Abstract
Abstract. One of the main features of the oceanic circulation along Antarctica is the Antarctic Slope Current (ASC). This circumpolar current flows westwards and contributes to communication between the three major oceanic basins around Antarctica. The ASC is not very well known due to remote location and the presence of sea ice during several months, allowing in situ studies only during summertime. Moreover, only few modelling studies of this current have been carried out. Here, we investigate the sensitivity of this simulated current to four different resolutions in a coupled ocean-sea ice model and to two different atmospheric forcing sets. Two series of simulations are conducted. For the first series, global model configurations are run at coarse (2°) to eddy-permitting (0.25°) resolutions with the same atmospheric forcing. For the second series, simulations with two different atmospheric forcings are performed using a regional circumpolar configuration (south of 30° S) at 0.5° resolution. The first atmospheric forcing is based on a global atmospheric reanalysis and satellite data, while the second is based on a downscaling of the global atmospheric reanalysis by a regional atmospheric model calibrated to Antarctic meteorological conditions. Sensitivity experiments to resolution indicate that a minimum model resolution of 0.5° is needed to capture the dynamics of the ASC in terms of water mass transport and recirculation. Sensitivity experiments to atmospheric forcing fields shows that the wind speed along the Antarctic coast strongly controls the water mass transport and the seasonal cycle of the ASC. An increase in annual mean of easterlies by about 30 % leads to an increase in the mean ASC transport by about 40 %. Similar effects are obtained on the seasonal cycle: using a wind forcing field with a larger seasonal cycle (+30 %) increases by more than 30 % the amplitude of the seasonal cycle of the ASC. To confirm the importance of wind seasonal cycle, a simulation without wind speed seasonal cycle is carried out. This simulation shows a decrease by more than 50 % of the amplitude of the ASC transport seasonal cycle without changing the mean value of ASC transport.
Highlights
The Antarctic Coastal Current (ACoC) or East Wind Drift (Deacon, 1937) is the southernmost current in the World Ocean
The main goal of this study was to investigate the sensitivity of the Antarctic Slope Current (ASC), defined for our purposes as the total westward flow between the Antarctic coast and the centers of the three Antarctic gyres, to different model characteristics such as the resolution and the atmospheric forcing, with a focus on the influence of the wind on the seasonal cycle of this current
The sensitivity experiments of the ASC to model resolutions were done in order to choose the model resolution best suited for the wind sensitivity experiments
Summary
The Antarctic Coastal Current (ACoC) or East Wind Drift (Deacon, 1937) is the southernmost current in the World Ocean. In parallel to the ACoC, the Antarctic Slope Front (ASF), described by Whitworth et al (1998), affects the exchanges of heat, salt and freshwater across the continental shelf and the transport of water masses around the continent. It is associated with a westward surface intensified flow, which we refer to here as the Antarctic Slope Current (ASC). The ASF extends continuously from 120◦ W near the Amundsen Sea westwards to 55◦ W at the tip of the Antarctic Peninsula (Whitworth et al, 1998) This front is mainly attributed to coastal downwelling caused by the prevailing easterly winds there (Sverdrup, 1953). For purposes of this paper, all westward flowing currents (ACoC, ASC, and southern branches of polar gyres) are grouped under the name Antarctic Slope Current (ASC), which can be taken to represent total westward transport along the Antarctic continental margin
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