Thermal Convection and Design Wind Speeds

This technical note presents estimates of the extent to which thermal convection effects cause mean wind profiles to deviate from the logarithmic law. It is shown that the deviations from the logarithmic law are significant for wind speeds corresponding to hourly means of the order of 5 m/s above ground in open terrain. However, for strong wind speeds of interest in structural engineering calculations (≥70 mph), these deviations are of the order of 4% or less at 200 m above ground, and 1% at 50 m above ground, and thus may be neglected in practice. For strong wind speeds of interest in extreme wind climatological estimates (≥30 mph), the deviations are of the order of 4% or less at 15 m above ground, and therefore are also negligible for practical purposes.