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Air-water gas exchange : mechanisms governing the combined effects of wind and rain on the gas transfer velocity and field measurements in a eutrophic region of the Everglades of the effects of wind

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Item Summary

Title: Air-water gas exchange : mechanisms governing the combined effects of wind and rain on the gas transfer velocity and field measurements in a eutrophic region of the Everglades of the effects of wind
Authors: Eggleston, Sarah Skye
Keywords: gas exchanges
Issue Date: Aug 2011
Publisher: [Honolulu] : [University of Hawaii at Manoa], [August 2011]
Abstract: Air-water gas exchange is an important process in many biogeochemical cycles, including the global carbon cycle. Quantifying the movement of gases across the air-water interface is important to understand cycling on global and regional scales, to constrain the magnitude of the oceanic source or sink of biologically and climatically important trace gases, and to study local ecosystem dynamics. Although our knowledge of the mechanisms driving gas exchange due to individual processes, such as wind or rain, has improved greatly over the past few decades, there are regions where multiple processes may be significant in determining rates of gas exchange, and questions remain regarding the combined effects on the gas transfer velocity. Additionally, while many field studies have been conducted to measure gas exchange in a variety of environments, including lakes and wetlands, and to parameterize the gas transfer velocity in terms of its governing mechanisms and driving forces, the applicability of these parameterizations has not yet been established for all systems.
In the first study presented here, the mechanisms responsible for gas exchange under conditions of wind and rain were studied in the laboratory and quantified. Measured variables included turbulent kinetic energy, bubble formation frequency, wave slope, wind speed profiles and raindrop impact velocity, allowing calculation of the kinetic energy flux due to wind and rain. It was determined that the impact of rain on air-water gas exchange is significantly reduced at elevated wind speeds (12-20 m sāˆ’1 in this study). While this result differs quantitatively from two previous studies at the same facility, the findings can all be described by a model for gas exchange in which the gas transfer velocity depends on wind speed, u10, and the excess mixing of rain beyond a critical depth of dissipation of TKE due to wind. This mixing is accounted for by taking into account depth scales relevant to rain and wind, zR and zu, which are assumed to scale by the kinetic energy fluxes of rain and wind, respectively. The parameterization k600 = au2 10 + b(KEFrain āˆ’ cKEFwind)B describes the results from each of the two previous studies as well as the present study. While this model predicts that the effect of rain would be negligible in high-wind, low-rain regions of the oceans such as the Southern Ocean, rain may be very important to take into account in regions with characteristically high rain rates and low wind speeds.
Description: M.S. University of Hawaii at Manoa 2011.
Includes bibliographical references.
URI/DOI: http://hdl.handle.net/10125/101565
Appears in Collections:M.S. - Oceanography



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