Alternative Approaches to Storm Statistics in the Ocean

Abstract

The classical approach to storm statistics in the ocean is an Eulerian analysis of wave time series at a given location, in which the wave data can be observations or results of wave models. The information obtained from this approach is storm frequency, duration and intensity, from which extremes at the particular location can be estimated. The availability of spatial information of wave characteristics at successive time intervals, which is available from large scale forecasts or hindcast allows the follow-up of storm evolution in space and time. Using this data it is possible to study the spatial evolution of storms, i.e to provide a Lagrangean description of storm characteristics. In this paper the principles for spatio-temporal identification and statistical analysis of storm variability are formulated. Using ten years of wave data the HIPOCAS North Atlantic hindcast data, storms were identified using both approaches and two different sets of storm characteristics were obtained. The enhanced information that is possible to obtain from the Lagrangean approach in comparison to the Eulerian is illustrated.

Hindcast of extreme sea states in North Atlantic extratropical storms

“…While storms move and change direction, some of the storm statistics are based on data from a single location not following the storm as discussed in Bernardino et al (2008). A noticeable shift of the location of the North Atlantic storm tracks was found in McCabe et al (2001) who showed that storm frequency in midlatitudes decreased during the second half of the twentieth century while an increase was found for the high latitudes north of 60°N.…”

Directional analysis of sea storms

“…Storms evolve in space and time often changing direction and thus one can choose an Eulerian or a Lagrangian description to model them as discussed by Bernardino et al (2008). However it is most common to adopt the Eulerian approach, which is the one considered in this paper.…”

Hindcast of the Hércules winter storm in the North Atlantic

“…Despite the scarcity of these events, they can be associated with severe consequences such as considerable damages to ships, offshore structures and potential loss of human life (Faulkner and Buckley 1997;Guedes Soares et al 2008). The statistical wave data used in climatic databases are normally at selected grid points, but to study the effect of a specific storm, a different approach needs to be adopted (Bernardino et al 2008). …”