地形对陆架拦截波性质及机制的影响

IMPACT OF BOTTOM TOPOGRAPHY ON THE CHARACTER AND MECHANISM OF COASTAL TRAPPED WAVES

陆架波的性质如频散关系、形成机制等受地形影响。研究地形对陆架波的性质影响具有重要意义。基于陆架拦截波理论,数值计算了分段线性地形下不同宽度陆架上陆架拦截波的频散关系、长波假设下波动的相速度、阻尼情况下的波动耗散率以及强迫波的外力影响因子。分析了陆架宽度及坡度对自由及强迫陆架拦截波性质的影响。陆架宽度影响陆架拦截波的频散关系。陆架变宽,使得长波频散曲线的斜率增大。陆架宽度的增加使第一模态陆架拦截波有明显的性质变化:相速度增大,波动受辐散影响的程度变大,摩擦衰减距离增大,且风应力旋度在波动的生成机制中起到的作用渐强。在宽的陆架上,研究陆架拦截波的生成及强迫波的振幅时,应充分考虑风应力旋度的作用。第二、三模态波动的相速度受陆架坡度的影响较大,但摩擦衰减距离基本都在200km左右,几乎不随陆架宽度改变,属于局地波。

The dispersion relation of coastal trapped waves on a piecewise linear bottom topography was derived using a numerical model; the phase speeds under long wave theory, the decay distance with finite bottom friction and the impact factor of the force wave were derived subsequently. By using a free and a force model, the impact of topography on coastal trapped waves were analyzed. The width of the continental shelf affects the dispersion relation of the waves. The gradient of the dispersion on the long wave portion could increase with the width of the continental shelf. The character of the first mode wave changed dramatically with the width of the continental shelf. The phase speed, the impact of the divergence, the decay distance in the alongshore direction due to bottom friction, and the effect of the wind stress curl can all increase with the width of the continental shelf. The phase speeds of the second and third mode waves are affected by the slope of the shelf significantly. The frictional decay distance is almost an invariant when width of the shelf change, and hence the high mode waves can be recognized as local waves.