The upper level wind speed also avoids t he local effect of topography and allows more consistent predictions within a geographical region. The analysis of the wind climate is carried out based on the statistics of the wind speed and direction, either obtained through long-term wind records or t hrough numerical simulation of wind storms. The second component is the aerodynamic data. These are obtained in wind tunnel tests. By reproducing the wind characteristics in the wind tunnel based on the reduced scale of the model, the scaled wind effects can be measured.
Instrumentation used for the measurements of different quantities is described in more detail below.
The predictions of wind loads and effects are obtained through the combination of the wind climate and the aerodynamic data. The testing of a reduced-size model in the wind tunnel requires the simulation of wind with the correct sizes of gusts and energy content at the range of scaled frequencies comparable to that of full scale. For testing of buildings, the simulation repr oduces the planetary boundary layer at the bottom 500 m of the atmosphere where the characteristics of the wind is significantly affected by the surface roughness such as topography, vegetation, buildings and other structures, etc. These wind characterist ics are generally expressed in the form of a wind speed profile, a wind turbulence profile and a wind energy spectrum. Together these represents the correct variation of wind speed with height, of the gustiness of wind with height and the size of wind gus ts in relation to the building or the building model.