Numerical diagnosis of a small, quasi‐tropical cyclone over the western Mediterranean: Dynamical vs. boundary factors

Abstract

SUMMARYA small, quasi-tropical cyclone occurred on 12 September 1996 over the western Mediterranean. Intense convective activity over the region during this period also produced a tornado outbreak in the Balearic Islands and torrential precipitation over eastern mainland Spain.Mesoscale model runs properly simulate the cyclone formation and show convection and heavy precipitation following the cyclone trajectory during its eastward progression. A sensitivity study examining the upper-level dynamic forcing, latent-and sensible-heat uxes from the sea, and orography is conducted. A potential-vorticity (PV) inversion technique is used to reduce the amplitude of the upper-level trough in the model initial conditions. The results show that neither the orography nor the sensible-heat ux from the sea play a signi cant role during this particular cyclone development. Conversely, both the latent-heat ux and the upper-level trough are shown to be crucial for low-level cyclogenesis. Features common to hurricane-like polar lows are found for the cyclone, and an analysis of the precise role of the upper-level structures and the convective development is conducted.A factor-separation technique is used to determine the individual effects of the aforementioned factors, as well as their interaction. At the rst stage of the cyclogenesis, the upper-level PV anomaly enhanced the low-level circulation of the synoptic-scale low and enhanced the latent-heat ux from the sea. During its mature stage, the circulation associated with the small-scale cyclone enhanced the latent-heat ux from the sea, thereby helping to maintain the development of deep convection, and inducing further cyclone deepening by diabatic heating. This scenario has many similarities with the air-sea interaction instability mechanism. Thus, the joint action of the upper-level anomaly, as a spin-up agent, and the latent-heat ux, as a sustainer of convection, emerges as the primary factor for the genesis and evolution of the small quasi-tropical cyclone.

Simulation of medicanes over the Mediterranean Sea in a regional climate model ensemble: impact of ocean–atmosphere coupling and increased resolution

“…Medicanes can produce considerable damage due to the combination of intense winds and heavy precipitation. Observed cases of tropical-like cyclones in the Mediterranean region have been analyzed in detail (Pytharoulis et al 2000;Reale and Atlas 2001;Homar et al 2003;Moscatello et al 2008).…”

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).…”

“…Reale and Atlas, 2001;Fita et al, 2007), which triggers the convective instability (e.g. Reale and Atlas, 2001;Homar et al, 2003;Pytharoulis et al, 2000). During the mature phase, the coupled interaction between deep convection and sea surface fluxes is seen as the central mechanism in the maintenance of the medicane.…”

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

“…The aim was to understand the impact of air-sea interactions in the maintenance/formation and the characteristics of the cyclone. In recent hurricane-like cyclones in the Mediterranean, convective instability has been shown to play an important role [6]. The means by which convective instability is produced has been the subject…”