Experiments and field observations have shown that there are at least two modes of behaviour for river plumes. In many cases, the plume turns to the right (in the Northern hemisphere) on leaving the river mouth and follows the direction of Kelvin-wave propagation. Alternatively, a ‘bulge’ can form in the plume and a fraction of the outflow volume becomes trapped near the mouth. This paper discusses how bulge formation can be affected by the vorticity profile at the river mouth. Due to the image effect, regions of cyclonic vorticity tend to propagate rightwards, while regions of anticyclonic vorticity propagate leftward upon exit from the source. If an outflow consists of regions of cyclonic vorticity to the left of regions of anticyclonic vorticity, the two image effects are in competition. We explore this phenomenon using a quasi-geostrophic model with piecewise-constant potential vorticity, which allows the vorticity profile at the source to be set as part of the problem. We present analytic solutions valid in the source region and at the head of the plume, and show that all of the outflow travels rightwards if and only if the region of cyclonic vorticity is dominant. The initial-value problem for the model is integrated numerically using the method of contour dynamics, and the full parameter space is explored. We find that if the cyclonic and anticyclonic contributions cancel, as in the experiments of Avicola and Huq (2003), then steady solutions are unstable and a bulge can form downstream of the river mouth.

中文翻译：

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沿海外流中的涡旋竞争

实验和实地观察表明，河流羽流至少有两种行为模式。在许多情况下，羽流在离开河口时向右转（在北半球），并遵循开尔文波传播的方向。或者，羽流中会形成一个“凸起”，一部分流出体积被困在嘴巴附近。本文讨论了河口涡度剖面如何影响凸起的形成。由于图像效应，气旋涡旋区域倾向于向右传播，而反气旋涡旋区域在离开震源时向左传播。如果流出由反气旋涡旋区域左侧的气旋涡旋区域组成，则两种图像效果是相互竞争的。我们使用具有分段恒定势涡度的准地转模型来探索这种现象，该模型允许将源处的涡度剖面设置为问题的一部分。我们提出了在源区和羽流顶部有效的解析解，并表明当且仅当气旋涡旋区占主导地位时，所有流出物都向右移动。利用轮廓动力学方法对模型的初值问题进行数值积分，探索全参数空间。我们发现，如果气旋和反气旋贡献抵消，如 Avicola 和 Huq (2003) 的实验，则稳定解不稳定，河口下游会形成凸起。这允许将源处的涡度分布设置为问题的一部分。我们提出了在源区和羽流顶部有效的解析解，并表明当且仅当气旋涡旋区占主导地位时，所有流出物都向右移动。利用轮廓动力学方法对模型的初值问题进行数值积分，探索全参数空间。我们发现，如果气旋和反气旋的贡献抵消，如 Avicola 和 Huq (2003) 的实验，则稳定解不稳定，河口下游会形成凸起。这允许将源处的涡度分布设置为问题的一部分。我们提出了在源区和羽流顶部有效的解析解，并表明当且仅当气旋涡旋区占主导地位时，所有流出物都向右移动。利用轮廓动力学方法对模型的初值问题进行数值积分，探索全参数空间。我们发现，如果气旋和反气旋贡献抵消，如 Avicola 和 Huq (2003) 的实验，则稳定解不稳定，河口下游会形成凸起。利用轮廓动力学方法对模型的初值问题进行数值积分，探索全参数空间。我们发现，如果气旋和反气旋贡献抵消，如 Avicola 和 Huq (2003) 的实验，则稳定解不稳定，河口下游会形成凸起。利用轮廓动力学方法对模型的初值问题进行数值积分，探索全参数空间。我们发现，如果气旋和反气旋贡献抵消，如 Avicola 和 Huq (2003) 的实验，则稳定解不稳定，河口下游会形成凸起。