The mixing of rain with near-surface water

The mixing of rain with otherwise calm near-surface water is investigated experimentally, using both uniform drops and crude drop-size distributions. The results are interpreted in terms of mixed-layer depths and the upward entrainment of quiescent water. Large drops, even in quite small numbers, are shown to play a very important role in the mixing process. Entrainment coefficients vary as the inverse of a suitably defined bulk Richardson number, and behave similarly in both fresh and salt receiving water.