Scintillation measurements of area-averaged turbulence characteristics over a densely built-up urban surface

Field observations to investigate area-averaged turbulence characteristics were performed in a densely built-up residential neighborhood in Tokyo, Japan. Besides eddy-correlation sensors a scintillometer was used for the first time in an urban environment. Several important results follow from this study: (1) A new technique which uses simultaneous scintillation measurements at two heights is developed to directly estimate area-averaged displacement height zd and heat flux H. The estimated zd is found to be slightly dependent on the atmospheric stability parameter (lower zd under more unstable conditions). (2) New similarity relationships for non-dimensional standard deviations and dissipation rates are proposed for urban areas. (3) Source areas for the scintillometer are 2–3 (1.2) times larger than those for the eddy correlation sensors under unstable (stable) conditions. (4) 30-min averaged H measured by eddy-correlation and scintillometer are compared. Whilst 30-min H agree well, short-term variability was generally larger for the eddy-correlation results. 1-min H from the scintillation method correlate well with net radiation. This result can be attributed to the superior spatial integration due to the longer averaging path (300 m) of the scintillometer. It is concluded that time-averaging requirements to obtain a representative flux measurement can be relaxed for scintillometer applications.