More Room at the Top: How Small Buoys Help Reveal the Detailed Dynamics of the Air–Sea Interface

Abstract The sea surface and air–sea exchange processes have been identified as essential for both short- and long-term atmospheric and ocean forecasts. The two phases of the fluid layer covering our planet interact across a vast range of scales that we need to explore to achieve a better understanding of the exchange processes. While satellites provide a distributed large-scale view of the sea surface situation, highly detailed measurements, e.g., from oceanographic towers, are necessarily local. An intermediate solution can be provided by swarms of miniature surface buoys that measure waves and other key parameters. As size, weight, and cost are reduced, these can be deployed in large numbers to investigate specific processes that are at present only crudely parameterized in our models, also because of the scarcity of good measurements. Perhaps the most crucial process is white capping in stormy conditions, where air–sea exchanges are enhanced by one or two orders of magnitude. Other applications include wave–current interactions, wave–ice interactions, and plunging breakers in the coastal zone. Stimulated by a dedicated workshop, we summarize here the main findings and possibilities derived from the different approaches and, in particular, the state of the art for a selection of miniature buoys. We list the presented solutions, as well as other, similar and larger, buoys, with their main characteristics and range of application. We describe the various possibilities of practical use and the scientific and engineering problems to be solved. Looking to the future, we also point out where the present technological improvements are leading to. Significance Statement The interactions between ocean and atmosphere, with the continuous and intense exchanges of energy, humidity, air, and spray, are fundamental in controlling Earth’s climate. Their correct quantification is one of the key pieces of information for any long-term forecast. Satellites provide large-scale views of the situation, but we need detailed local measurements at the sea surface to have the full physical picture. Some isolated oceanographic towers do provide detailed pictures of their local conditions, but distributed high-density information is also needed. In this respect, the present best solution is provided by small, even miniaturized, instrumented, telemetering buoys, cheap and potentially expendable, to be distributed in large numbers (tens of them or more) where a specific forecast (e.g., hurricanes) or a scientific purpose (e.g., wave breaking in a stormy sea) suggest to act. While the present smallest order of magnitude of the size of these buoys is around 10 × 10 × 10 cm 3 , the continuous technological improvement suggests that in near future volumes could be one or two orders of magnitude smaller, opening up possibilities to attack new problems.