Airflow modelling studies over the Isle of Arran, Scotland

A mesoscale meteorological model is applied to simulate turbulent airflow and eddy sheddingrnover the Isle of Arran, SW Scotland, UK. Under conditions of NW flow, the mountain ridge of Kintyre,rnlocated upwind of Arran, induces gravity waves that also affect the airflow over the island. The possibilityrnto nest domains allows description of the airflow over Arran with a very high resolution grid, while alsornincluding the effects of the surrounding mainland of Scotland, in particular of the mountain ridge ofrnKintyre. Initialised with a stably stratified NW flow, the mesoscale model simulates quasi-stationaryrngravity waves over the island induced by Kintyre. Embedded in the larger scale wave trains there isrncontinuous development of small-scale transient eddies, created at the Arran hill tops, that move downstreamrnthrough the stationary wave field. Although the transient eddies are more frequently simulated on thernnorthern island where the terrain is more pronounced, they are also produced over Tighvein, a hill of 458rnm on the southern island where measurements of surface pressure and 2 m meteorological variables havernbeen recorded at intermittent intervals between 1996 and 2000. Comparison between early observationsrnand simulations so far show qualitatively good agreement. Overall the computations demonstrate thatrnturbulent flow can be modelled with a horizontal resolution of 70 m, and describe turbulent eddy structurernon wavelength of only a few hundred metres.