Similarity relations seen in Manhattan turbulence observations

Extensive sonic anemometer observations of micrometeorological variables near street-level and at roof-top in built-up downtown areas in Manhattan have been analyzed. The Madison Square Garden–2005 (MSG05) experiment, in March, collected data from five street-level sites and two roof-top sites in the 500 m by 500 m area around MSG on two well-mixed days with moderate winds. The Midtown-2005 (MID05) experiment, in August, involved 10 street-level sites and five roof-top sites in an approximate 1 km by 1 km area south of Central Park on six days with light-to-moderate winds. There are many tall buildings in both domains, with average heights of about 60 m and a few buildings near 250 m. The results of the sonic anemometer analyses in Manhattan are compared with the results reported by the authors of similar sonic anemometer observations made during the Joint Urban 2003 (JU2003) experiment in Oklahoma City, and with urban similarity relations found by others in other cities. It is found that the turbulent standard deviations and the similarity relations (e.g., σu/u*) are fairly consistent from one city and one field experiment to another. For example, near the surface, σu is typically about 0.5 to 1 m/s and σT is about 0.5 °C. The local σw/u* is about 1.6 and the local u*/u is about 0.24 at the sites. The ratio σT/T* in the street-canyons is about -2 to -5 at the three sites, even at night during JU2003. These values of σT/T* are consistent with similarity theory for very-slightly unstable conditions and with the observed Monin-Obukov lengths (on the order of -100 m). The analysis of the surface and rooftop data suggests that most of the turbulent speed standard deviations at the surface are about 40 or 50 % of their values at the rooftops.