Multi-Physics Ensemble versus Atmosphere–Ocean Coupled Model Simulations for a Tropical-Like Cyclone in the Mediterranean Sea

Antonio Ricchi,Umberto Rizza,Guido Cioni,Mario Marcello Miglietta,Sandro Carniel,Davide Bonaldo

doi:10.3390/atmos10040202

Abstract

Between 19 and 22 January 2014, a baroclinic wave moving eastward from the Atlantic Ocean generated a cut-off low over the Strait of Gibraltar and was responsible for the subsequent intensification of an extra-tropical cyclone. This system exhibited tropical-like features in the following stages of its life cycle and remained active for approximately 80 h, moving along the Mediterranean Sea from west to east, eventually reaching the Adriatic Sea. Two different modeling approaches, which are comparable in terms of computational cost, are analyzed here to represent the cyclone evolution. First, a multi-physics ensemble using different microphysics and turbulence parameterization schemes available in the WRF (weather research and forecasting) model is employed. Second, the COAWST (coupled ocean–atmosphere wave sediment transport modeling system) suite, including WRF as an atmospheric model, ROMS (regional ocean modeling system) as an ocean model, and SWAN (simulating waves in nearshore) as a wave model, is used. The advantage of using a coupled modeling system is evaluated taking into account air–sea interaction processes at growing levels of complexity. First, a high-resolution sea surface temperature (SST) field, updated every 6 h, is used to force a WRF model stand-alone atmospheric simulation. Later, a two-way atmosphere–ocean coupled configuration is employed using COAWST, where SST is updated using consistent sea surface fluxes in the atmospheric and ocean models. Results show that a 1D ocean model is able to reproduce the evolution of the cyclone rather well, given a high-resolution initial SST field produced by ROMS after a long spin-up time. Additionally, coupled simulations reproduce more accurate (less intense) sea surface heat fluxes and a cyclone track and intensity, compared with a multi-physics ensemble of standalone atmospheric simulations.

Highlights

The Mediterranean basin is one of the most cyclogenetic areas in the world, with an average of one hundred pressure lows every year [1]
We describe the results of the multi-physics ensemble and the coupled model simulations
In order to compare the trajectory of the simulated MTLC with the observed track (Figure 1), the values of the minimum pressure are saved together with the maximum wind intensity within a radius of 200 km from the cyclone center

Summary

Introduction

The Mediterranean basin is one of the most cyclogenetic areas in the world, with an average of one hundred pressure lows every year [1]. Extra-tropical depressions, typical of this area, are often caused by the interaction of upper level disturbances with low-level baroclinicity, sometimes favored by the complex morphology of the basin, as in the case of so-called Genoa low [2] Such cyclones can be intense and associated with heavy precipitation events (HPEs) and severe wind gusts. Some Mediterranean cyclones may exhibit tropical-like features in their mature stage, such as a barotropic structure, the presence of a warm core in the center of the storm with structured and spiral convection around it, and sustained winds over 100 km/h [3,4,5,6,7,8,9]. Several studies have demonstrated that these systems, which usually originate from a baroclinic wave, can transition into barotropic structures when certain environmental conditions are met [12]

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Conclusion