Similarity theory and nocturnal locally scaled turbulence variances in the tropical urban roughness sublayer

Özet

We assessed the potential of the “local” MonineObukhov similarity theory to predict the relationshipbetween scaled turbulence standard deviations (si; i ¼ turbulence quantity) and atmospheric stability (z)in the nocturnal urban roughness sublayer using data collected in a tropical city of which data andresearch have been lacking as most works previously reported mainly concentrated on temperate midlatituderegions. The site was LCZ 5B in the Local Climate Zone classification system with open midrisebuildings with scattered trees. Unstable (convective) atmospheric conditions persisted through the nightwith infrequent and intermittent stable conditions. Nighttime turbulence statistics were lower thandaytime turbulence statistics due to the weak (<1 m/s) and variable mean wind speeds. Using localscales, the MonineObukhov similarity theory failed to predict the trend in the standard deviation ofvertical wind velocity (sw) scaled by local friction velocity (u*l) with local atmospheric stability (zl) butthe standard deviation of temperature (sT) scaled to the local friction temperature (T*l) fared better.However, we found that by using the local free convection velocity (uf, l) as the normalising scale with sW,the trend was better described with zl using simple power law relations for both unstable and stableconditions, but this situation was limited to neutral conditions.