scholarly journals THE MODEL STUDY OF THE WIND STRESS IMPACT TO THE INTERANNUAL VARIABILITY OF THE ANTARCTIC CIRCUMPOLAR CURRENT SOUTH OF AUSTRALIA

2019 ◽  
Vol 47 (2) ◽  
pp. 172-182 ◽  
Author(s):  
K.V. Lebedev
Keyword(s):  
Interannual Variability ◽  
Wind Stress ◽  
Numerical Experiments ◽  
Antarctic Circumpolar Current ◽  
Wind Forcing ◽  
Global Ocean ◽  
The Real ◽  
Key Factor ◽  
Circumpolar Current ◽  
The Antarctic

The interannual variability of the Antarctic Circumpolar Current (ACC) in the region south of Australia is studied on the base of numerical simulations performed with the use of the Argo-based model for Investigation of the Global Ocean (AMIGO). The model consists of a block for variational interpolation to a regular grid of Argo floats data and a block for model hydrodynamic adjustment of variationally interpolated fields. The mean ACC transport for the period of 2005–2014 through the Australia-Antarctica section was estimated at 178±6 Sv (1 Sv = 106m3/с-1). Additional numerical experiments were carried out in order to study the contribution of the wind forcing to the interannual variability of the ACC transport: the real thermohaline fields corresponding to the particular time period were replaced by climatic ones (1) and by replacing the real wind forcing data with the climatic ones (2). Analysis of the numerical experiments results has shown that the variable wind stress forcing is the key factor determining the interannual variability of the ACC transport through the Australia-Antarctica section.

scholarly journals THE MODEL STUDY OF THE WATER EXCHANGE INTERANNUAL VARIABILITY BETWEEN ATLANTIC, NORDIC SEAS, AND ARCTIC OCEAN

2020 ◽  
Vol 48 (2) ◽  
pp. 34-50
Author(s):  
K. V. Lebedev ◽  
B. N. Filyushkin ◽  
A. F. Shchepetkin
Keyword(s):  
Arctic Ocean ◽  
Interannual Variability ◽  
Numerical Experiments ◽  
Water Exchange ◽  
Barents Sea ◽  
Wind Forcing ◽  
Global Ocean ◽  
Nordic Seas ◽  
The Real ◽  
Key Factor

The interannual variability of the mass transports through the Denmark and Fram Straits, and through the sections separating the Nordic Seas from the Atlantic Ocean and Barents Sea is studied on the base of numerical simulations performed with the use of the Argobased Model for Investigation of the Global Ocean (AMIGO). The model consists of a block for variational interpolation to a regular grid of Argo floats data and a block for model hydrodynamic adjustment of variationally interpolated fields. Additional numerical experiments were carried out in order to study the contribution of the wind forcing to the interannual variability of the transports: the real thermohaline fields corresponding to the particular time period were replaced by climatic ones (1) and by replacing the real wind forcing data with the climatic ones (2). Analysis of the numerical experiments results has shown that the variable wind stress forcing is the key factor determining the interannual variability of the water exchange between Atlantic, Nordic Seas, and Arctic Ocean.

scholarly journals Role of Residual Overturning for the Sensitivity of Southern Ocean Isopycnal Slopes to Changes in Wind Forcing

2019 ◽  
Vol 49 (11) ◽  
pp. 2867-2881
Author(s):  
Madeleine K. Youngs ◽  
Glenn R. Flierl ◽  
Raffaele Ferrari
Keyword(s):  
Southern Ocean ◽  
Wind Stress ◽  
Antarctic Circumpolar Current ◽  
Channel Model ◽  
Critical Level ◽  
Wind Forcing ◽  
Global Ocean ◽  
Circumpolar Current ◽  
The Antarctic

AbstractThe Antarctic Circumpolar Current plays a central role in the ventilation of heat and carbon in the global ocean. In particular, the isopycnal slopes determine where each water mass outcrops and thus how the ocean interacts with the atmosphere. The region-integrated isopycnal slopes have been suggested to be eddy saturated, that is, stay relatively constant as the wind forcing changes, but whether or not the flow is saturated in realistic present day and future parameter regimes is unknown. This study analyzes an idealized two-layer quasigeostrophic channel model forced by a wind stress and a residual overturning generated by a mass flux across the interface between the two layers, with and without a blocking ridge. The sign and strength of the residual overturning set which way the isopycnal slopes change with the wind forcing, leading to an increase in slope with an increase in wind forcing for a positive overturning and a decrease in slope for a negative overturning, following the usual conventions; this behavior is caused by the dominant standing meander weakening as the wind stress weakens causing the isopycnal slopes to become more sensitive to changes in the wind stress and converge with the slopes of a flat-bottomed simulation. Eddy saturation only appears once the wind forcing passes a critical level. These results show that theories for saturation must have both topography and residual overturning in order to be complete and provide a framework for understanding how the isopycnal slopes in the Southern Ocean may change in response to future changes in wind forcing.

The Impact of Parameterized Lateral Mixing on the Antarctic Circumpolar Current in a Coupled Climate Model

2020 ◽  
Vol 50 (4) ◽  
pp. 965-982 ◽  
Author(s):  
Sarah Ragen ◽  
Marie-Aude Pradal ◽  
Anand Gnanadesikan
Keyword(s):  
Diffusion Coefficient ◽  
Wind Stress ◽  
Antarctic Circumpolar Current ◽  
Climate Model ◽  
Lateral Diffusion ◽  
Intermediate Waters ◽  
Circumpolar Current ◽  
The Antarctic ◽  
The Impact ◽  
Lateral Diffusion Coefficient

AbstractThis study examines the impact of changing the lateral diffusion coefficient ARedi on the transport of the Antarctic Circumpolar Current (ACC). The lateral diffusion coefficient ARedi is poorly constrained, with values ranging across an order of magnitude in climate models. The ACC is difficult to accurately simulate, and there is a large spread in eastward transport in the Southern Ocean (SO) in these models. This paper examines how much of that spread can be attributed to different eddy parameterization coefficients. A coarse-resolution, fully coupled model suite was run with ARedi = 400, 800, 1200, and 2400 m2 s−1. Additionally, two simulations were run with two-dimensional representations of the mixing coefficient based on satellite altimetry. Relative to the 400 m2 s−1 case, the 2400 m2 s−1 case exhibits 1) an 11% decrease in average wind stress from 50° to 65°S, 2) a 20% decrease in zonally averaged eastward transport in the SO, and 3) a 14% weaker transport through the Drake Passage. The decrease in transport is well explained by changes in the thermal current shear, largely due to increases in ocean density occurring on the northern side of the ACC. In intermediate waters these increases are associated with changes in the formation of intermediate waters in the North Pacific. We hypothesize that the deep increases are associated with changes in the wind stress curl allowing Antarctic Bottom Water to escape and flow northward.

Investigating the Dynamics of the Pacific Antarctic Circumpolar Current – Initial Results from International Ocean Discovery Program Expedition 383 (DYNAPACC)

2020 ◽  
Author(s):  
Frank Lamy ◽  
Gisela Winckler ◽  
Carlos Zarikian ◽  
Expedition 383 Scientists
Keyword(s):  
Antarctic Circumpolar Current ◽  
Global Climate ◽  
South Pacific ◽  
Global Ocean ◽  
Sedimentary Sequences ◽  
The Pacific ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Central South ◽  
Chilean Margin

<p>The Antarctic Circumpolar Current (ACC) is the world’s strongest zonal current system that connects all three major basins of the global ocean, and therefore integrates, forces and responds to global climate variability. In contrast to the Atlantic and Indian sectors of the ACC, and with the exception of drill cores from the Antarctic continental margin and off New Zealand, the Pacific sector of the ACC lacks information on its Cenozoic paleoceanography from deep-sea drilling records.</p><p>To advance our knowledge and understanding of Miocene to Holocene atmosphere-ocean-cryosphere dynamics in the Pacific and their implications for regional and global climate and atmospheric CO<sub>2</sub>, IODP Expedition 383 recovered sedimentary sequences at: (1) Three sites located in the central South Pacific (Sites U1539, U1540 and U1541); (2) two sites at the Chilean Margin (U1542, U1544); and (3) one site from the hemipelagic eastern South Pacific (U1543) close to the entrance to the Drake Passage. Age control based on magneto and bio-stratigraphically constrained orbital tuning of physical properties in the Plio-Pleistocene sediments is remarkable, with Sites U1541 and U1543 extending the record back to the late Miocene, and Site U1540 to the earliest Pliocene. Pleistocene sedimentary sequences with high sedimentation rates in the order of 40 cm/kyr were drilled in the Central South Pacific (U1539) and along the Chilean Margin. Taken together, the sites represent a depth transect from ~1100 m at the Chilean margin (U1542) to ~4070 m in the Central South Pacific (U1539), and allow reconstructing changes in the vertical structure of the ACC – a key issue for understanding the role of the Southern Ocean in the global carbon cycle- to be investigated. The sites are located at latitudes and water depths where sediments will allow the application of a wide range of siliciclastic, carbonate, and opal-based proxies to address our objectives of reconstructing, with unprecedented stratigraphic detail, surface to deep ocean variations and their relation to atmosphere and cryosphere changes through stadial-to-interstadial, glacial-to-interglacial and warmer than present time intervals.</p>

scholarly journals Study of the Antarctic Circumpolar Current via the Shallow Water Large Scale Modelling

2022 ◽  
Author(s):  
K. Marynets
Keyword(s):  
Boundary Value Problem ◽  
Ocean Circulation ◽  
Antarctic Circumpolar Current ◽  
Large Scale ◽  
Global Climate ◽  
Boundary Value ◽  
Global Ocean ◽  
Uniqueness Of Solutions ◽  
Circumpolar Current ◽  
The Antarctic

Abstract. This paper proposes a modelling of the Antarctic Circumpolar Current (ACC) by means of a two-point boundary value problem. As the major means of exchange of water between the great ocean basins (Atlantic, Pacific and Indian), the ACC plays a highly important role in the global climate. Despite its importance, it remains one of the most poorly understood components of global ocean circulation. We present some recent results on the existence and uniqueness of solutions of a two-point nonlinear boundary value problem that arises in the modeling of the flow of the (ACC) (see discussions in [4-9]).

scholarly journals Thermohaline and Wind Forcing of a Circumpolar Channel withBlocked Geostrophic Contours

2002 ◽  
Vol 32 (9) ◽  
pp. 2520-2540 ◽  
Author(s):  
Daniel Borowski ◽  
Rüdiger Gerdes ◽  
Dirk Olbers
Keyword(s):  
Potential Energy ◽  
Antarctic Circumpolar Current ◽  
Drake Passage ◽  
Wind Forcing ◽  
Wind Effect ◽  
Current Transport ◽  
Leading Order ◽  
Meridional Gradient ◽  
Circumpolar Current ◽  
The Antarctic

Abstract The Antarctic Circumpolar Current is governed by unique dynamics. Because the latitude belt of Drake Passage is not zonally bounded by continents, the Sverdrup theory does not apply to the Antarctic Circumpolar Current. However, most of the geostrophic contours are blocked at Drake Passage, which provides an important dynamic constraint for the vorticity equation of the depth averaged flow. This study addresses the effects of thermohaline and wind forcing on the large-scale transport of a circumpolar current with blocked geostrophic contours. Various numerical experiments with three different idealized model geometries were conducted. Based on the results and theoretical arguments, the authors promote an indirect wind effect on the circumpolar current: while the direct effects of the wind in driving the circumpolar current through a vertical transfer of the applied wind stress are of minor importance, the wind does substantially influence the circumpolar current transport through its effects on the density field. This indirect wind effect is discussed in two steps. First, at the latitudes of the circumpolar current and longitudes where the geostrophic contours are blocked, the meridional gradient of the mass transport streamfunction is to leading order balanced by the meridional gradient of the baroclinic potential energy. This balance implies that the total transport is to leading order baroclinic and that the deep transport is small. For this statement, some theoretical arguments are offered. Second, a simplified analytical model is used to obtain the distribution of the baroclinic potential energy. Assuming an advective–diffusive balance for the densities in the deep downwelling northern branch of the Deacon cell, this model reproduces the qualitative dependence of the circumpolar current transport on the imposed wind and thermohaline forcing as well as on the turbulent diffusivities.

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