Extended Abstract (636K)P4.6
Observations of flow over complex terrain within the stable nocturnal boundary layer
Justin T. Walters, University of Alabama, Huntsville, AL; and K. R. Knupp
Accurate depiction of the behavior of the stable nocturnal boundary layer (NBL) has been a difficult puzzle to solve. Variations of flow, turbulence and temperature are possible over short temporal and spatial scales, especially in the presence of heterogeneous terrain. An exploratory study to observe the variability of the stable NBL over complex terrain was conducted over the Redstone Arsenal region of northern Alabama on five consecutive stable nights during November 1999 with the use of surface instrumentation, instrumented towers, a sodar and a ceilometer. Observations show a wind maximum below 100 m associated with drainage flow occurred on all nights of the study. When flow above the NBL had a northerly component, the drainage flow decoupled from the flow above, and a two-level turbulence structure developed. Tower wind measurements at 100 m were compared with 100 m sodar winds from a site 8 km away. The data showed significant differences in wind direction between the two sites. There are instances when one instrument is within the drainage flow, times when both instruments are within the drainage flow, and instances when one instrument measured winds at the interface between the drainage flow and the flow above. Wind and temperature covariance at 30 m AGL showed significant negative covariance events on all nights, which suggests that stable NBL structure over complex terrain does not conform to the theoretical structure derived over simple terrain.
Poster Session 4, Stable BLs; Chemistry and Dispersion in the ABL
Tuesday, 16 July 2002, 2:00 PM-2:00 PM
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