Federico Porcù

Chemical characterization of cloud episodes at a ridge site in Tuscan Appennines, Italy

Cloudwater samples were collected from November 1992 to March 1995 in Vallombrosa, a mountain site of the Tuscan Apennines (central Italy). Chemical analyses show that all examined inorganic ions contributed significantly to the total ionic content (TIC). The ratio SO42−/NO4− ranged from 0.92 to 3.46 and was >1 for 86% of samples. There is a wide range in the chemical composition of the cloudwater. The total ionic content ranged from 640 to 7476 μeq l−1 and pH from 3.17 to 6.22. The liquid water content (LWC) ranged from 0.06 to 0.94 g m−3 and electrical conductivity from 47 to 485 μΩ−1. The total ionic content decreases while the liquid water content increases. Also analyzed were soluble trace metals (Fe, Pb, Cu, Mn, Cd, Al), synthetic anionic surfactants and the methanesulphonic acid. Chemical analyses evidenced in some cases a high concentration of organic matter. The meteorological analysis for a few samples of individual passages was carried out for the possibility of establishing a correspondence between meteorological events and chemical composition. The sources (marine, crustal and anthropogenic) of chemical components were deduced.

Cloud systems leading to flood events in Europe: an overview and classification

Over recent years most European countries have experienced destructive precipitation events, many of which have generated floods resulting in the loss of lives and economic damage. Rather surprisingly, Europe has no common database for flood events, which continue to be monitored by different national and/or local authorities, with different criteria. In the light of this situation, the main aim of the present work is to propose a classification scheme for a European-level flood database, in which severe flood episodes are related to meteorological conditions and mesoscale settings. The meteorological systems relating to the most severe events (22 events) over a five-year period (1992–1996) were analysed using Meteosat imagery and conventional meteorological data. Most of the observed events were related to extra tropical cyclone development. The results are discussed in terms of conceptual models currently used for extra tropical cyclones: the structure and dynamics of Atlantic cyclones can very often be interpreted in terms of well- known conceptual models, while characteristics of Mediterranean systems are not fully rendered by current descriptions. Our study underpins the need to improve the knowledge of Mediterranean systems, possibly introducing new conceptual models and/or refining the current ones. Copyright

Rainfall estimation by combining radar and infrared satellite data for nowcasting purposes

The aim is to evaluate the use of infrared satellite precipitation estimates for nowcasting purposes in the context of a real-time flood-warning scheme. A radar-based calibration technique is described which is applied to the Negri–Adler–Wetzel scheme. This procedure employs radar data over a defined calibration area to estimate, for each satellite image, actual rain-rates to be used in the Negri–Adler–Wetzel scheme. Calibrated satellite estimates obtained from this procedure can be used to diagnose areas of precipitation beyond radar range, thus allowing an extension of precipitation nowcasting lead time. Calibrated estimates are compared with radar rainfall measurements and results are discussed for various sizes of integration area. Calibration reduces consistently both bias and variance of the error of the original Negri–Adler–Wetzel estimates, even for integration areas as small as 2000 km2. This indicates the capabilities of the new technique for nowcasting purposes over mediumsized river basins. Copyright

Use of the GPM Constellation for Monitoring Heavy Precipitation Events Over the Mediterranean Region

Precipitation retrievals exploiting the available passive microwave (PMW) observations by cross-track and conically scanning satellite-borne radiometers in the Global Precipitation Measurement (GPM) mission era are used to monitor and characterize heavy precipitation events that occurred during the Fall 2014 in Italy. Different physically based PMW precipitation retrieval algorithms are used: the Cloud Dynamics and Radiation Database (CDRD) and Passive microwave Neural network Precipitation Retrieval (PNPR), used operationally in the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Satellite Application Facility on support to Operational Hydrology and Water Management (H-SAF), and the National Aeronautics and Space Administration (NASA) Goddard PROFiling algorithm (GPROF). Results show that PMW precipitation retrievals from the GPM constellation of radiometers provide a reliable and quantitative description of the precipitation (instantaneous and on the daily scale) throughout the evolution of the precipitation systems in the Mediterranean region. The comparable relative errors among gauges, radar, and combination of radiometer overpasses legitimize the use of PMW estimates as a valuable and independent tool for monitoring precipitation. The pixel-based comparison with dual-polarization radars and raingauges indicates the ability of the different sensors to identify different precipitation areas and regimes (0.60 <; POD <; 0.76; 0.28 <; FAR <; 0.45; 0.42 <; ETS <; 0.59;-1.6 mm/h <; ME <; 1.1 mm/h}, with values depending on the radiometer and on the precipitation product). This is particularly relevant in the presence of complex orography in proximity of coastal areas, as for the analyzed cases. The different characteristics of the radiometers (i.e., viewing geometry, spatial resolution, channel assortment) and of retrieval techniques, as well as the limitations of the ground-based reference datasets, are taken into consideration in the evaluation of the accuracy and consistency of the retrievals.

Identification and Analysis of Collisional Breakup in Natural Rain

AbstractNumerous laboratory and numerical studies have been dedicated to understanding collisional breakup as one of the most important processes in rain formation. The present study aims to identify when, in natural rain, collisional breakup is dominant and thus able to modify the shape of the raindrop size distribution (DSD), up to the equilibrium DSD. To this end, an automated objective algorithm has been developed and applied to a total of more than 6000 two-minute-averaged DSDs. Since breakup is mostly observed in heavy precipitation, the method was applied to the DSDs where rain rate was above 5 mm h−1. The selected breakup DSDs had good agreement with those predicted to be the equilibrium DSD by different theoretical models. The equilibrium DSD was found in a variable fraction of the total samples (0%–7%), confirming that the onset of equilibrium is a rare event in natural rain. The occurrence of a DSD in which breakup is dominant and modifies the DSD but the equilibrium DSD is not reached is highe...

Validation of GPM Dual-Frequency Precipitation Radar (DPR) Rainfall Products over Italy

AbstractThe Ka–Ku Dual-Frequency Precipitation Radar (DPR) and the Microwave Imager on board the Global Precipitation Measurement (GPM) mission core satellite have been collecting data for more tha...

A Field Study of Footprint-Scale Variability of Raindrop Size Distribution

AbstractA network of seven two-dimensional video disdrometers (2DVD), which were operated during the Midlatitude Continental Convective Clouds Experiment (MC3E) in northern Oklahoma, are employed to investigate the spatial variability of raindrop size distribution (DSD) within the footprint of the dual-frequency precipitation radar (DPR) on board the National Aeronautics and Space Administration’s Global Precipitation Measurement (GPM) mission core satellite. One-minute 2DVD DSD observations were interpolated uniformly to 13 points distributed within a nearly circular DPR footprint through an inverse distance weighting method. The presence of deep continental showers was a unique feature of the dataset resulting in a higher mean rain rate R with respect to previous studies. As a measure of spatial variability for the interpolated data, a three-parameter exponential function was applied to paired correlations of three parameters of normalized gamma DSD, R, reflectivity, and attenuation at Ka- and Ku-band f...