Numerical analysis of an intense rainstorm occurred in southern Italy

Abstract

Abstract. In this study we conduct a numerical analysis of an intense and destructive storm that occurred over Calabria, southern Italy, on 10-12 December 2003. More than 250 mm of precipitation was recorded over a large area in southern Calabria and one station reported about 660 mm in two days (more than half of the yearly climatological value). Precipitation fell mainly during 11 and 12 December. The storm was characterized by the entrance of an Atlantic upper-level trough associated with a deep surface low that advected humid marine air toward steep Calabrian orography. The steep mountain ridges favoured landslides, which were reported in several villages. Property damage was extensive.We study the storm at the mesoscale by means of the Regional Atmospheric Modeling System (RAMS). The model was successful at representing the observed accumulated rainfall patterns. This justifies our use of RAMS for further analysis of the physical and dynamic factors involved in the storm event. In particular, we use RAMS to evaluate the roles of Calabrian orography, surface latent heat flux, and upper level forcing.The key role of a potential vorticity (PV) streamer, which forced the entire meteorological system from the upper levels is assessed by the PV inversion technique in a Limited Area Model Ensemble Prediction System (LEPS) framework.Results show that the roles of Calabrian orography and surface latent heat flux are important in our simulations. Indeed, humid marine air masses were advected by the synoptic flow toward Calabrian steep coastal mountain ranges determining intense and abundant rainfall.

Numerical study of the October 2007 flash flood in the Valencia region (Eastern Spain): the role of orography

“…RAMS has previously been used by researchers at Fundación CEAM in the Valencia region to determine the optimal configuration of the model (Salvador et al, 1999), to study the effects of sea surface temperature on torrential rains (Pastor et al, 2001), to study air pollution dispersion (Palau et al, 2005;Pérez-Landa et al, 2007a,b) and to forecast heat waves (Estrela et al, 2007) in the Valencia region. RAMS has also been used in the study of torrential rains in the Mediterranean area by other authors like Meneguzzo et al (2000Meneguzzo et al ( , 2001Meneguzzo et al ( , 2004 and Federico et al (2008). In this study we have performed two different simulations of the event; the first is the control run (CTRL), aimed at evaluating the performance of the model while the second (NOORO1) is performed to investigate the role of local orography in the model results by removing orography in the area within grid 4.…”

“…After characterizing the rain event we evaluated the role of orography in its development, showing its importance in triggering the rainfall event. The role of orography in heavy rain events in the Western Mediterranean has previously been investigated in papers by Romero et al (1997), Horvath et al (2006), Federico et al (2008), and Miglietta and Regano (2008).…”

“…Numerous numerical modelling experiments on flash-floods have been conducted in this area in recent years. Some of these experiments have been focused on sensitivity testing (Federico et al, 2008;Bresson et al, 2009), development of forecasting systems (Davolio et al, 2009), air-sea interaction processes (Pastor et al, 2001;Lebeaupin et al, 2006Lebeaupin et al, , 2009 or investigation of the mechanisms involved in heavy rain events (Miglietta and Regano, 2008).…”

Prior history of Mistral and Tramontane winds modulates heavy precipitation events in southern France

“…All the events are recorded as HPE by raingauge networks [Colin (2012), annex D; Ricard et al (2012)] except 24 November 1993 and 27 October 1991. If we also take the 22 most extreme events in the rain analysis SAFRAN, we have to use a threshold of 190 mm and we get a hit rate for the model of 40% [as defined in Federico et al (2008)]. In conclusion, 90% of the events of the simulation are heavy rain events recorded in the literature and 40% of them are among the most extreme events in reality.…”

An observational and numerical study of a flash-flood event over south-eastern Italy

“…The levels located immediately below (down to 500 hPa) show a similar phase of the geopotential field. Incidentally, heavy-rain events in the Mediterranean basin are often associated with an upper-level trough, generally propagating eastward (Tripoli et al, 2005), and with the intrusion of stratospheric air into the upper troposphere (Federico et al, 2008). This feature is documented by the presence of a PV anomaly, that in the present case shows a maximum larger than 6 PVU on the 340 K surface (1 PVU=10 −6 m 2 s −1 K kg −1 ), elongated from central Europe into the middle of the Mediterranean Sea.…”