Influence of sea spray droplets on drag coefficient in high wind speed

Abstract

Sea spray droplets change the distribution of air-sea momentum fluxes in the sea surface, and then influence sea surface drag coefficient considerably. In order to estimate the influence of sea spray droplets on drag coefficient exactly, a new sea spray generation function (SSGF) which depends on wind and wave, is deduced. Then the SSGF is integrated into the spray momentum flux formula to calculate the spray momentum flux. The result shows that revised spray momentum flux formula are sensitive to the wave state remarkably. It indicates that the new sea spray flux formulae can be used in any wave state. The total momentum flux of sea surface contains sea spray momentum flux and air-sea interface momentum flux. Based on this theory, the formula of drag coefficient which is influenced by sea spray droplets at high wind speed is acquired. The theoretical result of the drag coefficient formula shows that the drag coefficient reduces at the high wind speed, which indicates that the sea spray droplets can restrict the increase of drag coefficient at high wind speed. Comparison between theoretical value and measured value of sea surface drag coefficient in field and laboratory shows that the theoretical value of drag coefficient cover the measured value almost. Meanwhile, with the new sea surface drag coefficient, ocean wave model can model the significant wave height very well in typhoon condition. All the results show that the new drag coefficient can be used properly at high wind speed.