Analysis of Long Time Series of Coastal Wind

Abstract

Abstract A study of a 14-yr time series of wind speed recorded on the coast outside the city of Trondheim in middle Norway is presented. Analysis of the time series shows that in this area there is, in general, no gap in the wind speed power spectrum in the 1 h−1 region. For heights below 20–40 m, dependent on the exact distance from the shoreline, there is a dip in the spectrum around 2 mHz; for higher elevations, there is a monotonical rise in the spectral energy for decreasing frequency f until the weather peak. Far below the weather peak, the spectrum decreases as f. Analyses of quasi-stationary 12-h time series indicate that in addition to weather (synoptic) variations and the turbulence due to ground friction peaking in the 0.01-Hz region, there are other mechanisms feeding energy into the spectrum in the mesoscalar (1 h) region, where the spectral gap conventionally is assumed to be found. As an example, a selected time series is analyzed that shows a pronounced peak in the spectrum at 0.4 mHz. Tim...