Turbulence in the stable near-surface atmosphere in the complex terrain of Owens Valley, California during T-REX

During the Terrain-induced Rotors Experiment (held 1 Mar – 30 Apr 2006 near Independence, CA) three densely instrumented tall towers were deployed in a complex terrain valley to study, in part, fluxes and transports in the near-surface stable atmosphere. These towers were 30 m in height and located such that cross- and along-valley differences in stable near-surface atmospheric behavior could be intercompared and the representativeness of any individual tower assessed. Each tower was outfitted with 6 (20Hz) sonic anemometers that were equally spaced at 5 m intervals, three heights of slow-response temperature and relative humidity sensors, 2 krypton hygrometers, along with additional equipment. One site was further instrumented with 3 NCAR OTIHS. Each OTIHS is comprised of a sonic anemometer with an embedded, automatically reorienting 3-d hot-film anemometer set to sample at 2000Hz. The OTIHSs were placed at 0.8, 1.4 and 2.4 m above the local displacement height of approximately 0.6 m (1.4, 2.0 and 3.0 m above ground). As such, the lowest OTIHS was in the theoretical roughness sublayer, the next at the theoretical boundary between the roughness sublayer and surface layer, and the uppermost OTIHS was in the lower surface layer.

In this study we utilize observations from these three tower sites and numerical simulations using the ARPS model to evaluate turbulence in the near-surface stable (RiB > 0) atmosphere. The towers are evaluated for composite near-surface stable atmospheric evolution in relatively undisturbed lower tropospheric conditions in the valley bottom and along the relatively uniform alluvial slope to the west of the town of Independence, CA. In addition, using thresholding, globally intermittent turbulence characteristics are evaluated to determine the frequency and magnitude of near surface heat and momentum fluxes in strongly stable conditions. ARPS simulations and other T-REX observations are used to evaluate the potential external sources of intermittent turbulence that cannot be evaluated using the tall towers themselves, given the ~ 2500 m relief in the Owens Valley. The tall-tower observations are used, in part, to evaluate the ARPS simulations in a companion paper.