Journal Article

Phase‐Resolved Swells Across Ocean Basins in SWOT Altimetry Data: Revealing Centimeter‐Scale Wave Heights Including Coastal Reflection

Molero, Beatriz, Bohé, Alejandro, Ardhuin, Fabrice, Nouguier, Frédéric, Houghton, Isabel, Collard, Fabrice, Hay, Andrea, Legresy, Benoit

2024

Overview

Severe storms produce ocean waves with periods of 18–26 s, corresponding to wavelengths 500–1,055 m. These waves radiate globally as swell, generating microseisms and affecting coastal areas. Despite their significance, long waves often elude detection by existing remote sensing systems when their height is below 0.2 m. The new Surface Water Ocean Topography (SWOT) satellite offers a breakthrough by resolving these waves in global sea level measurements. Here we show that SWOT can detect 25‐s waves with heights as low as 3 cm, and resolves period and direction better than in situ buoys. SWOT provides detailed maps of wave height, wavelength, and direction across ocean basins. These measurements unveil intricate spatial patterns, shedding light on wave generation in storms, currents that influence propagation, and refraction, diffraction and reflection in shallow regions. Notably, the magnitude of reflections exceeds previous expectations, illustrating SWOT's transformative impact. Plain Language Summary Wind storms at sea make waves that increase in size with wind speed, and with the distance over which the high winds have been able to amplify the waves. Once generated these waves propagate as swell around the world ocean: in that stage the wave period remains constant while the wave height decay away from the source. Waves with periods longer than 18 s are relatively infrequent, but they are an important source of seismic waves and coastal impacts. However, current remote sensing techniques miss long waves under 0.2 m high. The Surface Water Ocean Topography (SWOT) satellite mission changes this, spotting 25‐s waves with heights as low as 3 cm. SWOT maps wave height, wavelength, and direction worldwide, revealing the influence of winds, currents and water depth. For example, We found stronger than expected coastal reflection, which will help revise wave forecasting models and their application in seismology. Key Points Surface Water Ocean Topography (SWOT) data provide the first open ocean spatial measurements of phase‐resolved swells with wavelength 500–1,050 m Swells with heights as low as 3 cm are well detected by SWOT, allowing tracking across oceans Swell reflection off the coast can be separated from incident waves

• Publisher: John Wiley & Sons, Inc,American Geophysical Union,Wiley
• Subject: Altimetry / Buoys / Coastal currents / Coastal effects / coastal reflection / Coastal storms / Coastal waters / Coastal zone / Diffraction patterns / Engineering Sciences / Forecasting models / Global sea level / Light diffraction / Light reflection / Long waves / Microseisms / Ocean basins / Ocean wave heights / Ocean waves / Ocean, Atmosphere / Oceans / P-waves / Reflection / Remote sensing / Remote sensing systems / Remote sensing techniques / Satellites / Sciences of the Universe / Sea currents / Sea level measurement / Sea level measurements / Seismic waves / Seismology / Severe storms / Signal and Image processing / Storms / Surface water / Surface water waves / Swell / SWOT / Topography / Water currents / Water depth / Wave diffraction / Wave forecasting / Wave generation / Wave height / Wave period / Wave propagation / Wave reflection / Wavelength / Wavelengths / Wind speed / Wind storms / Winds