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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 9, issue 2
Nat. Hazards Earth Syst. Sci., 9, 551–562, 2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: The RISKMED Project (Weather Risk Reduction in the Central...

Nat. Hazards Earth Syst. Sci., 9, 551–562, 2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.

  03 Apr 2009

03 Apr 2009

Numerical forecast and analysis of a tropical-like cyclone in the Ionian Sea

S. Davolio1, M. M. Miglietta2, A. Moscatello2, F. Pacifico1,*, A. Buzzi1, and R. Rotunno3 S. Davolio et al.
  • 1Institute of Atmospheric Sciences and Climate, ISAC – CNR, Bologna, Italy
  • 2Institute of Atmospheric Sciences and Climate, ISAC – CNR, Lecce, Italy
  • 3National Center for Atmospheric Research (NCAR is sponsored by the National Science Foundation), Boulder, Colorado, USA
  • *now at: School of Geographical Science, University of Bristol, Bristol, UK; Met Office Hadley Centre, Exeter, UK

Abstract. A forecasting system has been implemented for operational weather prediction over southern Italy in the framework of the RISKMED (INTERREG IIIB) project, which aims at weather-risk reduction in the central and eastern Mediterranean area. The system comprises two different regional forecasting chains, one based on BOLAM and MOLOCH models, the second based on the Weather Research and Forecasting (WRF) model.

On 26 September 2006, a subsynoptic-scale vortex developed over the Mediterranean Sea and affected south-eastern Italy. The cyclone was documented by radar reflectivity maps, Meteosat Second Generation satellite images and surface stations data. The observational analysis showed that the cyclone possessed the typical characteristics of a Mediterranean tropical-like cyclone.

All the limited-area models employed in RISKMED were able to properly forecast the formation of the small-scale vortex, although with differences in intensity, trajectory and evolution. The predictability of the event has been evaluated employing a multi-model, multi-analysis approach. The simulation results show strong sensitivity to the specification of the initial and boundary conditions.

Sensitivity experiments were performed in order to analyse the mechanisms responsible for the development and the maintenance of the cyclone over the sea. The life cycle of the vortex turned out to be characterized by different phases: the orographic cyclogenesis on the lee side of the Atlas Mountains; the initial phase of development, characterised by the critical role played by the surface heat fluxes; the transition to a tropical-like cyclone mainly as a consequence of the latent-heat release associated with strong convective activity over the Ionian Sea; finally, the maintenance of the vortex strength due to both the surface fluxes and the release of latent heat.

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