R. Wanninkhof
John Crusius
2003
<p><span>The relationship between </span>gas<span> </span>transfer<span> </span>velocity<span> and </span>wind<span> </span>speed<span> was evaluated </span>at<span> </span>low<span> </span>wind<span> speeds by quantifying the rate of evasion of the deliberate tracer, SF</span><sub>6</sub><span>, from </span>a<span> small oligotrophic </span>lake<span>. Several possible relationships between </span>gas<span> </span>transfer<span> </span>velocity<span> and </span>low<span> </span>wind<span> </span>speed<span> were evaluated by using 1-min-averaged </span>wind<span> speeds as </span>a<span> measure of the instantaneous </span>wind<span> </span>speed<span> values. </span>Gas<span> </span>transfer<span> </span>velocities<span> in this data set can be estimated virtually equally well by assuming any of three widely used relationships between k</span><sub>600</sub><span> and winds referenced to 10-m height, U</span><sub>10</sub><span>: (1) </span>a<span> bilinear dependence with </span>a<span> break in the slope </span>at<span> ∼3.7 m s</span><sup>-1</sup><span>, which resulted in the best fit; (2) </span>a<span> power dependence; and (3) </span>a<span> constant </span>transfer<span> </span>velocity<span> for U</span><sub>10</sub><span> < ∼3.7 m s</span><sup>-1</sup><span>, with </span>a<span> linear dependence on </span>wind<span> </span>speed<span> </span>at<span> higher </span>wind<span> speeds. The lack of </span>a<span> unique relationship between </span>transfer<span> </span>velocity<span> and </span>wind<span> </span>speed<span> </span>at<span> </span>low<span> </span>wind<span> speeds suggests that other processes, such as convective cooling, contribute significantly to </span>gas<span> exchange when the </span>wind<span> speeds are </span>low<span>. All three proposed relationships clearly show </span>a<span> strong dependence on </span>wind<span> for winds >3.7 m s</span><sup>-1</sup><span> which, coupled with the typical variability in instantaneous </span>wind<span> speeds observed in the field, leads to average </span>transfer<span> </span>velocity<span> estimates that are higher than those predicted for steady </span>wind<span> trends. The </span>transfer<span> </span>velocities<span> predicted by the bilinear steady </span>wind<span> relationship for U</span><sub>10</sub><span> < ∼3.7 m s</span><sup>-1</sup><span> are virtually identical to the theoretical predictions for </span>transfer<span> across </span>a<span> smooth surface.</span></p>
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10.4319/lo.2003.48.3.1010
en
Association for the Sciences of Limnology and Oceanography
Gas transfer velocities measured at low wind speed over a lake
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