SAMPLING REQUIREMENTS FOR DRAINAGE FLOWS THAT TRANSPORT ATMOSPHERIC CONTAMINANTS IN COMPLEX TERRAIN

In complex terrain organised flow features such as jets may be present and may affect the dispersion of atmospheric contaminants, but these features may evade sampling by atmospheric surface station networks. I n the present study the NOAA/ERL Wave Propagation Laboratory Doppler l idar documented such a feature, a canyon drainage jet, that extended o ver the adjacent plains but escaped detected by a rather dense network of surface and upper air instruments. The spatial variability in this case was dominated by the jet, which had horizontal dimensions of 1-3 km and which reached maximum speeds almost-equal-to 600 m above the t errain. These features also varied significantly in time, with major c hanges in the structure of the jet occurring over time periods of 30-4 5 min. This implies that the observation-based wind field that would b e used to determine real-time dispersion of atmospheric pollutants for emergency response would be in error without high resolution observat ions such as those rom the lidar.