agulhas Current system. Large-scale measures such as the Drake Passage transport and the strength of the Atlantic meridional overturning circulation are rather robust among the different configurations, indicating the important role of the hosts in providing a consistent embedment of the regionally refined grids into the global circulation. The dynamics of the Agulhas Current system strongly depend on the representation of mesoscale processes. Both the southward-flowing Agulhas Current and the northward-flowing Agulhas Undercurrent increase in strength with increasing resolution towards more realistic values, which suggests the importance of improving mesoscale dynamics as well as bathymetric slopes along this narrow western boundary current regime. The exploration of numerical choices such as lateral boundary conditions and details of the implementation of surface wind stress forcing demonstrates the range of solutions within any given configuration.

scholarly journals Eddy–Wind Interaction in the California Current System: Dynamics and Impacts

2016 ◽  
Vol 46 (2) ◽  
pp. 439-459 ◽  
Author(s):  
Hyodae Seo ◽  
Arthur J. Miller ◽  
Joel R. Norris
Keyword(s):  
Wind Stress ◽  
Current System ◽  
California Current ◽  
Surface Current ◽  
Small Scale ◽  
Propagation Time ◽  
Ekman Pumping ◽  
Induced Current ◽  
California Current System ◽  
The Mean

AbstractThe summertime California Current System (CCS) is characterized by energetic mesoscale eddies, whose sea surface temperature (SST) and surface current can significantly modify the wind stress and Ekman pumping. Relative importance of the eddy–wind interactions via SST and surface current in the CCS is examined using a high-resolution (7 km) regional coupled model with a novel coupling approach to isolate the small-scale air–sea coupling by SST and surface current. Results show that when the eddy-induced surface current is allowed to modify the wind stress, the spatially averaged surface eddy kinetic energy (EKE) is reduced by 42%, and this is primarily due to enhanced surface eddy drag and reduced wind energy transfer. In contrast, the eddy-induced SST–wind coupling has no significant impact on the EKE. Furthermore, eddy-induced SST and surface current modify the Ekman pumping via their crosswind SST gradient and surface vorticity gradient, respectively. The resultant magnitudes of the Ekman pumping velocity are comparable, but the implied feedback effects on the eddy statistics are different. The surface current-induced Ekman pumping mainly attenuates the amplitude of cyclonic and anticyclonic eddies, acting to reduce the eddy activity, while the SST-induced Ekman pumping primarily affects the propagation. Time mean–rectified change in SST is determined by the altered offshore temperature advection by the mean and eddy currents, but the magnitude of the mean SST change is greater with the eddy-induced current effect. The demonstrated remarkably strong dynamical response in the CCS system to the eddy-induced current–wind coupling indicates that eddy-induced current should play an important role in the regional coupled ocean–atmosphere system.

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