Weatherwatch: how cat’s paws helped point sailors in the right direction

Surface ripples known as cat’s paws, caused by turbulence cascade, show where wind is – and were once seen as lucky On a windy day, the surface of a lake is not a continuous pattern of ripples but instead marked with patches of disturbance, as though a giant cat were patting the water. These surface patterns, known as cat’s paws, are caused by turbulent airflow in the atmosphere.Wind is caused by changing pressure at different spots on Earth’s surface but does not simply rush in a single mass from one place to another. The chaotic nature of the airflow, with slight differences between adjacent sections, breaks it up and splits out smaller swirls. This continues with large eddies breaking down into smaller ones, which break down further, a process known as turbulence cascade. At the lowest level, we get cat’s paws – which are usually a few metres across and last a few seconds. Continue reading...