Showing papers by "Wade R. McGillis published in 2003"

Variation in Surface Turbulence and the Gas Transfer Velocity over a Tidal Cycle in a Macro-tidal Estuary

Abstract: The gradient flux technique, which measures the gas transfer velocity (k), and new observational techniques that probe turbulence in the aqueous surface boundary layers were conducted over a tidal cycle in the Plum Island Sound, Massachusetts. Efforts were aimed at testing new methods in an estuarine system and to determine if turbulence created by tidal velocity can be responsible for the short-term variability ink. Measurements were made during a low wind day, at a site with tidal excursions of 2.7 m and a range in tidal velocity of nearly 1 m s−1. Estimates ofk using the gradient flux technique were made simultaneously with the Controlled Flux Technique (CFT), infrared imagery, and high-resolution turbulence measurements, which measure the surface renewal rate, turbulent scales, and the turbulent dissipation rate, respectively. All measurements were conducted from a small mobile catamaran that minimizes air- and water-side flow distortions. Infrared imagery showed considerable variability in the turbulent scales that affect air-water gas exchange. These measurements were consistent with variation in the surface renewal rate (range 0.02 to 2 s−1), the turbulent dissipation rate (range 10−7 to 10−5 W kg−1), andk (range 2.2 to 12.0 cm hr−1). During this low wind day, all variables were shown to correlate with tidal speed. Taken collectively our results indicate the promise of these methods for determining short-term variability in gas transfer and near surface turbulence in estuaries and demonstrate that turbulent transport associated with tidal velocity is a potentially important factor with respect to gas exchange in coastal systems.

Advances in Laboratory and Field Measurements

Abstract: The global distribution and the regional and temporal variations of chemical compounds in the atmosphere, both gases and aerosols, are still not well known. A full understanding of the atmospheric system can only be achieved through an integrated use of field measurements, modelling, and laboratory measurements. The past ten years have seen an impressive increase in the number of field measuring systems in use, while laboratory studies of reaction rate coefficients and mechanisms have benefited from advances in technology. The advances are often synergistic, with field instruments frequently being based on laboratory systems, and new versatile detectors brought into the lab to increase the capabilities there.