Martina Tudor

Use of high-resolution dynamical adaptation in operational suite and research impact studies

The article presents a very high-resolution dynamical adaptation of the wind field with the hydrostatic version of the ALADIN model used in the operational suite, including a sensitivity study of a recent case of bura and a MAP IOP 15 case study. Bura is a strong wind with severe gusts ; it occurs suddenly and affects traffic on the eastern Adriatic. It has a large spatial variability and depends on an upstream terrain configuration. The described approach makes it possible to predict the occurrence, strength and spatial variability of the wind field in the mountainous area of the eastern Adriatic coast. Although this area is often affected by severe wind events (bura), measured wind data do not provide adequate coverage and are usually not representative enough. Good performance of the operational wind prediction encouraged its use for estimating the expected extreme wind speeds on the route of a new highway. Two sensitivity tests were carried out to explore the impact of the neglected processes. It was found that the impact is negligible in the case of severe bura event.

Extreme cooling and dense water formation estimates in open and coastal regions of the Adriatic Sea during the winter of 2012

Generation of dense waters in the Adriatic Sea during an extreme cooling event in the winter of 2012, including its preconditioning and spreading phases, have been investigated using the one-way coupled ROMS and the ALADIN/HR modeling system. Both climatological and real river fluxes are used in the simulations. Aside from the “convenient” dense water formation areas located at the northernmost Adriatic shelf, we found that a similar amount of dense water, with slightly lower density, was formed in the eastern and deeper Adriatic coastal area, which was subjected to extreme heat losses (up to 2000 W/m2) during peak cooling periods. This part of the Adriatic has been known for extreme cooling during wintertime bora outbreaks ; nevertheless, no ocean model study has previously reproduced dense water formation in this area. The most likely reason for that was an overestimate of river discharges introduced to ocean models. From newly available data, we estimated that the contribution of eastern Adriatic rivers between the Neretva River and Rijeka Bay is more than six times lower than what has been previously documented. Transport of dense water toward the middle Adriatic had a peak value of about 0.6 Sv, while the speed of initial bottom density current surpassed 40–50 cm/s, which is several times faster than past events. Different pathways of the dense water toward the middle and south Adriatic depressions have also been documented. The contribution of the eastern coastal Adriatic area to the overall north Adriatic dense water formation has been quantified and discussed for average and low freshwater load conditions, indicating that this part of the Adriatic is a common place for dense water generation.

Self-Organizing Maps-based ocean currents forecasting system

An ocean surface currents forecasting system, based on a Self-Organizing Maps (SOM) neural network algorithm, high-frequency (HF) ocean radar measurements and numerical weather prediction (NWP) products, has been developed for a coastal area of the northern Adriatic and compared with operational ROMS-derived surface currents. The two systems differ significantly in architecture and algorithms, being based on either unsupervised learning techniques or ocean physics. To compare performance of the two methods, their forecasting skills were tested on independent datasets. The SOM-based forecasting system has a slightly better forecasting skill, especially during strong wind conditions, with potential for further improvement when data sets of higher quality and longer duration are used for training.

The case study of bura of 1st and 3rd February 2007

Two cases when the operational forecast seriously underestimated the wind speed maxima are analysed. The first one in the night between 1 st and 2 nd February 2007 and the second one in the evening of 3 rd February 2007. The two cases are analyzed using measured data from Split and Makarska automatic stations as well as vertical soundings from Zagreb and Zadar and ALADIN model simulations. For the purpose of this study, ALADIN 72 hour forecast was run on 2 km resolution using the complete set of physics parametrizations, hydrostatic and nonhydrostatic dynamics. Results show the potential benefit of nonhydrostatic dynamics for operational forecast does not lie in improvement of the 10 m wind forecast as much as in forecasting clear air turbulence associated with the lee waves.

Forecasting Weather in Croatia Using ALADIN Numerical Weather Prediction Model

This chapter gives an overview on weather forecasting using the set-up of the NWP model ALADIN that is used for operational weather forecast in CMHS as an example for operation weather forecasting. ALADIN is a state-of-the-art modern NWP model. Using ALADIN we exemplarily discuss short-comings and challenges in modern operational weather forecasting. A high-resolution LAM is intended to predict the sub-synoptic weather features forced by topography or other local characteristics that can be absent in the main synoptic pattern. Successful prediction of these small-scale features enables usage of the LAM forecast in predicting the conditions important for the flight safety, vehicle road safety or navigation at sea. The operational suite has to be tuned in order to predict the high-impact weather events of local character that could be missing in the large scale forecast. The domain properties as well as the forecast model complexity are formed according to the needs of the forecast users and the computing capabilities.

Sensitivity of HF radar-derived surface current self-organizing maps to various processing procedures and mesoscale wind forcing

We performed a number of sensitivity experiments by applying a mapping technique, self-organizing maps (SOM) method, to the surface current data measured by high-frequency (HF) radars in the northern Adriatic and surface winds modelled by two state-of-the-art mesoscale meteorological models, the Aladin (Aire Limitée Adaptation Dynamique Développement InterNational) and the Weather and Research Forecasting models. Surface current data used for the SOM training were collected during a period in which radar coverage was the highest: between February and November 2008. Different pre-processing techniques, such as removal of tides and low-pass filtering, were applied to the data in order to test the sensitivity of characteristic patterns and the connectivity between different SOM solutions. Topographic error did not exceed 15 %, indicating the applicability of the SOM method to the data. The largest difference has been obtained when comparing SOM patterns originating from unprocessed and low-pass filtered data. Introduction of modelled winds in joint SOM analyses stabilized the solutions, while sensitivity to wind forcing coming from the two different meteorological models was found to be small. Such a low sensitivity is considered to be favourable for creation of an operational ocean forecasting system based on neural networks, HF radar measurements and numerical weather prediction mesoscale models.

Operational Wave Modelling in the Adriatic Sea with the Wind Wave Model

AbstractThe accurate modelling of sea surface gravity waves is essential for accurate oceanic forecasting with high sea waves being a major concern for navigation and coastal activities. It is also very important for oceanic modelling, with the wave input being key to the accurate modelling of oceanic surface stress, sediment resuspension, and also to oceanic current modelling. In the Croatian Meteorological Institute, we have implemented the Wind Wave Model III as an operational model. The wind forcing used is based on the numerical weather prediction model ALADIN/HR. The model uses near-surface winds dynamically adapted to 2 km grid spacing over the 3-day forecast range. The boundary condition at the Otranto Strait is obtained from the WAM model forecasts computed at ECMWF. The model setup uses an unstructured grid to make the forecasts. The numerical modellization uses an implicit scheme that we describe. We found an underestimate of significant wave height by 8 cm, an absolute error of 21 cm and a correlation of 91% on comparing with the altimeter of the SARAL satellite. Comparison with wave radar and buoys show no underestimate and smaller absolute errors.