Extended Abstract (68K)11.5
Nocturnal LLJ evolution and its relationship to turbulence and fluxes
Robert M. Banta, NOAA/ETL, Boulder, CO; and R. K. Newsom, Y. L. Pichugina, and J. K. Lundquist
A major objective of CASES-99 was to relate surface fluxes to features of the evolving stable boundary layer (SBL), such as the low level jet (LLJ). On a recently completed study we used ETL's High-Resolution Doppler Lidar (HDRL) to probe the nighttime development of the LLJ, including the height, speed, and direction of the jet maximum. Also available from HRDL were vertical profiles of the horizontal-velocity variance, which were shown to correlate with TKE and fluxes measured on a 60-m tower. In the present study we relate episodes or patches of enhanced turbulence as measured by HRDL between the surface and 200 m AGL, to characteristics or changes in the LLJ on several CASES nights with different LLJ speeds and heights. We then explore the relationship of HRDL high-variance periods to fluxes measured on the 60-m tower. We find that the high-variance episodes correspond to periods when TKE is generated aloft near the jet max and transported downward, in agreement with the "upside-down" boundary-layer concept. These episodes are sometimes related to bursts of fluxes at the surface, and sometimes not. We show examples of both kinds of episode.
Session 11, Stable BLs - II
Thursday, 18 July 2002, 10:30 AM-12:30 PM
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