The Po Valley is an area prone to convective storms often associated with severe weather conditio... more The Po Valley is an area prone to convective storms often associated with severe weather conditions, such as hail and strong winds, especially during spring and summer. The large and flat valley is surrounded on three sides by orographic chains (Alps and Apennines) that ...
The availability of the 4-D VAR ECMWF reanalysis for the MAP Special Observing Period, allows us ... more The availability of the 4-D VAR ECMWF reanalysis for the MAP Special Observing Period, allows us to perform a numerical assessment of its impact on high resolution forecasts in comparison with the operational 3-D VAR ECMWF analysis. By means of the BOLAM (hydrostatic) and MOLOCH (non-hydrostatic) limited area models operating at different resolutions and using ECMWF analysis and reanalysis as initial conditions, we evaluated the quantitative precipitation forecasts in three MAP Intensive Observing Periods using statistical scores applied to the precipitation fields.
Recent developments in the normal mode theory of lee cyclogenesis are presented. The topographic ... more Recent developments in the normal mode theory of lee cyclogenesis are presented. The topographic modifications of the most unstable eigenmode are computed in the most general case of primitive equations and isolated topography. The basic state about which linearization is performed is a midlatitude jet with maximum speed at tropopause level. The orographic modification consists in a pressure dipole scaling on the Rossby deformation radius already found in previous theoretical and numerical studies. The modifications of the statistical properties introduced by topography on the nonlinear feedback between zonal wind and transient waves are determined using a simple quasi-geostrophic two-layer model. Systematic differences are found to be consistent with the predictions of linear theories. A brief discussion on the limits of the linear theory is also included.
ABSTRACT A monthly probabilistic forecasting system is experimentally operated at the ISAC instit... more ABSTRACT A monthly probabilistic forecasting system is experimentally operated at the ISAC institute of the National Council of Research of Italy. The forecasting system is based on GLOBO, an atmospheric general circulation model developed at the same institute. The model is presently run on a monthly basis to produce an ensemble of 32 forecasts initialized with GFS-NCEP perturbed analyses. Reforecasts, initialized with ECMWF ERA-Interim reanalyses of the 1989-2009 period, are also produced to determine modelled climatology of the month to forecast. The modelled monthly climatology is then used to calibrate the ensemble forecast of daily precipitation, geopotential height and temperature on standard pressure levels. In this work, we present the forecasting system and a preliminary evaluation of the model systematic and forecast errors in terms of non-probabilistic scores of the 500-hPa geopotential height. Results show that the proposed forecasting system outperforms the climatology in the first two weeks of integrations. The adopted calibration based on weighted bias correction is found to reduce the systematic and the forecast errors.
Natural Hazards and Earth System Sciences Discussions, 2013
ABSTRACT The Liguria coastal region in Italy was affected by two heavy rainfall and consequent se... more ABSTRACT The Liguria coastal region in Italy was affected by two heavy rainfall and consequent severe flood episodes that occurred at the end of October and beginning of November 2011. The very large accumulated precipitation maxima were associated, in both cases, with intense and quasi-stationary convective systems developed near the coast, both related to orographic lift and similar low-level mesoscale flow patterns over the Ligurian Sea, giving rise to pronounced convergence lines. This study aims at analyzing the main dynamical processes responsible for the onset, lifecycle, intensity and localization/propagation of the precipitating systems, using the ISAC convection-permitting model MOLOCH applied at different spatial resolutions and comparing model output fields with available observations. The ability of the model in forecasting quantitative precipitation (QPF) is tested with respect to initial analysis and model horizontal resolution. Although precipitation maxima remain underestimated in the model experiments, it is shown that forecast errors of QPF in both amount and position tend to decrease with increasing grid resolution. It is shown that model accuracy in forecasting rainfall amounts and localization of the precipitating systems critically depends, in both episodes, on the ability in representing the cold air outflow from the Po Valley to the Ligurian Sea, which determines the position and intensity of the mesoscale convergence lines over the sea. Such convergence lines controls, together with the lifting produced by the Apennines chain surrounding the coast, the onset of the severe convection.
The coupling of a suite of meteorological limited area models with a wave prediction system based... more The coupling of a suite of meteorological limited area models with a wave prediction system based on the nesting of different wave models provides for medium-range sea state forecasts at the Mediterranean, regional and coastal scale. The new system has been operational at ISPRA since September 2012, after the upgrade of both the meteorological BOLAM model and large-scale marine components of the original SIMM forecasting system and the implementation of the new regional and coastal (WAM-SWAN coupling) chain of models. The coastal system is composed of nine regional-scale high-resolution grids, covering all Italian seas and six coastal grids at very high resolution, capable of accounting for the effects of the interaction between the incoming waves and the bathymetry. A preliminary analysis of the performance of the system is discussed here focusing on the ability of the system to simulate the mean features of the wave climate at the regional and sub-regional scale. The results refer to two different verification studies. The first is the comparison of the directional distribution of almost one year of wave forecasts against the known wave climate in northwestern Sardinia and central Adriatic Sea. The second is a sensitivity test on the effect on wave forecasts of the spatial resolution of the wind forcing, being the comparison between wave forecast and buoy data at two locations in the northern Adriatic and Ligurian Sea during several storm episodes in the period autumn 2012-winter 2013.
ABSTRACT Atmospheric monthly forecast is intermediate between medium range forecast, an initial v... more ABSTRACT Atmospheric monthly forecast is intermediate between medium range forecast, an initial value problem, and seasonal forecast, a boundary value problem. The influence of sea surface temperature (SST) on the atmospheric dynamics in the time range of 10-40 days is still not well understood. As a consequence, there is no common approach for the representation of the SST in a monthly prediction system. At ISAC-CNR in Bologna a monthly ensemble forecasting system is run experimentally once a month, based on the GLOBO model. GLOBO is an atmospheric general circulation model developed at ISAC. The evolution of SST is represented by a simple slab ocean model based on surface flux balance with a relaxation term to climatological SST. Recently, a new definition of the slab ocean model which includes a flux correction term has been implemented to improve the SST simulation. It has been tested in parallel with the operational forecast for some months of 2011. The results show that the globally averaged root mean square forecast error of the SST simulated with the new model is slightly larger than the operational one. However, the ensemble spread of the SST predicted with the new model increases significantly and becomes very similar to the observed SST variability, in particular in the Northern Hemisphere. The atmospheric field differences between the new and operational forecasts show that SST has an impact in the second part of the month, especially in the Southern Hemisphere. The ensemble spread of atmospheric parameters shows a slight increase using the new slab model. However, its impact on the anomaly forecast fields is small.
ABSTRACT Satellite images of 30 October 2008 show the development over north-central Italy of rai... more ABSTRACT Satellite images of 30 October 2008 show the development over north-central Italy of rainbands and multiple waves during a strong south-westerly wind episode associated with a deepening synoptic trough and cold front passage. The event was studied by means of the ISAC model chain constituted of the hydrostatic model BOLAM and the nested non-hydrostatic model MOLOCH at 1 kilometer resolution. Diagnostics of model output were performed to reveal characteristic features of symmetric instability.
ABSTRACT The availability of the 4-D VAR ECMWF reanalysis for the MAP Special Observing Period, a... more ABSTRACT The availability of the 4-D VAR ECMWF reanalysis for the MAP Special Observing Period, allows us to perform a numerical assessment of its impact on high resolution forecasts in comparison with the operational 3-D VAR ECMWF analysis. By means of the BOLAM (hydrostatic) and MOLOCH (non-hydrostatic) limited area models operating at different resolutions and using ECMWF analysis and reanalysis as initial conditions, we evaluated the quantitative precipitation forecasts in three MAP Intensive Observing Periods using statistical scores applied to the precipitation fields.
The Po Valley is an area prone to convective storms often associated with severe weather conditio... more The Po Valley is an area prone to convective storms often associated with severe weather conditions, such as hail and strong winds, especially during spring and summer. The large and flat valley is surrounded on three sides by orographic chains (Alps and Apennines) that ...
The availability of the 4-D VAR ECMWF reanalysis for the MAP Special Observing Period, allows us ... more The availability of the 4-D VAR ECMWF reanalysis for the MAP Special Observing Period, allows us to perform a numerical assessment of its impact on high resolution forecasts in comparison with the operational 3-D VAR ECMWF analysis. By means of the BOLAM (hydrostatic) and MOLOCH (non-hydrostatic) limited area models operating at different resolutions and using ECMWF analysis and reanalysis as initial conditions, we evaluated the quantitative precipitation forecasts in three MAP Intensive Observing Periods using statistical scores applied to the precipitation fields.
Recent developments in the normal mode theory of lee cyclogenesis are presented. The topographic ... more Recent developments in the normal mode theory of lee cyclogenesis are presented. The topographic modifications of the most unstable eigenmode are computed in the most general case of primitive equations and isolated topography. The basic state about which linearization is performed is a midlatitude jet with maximum speed at tropopause level. The orographic modification consists in a pressure dipole scaling on the Rossby deformation radius already found in previous theoretical and numerical studies. The modifications of the statistical properties introduced by topography on the nonlinear feedback between zonal wind and transient waves are determined using a simple quasi-geostrophic two-layer model. Systematic differences are found to be consistent with the predictions of linear theories. A brief discussion on the limits of the linear theory is also included.
ABSTRACT A monthly probabilistic forecasting system is experimentally operated at the ISAC instit... more ABSTRACT A monthly probabilistic forecasting system is experimentally operated at the ISAC institute of the National Council of Research of Italy. The forecasting system is based on GLOBO, an atmospheric general circulation model developed at the same institute. The model is presently run on a monthly basis to produce an ensemble of 32 forecasts initialized with GFS-NCEP perturbed analyses. Reforecasts, initialized with ECMWF ERA-Interim reanalyses of the 1989-2009 period, are also produced to determine modelled climatology of the month to forecast. The modelled monthly climatology is then used to calibrate the ensemble forecast of daily precipitation, geopotential height and temperature on standard pressure levels. In this work, we present the forecasting system and a preliminary evaluation of the model systematic and forecast errors in terms of non-probabilistic scores of the 500-hPa geopotential height. Results show that the proposed forecasting system outperforms the climatology in the first two weeks of integrations. The adopted calibration based on weighted bias correction is found to reduce the systematic and the forecast errors.
Natural Hazards and Earth System Sciences Discussions, 2013
ABSTRACT The Liguria coastal region in Italy was affected by two heavy rainfall and consequent se... more ABSTRACT The Liguria coastal region in Italy was affected by two heavy rainfall and consequent severe flood episodes that occurred at the end of October and beginning of November 2011. The very large accumulated precipitation maxima were associated, in both cases, with intense and quasi-stationary convective systems developed near the coast, both related to orographic lift and similar low-level mesoscale flow patterns over the Ligurian Sea, giving rise to pronounced convergence lines. This study aims at analyzing the main dynamical processes responsible for the onset, lifecycle, intensity and localization/propagation of the precipitating systems, using the ISAC convection-permitting model MOLOCH applied at different spatial resolutions and comparing model output fields with available observations. The ability of the model in forecasting quantitative precipitation (QPF) is tested with respect to initial analysis and model horizontal resolution. Although precipitation maxima remain underestimated in the model experiments, it is shown that forecast errors of QPF in both amount and position tend to decrease with increasing grid resolution. It is shown that model accuracy in forecasting rainfall amounts and localization of the precipitating systems critically depends, in both episodes, on the ability in representing the cold air outflow from the Po Valley to the Ligurian Sea, which determines the position and intensity of the mesoscale convergence lines over the sea. Such convergence lines controls, together with the lifting produced by the Apennines chain surrounding the coast, the onset of the severe convection.
The coupling of a suite of meteorological limited area models with a wave prediction system based... more The coupling of a suite of meteorological limited area models with a wave prediction system based on the nesting of different wave models provides for medium-range sea state forecasts at the Mediterranean, regional and coastal scale. The new system has been operational at ISPRA since September 2012, after the upgrade of both the meteorological BOLAM model and large-scale marine components of the original SIMM forecasting system and the implementation of the new regional and coastal (WAM-SWAN coupling) chain of models. The coastal system is composed of nine regional-scale high-resolution grids, covering all Italian seas and six coastal grids at very high resolution, capable of accounting for the effects of the interaction between the incoming waves and the bathymetry. A preliminary analysis of the performance of the system is discussed here focusing on the ability of the system to simulate the mean features of the wave climate at the regional and sub-regional scale. The results refer to two different verification studies. The first is the comparison of the directional distribution of almost one year of wave forecasts against the known wave climate in northwestern Sardinia and central Adriatic Sea. The second is a sensitivity test on the effect on wave forecasts of the spatial resolution of the wind forcing, being the comparison between wave forecast and buoy data at two locations in the northern Adriatic and Ligurian Sea during several storm episodes in the period autumn 2012-winter 2013.
ABSTRACT Atmospheric monthly forecast is intermediate between medium range forecast, an initial v... more ABSTRACT Atmospheric monthly forecast is intermediate between medium range forecast, an initial value problem, and seasonal forecast, a boundary value problem. The influence of sea surface temperature (SST) on the atmospheric dynamics in the time range of 10-40 days is still not well understood. As a consequence, there is no common approach for the representation of the SST in a monthly prediction system. At ISAC-CNR in Bologna a monthly ensemble forecasting system is run experimentally once a month, based on the GLOBO model. GLOBO is an atmospheric general circulation model developed at ISAC. The evolution of SST is represented by a simple slab ocean model based on surface flux balance with a relaxation term to climatological SST. Recently, a new definition of the slab ocean model which includes a flux correction term has been implemented to improve the SST simulation. It has been tested in parallel with the operational forecast for some months of 2011. The results show that the globally averaged root mean square forecast error of the SST simulated with the new model is slightly larger than the operational one. However, the ensemble spread of the SST predicted with the new model increases significantly and becomes very similar to the observed SST variability, in particular in the Northern Hemisphere. The atmospheric field differences between the new and operational forecasts show that SST has an impact in the second part of the month, especially in the Southern Hemisphere. The ensemble spread of atmospheric parameters shows a slight increase using the new slab model. However, its impact on the anomaly forecast fields is small.
ABSTRACT Satellite images of 30 October 2008 show the development over north-central Italy of rai... more ABSTRACT Satellite images of 30 October 2008 show the development over north-central Italy of rainbands and multiple waves during a strong south-westerly wind episode associated with a deepening synoptic trough and cold front passage. The event was studied by means of the ISAC model chain constituted of the hydrostatic model BOLAM and the nested non-hydrostatic model MOLOCH at 1 kilometer resolution. Diagnostics of model output were performed to reveal characteristic features of symmetric instability.
ABSTRACT The availability of the 4-D VAR ECMWF reanalysis for the MAP Special Observing Period, a... more ABSTRACT The availability of the 4-D VAR ECMWF reanalysis for the MAP Special Observing Period, allows us to perform a numerical assessment of its impact on high resolution forecasts in comparison with the operational 3-D VAR ECMWF analysis. By means of the BOLAM (hydrostatic) and MOLOCH (non-hydrostatic) limited area models operating at different resolutions and using ECMWF analysis and reanalysis as initial conditions, we evaluated the quantitative precipitation forecasts in three MAP Intensive Observing Periods using statistical scores applied to the precipitation fields.
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Papers by P. Malguzzi