Multi-scale variability of winds in the complex topography of southwestern Norway

Abstract

A B S T R A C T Multi-scale variability of winds in the complex terrain of southwestern Norway is investigated using up to 20 yr of observations from nine automatic weather stations and reanalysis data. Significant differences between the large-and local-scale winds are found. These differences are mainly governed by the large-scale topography of Southern Norway. Winds from the southeast and statically stable flow from the northwest are found to be significantly reduced at the ground level due to large-scale wake and blocking effects. Southwesterly and northeasterly winds are orographically enhanced. At a local scale, there are differences in the wind speed distributions between the surface stations, both in space and time. These differences can to a large extent be quantified in terms of the Weibull distribution function and associated with the respective geographical locations as discretised in four characteristic surface categories: offshore, inland, coast and mountain. The inland category is found to be associated with relatively low but variable wind speeds, whereas the coastal and offshore locations are dominated by more steady and stronger winds. The mountain wind speed distribution is fundamentally different from the others; it shares the variability with the inland locations but the higher average wind speed with the other categories.

Simulations of the Bergen orographic wind shelter

“…When compared to the wind direction at Ulriken, which is on average found to be in reasonable agreement with the larger scale flow direction (Jonassen et al, 2012), the wind direction observed at the other AWSs show large deviations towards a more south and south-easterly direction for the south-westerly flow of Case 1. In the south-westerly flow of Case 2 (before 1800 UTC), the deviations are even larger and it is particularly large at Florida.…”

“…Although the studied windstorms are quite typical in terms of wind pattern (see climatology by Jonassen et al, 2012), there do exist cases where strong and gusty winds in south-westerly flow reach down to parts of the centre of Bergen (e.g. Harstveit, 2006).…”

“…The centre of Bergen, as represented by the weather station 'Florida', appears to be remarkably sheltered during strong south-westerly flow (Harstveit, 2006;Jonassen et al, 2012). It is, however, unclear if this sheltering effect (hereby referred to as the 'Bergen shelter') is caused by a wake of the upstream mountain massif of Løvstakken (e.g.…”

“…From the windstorm on 25 December 2011, data from a network of five additional stations in Bergen are available from a research project at GFI. Detailed statistics on the observations from Florida and Ulriken can be found in Jonassen et al (2012) and Valved (2012). An overview of the AWSs is given in Table 1 and their geographical locations are indicated in Fig.…”

Sedimentological characteristics of ice-wedge polygon terrain in Adventdalen (Svalbard) – environmental and climatic implications for the late Holocene

“…This pattern is even more significant in braided systems, where variations in fluvial dynamics through time may condition changes in the size of the particles mobilized and subsequently deposited in the surrounding areas. On a local scale, wind circulation is very complex especially in irregular topographic areas, which can increase or decrease wind intensity (Jonassen et al, 2012). Previous work on loess deposits observed that local wind systems in valleys can be important in the formation of aeolian deposits (Sun and Liu, 2000).…”