Seasonal distribution and variability of atmospheric freeze/thaw cycles in N orway over the last six decades (1950–2013)

This study focused on atmospheric freeze/thaw cycles in N orway and presents the results of processing daily thermal data from 20 Norwegian meteorological stations for the period 1950–2013. Its two major aims were: (i) to provide long‐term time series of atmospheric freeze/thaw cycle data for N orway, and (ii) to analyse their trends over the last six decades. The study highlights the spatial and temporal modalities of the distribution of freeze/thaw cycles in N orway. The differences in the seasonal distributions of cycles and their mean annual number are because of the geographical location of the stations (coastal or inland stations, lowland or mountainous stations) and result from the combined effects of oceanity, continentality, latitude and elevation. The annual average number of freeze/thaw cycles is similar in the north (90) and south of N orway (84) but shows notable differences between coastal stations (27) and inland and/or mountainous stations (114). Since the 1950s, prolonged periods of several years characterized by increasing numbers of cycles have given way to periods of decreasing freeze/thaw frequency. This cyclicity is linked with the N orthern A tlantic O scillation ( NAO ). Strong positive or negative phases of the NAO since the 1950s have induced marked increases (or decreases) in atmospheric freeze/thaw cycle frequency in N orway.