Sensitivity experiments of a severe rainfall event in north-western Italy: 17 August 2006

Milelli, Massimo; Oberto, E.; Parodi, Antonio

doi:10.5194/asr-2-133-2008

Cited by 6 publications

(3 citation statements)

References 14 publications

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“…The aim of this project is to assess to which extent COSMO-I7, the Italian operational limited area model, is able to provide a correct modelling of the main kinematic and thermodynamic ingredients typical for intense precipitation processes in complex orography regions (Elementi et al, 2005;Milelli et al, 2008) by characterizing the uncertainty affecting the first step of the predictive procedure in order to issue warnings.…”

Section: Introductionmentioning

confidence: 99%

Dealing with uncertainty: an analysis of the severe weather events over Italy in 2006

Molini

Parodi

Siccardi

2009

Nat. Hazards Earth Syst. Sci.

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Abstract. Forecast verification is a long-standing issue of the whole meteorologists' community. A common definition of a truly satisfying prediction skill has not been achieved so far. Even the definition of "event", due to its spatio-temporal discontinuity, is highly affected by uncertainty.Moreover, decision-making demands numerical weather prediction modellers to provide information about the "inner" uncertainty, i.e. the degree of uncertainty related to the choice of a specific setting of the model (microphysics, turbulence scheme, convective closure, etc.).Most European Mediterranean countries, due to dense development, steep coastal orography and short hydrological response time of the drainage basins, have to deal very frequently with flash floods and sudden shallow land sliding impacting on urban areas. Civil protection organizations are in place to issue early warnings in order to allow local authorities and population to take precautionary measures. To do so in Mediterranean catchments, hydrologists are required to use numerical rainfall predictions in place of rainfall observations on large European catchments.Estimating the measure of uncertainty is for this reason crucial.The goal of this work is to propose an objective evaluation of the performance of the currently operational weather prediction model COSMO-I7 over quite a long time period and to check forecast verification at different space-time scales by the comparison of predictions with observations.Due to large investments in the last years, in fact, Italy has built up one of the most dense hourly-reporting network of rain gauges. The network has a mean space density of about 1/100 km 2 , very similar to the horizontal resolution of currently operating limited area models.Correspondence to: L. Molini (luca.molini@cimafoundation.org) An objective procedure to identify and compare the extreme events of precipitation has been applied to the full set of rainfall observations and over the severe events forecast by COSMO-I7 and announced in official warnings by Italian Civil Protection Department.The procedure allows to classify rainfall events as longlived and spatially distributed or as having a shorter duration and a minor spatial extent. We show that long-lived events are less affected by overall uncertainty than short-lived ones, yet the inner uncertainty of the event affects both.

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Section: Introductionmentioning

confidence: 99%

Dealing with uncertainty: an analysis of the severe weather events over Italy in 2006

Molini

Parodi

Siccardi

2009

Nat. Hazards Earth Syst. Sci.

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“…The model also includes parameterization for the ground heat and water transport and the land-atmosphere interactions. The formation of precipitation fields is described by a bulk micro-physics parameterization including water vapour, cloud water and ice, rain and snow with a fully prognostic treatment of precipitation, i.e., three dimensional transport of rain, and snow is directly calculated (Milelli et al, 2008). Condensation and evaporation are parameterized by saturation adjustment whereas depositional growth 3 Nat.…”

Section: About the Cosmo Modelmentioning

confidence: 99%

Impact analysis of dynamical downscaling on the treatment of convection in a regional NWP model – COSMO: a case study during the passage of a very severe cyclonic storm OCKHI

Roshny

Subrahamanyam

Anurose

et al. 2018

Preprint

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Abstract. A significant source of uncertainty in Numerical Weather Prediction (NWP) models arises from the parameterization of sub-grid scale convection, whose inherent nature of complexity is amplified while applied to tropical regions where weather systems are controlled by many intricate factors. However, as the model resolution becomes finer, it is possible to switch off the convection parameterization, although it is still unclear at what resolution this can be achieved. Ambiguity arises due to the inter-linking of various parameterization schemes within a model, and efficiency of one scheme depends on the output of another. In order to explore these issues, an intense convective episode with very heavy precipitation over the coastal Arabian Sea associated with the passage of OCKHI, one of the very severe cyclonic storms, is chosen as a case study. A set of distinct numerical simulations are carried out using Consortium for Small-scale Modelling (COSMO) to assess the direct and indirect impacts of dynamical downscaling on the treatment of convection. Results obtained from the present investigation indicate dynamical downscaling together with switching off the convection parameterization could simulate the magnitudes of CAPE, one of the proxies for characterizing the occurrence of tropical convection, more realistically. But the downscaling did not improve the rainfall prediction, which were seen to deteriorate in the absence of convection parameterization.

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“…The flux of moist air continued for the whole day and during the evening of the first day of simulation the upper-level cold front crossed Piemonte region intensifying deep moist convection in complex orography areas. This test case has been also studied in the framework of a COSMO Priority Project (see Milelli et al, 2008 andDierer, 2008 for more details about the study and the project, respectively) because the operational COSMO Model forecast had some discrepancy regarding the correct localisation and intensity of the main precipitation structure.…”

Section: Data Set and Test Casesmentioning

confidence: 99%

Screen-level non-GTS data assimilation in a limited-area mesoscale model

Milelli¹,

Turco

Oberto³

2010

Nat. Hazards Earth Syst. Sci.

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Abstract. The forecast in areas of very complex topography, as for instance the Alpine region, is still a challenge even for the new generation of numerical weather prediction models which aim at reaching the km-scale. The problem is enhanced by a general lack of standard observations, which is even more evident over the southern side of the Alps. For this reason, it would be useful to increase the performance of the mathematical models by locally assimilating non-conventional data. Since in ARPA Piemonte there is the availability of a great number of non-GTS stations, it has been decided to assimilate the 2 m temperature, coming from this dataset, in the very-high resolution version of the COSMO model, which has a horizontal resolution of about 3 km, more similar to the average resolution of the thermometers. Four different weather situations have been considered, ranging from spring to winter, from cloudy to clear sky. The aim of the work is to investigate the effects of the assimilation of non-GTS data in order to create an operational very high-resolution analysis, but also to test the option of running in the future a very short-range forecast starting from these analyses (RUC or Rapid Update Cycle). The results, in terms of Root Mean Square Error, Mean Error and diurnal cycle of some surface variables such as 2 m temperature, 2 m relative humidity and 10 m wind intensity show a positive impact during the assimilation cycle which tends to dissipate a few hours after the end of it. Moreover, the 2 m temperature assimilation has a slightly positive or neutral impact on the vertical profiles of temperature, eventhough some calibration is needed for the precipitation field which is too much perturbed during the assimilation cycle, while it is unaffected in the forecast period. So the stability of the planetary boundary layer, on the one hand, has not been particu- Milelli (m.milelli@arpa.piemonte.it) larly improved by the new-data assimilation, but, on the other hand, it has not been destroyed. It has to be pointed out that a correct description of the planetary boundary layer, even only the lowest part of it, could be helpful to the forecasters and, in general, to the users, in order to deal with meteorological hazards such as snow (in particular snow/rain limit definition), or fog (description of temperature inversions).

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Sensitivity experiments of a severe rainfall event in north-western Italy: 17 August 2006

Cited by 6 publications

References 14 publications

Dealing with uncertainty: an analysis of the severe weather events over Italy in 2006

Dealing with uncertainty: an analysis of the severe weather events over Italy in 2006

Impact analysis of dynamical downscaling on the treatment of convection in a regional NWP model – COSMO: a case study during the passage of a very severe cyclonic storm OCKHI

Screen-level non-GTS data assimilation in a limited-area mesoscale model

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