Similarity on turbulent transfers of heat, water vapor, and carbon dioxide over a suburban surface under weakly unstable condition

The similarity of vertical turbulent transfer of heat, water vapor, and carbon dioxide, hereafter CO₂, within an urban surface layer was investigated using correlation coefficients, wavelet analysis, and quadrant analysis. The measurements were done in a residential area of Tokyo, Japan during midday on the fair-weather days in July 2001.

The correlation coefficients indicated that the transfer efficiencies of water vapor and CO₂ were generally smaller than that of heat. Using wavelet analysis, we found that heat is always efficiently transferred by thermal and organized motions. In contrast, water vapor and CO₂, which are passive quantities, were not transferred as efficiently as heat. The quadrant analyses showed that the heat transfer by ejection exceeded that by sweep, whereas the ratio of ejection to sweep for vapor and CO₂ transfer were less than that for heat. Hence, the quadrant analyses agreed with the findings from wavelet analysis. These differences between heat and both CO₂ and water vapor were probably caused both by the active role of temperature and the heterogeneity in the source distribution of scalars. Heat is an active scalar and produces the thermal structures. Hence, the heat is transferred most efficiently. Vapor and CO₂ are transferred passively. If their horizontal distributions were homogeneous, they would be transferred as well as heat. However, the sink/source of vapor and CO₂ is inhomogeneous. As a result, the heterogeneities of vapor and CO₂ concentration decrease their transfer efficiencies.