Mapping frequencies of icing on structures in Switzerland

Icing of structures is a problem for wind energy production in cold regions and makes careful planning of new projects essential. This study presents and evaluates a method to create a map showing the frequency of meteorological icing in Switzerland. Icing is simulated for two single years using an algorithm which calculates ice accumulation from temperature, wind speed, cloud and rain water content of the atmosphere. The driving meteorology was obtained from analysis runs of the weather forecast model COSMO-2 with 2.2 km grid size. The quality of the icing map is evaluated for the two years and compared to the 10 years average by using measurements of 165 meteorological stations in the Swiss Alps. Icing frequencies of the wind sensors at the stations were detected based on measured temperature, relative humidity and the standard deviation of the lateral movement of the wind sensor. The icing map shows appropriate regional patterns with icing frequencies ranging from zero to more than 100 day icing per year in accordance with our measurements. However, individual stations often showed strong deviations between modelled and measured icing frequency, especially in high alpine regions. These deviations are caused by a strong spatial icing variability due to local terrain features which cannot be captured by the model at 2.2 km resolution. (C) 2012 Elsevier Ltd. All rights reserved.

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Temperature

Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied on various reference points and thermometric substances for definition. The most common scales are the Celsius scale with the unit symbol °C (formerly called centigrade), the Fahrenheit scale (°F), and the Kelvin scale (K), the latter being used predominantly for scientific purposes.

Frequency

Frequency (symbol f) is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as temporal frequency for clarity and to distinguish it from spatial frequency. Frequency is measured in hertz (symbol Hz) which is equal to one event per second. Ordinary frequency is related to angular frequency (symbol ω, in radians per second) by a scaling factor of 2π. The period (symbol T) is the interval of time between events, so the period is the reciprocal of the frequency, f=1/T.

Swiss Alps

The Alpine region of Switzerland, conventionally referred to as the Swiss Alps (Schweizer Alpen, Alpes suisses, Alpi svizzere, Alps svizras), represents a major natural feature of the country and is, along with the Swiss Plateau and the Swiss portion of the Jura Mountains, one of its three main physiographic regions. The Swiss Alps extend over both the Western Alps and the Eastern Alps, encompassing an area sometimes called Central Alps.