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Copyright of Il Nuovo Cimento: B is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A number of forecast experiments were performed in order to assess the capability of reproducing, by means of a limited-area numerical model, the highly structured mesoscale circulations occurring in the Po Valley of Northern Italy during a north-westerly cold front passage across the Alpine chain, with particular attention to the modelling of the effects of organized convection. The case-study occurred during summer 1987 and the model used throughout was the 1989 version of the UB/NMC Limited Area Model (University of Belgrade, National Meteorological Centre of Washington). The model was integrated both with eta, η, and sigma, ϑ, as vertical coordinates and ECMWF initialized analyses were always used as initial conditions. ECMWF initialized analysis or operational forecast fields were also used for updating in time the lateral boundary conditions. Experiments show qualitative and quantitative agreement with observations, both in upper-air geopotential height fields, in MSLP and in cumulated precipitation. Several modelling issues were also investigated, e.g. sensitivity of the results to horizontal and vertical model resolution and to the influence of the lateral boundaries poitioning, finding large effects of the latter on quantitative precipitation fields. Difficulties in modelling very localized mesoscale phenomena, e.g. organized convective thunderstorms in the Po Valley and Alpine North Foehn in the Milan area, were generally encounted. [ABSTRACT FROM AUTHOR]

Copyright of Meteorology & Atmospheric Physics is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We outline here the logical flow of papers that attack the problem of estimating the wave conditions in front of and at the Venetian littoral. We start from the determination of the wind fields, followed by that of the wave fields. The wave data are then transferred to the coast. We end by analysing the wave conditions inside the main inlet to the Venice lagoon. This paper gives a brief account of the logical flow of arguments from paper to paper, indicating the main results and outlining the robust structure of the overall research. We end with a discussion on the accuracy of the results, and with an indication of the possible lines for further research. [ABSTRACT FROM AUTHOR]

A severe storm in the Adriatic Sea has been hindcast with two meteorological models, respectively at the local (LAMBO) and global scale (T213). We have found that the increase of resolution is not paralleled by a corresponding increase of the overall accuracy. This is particularly true when the wind fields are used to evaluate the corresponding wave fields. The LAMBO data have then been used to validate a simpler wind model that, when properly tuned to the specific basin and starting from the correct pressure fields, is capable to supply surface wind fields of acceptable quality. [ABSTRACT FROM AUTHOR]

Copyright of Il Nuovo Cimento: C is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In part II of this paper, the effects of diabatic heating and the Tibetan Plateau on the seasonal transition of the general circulation over Asia is investigated. It is shown that the effect of diffefential heating mainly due to land-sea contrast dominates even for a medium time scale. The effect of the Piateau seems to reinforce but not radically change the basic features of the events. [ABSTRACT FROM AUTHOR]

The onset of the 1979 summer monsoon is investigated using the ECMWF grid-point model. The role of the Tibetan Plateau in this process is investigated by means of parallel model integrations with different orographies. Similarly, the relative roles of land-sea thermal contrast, latent heat release and Southern Hemisphere influence are studied. The influence of the African Highland on the onset of the Somali jet is also explored. A generally satisfactory performance of the model in representing the onset of the monsoon is documented and various contributions to this from different model components are discussed. In Part I of this paper the impact from the Southern Hemisphere is presented. [ABSTRACT FROM AUTHOR]

As a part of the Atmospheric Model Intercomparison Project (AMIP), the behaviour of 15 general circulation models has been analysed in order to diagnose and compare the ability of the different models in simulating Northern Hemisphere midlatitude atmospheric blocking. In accordance with the established AMIP procedure, the 10-year model integrations were performed using prescribed, time-evolving monthly mean observed SSTs spanning the period January 1979–December 1988. Atmospheric observational data (ECMWF analyses) over the same period have been also used to verify the models results. The models involved in this comparison represent a wide spectrum of model complexity, with different horizontal and vertical resolution, numerical techniques and physical parametrizations, and exhibit large differences in blocking behaviour. Nevertheless, a few common features can be found, such as the general tendency to underestimate both blocking frequency and the average duration of blocks. The problem of the possible relationship between model blocking and model systematic errors has also been assessed, although without resorting to ad-hoc numerical experimentation it is impossible to relate with certainty particular model deficiencies in representing blocking to precise parts of the model formulation. [ABSTRACT FROM AUTHOR]

To assess the extent to which atmospheric low-frequency variability can be ascribed to internal dynamical causes, two extended runs (1200 winter seasons) of a three level quasi-geostrophic model have been carried out. In the first experiment the model was forced by an average forcing field computed from nine winter seasons; in the second experiment we used a periodically variable forcing in order to simulate a seasonal cycle. The analysis has been focused on the leading Northern Hemisphere teleconnection patterns, namely the Pacific North American (PNA) and the North Atlantic Oscillation (NAO) patterns, and on blocking, both in the Euro-Atlantic and Pacific sectors. The NAO and PNA patterns are realistically simulated by the model; the main difference with observations is a westward shift of the centres of action of the NAO. Related to this, the region of maximum frequency of Atlantic blocking is shifted from the eastern boundary of the North Atlantic to its central part. Apart from this shift, the statistics of blocking frequency and duration compare favourably with their observed counterparts. In particular, the model exhibits a level of interannual and interdecadal variability in blocking frequency which is (at least) as large as the observed one, despite the absence of any variability in the atmospheric energy sources and boundary conditions on such time scales. [ABSTRACT FROM AUTHOR]

An analysis of blocking events is conducted on the output of four integrations of the ECHAM3 atmospheric general circulation model with different configurations of horizontal spectral truncation and oceanic surface temperatures. The definition of local blocking and sector blocking is obtained by using an objective index based on a measure of the local zonality of the flow. Model variability and systematic errors are assessed and frequency diagrams of different quantities relative to blocking statistical and synoptic properties are produced. Effects of resolution and of physical parametrizations on model performance are considered. All versions of the model show a tendency to underestimate blocking occurrence. Evidence of a different nature of the blocking phenomenon in the Euro-Atlantic and in the Pacific sectors is found. The two sectors are characterized by a different sensitivity of blocking frequency to SST prescription, by a different annual cycle and by a different sensitivity of the distribution of blocking lifetime to model resolution. Euro-Atlantic blocking is found to be more the result of internal dynamics of the flow, while Pacific blocking appears more dependent on the oceanic boundary conditions. [ABSTRACT FROM AUTHOR]

Copyright of Il Nuovo Cimento: C is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Pollutant concentrations relative to the years 1993--1995 measured in the Bologna urban area by a network of automatic stations (S.A.R.A.Sistema Automatico di Rilevamento Ambientale) are analysed to estimate the typical behaviour of the pollutants, especially with regard toperiodicities and meteorological dependencies and to attempt prediction for the pollutant daily concentration up to a few days using a statistically based model. The results obtained show the presence of a very significant weekly periodicity for all the analysed pollutants. A yearly periodicity has been found only for the primary pollutants analysed. The statistical prediction, using an ARMA model with meteorological variables as transfer functions, shows good predicting capabilities up to one day for carbon monoxide (CO) and sulphur dioxide (SO2) and up to two days for nitrogen dioxide (NO2). [ABSTRACT FROM AUTHOR]