In Part 1 a study is made of the internal solitary wave on the pycnocline of a continuously stratified fluid. A Korteweg–de Vries (KdV) equation for the ‘interfacial’ displacement is developed following Benney's method for long nonlinear waves. Experiments were conducted in a long wave tank with the pycnocline at several different depths below the free surface, while keeping the total depth approximately constant. A step-like pool of light water, trapped behind a sliding gate, served as the initial disturbance condition. The number of solitons generated was verified to satisfy the prediction of inverse-scattering theory. The fully developed soliton was found to satisfy the KdV theory for all ratios of upper-layer thickness to total depth.In Part 2 of this study we investigate experimentally the evolution and breaking of an internal solitary wave as it shoals on a sloping bottom connecting the deeper region where the waves were generated to a shallower shelf region. It is found through quantitative measurements that the onset of wave-breaking was governed by shear instability, which was initiated when the local gradient Richardson number became less than ¼. The internal solitary wave of depression was found to steepen at the back of the wave before breaking, in contrast with waves of elevation. Two slopes were used, with ratios 1:16 and 1:9, and the fluid was a Boussinesq fluid with weak stratification using brine solutions.

A three‐dimensional hydrodynamic model is developed to study the circulation in the Arabian Gulf. The model contains realistic basin geometries and bathymetries of the Arabian Gulf and a good portion of the Gulf of Oman and is driven by monthly climatological winds, evaporation, and net ocean heat gain in both gulfs and the Shatt‐al‐Arab discharge. It is found that the cyclonic circulation in the southern portion of the gulf is primarily driven by the evaporation‐induced freshening from the Strait of Hormuz. In the northwestern corner of the gulf, the Shatt‐al‐Arab discharge maintains the cyclonic circulation, which would otherwise be anticyclonic. The northwestward intrusion of fresher water along the Iranian coast is weakened by northwesterly winds in winter but strengthens and extends almost to the head of the gulf in summer owing to the warming of the Gulf of Oman waters, the development of the summer thermocline in the Arabian Gulf, and diminishing winds. The southward coastal current along the Arabian coast is most prominent between the head of the gulf and Qatar. The model also predicts a strong southward coastal jet east of Qatar which is primarily wind driven. No similar coastal jet can be developed in the Gulf of Salwa, west of Qatar.

a dThe stability of flow down an inclined plane is investigated for the case o f a stratified fluid system consisting o f two layers of viscous fluids of different densities. This problem is an extension of the works of Benjamin and Yih for a homogeneous fluid; thus their results are a special case of the solution for this more general problem. Asymptotic cases for long and short wave length disturbances are considered, and the neutral curve i s estimated. Reynolds numbers for the bifurcation point of the neutral curve are found for various ratios of density and depth o f the two layers. For long waves, shear wave instability i s also studied and is found to be danped. For the purpose of comparing the Elative stability between different configurations, a stability index i s defined. It i s found that the two-layer flow i s more stable or unstable than the homogeneous case of equat total &ph, depending whether the upper fluid i s lighter or heavier than the lower one. The source of instability i s to be found in the presence of the interface.