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 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.

Drifting buoy observations in Hurricane Idalia (2023) are used to investigate the dependence of ocean surface wave mean square slope on wind, wave, and storm characteristics. Mean square slope has a primary dependence on wind speed that is linear at low-to-moderate wind speeds and approaches saturation at high wind speeds (>20 m s^-1 ). Inside Hurricane Idalia, buoy-measured mean square slopes have a secondary dependence on wind-wave alignment: at a given wind speed, slopes are higher where wind and waves are aligned compared to where wind and waves are crossing. At moderate wind speeds, differences in mean square slope between aligned and crossing conditions can vary 15–20% relative to their mean. These changes in wave slopes may be related to the reported dependence of air-sea drag coefficients on wind-wave alignment.

The processes important to hurricane wave generation cover scales from kilometers to centimeters. Within a storm, waves have complex spatial variations that are sensitive to hurricane size, strength and speed. This makes it challenging to measure the spatial variability of hurricane waves with any single instrument. To obtain both broad spatial coverage and resolve the full range of wave scales, we combine arrays of drifting wave buoys with airborne radar altimetry. The microSWIFT (UW-APL) and Spotter (Sofar) buoys are air-deployed along a given storm track. These buoys resolve the scalar wave frequency spectrum from 0.05 Hz to 0.5 Hz, which is approximately 600 m to 6 m wavelength (in deep water). The Wide Swath Radar Altimeter (WSRA) flies into hurricanes aboard the NOAA Hurricane Hunter P-3 aircraft. The radar altimetry data is processed to produce a 2D directional spectrum from 2.5 km to 80 m wavelength, and the radar backscatter provides an estimate of the mean square slope down to centimeter wavelengths. We introduce a method to use colocated mean square slope observations from each instrument to infer the shape of the spectral tail from 0.5 Hz to almost 3 Hz. The method is able to recover the frequency f^–5 tail characteristic of the saturation range expected at these frequencies (based on theory and measurements in lower wind speeds). We also explore the differences between WSRA and buoy mean square slopes, which represent the mean square slope of the intermediate wavelength waves (6 m down to 20 cm). Together, the fusion of these wave measurements provides a multiscale view of the hurricane-generated waves. These ocean surface waves are critical as drivers of the air-sea coupling that controls storm evolution and as drivers of coastal impacts by hurricanes.