Meteorologically induced strong seiches observed at Arraial do Cabo, RJ, Brazil

Abstract

Meteorologically seiche oscillations can sometimes reach significant heights, causing severe damage. There is only one reference to an extreme event of this type in Brazil, but it is based on only eyewitness reports, without data confirmation. However, this lack of observed events is due to the very small number of high-resolution sea level measurements along the coast. The main purposes of the present study were to analyze a 4-year high-resolution series, collected at Arraial do Cabo, RJ, Brazil, to identify the main high-frequency sea level events and to relate them to possible forcing. In the series examined, high-frequency oscillations ( T < 1 h) were almost always present, with a dominant period close to the fundamental mode of the bay (Helmholtz mode, n = 0), about 20 min. Although their average height was 20 cm, in some situations, these waves exceeded 30 cm, and in an extreme event, associated with an atmospheric pressure jump of 10 hPa/2 h, the oscillations reached 60 cm. That is comparable to the largest amplitude low-frequency variation ( T > 36 h) measured in the region between 1999 and 2008.