Numerical Analysis of a Mediterranean “Hurricane” over Southeastern Italy

Abstract

The presence of a subsynoptic-scale vortex over the Mediterranean Sea in southeastern Italy on 26 September 2006 has been recently documented by the authors. The transit of the cyclone over land allowed an accurate diagnosis of the structure of the vortex, based on radar and surface station data, showing that the cyclone had features similar to those observed in tropical cyclones. To investigate the cyclone in greater depth, numerical simulations have been performed using the Weather Research and Forecasting (WRF) model, set up with two domains, in a two-way-nested configuration. Model simulations are able to properly capture the timing and intensity of the small-scale cyclone. Moreover, the present simulated cyclone agrees with the observational analysis of this case, identifying in this small-scale depression the typical characteristics of a Mediterranean tropical-like cyclone. An analysis of the mechanisms responsible for the genesis, development, and maintenance of the cyclone has also been performed. Sensitivity experiments show that cyclogenesis on the lee side of the Atlas Mountains is responsible for the generation of the cyclone. Surface sensible and latent heat fluxes become important during the subsequent phase of development in which the lee-vortex shallow depression evolved as it moved toward the south of Sicily. During this phase, the latent heating, associated with convective motions triggered by a cold front entering the central Mediterranean area, was important for the intensification and contraction of the horizontal scale of the vortex. The small-scale cyclone subsequently deepened as it moved over the Ionian Sea and then maintained its intensity during its later transit over the Adriatic Sea; in this later stage, latent heat release continued to play a major role in amplifying and maintaining the vortex, while the importance of the surface fluxes diminished.

Tropical transition of a Mediterranean storm by jet crossing

“…Among the Mediterranean cyclones accompanied by upper-level anomalies and deep convection, about 15 mesocyclones have been observed over the last 20 years, preferentially in autumn (Fita et al, 2007). They share some similarities with tropical cyclones and a number of case studies have been made on these hurricanelike cyclones or medicanes (Mediterranean 'hurricanes'; Lagouvardos et al, 1999;Pytharoulis et al, 2000;Reale and Copyright c 2011 Royal Meteorological Society Atlas, 2001;Homar et al, 2003;Fita et al, 2007;Moscatello et al, 2008aMoscatello et al, , 2008bDavolio et al, 2009;Claud et al, 2010;McTaggart-Cowan et al, 2010;among others). A medicane exhibits a clearly defined eye, quasi-circular cloud patterns, strong surface winds sometimes reaching the intensity of a tropical storm, deep convection and the presence of a warm core.…”

“…Homar et al, 2003;Moscatello et al, 2008b) or formed at the edge of a wider cyclone (e.g. Lagouvardos et al, 1999;Pytharoulis et al, 2000).…”

“…A mean-sea-level-pressure (MSLP) minimum of 986 hPa and wind gusts exceeding 40 m s −1 (78 kt) were recorded (Moscatello et al, 2008b), the most intense values ever registered for a medicane. It was also the medicane that experienced the most rapid development.…”

“…Although the low formed as early as 24 September, we focus on the intensification phase over the Ionian Sea, when the cyclone took on the characteristics of a tropicallike cyclone on the morning of 26 September. Based on numerical experiments, Moscatello et al(2008a) and Davolio et al(2009) attributed the rapid deepening of the cyclone to its interaction with convection enhanced by the orography of Calabria (a small lee cyclogenesis was noted to occur east of Calabria in this phase; Moscatello et al,2008a;Davolio et al, 2009). Although they noted that an upper-level PV anomaly moved close to the vicinity of the mesocyclone during this phase, they did not explore its role further.…”

Impact of Sea Surface Temperature on COSMO Forecasts of a Medicane over the Western Mediterranean Sea

“…The Mediterranean is a large and sometimes warm body of water, thus it can be an area of cyclogenesis influenced by convective instability and air-sea interaction, producing cyclones with some of the characteristics of hurricanes [2,3]. The western Mediterranean Sea is an important cyclogenetic area [4].…”