Sea level surges of June 2011 in the NE Atlantic Ocean: observations and possible interpretation

Abstract

We present a synthesis of tide gauge data recorded on June 26–28, 2011, along the NE Atlantic and the English Channel coastlines, which show a significant sea level disturbance observed from Portugal to England during several hours. Though the amplitude was low (a few centimeters at most), the main disturbance was observed in about 30 harbors. The phenomenon started in south Spain and Portugal in the last hours of 26 June and reached the French west coastline on 27 June, at about noon. Finally, it was observed in the English Channel (UK and France) from 27 June to 28 June and also noticed by witnesses as tidal bores in Cornwall. For some of the places investigated, it was followed by a second signal about 12 h later, especially in the SE of the Bay of Biscay. Spectral analyses show a dominant periods of 25 min present on almost all data and that the phenomenon highlighted the resonant periods of the harbors. Using travel time modeling, we observe that the disturbance traveled much more slowly than long-wave propagation and that the timing does not compel with a single source for all the recordings. A comparison with available atmospheric data reveals that a pressure anomaly traveled the same day across the area, from south Portugal to the English Channel and was probably the origin of several sources for the phenomenon, with a second one completing the later signals. Finally, historic facts present that these kinds of event can be potentially lethal or damaging.