the height at which the velocity ceases to increase is called the graient height, and the corresponding velocity, the gradient velocity. the height through which the wind speed is affected by the topography is called the atmospheric boundary layer.

wind speed variation is given by a simpler power-law expression as below:

Vz = Vg (Z/Zg)^a

Vz = main wind speed at height of Z

Vg = gradiant wind speed, assume constant above boundry layer

Z = heigh above ground

Zg = depth of boundary layer

a = power law coefficient

wind speed of Z can be calculated using aboive equation by knowing mean wind speed at gradient height and the value of exponent a. value of a ranges from low of 0.14 for open country to about 0.5 for built-up urban areas. the pressure and suction generated by wind are a function of the wind speed, and in general increase with the building height.