Orografiske forsterkninger av vinden på Jæren og ved Stad

Abstract

Orographically enhanced winds near the coast of Norway were investigated by changing the height of the orography. Two cases were chosen, one for Stad (Sta97) and one for Jæren (Jæ96), both being winter situations with stable conditions and wind directions known to make wind enhancements at those places. In Jæ96 the wind is south-easterly and for Sta97 it's south-westerly. The orography was defined as geopotential height in HIRLAM, so the changes in orography were made by changing this parameter. Then six different runs were done, three for each case: one with increased mountain height, one with decreased height and a control-run with no changes done. The difference between the highest and lowest mountain height was investigated closer.

The results with increased height were an increased tip-jet to the left of the upstream flow, enhanced pressure ridge over the mountains, increased orographic rain upslope, increased temperature in the wake downslope and lifting above a layer with flow-splitting. All of this being a confirmation of the assumption that the mountain height has a large influence on the winds near Stad and Jæren. The steepness of the upstream slopes also has an influence on the strength and direction of the left side tip-jet. In addition it was evident that the model had some problems dealing with the changed orography. The results may be influenced a little by that.