SURFACE PRESSURE PERTURBATIONS PRODUCED BY AN ISOLATED MESOSCALE TOPOGRAPHIC BARRIER .1. GENERAL-CHARACTERISTICS AND DYNAMICS

This paper presents and analyzes the results of the Olympex Field Experiment, during which the operational observational network around the Olympic Mountains of Washington state was enhanced with eleven high-accuracy microbarographs. It is found that this isolated mesoscale topographic barrier produces both a windward high and lee low at the surface, with the latter generally possessing greater amplitude. The difference in amplitude between these two features lessens for higher Froude numbers. The mesoscale pressure perturbation produced by the barrier is highly correlated with the incoming wind speed averaged over a 100 mb layer centered at 850 mb. A comparison between the results of this experiment and linear theory reveals that linear theory does quite well in predicting the shape and amplitude of the mesoscale surface pressure perturbations for higher Froude numbers. This fact, and the high correlation of surface pressure perturbations with incoming wind speed, suggests that the surface mesoscale pressure distribution around the Olympics (and the resulting regional wind field) should be predictable if a skillful forecast of the characteristics of the incoming flow is available. Finally, it is noted that during periods in which the mesoscale pressure perturbations are large, this mountain barrier contributes substantially to the global pressure drag on the atmosphere.