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.

Time-Resolved Integrative Optical Imaging of Diffusion during Spreading Depression

ABSTRACTAn improved version of Integrative Optical Imaging method has been developed which substantially increases the time resolution of diffusion measurements. We present a theory for Time-Resolved Integrative Optical Imaging (TR-IOI) that incorporates time-dependent effective diffusion coefficient in homogeneous anisotropic media and time-dependent nonspecific linear clearance. The method was applied to measure the very fast changes in extracellular diffusion that occur during spreading depression in rat hippocampal slices. We were able to achieve time resolution of approximately one second, an improvement of at least ten times compared to the standard methods for extracellular diffusion measurement. We have found that diffusion of a small fluorescent extracellular marker (MW 3000) completely stopped during the maximum DC shift associated with the spreading depression wave, then gradually resumed over several minutes afterward. The effect of spreading depression on extracellular space is much larger than previously estimated by other methods with lower time resolution.

Comparative potency of sensory-induced brainstem activation to trigger spreading depression and seizures in the cortex of awake rats: Implications for the pathophysiology of migraine aura

Background Migraine and epilepsy are highly co-morbid neurological disorders associated with episodic dysfunction of both cortical and subcortical networks. The study examined the interrelation between cortical spreading depression, the electrophysiological correlate of migraine aura and seizures triggered at cortical and brainstem levels by repeated sound stimulation in rats with acoustic hypersensitivity (reflex audiogenic epilepsy). Method In awake, freely moving rats with innate audiogenic epilepsy, 25 episodes of running seizure (brainstem seizures) were induced by repeated sound stimulation. Spreading depression and seizures were recorded using implanted cortical electrodes. Results The first sound-induced brainstem seizures evoked neither spreading depression nor seizures in the cortex. With repetition, brainstem seizures began to be followed by a single cortical spreading depression wave and an epileptiform discharge. Spreading depression was more frequent an early cortical event than seizures: spreading depression appeared after 8.4 ± 1.0 repeated stimulations in 100% rats ( n = 24) while cortical seizures were recorded after 12.9 ± 1.2 tests in 46% rats. Brainstem seizure triggered unilateral long-latency spreading depression. Bilateral short-latency cortical spreading depression was recorded only after intense cortical seizures. Conclusion These data show that episodic brainstem activation is a potent trigger of unilateral cortical spreading depression. Development of intense seizures in the cortex leads to initiation of spreading depression in multiple cortical sites of both hemispheres.

On the Dynamics of Two-Dimensional Capillary-Gravity Solitary Waves with a Linear Shear Current

The numerical study of the dynamics of two-dimensional capillary-gravity solitary waves on a linear shear current is presented in this paper. The numerical method is based on the time-dependent conformal mapping. The stability of different kinds of solitary waves is considered. Both depression wave and large amplitude elevation wave are found to be stable, while small amplitude elevation wave is unstable to the small perturbation, and it finally evolves to be a depression wave with tails, which is similar to the irrotational capillary-gravity waves.

The Behaviors of Internal Solitary Waves near the Continental Shelf of South China Sea Inferred from Satellite Images

The behaviors of internal solitary waves (ISWs) near the continental shelf of SCS are analyzed. We interpret manifestations of four kinds of ISWs in MODIS images: mode-1 depression wave, bolus, mode-1 elevation wave, and mode-2 convex wave. The geographical distributions of these ISWs are investigated. Bolus and mode-1 elevation wave, the two evolution stages of polarity conversion process of depression ISW, only exists around 22˚N, which is in agreement with the sign of mode-1 nonlinear coefficient α1. The mode-2 convex waves generally follow the southern part of mode-1 depression ISW, where the steep terrain favors their generation. The information of a mode-1 depression ISW, such as amplitude and propagation speed, is also derived from the MODIS image.

Observations of Polarity Reversal in Shoaling Nonlinear Internal Waves

Observations off the New Jersey coast document the shoaling of three groups of nonlinear internal waves of depression over 35 km across the shelf. Each wave group experienced changing background conditions along its shoreward transit. Despite different wave environments, a clear pattern emerges. Nearly symmetric waves propagating into shallow water develop an asymmetric shape; in the wave reference frame, the leading edge accelerates causing the front face to broaden while the trailing face remains steep. This trend continues until the front edge and face of the leading depression wave become unidentifiable and a near-bottom elevation wave emerges, formed from the trailing face of the initial depression wave and the leading face of the following wave. The transition from depression to elevation waves is diagnosed by the integrated wave vorticity, which changes sign as the wave’s polarity changes sign. This transition is predicted by the sign change of the coefficient of the nonlinear term in the KdV equation, when evaluated using observed profiles of stratification and velocity.