The effect of
rainfall on mass transfer across the air-water interface was investigated
through the CO2 absorption experiments in a turbulent open-channel
flow with the free surface. The results show that the rainfall enhances both
the turbulent mixing near the free surface on the liquid side and the CO2
transfer across the interface. The mass transfer coefficient on the liquid side
is well correlated by both the mean vertical momentum flux of rainfall, M, and the mean kinetic energy of rain
droplets impinging on the unit area of the air-water interface, KEF. However, it was not concluded which
of M and KEF is a better parameter for expressing
the rainfall effects on the mass transfer. The comparison between the mass
transfer coefficient obtained in this study and that obtained in wind-driven
turbulence suggests that it is of great importance to consider the rainfall
effect on the CO2 exchange rate between the atmosphere and ocean in
precisely estimating the global carbon cycle in a climate model.
Author: N. Takagaki1 and S. Komori (komori at mech dot kyoto-u dot ac dot jp)
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