The new recordThe giant waves from Quirin were measured by the radar altimeter onboard the Jason 2 satellite. 20.1 m is the largest significant wave height recorded by a satellite altimeter ever since the first routine space-borne measurements in the late 1980s. The significant wave height is an average of the top third of the highest waves. Although the radar cannot measure individual waves from space, usual statistics tell us that the highest wave in Quirin was probably higher than 36m. Larger waves have probably existed, but we still have not measured them in the open ocean.
Heights ... and periodsSatellite altimeters were not designed to record such high waves and thus we may question the accuracy of the reported value. However, the measurement is consistent with all other measurements, in particular we know that very high waves must have very long periods, a property that is almost conserved as waves disperse in the oceans. Indeed, the Quirin waves turned into extremely long swells with peak periods up to 25 s recorded 2 days later to the North of Ireland.
A surfer's dream and a harbor master nightmare
These long swells can be strongly amplified by underwater reefs, and cause strong long period motions in harbours. Thanks to Quirin, French surfer Benjamin Sanchis rode the 'biggest wave of the year' on February 16 to claim the Billabong XXL prize for 2011, while severe damage was inflicted in Royan harbor du to seiche resonance. The analysis of the storm confirms that the biggest waves appear when the low pressure systems move at the speed of the waves, a phenomenon that is well reproduced by numerical wave models, even for such huge waves. That is if we believe in numerical models for winds: the high winds in the storm center are well observed by modern satellite sensors but the magnitude of measured wind speeds above 50 knots is very uncertain.