Abstract
Four microbarographs, accompanied by wind vanes and anemometers, were deployed on a mountain called Black Combe (height 600 m) in Cumbria during a field experiment that took place in Novemberer 1991. the aims of the experiment were to measure the small flowβinduced pressure differences across the mountain and relate these to the local wind. These pressure differences may be used to calculate directly the drag exerted by the atmosphere on Black Combe.
The mean pressure difference between pairs of sites calculated over periods when the wind speed is small is due to the hydrostatic pressure difference caused by the height differences between the instruments. Removing this component reveals pressure differences across the mountain of up to 2 hPa. the main result of the experiment is the high correlation of the pressure differences with differences of the quantity pu^2^/2, where p is the air density and u is the wind speed. It is shown that this result holds for a stratified fluid when far upstream the streamlines originate from levels of similar wind speed.
Although reliable data were only obtained at three of the four stations, making the assumption that the dynamic pressure varies linearly across the mountain surface enables an estimate of the drag to be made. the average drag exerted on Black Combe over the period of the experiment is estimated to be 3.6 Pa.