Wind stress is an important quantity in the process of wind driving ocean currents.
For practical applications in oceanography, it is enough for us to use an empirical formula to calculate wind stress from wind speed
U = wind speed at 10 m above the sea surface
p = air density (about 1.22 kg m-3)
Cd = dimensionless drag coefficient a typical value might be 0.0013
Unit: Kg m-1 s-2, N m-2, or Pascals(Pa)
Wind stress is a square function of wind speed because the wind forcing depends on wind speed and sea roughness, which in turn depends on wind speed.