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Bertotti L.,CNR Institute of Neuroscience | Bidlot J.-R.,European Center for Medium Range Weather Forecasts | Bunney C.,UK Met Office | Cavaleri L.,CNR Institute of Neuroscience | And 6 more authors.
Quarterly Journal of the Royal Meteorological Society | Year: 2012

We consider an exceptional storm-'Klaus' (January 2009)-its evolution on the Western Mediterranean Sea, and how the associated wind and wave conditions were modelled by seven of the major systems presently operational in this area. We intercompare the model results and then verify them and the related model ensemble versus the available measured data. Working with short-term forecasts (24 h) only, as expected, each model correctly anticipates the incoming of an exceptional storm. However, even at such limited range, we have found substantial differences among the results of the different models. The differences concern the time the storm should have entered the Western Mediterranean Sea, the peak values of wind speed and significant wave height, the general distribution of the fields, and the locations where the maxima were achieved. We have compared the model results versus the available measured data, wind from scatterometer, waves from altimeter, plus a few buoy data. We have found some inconsistencies in the results, model wind data being on average larger than the measured one, while the opposite was true for wave heights. However, the limited amount of data available and its different times and positions, at and off the centre of the storm, impede the drawing of any definite conclusion in this respect. On the whole we feel that our results, although related to a single storm, cast doubts on the reliability of a single forecast system to provide sufficiently reliable and accurate forecasts in case of an incoming exceptional storm. The results, both for wind and waves, have improved using an ensemble of the seven considered models. This suggests that there is no relevant systematic error in the used models except, as possibly suggested by our results, in the case of wave generation under very strong wind and very young sea conditions. © 2011 Royal Meteorological Society and British Crown, the Met Office.

Chiggiato J.,Undersea Research Center | Jarosz E.,U.S. Navy | Book J.W.,U.S. Navy | Dykes J.,U.S. Navy | And 5 more authors.
Ocean Dynamics | Year: 2012

During September 2008 and February 2009, the NR/V Alliance extensively sampled the waters of the Sea of Marmara within the framework of the Turkish Straits System (TSS) experiment coordinated by the NATO Undersea Research Centre. The observational effort provided an opportunity to set up realistic numerical experiments for modeling the observed variability of the Marmara Sea upper layer circulation at mesoscale resolution over the entire basin during the trial period, complementing relevant features and forcing factors revealed by numerical model results with information acquired from in situ and remote sensing datasets. Numerical model solutions from realistic runs using the Regional Ocean Modeling System (ROMS) produce a general circulation in the Sea of Marmara that is consistent with previous knowledge of the circulation drawn from past hydrographic measurements, with a westward meandering current associated with a recurrent large anticyclone. Additional idealized numerical experiments illuminate the role various dynamics play in determining the Sea of Marmara circulation and pycnocline structure. Both the wind curl and the strait flows are found to strongly influence the strength and location of the main mesoscale features. Large displacements of the pycnocline depth were observed during the sea trials. These displacements can be interpreted as storm-driven upwelling/ downwelling dynamics associated with northeasterly winds; however, lateral advection associated with flow from the Straits also played a role in some displacements. © 2011 Springer Science+Business Media, LLC.

Bonasoni P.,CNR Institute of Neuroscience | Laj P.,CNRS Laboratory for Glaciology and Environmental Geophysics | Marinoni A.,CNR Institute of Neuroscience | Sprenger M.,ETH Zurich | And 22 more authors.
Atmospheric Chemistry and Physics | Year: 2010

This paper provides a detailed description of the atmospheric conditions characterizing the high Himalayas, thanks to continuous observations begun in March 2006 at the Nepal Climate Observatory-Pyramid (NCO-P) located at 5079 m a.s.l. on the southern foothills of Mt. Everest, in the framework of ABC-UNEP and SHARE-Ev-K2-CNR projects. The work presents a characterization of meteorological conditions and air-mass circulation at NCO-P during the first two years of activity. The mean values of atmospheric pressure, temperature and wind speed recorded at the site were: 551 hPa,-3.0 °C, 4.7 m s-1, respectively. The highest seasonal values of temperature (1.7 °C) and relative humidity (94%) were registered during the monsoon season, which was also characterized by thick clouds, present in about 80% of the afternoon hours, and by a frequency of cloud-free sky of less than 10%. The lowest temperature and relative humidity seasonal values were registered during winter,-6.3 °C and 22%, respectively, the season being characterised by mainly cloud-free sky conditions and rare thick clouds. The summer monsoon influenced rain precipitation (seasonal mean: 237 mm), while wind was dominated by flows from the bottom of the valley (S-SW) and upper mountain (N-NE). The atmospheric composition at NCO-P has been studied thanks to measurements of black carbon (BC), aerosol scattering coefficient, PM1, coarse particles and ozone. The annual behaviour of the measured parameters shows the highest seasonal values during the pre-monsoon (BC: 316.9 ng m-3, PM 1: 3.9 μgm-3, scattering coefficient: 11.9 Mm -1, coarse particles: 0.37 cm-3 and O3: 60.9 ppbv), while the lowest concentrations occurred during the monsoon (BC: 49.6 ng m-3, PM1: 0.6 μg m-3, scattering coefficient: 2.2 Mm-1, and O3: 38.9 ppbv) and, for coarse particles, during the post-monsoon (0.07 cm-3. At NCO-P, the synoptic-scale circulation regimes present three principal contributions: Westerly, South-Westerly and Regional, as shown by the analysis of in-situ meteorological parameters and 5-day LAGRANTO back-trajectories. The influence of the brown cloud (AOD>0.4) extending over Indo-Gangetic Plains up to the Himalayan foothills has been evaluated by analysing the in-situ concentrations of the ABC constituents. This analysis revealed that brown cloud hot spots mainly influence the South Himalayas during the pre-monsoon, in the presence of very high levels of atmospheric compounds (BC: 1974.1 ng m-3, PM 1: 23.5 μg m-3, scattering coefficient: 57.7 Mm -1, coarse particles: 0.64 cm-3, O3: 69.2 ppbv, respectively). During this season 20% of the days were characterised by a strong brown cloud influence during the afternoon, leading to a 5-fold increased in the BC and PM1 values, in comparison with seasonal means. Our investigations provide clear evidence that, especially during the pre-monsoon, the southern side of the high Himalayan valleys represent a "direct channel" able to transport brown cloud pollutants up to 5000 m a.s.l., where the pristine atmospheric composition can be strongly influenced. © 2010 Author(s).

Cavaleri L.,CNR Institute of Neuroscience | Bertotti L.,CNR Institute of Neuroscience | Torrisi L.,CNMCA | Bitner-Gregersen E.,DNV GL | And 3 more authors.
Journal of Geophysical Research: Oceans | Year: 2012

We analyze the sea state conditions during which the accident of the cruise ship Louis Majesty took place. The ship was hit by a large wave that destroyed some windows at deck number five and caused two fatalities. Using the wave model (WAM), driven by the Consortium for Small-Scale Modelling (COSMO-ME) winds, we perform a detailed hindcast of the local wave conditions. The results reveal the presence of two comparable wave systems characterized almost by the same frequency. We discuss such sea state conditions in the framework of a system of two coupled Nonlinear Schrdinger (CNLS) equations, each of which describe the dynamics of a single spectral peak. For some specific parameters, we discuss the breather solutions of the CNLS equations and estimate the maximum wave amplitude. Even though, due to the lack of measurements, it is impossible to establish the nature of the wave that caused the accident, we show that the angle between the two wave systems during the accident was close to the condition for which the maximum amplitude of the breather solution is observed. Copyright 2012 by the American Geophysical Union.

Bertotti L.,Institute of Marine science | Cavaleri L.,Institute of Marine science | Loffredo L.,Catholic University of Leuven | TorrisiZ L.,CNMCA
Monthly Weather Review | Year: 2013

Nettuno is a wind and wave forecast system for the Mediterranean Sea. It has been operational since 2009 producing twice-daily high-resolution forecasts for the next 72 h. The authorshave carried out a detailed analysis of the results, both in space and time, using scatterometer and altimeter data from four different satellites. The findings suggest that there are appreciable differences in the measurements from the different instruments. Within the overall positive results, there is also evidence of differences in Nettuno performance for the various subbasins. The related geographical distributions in Nettuno performance are consistent with thevarious satellite instruments used in the comparisons. The extensive system of buoys around Italy is used to highlight the difficulties involved in a correct modeling of wave heights in Italy's coastal areas © 2013 American Meteorological Society.

Bastianini M.,CNR Marine Science Institute | Cavaleri L.,CNR Marine Science Institute | La Rocca T.,CNMCA
Natural Hazards and Earth System Sciences | Year: 2012

We report the evidence of a remarkable meteorological event in the Northern Adriatic Sea. Following the irruption of cold northerly air into the previously hot and humid eastern part of the Po valley, a strong instability developed with violent thunderstorms. At the ISMAR oceanographic tower, 15 km off the coast of the Venice lagoon, although no one was on board, the records of 6 July 2008 from the various instruments coherently show the presence of an extreme and short-lived event that we associate either to a water spout or, more likely, to the strong downdraft of a mesoscale convective system. © 2012 Author(s).

Bonavita M.,CNMCA | Torrisi L.,CNMCA | Marcucci F.,CNMCA
Quarterly Journal of the Royal Meteorological Society | Year: 2010

The Ensemble Kalman Filter (EnKF) is likely to become a viable alternative to variational methods for the next generation of meteorological and oceanographic dataassimilationsystems. In this work we present results from real-data as similation experiments using the CNMCA regional numerical weather prediction (NWP) forecasting system and compare them to the currently operational variational-based analysis. The set of observations used is the same as the one ingested in the operational data stream, with the exception of satellite radiances and scatterometer winds. Results show that the EnKF-based assimilation cycle is capable of producing analyses and forecasts of consistently superior skill in the root mean square error metric than CNMCA operational 3D-Var. One of the most important issues in EnKF implementations lies in the filter tendency to become underdispersive for practical ensemble sizes. To combat this problem a number of different parametrizations of the model error unaccounted for in the assimilation cycle have been proposed. In the CNMCA system a combination of adaptive multiplicative and additive background covariance inflations has been found to give adequate results and to be capable of avoiding filter divergence in extended assimilation trials. The additive component of the covariance inflation has been implemented through the use of scaled forecast differences. Following suggestions that ensemble square-root filters can violate the gaussianity assumptionwhen used with nonlinear prognostic models, the statistical distribution of the forecast and analysis ensembles has been studied. No sign of the ensemble collapsing onto one or a few model states has been found, and the forecast and analysis ensembles appear to stay remarkably close to the assumed probability distribution functions. © 2010 Royal Meteorological Society.

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