Extreme Storm Surge Events and Associated Dynamics in the North Atlantic

Storm surges events are investigated using the ECHAR method, which identifies and quantifies the different dynamical structures of a typical storm surge event. In the North Atlantic, analysis of 65 tide gauges revealed that storm surge events display two major and two minor structures, each of them corresponding to specific ocean dynamics. The two major structures refer to a slow‐time Gaussian structure, lasting around 24 days, associated with the impact of the atmospheric pressure and a fast‐time Laplace structure, lasting around 1.4 days, mainly wind‐driven. The absence of the Gaussian structure along the North America coasts is explained by storms of smaller spatial extension, compared to Europe. Concerning the minor structures, a negative surge of around 6 cm just after the peak surge is observed over North America only. Such a sudden drop of the sea level is explained by the turning winds during the storm event, favored by the smaller spatial extension of storms. Finally, high frequency oscillations, with amplitude typically of 3 cm and up to 25 cm, are observed at some tide gauges. These oscillations refer to tide‐surge interactions and they are often maximum at a specific phase of the tide and/or enhanced because of resonant basins. Plain Language Summary The storm surges refer to the extreme values of the sea level time series, after the removal of tides and the mean sea level. The storm surges are due to extreme weather systems such as storms and are responsible for coastal flooding. Rather than focusing on the maximum values of the sea level during storm events, we consider the full dynamics of the events from 20 days before to 20 days after each maximum. Doing so helps to properly describe the different types of storm surge events and explain the atmospheric and ocean dynamics leading to such extremes. Key Points The new ECHAR method decomposes storm surge events in two major and two minor structures each of them reflecting specific ocean dynamics In North America a large drop of the sea level 1.5 days after the peak surge is explained by turning winds and storms of small extent Observed oscillations with amplitude up to 10 cm are the signature of tide‐surge interaction