Atmospheric icing in a coastal mountainous terrain. Measurements and numerical simulations, a case study

Icing on structures occurs as rime ice, clear ice or wet snow deposit. Reliable forecasts of duration and intensity of this icing require prognoses of standard meteorological parameters, in addition to more specific parameters such as the density (ρLWC) of cloud Liquid Water Content (LWC). Icing conditions on the mountain Brosviksåta (723 m a.s.l., 61° 2′ N, 5° 9′ E), on the western coast of Norway were investigated from March 21–24, 2003. A non-rotating vertical steel rod mounted on a scale was used to measure the accumulated ice load. Air temperature, relative humidity and wind were measured at three levels along the mountain slope. The maximum build-up of ice, in this case study, was measured to 4.5 kg on a 1 m high 0.14 m diameter rod. Comparison of measured ice-growth rate and calculated ρLWC gave a correlation coefficient of 0.85.A mesoscale atmospheric model (MM5) has also been tested at a high horizontal resolution (1 km) in order to evaluate its ability to reproduce weather conditions where freezing occurs. Comparison from the direct measurements and calculations, with results from MM5, gave 58% of the measured accumulated ice growth. Further studies of real-time cases on a real-time system at a coarser model resolution will reveal its capability for forecasting freezing events.