Multisensor analysis of convection in Mediterranean cyclones

.A recent climatological study (Trigo et al., 1999) shown that the cyclonic activity is a key feature of the meteorology of the Mediterranean basin during the whole year. In particular, during warm months, short-living cyclones (averaged lifetime about 30 hours) rise from well known birthplaces (Gulf of Genoa, Gibraltar area, Atlas Mountains are the most effective) and affect the weather in the Mediterranean area. Following a different approach Porcú et al. (1997) shown that very often such cyclones force convective initialisation and development. Moreover those episodes are responsible for the most severe rainfall events sometime related with flood/flash flood occurrence in coastal and continental areas. The combination of long- lasting, moderate precipitation with heavy showers is the more common mechanism originating such floods. The cloud systems related to the cyclonic structure often develop over the sea: the scarcity of conventional observation available in the Mediterranean basin makes satellites peculiar points of view for a detailed study of these events. A complete analysis will include the use of ECMWF fields to assess the larger scale setting: in particular we'll consider the presence and intensity of Potential Vorticity Anomalies (PVAs) related to the cyclonic depression. PVAs are suspected to be precursor of heavy rainfall episodes (Massacand et al., 1999) and are powerful tools in classify cyclonic systems (Georgev, 1999). A further approach will be developed will include combined SSM/I-Meteosat water vapour retrieval over cloud-free areas, in order to evaluate the potential of convective initiation. In this work we present preliminary results of a multi-sensor, multi-frequency analysis of convective patterns in cyclonic structure. We modified a cloud classification algorithm originally developed for visible-infrared (VIS-IR) data (Porcù and Levizzani, 1992) to include also microwave radiances, to increase the informative content of the classification. In particular the SSM/I brightness temperature at 85 GHz is used together with the equivalent black body temperature as measured by the Meteosat infrared channel. The results show potential in understanding of the convective patterns, especially if embedded in cyclonic cloud bands, as it is common at mid-latitude

High-impact floods and flash floods in mediterranean countries: the FLASH preliminary database

This paper contains a preliminary analysis of flood risk in Mediterranean countries, conducted within the framework of the FLASH European Project. All flood events recorded between 1990 and 2006 in the Mediterranean region have been included in the study. Results of previous international projects (STORM, SPHERE, AMPHORE, RINAMED and MEDEX), as well as information provided by FLASH Project partners and data included in scientific papers were the main source used in building this database. All the above information had been dispersed in various places, and an attempt was made here to create, for the first time, a verified and complete single database for the entire Mediterranean region. The work analyses the spatial and temporal distribution of flood events, as well as their social impact, with special attention to certain case studies that have been analysed in detail

MEFFE, satellite and combined satellite-radar techniques in meteorological forecasting for flood events; research activities and results.

The risk management process implies a sequence of: 1) a long term meteorological forecasting (up to 7-10 days, done by Global Circulation Models); 2) a short term forecasting (up to 72 hours, done by Limited Area Models, LAM); 3) a very short term forecasting by observational tools (satellites and radar). A skilled rainfall rate forecast to minimize loss of life and economic damage is therefore important. The MEFFE project was concerted to produce improvements in rainfall intensity estimates for mitigating the risk of flood events using nowcasting techniques (meteorological satellite sensors, combined satellite-radar data and numerical models). The main goal was achieved by: 1) better knowledge of meteorological systems generating different flood events; 2) coupling satellite data, radar data and numerical Limited Area Models; 3) improving MW and VIS-IR algorithms for precipitation retrieval; 4) improving weather numerical models (LAM and Cloud Mesoscale Models) that combine surface and upper air measurements, and radar-satellite data; 5) defining the characteristics of Nowcasting procedures for rainfall rate intensity. The following points were considered: i) climatology of floods in Europe; ii) Rainfall estimates from VIS and IR satellites; iii) Microwave Radiometry; iv) Precipitating Cloud Models and Retrieval Algorithms; v) Short range weather forecasting by Limited Area Model; vi) The individual radar and networks of radars in nowcasting

High-impact floods and flash floods in mediterranean countries: the FLASH preliminary database

This paper contains a preliminary analysis of flood risk in Mediterranean countries, conducted within the framework of the FLASH European Project. All flood events recorded between 1990 and 2006 in the Mediterranean region have been included in the study. Results of previous international projects (STORM, SPHERE, AMPHORE, RINAMED and MEDEX), as well as information provided by FLASH Project partners and data included in scientific papers were the main source used in building this database. All the above information had been dispersed in various places, and an attempt was made here to create, for the first time, a verified and complete single database for the entire Mediterranean region. The work analyses the spatial and temporal distribution of flood events, as well as their social impact, with special attention to certain case studies that have been analysed in detail

Cloud cover analysis associated to cut-off low-pressure systems over Europe using Meteosat Imagery

This paper reports a cloud cover analysis of cut-off low pressure systems (COL) using a pattern recognition method applied to IR and VIS bispectral histograms. 35 COL occurrences were studied over five years (1994-1998). Five cloud types were identified in COLs, of which high clouds (HCC) and deep convective clouds (DCC) were found to be the most relevant to characterize COL systems, though not the most numerous. Cloud cover in a COL is highly dependent on its stage of development, but a higher percentage of cloud cover is always present in the frontal zone, attributable due to higher amounts of high and deep convective clouds. These general characteristics are most marked during the first stage (when the amplitude of the geopotencial wave increases) and second stage (characterized by the development of a cold upper level low), closed cyclonic circulation minimizing differences between rearward and frontal zones during the third stage. The probability of heavy rains during this stage decreases considerably. The centres of mass of high and deep convective clouds move towards the COL-axis centre during COL evolution