Seven mountain wave case studies from the Mesoscale Alpine Programme (MAP) have been used to investigate the variation in the resolved surface pressure drag due to the Alps with model horizontal resolution. The three independent modelling systems tell the same story. For cases with small southerly (or northerly) wind-speeds near mountain crest level (< 10 m s-1), most of the drag was produced by low-level flow splitting around the Alpine barrier and the drags were converging. For situations where the southerly (or northerly) wind component increased strongly with height due to the location of the jet-stream directly above the Alps, the larger wind-speeds near mountain crest level forced much stronger mountain waves in the flow aloft. For such cases, the drag increased strongly as the grid-spacing was reduced from 12km to 4km. This has important consequences for the use of drag parameterisations
