Extended Abstract (288K)12.6
Katabatic flow and turbulence as seen from airborne in-situ measurements and ground-based profiler measurements during VTMX
Ronald J. Dobosy, NOAA/ARL, Oak Ridge, TN; and E. J. Dumas and G. H. Crescenti
The Vertical Turbulence and Mixing Experiment (VTMX) of 2000 provided an intensive four-dimensional survey of wind and turbulence in and around Salt Lake City. Complementing the many surface-based and vertically-looking sensors, a light airplane (Long-EZ) sampled the horizontal structure of wind and turbulence over the valley at the minimum safe altitude (300 m to 500 m AGL). In this preliminary examination we look at the structure of the drainage out of the Wasatch Mountains as revealed in the airplane's measurements coordinated with observation from a 915 MHz radar profiler, a Doppler sodar, and a 10-m meteorological tower.
The Long-EZ flew pre-dawn missions, four hours each, on five separate days. Each mission included an hour over a north/south "racetrack" pattern east of highway I15 and south of I80. During a particular intensive observation period on 26 October 2000, the data suggest a deepening of the drainage from the Wasatch Mountains to engulf the airplane's flight altitude. On this hypothesis, the east leg of the racetrack passed above the drainage flow, then through the turbulent entrainment layer at the top of the flow, and finally within the drainage itself. Wind on the west leg of the racetrack remained southerly at flight altitude throughout the period. This followed the primary pattern of flow down the valley toward the Great Salt Lake. Meanwhile the profilers about 4 km to the west of the northwest corner of the flight pattern reported a recurring sequence. Wind at low altitudes, beneath flight altitude, backed over time from south to southeast, to be replaced periodically by south flow eroding downward to the surface. Such a pattern, strongly variable in time and space, will significantly effect the generation and transport of turbulence over the valley. In turn it will influence dispersion of any pollutant. Other days of airplane flights also had well-developed drainage flow and may exhibit patterns of the same type.
We will examine the patterns on the additional flight days to assemble as thorough a picture as we can with the horizontal and vertical tools we are currently using. Starting from this preliminary examination, we expect to broaden our interaction with the other observation and modeling activities of this experiment. Our goal is to fill in a picture of the structure of turbulence generation and transport as it influences the dispersion of contaminants.
Session 12, Urban field projects: URBAN-VTMX
Thursday, 23 May 2002, 1:30 PM-3:44 PM
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