Extended Abstract (788K)P1.6
Radar and acoustic observations during VTMX field-campaign
Paco Lopez Dekker, Univ. of Massachusetts, Amherst, MA; and A. N. Bajaj and S. J. Frasier
The first field campaign of the Vertical Transport and Mixing program occurred during Oct 2000 in the Salt Lake Valley focusing on processes in the nocturnal boundary layer and during morning and evening transitions. The University of Massachusetts Microwave Remote Sensing Laboratory participated in this campaign with a suite of remote sensing instruments including the Turbulent Eddy Profiler (TEP), which is a 915 MHz volume imaging radar, a high-resolution 2.9 GHz FMCW radar, a Doppler sodar, and sonic anemometers. The stable nocturnal boundary layer is characterized by sporadic, short-lived turbulent events which are believed to be responsible for significant mixing. The degree to which these events can be observed and characterized by high resolution radar instruments is the focus of our participation in the VTMX program.
These instruments were located at the Salt Lake Visitor Center located along I-80 approximately 5 miles west of the SLC airport in the northwest corner of the valley. TEP provides a volumetric picture of refractive index turbulence features within a 25 degree cone above the radar with 30-m range resolution. The FMCW yields a finer, 2.5 m resolution profile within a narrower, 3 degree cone, while the sodar provides coverage of the lowest 100-200 m (below the first range gates of the radars). In this paper we present a survey of the data acquired during this field campaign.
Typical observations during VTMX include late afternoon lake breezes producing boundary layer depth of around 400 m (as seen by the radar). Wave-like structures about 1200 m AGL were present during several IOPs. Some of these may be induced by flow over the Oquirrh Mountains to the WSW of our site. At night, weak down-valley flows are measured, accompanied by little detectable clear-air radar-backscattering. Only sporadic episodes of turbulent activity are observed by the radars, which are typically confined to the lowest 200 m of the NBL. As TEP measurements were hindered by ground-clutter in the lowest 150 m, these events are best studied with the FM-CW and sodar. At dawn, the growth of the CBL is observed. Comparison between the FMCW and TEP often reveals very thin layers of clear-air echo.
The clear-air radar echo depends on fluctuations in refractive index, which at microwave frequencies depends primarily upon humidity fluctuations. The combination of low night-time temperatures and high elevation of the experiment locale result in low humidity, and therefore contribute to weak radar echoes overall, limiting the fine-scale observation of turbulent events.
Supplementary URL: http://http:/abyss.ecs.umass.edu/tep/
Poster Session 1, PBL Processes and Modeling (with Coffee Break)
Monday, 17 June 2002, 2:45 PM-4:15 PM
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