3.12 A COMPARATIVE STUDY OF DISSIPATION RATES IN URBAN AND SUBURBAN ENVIRONMENTS USING SODAR DATA

Data from field studies in Phoenix, AZ, during June 2001 and Oklahoma City, OK, during July 2003 are used to calculate the structure function of velocity by using the velocity differencing technique. We found that this technique can often be applied for these locations during summer, because strong solar forcing generates significant low-frequency energy in the turbulence spectrum. At other times, usually during stable nighttime conditions, this technique is inappropriate. During nighttime the method is sometimes useful at altitudes well above the surface — even when conditions near the surface are not sufficiently turbulent. This may be because the source of nighttime turbulence (the nocturnal low-level jet) is well above the surface, particularly in Oklahoma City. For a total of seven different sites in the two field studies, we compare velocity structure parameters, dissipation rates, and vertical velocity variances within the urban heat island (including measurements from the top of a building) and in suburban locations