Rossella Ferretti

Mechanisms of Intense Alpine Rainfall

Abstract Numerical studies by the authors and others of the 1994 Piedmont flood show that the orographically modified flow was a critical element for the production of extraordinary rainfall. To uncover the precise mechanism of orographic rainfall occurring in full-physics MM5 simulations of the 1994 Piedmont flood, the authors carried out simulations with the same real-data initial and boundary conditions, but with the real orography replaced by an idealized one. With excellent agreement between real and idealized orography on the rainfall rate versus time in the Piedmont area, analysis of the idealized-orography simulation provides a clear picture of the models mechanism of orographically induced rainfall. As noted in previous studies of the 1994 Piedmont case, a moist saturated airflow has a reduced effective static stability and tends to flow over the mountains, while an unsaturated airstream is stable and tries to flow around (toward the left in the Northern Hemisphere). In the 1994 Piedmont case, t...

HyMeX-SOP1: The Field Campaign Dedicated to Heavy Precipitation and Flash Flooding in the Northwestern Mediterranean

The Mediterranean region is frequently affected by heavy precipitation events associated with flash floods, landslides, and mudslides that cause hundreds of millions of euros in damages per year and often, casualties. A major field campaign was devoted to heavy precipitation and flash floods from 5 September to 6 November 2012 within the framework of the 10-year international HyMeX (Hydrological cycle in the Mediterranean Experiment) dedicated to the hydrological cycle and related high-impact events. The 2- month field campaign took place over the Northwestern Mediterranean Sea and its surrounding coastal regions in France, Italy, and Spain. The observation strategy of the field experiment was devised to improve our knowledge on the following key components leading to heavy precipitation and flash flooding in the region: i) the marine atmospheric flows that transport moist and conditionally unstable air towards the coasts; ii) the Mediterranean Sea acting as a moisture and energy source; iii) the dynamics and microphysics of the convective systems producing heavy precipitation; iv) the hydrological processes during flash floods. This article provides the rationale for developing this first HyMeX field experiment and an overview of its design and execution. Highlights of some Intense Observation Periods illustrate the potential of the unique datasets collected for process understanding, model improvement and data assimilation.

Multiparameter Raman Lidar Measurements for the Characterization of a Dry Stratospheric Intrusion Event

Abstract The University of Basilicata Raman lidar system (BASIL) is operational in Potenza, Italy, and it is capable of performing high-resolution and accurate measurements of atmospheric temperature and water vapor based on the application of the rotational and vibrational Raman lidar techniques in the ultraviolet region. BASIL was recently involved in the 2005 International Lindenberg campaign for Assessment of Humidity and Cloud Profiling Systems and Its Impact on High-Resolution Modeling (LAUNCH 2005) experiment held from 12 September to 31 October 2005. A thorough description of the technical characteristics, measurement capabilities, and performances of BASIL is given in this paper. Measurements were continuously run between 1 and 3 October 2005, covering a dry stratospheric intrusion episode associated with a tropopause folding event. The measurements in this paper represent the first simultaneous Raman lidar measurements of atmospheric temperature, water vapor mixing ratio, and thus relative humid...

Analyses of the Precipitation Pattern on the Alpine Region Using Different Cumulus Convection Parameterizations

Abstract The analysis of several precipitation events occurring during June 1990 in the Alpine region is performed using the Pennsylvania State University–National Center for Atmospheric Research Fifth-Generation Mesoscale Model, version 1. A high-resolution dataset provided by Monitoring Precipitation Activity in the Padana Region observational campaign (June 1990) is used to verify the model forecast. Comparisons between model simulations, using different cumulus convective schemes associated with either an explicit computation of cloud water and rain (EXP) or a nonconvective scheme (NEXP), have been performed. The comparisons of EXP versus NEXP give indications of the ability of a cumulus scheme to handle nonconvective precipitation. On the other hand, comparing the schemes allows for evaluation of the ability to reproduce total and convective precipitation. The results show that the amount and the areal extent of the total precipitation are well reproduced if a cumulus scheme is associated with EXP; t...

A model‐aided investigation of winter thermally driven circulation on the Italian Tyrrhenian coast: A case study

[1] Data collected during a campaign carried out in and around Rome in February 1996 using sodars, tethered balloon, and surface data suggest the development of a winter sea breeze that could not be detected by conventional data and analyses. A model-aided study is performed to verify the development of thermally driven local circulation and to prove the onset of a winter sea breeze regime, propagating inland and interacting with the urban heat island (UHI). The area of interest for the study is the central part of Italy (latitude 41– 43N, longitude 10–16E). The MM5 mesoscale model was used at high resolution: three nested domains with up to 3 km of grid resolution were used in the area where the sea breeze was observed. To highlight the effect of the sea breeze, a simulation with a thick cloud layer in the innermost domain was performed. By removing the cloud layer the diurnal evolutionofthehorizontaltemperature gradientledtothedevelopmentoftheseabreezeand the UHI circulation, in agreement with the data. Sensitivity tests were carried out to evaluate the effect of land use resolution and of satellite-retrieved/climatological sea surface temperatureonthesimulationresults.Doppler-sodardatarecordedatthreesites,tethersonde profiles, and surface data were used to verify the results. As expected, using high-resolution land use and the daily sea surface temperature retrieved by satellite observations led to improvementsinthelocalcirculationproducedbythemodel.However,themodelfallsshort in reproducing some of the sea breeze characteristics. It finds that the sea breeze starts too early and lasts for a shorter time than the observed one does, and the wind direction shows a too strong northerly component. Also, it slightly underestimates the daily temperature pattern. The interaction of the urban heat islands of Rome and Ostia with the sea breeze flow is analyzed to explain the causes of these discrepancies. INDEX TERMS: 3307 Meteorology and Atmospheric Dynamics: Boundary layer processes; 3322 Meteorology and Atmospheric Dynamics: Land/ atmosphere interactions; 3329 Meteorology and Atmospheric Dynamics: Mesoscale meteorology; KEYWORDS: sea breeze, modeling, urban heat island Citation: Ferretti, R., G. Mastrantonio, S. Argentini, R. Santoleri, and A. Viola, A model-aided investigation of winter thermally driven circulation on the Italian Tyrrhenian coast: A case study, J. Geophys. Res., 108(D24), 4777, doi:10.1029/2003JD003424, 2003.

InSAR Water Vapor Data Assimilation into Mesoscale Model MM5: Technique and Pilot Study

In this study, a technique developed to retrieve integrated water vapor from interferometric synthetic aperture radar (InSAR) data is described, and a three-dimensional variational assimilation experiment of the retrieved precipitable water vapor into the mesoscale weather prediction model MM5 is carried out. The InSAR measurements were available in the framework of the European Space Agency (ESA) project for the “Mitigation of electromagnetic transmission errors induced by atmospheric water vapor effects” (METAWAVE), whose goal was to analyze and possibly predict the phase delay induced by atmospheric water vapor on the spaceborne radar signal. The impact of the assimilation on the model forecast is investigated in terms of temperature, water vapor, wind, and precipitation forecast. Changes in the modeled dynamics and an impact on the precipitation forecast are found. A positive effect on the forecast of the precipitation is found for structures at the model grid scale or larger (1 km), whereas a negative effect is found on convective cells at the subgrid scale that develops within 1 h time intervals. The computation of statistical indices shows that the InSAR assimilation improves the forecast of weak to moderate precipitation (<;15 mm/3 h).

High-Resolution Weather Forecasting over Complex Orography: Sensitivity to the Assimilation of Conventional Data

Abstract Weather forecasting for regions with complex orography, as the Alps, presents several challenges and the task becomes even more difficult when high resolution is required. Moreover, for the Alpine region, some of the problems are due to the lack of observations especially over the Mediterranean Sea. A possibility for improving forecasts is to reuse assimilation techniques locally. In this paper, results obtained through data assimilation are presented: objective analysis (OA) of observations and data analyses from the European Centre for Medium-Range Weather Forecasts (ECMWF) are used together to generate a new set of mesoscale initial (ICs) and boundary conditions (BCs). In particular, OA is applied to surface data and radiosoundings using two methods: Cressman and multiquadric. The sensitivity of the weather forecast to the number of upper-air stations assimilated by OA is tested using data from the Piedmont flood (4–6 November 1994). At first, a comparison is made between ICs, obtained through...

Atmospheric water vapor effects on spaceborne interferometric SAR imaging: Comparison with ground-based measurements and meteorological model simulations at different scales

Spaceborne Interferometric Synthetic Aperture Radar (InSAR) is a well established technique useful in many land applications, such as monitoring tectonic movements and landslides or extracting digital elevation models. One of its major limitations is the atmospheric variability, and in particular the high water vapor spatial and temporal variability, which introduces an unknown delay in the signal propagation. On the other hand, these effects might be exploited, so as InSAR could become a tool for highresolution water vapor mapping. This paper describes the approach and some preliminary results achieved in the framework of an ESA funded project devoted to the mitigation of the water vapor effects in InSAR applications. Although very preliminary, the acquired experimental data and their comparison give a first idea of what can be done to gather valuable information on water vapor, which play a fundamental role in weather prediction and radio propagation studies.

Synergic use of EO, NWP and ground based measurements for the mitigation of vapour artefacts in SAR interferometry

Spaceborne Interferometric Synthetic Aperture Radar (InSAR) is a well established technique useful in many land applications, such as tectonic movements, landslide monitoring and digital elevation model extraction. One of its major limitation is the atmospheric effect, and in particular the high water vapour spatial and temporal variability which introduces an unknown delay in the signal propagation. This paper describes the general approach and some results achieved in the framework of an ESA funded project devoted to the mapping of the water vapour with the aim to mitigate its effect in InSAR applications. Ground based (microwave radiometers, radiosoundings, GPS) and spaceborne observations (AMSR-E, MERIS, MODIS) of columnar water vapour were compared with Numerical Weather Prediction model runs in Central Italy during a 15-day experiment. A dense network of GPS receivers was deployed close to Como, in Northern Italy, to complement the operational network in order to derive Zenith Total Delay as well as Slant Delay which can support InSAR processing. A comparison with Atmospheric Phase Screens (APS) derived from a sequence of Envisat multi pass interferometric acquisitions processed using the Permanent Scatters technique on the two test sites has been also performed. The acquired experimental data and their comparison give a valuable idea of what can be done to gather information on water vapour, which, besides InSAR applications, plays a fundamental role in weather prediction and radio propagation studies. The work has been carried out in the framework of an ESA funded project, named “Mitigation of Electromagnetic Transmission errors induced by Atmospheric Water Vapour Effects” (METAWAVE). This paper presents the general approach an the various methodologies exploited in the project, together with the overall intercomparison of the results. In deep details on the comparison with the InSAR APS maps derived by the PS technique, as well as on GPS receiver processing and water vapour tomography are reported in two companion papers.

Dynamical and radiative response to the massive injection of aerosol from Kuwait oil burning fires

The effects of the injection of large amount of soot comparable to that produced in the burning of oil wells in Kuwait were studied using a 2-D mesoscale model. During the three day numerical simulation the ground-atmosphere system appears to be strongly perturbed. A surface cooling is produced in the first two days above and downwind of the sources. The cooling, between −10 C over the desert and −0.5 C over the sea is dependent on the surface characteristics. The temperature decrease at the ground results in a stratified troposphere which inhibits convection and perturbs the normal diurnal variability of the boundary layer while the upper levels are driven by the radiative warming of the aerosol layer. In this region after few hours the simulation produces a warming of 0.8 C reaching a maximum of 6 C is after 60 hours. During the last 2 days of simulation the long wave radiation emitted by the low altitude atmospheric layers contribute to mitigate the surface cooling. A detailed discussion of the radiative and the dynamical interactions is given and it is shown that beside the specific interest in the short term effects these results may be useful to parameterize the smoke source for a GCM simulation.