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Observational studies suggest that part of the North Atlantic Oscillation (NAO) variability may be attributed to the spectral ultra-violet (UV) irradiance variations associated to the 11-year solar cycle. The observed maximum surface pressure response in the North Atlantic occurs 2–4 years after solar maximum, and some model studies have identified that atmosphere–ocean feedbacks explain the multi-year lag. Alternatively, medium-to-high energy electron (MEE) precipitation, which peaks in the declining phase of the solar cycle, has been suggested as a potential cause of this lag. We use a coupled (ocean–atmosphere) climate prediction model and a state-of-the-art MEE forcing to explore the respective roles of irradiance and MEE precipitation on the NAO variability. Three decadal ensemble experiments were conducted over solar cycle 23 in an idealized setting. We found a weak ensemble-mean positive NAO response to the irradiance. The simulated signal-to-noise ratio remained very small, indicating the predominance of internal NAO variability. The lack of multi-annual lag in the NAO response was likely due to lagged solar signals imprinted in temperatures below the oceanic mixed-layer re-emerging equatorward of the oceanic frontal zones, which anchor ocean–atmosphere feedbacks. While there is a clear, yet weak, signature from UV irradiance in the atmosphere and upper ocean over the North Atlantic, enhanced MEE precipitation on the other hand does not lead to any systematic changes in the stratospheric circulation, despite its marked chemical signatures. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

It is generally accepted that volcanic eruptions may have a climatic impact involving overall cooling of the troposphere, as the sulfur injected into the stratosphere is transformed into sulfate. However, it is intrinsically difficulty to distinguish this impact because of natural climate variability. In this paper, we look for a relationship between sulfate in the Northern Hemisphere (NH) and European temperature during the last 500 years using two independent data sets: stratospheric sulfate retrieved from ice cores and European seasonally and annually averaged temperature. Relationships between temperature and sulfate are obtained as a function of the season (summer and winter) and location (tropics vs extra‐tropics) one and two years after the sulfate record year. After one year, we always find a negative correlation in the winter for both tropical and extra‐tropical eruptions. A correlation value of ‐0.56 is obtained for the relationship between sulfate and annually averaged temperature anomalies after one year, and a linear regression predicts a cooling of 1 °C for an eruption of 100 Tg of sul‐ fate, an amount similar to that estimated to have been emitted by the Laki eruption in 1783.The variability of the cooling effect after one year is evaluated by introducing a multiplicative error model for sulfate that accounts for sys‐ tematic as well as random errors in retrieved sulfate. To evaluate the impact of sulfate uncertainties on the regression slope, a resampling approach with 104 simulations is applied. Results indicate that when uncertainties in sulfate are introduced, the variability of cooling is in the order of several 10‐3 °C/Tg. Temperature anomaly uncertainties impact slope uncertainty but have little influence on slope variability.

The response of the atmosphere to solar irradiance and geomagnetic activity is analyzed in experiments with the Whole Atmosphere Community Climate Model (WACCM) under idealized forcings. Four experiments are carried out combining high (H) and low (L) solar radiative forcing with high (7) and low (3) geomagnetic activity: H7 (with high radiative forcing and high geomagnetic activity), H3, (high/low), L7 (low/high), and L3 (low/low). The comparison between these experiment is used to assess the effects of solar radiative forcing and geomagnetic activity mainly on the stratosphere. A two-step Monte Carlo-based statistical test, which defines an impact score, is used to assess statistically significant impacts on regional scales, on pressure levels, for a few key model variables, like NOx, ozone, and temperature. Under low solar forcing (L7/L3), a statistically significant relationship between geomagnetic activity and NOx is found in both hemispheres and for all seasons. An equally strong relationship is lacking for ozone and temperature when analyzing these fields on isobaric levels. A statistically significant impact on stratospheric ozone is only seen in austral winter and spring. However, vertical cross sections show statistically significant impact on temperature and ozone mainly in the southern hemisphere (SH) during austral winter and the following spring. Significant and persistent signals in both SH NOx and ozone concentrations are only produced when the effect of high solar forcing is added to high geomagnetic activity (H7). In this case, statistically significant differences are also found for mesospheric temperatures, ozone and NOx. This latter result appears also under low geomagnetic activity as a result of solar forcing alone, suggesting that solar irradiance significantly affects NOx, ozone and stratospheric temperatures and, in some seasons, even tropospheric temperature. In summary, geomagnetic activity primarily affects NOx and ozone concentrations in the SH. Solar maximum conditions can reduce the amount of NOx in the stratosphere because of higher ozone production. Thus, we conclude that correlations between changes in solar irradiance and geomagnetic activity are important with respect to their effects on the atmosphere. In particular, geomagnetic activity can modulate atmospheric ozone concentrations and other associated stratospheric and tropospheric variables under conditions of high solar activity. publishedVersion

We employ JRA-55, a recent second-generation global reanalysis providing data of high-quality in the stratosphere, to examine whether a distinguishable effect of geomagnetic activity on northern hemisphere stratospheric temperatures can be detected. We focus on how the statistical significance of stratospheric temperature differences may be robustly assessed during years with high and low geomagnetic activity. Two problems must be overcome. The first is the temporal autocorrelation of the data, which is addressed with a correction of the t-statistics by means of the estimate of the number of independent values in the series of correlated values. The second is the problem of multiplicity due to strong spatial autocorrelations, which is addressed by means of a false discovery rate (FDR) procedure. We find that the statistical tests fail to formally reject the null hypothesis, i.e. no significant response to geomagnetic activity can be found in the seasonal-mean northern-hemisphere stratospheric temperature record.

Discharge time series of major large-catchment European rivers are known to display significant decadal and interdecadal fluctuations. However, the hydroclimate variability causing such fluctuations remains poorly understood, particularly due to a lack of a spatio-temporal integrated assessment. Here, we demonstrate for the first time that European hydroclimate variability is dominated by a meridional delayed oscillation characterized by a lag of approximately 5 years in interdecadal discharge fluctuations of continental (northern) European rivers with respect to those of Euro-Mediterranean (southern) rivers. We demonstrate a connection of this coherent signal with the large-scale atmospheric circulation over the North Atlantic, and suggest a hitherto unexplored multiannual atmosphere-ocean mechanism in the subpolar North Atlantic at its root.

Surface wind is a variable of great importance in forcing marine waves and circulations, modulating surface fluxes, etc. Surface wind defined on numerical grids is currently used in forecast-analysis, as well as in climatology. Gridded fields, however, suffer for systematic errors associated with the numerical procedures adopted in computing them. In this paper the climatology of surface wind produced by three different numerical models in the European-Mediterranean area is analyzed. The systematic loss of power at the smallest grid-scales appears in the power spectrum of all the different models. Some prototype numerical integrations show that this systematic over-smoothing is due to numerical stabilization operators that represent the main source of the diagnosed error; the error progression in space and time is also analyzed. Key words. Meteorology and atmospheric dynamics (Mesoscale meteorology; Ocean-atmosphere interaction; Climatology)

The time-dependent response of the Hadley circulation to a periodic forcing is explored via a simplified nonlinear axisymmetric model. Thermal forcing towards a given equilibrium potential temperature drives the model atmosphere. The vertical stratification of this temperature is forced to become periodically neutral with a period t0. Simulations performed with values of t0 ranging from 10 to 90 days exhibit stronger circulation compared to the results of a constant thermal forcing experiment. As the period increases, a transition occurs first from a stationary regime, obtained when forcing is constant, to a periodic (and possibly quasi-periodic) regime, and then to an intermittent regime, albeit one with a strong periodic component. The stream-function response to periodic forcing is generally a periodic oscillation, with two main frequencies dominating: one with a period equal or close to the forcing period and another with a period that is half of the forcing period. The former is dominant for values of t0 larger than 30 days, whereas the latter is prevalent for t0 smaller than 30 days. The periodic oscillations obtained in this model may be associated with the periodic oscillations observed in the tropical regions. In this case the periodic charge and discharge of moisture in the tropical atmosphere, with consequent change of stratification, may be linked to those oscillations. In the model, at forcing periods of over 63 days the response of the stream function periodically enters into a quasi-intermittent regime, exhibiting high-frequency chaotic oscillations that are modulated by the slow timescale of forcing. Sensitivity experiments for model parameters and configuration were performed to check whether results obtained are still valid under different conditions. Although for small changes of parameters the results are still valid, when parameters depart from the prescribed ones, we can observe change in the Hadley circulation dynamics.

The impact of the equilibrium temperature distribution, θE, on the Hadley circulation simulated by an axisymmetric model is studied. The θE distributions that drive the model are modulated here by two parameters, n and k, the former controlling the horizontal broadness and the latter controlling the vertical stratification of θE. In the present study, variations in the θE distribution mimic changes in the energy input of the atmospheric system, leaving as almost invariant the Equator–poles θE difference. Both equinoctial and time-dependent Hadley circulations are simulated and the results compared. The results give evidence that concentrated θE distributions enhance the meridional circulation and jet wind speed intensities, even with a lower energy input. The meridional circulation and the subtropical jet stream widths are controlled by the broadness of horizontal θE rather than by the vertical stratification, which is important only when θE distribution is concentrated at the Equator. The jet stream position does not show any dependence with n and k, except when the θE distribution is very wide (n = 3) and, in such a case, the jet is located at the mid-latitudes and the model temperature clamps to forcing θE. Using n = 2 and k = 1, we have the formulation of the potential temperature adopted in the classical literature. A comparison with other works is performed, and our results show that the model running in different configurations (equinoctial, solstitial and time dependent) yields results similar to one another.

In this paper, the sensitivities of the equitable threat score (ETS) and the true skill score (TSS), obtained with a 2 × 2 contingency table, to continuous precipitation forecast errors are investigated. Two idealized error models are adopted to describe the difference between forecasts and perfect observations. The observations consist of a time series generated by a multiplicative cascade model. The forecasts are constructed by adding the modeled errors to the observations. Two examples that are representative of two precipitation regimes are considered. Monte Carlo simulations of the modeled errors are performed to compute the score uncertainties. Monotonic relationships between the precipitation forecast errors and the two skill scores are found. It is shown that the precipitation regime and the event frequency influence these relationships and the score uncertainties. The score uncertainties also depend on the forecast errors. Furthermore, it is shown that a relationship exists between the ETS and TSS when the forecast errors are very large. Results suggest that more information should be provided together with the scores and their uncertainties in order to provide a complete picture of the forecast performance.

Sharing knowledge and experience about NWP verification among forecasting centres, research institutions and environmental agencies in the Alpine area has been one of the main goals of the EU FORALPS project - INTERREG IIIB Alpine Space. In this framework, state-of-the-art verification techniques employed by project partners have been shared and applied to numerical simulations of selected case studies of rainfall events on the north-eastern Alpine area. In this work, a multi-method approach is presented. Simulations of two events with three limited area models (LAMs) are verified with traditional and more innovative techniques, including both traditional eyeball methods, categorical scores and skill scores, along with advanced object-oriented techniques such as the continuous rain area (CRA) analysis. Simulations of satellite observed fields (METEOSAT-7 Water Vapour channel) are also employed, to check qualitatively the impact of initialisation on the model error growth. Most importantly, it is shown how this multiplicity of perspective allows a deeper understanding of the results and facilitates their interpretation, thus suggesting that this multi-method approach should be followed in future works.

This article statistically analyses the location errors of the precipitation patterns forecast by three limited area models, namely the Fifth-Generation NCAR/Penn State Mesoscale Model (MM5), the QUADRICS BOlogna Limited Area Model (QBOLAM) and the Regional Atmospheric Modelling System (RAMS), over the Calabria region (Italy) for the period October 2000–May 2002. Contiguous rain area (CRA) analysis is the diagnostic tool used to assess and quantify the position errors of the precipitation forecasts with respect to the observed precipitation patterns. Observation gridded analyses were obtained by means of the Barnes algorithm on the available rain gauge observations. Moreover, an approach to measure the quality of precipitation forecasts routinely by means of a global indicator called CRA Mean Shift (CMS) that summarizes the CRA verification outcomes is proposed. The CMS index would represent a statistical indicator of model quality in forecasting the correct positions of precipitation patterns. The model's tendency to misplace the forecast precipitation patterns towards a particular direction was tested by using a bootstrap procedure. All models seem to show statistically poor abilities in forecasting the correct precipitation pattern position over the verification domain considered. As far as the tendency towards a particular direction is concerned, only the RAMS model seems to show a systematic horizontal misplacement of precipitation patterns towards a particular direction. Copyright © 2008 Royal Meteorological Society

Many ‘high-impact’ meteorological, marine and hydrological events in the Mediterranean area are characterized by horizontal spatial scales of the order of 10–100 km. Such events are, sometimes, driven by complex dynamical processes involving planetary scale atmospheric flows. Several international programs (ALPEX, POEM, MAP, PYREX, MEDEX) have improved the understanding of some of these processes. However, because of the Mediterranean's geomorphological structure, characterized by mountain chains (e.g. the Alps), semi-enclosed sea basins and small river catchments, many problems remain. It is clear that such problems have to be faced in the context of analysis-prediction systems bridging the gap between global and local scales of motion. These systems should allow for an adequate representation of key dynamical processes at all the relevant scales of motion. The Hydro-Meteorological-Marine System (‘Sistema Idro-Meteo-Mare’, SIMM) is a first step in developing an integrated system, adequately covering all scales of motion from global to local. A short description of the system is presented, highlighting scientific concepts behind design choices. A summary of the results of verification tests is also illustrated, together with a general evaluation of the whole process in planning, developing and running SIMM in order to assist future updates of the system, currently under development. Copyright © 2007 Royal Meteorological Society

A ground-based radar (GR) has to measure rain from close to the radar to large distances from it. Consequently, the scattering volume of the GR changes significantly. As an advantage, the scattering volume of a space-borne radar is of similar size at all locations, thus allowing the compensation of the decreasing spatial resolution of the GR with range (range-adjustment). Adjustment with range is here performed by means of data observed by the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) using a ∼10 dB per decade factor. For instance, about 8 dB are added to the measured reflectivity at 100 km, while 2 dB are subtracted at 10 km from the radar site. Thus, two different radar datasets, the range-adjusted data and the original ones, can be compared with forecast precipitation. In the framework of the EU VOLTAIRE project (Fifth Framework Programme), where observations from rain gauges, GR, TRMM PR and forecast precipitation were available for the island of Cyprus, such a kind of study was performed. The chosen comparison method was a contiguous rain area (CRA) analysis. Three pattern-matching criteria, involving mean square error, mean absolute error and correlation, have been used to match forecast and observed precipitation patterns. In this paper, we show that the results of the comparison in a selected case study are sensitive to the application of a range-adjustment technique. Observational analysis, obtained by merging rain gauge data with the adjusted GR data, seems to give more stable results when changing the pattern-matching criterion, and proposing it as the better field reconstruction in the comparison.

Verification of modeled rainfall with precipitation observed by a rain gauge network has been performed in a case study over the Cyprus Island. Cyprus has a relatively dense rain gauge network. The applied verification method is the Contiguous Rain Area (CRA) analysis. In this work some drawbacks are pointed out when CRA method is applied in such a case study. Impact on CRA results, when considering different dimensions of the compared model domain and different types of indicators (correlation and mean square error) used in the comparison, are discussed. Results indicate that care has to be taken when verification of modeled rainfall is performed over some of islands or hydrological basins.

The impact of the temperature distribution on the Hadley circulation simulated by an axisymmetric model is studied. The temperature distributions that drive the model are modulated here by two parameters, n and k, the former controlling the horizontal broadness and the latter defining change in the vertical lapse rate. In the present study, the changes of the temperature distribution mimic changes of the energy input of the atmospheric system leaving as an invariant the equator-poles difference. Both equinoctial and time-dependent Hadley circulations are simulated and results compared. The results give evidence that concentrated temperature distributions enhance the meridional circulation and jet wind speed intensities even with a lower energy input. The meridional circulation and the subtropical jet stream widths are controlled by the broadness of horizontal temperature rather than the vertical lapse rate k, which is important only when the temperature distribution is concentrated at the equator. The jet stream position does not show any dependence with n and k, except when the temperature distribution is very wide and in such a case the jet is located at the mid-latitude. Using n = 2 and k = 1 we have the formulation of the potential temperature adopted in classical literature. A comparison with other works is performed and our results show that the model running in different configurations (equinoctial, solstitial and time-dependent) yields results similar to one another.

This article investigates the role of sea surface temperature (SST) as well as the effects of evaporation and moisture convergence on the evolution of cyclone Klaus, which occurred on January 23 and 24, 2009. To elucidate the role of sea surface temperature (SST) and air–sea fluxes in the dynamics of the cyclone, ten hydrostatic mesoscale simulations were performed by Bologna Limited Area Model (BOLAM). The first one was a control experiment with European Centre for Medium-Range Weather Forecasts (ECMWF) SST analysis. The nine following simulations are sensitivity experiments where the SST are obtained by adding a constant value by 1 to 9 K to the ECMWF field. Results show that a warmer sea increases the surface latent heat fluxes and the moisture convergence, favoring the development of convection in the storm. Convection is affected immediately by the increased SST. Later on, drop of mean sea level pressure (MSLP) occurs together with increasing of surface winds. The cyclone trajectory is not sensitive to change in SST differently from MSLP and convective precipitation.

This study has been carried out in order to investigate the predictability of a rapidly developing storm over the Mediterranean area, by comparing the behaviour of three different meteorological models. The models chosen are the global, variable mesh, model ARPEGE, which is running operationally at Meteo-France, and two limited area models, namely ALADIN (also developed at Meteo-France) and BOLAM (developed in Italy, mainly at FISBAT). This comparison study has been performed by a cooperation among the French Meteorological Service and the National Research Council of Italy (CNR) FISBAT and IFA institutes. In this paper we present the results obtained by integrating the models on a short time-range, corresponding to the developing stage of a strong cyclone that moved rather quickly to the North from Northern Africa, associated with perturbed weather and distinct mesoscale features. In particular, this cyclone was characterized by a low-level warm core, associated with very strong winds and precipitation. All the three models were successful in describing the main characteristics of this cyclogenesis event, in particular the rapid evolution of the low level vortex. However, important differences emerged in “forecasting” the value of the pressure minimum, its position and time evolution, and the associated distribution of precipitation. When the large scales are treated by using analyzed rather than forecast lateral boundary conditions, the two LAMs perform better than the global model in simulating the low evolution but the global high resolution model better describes the general features of the cyclogenesis. Differences in model performance are found especially in the distribution of precipitation forecasts, suggesting two main conclusions: insufficient descriptions of mountains can change the location of the precipitation release, the precipitation scheme of the ALADIN model is sensitive to the lateral boundary conditions. The overestimation of the cyclone in BOLAM seems due to an oversensitivity to the latent heat release that intensifies the circulation in the cyclone core.

A three-dimensional cloud model derived from the Klemp-Wilhelmson model has been used to perform simulations of a right-moving supercell with the purpose of testing the effects of terminal velocity of precipitation on the storm dynamics. The model has no ice variables and computes a fall velocity for condensed water. We simulate one of the effects of ice presence, without including phase transition, by reducing the fall velocity of the precipitation in the coldest cloud layers. The reduction of precipitation terminal velocity is shown to have a strong influence on supercell dynamics and to be responsible for nearly all the improvements in the simulation of supercells that are obtained with full ice microphysics. This includes the transition to tornadic phase, which is sharper than in the case of a pure rain supercell. The vertical component of vorticity is seen to increase at all levels, as observed in real storms, instead of just at the surface as is common in simulations with no ice phase. Our results indicate the primary importance of terminal fall speed among the effects due to the presence of ice.

This contribution deals with the description of the Italian Radio Occultation experiment on board the Indian OCEANSAT-2 Mission. Details of the Italian Radio Occultation Ground Segment and results obtained within the validation activity will be discussed. Atmospheric profiles (in terms of refractivity, temperature, and electron density) obtained processing ROSA raw observations will be presented.

At the beginning of 2008 the Indian satellite OCEANSAT-2 will be launched. This satellite will carry on-board two payloads for ocean studies and the Italian Radio Occultation GPS receiver (ROSA) devoted to atmospheric studies. In the framework of thismission, the ROSA instrument will only be able to observe rising occultations collecting data both in Open-Loop and in Close-Loop modes. These data will be downloaded both to the Indian and the Italian receiving stations where they will be processed by the ROSA ground segment, completely developed by Italian universities and research centres. In particular, this ground segment will be implemented at a first level in an integrated computing infrastructure installed in Matera and mirrored at Hyderbad in India and, at a second level, on a distributed software and hardware infrastructure. This second infrastructure will perform the rapid and precise Orbit Determination and Prediction, the unambiguous bending and impact parameters profiles extraction, the ionospheric correction and the stratospheric initialization, the refractivity, pressure, temperature and humidity profile retrieval, the value added services for meteorology, climate and space weather applications. This will identify a prototype of distributed and Multimission Ground Processing Centre distributed through the various research centres and universities involved, connected through a Web-based GRID computing infrastructure. After a description of these two different implementations of the ROSA Ground Segment, this contribution will focus on the scientific activities carried on by the Italian institution involved in the project: - Physics Dept. of Universita' di ROMA: development of climatological indexes. These activity is based on the utilization of RO data for climatic study. The main work will be focused on tropopause temperature and height determination, large scale water vapour analysis, geopotential field retrieving for dynamic indexes, evaluation and comparisonof RO data with LIDAR profiles in stratosphere. ... ... ...

Multiscale methods, such as the power spectrum, are suitable diagnostic tools for studying the second order statistics of a gridded field. For instance, in the case of Numerical Weather Prediction models, a drop in the power spectrum for a given scale indicates the inability of the model to reproduce the variance of the phenomenon below the correspondent spatial scale. Hence, these statistics provide an insight into the real resolution of a gridded field and must be accurately known for interpolation and downscaling purposes. In this work, belonging to the EU INTERREG IIIB Alpine Space FORALPS project, the power spectra of the precipitation fields for two intense rain events, which occurred over the north-eastern alpine region, have been studied in detail. A drop in the power spectrum at the shortest scales (about 30 km) has been found, as well as a strong matching between the precipitation spectrum and the spectrum of the orography. Furthermore, it has also been shown how the spectra help understand the behavior of the skill scores traditionally used in Quantitative Precipitation Forecast verification, as these are sensitive to the amount of small scale detail present in the fields.

How strong is the resemblance between two states of the atmosphere leading to the same outcome? In the following pages this question was addressed by studying the resemblance of the surface pressure fields, obtained by NCEP reanalyses, corresponding to “intense” precipitation events over 5 Italian climatic areas. Such “intense” precipitation events were selected by means of 45 daily precipitation records covering the period from 1951 to 2000.

This paper presents a study performed within the framework of the European Union’s (EU) VOLTAIRE project (Fifth Framework Programme). Among other tasks, the project aimed at the integration of the Tropical Rainfall Measuring Mission (TRMM) data with ground-based observations and at the comparison between water fields (precipitation and total column water vapor) as estimated by multisensor observations and predicted by NWP models. In particular, the VOLTAIRE project had as one of its main objectives the goal of assessing the application of satellite-borne instrument measures to model verification. The island of Cyprus was chosen as the main “test bed,” because it is one of the few European territories covered by the passage of the TRMM Precipitation Radar (PR) and it has a dense rain gauge network and an operational weather radar. TRMM PR provides, until now, the most reliable space-borne spatial high-resolution precipitation measurements. Attention is focused on the attempt to define a methodology, using state-of-the-art diagnostic methods, for a comprehensive evaluation of water fields as forecast by a limited area model (LAM). An event that occurred on 5 March 2003, associated with a slow cyclone moving eastward over the Mediterranean Sea, is presented as a case study. The atmospheric water fields were forecast over the eastern Mediterranean Sea using the Bologna Limited Area Model (BOLAM). Data from the Cyprus ground-based radar, the Cyprus rain gauge network, the Special Sensor Microwave Imager (SSM/I), and the TRMM PR were used in the comparison. Ground-based radar and rain gauge data were merged together in order to obtain a better representation of the rainfall event over the island. TRMM PR measurements were employed to range-adjust the ground-based radar data using a linear regression algorithm. The observed total column water vapor has been employed to assess the forecast quality of large-scale atmospheric patterns; such an assessment has been performed by means of the Hoffman diagnostic method applied to the entire total column water vapor field. Subsequently, in order to quantify the spatial forecast error at the finer BOLAM scale (0.09°), the object-oriented contiguous rain area (CRA) analysis was chosen as a comparison method for precipitation. An assessment of the main difficulties in employing CRA in an operational framework, especially over such a small verification domain, is also discussed in the paper.

On 16–17 November 2000, a relatively intense precipitation event on the north-western Italy was heavily underestimated, mainly due to shifting error, by three operational 10-km limited area models (LAMs) which differ about basic equations, domain size, and parameterisation schemes. The scope of the work is to investigate possible common error-sources independent from the single model, in particular the effect of initialisation. Thus, the complex evolution over the western Mediterranean Sea of the cyclone responsible for the event was investigated. Several objective and subjective verification techniques have been employed to check one of the LAMs' forecast against the available observations (precipitation from rain gauge and retrieved from ground-based radar, and satellite-retrieved atmospheric humidity patterns). Despite a clear statement is not achieved, results indicate that high sensitivity to the initial conditions, and the inadequacy of the observational network on the southern Mediterranean area, can play a major role in producing the forecast shifting error on the target area.

International audience; In the framework of the European VOLTAIRE project (Fifth Framework Programme), simulations of relatively heavy precipitation events, which occurred over the island of Cyprus, by means of numerical atmospheric models were performed. One of the aims of the project was indeed the comparison of modelled rainfall fields with multi-sensor observations. Thus, for the 5 March 2003 event, the 24-h accumulated precipitation BOlogna Limited Area Model (BOLAM) forecast was compared with the available observations reconstructed from ground-based radar data and estimated by rain gauge data. Since radar data may be affected by errors depending on the distance from the radar, these data could be range-adjusted by using other sensors. In this case, the Precipitation Radar aboard the Tropical Rainfall Measuring Mission (TRMM) satellite was used to adjust the ground-based radar data with a two-parameter scheme. Thus, in this work, two observational fields were employed: the rain gauge gridded analysis and the observational analysis obtained by merging the range-adjusted radar and rain gauge fields. In order to verify the modelled precipitation, both non-parametric skill scores and the contiguous rain area (CRA) analysis were applied. Skill score results show some differences when using the two observational fields. CRA results are instead quite in agreement, showing that in general a 0.27° eastward shift optimizes the forecast with respect to the two observational analyses. This result is also supported by a subjective inspection of the shifted forecast field, whose gross features agree with the analysis pattern more than the non-shifted forecast one. However, some open questions, especially regarding the effect of other range adjustment techniques, remain open and need to be addressed in future works.

The intense precipitation event that occurred between 3 and 6 November 1994 and caused extensive flooding over Piedmont in northwestern Italy is simulated and tested with respect to various physical aspects, using a meteorological mesoscale model (BOLAM). The period when the most intense rain occurred, mainly covering the second half of 4 and all of 5 November, is examined. A control experiment, starting at 1200 UTC 4 November, simulates the two observed precipitation peaks and captures the magnitude and timing of the most intense precipitation well even at relatively low horizontal resolution (about 30 km). The European Centre for Medium-Range Weather Forecasts analyses are used to provide the initial and boundary conditions. Model output diagnostics and comparison with observations indicate that most of the precipitation is associated with a prefrontal low-level jet, ahead of the cold front, impinging upon the orography of the region (Alps and Apennines). The model simulates a multiple rainband...

A previsional system for the forecast of the state of the Mediterranean Sea and of surges in the northern Adriatic Sea has been designed and tested. The system consists of a limited area model (the Bologna Limited Area Model, BOLAM), which computes high-resolution pressure and surface wind fields, to serve as the input of a wave model (WAM) and of a shallow water model (two-dimensional Princeton Ocean Model, POM-2D). Results of two case studies are presented, chosen to test the ability of the system to predict extreme surge events originating from cyclonic circulation over the Mediterranean basin. The two case studies cover the periods 4–9 October 1998 and 11–22 November 1996. Comparison with observed buoy data shows that the results of the WAM simulations forced by the wind fields obtained from the high-resolution BOLAM model are significantly better than those obtained using a lower-resolution forcing from the ECMWF analyses. Two domains corresponding to the entire Mediterranean basin and to th...