什么是 Wind stress？

The wind stress $\vec T$ is the horizontal force per unit area exerted by the wind on the sea surface, in pascals. It is the downward transfer of the horizontal momentum of the air into the ocean, and points nearly along the wind. Its size is given by the bulk formula

where $\rho_a = 1.3\,\mathrm{kg}\,\mathrm{m}^{-3}$ is the density of air, $U_{10}$ the wind speed $10\,\mathrm{m}$ above the sea and $C_D$ a dimensionless drag coefficient.