An observational and numerical case study of a flash sea storm over the Gulf of Genoa

A Orlandi,L F Onorato,F Pasi,S Gallino

doi:10.5194/asr-2-107-2008

Abstract

Abstract. During the night between the 8 and 9 December 2006 the seawall of the Savona harbour (Liguria Region in north west of Italy) was overtopped by waves. In this work the "Savona flash sea storm" has been studied by analyzing the data recorded by meteo-marine observing stations and the data produced by high resolution meteo-marine numerical models. The data show that, due to the presence of a fast moving low pressure system, the event was characterized by a rapid transition and interaction between two different regimes of winds and related sea states. The results of the study suggest that the most damaging dynamics of the event could be correlated to a bi-modal structure of the wave spectrum. Based on this the authors suggest that a deeper study of the spectral structure of sea storms could lead to define new operational forecasting tools for the preventive evaluation of sea storms damaging potential.

Highlights

The Gulf of Genoa is located in one of the most cyclogenetic area of the Mediterranean basin (Trigo et al, 2002), where the interaction of the synoptic flow with the complex alpine topography cause the development of deep orographic lows, which are usually very dynamic and tend to move quickly to the east driven by the upper level flow
As a consequence low level winds show a very rapid transition from “Scirocco” to “Libeccio”, with intensity strongly enhanced by coastal effects (Onorato et al, 2006)
In these cases the sea conditions are characterized by a complex crossed sea state, resulting from the superposition of wave components generated by different strong wind fetches

Summary

Introduction

The Gulf of Genoa is located in one of the most cyclogenetic area of the Mediterranean basin (Trigo et al, 2002), where the interaction of the synoptic flow with the complex alpine topography cause the development of deep orographic lows, which are usually very dynamic and tend to move quickly to the east driven by the upper level flow. As a consequence low level winds show a very rapid transition from “Scirocco” (south-east) to “Libeccio” (south-west), with intensity strongly enhanced by coastal effects (Onorato et al, 2006). In these cases the sea conditions are characterized by a complex crossed sea state, resulting from the superposition of wave components generated by different strong wind fetches. The modelling chain is implemented and used for operational weather forecasting at La.M.Ma (Laboratory for Meteorology and environmental Modelling, http://www.lamma.rete.toscana.it) and is composed by a meteorological model and a wave model running in cascade The former is the atmospheric model WRF-ARW (http://www.wrf-model.org, Janiic, 2003), at a resolution of 0.12 deg with initial and boundary conditions from NCEP-GFS (T382L64) at 0.5 deg resolution. In this work the meteo-marine conditions of the above described sea storm are studied, trough the analysis of observations and high resolution numerical models results, in order to better comprehend and describe the dynamics that might have caused the event

Observation

Numerical simulation

Conclusions