A Strong Internal Solitary Wave with Extreme Velocity Captured Northeast of Dong-Sha Atoll in the Northern South China Sea

Internal solitary waves (ISWs) in the South China Sea (SCS) have received considerable attention. This paper reports on a strong ISW captured northeast of Dong-Sha Atoll on 22 May 2011 by shipboard Acoustic Doppler Current Profiler (ADCP), which had the largest velocity among the ISWs so far reported in the global ocean. The peak westward velocity (u) was 2.94 m/s, and the peak downward velocity (w) was 0.63 m/s, indicating a first baroclinic mode depression wave. The amplitude of ISW inferred from ADCP backscatter was about 97 m. 2.2 h later, a trailing wave was captured with a peak westward velocity and downward velocity of 2.24 m/s and 0.42 m/s, respectively, surprisingly large for a trailing wave, suggesting that the ISW is type-A wave. The estimated baroclinic current induced by the leading ISW was much larger than the barotropic current. The Korteweg-De Vries (KdV) theoretical phase speed and the phase speed inferred from the satellite images were 1.76 m/s and 1.59 m/s, respectively. The peak horizontal velocity exceeded the phase speed, suggesting the ISW was close to or already in the process of breaking and may have formed a trapped core.

Dynamics of a barotropic current at an ice shelf front

<p>Ice shelves in West Antarctica are melting at an increasing rate due to the flow of relatively warm<br>Circumpolar Deep Water into the ice shelf cavities. The current that brings heat southward along the<br>eastern side of a trough towards an ice shelf front is found to have a barotropic and a baroclinic<br>component. Mooring observations in front of Getz Ice Shelf suggest that 90% (roughly 0.6 Sv) of the<br>volume transport and 65% of the temperature transport is linked to the barotropic component of the<br>current towards the ice shelf. It is unknown whether and how much of a barotropic current can<br>penetrate under the ice shelf across the about 300 m deep ice shelf front, where lines of constant water<br>column thickness discontinue.<br>We conduct idealized modelling with MITgcm to investigate the dynamics of a barotropic current at the<br>ice shelf front. Friction and strong vertical velocities at the ice shelf front break the potential vorticity<br>constraint and allow the flow to partly enter the ice shelf cavity. Only a small fraction of the current<br>penetrates deep into the cavity, while a strong current flows parallel to the ice shelf front, where basal<br>melt is largely enhanced. How much of the current enters the cavity and how far it reaches depends on<br>the ice shelf- and bedrock topography.</p>

Wave-Forced Barotropic Currents

Waves rolling in to shallow seas will start to dissipate as a result of the bottom friction. The wave momentum will decrease from the dissipation process, and there is a transfer of momentum that accelerates an Eulerian bottom current. Water piles up toward the coast, thereby generating a return flow. When rotation is included, the return flows accelerate an alongshore current that moves to the left of the direction of the incoming wave field (Northern Hemisphere). With the assumption that the turbulent exchange can be mimicked by a constant exchange coefficient, there is a fairly simple analytical solution that relates the strength of the barotropic current to the incoming wave field. For deep water, that is, H ≫ 2υt/f, where f is the Coriolis force and νt is the turbulent exchange coefficient, the strength of the alongshore barotropic current becomes 3/2 of the Stokes drift near the bottom or 3ωka2/4 sinh(kH), where ω and k are the wave angular frequency and wavenumber, and a is the amplitude of the wave. Notably, the above expression is equal to the strength of the Eulerian streaming generated under a progressive wave by the wave-induced Reynold stresses in the viscous wave bottom boundary layer.

Numerical Model of the Circulation in an Open Bay

An external alongshore current setting to the east and across the mouth is proposed as the driving mechanism for the measured clockwise circulation in St. Georges Bay, Nova Scotia. A barotropic numerical model of an open bay forced by an alongshore current was able to produce a clockwise gyre in the bay. The model current velocities were in good agreement with the data. The generation, size, and intensity of the gyre required low values of vertical viscosity relative to horizontal viscosity. Key words: numerical model, bay, gyre, circulation, barotropic, current, coastal

The barotropic stability of the mean winds in the atmosphere

This paper considers the stability of a barotropic current on a beta earth. The motion is assumed to be horizontal, non-divergent and barotropic. The current is taken to be of the formU(y)=Asech2by+B. The perturbations are required to approach zero asyapproaches ± ∞. We introduce the non-dimensional wave-numberland a parameter χ, which is a measure of the rotation effect. χ is inversely proportional to β.There are only two kinds of perturbations: symmetric disturbances (those with maximum amplitude aty= 0) and antisymmetric disturbances (those with zero amplitude aty= 0). We find the neutral curve in the (χ,l2)-plane for both types of disturbances. The rates of amplification in the immediate vicinity of the neutral curves are also found. It is seen that the beta effect, which is due to the earth's rotation, tends to stabilize the current. For the symmetric disturbances we find a band of unstable wavelengths when χ > 1/2; and for large χ the estimated curve of the maximum value of the imaginary part of the phase velocity is asymptotic to the lower branch of the neutral curve. The antisymmetric disturbances are more stable than the symmetric disturbances.