The Impact of Rain on Ocean Surface Waves and Currents

Precipitation is an important component of the interaction between Earth's atmosphere and oceans, modifying air-sea fluxes of momentum, heat, and gas. It has been hypothesized that rain's suppression of ocean surface gravity waves and centimeter-scale wave enhancement should alter the nature of air-sea momentum flux, resulting in increased near-surface current. Here, we use field observations to describe this impact and measure the very near-surface current response to rainfall. During heavy rain, surface-roughening ring waves were generated and longer gravity waves were suppressed; immediately following, the magnitude of the near-surface current increased in response to wind forcing but died as the rain subsided and long waves recovered. These first-of-their-kind field observations indicate that rain reduces ocean wave form drag in favor of tangential stress, resulting in the acceleration of current near the sea surface. Plain Language Summary Rain is known to be an important component of atmosphere-ocean interactions. However, the specific response of short-scale waves and very near-surface current to precipitation has not yet been described in the Earth's ocean. We observe that rainfall suppresses long waves and grows centimeter-scale ring waves. This alteration facilitates the acceleration of current, which ceases in favor of longer wave growth as the rain subsides. This is the first observation of this phenomenon in the Earth's real ocean.