资源环境科技发展态势分析平台

Eddy correlation measurements have been carried out at six different heights above the urban canopy in three cities of China, that is, Nanjing, Changzhou, and Suzhou. Observations at these heights are used to evaluate the dependence of normalized standard deviations of velocity components sigma(i)/u(*l) (i = u, v, w) and temperature sigma(Tv)/T-v*l on local atmospheric stability zeta (=(z - z(d))/Lambda), where u(*l) is the local friction velocity, T-v*l is the local temperature scale, z(d) is the displacement height, and Lambda is the local Obukhov length. It is found that the universal functions a(i)(1 + b(i)vertical bar zeta vertical bar)(-1/3) and b(Tv)vertical bar zeta vertical bar(-1/3), in which a(i), b(i), and b(Tv) are empirical coefficients, are suitable for describing the behaviors of sigma(i)/u(*l) and sigma T-Tv/(v*l), respectively. Under neutral conditions (vertical bar zeta vertical bar < 0.05), the value of sigma(i)/u(*l) (approximately equal to a(i)) decreases with height. On the other hand, b(i) increases with height under both unstable (zeta < -0.05) and stable (zeta > 0.05) conditions, suggesting that the thermal effect of stratification on the standard deviations of velocity components increases with height in the urban roughness sublayer. However, the behavior of sigma(Tv)/T-v*l is different from that of sigma(i)/(u*l). b(Tv) remains constant with height under unstable conditions but increases with height under stable conditions. Vertical variations of these coefficients in the universal functions are consistent with the concept of local similarity, suggesting that the turbulence behavior in the urban roughness sublayer is different from that over the flat terrain.