Yukio Tamura - Advanced Structural Wind Engineering

Tongji University, Siping Road 1239, Shanghai, 200092, China

Shuyang Cao

Email:

Wind is basically caused by the temperature gradient of the atmosphere due to variable solar heating of the earths surface. It is initiated, in a more immediate sense, by density difference or pressure gradient between points of equal elevation. Mechanical effect (velocity shear effect) and temperature effect (buoyancy effect) are the sources of turbulence production of atmospheric flow. Variation of solar heating with time makes the atmospheric boundary layer at different metrological conditions, i.e., stable, unstable or neural conditions, which can be defined by gradient Richardson number or Richardson numbers in variable formations. Generally, a negative Richardson number corresponds to an unstable condition in which the mechanical and convective effects co-exist, while a positive Richardson number means a stable condition with mechanical effect only. A temperature inversion, i.e. an increase in temperature with height near the ground, can lead to pollution such as smog being trapped close to the ground. Generation of strong winds is closely related with the global atmospheric circulations, and also related with smaller scale temperature differences. However, in the case of strong wind, the buoyancy effect is usually weaker than the mechanical effect and can be neglected. Therefore, in the structural wind engineering field, usually a neutral condition is assumed.