7.6 Toward explaining the cause of large-amplitude variations in basin-scale flow and how they impact vertical transport and turbulent mixing

Tuesday, 22 June 2004: 11:45 AM
James O. Pinto, NCAR, Boulder, CO; and D. B. Parsons, W. O. J. Brown, B. Morley, and R. M. Banta

Under conditions of strong radiative cooling, downvalley flow develops in the Salt Lake basin resulting in a basin-scale nocturnal jet. On several nights, large amplitude pulsing of this flow was observed throughout the basin. These large-amplitude pulses in flow strength extend through the depth of the nocturnal jet and across the entire basin on some nights; however, their origin is uncertain. These pulses are vital in the creation of vertical transport and the temporal patterning of mixing. The importance of the pulses in driving vertical transport and mixing is inferred from the local data at the NCAR site and the large-scale observation afforded by the NOAA/ETL lidar. To study the cause of these pulses we employ the NCAR/PSU mesoscale model using 3 km resolution on the finest mesh. Sensitivity studies are performed to determine first, whether or not these features can be simulated, and if so, what the importance of PBL parameterization, surface characterization and horizontal resolution is in simulating the observed variability of the flow. Relationships between the modeled large-scale mass field and the modeled local terrain-driven flow are explored and compared with observed relationships.
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