Firstly, the carriageway has a highest point of 72 metres above sea level, making it highly exposed to strong winds. Statistically speaking, for 200 hours per year the bridge will be closed off for light traffic due to a side wind exceeding the set limit of 15 m/s.
Another potential hazard is ice collecting on the suspension cables, the longest of which stretch to the top of the pylons, about 250 metres above sea level. When such ice starts to melt, it may fall down in large chunks, making traffic on the bridge impossible. This is expected to occur a few times per year on average.
Together with Great Belt Contractors, the Danish Meteorological Institute (DMI) has developed a forecasting and warning system which allows the authorities at the bridge to take the necessary precautions in critical situations. The system is fully automatic, and can be supplemented by telephonic advice from the forecaster on duty at DMI.
The Great Belt forecasts are based on Kalman predictions of wind, temperature and liquid water content at a few specific points on or near the bridge where road weather stations have been put up. One station is placed near the top of one of the pylons. NWP input comes from DMI-HIRLAM-E, the 21 km, 31 level version of the Danish HIRLAM model.
The data distribution and presentation parts of the system are extensions of the Danish road-weather prediction system, which is operated by the Danish Road Authorities, the counties and DMI. The Great Belt forecasting system will become fully operational in October 1999.
In my talk I will describe the forecasting system and the methodology applied herein, show screen images from the data presentation at the Great Belt surveillance facility, and present some verification results.
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