Intrinsic error in the air-sea CO<sub>2</sub> exchange coefficient resulting from the use of satellite wind speeds

Abstract

This paper is aimed at justifying the use of satellite wind speed measurements for the determination of the carbon dioxide exchange coefficient at the air–sea interface. We relate it to the wind speed using a relationship determined by Liss and Merlivat, which enables us to monitor the spatio-temporal variations of the CO 2 exchange coefficient on a global scale, using satellite measurements of the wind speed. Yet these measurements integrate the wind speed over areas having a diameter ranging from 25 to 100 km. Moreover, a satellite has a global coverage only after a few days and samples a given place every few days (usually 3 days). We simulate the spatial integration and temporal sampling of spacecraft measurements from in-situ wind speed measurements to infer the errors induced. While the space integration results in a negligible error (a few tenths of cm h -1 at most), a caveat should be given about the sampling error. It is of the order of the statistical error of a normal distribution, depending on the standard deviation and number of measurements. An example of the statistical error resulting from the use of 1 month of SEASAT scatterometer data is shown. Provided this caution about the statistical error is kept in mind and the space and time integration is properly chosen, satellite data, after careful validation of the wind speed retrieval, are well suited for long-term global survey of the CO 2 exchange coefficient space and time variations. The use of a relationship between the exchange coefficient and the wind speed, which accuracy is presently discussed, is the only way to access these variations. DOI: 10.1034/j.1600-0889.1991.00016.x