Variations of Boundary Layer Mean and Turbulence Structure Using Synthesized Observations

As part of the Coupled Boundary Layer Air-Sea Transfer (CBLAST) project, we made intensive measurements of the atmospheric boundary layers on Nantucket, MA during July/August of 2003. These measurements include both high-rate and low-rate measurements of wind and water vapor on a 20 m tower, sodar measurements for low-level wind and turbulence profiles, basic meteorological measurements from a surface met station, ground properties, cloud base height from a laser ceilometer, and rawinsonde soundings. The turbulence measurements on the tower were made at 10 and 20 m above the ground, while the high-rate water vapor was sampled at the 20 m. The slow sensors on the mast for mean wind, temperature, and humidity were set up at 5, 10, and 20 m, respectively. The sodar measurements provide vertical profiles of the mean wind speed and direction as well as the velocity variance up to about 800 m. These measurements, together with rawinsonde soundings every six hours, provide a valuable dataset for characterizing boundary layer mean and turbulent structure under typical summertime weather conditions. In addition, we also made tethered soundings for a few selected days that were designed to examine the diurnal variation of the island boundary layer. In this presentation, results from our data analysis will be shown to illustrate the boundary layer development using the combined measurements. Together with the available aircraft measurements upwind of the tower, we will also discuss the marine boundary layer properties in onshore wind conditions. Several boundary layer and surface flux parameterizations will also be evaluated using this dataset and the results will be discussed in terms of Monin_Obukhov similarity and surface flux parameterizations.