The 11?12 December 2003 storm in Southern Italy

International audienceWe review an intense and heavy impact storm that occurred over Calabria, southern Italy, during the 11 and 12 December 2003. The event is traced back, at synoptic and planetary scales, up to 5 December 2003 by National Centre for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalysis fields and backtrajectories. The role of tropical storm Odette is clearly shown as well as that of the Azores high. Even if non negligible water vapour sources are expected from the Mediterranean sea, unusually large precipitable water was present over the Atlantic mid-latitudes. It is shown that tropical storm Odette determined large evaporation from Atlantic Tropics and the cooperative action of synoptic scale and planetary scale pressure centres focused this humidity into a plume and conveyed it into the Mediterranean area

Sea storms hindcast around Calabrian coasts: Seven cases study

The impact of wind field enhanced horizontal resolution on seven sea storms hindcast occurred around Calabrian coasts, the southernmost tip of Italian peninsula, is investigated. Cases studies are simulated by WAM (WAve Model), a third-generation state-of-the-art wave model. In order to study the effects produced on wave hindcast by surface wind enhanced horizontal resolution, two simulations sets are discussed. The first set uses ECMWF (European Centre for Medium Weather range Forecast) surface wind fields analysis to force WAM model; a second simulations set is produced by forcing WAM model with RAMS (Regional Atmospheric Modeling System) surface wind fields. RAMS simulations use ECMWF analysis as initial and dynamic boundary conditions. Performances are evaluated comparing WAM-modelled wave heights and directions with data at Cetraro and Crotone Wave measuring Buoys (WBs). While wave directions are well reproduced by both simulations sets, i.e. using ECMWF or RAMS wind fields to force WAM, differences arise for wave heights. Results show better performances of WAM model when RAMS surface wind field is used. However for two events results are still unsatisfactory using RAMS-modelled wind fields. A possible explanation is given

The upper-tropospheric forcing during the 10th-12th December 2003 storm over Calabria

In this study we revisit an intense and destructive storm that occurred over Calabria, southern Italy, on 10th-12th December 2003. This event was already analyzed by two of the authors at synoptic and planetary scales, however in this work we investigate the mesoscale of the storm by the RAMS (Regional Atmospheric Modeling System) model. Firstly it is shown that large-scale moisture source was mainly from the Mediterranean basin, then RAMS simulations are discussed to focus on the mesoscale of the storm. More precisely we evaluate the roles of Calabrian orography and the surface latent heat fluxes by the factor separation technique. Results show that the role of Calabrian orography, even if important, decreased during the event whilst the role of surface latent heat fluxes was less affected through the entire event. A prominent mid tropospheric trough or cut-off low can be identified through this event prior and during the period of heavy rain. The upper-tropospheric level disturbance, associated with high potential vorticity (PV) values, consequence of a deep tropospheric intrusion of stratospheric air masses, coupled with the surface cyclone and reinforced the whole meteorological system which resulted in the heavy impact rainstorm over Calabria, mainly during 11th and 12th December 2003

Quantitative precipitation forecast of the Soverato flood: The role of orography and surface fluxes

During the night between 9 and 10 September 2000 a strong flood occurred in Soverato, a small town of Ionian coast of Calabria, killing 13 people. This was the top of an intense precipitation event occurred over the region during 8th, 9th, 10th September. In this paper the study of this event is performed, both analysing the synoptical aspects and using a numerical meteorological model either to reproduce the precipitation fields or to highlight some mesoscale features that determined the very intense and abundant rainfall. After a short description of the case study and presentation of measured rainfall fields, simulations are discussed. The study is based on three numerical simulations performed using the CSU-RAMS model (Regional mesoscale Modeling System) developed at Colorado State University and daily used at Crati Scrl to produce weather forecasts over Calabria peninsula. The first run is the control case and assesses the model ability to reproduce the flood cumulated rainfall by comparison with rain gauge data collected by the “Istituto Idrografico e Mareografico-Dipartimento di Catanzaro”. Second simulation is made to assess the influence of orographic barriers on the precipitation field, while third simulation evaluates the sensitivity to latent and sensible heat fluxes. Results indicate that the model simulate in satisfactory way the location and amount of rainfall, even if some problems are open and require more investigations

Numerical simulation of Crotone flood: Storm evolution

A nested-grid primitive equation model (RAMS, version 4.3) is used to simulate a high-precipitation (HP) storm which occurred in Calabria, Southern Italy. Storm produced intense rainfall over the city of Crotone, in the central Ionian coast of Calabrian peninsula, during the morning of 14 October 1996. Precipitation spell lasted for two hours, was highly localized and rainfall rates were intense (> 60 mm/h). The aim of this paper is to reproduce precipitation measured by raingauges and to highlight local and synoptic conditions that determined the storm, in order to acquire insight into the convective environment that produced the event. Four telescoping nested grids allow to simulate scales ranging from the synoptic scale down to the high-precipitation storm. All convection in the simulation is initiated by resolving explicitly vertical motion and subsequent condensation-latent heating from the model microphysics;no warm bubbles are used to start or trigger the storm. The model is able to well simulate measured precipitation both in terms of total precipitation and rain intensity. Also the position of the major spell is acceptable

A LEPS approach to the predictability of intense rain storms in the Central Mediterranean basin

International audienceThis study investigates a method for best member selection of a Limited area model Ensemble Prediction System (LEPS) with the goal to increase quantitative precipitation forecast. A case study that occurred between 22-24 May 2002 over Calabria, southern Italy, is discussed. Mediterranean storms often develop under upper level disturbances which are usually associated with high values of potential vorticity. Anomalously high values of potential vorticity can be identified by the METEOSAT water vapor channel centered around 6.3 ?m because they are associated with dark band on the METEOSAT image. This signature offers a chance to identify the upper level disturbance that can be exploited in data void countries as Calabria. The working hypothesis is that the uncertainty in the representation of the upper-level disturbance has a major impact on the precipitation forecast. This issue is utilized in an ensemble forecast where member forecasts are compatible with the analysis and forecast errors. These members are grouped in five clusters by a hierarchical clustering technique which utilizes the height of the dynamical tropopause to compute distances between members. Therefore the members of a cluster have a similar representation of the upper level disturbance. For each cluster a representative member is selected and its pseudo water vapor image is compared with the corresponding METEOSAT 7 water vapor image at a specific time, antecedent to the rain occurrence over Calabria. The subjective evaluation of the comparison allows to gain physical insight in the storm evolution and to select representative members which are more in agreement with the METEOSAT image. Results, even if for a case study, show the feasibility of the methodology that, if confirmed by further investigations, could be valuable in data void countries as the central Mediterranean basin

The meteorological model RAMS at Crati Scrl

International audienceAt Crati Scrl an operational version of RAMS 4.3 (Regional Atmospheric Modeling System) was implemented in January 2001. This paper aims to give a first assessment of model performances for quantitative precipitation forecast (QPF). In essence, the effects of enhanced horizontal grid resolution over Calabria, using a 6km spacing domain nested in a 30km resolution parent grid, is studied. To cope with this problem two integrations sets are discussed using two model resolutions. Integrations are performed daily for six months. ECMWF 12:00UTC forecast cycle is used for initial and dynamic boundary conditions. Performances are evaluated by scores computed from model outputs and raingauge measurements coming from Calabrian regional network

On the performance of a limited area model for quantitative precipitation forecast over Calabria

At Crati Scrl an operational version of RAMS 4.3 (Regional Atmospheric Modeling System), with a son grid over Calabria, was implemented in January 2001. This paper aims to give a first assessment of model performances for quantitative precipitation forecast (QPF). In particular two issues of weather forecast are discussed. First problem refers to effects introduced by enhanced resolution over Calabria, using a 6 km resolution grid nested in a 30 km parent grid. Second issue discusses forecast deterioration with increasing forecast time. To cope with these problems, two sets of integrations are discussed using two different model configurations. Differences between configurations are only due to model resolutions. Integrations are performed daily for six months. Each integration starts at 12 UTC and lasts for 60 h, with 12 h spin-up time. ECMWF 12 UTC analysis and following forecast are used as initial and dynamic boundary conditions. Models performances are evaluated computing scores by comparing model outputs with raingauges data coming from Calabria regional network. Results show better performances of finergrid resolution compared to the coarser one and confirms the usefulness of enhanced resolution over complex terrain. In addition, performances decrease with increasing forecast time with first integration day performing better than second forecast day but differences are not statistically significant at 5% level

The precipitation field over Calabria: Large-scale correlations

In this paper we analyze the variability of the precipitation field over Calabria for the period 1948-1990 and its correlation with large-scale flow. Precipitation data are from “Istituto Mareografico ed Idrografico” database, have a monthly basis and cover the period 1921-1990. It is shown that precipitation is concentrated in the cold semester, from October to April, and that there is a large annual-to-annual variability. After studying correlation between precipitation and North Atlantic Oscillation (NAO), rainfall variability is further discussed by relating the precipitation standardized anomaly index to surface pressure, 500 hPa geopotential height and sea surface temperature. These dataset are derived from NCAR reanalysis project, and cover the 1948-2002 period. Due to temporal coverage of our databases the analysis is limited to 1948-1990. While a weaker correlation with NAO emerges, compared to other areas of the Mediterranean basin, precipitation over Calabria shows an interesting correlation with another dipolar structure located further East. This correlation is mainly related to the strength of Azores anticyclone over the Mediterranean area in the cold season and to the oscillation of Siberian high

The application of LEPS technique for Quantitative Precipitation Forecast (QPF) in Southern Italy

International audienceThis paper reports preliminary results of a Limited area model Ensemble Prediction System (LEPS), based on RAMS, for eight case studies of moderate-intense precipitation over Calabria, the southernmost tip of the Italian peninsula. LEPS aims to transfer the benefits of a probabilistic forecast from global to regional scales in countries where local orographic forcing is a key factor to force convection. To accomplish this task and to limit computational time, in order to implement LEPS operational, we perform a cluster analysis of ECMWF-EPS runs. Starting from the 51 members that forms the ECMWF-EPS we generate five clusters. For each cluster a representative member is selected and used to provide initial and dynamic boundary conditions to RAMS, whose integrations generate LEPS. RAMS runs have 12 km horizontal resolution. Hereafter this ensemble will be referred also as LEPS_12L30. To analyze the impact of enhanced horizontal resolution on quantitative precipitation forecast, LEPS_12L30 forecasts are compared to a lower resolution ensemble, based on RAMS that has 50 km horizontal resolution and 51 members, nested in each ECMWF-EPS member. Hereafter this ensemble will be also referred as LEPS_50L30. LEPS_12L30 and LEPS_50L30 results were compared subjectively for all case studies but, for brevity, results are reported for two "representative" cases only. Subjective analysis is based on ensemble-mean precipitation and probability maps. Moreover, a short summary of objective scores. Maps and scores are evaluated against reports of Calabria regional raingauges network. Results show better LEPS_12L30 performance compared to LEPS_50L30. This is obtained for all case studies selected and strongly suggests the importance of the enhanced horizontal resolution, compared to ensemble population, for Calabria, at least for set-ups and case studies selected in this work