A Multi-Year Time Series of Global Gas Transfer Velocity from the TOPEX Dual Frequency, Normalized Radar Backscatter Algorithm

Abstract

The feasibility of calculating gas transfer velocity directly from a remotely sensed measure of the sea surface roughness presents an unique opportunity. We present here the six year time series (1993-1998) of TOPEX data processed into gas transfer velocity and examine the variability of these results in space and time. The seasonal and interannual variability of the regional patterns yield insight into the sensitivity of the altimeter-based gas transfer velocity to phenomena such as ENSO. We compare the results of this time series to a similar time series created through the application of more traditional wind speed-gas transfer velocity parameterizations to the wind speed estimates made by the National Center for Environmental Prediction reanalysis project for the same period. Our approach to deriving transfer velocity is subject to parameters calibrated against field and laboratory measurements. The intercomparison would be greatly enhanced by in situ measurements contemporaneous with the altimetry and the newly launched QuikScat scatterometry mission. These in situ measurements are one of our best constraints on the remote observations: wind stress vs. surface roughness. Examples are given of how, even at a limited number of sites around the globe, these in situ measurements may improve the remotely sensed time series of air-sea gas transfer velocity.